HANDBOOK OF Human Factors in Litigation
HANDBOOK OF Human Factors in Litigation EDITED BY
Y.Ian Noy Waldemar Karwowski
CRC PRESS Boca Raton London New York Washington, D.C.
This edition published in the Taylor & Francis e-Library, 2006. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to http://www.ebookstore.tandf.co.uk/.” Library of Congress Cataloging-in-Publication Data Handbook of human factors in litigation/edited by Y.Ian Noy and Waldemar Karwowski. p. cm. Includes bibliographical references and index. ISBN 0-415-28870-3 (alk. paper) 1. Evidence, Expert—United States. 2. Forensic engineering—United States. 3. Human engineering—United States. I. Noy, Ian.Y. II. Karwowski, Waldemar, 1953– KF8968.25.H36 2004 347.73′67–dc22 2004056121 This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage or retrieval system, without prior permission in writing from the publisher. All rights reserved. Authorization to photocopy items for internal or personal use, or the personal or internal use of specific clients, may be granted by CRC Press, provided that $1.50 per page photocopied is paid directly to Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923 USA. The fee code for users of the Transactional Reporting Service is ISBN 0-415-28870-3 (Print Edition)/05/$0.00+$ 1.50. The fee is subject to change without notice. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. The consent of CRC Press does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from CRC Press for such copying. Direct all inquiries to CRC Press, 2000 N.W. Corporate Blvd., Boca Raton, Florida 33431. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. Visit the CRC Press Web site at www.crcpress.com © 2005 by CRC Press No claim to original U.S. Government works ISBN 0-203-49029-0 Master e-book ISBN
ISBN 0-203-57160-6 (Adobe e-Reader Format) International Standard Book Number 0-415-28870-3 (Print Edition) Library of Congress Card Number 2004056121
Preface Forensic ergonomics and human factors is the application of ergonomics theory, principles, and data to determine causes of system failures, often involving personal injury, considered in the context of litigation. The International Ergonomics Association defines ergonomics (or human factors) as the scientific discipline concerned with the understanding of interactions among humans and other elements of a system, and the profession that applies theory, principles, data, and methods to design in order to optimize human well-being and overall system performance. Derived from the Greek ergon (work) and nomos (laws) to denote the science of work, ergonomics is a systems-oriented discipline which now extends across all aspects of human activity. Ergonomics promotes a holistic approach in which considerations of physical, cognitive, social, organizational, environmental, and other relevant factors are taken into account. Whereas the vast majority of ergonomics and human factors practitioners are involved in the design of human-machine systems to prevent occurrences of human error, forensic practitioners seek to answer the question “What went wrong?” Most of forensic practice falls within the domain of civil litigation, though there are important applications in criminal cases, for example, that relate to the fallibility of eyewitness reports or human actions that may constitute criminal negligence. Analyses of human causes of system failures can uncover valuable information that can help prevent recurrence through engineering or administrative controls. In addition, expert testimony during the litigation process assists the court in determining liability by interjecting scientific evidence concerning human performance and behavior. In the aggregate, this improves the fairness and objectivity of the judicial system in protecting individuals and society. As a result of ergonomics-based evidence, liability attributable to inappropriate designs or business practices has become a significant consideration in corporate decisions influencing the nature and extent of product research and development, workplace and infrastructure interventions, and the manner of service provision. The need to minimize exposure to liability provides strong motivation to designers, service providers, and employers to elevate the safety of their products, workplace, or service to a level higher than might otherwise be the case. Forensic human factors is a professional endeavor that is neither taught nor systematically practiced, even in the U.S., where it is most prevalent. While the profession is anchored in the science of human factors, forensic practice today relies on individually acquired skills and experience. There is little documented material available to help practitioners develop expertise in a systematic manner. When we decided to create this handbook, we intended to produce a reference that was sufficiently comprehensive in scope and having sufficient depth to be a valuable tool for forensic experts, students, and legal practitioners alike. This handbook was not intended to teach the science of ergonomics and human factors—there are several excellent resources
available to satisfy readers interested in the science; rather, it was intended to provide guidance on the preparation, analyses, and presentation of forensic evidence as well as current scientific knowledge in key applications. The Handbook of Human Factors in Litigation is a resource for forensic and legal professionals and includes chapters relating to the litigation process, forensic approaches and methods, and important scientific data in the major application areas, including case studies. It is a compilation of the current state-of-the-art knowledge and practice, written by authors with vast experience in the field, and it reflects their individual expertise and views. The handbook contains a total of 38 chapters organized under six main headlines, including: Professional Issues (7 chapters), Human Performance in the Legal Context (5 chapters), Driving Environments (6 chapters), Physical and Cognitive Factors (6 chapters), Product Liability and Warnings (9 chapters), Human Factors Applications (4 chapters), and a Guide to Human Factors Terminology. Readers will note that some chapters deal with common topics, but from a different perspective. We tried to minimize overlap, but in this kind of endeavor some overlap among chapters is unavoidable. Meeting our initial goals proved a greater challenge than we had anticipated. Forensic application of ergonomics and human factors is an ever-evolving field and the number of qualified forensic practitioners is very small indeed. Although current emphasis is on consumer product deficiencies, slips and falls, and motor vehicle crashes, new applications are emerging. The handbook represents the current state-of-practice. It is the first text of its kind and we are confident that it will serve as an important resource and pave the way for the establishment of a more formal body of relevant knowledge in the area. We are indebted to the contributors to this handbook, who are individually renowned scholars and experts. We are also indebted to Taylor & Francis for encouraging us to edit this volume, and would like to acknowledge editorial assistance provided by Cindi Carelli and Jessica Vakili of CRC Press. Our goal was twofold: to assist legal professionals in recognizing the role and contribution of ergonomics and human factors in litigation, and to assist forensic experts in performing their work in an objective and effective manner. In realizing this handbook, it is our fervent hope that it will contribute to the efficacy and equitability of the justice system, and thereby lead to the safer design and use of technology. Y.Ian Noy Waldemar Karwowski
The Editors
Y.Ian Noy, Ph.D., P.Eng., CPE, is President of Systems Ergonomics, Inc., a consulting firm specializing in industrial and forensic ergonomics. He holds a doctorate degree in Industrial Engineering from the University of Toronto, specializing in human factors. He is a Board Certified Professional Ergonomist (BCPE) with more than 30 years of professional experience in a variety of private and public sector applications. Forensic experience includes expert testimony in civil litigation arising from motor vehicle collisions and slips and falls. He is a recipient of several awards, including the U.S. National Highway Traffic Safety Administration’s Engineering Excellence Award. His career began in 1973 as a behavioral scientist at the Canadian Defence and Civil Institute of Environmental Medicine (DCIEM) working on a variety of military human— machine systems. In 1982 he joined Transport Canada to undertake traffic safety research to support the development of vehicle safety standards and other collision interventions. He was quickly promoted to Chief of the Ergonomics Division and, in 2001, to the position of Director, Standards Research and Development, where he is responsible for motor vehicle safety regulations, crashworthiness, ergonomics and vehicle systems research, and motor carrier safety. Dr. Noy’s applied research experience spans applications in the air, on the ground, and underwater, including military R&D. He has published more than 100 scientific and technical reports, as well as conference and journal articles. He has prepared and presented lectures in human factors on a variety of topics, such as traffic safety, human factors in intelligent transport systems, human-machine interface design and evaluation, human performance and behavior, and the role of ergonomics in civil litigation. He serves on the editorial board of several journals, including Applied Ergonomics, and is Associate Editor of the International Encyclopedia of Ergonomics and Human Factors. In addition, he edited the book The Ergonomics and Safety of Intelligent Driver Interfaces (Lawrence Erlbaum & Associates, 1997).
Dr. Noy is Past President of the International Ergonomics Association (IEA). He is a Fellow of the Human Factors and Ergonomics Society (HFES), a Past President and Honorary Fellow of the Association of Canadian Ergonomists/Association Canadienne d’Ergonomie (ACE), and a member of the Association of Professional Engineers of the Province of Ontario (PEO). He is also a member of the Transportation Research Board Committee on Simulation and the Measurement of Driving. Dr. Noy was the chairman of the 12th Congress of the IEA held in Toronto in 1994. In 1998, he was leader of the People to People Ambassador Programs’ Ergonomics Delegation to the People’s Republic of China.
Waldemar Karwowski, Sc.D., Ph.D., P.E., is Professor of Industrial Engineering and Director of the Center for Industrial Ergonomics at the University of Louisville, Louisville, Kentucky. He holds an M.S. (1978) in Production Engineering and Management from the Technical University of Wroclaw, Poland, and a Ph.D. (1982) in Industrial Engineering from Texas Tech University. He was awarded the Sc.D. (dr hab.) degree in Management Science by the Institute for Organization and Management in Industry (ORGMASZ), Warsaw, Poland (June 2004). He is also a Board Certified Professional Ergonomist (BCPE). His research, teaching, and consulting activities focus on human system integration and safety aspects of advanced manufacturing enterprises, human-computer interaction, prevention of work-related musculoskeletal disorders, workplace and equipment design, and theoretical aspects of ergonomics science. Dr. Karwowski is the author or co-author of more than 300 scientific publications (including more than 100 peer-reviewed archival journal papers) in the areas of work systems design, organization, and management; macroergonomics; human-system integration and safety of advanced manufacturing; industrial ergonomics; neuro-fuzzy modeling in human factors; fuzzy systems; and forensics. He has edited or co-edited 35 books, including the International Encyclopedia of Ergonomics and Human Factors, Taylor & Francis, London (2001). He was a winner of the Best Reference Award 2002 from the Engineering Libraries Division, American Society of Engineering Education, and the Outstanding Academic Title 2002 from Choice magazine. Dr. Karwowski serves as editor of the Human Factors and Ergonomics in Manufacturing international journal published by John Wiley & Sons, New York, and is the editor-in-chief of Theoretical Issue in Ergonomics Science (TIES) (Taylor & Francis, London). Dr. Karwowski serves as co-editor of the International Journal of Occupational Safety and Ergonomics and
consulting editor of the Ergonomics Journal. He is also a member of editorial boards for several peer-reviewed journals, including Human Factors, Applied Ergonomics, International Journal of Human-Computer Interaction, Universal Access to the Information Society: An International Interdisciplinary Journal, Occupational Ergonomics, and Industrial Engineering Research: An International Journal of RE Theory and Application (Hong Kong). Dr. Karwowski served as Secretary-General (1997–2000) and President (2000–2003) of the International Ergonomics Association (IEA). He was elected an Honorary Academician of the International Academy of Human Problems in Aviation and Astronautics (Moscow, Russia, 2003), and was named the Alumni Scholar for Research (2004–2006) by the J.B. Speed School of Engineering of the University of Louisville. He also received the University of Louisville Presidential Award for Outstanding Scholarship, Research and Creative Activity in the Category of Basic and Applied Science (1995), Presidential Award for Outstanding International Service (2000), and the W.Jastrzebowski Medal for Lifetime Achievements from the Polish Ergonomics Society (1995). Dr. Karwowski is Fellow of the International Ergonomics Association (IEA), the Human Factors and Ergonomics Society (HFES, USA), the Institute of Industrial Engineers (IIE, USA), and the Ergonomics Society (United Kingdom). He is past President of the International Foundation for Industrial Ergonomics and Safety Research, as well as past Chair of the U.S. TAG to the ISO TC159: Ergonomics/SC3 Anthropometry and Biomechanics. He served as Fulbright Scholar and Visiting Professor at Tampere University of Technology, Finland (1990–1991), and was named an Outstanding Young Engineer of the Year by the Institute of Industrial Engineers (1989). He can be reached via e-mail at
[email protected].
Contributors Gerson J.Alexander Positive Guidance Applications Rockville, Maryland William B.Askren Human Factors Services Dayton, Ohio Gary M.Bakken Analytica Systems International, Inc. Tuscon, Arizona Richard D.Blomberg Dunlap and Associates, Inc. Stamford, Connecticut Francisco J.Bricio The Bricio Law Firm Gary, North Carolina Daniel A.Bronstein Michigan State University East Lansing, Michigan C.Shawn Burke University of Central Florida Orlando, Florida H.Harvey Cohen Error Analysis, Inc. La Mesa, California Deborah Davis University of Nevada Reno, Nevada Patrick G.Dempsey Liberty Mutual Research Institute for Safety Hopkinton, Massachusetts Sidney W.A.Dekker Lund University Lund, Sweden Jason Devereux University of Surrey Guilford, Surrey, U.K. Robert Dewar Western Ergonomics, Inc. Calgary, Alberta, Canada
William C.Follette University of Nevada Reno, Nevada Magdalen Galley Ergonomics Consultant Leicestershire, England Peter A.Hancock University of Central Florida Orlando, Florida Martin G.Helander Nanyang Technological University Singapore Max Hely Safety Science Associates Pty., Ltd. Sydney, Australia Allen K.Hess Auburn University at Montgomery Montgomery, Alabama Henry M.Hobschied Products Liability Consultant and Legal Editor Shawano, Wisconsin Donald P.Horst Private Consultant Sunnyvale, California John M.Howard Crossroads Machine, Inc. Dayton, Ohio Roger C.Jensen Montana Tech Butte, Montana Daniel A.Johnson Daniel A.Johnson, Inc. Olympia, Washington Murray Kaiserman Health Canada Ottawa, Ontario, Canada Waldemar Karwowski University of Louisville Louisville, Kentucky Vincent Kelly University of Surrey Guildford, Surrey, U.K. Markus Kemmelmeier University of Nevada Reno, Nevada
Martin I.Kurke Kurke Associates Springfield, Virginia Frank J.Landy SHL Litigation Support Boulder, Colorado Cindy A.LaRue Error Analysis, Inc. La Mesa, California Kenneth R.Laughery Rice University Houston, Texas Elizabeth E Loftus University of California Irvine, California Celine McKeown Link Ergonomics Nottingham, England Dick Moll University of Wisconsin Madison, Wisconsin Rudolf G.Mortimer Human Factors Engineering Urbana, Illinois Jeffrey W.Muttart Accident Dynamics Research Uncasville, Connecticut Jone McFadden Papinchock SHL Litigation Support Boulder, Colorado Christopher P.Nemeth University of Chicago Chicago, Illinois Thorny Nilsson University of Prince Edward Island Charlottetown, Prince Edward Island, Canada Richard A.Olsen Human Performance: Limited Santa Clara, California Tal Oron-Gilad University of Central Florida Orlando, Florida Heather A.Priest University of Central Florida Orlando, Florida
Patricia Robinson Coronado Consulting Services, LLC Sonoita, Arizona Eduardo Salas University of Central Florida Orlando, Florida Stuart M.Statler Safety Strategies Arlington, Virginia Donald I.Tepas University of Connecticut Storrs, Connecticut David R.Thom Collision and Injury Dynamics, Inc. El Segundo, California David A.Thompson Stanford University Palo Alto, California Alison G.Vredenburgh Vredenburgh & Associates, Inc. Carlsbad, California Evelyn Vingilis University of Western Ontario London, Ontario, Canada Ron Wardell University of Calgary Calgary, Alberta, Canada Katherine A.Wilson University of Central Florida Orlando, Florida Michael S.Wogalter North Carolina State University Raleigh, North Carolina Dennis Wylie D.Wylie Associates Santa Barbara, California Ilene B.Zackowitz Vredenburgh & Associates, Inc. Carlsbad, California
Contents I Professional Issues 1 The Discipline of Human Factors Engineering and Ergonomics 3 Martin G.Helander 2 Preparing and Presenting Evidence in Court 33 Daniel A.Bronstein 3 Presenting Behavioral Science Data as Legal Evidence: Legal Standards 43 that the Ergonomic and Human Factors Expert Needs to Know Allen K.Hess 56 4 Practical Ethics for the Expert Witness in Ergonomics and Human Factors Forensic Cases Allen K.Hess 71 5 A Road Map for the Practice of Forensic Human Factors and Ergonomics William B.Askren and John M.Howard 91 6 Can Training for Safe Practices Reduce the Risk of Organizational Liability? Katherine A.Wilson , Heather A.Priest , Eduardo Salas , and C.Shawn Burke 131 7 The Influence of Daubert on Expert Witness Testimony—The Human Factors Context Jone McFadden Papinchock and Frank J.Landy II Human Performance in the Legal Context 8 Reconstructing Situated Performance in Human Error Investigations Sidney W.A.Dekker 9 Causation Issues in Workers’ Compensation Roger C.Jensen and Francisco J.Bricio 10 Legal Issues in Work-Related Musculoskeletal Disorders: a European Perspective from the U.K Vincent Kelly and Jason Devereux 11 Age and Functioning in the Legal System: Victims, Witnesses, and Jurors Deborah Davis and Elizabeth F.Loftus
148 174 187
215
12 Memory for Conversation on Trial Deborah Davis , Markus Kemmelmeier , and William C.Follette
281
III Driving Environments 13 Human Factors in Traffic Crashes Rudolf G.Mortimer , Richard D.Blomberg , Gerson J.Alexander , and Evelyn Vingilis 14 Estimating Driver Response Times Jeffrey W.Muttart 15 Pedestrian Injury Issues in Litigation Richard A.Olsen 16 Pedestrian Accidents in Traffic Robert Dewar 17 Commercial Motor Vehicle Collisions Dennis Wylie 18 Human Factors Issues in Motorcycle Collisions Peter A.Hancock , Tal Oron-Gilad , and David R.Thom
320
403 436 466 487 512
IV Physical and Cognitive Factors 19 Perceptual-Cognitive and Biomechanical Factors in Pedestrian Falls H.Harvey Cohen and Cindy A.LaRue 20 Measurement in Pedestrian Falls Daniel A.Johnson 21 Balcony Falls Magdalen Galley 22 Preplacement Strength and Capacity Assessment for Manual Materials Handling Jobs Patrick G.Dempsey 23 Identifying the Real Issues in Work-Related Upper Limb Disorders Celine McKeown 24 Exercise Injuries: Human Factors in Fitness Facilities Max Hely
539 567 602 622
629 656
V Product Liability and Warnings 25 Preventing “Accidental” Injury: Accountability for Safer Products by Anticipating Product Risks and User Behaviors Stuart M.Statler 26 Human Factors Issues to Be Considered by Product Liability Experts Alison G.Vredenburgh and Ilene B.Zackowitz 27 Products Liability Law: What Engineering Experts Need to Know Dick Moll , Patricia A.Robinson , and Henry M.Hobscheid 28 Human-Centric Approach to Forensic Analysis for System Liability Gary M.Bakken 29 Product Liability for the Human Factors Practitioner Ron Wardell 30 The Warning Expert Kenneth R.Laughery and Michael S.Wogalter 31 Effectiveness of Consumer Product Warnings: Design and Forensic Considerations Michael S.Wogalter and Kenneth R.Laughery 32 Legibility of Warnings in Color Thorny Nilsson and Murray Kaiserman 33 A Human Factors View of Product Liability and Malpractice Litigation Martin I.Kurke
682
700 715 727 755 763 780
794 819
VI Human Factors Applications 34 The Impact of Shiftwork on Manufacturing and Transportation Workers Donald I.epas 35 Preschoolers, Adolescents, and Seniors: Age-Related Factors Pertaining to Forensic Human Factors Analyses Ilene B.Zackowitz and Alison G.Vredenburgh 36 Sexual Harassment: A Forensic Human Factors Perspective Alison G.Vredenburgh and Ilene B.Zackowitz 37 Health Care Forensics Christopher P.Nemeth
833
851
865 877
VII Human Factors Terminology 38 A Guide to Forensic Human Factors Terminology 902 David A.Thompson , H.Harvey Cohen , Donald P.Horst , Daniel A.Johnson , and Richard A.Olsen Index
960
I Professional Issues
1 The Discipline of Human Factors Engineering and Ergonomics Martin G.Helander Nanyang Technological University 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
1.1 Introduction Human factors and ergonomics (HFE) are two branches of a scientific discipline concerned with: (1) interaction and design of systems that people use at work and in leisure and (2) appropriate work procedures and practices, tools, and computer systems that encompass the work system. The purpose of the design activities is to match systems, jobs, products, and environments to the physical and mental abilities and limitations of people. HFE professionals are involved in these activities. They are also involved in training or educating operators in the use of the system. Ideally, systems should be well designed so that they are intuitive to use and do not require special training or education. However, this turns out to be a very challenging design task as gauged from various usability problems experienced by operators. In Europe, ergonomics started with industrial applications in the 1950s. Information from work physiology, biomechanics, and anthropometry was applied in the design of workstations and industrial processes. The aim was to enhance the well-being of workers and improve manufacturing productivity. In the United States, human factors and its sister disciplines, human factors engineering and engineering psychology, developed from military applications. Knowledge from experimental psychology and systems engineering was used to improve systems performance and system quality. Despite the historical differences between human factors and ergonomics in the type of knowledge used and in the goals for design, the two approaches are merging. In the Western world, physical workload is no longer common. In manufacturing, hard physical labor has been taken over by materials-handling aids, mechanical processes, and automation. Legislation has also put limits to the amount of workload to which employees can be exposed. At the same time, the introduction of automation and computers in the workplace has transformed many factories, as well as offices. A modern factory can now be demanding because of its high mental demands—rather than physical demands. Similarly, during the last 15 years in the U.S., there has been a great interest in physical workload, including biomechanics of work postures and correct lifting
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techniques. Many companies today employ HFE staff to help with improving the work environment from safety as well as productivity perspectives. Human factors and ergonomics (HFE) have since drawn closer. One indication is the change of name of the Human Factors Society in the U.S. to the Human Factors and Ergonomics Society. As such, the terms human factors and ergonomics are used synonymously in this chapter. 1.2 History of Human Factors and Ergonomics The word ergonomics is derived from the Greek ergo (work) and nomos (rules, law). It was first used by Wojciech Jastrzebowski in a Polish newspaper in 1857 (Karwowski, 1991). One may argue that ergonomics is nothing new. Hand tools, for example, have been used since the beginning of human kind. Various types of hand tools have been developed since the Stone Age, and the interest in ergonomic design can be traced back in history (Childe, 1944; Braidwood, 1951). HFE in the 18th and 19th Centuries In the 18th century Ramazzini (1713) published a book, The Diseases of Workers, in which he documented links between many occupational hazards and the type of work performed. He described, for example, the development of cumulative trauma disorder and believed that these events were caused by repetitive motions of the hand, constrained body posture, and excessive mental stress. La Mettrie’s controversial book L’homme Machine was published in 1748, at the beginning of the Industrial Revolution. Two things can be learned from La Mettrie’s writings. First, the comparison of human capabilities and machine capabilities was a sensitive issue already in the 18th century. Second, by considering how machines operate, one can also learn much about human behavior: “to be a machine, to feel, to think, to know how to distinguish good from bad, as well as blue from yellow, in a word, to be born with an intelligence and a sure moral instinct” (La Mettrie, 1748). Some of these issues remain debated in ergonomics today. For example, an analysis of the constraints in utilizing industrial robots helps us understand how industrial tasks should be designed to better fit humans (Helander, 1995). Rosenbrock (1983) pointed out that, during the Industrial Revolution, efforts were made to apply the concepts of a “human-centered design” to new machines, such as the spinning Jenny and the spinning mule. The concern then was to allocate interesting tasks to the human operator, leaving the machine to perform the more boring and repetitive tasks. Taylorism At the beginning of the 20th century, Frederick Taylor introduced the “scientific” study of work. The tasks of industrial workers were analyzed and opportunities were sought to enhance productivity by simplifying the worker’s movement patterns. Many of Taylor’s studies analyzed the work of bricklayers; he proposed many useful recommendations
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concerning how many bricks a mason can lift at the same time, and at what height the bricks should be stored to minimize physical work. In line with Taylor’s tradition, Frank and Lillian Gilbreth developed the time and motion study. Ordinary jobs were divided into several microelements called “therbligs” (Konz and Johnson, 1990). The motions of the workers were classified in elements such as “reach,” “grasp,” and “move.” The motion times were then calculated and used for redesigning jobs as well as for calculating workers’ salaries. Today, there are often objections against the time and motion study, which is seen as a tool for exploiting workers. Nonetheless, these methods remain useful for measuring and predicting work performance time. The time and motion study, if used for the right purpose, is a valuable tool. Accident Proneness In the beginning of the 20th century, research in industrial psychology emphasized how one should select operators who are suitable for certain tasks. This was based on studies of human skills. The research on accident proneness is typical of this era. Accident proneness implies that certain individuals are more likely to have accidents than others because they have enduring personality characteristics that make them unsafe. The research in this time period centered on understanding how accident-prone individuals differed from “normal” people, so that one could exclude them from participating in activities in which they were likely to incur accidents. For example, one could revoke a driver’s license. This approach dominated accident research for about 40 years, but it was not fruitful. The results of many research studies have in retrospect proven to be useless because accident proneness and many personality features are not stable—they fluctuate with age and experience (Shaw and Sichel, 1975). In the 21st century, this approach is considered totally misleading. In fact, automobile drivers who have been involved in accidents do not necessarily incur future accidents. Likewise, factory workers who experience accidents in the workplace cannot be seen as accident prone. The tendency to blame individuals for accidents is seemingly counterproductive. With greater awareness of ergonomics, it is now realized that human errors are mostly caused by poor design, and the modern approach is to design environments and artifacts so that they fit the limitations and capabilities of the users. What is needed is a greater focus on environmental and machine designs to make environments and machines safer. For similar reasons, safety training is only partially valid. Many accidents involve unexpected scenarios for which it is difficult to prepare by training. For example, injuries due to manual materials handling are often due to a combination of unexpected events, and asking workers to train in “correct lifting techniques” does not help (Kroemer et al., 1994). International Proliferation of HFE Since the 1950s, HFE has proliferated on the other large continents: Asia, Africa, South America, and Australia (Luczak, 1997). In many developing countries, in particular Southeast Asia, new problems are resulting from rapid industrialization; these have led to the situation in which workers have difficulties in adapting to new technologies. The
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transition from a rural, agrarian life to urban industries comes at a cost. Workers are paying a price in terms of a tremendous increase of industrial injuries and stress. Many of these problems remain hidden or unreported, and official statistics are rarely available to illuminate the true state of affairs. As Vanwonterghem (1994) claimed, the industrialization has come about too quickly. Thus, developing countries have a great need for ergonomics.
TABLE 1.1 Five Most Important Early and Current Applications of Ergonomics in 25 Ergonomics Societies Importance
Early applications
Current applications
1 Anthropometry Safety 2 Work physiology Industrial engineering 3 Industrial engineering Biomechanics 4 Biomechanics Macroergonomics 5 Psychology Human-computer interaction Source: Brown, O. Jr., Noy, I., and Robertson, M. (1995). Special survey of IEA Federated Societies. Santa Monica, CA: International Ergonomics Association, c/o Human Factors and Ergonomics Society.
In developing countries in which ergonomics is adopted, the emphasis has been on job design including biomechanics, heat stress, and work physiology (Khalid, 2003). However, with the introduction of computers, there is now a sudden shift in focus to the problems of usability of complex systems. Usability is a universal problem that cuts across cultures. In the transition to the new, computerized world, many developing countries are bypassing several stages of development and find themselves immediately immersed in the computerized global environment. What took the Western World 200 years to accomplish has taken the developing countries 30-odd years. Associated with this development are new ergonomics problems in dealing with the globalization of communication, integration of resources, and global management. The Asian tigers are well positioned to take a lead in this area but, at present, lack the necessary infrastructure in terms of experience and trained personnel. Tremendous economic potential lies in designing usable systems for global communication and customized markets. Technology transfer from the Western world may no longer be critical. A survey among ergonomists in 25 countries clearly demonstrates the change in emphasis (Brown et al., 1995). Although biomechanics remains important, a need is emerging for cognitive ergonomics and macroergonomics, as summarized in Table 1.1. It is interesting to note that this trend was valid not only for industrialized countries but also for industrially developing countries. Educational Background of HFE Professionals Ergonomists come from a variety of professional fields. The mixed background is well demonstrated in the composition of the membership of professional societies, which typically consists of engineers, psychologists, and individuals from the medical
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profession. HFE professionals have received academic training in engineering, ergonomics, medicine, physiology, physiotherapy, psychology, and safety. These educational programs accounted for about 70% of all members. Of the current U.S. membership, 29% are academics, 27% practice in industry, 15% do research, 10% are private consultants, 8% work for the government, and 11% work in other occupations. Certification and licensing of ergonomists are important issues to the practicing professional. Several organizations uphold rules for professional certification, including the Board for Certification of Professional Ergonomists (BCPE) in the U.S. and the Centre for Registration of European Ergonomists (CREE) in Europe. The International Ergonomics Association upholds a set of recommendations that can be used by member countries in certifying HFE professionals. 1.3 International Ergonomics Association (IEA) Although the profession has been strongly developed in many individual countries, there is also an increasing internationalization of HFE. This is managed by IEA, an organization for HFE organizations around the world. Its origin can be traced to a seminar on fitting the job to the worker, which took place in The Netherlands in 1957. The first Congress of IEA was held in Stockholm in 1961 (IEA, 2004). For many years, the focus of IEA was on the welfare and productivity of workers from the point of view of the biological sciences (Smith, 1988). Due to rapid technological development, this perspective has since changed radically. Today, IEA considers also nonwork activities including play, leisure, home, and travel. The new focus is on mental demands and organizational prerequisites. Definitions of Ergonomics Over the years, there have been many definitions of ergonomics. Licht and colleagues (1991) identified 130 definitions of human factors and ergonomics. These keep changing, thereby emphasizing the more recent advances. IEA (2004) defined the discipline of ergonomics in the following way: Ergonomics (or human factors) is the scientific discipline concerned with the understanding of interactions among humans and other elements of a system, and the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance…. Ergonomists contribute to the design and evaluation of tasks, jobs, products, environments and systems in order to make them compatible with the needs, abilities and limitations of people. The following definition is inspired by Chapanis (1995) and Helander (1997): Ergonomics and human factors use knowledge of human abilities and limitations to the design of systems, organizations, jobs, machines, tools, and consumer products for safe, efficient, comfortable and satisfying human use.
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Note that design is the main purpose. As such, ergonomics differs from the sciences that support the ergonomics discipline. In anthropology, cognitive science, psychology, sociology, and medical sciences, the primary purpose is to understand and model human behavior, rather than to utilize knowledge for design. Ergonomics may have more in common with engineering, which is design oriented (Moray, 1994). This makes the practice of ergonomics/human factors an applied science. Ergonomics may thus be thought of as a technology, not merely a science. Today, most ergonomics education takes place within engineering programs, which is indicative of the importance of design. 1.4 Development of HFE since 1950 In exploring the field of ergonomics, there may be reasons to look at its evolution in Europe and the U.S., starting around 1950. In the U.S., human factors emerged as a discipline after World War II. Many design problems were encountered in the use of sophisticated war equipment such as airplanes, radar and sonar stations, and tanks. Sometimes these caused human errors with grave consequences. For example, during the Korean War, reputedly more U.S. pilots were killed during training than in war activities. This raised the issues of appropriate design of controls and displays in cockpits: how can information be displayed better in the cockpit, and how can controls be integrated with the task so that they are easier to handle? Improvements were implemented, such as controls that combined several functions, and displays were laid out so that the relationship between controls and displays was clear; control-display compatibility became an important design concept. As a result of these improvements and new pilot training programs, the number of fatalities in pilot training decreased to a fraction (5%) of what they had been. Ever since, much of the research in human factors in the U.S. has been sponsored by the Department of Defense. Consequently, the information in textbooks on human factors is heavily influenced by results from military research. This is not necessarily a disadvantage because most models, theories, and findings are applicable to the design of civilian systems as well; the human operator remains the same. Other U.S. federal agencies have sponsored research on many civilian applications, including: • Federal Highway Administration: design of highways and road signs • National Aeronautics and Space Administration: physiological impact; human factors design of space stations • National Highway Traffic Safety Administration: design of cars to improve crash worthiness, lighting system, and controls • Department of the Interior: ergonomics in mining • National Bureau of Standards (now called National Institute of Standards and Technology): consumer product safety • National Institute of Occupational Health: ergonomic injuries at work; industrial safety; work stress • Nuclear Regulatory Commission: design requirements for nuclear power plants • Federal Aviation Administration: aviation safety; air traffic control
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Eastman Kodak in Rochester, New York, was the first company in the U.S. to implement a substantial industrial ergonomics program, circa 1965 (Chengalur et al., 2004). In Europe, ergonomics had a different history due to various influences. For example, in Great Britain, the coal mining industry sparked tremendous ergonomics interest, especially in the area of safety and occupational hazards. Ergonomics is also well established in Belgium, France, Germany, Holland, Italy, Poland, the Scandinavian countries, and Spain. In most European countries, the driving factors for ergonomics have been worker safety, health, and comfort. Particularly in the Scandinavian countries and Germany, labor unions have taken a strong interest, and they often dictate the type of production machinery to be purchased. Today, ergonomics in industry has the dual purpose of promoting productivity and improved conditions of work. Several recent studies have pointed to significant improvements in productivity as a result of ergonomic measures taken in industry. With rather modest investments, benefit-cost ratios of 50:1 have been obtained (Helander, 1995). 1.5 Research and Development in Human Factors and Ergonomics— a Systems Approach Ergonomics research can be applied as well as basic. Good research should be supported by theories of human behavior and human functionality. Often theories in the behavioral and cognitive sciences are used. However, other sciences, such as engineering, medicine, biomechanics, and computer science, also contribute toward understanding human behavior and functionality. In formulating research topics and design solutions, not only basic human characteristics such as perception, memory, and manual response but also a host of other related issues should be considered. For example, realizing that human response is different between individuals, one can try to measure some of the cognitive and biomechanical characteristics and relate these to the performance of users. For example, in human computer interaction, good cognitive abilities such as visual memory and logical reasoning are very important. Users with low visual memory capacity do perform as well as users with high visual memory (Egan, 1988). In other words, HFE applies knowledge from related disciplines in its basic research to derive good design solutions. It can be said that HFE engages in basic and applied research to seek support for design solutions. Therefore, it is a science as well as a craft (see Long and Dowell, 1989). “Science” denotes its empirical and systematic approach, while “craft” refers to the art and creativity of its application. A Systems Description of HFE In this subsection, the science of HFE is described by taking a systems approach (see Christensen, 1962). Most ergonomics problems may be explained in a systems context and, for HFE, one may use an environment-operator-machine system, as illustrated in Figure 1.1. The operator is the central focus in HFE and should be described in an organizational context; this is the purpose of Figure 1.1, which illustrates only the most important operator concepts. In reality, human perception, information processing, and
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response are much more complex, with many feedback loops and variables that are not detailed in Figure 1.1 (for an overview, see Wickens and Hollands, 2000).
FIGURE 1.1 Ergonomics systems model for measurement of safety and productivity. In HFE, a classification of independent and dependent variables is often used to analyze a problem. The independent variables are associated with design parameters of the environment and the machine (such as alternative task allocation, controls, and displays). The dependent variables are associated with the operator subsystem and measure the effect of a proposed design on the operator. These are detailed in Figure 1.1 and include measures of negative as well as positive outcome and satisfaction. The operator (or user) is central to HFE, so the operator or user subsystem will be discussed first. The operator first perceives the environment—mainly through the visual and auditory senses—and then considers the information, makes a decision, and finally produces a control response. Perception is guided by the operator’s attention. From the millions of bits of information available in the visual field, the operator will, by instinct (or deliberately), select the information most relevant to the task. Some attentional processes are automatic and subconscious (preattentive) and thereby, executed instantaneously (Neisser, 1976). Some processes become automatic with training, while some are deliberate with slow strategies that require more time to analyze. For new or unusual tasks, decision making can be time consuming. The operator will need to interpret the information, the alternatives for action, and to what extent those actions are relevant to achieve the goals of the task. For routine tasks, decisions are more or less automatic and can be accomplished more quickly. In this context, researchers rightly question whether “decision making” is an appropriate term. Because there is not a formal decision, “situated action” may be more appropriate to describe the automaticity in response. The perception and following actions flow—just as for an experienced car driver (for example, see Klein, 1998).
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The purpose of the operator’s response is to convey information through manual response such as control of a machine (e.g., computer) or a tool (e.g., hammer) or an artifact (e.g., football). It can also be a verbal response such as computer voice control of a machine or verbal message to a co-worker. Modulating Variables Several modulating variables affect task performance. These include: operator needs, attitudes, competence, expertise, motivation, age, gender, body size, and strength. These variables describe the fact that different people react or behave differently. For example, an experienced, competent operator will perceive a task differently than a novice operator will. He will focus on different details of importance, filter irrelevant information, and “chunk” the information into larger units so that it is possible to make faster and more efficient decisions. For example, a football professional who watches a football game will see many details of the game and can predict what will happen. Another example of a modulating variable is body size. Small and large individuals require differently sized workstations. One purpose of anthropometry is to design a workspace to fit operators with different body sizes. Effects of Stress Stress is an important variable that affects perception and decision making as well as response selection. High psychological stress levels usually occur when the time to perform a task is limited, or when too much information must be processed. Under stressful conditions, the bandwidth of attention may narrow, and operators develop “tunnel vision.” It becomes difficult for the operator to consider information “outside” the tunnel. Therefore, the probability of operator error increases. High stress levels lead to increased physiological arousal and can be monitored or measured by using various physiological measures, such as heart rate, EEC, blink rate, and excretion of stress hormones (catecholamines such as nor adrenalin). For example, after a long day of stressful work, the level of noradrenalin in the blood will be higher. The Environment The subsystem Environment is used to conceptualize the task as well as the context in which the task is performed. It could be a steel-worker monitoring an oven; in this instance, the organization of work determines the task allocation: some tasks may be allocated to fellow workers, supervisors, or computers. Task allocation is a central problem in ergonomics: how can one best allocate work tasks among machines and operators so as to realize company goals and individual goals? Task allocation affects how information is communicated between employees and computers, and it also affects systems performance. How can one achieve job satisfaction and productivity at the same time? The operator receives various forms of feedback from his actions, for example, from task performance, co-workers, and management. To enhance task performance, communication, and job satisfaction, feedback must be informative. This means that
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individuals must receive feedback on how well or poorly they are doing. An operator may perform well and his colleague may perform poorly. Both must be informed and receive feedback on their performance. The ambient environment describes the influence of environmental variables on the operator. For example, a steel-worker is exposed to high levels of noise and heat. This increases physiological arousal and stress, thereby affecting task performance, safety, and satisfaction. The importance of the organizational environment has come to fore in the last few years, resulting in a branch of HFE termed macroergonomics (Hendrick and Kleiner, 2002). In the organizational work environment, company policies with respect to communication patterns, decentralization of responsibilities, and task allocation can have an impact on ergonomics design in terms of appropriate design measures. One consideration is to decide first who should do what and how people should communicate. Following these decisions, design of tasks, displays, and controls for the team can be undertaken. Although macroergonomics is important, there is still not enough research to date. One notable exception is the sociotechnical research by the Tavistock Group in the U.K. in the 1950s, which addressed the design of mining equipment and the effect of task allocation. DeGreene (1973) was quick to comment that human factors research has ignored the motivational, morale, and social stress problems created in systems design. Perhaps the dominant influence of military HFE research in the U.S. has ignored many of the organizational concerns, given that the military organization is well established relative to other organizations in industry (Helander, 1997). For the purpose of completeness, it should be mentioned that, although organizational considerations are important in the work context, they are less important for design of leisure systems and consumer products. This is because such systems and products are used by individuals who typically do not need to consider collaboration and task delegation. The Machine Subsystem The Machine subsystem is broadly conceptualized in Figure 1.1. The term “machine” is in a sense misleading, but it is used here to symbolize any artifact. The machine could be a computer, VCR, or football. The term “controls” in Figure 1.1 denotes machine controls used by the operator. The control of the machine may be taken over by automation and computers through delegation of tasks to autonomous processes. As a result of machine control, a changing state is displayed. The changing state can be seen or heard: a pocket calculator will show the results of a calculation; the melting iron in a steel plant will change temperature and color; a computer will produce a sound; and the toaster will pop out the bread. All of these are examples of displays. They convey visual or auditory information and can be designed to optimize systems performance. It is important to note that the system in Figure 1.1 has feedback. Machine information is fed back to the environment subsystem and becomes integrated with the task. Ergonomics is concerned with dynamic systems. It is always necessary to complete the loop. In this regard, ergonomics is different from other disciplines; in experimental psychology, for example, it is not necessary to study dynamic systems. The system in
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Figure 1.1 will be used to discuss three major systems goals in ergonomics: safety, productivity, and operator satisfaction. 1.6 The Goals of Ergonomics Ergonomics is rarely a goal by itself; safety, operator satisfaction, and productivity are common goals. Rather, ergonomics is a design methodology that is used to arrive at safety, productivity, and satisfaction. The Goal of Safety The safety status of a system can be assessed by comparing the performance requirements of the environment with the performance limitations of the operator (Figure 1.1). A task will impose a demand for operator attention, and this demand varies in different context and over time. For example, a car driver must look constantly at the traffic when the traffic situation is demanding and adjust the attention level when the situation becomes less demanding. The same driver may become sleepy after driving for a long time and have a low level of attention, but a driver of a race car would not be sleepy—the attention level is always high, thus keeping the driver constantly alert. If the task demands for attention are greater than the available attention, there is an increased risk for accidents or errors. Thus, it is important to understand how the limitations imposed by operator perception, decision making, and control action can be taken into consideration in design, so as to create systems with low and stable performance requirements. Injuries and accidents are relatively rare in the workplace, and therefore it may be difficult to analyze safety. Rather than waiting for accidents to happen, it may be necessary to predict safety problems by analyzing other indicators (or dependent variables) such as operator errors, subjective assessments, and physiological response variables. These measures are indicated in Figure 1.1 under the heading of “measures of negative outcome.” When a system is redesigned to make it safer, several different options may be available, such as: • Tasks between workers and machines/computers can be reallocated; workers may be moved from a hazardous area and automation may take over their jobs. • Work processes and workstation can be redesigned to improve work posture, comfort, and convenience. • The exposure to ambient stressors can be reduced, including noise and heat stress. • Organizational factors can be improved, such as allocation of responsibility and autonomy as well as policies for communication among workers and supervisors. • Design features of a machine can be improved, including changes of controls and displays.
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The Goal of Productivity In any work context, it is important to improve productivity. This can sometimes be accomplished through thoughtful human factors design. The use of Taylorism has already been mentioned; through measurement of the time involved in assembling a product, Taylorism can split up tasks in many short elements, each performed by a dedicated operator. This can create very short job cycles (of less than a minute); in the long term, there may be poor job satisfaction and biomechanical injuries due to repetitive work. There are better ways to enhance productivity; one can design a system that improves performance affordances. For example, one can design a machine so that handling of the machine controls becomes intuitive, such as high control-response compatibility. One can also design display information using principles of ecological display design, which makes it easy to interpret the information and act quickly (for example, see Vincente, 1999). This means that, through efficient design of the system, the operator can excel in exercising his skills. Such system design makes it possible to perceive quickly, make fast decisions, and exercise efficient control. In general, operators like to excel because the work flows smoothly under full control. The operator will perceive the flow and will think that the situation is enjoyable (Czikszentmihalyi, 1990). In Figure 1.1, several measures of positive outcome are indicated. One can measure productivity, quality, and time on task. One can also ask the operator how well the system works, which is a subjective assessment. These measures are common dependent variables used to measure the productivity of a system. The Trade-Off between Productivity and Safety Ergonomic improvements may focus on reducing operator errors as well as increasing efficiency or speed of operation. It is, however, difficult to improve safety and productivity simultaneously. In general, the greater the speed (of vehicles, production machinery, etc.) is, the less time will be available for the operator to react. A shorter time for operator reaction will compromise safety but increase productivity. Operators therefore have a choice between increased speed and increased accuracy. This is referred to as the speed-accuracy trade-off or SATO (Wickens and Hollands, 2000). Industrial managers often encourage employees to increase speed and accuracy (work more quickly and with better quality). This is contrary to the concept of SATO and difficult or impossible to achieve. In some work environments, such as a process plant or nuclear power plant, safety and production of electricity are two self-evident goals, and together they determine the design of the plant. In this case, safety and productivity must be decoupled through a thoughtful design. It cannot be the case that productivity overrules safety—the consequences could be a disaster. However, safety and quality are coupled. If the number of operator errors can be reduced, safety as well as production quality may be improved. An emphasis on quality and safety is therefore more appropriate than the traditional approach on quantity and quality. The goal, then, is to design a safer environment. This can be done most efficiently if the operator’s reactions and actions can be predicted by
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the designer. The operator’s perception, decision making, and actions are therefore always central to ergonomics design. The Goal of Operator Satisfaction The last systems goal is operator satisfaction and this will be addressed in a broad sense: from work satisfaction to satisfaction of use. Various aspects of dissatisfaction, such as job dissatisfaction or consumer dissatisfaction, will also be considered. The main point in Figure 1.1 is that satisfaction or dissatisfaction may be predicted by comparing operator needs and attitudes with the performance requirements of the environment and the performance affordances of the machine. Satisfaction and dissatisfaction are mediated through the operators’ needs and attitudes, which can be very different among operators. Some can be fully satisfied by a particular job, while others are dissatisfied. Needs and attitudes also vary substantially between countries and cultures. What are con-sidered workers’ rights in Sweden (e.g., to have a window in the office) are less important in other countries. In Sweden, a lack of window would cause great dissatisfaction because office workers have “acquired” a personal need, but office workers in U.S. or Asia may not think twice. In terms of productivity and safety, the trade-off is obvious: increased productivity, which can lead to an increase in error rate and safety problems. Similarly, a lower error rate and greater safety typically lead to a lower speed of production. In job satisfaction or dissatisfaction, no similar trade-off appears to exist. One would think that a satisfied worker would produce more and a dissatisfied worker would produce less and that a satisfied worker would be safer and a dissatisfied worker may not be so safe. However, extensive research on these issues has demonstrated that no connection is present. Rather, job satisfaction often follows from effective job performance. 1.7 The Measurement Problem In Figure 1.1, several dependent variables such as operator errors, satisfaction, and productivity are defined. These can be used to assess the state of the system and evaluate proposed design solutions. In this section, independent variables are defined. Independent variables are design variables; most of them describe design features that the HFE expert may want to implement or test out. For example, an HFE professional may want to design a warning sign to enhance safety. The design question could be: how many words should be used? If the message is short, operators may not understand; if it is too long, they may not read it, or if the lettering is too small, it may be difficult to see. To investigate this problem, one can set up an experiment in a laboratory in which test subjects can read different warning signs. These types of design questions are easier to research in a laboratory experiment than in the real world (Chapanis, 1967). A laboratory experiment offers better control; one can try out different messages and different sizes of letterings and measure the effect on perception and understanding. Unfortunately, a laboratory study misses out on “ecological validity.” That is, what was found in the laboratory may not be true or applicable in the real world. For example, consider a construction site. A safety sign developed in a laboratory may turn out to be barely
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visible in the cluttered environment of a construction site; also, environmental stressors (e.g., noise and heat) may distract the operator. Therefore, the sign has little effect and utility. Another problem relates to a conceptual gap between some of the dependent variables and the design variables. Consider as an example the measurement of stress in traffic. Assume that we use galvanic skin response (GSR) to measure stress. It can be argued that a high GSR is bad because it is likely that some drivers will be overly stressed and perform worse. A moderate level of GSR is good because it means that the driver is alert. The question is then: how can one distinguish a moderate level of measurement from a high level? For GSR, there are no absolute levels—the base line shifts constantly. It is different with heart rate because one can simply measure the number of beats per minute. Should one then use heart rate instead to measure stress in traffic? Probably not, because an elevation in heart rate may be due to the physical work in turning the steering wheel rather than the mental stress. Many similar questions exist: will slow, rather than quick, decision making improve the quality of decisions and reduce errors? Will quick movements of the steering wheel in a car, rather than slow movements, improve safety? Do moderate levels of stress lead to greater quality in manufacturing? Such questions are sometimes very difficult to prove in research. It is usually accepted that improved visibility, fast decision making, highfrequency steering wheel movements, and moderate stress levels are beneficial. However, in many cases, the correct answer depends on the situation; there are trade-offs and exceptions. An experienced HFE professional will know how to evaluate different situations. Methods, Measurements, and Procedures in Human Factors and Ergonomics To collect data, to evaluate situations, and to design systems, many new methods and procedures have been developed in the human factors arena. Although most of these methods are unique to HFE, some are also used in industrial psychology and in systems engineering. Table 1.2 provides a list of methods without any explanation of how they can be used. The main purpose here is to illustrate that the number of methods is very large. Detailed information is given in Chapanis (1996), Wilson and Corlett (2002), and Salvendy (1997). Human factors experts will know the method to select.
TABLE 1.2 One Hundred Methods to Collect and Analyze Data in Human Factors and Ergonomics Accident analysis Activity analysis Anthropometric analysis/design Biomechanical analysis Body rhythms and shift work design Checklist analysis Climate analysis Cognitive abilities testing Cognitive systems design Cognitive task analysis
Multimedia design Natural language interface design Operational sequence analysis Operator performance assessment Organizational analysis Organizational design Performance measures (time and error) Performance ratings Physical work load assessment Predetermined time analysis
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Production systems analysis Cognitive walkthrough Psychomotor proficiency testing Cognitive work analysis Psychophysics and scaling Comfort rating Psychophysiological measurements Communication analysis Questionnaire design Cost/benefit analysis Rapid prototyping Critical incident technique Repetitive motion injury assessment Decision support system design Scenario-based design Decision/action analysis Screen design Design reviews Direct observation/activity analysis Selection testing Simulation design/evaluation Discomfort rating Standards and guidelines for design Environmental sampling Stress measurement Error analysis Survey design Error classification Systems analysis Experimental design Systems safety Failure mode and effects analysis Task analysis Fatigue measurement Task performance measures Fault tree analysis Human error rate prediction (therp) Function allocation Thermal stress measurement Goals-means task analysis Time and motion study GOMS analysis Time lapse photography Hazard analysis Training needs assessment Human reliability assessment Usability analysis Human-computer interaction Usability engineering Illumination measurement Usability testing Information analysis User log books Information visualization User population definition Injury analysis Verbal protocol analysis Intervention studies Vibration measurement Interview technique Video recording Job motivation assessment Virtual environment design Job satisfaction measurement Visibility/legibility analysis Kansei engineering Vision/hearing testing Link analysis Visual performance assessment Macroergonomics Manual materials handling assessment Walkthrough analysis Work condition evaluation Mental model assessment Working posture analysis Mental workload assessment Workload analysis Menu design Workspace design Mockup design/analysis
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FIGURE 1.2 Procedure for design and redesign of a system. 1.8 Analyzing Design Activity Many HFE specialists are involved in design; it is therefore of interest to analyze the steps that lead to a new design. A procedure for design activity is given in Figure 1.2. Systems goals for design are formulated based on requirements by users, markets, or organizations. User and market requirements specify the types of products that should be manufactured. User and organizational requirements may specify how a job should be designed. There may also be legal requirements, for example, that a robotics workplace should be safe, or company requirements that certain existing machines must be used for production. The latter requirements are usually handled as constraints in design, rather than goals (Suh, 1990). Constraints are different from goals; goals define the design space whereas constraints delimit the design space by invalidating certain designs. Based on the systems goals, functional requirements are specified, and the task is then to design a new system, artifact, or job that will satisfy functional requirements. The two main activities in design work are synthesis and analysis. The synthesis stage is when designers use their knowledge and experience to come up with a design solution that will satisfy the functional requirements. Thus, it is a creative task. Studies of designers’ decision making have produced some interesting results. Goel and Pirolli (1992) investigated engineers’ design decisions for design of new products and found that only 2% of the decisions were logical, in the sense that B follows from A. The remaining 98% were decisions based on associations and experiences. This means that designers will first try to apply what they already know and then see if it works. This trial-anderror-based procedure resembles case-based reasoning; that is, take a previous design solution or experience, modify it slightly so that it can fit the present scenario, then evaluate the results. This is a rather erratic process and has been validated by other researchers. Guindon (1990) found that software programmers tend to jump back and forth between different tasks following their associations. The situation was the following: the programmer would be writing code for solving a problem; he would then (out of the blue) think about
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a good solution for another problem and, as a result, would leave the first (still unsolved) problem and focus on the second. Guindon termed this behavior “situated cognition”; programmers deal with the problem with which it is practical to deal at any given time. It would take more effort to write down the solution to the second problem, so the first problem is delayed until later. There is no predetermined top-down order. Seemingly, such irrational process, driven by the designer’s associations and evaluations of trade-offs, may be the basis for creativity. New combinations are generated and evaluated immediately by the designer and then abandoned or retained. The associative and negotiable nature of creative cognition is probably why artificial intelligence (AI) has failed. Design-based AI cannot consider associations other than those based on logic and has a poor sense of evaluation (Gero, 1990). To be successful in design, the ergonomist must have knowledge and experience that can produce good design solutions. Moray (1994) argued that ergonomists must have an interdisciplinary background. For example, to develop good design solutions in a manufacturing plant, the ergonomist should also be an engineer. Assume that a production machine has caused repetitive motion injuries for the machine tenders, and the company is considering buying a replacement machine. An occupational nurse, who is an expert at diagnosing ergonomic injuries, could not predict if the ergonomic as well as the industrial production problems would be solved by a new machine (Helander, 1995). To deal with such design problems, an ergonomist needs broad background knowledge. To suggest appropriate design solutions, a combination of HFE knowledge and domain knowledge is required. Another example is from human-computer interaction. In a review of usability studies of human-computer interfaces, Landauer (1995) claimed that, on average, the interface had 40 usability bugs (the range of variation for different interfaces was 17 to 140). During a test session with the software, a domain expert can, on average, identify 20% of the bugs. An HFE (or HCI) expert will identify 40%, and an individual who is a domain and HFE expert will identify 60% of the bugs. In short, a combination of human factors and domain expertise is therefore desirable in problemsolution analysis. It takes much experience to come up with a good design solution (called design synthesis). On the other hand, it is fairly easy to evaluate a new design because analytical methods can be proceduralized and computerized. Laboratory studies or studies of realworld performance can be conducted. Typically, the types of dependent variables referred to in Figure 1.1 are used for such evaluation: human performance data, physiological data, and subjective assessments. Based on the outcome of the analysis, an improved design may be proposed, the purpose of which is to improve operator performance and safety. The system is then implemented. Implementation gives an opportunity to collect real data in the real setting for identifying usability problems as well as new customer requirements. A designer will encounter situations in which the customer requirements have not been identified. This is particularly common in software design in which a company is marketing a new computer program. The market for the program has not been tested and the company is waiting for the sales figures and customer comments on the software. For the second version of the software, the company is armed with better estimates of customer requirements and can reformulate the functional requirements and improve the design solution. To compensate for the time delay, the company can perform usability
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testing of partial or rapid prototypes, but realistic data will only be available when the product is available on the market. Then the feedback loop in Figure 1.2 is closed. 1.9 Standards in Human Factors and Ergonomics In forensic activity, it is crucial to keep track of the various HFE standards that apply to design. About 150 standards documents have been issued by the International Standards Organization (ISO), as listed in Appendix 1.1. These standards were selected based on the criteria that they have the words “ergonomics” or “human factors” in the title or in the text. Most of these standards deal with HFE design; the remainder reference ergonomics design problems and recommend other relevant ISO standards. International Standards Organization ISO standards are important in all countries around the world and can readily be referred to in legal matters; information about ISO standards is available at http://www.iso.org./ ISO standards often take precedence over local country standards, such as those issued by ANSI in the U.S. or by other countries. They are important for good reasons: they are developed by international teams of experts and they have been approved by several countries. The ISO standards regulate HFE design in several different areas, including: • General ergonomics, e.g., anthropometry • Principles for human-centered design • Design of signals and controls and displays • Design of systems for speech communication • Ergonomic principles related to mental workload • Measurement of heat stress and cold stress • Ergonomic design for the safety of machinery • Ergonomic design of control centers and evaluation of control rooms • Evaluation of static working postures • Principles of visual ergonomics—indoor lighting • Ergonomic requirements for office work with visual display terminals • Hardware requirements of visual display, colors, keyboard, and input devices • Software requirements—usability, dialogue principles, dialogues of menu, command, form filling, and direct manipulation • Ergonomic requirements for work with visual displays based on flat panels • Ergonomics in manual materials handling, including lifting and carrying There are also many important ISO standards in safety, only a few of which are referred to in Appendix 1.1. Standards Development in the U.S. In the U.S., interest in HFE standards has been great, particularly in the military community. The best known is “Design Criteria Standard—Human Engineering,” referred to as MIL-STD 1472F. This document is used in the procurement of military
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equipment. The Handbook for Human Engineering Design Guidelines (MIL-HDBK759C) is also important. These and other military standards documents can be downloaded from: http://iac.dtic.mil/hsiac/Health_Hazards.htm. In recent directives, the U.S. military refers to ISO and U.S. standards, which are given priority over the MIL standards. Many documents have been published by other standards-developing agencies in the U.S. These include: • The Occupational Safety and Health Act of 1970 (http://www.osha.gov/) • The Americans with Disabilities Act (ADA) of 1990 (http://www.access.gpo.gov/) • The California Ergonomics Standard of 1997, which addresses primarily the prevention of repetitive motion injuries (RMI) (http://www.dir.ca.gov/) The development of standards in the U.S. has had its ups and downs, and often seems to be driven by political arguments rather then measures of benefit-cost. The U.S. Ergonomics Program Standard developed under the Clinton administration was repealed by the Bush administration. Similarly, the Ergonomics Rule implemented in Washington State in 2000 was removed in 2003. The American National Standards Institute ANSI Z365 committee was formed in 1991 with the objective of developing a standard related to musculoskeletal injuries. The National Safety Council withdrew its role as chair for this committee in 2003, and the committee’s work seems to be in limbo. Industry appears to have realized that repetitive motion injuries are not important to standardize—they seem to be less important than ergonomic injuries caused by manual materials handling. Under the umbrella of the American National Standards Institute, several successful developments have occurred. The first was ANSI/HFS 100–1988, American National Standard for Human Factors Design of Visual Display Terminals. This document inspired several ISO standards, in particular a series of documents: ISO 9241–1 to ISO 9241–8. The Z10 Committee, Occupational Safety and Health, was formed in 2001. It has the objective of developing a standard for management of occupational safety and health. This committee recently delivered a draft standard (American Industrial Hygiene Association, 2004). European Standards European standards are developed by the European Union. In selecting areas for standardization, the E.U. collaborates with ISO. Members of the E.U. will support important ISO efforts but take their own initiatives in areas in which ISO has not yet proposed a standard. Directive 89/39/EEC, given in 1989, regulates workplaces, use of work equipment, use of personal protective equipment, work with display screen equipment, safety signs, plus a few other activities (europe.osha.eu.int/legislation/directives/al.php3). Three particularly important safety standards have been developed: • EN 1005–1:2001 Safety of machinery. Human physical performance. Terms and definitions • EN 1005–2:2003 Safety of machinery. Human physical performance. Manual handling of machinery and component parts of machinery
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• EN 1005–3:2002 Safety of machinery. Human physical performance. Recommended force limits for machinery operation Standards Development in Other Countries Many other countries have developed HFE standards, including most countries in Europe and several countries in Asia, plus Australia and New Zealand. Of particular interest are the “six pack” regulations developed by the Health and Safety Executive in the U.K. This set of standards gives sound and practical advice for design of working environments (http://www.hsebooks.co.uk/books/static/whatsnew.htm #SixPack). 1.10 Conclusion This chapter has given an overview of the historical and conceptual background of human factors and ergonomics. Systems design remains an essential methodology for the analyst/designer. This design serves the purpose of clarifying important dependent variables and interactions in design. If possible, it would be necessary to conceptualize and predict cause-effect relationships. A large battery of methods to use to analyze and/or design systems and artifacts exists. Design constraints will usually determine the method to choose. The ergonomics standards published by the International Standards Organization and other standardization organizations are based on thorough research and international consensus. These are very important in the forensic perspective. The HFE profession is driven by design requirements from users, markets, industries, organizations, and governments. HFE must be able to respond quickly to the changing needs of society. Training programs in HFE must be able to incorporate new areas of interest. Certification programs for HFE professionals must be flexible enough to reconsider changes in current needs, and teaching programs must incorporate new knowledge. Formal education in HFE is required in order to understand how methods for analysis and design of HFE systems can be used. For forensic purposes it is most appropriate to refer to HFE experts who have been certified. In the U.S., certification is handled by the Board of Certification in Professional Ergonomics (BCPE; see http://www.bcpe.org/) under the auspices of IEA. In European countries, many of the ergonomics. societies can certify members under the auspices of CREE (www.eurerg.org/aboutCREE.htm) and IEA. Acknowledgment I acknowledge the help of Halimahtun M.Khalid for her comments on and editorial input into this chapter.
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References American Industrial Hygiene Association. (2004). BSR AIHA Z10–200x, Occupational Health and Safety Management Systems. Fairfax, VA: American Industrial Hygiene Association. Braidwood, R. (1951). Prehistoric Men . Chicago, IL: Natural History Museum. Brown, O. Jr., Noy, I., and Robertson, M. (1995). Special survey of IEA Federated Societies. Santa Monica, CA: International Ergonomics Association, c/o Human Factors and Ergonomics Society. Chapanis, A. (1967). The relevance of laboratory studies to practical situations. Ergonomics , 10(5), 557–577. Chapanis, A. (1995). Ergonomics in product development: a personal view. Ergonomics , 38, 1625–1638. Chapanis, A. (1996). Human Factors in Systems Engineering . New York: John Wiley & Sons. Chengalur, N., Rodgers, S.H., and Bernard, T.E. (2004). Kodak’s Ergonomics Design for People at Work . New York: John Wiley & Sons. Childe, G. (1944). The Story of Tools . London: Cobbot. Christensen, J.M. (1962). The evaluation of the systems approach in human factors engineering. Hum. Factors , 4(1), 7–22. Czikszentmihalyi, M. (1990). Flow: the Psychology of Optimal Experience . New York: Harper Collins. DeGreene, K.B. (1973). Sociotechnical Systems . Englewood Cliffs, NJ: Prentice Hall. Eriksson, R. (1976). Personal communication. International Labor Organization, Geneva, Switzerland. Egan, D.E. (1988). Individual differences in human-computer interaction. In M.G.Helander (Ed.), Handbook of Human Computer Interaction . Amsterdam, The Netherlands: New Holland. Gero, J. (1990). University of Sydney. Personal communication. State University of New York at Buffalo, Buffalo, New York, April 1990. Goel, V. and Pirolli, P. (1992). The structure of design problem spaces. Cognitive Sci. , 16, 35–429. Guindon, R. (1990). Designing the design process: exploiting opportunistic thoughts. Hum. Computer Interaction , 5, 305–344. Helander, M.G. (1995). A Guide to the Ergonomics of Manufacturing . London: Taylor & Francis. Helander, M.G. (1997). Forty years of IEA: some reflections on the evolution of ergonomics. Ergonomics , 40, 952–961. Hendrick, H.W. and Kleiner, B.W. (2002). Macroergonomics. An Introduction to Work Systems Design . Santa Monica, CA: The Human Factors and Ergonomics Society. Hendrick, H.W. (1995). Future directions in macroergonornics. Ergonomics , 38, 1617–1624. International Ergonomics Association (2004). Downloaded from http://www.iea.cc/. Karwowski, W. (1991). Complexity, fuzziness, and ergonomic incompatibility issues in the control of dynamic work environments. Ergonomics , 34, 671–686. Khalid, H.M. (2003). ASEAN ergonomics and prioritizing research. Proc. 15th Triennial Congr. Int. Ergonomics Assoc. Seoul: The Ergonomics Society of Korea (CD-ROM). Klein, G. (1998). Sources of Power. How People Make Decisions . Cambridge, MA: MIT Press Konz, S. and Johnson, S. (1990). Work Design: Industrial Ergonomics . 5th ed. Scottsdale, AZ: Holcomb Hathaway Publishers, Inc. Kroemer, K., Kroemer, H., and Kroemer-Elbert, K. (1994). Ergonomics: How to Design for Ease and Efficiency . Englewood Cliffs, NJ: Prentice Hall. La Mettrie, J.O. (1748). L’homme Machine . Leyden, The Netherlands: Elie Luzac. Available in English at http://www.%20cscs.%20umich.%20edu/cr%20shalizi/LaMattrie%20ie/Machine/. Landauer, T. (1995). The Trouble with Computers . Cambridge, MA: MIT Press.
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Licht, D.M., Polzella, D.J., and Boff, K.R. (1991). Human factors, ergonomics and human factors engineering. An analysis of definitions (Report No 89–01). Wright-Patterson AFB, OH: CSERIAC Program Office. Long, J. and Dowell, A. (1989). Conceptions for the discipline of HCI: craft, applied science and engineering. Proc. BCS HCI SIG Conf. , 9–32. UK: University of Nottingham. Luczak, H. (1997). Arbeitswissenschaft in internationalen Vergleich. In H.Luczak and E.Volpert, Eds., Handbuch der Arbeitwissenschaft . Stuttgart: Verlag Schaeffer-Poeschel. Neisser, U. (1976). Cognition and Reality . San Francisco, CA: Freeman. Meister, D. (1985). Behavioral Analysis and Measurement Methods . New York: John Wiley & Sons. Moray, M. (1994). The future of ergonomics—the need for interdisciplinary integration. Proc. IEA Congr. , 1791–1793. Santa Monica, CA: The Human Factors and Ergonomics Society. Ramazzini, B. 1940 (1713). In Wright, W. (translation). The Diseases of Workers . Chicago, IL: University of Chicago Press. Rosenbrock, H.H. (1983). Seeking an appropriate technology. Proc. IFAC Symp. Syst. Approach Appropriate Technol. Transfer , 127–134. Vienna Austria: IFAC. Salvendy, G. (1997). Handbook of Human Factors and Ergonomics . New York: WileyInterscience. Shaw, L. and Sichel, H. (1975). Accident Proneness . New York: Pergamon Press. Smith, K.U. (1988). Origins of ergonomics and the International Ergonomics Association. Human Factors Soc. Bull , 31(1). Santa Monica, CA: Human Factors and Ergonomics Society. Suh, N.P. (1990). The Principles of Design . New York: Oxford University Press. Vanwonterghem, K. (1994). Personal communication. Brussels, Belgium. Vincente, K. (1999). Cognitive Work Analysis . Mahwah, NJ: Lawrence Erlbaum. Wickens, C.D. and Hollands, J.G. (2000). Engineering Psychology and Human Performance , 3rd ed. New York: Prentice Hall. Wilson, J.R. and Corlett, E.N. (2002). Evaluation of Human Work. A Practical Ergonomics Methodology , 2nd ed. London: Taylor & Francis.
Appendix 1.1 HFE Standards Issued by International Standards Organization ISO Road vehicles 2575:2000 ISO 2631– Mechanical vibration and shock 1:1997 ISO Earth-moving machinery 3411:1995 ISO 3767– Tractors, machinery for agriculture and 1:1998 forestry, powered lawn and garden equipment ISO 3767– Tractors, machinery for agriculture and 2:1991 forestry, powered lawn and garden equipment ISO 3767– Tractors, machinery for agriculture and 3:1995 forestry, powered lawn and garden
Symbols for controls, indicators, and telltales. Cor 1:2001; Amd 1:2001; Amd 4:2001 Evaluation of human exposure to wholebody vibration—part 1: general requirements Human physical dimensions of operators and minimum operator space envelope Symbols for operator controls and other displays—part 1: common symbols Symbols for operator controls and other displays—part 2: symbols for agricultural tractors and machinery Amd 2:1998 additional symbols Symbols for operator controls and other displays—part 3: symbols for powered
The discipline of human factors engineering and ergonomics
equipment ISO 3767– Tractors, machinery for agriculture and 5:1992 forestry, powered lawn and garden equipment ISO Passenger cars 3958:1996 ISO Road vehicles 4040:2001 ISO Agricultural tractors 4253:1993 ISO 4254– Tractors and machinery for agriculture and 1:1989 forestry ISO Hydraulic fluid power 4413:1998 ISO Pneumatic fluid power 4414:1998 ISO 5349– Mechanical vibration 1:2001 ISO Tractors for agriculture 5721:1989 ISO Mechanical vibration and shock 5982:2001 ISO 6242– 1:1992 ISO 6385:2004 ISO 6549:1999 ISO 6682:1986 ISO 6858:1982 ISO 6897:1984
Building construction
lawn and garden equipment Symbols for operator controls and other displays—part 5: symbols for manual portable forestry machinery Driver hand-control reach Location of hand controls, indicators, and tell-tales in motor vehicles Operator’s seating accommodation— dimensions Technical means for ensuring safety— part 1: general General rules relating to systems General rules relating to systems Measurement and evaluation of human exposure to hand-transmitted vibration— part 1: general requirements Operator’s field of vision Range of idealized values to characterize seated-body biodynamic response under vertical vibration Expression of users’ requirements—part 1: thermal requirements
Ergonomic principles in the design of work systems Road vehicles Procedure for H- and R-point determination Earth-moving machinery Zones of comfort and reach for controls. Amd 1:1989 Aircraft Ground support electrical supplies— general requirements Guidelines for the evaluation of the response of occupants of fixed structures, especially buildings and off-shore structures, to lowfrequency horizontal motion (0.063 to 1 Hz) Information and documentation Presentation of catalogues of standards
ISO 7220:1996 ISO Hot environments 7243:1989 ISO 7250:1996 ISO 7397– 1:1993
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Estimation of the heat stress on working man, based on the WBGT-index (wet bulb globe temperature)
Basic human body measurements for technological design Passenger cars Verification of driver’s direct field of view—part 1: vehicle positioning for static measurement
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ISO 7397– 2:1993 ISO 7726:1998
Passenger cars
26
Verification of driver’s direct field of view—part 2: test method Instruments for measuring physical quantities Determination of the PMV and PPD indices and specification of the conditions for thermal comfort Danger signals for public and work areas—auditory danger signals Analytical determination and interpretation of thermal stress using calculation of required sweat rate Combine harvesters—test procedure
ISO 7730:1994
Ergonomics of the thermal environment Moderate thermal environments
ISO 7731:2003
Ergonomics
ISO 7933:1989
Hot environments
ISO 8210:1989 ISO 8230:1997
Equipment for harvesting Safety requirements for dry-cleaning machines using perchloroethylene Forestry machinery Portable chain saws—determination of balance Ship’s bridge layout and associated Requirements and guidelines equipment Mechanical vibration and shock Human exposure—biodynamic coordinate systems Lighting of indoor work places
ISO 8334:1985 ISO 8468:1990 ISO 8727:1997 ISO/CIE 8995:2002 ISO 8996:1990 ISO 9000:2000 ISO 9004:2000 ISO/IEC TR 9126–2:2003 ISO/IEC TR 9126–3:2003 ISO 9241– 1:1997 ISO 9241– 2:1992 ISO 9241– 3:1992 ISO 9241– 4:1998 ISO 9241– 4:1998/Cor 1:2000
Ergonomics Quality management systems Quality management systems Software engineering
Determination of metabolic heat production Fundamentals and vocabulary Guidelines for performance improvements Product quality—part 2: external metrics
Software engineering
Product quality—part 3: internal metrics
Ergonomic requirements for office work with visual display terminals (VDTs) Ergonomic requirements for office work with visual display terminals (VDTs) Ergonomic requirements for office work with visual display terminals (VDTs) Ergonomic requirements for office work with visual display terminals (VDTs)
Part 1: general introduction. Amd 1:2001
Part 2: guidance on task requirements
Part 3: visual display requirements. Amd 1:2000 Part 4: keyboard requirements
The discipline of human factors engineering and ergonomics
ISO 9241– 5:1998 ISO 9241– 6:1999 ISO 9241– 7:1998 ISO 9241– 8:1997 ISO 9241– 9:2000 ISO 9241– 10:1996 ISO 9241– 11:1998 ISO 9241– 12:1998 ISO 9241– 13:1998 ISO 9241– 14:1997 ISO 9241– 15:1997 ISO 9241– 16:1999 ISO 9241– 17:1998 ISO 9355– 1:1999 ISO 9355– 2:1999 ISO 9886:1992 ISO 9920:1995 ISO 9921:2003 ISO 10068:1998 ISO 10075:1991 ISO 10075– 2:1996
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Ergonomic requirements for office work with Part 5: workstation layout and visual display terminals (VDTs) postural requirements Ergonomic requirements for office work with Part 6: guidance on the work visual display terminals (VDTs) environment Ergonomic requirements for office work with Part 7: requirements for display visual display terminals (VDTs) with reflections Ergonomic requirements for office work with Part 8: requirements for displayed visual display terminals (VDTs) colors Ergonomic requirements for office work with Part 9: requirements for visual display terminals (VDTs) nonkeyboard input devices Ergonomic requirements for office work with Part 10: dialogue principles visual display terminals (VDTs) Ergonomic requirements for office work with Part 11: guidance on usability visual display terminals (VDTs) Ergonomic requirements for office work with Part 12: presentation of visual display terminals (VDTs) information Ergonomic requirements for office work with Part 13: user guidance visual display terminals (VDTs) Ergonomic requirements for Part 14: menu dialogues office work with visual display terminals (VDTs) Ergonomic requirements for Part 15: command dialogues office work with visual display terminals (VDTs) Ergonomic requirements for Part 16: direct manipulation dialogues office work with visual display terminals (VDTs) Ergonomic requirements for Part 17: form filling dialogues office work with visual display terminals (VDTs) Ergonomic requirements for the Part 1: human interactions with displays and design of displays and control control actuators actuators Ergonomic requirements for the Part 2: displays design of displays and control actuators Evaluation of thermal strain by physiological measurements Ergonomics of the thermal Estimation of the thermal insulation and environment evaporative resistance of a clothing ensemble Ergonomics Assessment of speech communication Mechanical vibration and shock Free, mechanical impedance of the human handarm system at the driving point Ergonomic principles related to General terms and definitions mental workload Ergonomic principles related to Part 2: design principles mental workload
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ISO 10303– 214:2003
Industrial automation systems and integration
ISO 10333– 6:2004 ISO 10472– 1:1997 ISO 10535:1998 ISO 10551:1995 ISO 10968:1995 ISO 11064– 1:2000 ISO 11064– 2:2000 ISO 11064– 3:1999 ISO 11111:1995 ISO 11112:1995 ISO 11199– 1:1999 ISO 11199– 2:1999 ISO 11226:2000 ISO 11228– 1:2003 ISO 11334– 1:1994 ISO 11334– 4:1999 ISO 11393– 4:2003 ISO 11399:1995 ISO 11428:1996 ISO 11429:1996 ISO 11553:1996 ISO 11680– 1:2000
Personal fall-arrest systems
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Product data representation and exchange—part 214: application protocol: core data for automotive mechanical design processes Part 6: system performance tests
Safety requirements for industrial Part 1: common requirements laundry machinery Hoists for the transfer of disabled Requirements and test methods persons Ergonomics of the thermal Assessment of the influence of the thermal environment environment using subjective judgment scales Earth-moving machinery Operator’s controls Ergonomic design of control centers Ergonomic design of control centers Ergonomic design of control centers Safety requirements for textile machinery Earth-moving machinery
Part 1: principles for the design of control centers
Walking aids manipulated by both arms Walking aids manipulated by both arms Ergonomics
Requirements and test methods—part 1: walking frames Requirements and test methods—part 2: rollators
Ergonomics
Manual handling—part 1: lifting and carrying
Part 2: principles for the arrangement of control suites Part 3: control room layout. Cor 1:2002
Operator’s seat—dimensions and requirements
Evaluation of static working postures
Walking aids manipulated by one Requirements and test methods—part 1: elbow arm crutches Walking aids manipulated by one Requirements and test methods—part 4: walking arm sticks with three or more legs Protective clothing for users of Part 4: test methods and performance handheld chain saws requirements for protective gloves Ergonomics of the thermal Principles and application of relevant environment international standards Ergonomics Visual danger signals—general requirements, design and testing Ergonomics System of auditory and visual danger and information signals Safety of machinery Laser processing machines—safety requirements Machinery for forestry
Safety requirements and testing for pole-mounted powered pruners—part 1: units fitted with an integral combustion engine
The discipline of human factors engineering and ergonomics
ISO 11680– 2:2000
Machinery for forestry
ISO 11681– 2:1998 ISO 11690– 1:1996
Machinery for forestry
ISO 11748– 2:2001 ISO 11806:1997 ISO 11850:2003 ISO 12100– 2:2003 ISO/IEC 12119:1994 ISO/IEC 12207:1995 ISO 12214:2002 ISO 12239:2003 ISO 12648:2003 ISO 12894:2001 ISO 13090– 1:1998
Acoustics
Road vehicles Agricultural and forestry machinery Machinery for forestry Safety of machinery Information technology Information technology Road vehicles Fire detection and fire alarm systems Graphic technology Ergonomics of the thermal environment Mechanical vibration and shock
ISO 13091– 1:2001
Mechanical vibration
ISO 13091– 2:2003
Mechanical vibration
ISO 13406– 1:1999
Ergonomic requirements for work with visual displays based on flat panels Ergonomic requirements for work with visual displays based on flat panels Human-centered design processes for interactive systems Protective clothing
ISO 13406– 2:2001 ISO 13407:1999 ISO 13688:1998 ISO
Ergonomics of the thermal
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Safety requirements and testing for pole-mounted powered pruners—part 2: units for use with a backpack power source Portable chain saws—safety requirements and testing—part 2: chain saws for tree service Recommended practice for the design of low-noise workplaces containing machinery—part 1: noisecontrol strategies Technical documentation of electrical and electronic systems—part 2: documentation agreement Portable handheld combustion engine-driven brush cutters and grass trimmers—safety Self-propelled machinery—safety requirements Basic concepts, general principles for design—part 2: technical principles Software packages—quality requirements and testing Software life cycle processes. Amd 1:2002 Direction-of-motion stereotypes for automotive hand controls Smoke alarms Safety requirements for printing press systems Medical supervision of individuals exposed to extreme hot or cold environments Guidance on safety aspects of tests and experiments with people—part 1: exposure to whole-body mechanical vibration and repeated shock Vibrotactile perception thresholds for the assessment of nerve dysfunction—part 1: methods of measurement at the fingertips Vibrotactile perception thresholds for the assessment of nerve dysfunction—part 2: analysis and interpretation of measurements at the fingertips Part 1: introduction
Part 2: ergonomic requirements for flat-panel displays
General requirements Vocabulary and symbols
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13731:2001 environment ISO/TS Ergonomics of the thermal 13732–2:2001 environment
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Methods for the assessment of human responses to contact with surfaces—part 2: human contact with surfaces at moderate temperature Safety-related parts of control systems—part 1: general principles for design Two-hand control devices—functional aspects and design principles Pressure-sensitive protective devices—part 1: general principles for design and testing of pressure-sensitive mats and pressure-sensitive floors Content and drafting of a functional specification
ISO 13849– 1:1999 ISO 13851:2002 ISO 13856– 1:2001
Safety of machinery
ISO 13879:1999 ISO 13880:1999 ISO 14123– 2:1998
Petroleum and natural gas industries Petroleum and natural gas industries Safety of machinery
ISO/IEC 14598–4:1999 ISO 14644– 4:2001 ISO 14738:2002 ISO 14740:1998
Software engineering
ISO 14915– 1:2002 ISO 14915– 2:2003 ISO 14915– 3:2002 ISO 14969:1999 ISO 15005:2002
Software ergonomics for multimedia user interfaces Software ergonomics for multimedia user interfaces Software ergonomics for multimedia user interfaces Quality systems
ISO 15007– 1:2002
Road vehicles
ISO 15008:2003
Road vehicles
ISO 15027– 3:2002 ISO 15190:2003
Immersion suits
Medical devices—guidance on the application of ISO 13485 and ISO 13488 Ergonomic aspects of transport information and control systems—dialogue management principles and compliance procedures Measurement of driver visual behavior with respect to transport information and control systems—part 1: definitions and parameters Ergonomic aspects of transport information and control systems—specifications and compliance procedures for in-vehicle visual presentation Part 3: test methods
Medical laboratories
Requirements for safety
Safety of machinery Safety of machinery
Cleanrooms and associated controlled environments Safety of machinery Forest machinery
Road vehicles
Content and drafting of a technical specification Reduction of risks to health from hazardous substances emitted by machinery—part 2: methodology leading to verification procedures Product evaluation—part 4: process for acquirers Part 4: design, construction and start-up Anthropometric requirements for the design of workstations at machinery Backpack power units for brush cutters, grass trimmers, pole cutters and similar appliances—safety requirements and testing Part 1: design principles and framework Part 2: multimedia navigation and control Part 3: media selection and combination
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ISO/IEC 15288:2002 ISO/IEC 15411:1999 ISO 15534– 1:2000
Systems engineering
System life cycle processes
Information technology
Segmented keyboard layouts
Ergonomic design for the safety of machinery
ISO 15534– 2:2000 ISO 15534– 3:2000 ISO 15535:2003
Part 1: principles for determining the dimensions required for openings for whole-body access into machinery Part 2: principles for determining the dimensions required for access openings Part 3: anthropometric data
Ergonomic design for the safety of machinery Ergonomic design for the safety of machinery General requirements for establishing anthropometric databases Urine-absorbing aids General guidance on evaluation
ISO 15621:1999 ISO 15667:2000 ISO/TS 16071:2003 ISO 16091:2002 ISO 16100– 1:2002 ISO 16273:2003 ISO/TR 16982:2002 ISO 17287:2003 ISO 17776:2000 ISO/IEC 18019:2004 ISO/IEC 18035:2003 ISO/PAS 18152:2003 ISO/TR 19358:2002
Acoustics
Guidelines for noise control by enclosures and cabins
Ergonomics of human- Guidance on accessibility for human-computer interfaces system interaction Space systems Integrated logistic support Industrial automation systems and integration Ships and marine technology
Manufacturing software capability profiling for interoperability—part 1: framework Night vision equipment for high-speed craft—operational and performance requirements, methods of testing, and required test results Ergonomics of human- Usability methods supporting human-centered design system interaction Road vehicles Ergonomic aspects of transport information and control systems—procedure for assessing suitability for use while driving Petroleum and natural Offshore production installations—guidelines on tools and gas industries techniques for hazard identification and risk assessment Software and system Guidelines for the design and preparation of user engineering documentation for application software Information technology Icon symbols and functions for controlling multimedia software applications Ergonomics of human- Specification for the process assessment of human-system system interaction issues Ergonomics Construction and application of tests for speech technology
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IEC 60601– Medical Part 1–8: General requirements for safety—collateral standard: 1–8:2003 electrical general requirements, tests and guidance for alarm systems in equipment medical electrical equipment and medical electrical systems Notes: The words “ergonomics” or “human factors” appear in titles or texts of these standards. The numbers indicate the number of the standard and the latest publication date. Cor=correction; Amd=amendment; TR=technical report; TS = technical specification; CIE=International Commission on Illumination; IEC=International Electrotechnical Commission; PAS=publicly available specification.
2 Preparing and Presenting Evidence in Court Daniel A.Bronstein Michigan State University 0-415-28870-3/05/$0.00+$1.50 © 2005 by CRC Press
2.1 Objectives and Scope of This Chapter This chapter will operate under the assumption that it has already been decided that you can qualify to testify under the standards used in the jurisdiction, for example, under the test of Daubert v.Merrill Dow Pharmaceuticals, 1993, in the United States federal courts. What we will discuss in this chapter is how to organize your testimony, prepare exhibits and use illustrative materials, and make a good impression on the fact finder. We will also discuss some things to watch out for on cross-examination. 2.2 Using Exhibits and Demonstrations One should always keep in mind the difference between things introduced into evidence at a trial and things used to illustrate points to be made. The two formal rules regarding things that are actually introduced into evidence and marked as exhibits are: the exhibits must be authenticated and they must be verified. Authentication is proving that the exhibit actually is what it claims to be. This means showing that the six-page report from the laboratory, for example, really is the report from the laboratory. This is a legal type of issue and is for the attorney to handle, not you as a witness. Verification, on the other hand, deals with the accuracy of the content of the exhibit and is a factual issue. As such, it is one you may have to handle. The questioning would go somewhat along the following lines: Q: Is this the report regarding the tests you ran on the control console? A: Yes. Q: And these tests were performed by you or under your supervision? A: Yes. Q: And the report is accurate regarding your findings? A: Yes.
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The reason for these formal requirements for things introduced into evidence is that, with the approval of the judge, such exhibits can be taken into the jury room for examination during deliberations. Thus, they can be particularly subject to abuse because the jury can examine them at its leisure. Things you do to help the fact finder understand your testimony, on the other hand, are not allowed into the jury room. All the jury has is its collective memory of what you did or showed while testifying. Thus, there are few restrictions on demonstrations or things used for illustrative purposes. Legally, all that is necessary is the following exchange: Q: Do you have something that would help explain your testimony? A: Yes, I have two signs, one with white letters on a green background and one with black letters on a white background so that you can see how much easier it is to read the first. Psychologists tell us that things that people see and hear make more of an impact than things that are only heard. For this reason, it is very useful to have things to show during the course of your testimony. The limits are those imposed by the physical layout of the courtroom and by the judge’s patience. Of the two, the physical limitations of the courtroom are frequently the greater problem. In an “old style” courtroom, it is very difficult to use such things as slides, movies, videos, or computer animations. The room must be darkened, equipment set up, power lines run, testing performed, etc. If you and the attorney agree that the things of this type that you wish to use are really valuable to your testimony, the attorney will probably try to get you scheduled at the beginning of the day or after the lunch break so that the equipment can be set up and tested without disrupting the courtroom. It is very distracting to everyone if you must interrupt the middle of your testimony to set this equipment up. In a “modern” courtroom, on the other hand, most of the equipment will already be in place and connected. All you will need to do is provide the material. This is an issue you must discuss with the attorney in the case long before trial (and he may discuss with the opponent and the judge), because it would be a waste of time and money to prepare materials that are never used due to the physical limitations of the court facilities. This use of illustrative materials can be most helpful for a clear presentation of your points. In a case to which I frequently refer, Rogers v.Raymark Industries (1991), a doctor was arguing that the plaintiff did not have pleural plaques in his lungs because pleural plaques are three-dimensional and the spots on the patient’s x-rays only showed in the front-to-back pictures, not in the side-to-side pictures. To show what he meant, he brought into court and showed x-rays of some other, unidentified patient in which the spots were visible in both views. I am sure this really helped explain his point. If the equipment is simple and portable enough, you can bring it into the courtroom and perform a demonstration right there. In any case, you should probably show some pictures of the equipment and explain how it is operated. A forensic chemist, for example, can bring in a picture of the GC/MS and explain where the sample is inserted and where the results appear, and then say, “When I inserted the sample and the standard, I got the following printouts.” Then he can show the printouts and explain how the peaks correspond, thus making visual his conclusion that the control substance is present in the tested sample.
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The limitations on visual presentations, then, are not really difficult. As long as you and the attorney discuss things in advance, the only limitations are those that the judge might impose due to problems with the courtroom. 2.3 Using “Learned Treatises” This is a problem in the law of hearsay. After all, the author of the book or article is not present to be cross-examined. The rules of evidence on this topic vary by jurisdiction. In many U.S. states and the federal courts, you cannot quote from treatises and journal articles in your direct testimony; in others you can. In either case, however, you can always testify that you relied on a particular item in the professional literature in performing your analysis; the limitation, if it exists in your jurisdiction, is simply whether you can actually quote from it. We will discuss the use of such professional literature in cross-examination later in this chapter. 2.4 Organizing Your Testimony The first thing you need to do when organizing your testimony is to decide which are the strongest and weakest points in your presentation. You should be aware that each point can be strong in two dimensions. It can be strong in that it is a major support to your ultimate conclusion or weak in that it does not greatly contribute to your conclusion. It can also be strong in that there is a great deal of laboratory or other evidentiary support for it or weak in that there is not a great deal of support for it in the evidence. It is necessary for you to decide which are your strong points, which are your weak points, and which points are between them. Let us assume that seven subsidiary points lend support to your conclusion. For example, look at Figure 2.1. We would all agree that item number one is the strongest point; it lies on the 45° line, indicating good support in the evidence and that it is a strong aid to the ultimate conclusion. We would probably also agree that number two is the second strongest point, although it is perfectly possible to argue that numbers three and four should be switched. Items five, six, and seven are clearly significantly weaker than the others. The idea that you should use for organizing your testimony is to try to end with the strongest point you can make. This does not mean that you should simply take the list and invert it because that would not get people’s interest when you first start your testimony. We would like to get them interested by starting with a reasonably strong point, perhaps point three. You then go quickly down to your weakest point and build up to end with your strongest point. For example, you might use the sequence: three, six, seven, five, four, two, one.
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FIGURE 2.1 The dimensions of strength of points. This, of course, is rather idealized. In the real situation, you may need to cover point four before you can cover point seven because point seven relies upon point four. If this is so, then, in our example, you would invert points six and four. In other words, do not let your striving for effect interfere with the technical accuracy of the testimony you give. Next, you sit down and write the question for the lawyer to ask you that will raise each of the points. After the question, write some short notes for yourself regarding what you intend to offer in your answer to the question. Included in the notes should be small reminders of the documents to which you will refer, the exhibits that you will introduce into evidence, and the things that you will use to illustrate your points. I frequently suggest that these be included in “curly brackets” like this: {letter from OSHA to defendant} or {photo of scene} or {diagram of work station}. After you have done this, it is time to consult with the attorney and get his input. After all, it is his case that you are attempting to support, so he certainly has a say in how your testimony is presented. My preferred method would be face to face, but e-mailing the outline as attachments can also work. Be sure to give careful consideration to what the attorney says, but do not necessarily agree to all of the suggestions. After all, you are the expert and, if you disagree with some of the suggestions, do not hesitate to say so. However, in the end, he will have the final say. After you and the attorney have agreed on your testimony, redo the list of questions and the notes. You will take this on the witness stand with you and the attorney will have a copy. That way both of you will know what you intended to say and, if one of you misses an item, the other can bring it up. Do not worry about taking notes to the witness stand; it does not make you look weak or uncertain. Everybody knows that the President
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speaks from a teleprompter; the fact that you need notes does not detract from your expert standing. The rules in the U.S. say that the other side is entitled to see anything you take on the stand with you, but this is not important. They have already read your reports and, probably, taken your deposition, so they already know what you are going to say. The last point is more a personal preference of mine than a suggestion, but I do believe it makes a difference. Start out with questions asking for your ultimate conclusion: Q: Do you have an opinion regarding the safety of the design of this control panel? A: Yes. Q: What is your opinion? A: I believe that it was properly designed. This provides the listeners with a “road map”; they know where you are going, even if they do not know the exact route you will take. At the end of your testimony, briefly recap the major points you have made: Q: Now, because you have been testifying for some time today, could you please briefly restate the reasons for your conclusion? A: Yes. This device was designed to enable the operator to switch easily among operations A, B, and C. It was never intended that the operator be able to access functions D or E. The design is better than that of most competitive consoles. If it had been used as designed and if it had not been modified, it would never have allowed the problems encountered in this case to occur. Thus, I believe it was properly designed and manufactured. Again, consult with the attorney, but I believe he will greatly approve of such introductions and summaries. 2.5 The Role of the Expert Witness The most important thing to remember when testifying is that your role is that of an educator. You are there to teach the judge and/or jury enough about your specialty so that they can see that your conclusions are obviously correct and should be believed. This brings up the question “What level class am I teaching?” If you have a bench (judge without jury) trial, then it is safe to assume that the judge has a college education, although you cannot assume anything about his scientific or technical knowledge. That information is available to the attorney, however, who can check the judge’s biography and learn if it contains some scientific content. If it does not, then, obviously, you are teaching to the “educated layman.” If you have a jury trial, then the normal assumption most attorneys make is that you should teach to the secondary school graduate. The basis for this is the belief that any college graduates on the jury will understand why you are teaching at that level, but people who stopped their education at that point might be insulted if you were to teach to
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a lower level. Again, information about the jury is available to the attorney and you should discuss the issue with him or her before you take the stand. 2.6 Use of Language It is not often stated, even by attorneys who are preparing expert witnesses, but I and many other trial lawyers firmly believe that, when you are on the witness stand testifying, you should use completely different language from that which you use when writing reports. Following are a few examples: • Use the active voice, not the passive voice. The idea is to present yourself to the fact finder as a likable, believable person who also has some specialized knowledge and not to appear as a “walking, talking textbook.” In your written report, you probably said something like “the examination of the control panel revealed that it had been modified to provide extra functions”; however, when you are on the witness stand, you should say, “I looked at the panel and saw that it had been changed.” Notice, in this example, the use of the active voice, the first person, and simpler language. Again, the idea is to appear human. You are an actor in the events you are narrating and should speak that way. • Avoid jargon. Technical terms have little content to persons not intimately familiar with your specialty. Avoid them whenever you can. Hopefully, your attorney will catch it when you slip back into “tech speak” and interrupt to ask you to clarify what you mean. • Use analogies. This is the “painting of verbal pictures” and can get as much attention as the use of demonstrations and illustrations. I still remember one I encountered back in 1968 when I was in practice. An expert defined “one part per million” as “the same as putting one teaspoon of dye into an Olympic swimming pool.” I have never done the calculations to see if that is really correct, but it certainly draws a mental and verbal picture for everyone of how small one part per million is. • Tell stories. By this I mean that you should be writing a detective story. The mystery is “what happened and why?” We know what your conclusion is, but you are giving us the clues and your interpretation of them as you go through your testimony. You can also tell stories to illustrate your points as you go. I did just that in the previous paragraph with the “teaspoon in a pool” example. This helps understanding and also provides a bit of a break from straight technical testimony, which all in the courtroom will appreciate. • Be likeable, honest, and human. Even if the jury cannot understand all of your testimony, if you impress them as a person they would “buy a used car from,” they will give your conclusions greater weight than they would to a “talking computer.”
2.7 Courtroom Behavior The most important thing to do when testifying is to make eye contact with the jury. The same holds true at a bench trial if you are in a “modern” courtroom and can see the judge. Do not get into a conversation with the attorney; you are not attempting to convince him
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or her. Because none of us really trusts a person who does not make eye contact, you should look at the attorney when he or she asks you a question and then turn your whole body in the witness chair and look at the jury (or judge in a bench trial). When you have finished your answer, turn your whole body again to look at the attorney for the next question. When using exhibits or conducting a demonstration, make certain that you do not block the view of the jury or judge. You should make certain that you stand to the side so that the beautiful thing you prepared can be appreciated by its intended audience. The attorney is not the intended audience, and you can block his or her view without worrying about it. Whenever the opportunity presents itself during your testimony, get out of the witness chair and move around the room a little. You know what advertisers think of “talking heads” on television; they hate them. Even the network TV news anchors get up out of their chairs at some point during their shows. If you are stuck in the same place the entire time, it gets boring for the jury. Talk with the attorney in advance to find places in your testimony during which you can get out of the chair, and then do it. It sounds silly, but clothing can be important. Logically, the validity of the argument is not dependent on the appearance of the person making it. Many judges, however, appear to believe that people who are badly dressed are showing disrespect for the court. Therefore, if you appear in what the judge believes is improper clothing, the judge’s nonverbal clues to the jury will say “ignore this lout.” Proper dress is a solid-color, conservative suit with quiet striped or foulard tie (for men) or blouse (for women). Pantsuits are perfectly acceptable for women. 2.8 Cross-Examination The fundamental rule for you to remember when being cross-examined is that you are the expert; the lawyer asking the questions is not. This has several important implications. First, if the cross-examiner manages to “back you up against a wall,” you always have the safe exit of “that is my expert opinion.” Second, only you know when you have finished answering the question. On television we see lawyers saying, “Thank you witness, but that is enough.” You, as an expert, have the right to say, “I am sorry, but I do not believe I have finished answering,” and then go on to finish what you wanted to say. The judge, of course, has the right to cut in and say, “Well, I think you are done,” but I have never heard of this happening. If you have more you want to say, do not let the lawyer cut you off. It is very important that you never agree in advance to respond to questions with only a “yes” or a “no.” This is an old trick of lawyers. If asked to do this, you can reasonably say, “Well, until I hear the questions, I do not believe I can agree to that; I do not know what you are going to ask me.” To return to “learned treatises,” beware of the lawyer quoting out of context. The article may really say, “One should always be aware of the small but nevertheless real possibility of A,” but all the lawyer reads to you is “one should always be aware of A.” If what is read to you seems very unlikely or unreasonable, you have the right to ask to see the quoted publication. Then you can point out that the quote was taken out of context.
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Similarly, you can refute the quoted material by saying, “Well, we used to think that, but more recent research has shown…” or, you might say, “Well, Dr. Ivory is sort of out there alone in that opinion; the majority view, as most recently summarized in the review article by Professor Tower, is that…” or, again, “Well, the journal you are quoting from is not regarded particularly well in our field; it would be classified as a fourth-tier publication and very few people pay attention to what appears there.” However, this does mean that you need to keep up with the top journals in your field and be aware of the most recent developments. In all cases, remember that you are the “living, breathing” person the jury sees. We, as professionals, have much more respect for the printed word than do most people. To most people, it is more important that you, a knowledgeable, personable expert they can see, says “A is true” than that some unknown other person says “B is true.” On the topic of out-of-context quotes, if the lawyer asks you, “Now, did you not say X in your direct testimony?” and you are reasonably sure you did not, you can say, “I do not believe that I said that. Could we have the reporter read it back?” That is the reason, after all, that we use court reporters instead of depending solely on tape recorders. Do not answer a question unless you are sure you understand it. This means that if the lawyer misuses a technical term, ask him or her to rephrase the question; do not simply assume that you know what he or she is driving at. Also, be sure to confine yourself to your specialty. I am sure you know a great deal about adjacent subject areas, but you are not an expert in them. If you get led into them, you might make a mistake, so stop the process before it gets started. For example, if an environmental chemist testifies that substance X was present in the groundwater at 0.1 ppm, upon being asked, “Is 0.1 ppm dangerous?” he or she should reply, “Well, I think you need to ask a toxicologist that question.” “I don’t know” is an acceptable answer, but be sure to explain why, for example, “I did not think that important to my opinion in this case.” Be certain to add, “But I can find out if you wish.” It is also acceptable to say “I know I know that; it is on the tip of my tongue. Could we come back to it?” All of us have that sort of experience occasionally, and it does not hurt your professional expertise to admit it when it happens. If asked where a number came from, if it came from a recognized source, e.g., the Handbook of Physics and Chemistry or the Merck Manual you are entitled to say so. Furthermore, your attorney can, if he or she wishes, move to have the source admitted into evidence under either of two evidentiary rules, one related to “published compilations” (Federal Rules of Evidence 803(17)) and the other to “judicial notice” (Federal Rules of Evidence 201). Always watch for what are called “argumentative questions.” These are exemplified by the classic “Have you stopped beating your spouse?” Point out that the question cannot be answered in the form presented, and explain why. You should regard cross-examination as an opportunity to repeat as much of your direct testimony as you can. When answering, you can say, “Well, as I said earlier,…” A good lawyer will not give you the chance to do this by not asking such questions, but if presented with the chance, grab it and run with it. Again, remember that it is the jury or the judge you are trying to convince. Make eye contact with them when answering, not with the lawyer asking the questions.
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Perhaps the two most important things to remember when being cross-examined are “do not get mad” and “be sure brain is engaged before putting mouth into gear.” The first means you should not get into a shouting match with the lawyer, even if he or she resorts to personal attacks. The second means you should always stop and think for a second before starting to answer the question. 2.9 Summary The techniques and tips presented in this chapter are not exclusive. They are based on my years of trial practice and as a consultant helping to prepare experts to testify. I am sure that the attorney with whom you are working will have other, and possibly contradictory, advice for you. Pay attention to what the attorney says, but always remember that you are the expert and must present the material on the witness stand, not the attorney. In any case, what was presented here should serve as a helpful starting point for you. References Daubert v.Merrill Dow Pharmaceuticals , 509 U.S. 579 (1993). Rogers v.Raymark Industries , 922 F. 2d 1426 (9th Cir. 1991).
Further Information For readers in the U.S., two items can be recommended for further reading: Bronstein, D.A., 1999, Law for the Expert Witness , 2nd ed., Boca Raton: Lewis Publishers; discusses the legal issues regarding being an expert witness. Kumho Tire Co. Ltd. v.Carmichael , 526 U.S. 137 (1999) is a recent Supreme Court opinion regarding the admissibility of expert testimony.
3 Presenting Behavioral Science Data as Legal Evidence: Legal Standards that the Ergonomic and Human Factors Expert Needs to Know Allen K.Hess 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
Auburn University at Montgomery For most of the last millennium, educated people entered four professions: the priesthood, engineering, medicine, and the law. During the past century, a profusion of professions abounded. The mission of universities shifted from educating a well-rounded gentleman capped by awarding the baccalaureate degree to offering a staggering menu of advanced (graduate and professional) degrees. The explosion of knowledge, the fruit of the Enlightenment, led to differentiation and specialization of knowledge. Consider how few physicians are general practitioners; even the “GP” is now a specialist in “family practice.” This proliferation of knowledge and technical specialties has implications for the justice system. A jury of one’s peers was once composed of educated gentlemen who could understand evidence presented at trials. In fact, most cases were (and still are) heard by judges. As knowledge and technical developments blossomed, the evidence presented in courts grew beyond the grasp of most fact finders (judges and jurors). The duty of a lawyer is to provide a complete and spirited advocacy of his or her client. If technical information may be probative or informing and helpful to a case, an ethical lawyer is bound to seek the best and most favorable testimony for his or her client. At the beginning of the 20th century, Terman introduced an early version of the test he was to adapt from France, which would be known as the Stanford-Binet, into court in defense of a murder suspect. In Europe, the Sterns (current specialization would classify them as developmental psychologists) experimented with the ability of children to provide veridical testimony. This introduction of the “softer” or social and behavioral sciences to the Court reached its apotheosis with two noteworthy figures. Munsterberg issued his clarion call for psychology to enter court with his book On the Witness Stand (1908) and his demonstration of the inaccuracy of eyewitness testimony. He conducted the iconic experiment of having a mock shooting in class and then asking students for their account of what happened. His call was answered by Wigmore’s (1909) satire, which pilloried psychology and Munsterberg as not ready for the Court by a long
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shot. Munsterberg’s student, Marston, received his Ph.D. and law degree and applied his interests to a number of forensic psychology concerns. A frequent consultant to the police, he determined …that written evidence was superior to oral evidence; that free narration, while less complete, was more accurate than cross examination or direct questioning (see recent cognitive psychology literature concerning recall vs. recognition—how often do we simply put old wine in new bottles!) 1 ; that a witness’s caution in answering was a good indicator of accuracy; and that female jurors considered evidence more carefully than male jurors (Bartol, 1999, p. 8). Marston created the successful comic strip “Wonder Woman,” under the pen name of Charles Moulton. Foreshadowing his scientific and forensic thinking, he had Wonder Woman wear a bracelet that could detect falsehoods in people with whom she interacted. Marston conducted research that found significant elevation of systolic blood pressure when someone lied, thus creating the modern polygraph. The polygraph plays a key role in the development of the concept of the expert witness because of its role in the Frye case. 3.1 Frye Mustering all the evidence possible in the client’s defense, a defendant’s attorney presented evidence through an expert witness that the client was not deceptive. The courts held that …just when a scientific principle of discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while the courts will go long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs (Blau, 1998, p. 422). Frye shows how evidence, in this case the relationship between biophysical measures and emotions, became more technical and required experts to present and explain its features and significance. More specifically, the Frye test or standard of “general acceptance” became the criterion by which scientific evidence became admissible or inadmissible for most of the rest of the century. Many jurisdictions still use the Frye test to determine whether expert testimony is admissible as legal evidence. 1
Author’s insert in parentheses.
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3.2 Evidence Perhaps it is a fortuitous time to introduce a more formal definition of the term we have used in a general sense. “Evidence” is used in several senses. It means “to prove an unknown or disputed fact”; it is “oral and documentary evidence of reasonable and substantial character to prove a point, not to raise a mere suspicion”; and it is “that which demonstrates or makes clear or ascertains the truth of the fact or point in issue, on either one side or the other” (Klotter, 2000). As specialization of knowledge occurred, what constituted a demonstrable truth, fact, or point in issue grew beyond the ken of the typical juror and jurist. The latter is a point that we will revisit when we consider Joiner (General Electric v.Joiner, 1997). 3.3 Jenkins For many years, psychologists were considered somewhat less than their medical brethren because they were not “real doctors.” Lawyers claimed psychologists did not cut patients and prescribe medications and thus were less than physicians and not really entitled to the appellation “doctor.” This challenge to psychologists is still heard in courts. Jenkins v. United States (1962) held that The determination of a psychologist’s competence to render an expert opinion based on his findings as to presence or absence of mental disease or defect must depend upon the nature and extent of his knowledge. It does not depend upon his claim to the title “psychologist.” And that determination, after hearings, must be left in each case to traditional discretion of trial court subject to appellate review (Blau, 1998, p. 346). The Jenkins court further defined the expert witness as qualified to testify because he has firsthand knowledge of the situation or transaction at issue that the jury does not have. The expert has something different to contribute: the power to draw inferences from the facts that the jury would not be competent to draw. To warrant the use of expert testimony, then, two elements are required. First, the subject of the inference must be so distinctively beyond the ken of the average layman. Second, the witness must have such skill, knowledge, or experience in that field or calling as to make it appear that his opinion of [sic] inference will probably aid the trier of fact in his search for truth. The knowledge may in some fields be derived from reading alone and in some from practice alone, or as is more commonly the case, from both (Beis, 1984, p. 234). The key point in Jenkins for all psychologists, not just clinical psychologists, is that challenges for ergonomics and human factors experts as not being engineers or some other “hard” science experts is hardly a disqualifying objection. Although experts concerning pain, fatigue, disability, and other subjectively experienced phenomena will be subject to just as scathing an attack on their presence in court as clinical psychologists
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have been, their presence in court is just and justifiable. Jenkins, then, becomes a compelling line of reasoning for the expert and the retaining attorney. However, time does not stand still and, following Jenkins, the Supreme Court had a commission study the rules of evidence. In 1975, Congress approved the Federal Rules of Evidence (Green and Nesson, 1984) under which federal jurisdictions now function. 3.4 Federal Rules of Evidence (FRE) Although the whole of the rules is fascinating, the pertinent part concerns Article VII. These rules are promulgated for the federal bench; however, such rules form the template for state courts. Many state courts have adapted them or a variation of the rules. Rule 701 If the witness is not testifying as an expert, his testimony in [the] form of opinions or inferences is limited to those opinions or inferences which are (a) rationally based on the perception of the witness and (b) helpful to a clear understanding of his testimony or the determination of a fact in issue. The sum and substance of this rule introduces several predicates. First, there will be a distinction between the lay and expert witness. Then, any lay opinions must be tied to direct experience and helpful to the trier of fact (judge or jury). Rule 702 If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or determination of a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education may testify thereto in the form of an opinion or otherwise.
The upshot of this key rule is (1) to admit specialized knowledge or expertise, (2) to establish how an expert attains that status (knowledge, skill, education, experience, or training), and (3) to allow the expert to proffer an opinion, as opposed to other experts who are limited in testifying to evidence based on their sense experience.
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Rule 703 The facts or dat[a] in the particular case upon which an expert bases an opinion or inference may be those perceived by or made know[n] to him at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inference upon the subject, the facts or data need not be admissible in evidence.
The import of Rule 703 is to allow three sources of information from the expert: (1) that which is traditionally based on sense experience, (2) that of allowing the expert to answer hypothetical questions by way of illuminating the current case, and (3) that having thirdparty evidence admitted through the expert. The latter might include scientific findings by others, evidence from research conducted by members of the expert’s research team, and such third-party data as public opinion polls. For example, the infamous case of preschoolers who recognized Joe Camel more than Mickey Mouse relied on a pediatrician’s questioning of several hundred 3- to 6-year-old children. This rule allows such data entry to the Court without its being barred per se by hearsay rulings. Hearsay rulings generally do not admit testimony from a third party that is not subject to crossexamination. Rule 704 Testimony in the form of an opinion or inference otherwise admissible is not objectionable because it embraces an ultimate issue to be decided by the tried fact.
The import of the deceptively simply stated Rule 704 is to allow the expert witness to use the word “did” rather than the words “might” or “could.” For example, testifying as to the ultimate issue or whether the individual did or did not have criminal responsibility or intent was no longer “usurping the province of the jury.” The expert could now make stronger assertions in such matters as intoxication, speed of vehicles, handwriting similarity, and other provinces of the expert. Rule 705 The expert may testify in terms of opinion or inference and give his reasons therefore without prior disclosure of the underlying facts or data, unless the court requires
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otherwise. The expert may in any event be required to disclose the underlying facts or data on cross-examination. This rule lifts the requirement leading to the “song-and-dance” routine of introducing predicates of a hypothetical question. However, the burden now shifts to the opposing counsel as to questioning the basis for the expert’s opinions. The judge, too, can ask for preliminary disclosure for the opinion’s basis. Rule 706 (a) Appointment. The court may on its own motion or on the motion of any party enter an order to show cause why expert witnesses should not be appointed, and may request the parties to submit nominations. The court may appoint any expert witnesses agreed upon by the parties, and may appoint expert witnesses of its own selection. An expert witness shall not be appointed by the court unless he consents to act. A witness so appointed shall be informed of his duties by the court in writing, a copy of which shall be filed with the clerk, or at a conference in which the parties shall have opportunity to participate. A witness so appointed shall advise the parties of his findings, if any; his deposition may be taken by any party; and he may be called to testify by the court or any party. He shall be subject to cross-examination by each party, including a party calling him as a witness. (b) Compensation. Expert witnesses so appointed are entitled to reasonable compensation in whatever sum the court may allow. The compensation thus fixed is payable from funds which may be provided by law in criminal cases and civil actions and proceeding involving just compensation under the Fifth Amendment. In other civil actions and proceedings the compensation shall be paid by the parties in such proportion and at such time as the court directs. And thereafter charged in like manner as other costs. (c) Disclosure of Appointment. In the exercise of its discretion, the court may authorize disclosure to the jury of the fact that the court appointed the expert witness. (d) Parties’ Experts of Own Selection. Nothing in this rule limits the parties in calling expert witnesses of their own selection.
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This lengthy rule tempers the shopping for expert or “hired gun” practice by specifying an already existing option for the Court—that of appointing its own expert. This is designed to make the counsels aware that their experts might be impeached by the Court’s expert. Although federal courts since 1946 (Rule 46 of the Federal Rules of Criminal Procedure) allowed for such experts, Rule 706 broadens this access to civil cases. These rules have percolated through the judicial system for the last three decades. However, events in the 1980s and 1990s led to several important findings that have changed the face of articulating scientific, technical, and expert evidence to courtroom testimony. 3.5 The Daubert-Joiner-Kumho (DJK) Trilogy In the two decades following the advent of the Federal Rules of Evidence, there arose a flood of experts into the courts and defenses that stretched credulity (e.g., Mike White’s “Twinkie” defense, the Zamora “TV made me do it” defense, and the “lawn-fertilizermade-me-crazy” defense). This flood swept the term “junk science” into the public lexicon as a term of scorn. Books such as Galileo’s Revenge (Huber, 1993) and Whores of the Court (Hagan, 1997) dissected the horrors visited by some “experts” upon the courts. This public tumult led to three cases decided by the Supreme Court that now define the expert and expert testimony. Daubert Benedictin prescribed for mothers suffering morning sickness resulted in children born with limb reduction birth defects. In Daubert v.Merrell (1993), the U.S. Supreme Court established a four-pronged test (or set of definitions) to guide judges in screening experts and their testimony. Daubert replaced Frye with the FRE; it emphasized FRE Rule 702 by having the judge ensure that the testimony has a reliable foundation and is relevant to the task at hand and offered the four-pronged test. The first prong is based on the philosophy of the Vienna Circle, which holds that (1) a theory must be falsifiable (or is the theory so amorphous as to be untestable, incapable of being disproved, and philosophically and scientifically useless?). Second, Daubert holds a theory or technique in better regard if it has been (2) subjected to peer review and publication. Although not a sine qua non, publication in peer-reviewed journals increases the likelihood that substantive flaws in methodology will be detected. To be sure, we seem to have a scientific fraud eruption at least twice a decade in medicine and physics. Highly regarded breakthrough papers that top journals compete to publish first (establishing priority) are sometimes retracted in small print. Although published peerreviewed papers are an excellent filter, neither we nor the courts should regard them as fool- or tamper-proof. No measure exists without variation or “error” This error is often translated in psychological, physical, and pharmaceutical measurement as one of the family of standard error terms (e.g., standard deviation, standard error of measurement, standard error of the means) or in “hits and misses” in diagnostics. Thus, the third prong calls for
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consideration of (3) the known or potential rate of error. Finally, (4) the Frye test of general acceptance has a place. It defines the relevant scientific community and allows inference based on whether widespread or only minimal support within the scientific community lends to acceptance by the Court or leads the Court to view the evidence with skepticism. More detailed examination of Daubert, subject to many articles in the legal literature, is beyond our scope. Suffice it to say that Daubert defined the contours of experts and their evidence but did leave a few questions unanswered. To be sure, Daubert is not a one-sided affair. It does not exclude wholesale and, in an uncompromising fashion, any evidence that is not generally accepted (Frye). Because the pace of scientific progress seems to have accelerated, some valid and probative findings may take time to become generally accepted, but might have served justice if admitted before being wholly or generally accepted canon. Daubert says, then, that expert evidence is subject to cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof. However, who says what can enter the Court and how is that to be decided? Joiner Did Daubert liberalize the rules rather than restrict junk science entering the Court? Are we in for a “free-for-all?”’ General Electric v. Joiner concerned whether Robert Joiner, working as an electrician in and around Thomasville, Georgia’s electric transformers, was exposed to polychlorinated biphenyls (PCBs), which led to his contracting small cell lung cancer. The testimony—about quite technical matters as to whether PCBs by themselves or with the aid of furans and dioxins caused the cancer—was central to deciding the case. In order to grasp the essential issues in a case brought before it, a jury of one’s peers needs experts. Who decides what is admitted in court? Joiner holds the judge, as the gatekeeper, responsible for deciding what is admissible to the Court’s consideration, subject, as usual, to the “abuse of discretion” standard. That is, the judge in Joiner decided animal research should be excluded because the evidence “did not rise above ‘subjective belief or unsupported speculation’” (Hess, 1999, p. 525). The Court held that the judge must ignore logic, settled law, relevance, or reliability issues to have abused his or her discretion. Going from Frye to Daubert did nothing to diminish the judge’s gatekeeper role. In fact, one real problem remaining is that judges, schooled in the law, may not have a clue about force vectors in an automobile seat belt case, about psychosis in an insanity defense, or about potentiation of PCBs by furons in the Joiner case. Yet, the status is that the judge determines whether the witness and the testimony proffered are more probative than prejudicial and that is subject to cross-examination, contradictory evidence (and witnesses), and instructions as to the burden of proof in the case at hand. The judge really must “lose it” in terms of logic and the settled law and basic rules of reliability of evidence to abuse his or her discretion. However, one more question confronts us. Kumho What happens when a fire breaks out in a restaurant and the owners claim the hundreds of thousands of dollars of wine stored in the wine cellar are now tainted and have lost all
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their value? How does one value a one-of-a-kind gem? When science meets application, the relevant expert might be more of an artist than a scientist. Do Daubert and Joiner speak to the nonscience expert? Patrick Carmichael’s tire blew out and his vehicle rolled over, killing one person and injuring others. Tire failure expert Dennis Carlson, Jr., intended to testify that a defect in the tire’s manufacture or design caused the blowout. However, although accepting Carlson as an expert, the Court found so many problems with the consistency of his testimony and the bases or methodologies he employed that it dismissed his testimony as unreliable. The essence of Kumho for us is that a lower court held Daubert’s factors did not apply to Carlson because his evidence was based on skill or experience. However, the Court held that technical and expert testimony was subject to Daubert, which was not limited to scientists but applicable to all experts ordered by the courts or offered to the courts. Thus, although perfume experts who rely on physical measures would be welcome to the Court, so would experts who could testify as to the noxiousness of certain aromas, subject to the DJK trilogy. 3.6 Presenting Behavioral Science Evidence It took time to lay the groundwork in reviewing the legal basis for the expert witness and expert testimony. Now how do we articulate and judge psychological testimony relative to the DJK (and Frye, which is still used in many states)? Actually, psychological data stand in good stead. Qualifying the Expert Witness First, a potential witness must qualify through a process called voir dire. The potential expert should bring a complete curriculum vitae (I always bring copies for the judge, court clerk, and opposing counsel as well as one for the attorney retaining me and for myself), which he or she has reviewed and updated recently. The attorneys will then have the expert recite qualifications based on knowledge, skills, education, experience, and training. If the qualifications seem to be probative or will lend to some factual understanding of the case, the judge qualifies the expert or accepts him or her. The judge can qualify the expert for some areas of inquiry but not others. For example, I was asked to testify as to whether a defendant could understand his Miranda warning against selfincrimination despite his consuming between a pint to a quart of bourbon while fishing. I was disqualified as an expert regarding the effects of alcohol on his cognitive capacities but qualified regarding my estimates of his intelligence vis-à-vis understanding a text such as Miranda, irrespective of alcohol intake. The Nature of Psychological Theory and Data Behavioral science has probably the most voluminous literature as well as journals with high rejection rates. Thus, a tremendous font of knowledge is available and the standards for its peer-reviewed published literature are high. Before presentation to the Court, in order to be admissible, the data upon which our opinions rest should pass the Daubert
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screens: generally accepted, peer-reviewed, testable, and having a known error rate. The adversarial attorney should insist on no less; the conscientious and ethical witness, too, should offer to his or her retaining attorney no less than “Daubertized” data or the ugly spector of malpractice will arise. Do one’s data and opinions need to pass each criterion? No, the courts use a criterion sometimes termed the “totality” of the evidence in reaching a conclusion, in this case as to admissibility of evidence. That is, unpublished data might have a well-established error rate and be so compelling and probative that the Court will look at the totality of the evidence and admit them. Conversely, well-published evidence, meeting all the other three Daubert criteria as well, simply may not be relevant and might be seen by the judge as more prejudicial than probative and thus not be admitted. Is the key issue the data or the witness? Validity What the courts know as “reliability,” social and behavioral scientists term “validity.” The Standards for Education and Psychological Testing (American Educational Research Association, American Psychological Association, and National Council on Measurement in Education, 1999) defines validity as: …the degree to which evidence and theory support the interpretation of test scores entailing by proposed uses of the test. Validity is, therefore, the most fundamental consideration in developing and evaluating tests. The process of validation involves accumulating evidence to provide a sound scientific basis for the proposed score interpretations. It is the interpretations of test scores required by proposed uses that are evaluated, not the test itself. When test scores are used or interpreted in more than one way, each intended interpretation must be validated (Standards for Educational and Psychological Testing, 2000, p. 9). Thus, the crux of expert testimony is in the soundness of the interpretations rendered by the expert. This is necessarily so. Consider the Rorschach test; more heat than light seems to have been showered upon this controversial assessment method. Although some have condemned the Rorschach as the current incarnation of phrenology or Tarot cards, others stand by the technique with equal resoluteness. In fact, I have seen some licensed psychologists who should never be allowed near a set of inkblots. However, I have also seen a few masters of the technique in whose hands this instrument is of superb assistance in clinical and forensic arenas. How does one judge the admissibility of such a method? Simply put, has the expert mastered the literature; had experience, training, and education in its application; and developed skills that would endow the proffered testimony with validity that helps in resolving the question at hand? In the case of the Rorschach, Hess and colleagues (2001) have found some indices on the Exner system of the Rorschach to be as refined and confirmed as any of psychology’s objective inventories tests, while other indices are unproven as yet or have no claims to validity. The Rorschach, as with most measures, has a more nuanced literature than partisans on
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either side of the debate care to acknowledge. However, the critical question for us rests not solely or even mostly with the measure, but, as in the Joiner case, with the way in which the expert has mastered the subject matter and applies it to the question at hand. 3.7 Conclusion Unlike almost a century ago when psychology was still young and the concept of the expert witness was yet to be distilled by the courts, the social and behavioral sciences are not merely ready for the courts but also indispensable in helping the courts decide questions. The remaining questions for the potential expert are whether he or she is qualified in an area and whether the expert and attorney are able to articulate the legal questions with the psychological answers. We should be careful in answering these questions so that we are not purveyors of “junk science,” but rather can bring data and evidence to court that serve justice and better society. Acknowledgment I appreciate the contributions of Kathryn D.Hess in the development of this chapter. References American Educational Research Association, American Psychological Association, and National Council on Measurement in Education. (1999). Standards for Education and Psychological Testing . Washington, D.C.: Author (APA). Bartol, C. (1999). History of forensic psychology. In A.K.Hess and T.E.Weiner, Eds., The Handbook of Forensic Psychology , 2nd ed. New York: John Wiley & Sons, 3–22. Beis, E.B. (1984). Mental Health and the Law . Rockville, MD: Aspen. Blau, T.H. (1998). The Psychologist as Expert Witness , 2nd ed. New York: John Wiley & Sons. Daubert v. Merrell Dow Pharmaceuticals , 509 U.S. 579 (1993). Frye v. United States, 293 E 1013 (D. C. Cir. 1923). General Electric Co. v. Joiner , 522 U.S. 136 (1997). Green, E.D. and Nesson, C.R. (1984). Federal Rules of Evidence: with Selected Legislative History and New Cases and Problems . Boston: Little, Brown. Hagan, M.A. (1997). Whores of the Court: the Fraud of Psychiatric Testimony and the Rape of American Justice . New York: HarperCollins. Hess, A.K. (1999). Serving as an expert witness. In A.K.Hess and T.E.Weiner, Eds., The Handbook of Forensic Psychology , 3rd ed. New York: John Wiley & Sons, 521–555. Hess, A.K., Zachar, P., and Cramer, J. (2001). Rorschach [review of the Rorschach inkblot method]. In B.S.Plake and J.C.Impara, Eds., The Fourteenth Mental Measurements Yearbook . Lincoln, NE: Buros Institute, 1033–1038. Huber, P.W. (1993). Galileo’s Revenge: Junk Science in the Courtroom . New York: Basic Books. Jenkins v. United States , 307 F. 2d 637 (D. C. App. 1962). Klotter, J.C. (2000). Criminal Evidence , 7th ed. Cincinnati, OH: Anderson. Kumho Tire Co. v. Carmichael , 526 U.S. 137 (1999).
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Munsterberg, H. (1908). On the Witness Stand: Essays on Psychology and Crime . New York: McClure. Wigmore, J.H. (1909). Professor Muensterberg and the psychology of testimony: being a report of the case of Cokeston v. Munsterberg . Illinois Law Rev. , 3, 399–445.
4 Practical Ethics for the Expert Witness in Ergonomics and Human Factors Forensic Cases Allen K.Hess 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
Auburn University at Montgomery Many texts concerning the intersection of law and applied disciplines address ethical concerns in passing or do not address them at all. Ethical concerns are like our skin. Skin is our largest organ and the one that interacts with the world around us. However, it is simply overlooked until something goes wrong—and so it is with ethics. If ethical concerns are unaddressed, they will surely emerge during forensic consultation, with potentially disastrous results. Thus, I am happy the editors of this volume see fit to feature a chapter on ethics and the expert witness in forensic ergonomics and human factors. The goal of this chapter is to alert the reader to some concerns which, if addressed appropriately, lead to the immense satisfaction of doing a job professionally and serving society. We will address the ethical questions that face the expert at the beginning of a case, followed by some questions that might arise during the datagathering and consultation stage, and conclude with questions that arise during the concluding stage. 4.1 Accepting the Forensic Referral There are more pitfalls at this stage than at any other. The expert needs to consider the person (usually an attorney) who asks for his or her help. The expert needs to determine whether (1) any parties in the case might contribute to a conflict of interest or the appearance of such a conflict and (2) this attorney understands the articulation of the legal and psychological issues. Conflict of Interest A conflict of interest is when a public duty is compromised or appears to be compromised by a private or a pecuniary benefit. Thus, ethical practice dictates that the
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practitioner should ask the attorney to identify the parties in the case: individuals such as attorneys on both sides of the case, the plaintiff and defendant, and the judge hearing the case. If the professional knows any of the parties or has a financial interest in a plaintiff or defendant company or agency, he or she should disclose this to the attorney. In practical terms, within many communities, roles such as psychologist, coach, adjunct instructor at a local college, and scout leader or parent of a scout can intersect. Suppose an opposing attorney is the coach of a gymnastics team on which the psychologist’s child participates. Will this possible role conflict jeopardize the child’s chances of competing in tournaments as the first uneven parallel bar contestant? If this is a concern to the potential expert witness so that he might modify forthcoming testimony to the detriment of the client attorney, a conflict of interest exists and the professional might be advised to recuse himself. With other people this might not be a factor at all and no conflict of interest would be present. The key is to be aware of the possible conflicts of interest that could arise, to bring this issue up with the attorney during the first phone call, and to be clear about one’s own vulnerabilities to influence. Interestingly, these factors are not engraved in stone but involve judgments about a shifting set of variables. For example, with a large litigation such as a class-action suit, the boundaries might be different than with a more local case. With the larger case, one might be practicing in another community and not know any of the parties. On the other hand, with a class-action suit, one might be personally affected or be more likely by chance to know someone in the suit. Another variable is the size of the community in which the suit and the expert are situated. In a smaller community, one is more connected with other parties; if the judge or attorneys were to start excluding anyone who might know anyone else, there is little chance the case would be heard. In such a case, the expert might be asked whether he can work with disregard to the interests of the people in the case and, instead, provide unbiased and professional testimony. In smaller and more isolated communities, a professional might be asked to practice on the fringes of his competence because other, more knowledgeable experts might not be available. Then the question becomes one of whether, by reading and consultation, the professional can become expert enough to serve the case competently. We will return to considerations of competence shortly, but now consider personal and political philosophies. These examinations of interests and competencies extend to personal and political philosophies as well. Consider a person who is a champion of the “little people” and has written and spoken out on issues regarding automobile safety. Could this person serve as an expert witness in a personal injury case in which the issue is whether the large automobile companies provided enough safety belt protection or cut costs to use a cheaper and less safe material in the belts? Will the astute opposing attorney bring up past statements to impeach the integrity of the expert’s testimony? A person can hardly live a textured life without having interests, so a frank discussion with the attorney can help anticipate a possible ethical problem or an attack by opposing counsel as to the motives of the expert witness in an attempt to impeach the testimony as serving a personal, financial, or political interest. On a tactical level, the hiring attorney should be impressed by the professional’s sensitivity to these issues that could hurt the case.
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Attorney’s Qualities If the attorney does not understand the psychological issues or has no interest in being educated about them, several unfortunate consequences will result. During the case, the expert will not be regarded well, so access to people and records will have a lower priority for the lawyer. Then the expert’s work product will suffer because of gaps in the information that he has gathered; the expert can be vulnerable to cross-examination that he has not prepared his testimony in a professional manner. Attorneys who do not value the expert will be resistant to paying the witness. Also, the attorney will not be able or willing to rehearse the types of questions that will elicit the best testimony from the expert during the trial. Naturally, attorneys are interested in winning their cases—their professional survival depends on winning. It would be inconsistent with their interests to secure a witness who will not help the case or even proffer testimony that hurts the case. (Note that attorneys might retain an expert who is a highly regarded proponent of the issues or theories that the other side of the case is pursuing. The retention of the expert ensures that the expert will not be testifying on behalf of the opposing side because a person hired by one side cannot be retained by the other.) However, the attorney’s zeal about winning can lead to the lawyer wanting an expert who is simply a “hired gun,” or one who will testify in whatever fashion the lawyer wants, irrespective of the facts of the case. For example, one psychologist I know, who has state contracts with the prison system and is on retainer with the district attorney’s office, has never found a defendant insane, no matter how much debilitation the person presents. How does the ethical expert find out about the lawyer’s orientation? During the initial telephone call, the expert needs to have the attorney articulate the theory that he or she is using in the case and how the psychologist might provide information that would support or at least test the theory. For example, the psychologist is asked whether he might be interested in a tort case concerning contracts that people have signed, not realizing the usurious interest rates being charged and that the consumers have been misled by advertisements concerning compressed speech on radio and television advertisements that virtually no one could have been reasonably expected to understand. At that point, the psychologist might mention one or two theories concerning the size of the sensory register in understanding information. If the attorney appears interested and can comprehend why the psychologist might be thinking about sensory register and shortterm information storage, then the lawyer is articulating the legal and psychological constructs. Also, this helps the attorney feel confidence in the psychologist. Because virtually all the activities of any profession are verbal, the expert witness and the lawyer have ample opportunities during the phone call to assess each other’s verbal facility. The initial call should not be jargon filled; an excellent rule of thumb is that the best professionals can explain $25 concepts in 254 terms. The initial call allows the attorney and the potential expert witness to see how each conceptualizes and whether they can work together. Most ethical problems arise when people are angry or disappointed with each other and communication and trust have not been established or have broken down.
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The professional needs to be careful in judging the attorney’s skills and ethicality. The success of our practice depends largely on our talents and motivation. When practicing jointly, our efforts may be enhanced or diminished by others. However, in forensic work, a great deal of the effectiveness of the professional will depend on the retaining attorney’s efforts, talents, and ethics. How the forensic psychologist’s evidence and case are presented is almost wholly a function of the attorney. Consequently, the lawyerexpert interaction is vital in determining whether forensic practice is satisfying and successful, or not. We will decline to work with some attorneys. The crucial reason is that they have demonstrated an inability to use the psychologist’s efforts in a way that benefits the client. In one case, the attorney seemed unaware that the expert must be disclosed to the opposing counsel a minimum of 10 days before trial. This allows the opposing counsel the opportunity to depose the witness and discover the nature of his testimony, a firstyear law school topic. In this eye-witness accuracy case, the judge accepted the psychologist as an expert but did not let him testify because the opposing counsel had no opportunity to impeach the expert’s testimony. The defendant was eventually sentenced to 20 years for a simple assault when the eye-witness accounts were clearly in error (in the psychologist’s opinion); the witnesses described a 5-ft 11 in. narrow-faced, righthanded assailant, but the accused was 5 ft 4 in., round faced, and left handed (facts that the police and lawyers did not present during the case but were to be presented by the expert witness). This was the critical evidence in the case; no other evidence— fingerprints, DNA, other witnesses, stolen property, guns, wigs used by the perpetrator, or any other evidence—was presented. Although the psychologist was paid and stayed on to help the attorney structure the closing argument, the case left a bitter taste. Imagine how unsatisfying it is to be a party to sending a most likely innocent 24-year-old person to a career as a felon because the attorney did not do what a first-year law student learns to do—present a witness list to the opposing attorney. Who, besides the attorney, might try to retain the expert? From time to time, people other than attorneys might call the potential expert witness. Too often, the call might lead to undue complications. For example, a patient with temporal mandibular joint disorder asked her psychotherapist (treating her for suppressed anger, which led to jaw clenching) to testify as an expert witness. He asked her to consult with her attorney about contacting him. The lawyer specializing in TMJ disorder litigation might have a stable of experts he or she uses regularly and might not be able to use the therapist within the regular preparation of the case, might prefer not to use the therapist as a potentially biased professional, or might prefer to use the expert to establish damages during that phase of the trial. Thus, the expert is almost always best served by having the attorney as the client. Also, this makes billing and privilege more easily handled. With the attorney as client, the expert and attorney can fully disclose to each other. With a third person retaining the expert, the expert’s first allegiance would be owed to the third party and that person might reveal information to the expert, not wanting it to go to the attorney, which then places the expert in a dilemma about withholding information that the attorney should have in the best interests of the case. Billing is generally easier if the attorney has signed some form of contract with the expert that the attorney is to pay the expert. That way, the expert’s time later in the case
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and even after the case is not consumed by chasing the third party. Attorneys are more expert at collecting fees than are most experts. Thus, expert time is saved by billing and receiving payments from the attorney. Again, this is best clarified during the first phone call. More money matters will be discussed later. Expertise or Competence Personal Skills Perhaps before answering or returning the attorney’s initial phone call, the potential expert should have assessed himself to see whether he has the requisite skills for courtroom combat. Some people are naturally averse to conflict. The American legal system is adversarial. If the expert is uncomfortable with the professional, and sometimes personal, attacks that the opposing attorneys will mount (they owe their clients a spirited representation, which might include a virtual assault on the expert’s professional life and personal integrity), forensic work may not be his métier. Is the expert able to cope with this kind of attack? Professional Competence Does the professional have the expertise needed for the question at hand? While the psychologist whom the attorney called might be an “expert forensic psychologist,” is he versed in psycholinguistic processing? Does the psychologist have the skill, knowledge, education, experience, and training in how people process compressed speech to the extent that he should be offering professional services? In the American Psychological Association’s Code of Professional Conduct (1992) and in every other profession’s code of ethical conduct, the issue is framed as “competence”: is the expert professionally competent in the area of service offered? This question is seemingly simple; however, the most skilled psycholinguist might not be able to articulate the research on compressed speech with the legal concept of the reasonable person being duly informed by the advertisement. Even more subtly, can the way the advertisement was posed actually lead to the inference that the company offering the loan misled the consumers? This implies the legal construct of “intent.” The psychologist who was contacted might not have mastered the subtleties of the psycholinguistics research base, but that might not be the level of discourse needed in the case. The case might simply need someone who can read and metabolize the scientific literature and then articulate the psychological knowledge about sensory register capacity and short-term memory development to testify that no reasonable or even highly educated person could have registered or stored the disclaimers in the advertisement on loans. If the information needed is more complex than the expert’s skill level, might the expert then be able to retain the services of other experts—in effect, forming a team? Perhaps some research directly related to this case—taping the putatively offending advertisements and showing them to a sample of college students to show that they were unable to process the disclaimers—might be subcontracted to a psycholinguist. To the extent to which they can be anticipated, these issues are best discussed at the inception of the case. Even more so, the attorney may feel comforted if the expert can draw on the
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skills of a team, to the extent to which the case financially warrants this degree of expertise. Attorneys are used to working in teams in which a partner will assist on certain technical features of a case and are aware of billing issues in which extra expenses need to be justified. Standards of Practice In areas such as child custody, in which psychologists have been routinely employed for decades, standards have been developed concerning how psychologists should function in child custody evaluations. The expert should know the guidelines and standards of performance available before proceeding in a case. Sometimes the standards might be available in a cognate or related discipline. Although they may not be binding for people who are not members of that profession, they are informing. For example, if certain tests are conducted on products in an industry, the expert should be knowledgeable about these tests, even if they are not ones that he is qualified to run. Being informed about them, as well as the results of such testing in the particular case, might inform the expert’s testimony; at the least, he would not seem adrift if queried about such information by opposing counsel. Even more telling, knowledge of these standards will show the expert to be ethical and careful, with an awareness of professional issues and standards. For example, in a case in which the levels of noise in a factory are at issue because of damaged hearing ability in workers, the acoustical expert witness psychologist would need to know how acoustical engineers conduct their tests. In a real sense, such an informed expert is at a great advantage. The expert psychologist, conversant with the engineer’s tests and able to articulate them with how a worker’s hearing is damaged, is much more valuable than the engineer who cannot address the subsequent functional and emotional damages resulting from the physical conditions. The engineer’s tests and standards are not binding on the psychologist, but do provide interesting approaches to the case. Such knowledge helps the psychologist understand how other professionals might approach the case and allows the psychologist to subsume the other side’s theory and evidence. This kind of awareness and professionalism is what is called practicing with aspirational ethics, as opposed to practicing to minimal standards. Standards of practice are held to be across the profession as opposed to practicing to the standards of local practitioners. There are emerging standards for expert witnesses (Committee on Ethical Guidelines for Forensic Psychologists, 1991; Perrin and Sales, 1994) that the expert-witness psychologist should know. Similarly, when the expert witness is testifying about another professional’s conduct or in a product liability case, the material standards are national, not local. In one case, an anesthesiologist’s defense about leaving a sedated patient who subsequently suffered irreversible brain damage was based on the fact that, in that rural area, no one else was available to assist in another surgery at another hospital. In a more urban area, he argued, other anesthesiologists would have been available to cover at the other surgery. Thus, the anesthesiologist left the patient, assuming he would come out of the anesthesia in good shape, but he did not. The verdict held that standards of professional conduct in such cases are national. On the other hand, when there are state laws or more local practices, the contours of the case, of which the attorney should make the expert aware, might involve the “usual,
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customary, and reasonable” customs of the local jurisdiction. The expert needs to be sensitive to these issues and inquire of the attorney; however, they are more the central concern of the attorney and another way of determining the professionalism of the attorney retaining the expert. Again, the forensic professional’s level of practice, to a greater extent than when practicing within his usual activities, is dependent upon the attorney retaining the practitioner. Legal Knowledge Although the expert is retained for his or her professional knowledge, how much law does the forensic expert need to know? The answer to this question focuses on the core question—one needs to know about the legal construct in order to articulate it with the professional’s knowledge base and to know enough about legal procedure so that the expert is aware, not ignorant, of court. On the other hand, the expert need not be a lawyer; to some extent, even if the expert has a law degree, he or she should not be practicing law, but proffering the professional service that the attorney is seeking. The attorney should be able to teach the professional the law concerning the case, and the expert would be well served to be able to understand how lawyers think about a case. The issue, for example, might not be whether people can understand compressed speech. After all, the law is clear: if the consumer has signed a written contract, that contract usually overrides the advertisements that brought the consumer to the loan agency. The attorney might now suggest that the question is a combination of whether the advertisement, the sales pitch, and the foreboding legal language of the contract reached such proportions that the cognitive psychologist, who is knowledgeable about information processing, can testify that the consumer never had a chance to understand the terms of the loan. The question now is whether the psychologist can understand enough of the theory of tort law to articulate cognitive science with the legal questions to be helpful. The psychologist can read learned law treatises or relevant legal codes in order to understand the legal constructs. The expert is not expected to know the nuances between thresholds in state and federal consumer law (most lawyers do not know such specialized areas). However, the expert should take the opportunity to be educated by the case, to the extent that he has the aptitude to master legal reasoning. Money Matters If the expert has contracted with the attorney, then the attorney is the paying client. Naturally, the attorney is retained by an injured party or by a corporation and is paid by the client. Thus, the expert is ultimately paid by the party or the company, although, in reality, the expert’s client is the attorney and, if the “ultimately paying party” does not pay, the attorney is still liable for the expert’s fees (and expenses), assuming that the wise expert structured the relationship correctly. As mentioned earlier, the expert should not be in the business of collecting fees from recalcitrant payers. The wise expert should ask for a retainer and be sure that billing is current so that the money flow is not backed up. It is good practice to receive payments so that one can devote full attention to the case and not be worried by the fees.
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In no case should the expert work for contingency fees, as attorneys sometimes do. Contingency fees for an expert witness create an immediate conflict of interest in which the testimony must be skewed, or appear to be so, in order for the expert to be paid. In cases in which the attorney is working for a contingent fee, he or she must understand that the expert is working for a per-hour or per-case fee, not on a contingency basis. The expert should determine the suitable fee based on the type of work, the reputation of the expert, and the norm for the profession. The term of art is “usual, customary, and reasonable” fee. If the expert charges too much, the sensibilities of the lawyers, judge, and jurors might be offended. If the expert charges too little, the question might arise about whether he or she has a financial interest in the case. In a disability case regarding a relatively poor client, fees could be adjusted, although it would be better to charge one’s usual fees so that the court or juror does not see a question of bias due to pity for the client. In such a case, the expert might reasonably excuse part of the bill later, but even this should be done with legal guidance of the attorney so as not to prejudice any appeal or subsequent legal action. Of course, many professions have pro bono practice, whereby one donates services to indigent clients. This must be done with care so as not to have testimony appear biased. 4.2 Data-Gathering and Consultative Stage Once the attorney wishes to retain the expert and the expert agrees to consult with the attorney, a number of questions tinged with ethical implications arise. We will consider several of them. Who Else Has Access to the Expert? The expert and those retained by him or her should communicate only through the retaining attorney to any other parties. Thus, when the expert examines people for disability, for example, the contacts are made with the attorney’s knowledge of the type, time, and extent of the examination. When the expert examines people who helped design or manufacture a product, the examination is conducted through the attorney’s aegis. When the expert receives any inquiries from other parties, particularly the attorney or clients from the other side of the case, the attorney who hired the expert needs to know. Also, no information should flow from the expert or his office to the third parties. It is best to instruct one’s secretary to say that one is out of the office (rather than out of town or, heaven forbid, out of town working on the Smith v. Jones case). It is much better to instruct office personnel not to be afraid of seeming uninformed than to be flattered into revealing information that, once released, cannot be retracted. Legal cases make people desperate, and desperate people behave desperately. In one case, the father of a woman in a divorce case called the expert and offered him vast sums of money not to testify. This was immediately reported to the attorney retaining the expert. In another case, the law intern to the district attorney posed as a student interested in forensic psychology and went to the expert’s faculty office. In his guise as a student, he asked “innocent” questions of the professor, but he was soon discovered when he began to pose questions specific to the case in which the professor had been retained.
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Again, the expert immediately terminated the interview and called the retaining attorney, who could then choose an appropriate course of action regarding the district attorney’s office. Defining Privacy, Confidentiality, and Privilege What obligations does the expert have in keeping information private? Who else does the expert need to consider in guarding information? Privacy In order for our day-to-day relationships to work, we observe courtesy. When a colleague tells us about his or her feelings about the boss, privacy would dictate that we hold these utterances to ourselves. Our colleague might be damaged by the revelation of his or her feelings. This is privacy. It is a duty we owe to others by virtue of our acquaintance. Violation of privacy is typically not actionable unless defamation with attendant damages results. However, it is a lamentable person who does not hold a friend’s or colleague’s comments, unless such a withholding can damage others. Confidentiality Confidentiality is typically owed to another in a fiduciary relationship. A supervisor owes a worker confidentiality regarding employee evaluations, salary considerations, medical leave information, and a host of other personal information that becomes available in order for the work relationship to function. (Others in the organization do have access to this information by virtue of their status in the organization, e.g., the supervisor’s supervisor, the human resource or personnel office, and the finance office.) One’s stockbroker holds a fiduciary role regarding revelation of one’s financial holdings. However, the expert witness, to the extent that the information is safeguarded by a practice law, might hold a privileged relationship. Privilege Privilege is a standard that calls for a higher level or threshold of urgency in order to breach it. That is, privilege is a protection against court-compelled disclosure of information deemed so important that the relationship cannot function without such protection. Nine relationships are guarded by privilege: • Husband-wife • Priest-penitent • Physician-patient • Psychotherapist-patient • Lawyer-client • Political voting • Trade secrets • State secrets • Informer identities
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If the professional is covered by a licensing law in the state in which the information is gathered and the case is heard, then communication between the lawyer and expert is privileged. In some cases, the attorney may want to guard against a particularly wellknown professional being retained by the other side or may become aware of the expert’s planned testimony as not being helpful to the case. Then the lawyer, who has retained the expert, may never call the expert and his or her testimony might be regarded as privileged. If the attorney never reveals that the expert was retained, then the information is privileged. Privilege belongs to the client—in this case, the attorney—and cannot be breached by the professional. If the court or other side has learned of the expert’s involvement in the case, perhaps by virtue of the witness disclosure list furnished by the attorney to the court and other side, then the expert may be guided by the court in the event that he or she is ordered to testify. In some cases, the expert may need to retain an attorney for guidance through the thicket of what is privileged. The expert needs to err on the side of caution; therefore, when writing, lecturing, or simply seeking consultation with an attorney or trusted colleague, the expert may want to not disclose or disclose so that the revelation is so abstrusely related to the case as not to be identifiable. Of course, when the attorney offers the expert to the court, privilege has been waived. The expert cannot offer some testimony and withhold other evidence, claiming privilege. If the lawyer does not want potentially damaging evidence offered, then he or she has a choice of not questioning in that area and hoping the other side will not query there, or simply not calling the expert. The expert, when taking the oath, has pledged to testify to the truth, the whole truth, and nothing but the truth. To do otherwise, barring the judge ruling some areas inviolate, could lead to perjured testimony. All the people whom the expert retains in his or her employ are guarded under the umbrella of the expert’s license or confidentiality. The expert must guarantee that the employees understand this and do not reveal any information to third parties. The logic is clear: but for the employment relationship, the janitor, secretary, colleagues, or other people employed by the expert would not have known of the information. Under the “respondent superior” or “captain-of-the-ship” doctrine, the expert has ultimate authority for receiving, retaining, and releasing information. Hurry Up and Wait Attorneys seem to be in a chronic rush. Having retained the expert, the attorney may then seem to have forgotten about him. The expert needs to be sure that he understands the attorney’s calendar regarding the case. When the expert is retained, it is a good idea for him to discuss when the case calendar dates are upcoming. Perhaps the expert was retained so that the attorney could turn in a name on a witness list due the next Monday. Perhaps the case has a half-year postponement. After weeks or months of no contact, the expert may be contacted and asked to provide information within an impossible timetable. It is a good idea to discuss with the attorney any impending vacation plans; other time commitments the expert has made; and the amount of time any investigations, examinations, or studies will take. In that way, the attorney and expert can make a schedule that will not compromise the case or the professional functioning of either. It is
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in their interests that they perform well. This may involve buttonholing the attorney so that a reasonable time frame can be sketched out. Of course, many variables, such as the judge’s calendar, other attorneys’ schedules, and supervention by other cases, can ruin a schedule. However, these events usually involve delay so that required assessment of a client or conducting of research may be carried out in a timely fashion. Science vs. Junk Science Two related forces led to the increasing use of expert witnesses. Because of the great strides in health and technology over the past several centuries, we live in an age that holds science in high regard. The prestige with which we regard science makes an expert witness particularly attractive for attorneys to use to present evidence to fact finders (jurors and judges). The prestige of science coupled with the increasingly complex technology that face fact finders led to the need for expert witnesses in court. With the advent of the expert witness, it was only a matter time before many charlatans presented themselves as experts. For scorching analyses of “junk science,” Huber’s Galileo’s Revenge: Junk Science in the Courtroom (1993) and Hagen’s Whores of the Court: the Fraud of Psychiatric Testimony and the Rape of American Justice Evidence (1997) are unforgettable primers for the ethical expert witness, matched only by Ziskin and Faust’s Coping with Psychiatric and Psychological Testimony (1994). The latter is a text on disassembling the expert witness and any testimony he or she offers. Any expert will be well served in reading one or all of these before testifying; failure to read these critiques may render the expert unarmed and unprepared for the combat awaiting him in court. Among the key lessons to keep in mind is to be sure that what one is presenting has a basis in fact and that any expression of opinion is accompanied by the appropriate statement of a certainty or probability of certainty or qualifying statements. A number of lessons are distilled in Chapter 3 in this volume, which articulates how the expert answers legal questions with psychological evidence. Recordkeeping Records need to be kept completely. An old correctional psychology dictum regarding correctional officers making their rounds says, “If it is not recorded, you did not make your rounds.” The ethical psychologist keeps complete records and is aware of the work product rule. This safeguards certain notes and records of attorney-expert interactions from discovery; without this, an attorney could not fully function in presenting his or her client’s case. Any questions about the inviolate nature of a particular record ought to be referred to the attorney. Records need to be kept securely. As mentioned earlier, privilege extends to one’s records and test data. If privilege is to be ensured, records must be kept secret and in a place available only to the expert and his direct adjuncts, who should be made aware of privilege. Records should be kept for an amount of time that exceeds any statutory limits that may be imposed on a case. In a case involving termination of a worker who was not fit to return to duty, the psychologist needs to learn from the attorney, and verify in the
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statutes, the amount of time that the former employee has to file any claims and appeals regarding termination of employment. Also, when disposing of records, the psychologist must be sure that any information no longer needed to be stored is truly destroyed and will not appear on a discarded hard drive of a secretary’s computer. Recordkeeping guidelines have been broached by the American Psychological Association (1993). Getting All the Information or Making a Reasonable Attempt The ethical expert tries to get all needed information. If information from the opposing side is not made available, one’s retaining attorney needs to be notified. If he or she is still unable to obtain it, then records should be kept (e.g., unanswered phone calls and emails, certified mail receipts that show attempts to obtain the data) so that, when appearing in court, the expert can show that all possible attempts to present a complete record were attempted. Then any bad faith dealings by the opposing side may be made evident by the retaining attorney, as he or she sees fit. Conducting Research As part of the development of the case, the attorney and expert need to keep contact as to how much effort the expert needs to expend. In some cases, conducting examinations and research may be unnecessary. If the attorney knows that he or she may settle the case, the expenditures by the expert for research and examinations may be in vain. This calls for continual communication between the two. Pretrial Meetings The attorney and expert should be in communication about evidence that is favorable and unfavorable to the retaining side. The attorney does have the option not to present the expert or not to ask questions that would be adverse to the client. The expert should answer questions asked and is under no obligation to tell all that he ever learned. The expert should be honestly responsive to both attorneys’ queries in deposition and in court. Also, if unfavorable information may come to light in court, the attorney and expert certainly may discuss how to handle it, perhaps on redirect examination. Communication is key; the psychologist and attorney need to “be on the same page” during the case. 4.3 Presenting the Case Testifying All the expert’s efforts may be undone if testimony is presented poorly. Books have been written on presenting expert testimony (and how to tear experts apart), so our comments are simple and limited to the ethics of testifying. Make sure that you have copies of all your communications, in at least duplicate form. Any evidence might be seized by the court, so having a backup copy is indispensable. Be sure all records (including and especially your curriculum vitae) are accurate and that you are familiar with all the data.
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When presenting evidence, the court-wise expert takes all needed time and teaches the court, without any arrogance. Errors can be made in any number of ways and the expert is sure to make one sooner or later. As soon as the expert realizes that he has made an error, at the next opportunity he should offer the correction in as low-key and sincere a manner as possible. The oath, as mentioned earlier, is to tell the truth, the whole truth, and nothing but the truth. This means that the court-wise expert does not simply volunteer information, but answers the question. If the evidence if unfavorable to the retaining side, it should not be a surprise to the retaining attorney. As mentioned earlier, evidence should be reviewed with the attorney beforehand. Hess (1999) describes more about preparing and presenting testimony, a topic deserving more attention than can be afforded in this chapter devoted to ethics. 4.4 After the Case There is little so final as ending a forensic case. The parties—plaintiff, victim, or defendant, or winner or loser—have been seared and scarred by the legal system. Few will have much time to delight or mourn with the expert. Attorneys who have been adversaries have a drink and perhaps dinner because they might be working together on the next case and both have another case the next morning to prepare and present. If the expert has performed ethically and professionally, he might be thanked, paid, and bid adieu. Records need to be retained; any appeals by either side need to be considered, although appeals are few. The best reward for the expert is the satisfaction in a job done well and perhaps to have served justice and presented psychology to the public as a wellregarded profession. Just perhaps, he will be asked to help again. Acknowledgments I appreciate the contributions of Kathryn D.Hess, Tanya H.Hess, and Steven Walfish to the development of this chapter. References American Psychological Association. (1992). Ethical principles of psychologists and code of conduct Am.Psychologist , 47, 2597–1628. American Psychological Association. (1993). Record keeping guidelines. Am. Psychologist , 48, 984–986. Committee on Ethical Guidelines for Forensic Psychologists. (1991). Speciality guidelines for forensic psychologists. Law Hum. Behav ., 15, 655–665. Hagen, M.A. (1997). Whores of the Court: The Fraud of Psychiatric Testimony and the Rape of American Justice Evidence . New York: HarperCollins. Hess, A.K. (1999). Serving as an expert witness. In A.K.Hess and I.B.Weiner, Eds., The Handbook of Forensic Psychology . 3rd ed. New York: John Wiley & Sons, 521–555.
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Huber, P.W. (1993). Galileo’s Revenge: Junk Science in the Courtroom . New York: Basic Books. Perrin, G.L and Sales, B.D. (1994). Forensic standards in the American Psychological Association’s new ethics code. Prof. Psychol: Res. Pract. , 25, 376–381. Ziskin, J. and Faust, D. (1994). Coping with Psychiatric and Psychological Testimony . Beverly Hills, CA: Law and Psychology Press.
5 A Road Map for the Practice of Forensic Human Factors and Ergonomics William B.Askren Human Factors Services John M.Howard Crossroads Machine, Inc. 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
5.1 Introduction This chapter is based on the authors’ many years of experience in the practice of forensic human factors and ergonomics for plaintiff and defense attorneys. The authors have observed that over the past 30 years human factors and ergonomics professionals have been used increasingly as expert witnesses in litigation. Peters (1971) described the early years of product liability and product safety. Initially, the use was by the plaintiff’s bar. Subsequently, the defense bar began employing these professionals to support their clients’ cases and to challenge the opinions of the plaintiffs’ human factors and ergonomics experts. With this increasing use of human factors and ergonomics professionals in litigation, it seems timely to provide a “road map” to guide professionals new to the field in the performance of their forensic practice. A useful background reference regarding product liability and forensic human factors and ergonomics is Weinstein et al. (1978). The types of litigation that serve as the authors’ experience base for this “road map” are personal injury and property damage accidents involving motor vehicles; consumer products; industrial machines and processes; and slips, trips, and falls for plaintiff and defense lawsuits. The human factors and ergonomics principles of the experience base cover a wide variety of topics, such as human use and misuse; human error; human senses, especially visual and auditory perception; biomechanics; anthropometries; decision making; reaction times; skill level; fatigue; training; and corporate safety and organizational policies. Also, physical technologies, such as electrical, mechanical, and chemical parameters that interact with the human factors and ergonomics issues, are part of the experience base.
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5.2 Objective The objective of the chapter is to present a road map for the practice of forensic human factors and ergonomics from initial contact with the attorney through trial testimony. The intent is to list and discuss the general sequence of activities, grouped by phases, that should be addressed while the professional is serving as a forensic expert witness and consultant. The consultant role to the attorney often is as important as the expert witness role. As a consultant, the human factors and ergonomics specialist may help the attorney develop case strategy as it relates to human involvement in the incident, as well as provide specific services such as developing and reviewing interrogatory questions and developing questions for examining the opposing human factors and ergonomics expert during deposition or trial. 5.3 Principal Issues The principal issues are the five basic phases that make up the road map. The phases are case initiation; understanding the accident scenario; analysis, findings, and opinions; reports; and deposition and trial testimony. These are presented in this section in the order in which they usually are performed by the expert. Included in each phase are its general purpose and intent and a listing of topics and activities to be considered and/or performed during that phase of the road map. Phase I. Case Initiation This is generally the first contact with the attorney. The purpose is to understand the general nature of the case and the time schedule, to decide whether the expert’s credentials and interests are appropriate, to decide whether to work on the case, to establish a financial relationship with the attorney if the expert decides to get involved, and to obtain from the attorney the immediately available case information and data. The following topics and activities should be addressed in the first contact with the attorney: • How did the attorney learn of the specialist’s expertise and availability? This becomes important later, during deposition and/or trial, when he is examined by opposing counsel. Opposing counsel will want to reveal whether his work on the case is the result of aggressive marketing on his part, referral from another attorney, or another case with the same attorney. The opposing counsel will be attempting to set the stage to impugn the expert’s objectivity. • Is this a defense or plaintiff case? Some experts are more comfortable with defense cases and others with the plaintiff. In general, it is suggested that experts try to work on plaintiff and defense cases to indicate their professional objectivity.
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• Conduct an initial review of the incident with as much detail as possible. Included in this detail might be the accident scenario, the persons involved, description of the equipment involved, and the environment. • Determine whether any conflicts of interest could prevent the expert from being a witness in a particular accident litigation. For example, has he been approached to testify against a defendant whom he has defended before or with whom he has consulted previously? • What role does the attorney want the human factors and ergonomics specialist to serve? Does the attorney have other experts dealing with other areas of the litigation accident? Avoid being an expert on everything. Even within the field of human factors and ergonomics, the specialist will probably have specific areas of expertise. • What is the time schedule of the case? Critical dates are discovery cutoff, deposition, and trial. The expert should consider whether time is sufficient for investigation, analysis, and development of opinions. • Decide whether the expert should serve as the human factors and ergonomics specialist for the case, or possibly recommend another person. Are the human factors and ergonomics issues within his area of expertise? He should be selective about accepting a case. • Request available documentation on the case. Documentation might include accident reports; photographs, witness statements, depositions, interrogatory answers, motions to produce, manuals, etc. • Establish the financial arrangements. It is suggested that the expert have a printed schedule of charges and fees for services, which can be provided to the attorney. A clear understanding of payment of fees is necessary. Such a fee schedule should include: retainer amount (if required), hourly rates for services, what services are included, and fee for deposition and trial testimony if different from the hourly rate. • Provide a curriculum vitae (CV), or resume, to the attorney. Everything written in the CV probably will be examined during deposition and/or trial by opposing counsel. The CV will help establish expertise. • Set up a file with several sections, such as: (1) significant dates, e.g., first contact by counsel, date of accident, potential deposition and trial; (2) documents and material provided by the attorney; (3) documents and material compiled by the expert; (4) analyses and opinions; and (5) date log of the expert’s labor, trips, expenses, etc. During deposition the opposing counsel will thoroughly examine this file and probably will question the expert about every document in it. Phase II. Understand the Accident Scenario The purpose of this phase is to gain as complete an understanding of the nature of the accident as possible. This is essential for follow-on analysis and for development of findings and opinions of the human factors and ergonomics issues of the accident. This understanding will involve learning about any environmental, equipment, human, process, and organizational conditions relevant to the accident. This learning is a continuing, evolving activity over the early life of the case. In fact, the expert may be exposed to several different possible accident scenarios during his analysis. However, the final accident scenario selected must be supported by the analysis.
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Generally, the more of these topics and activities that can be addressed, the better is the grasp of the accident scenario (see Section 5.6 for a more detailed description): • Read available case documentation, such as accident reports, police reports, insurance reports, witness statements, depositions, interrogatories, requests for admissions, medical reports, and product reports. • Review videotapes and photographs of the accident scene, equipment, etc. • Visit the scene of the accident. At a minimum, develop a plan view of the accident scene and place on the drawing the location of any witnesses. This assumes that the accident scene has not substantially changed since the time of the accident. The visit could possibly be coordinated to be close to the time of day of the accident and, in some cases, the time of year and similar weather conditions. • Inspect equipment or products involved. Develop a checklist for these inspection procedures. • Take photographs and measurements. If human visual perspective in an accident is to be evaluated, be sure to position the camera at the subject’s eye level. Also, to establish sizes and distances of objects, place a measuring tape next to the object being photographed. • Useful accident investigation tools include: still and video camera, audio recorder, 50-ft tape measure, roadway distance-measuring wheel, gauges for measuring push/pull/lift forces, inclinom-eter, level, marking implements such as chalk and adhesive tape, plumb bob, calculator, stop watch, and protractor. • Interview witnesses of the accident. Pay particular attention to the witness’s location or ability to evaluate the accident. Attention should be paid to such factors as the witness’s visual, auditory, timing, and accident-event-sequence perspectives of the accident. • Develop a timeline of events leading up to and during the accident. • Acquire weather reports for the date of outside accidents. Sometimes the sunrise/sunset times and moon phases are also important. Phase III. Analysis, Findings, and Opinions In general, the purpose of this phase is to compare the information and data collected in Phase II with human factors and ergonomics criteria that have been established to provide for adequate human performance and safety in the commercial, industrial, and technological world. This is followed by the development of opinions as to whether the human factors and ergonomics characteristics of the litigation case meet or fail these criteria and whether these characteristics are relevant to the cause of the accident. Generally, this is not a two-step process because opinions are continually formulated during analysis and then are accepted, refined, or refuted as the analysis and findings progress. Thus, analysis, findings, and opinion formulation is an iterative procedure. A suggested three-step technical approach to performing the analysis and developing opinions is given in Section 5.6. The three steps are: (1) a forensic accident analysis model, which guides the investigative procedure; (2) applying this model to a specific accident case; and (3) evaluating the analysis results and findings and developing opinions.
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The suggested topics and activities to be addressed while performing the analysis, developing findings, and developing opinions are: • Compile and review the information and data collected in Phase II. • Adapt the forensic accident analysis model described in Section 5.6 to the specific type of accident and litigation. • Apply the adapted forensic accident analysis model to the accident scenario and determine potential human factors and ergonomics issues of the accident. • Evaluate the results from application of the forensic accident analysis model using the criteria described in Section 5.6. • Formulate opinions as to the adequacy or inadequacy of the preaccident considerations for the human factors and ergonomics parameters. Phase IV. Reports The purposes of the report are to provide a record of the expert’s credentials and qualifications, the analysis performed by the expert, the opinions developed by the expert, and the basis for the opinions regarding the accident that is the subject of the litigation. The report should be in a format that is acceptable to the expert, the attorney, and the court. In some litigation venues such as local, county, and state courts, a written report is not required. The written report may be in the form of a preliminary report, a final report, or an affidavit or declaration, both of which are notarized (witnessed) signed documents. When a preliminary report that probably will become a piece of evidence is provided, the title should reflect that these are the expert’s findings to date. The preliminary report should state that the analysis is not yet complete, state why the findings are tentative, and identify remaining analysis tasks. The final report should reflect the expert’s final opinions based upon the performed human factors and ergonomics analysis. However, it should state that the expert reserves the right to change or alter the opinions as the facts change or as the understanding of the facts changes. In general, the final report should include sections providing: • When and by whom the expert was contacted, what the assignment was, a short description of the date and accident scenario, scene layout and the persons and equipment involved • The case documentation (e.g., depositions, interrogatories, accident reports) provided and reviewed • Investigation activities conducted by the expert, e.g., review of the case documentation, review of other related literature, product and/or accident scene analysis, and analysis of accident data bases • A description of the findings and opinions regarding the human factors and ergonomics issues of the case, with a statement that the findings and opinions are based on the expert’s general professional experience; on training, knowledge, and education in human factors and ergonomics; and on the aforementioned analysis of the specific issues involved in the investigated accident • A copy of the expert’s curriculum vitae (CV), usually attached as an appendix
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The formats for the declaration and the affidavit are nearly identical and very similar to a final report. A final report usually has a CV included with its submission; however, the affidavit and declaration are usually stand-alone documents and thus require a section detailing the present and past credentials and qualifications of the expert. Reports submitted to a federal court must follow specific guidelines. Under Rule 26 of the Federal Rules of Civil Procedure, filing of expert witness written reports is mandatory and must follow these guidelines for recording the analysis and opinions: • The report must be prepared by the expert witness. • The expert must sign the report. • The report must include a complete statement of all opinions to be expressed. • The basis and reasoning for each opinion must be included. • The data or other significant information considered by the expert in forming the opinions must be listed. • Exhibits to be used as a summary or as support for opinions must be included. • All publications authored by the expert within the past 10 years, regardless of relevance, must be listed; this is usually done with a copy of the expert’s CV attached as an appendix to the report. • The compensation to be paid for the testimony and analysis must be included; this can be provided by the expert’s schedule of fees as an attachment to the report. • A list of other cases in which the expert gave depositions or trial testimony within the past four years, without regard to relevance or relationship to the subject matter of the litigation, must be submitted with the report. This list may also be provided as an attachment to the report. The topics and activities to be considered for reports include: • The length of the report should be as short as possible, yet include all necessary information and data. Typically, three to four pages, plus attachments, is an acceptable length. • All written reports are evidence and therefore are discoverable; they probably will be used for examination during deposition and/or trial. • The report format should be reviewed with the attorney before beginning preparation, to ensure acceptance with the litigation venue, i.e., the local, county, state, or federal jurisdiction. • The report should be submitted on time. Report submission deadlines are very important for compliance with legal system requirements. Phase V. Deposition and Trial Testimony The overall purposes of deposition and trial testimony are similar in that they provide a forum for the expert witness to present opinions and the basis for the opinions. Deposition Testimony However, a clear distinction can be made in that the deposition is primarily for the opposing counsel through direct examination to discover the expert’s qualifications to be
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a human factors and ergonomics expert, analyses and investigations that have been performed, concluded findings and opinions, and the specific basis for those opinions. Sometimes when opposing counsel is finished, the engaging counsel will ask clarifying questions before the deposition is concluded. In general, an expert’s deposition will follow the report phase; however, a report is not always required. Usually, the plaintiff’s expert witnesses will be deposed first in sequence, followed by the defense experts. Usually, the opposing attorney will call for, and pay for, the deposition, subject to jurisdiction rules and deadlines. Sometimes before deposition and usually before trial, the engaging attorney will want to conduct an examination practice session. This will occur less frequently as the expert becomes more experienced. At the conclusion of the deposition, the expert will be asked whether or not he would like to read and sign the deposition. It is suggested that the expert do this and indicate “form” only changes on the errata sheet. If possible, he should retain a copy of the deposition for use in preparation for, and at, trial. Trial Testimony In trial testimony, the expert’s credentials to be a human factors and ergonomics expert are first presented through direct examination by the employing counsel. Opposing counsel may challenge credentials and expertise at this point in the trial proceedings and question the expert. Assuming that the expert is acceptable to the judge or court as a human factors and ergonomics expert witness, direct examination will continue by engaging counsel until finished. The opposing counsel now begins cross-examination of the subject matter covered during direct examination. Cross-examination is followed by redirect and recrossexamination, continuing until all areas on a limiting basis have been covered. “Limiting basis” means that only issues included in testimony in the immediately preceding examination may be addressed. The judge or court will then excuse the expert witness from the stand and he should exit the courtroom. From time to time during cross-examination, the opposing counsel will present various challenges to the introduction of human factors and ergonomics testimony at trial. Some of the challenges human factors and ergonomics experts may encounter are: • Opposing counsel has chosen not to use a human factors and ergonomics expert for his own case and now realizes the likely effectiveness of the human factors and ergonomics professional’s testimony. • Opposing counsel challenges the utility of the human factors and ergonomics discipline and information in assisting judicial decisions (i.e., jurors would know based on their own expertise or it is “just common sense”). • Opposing counsel cites the Daubert decision challenging the acceptance of the human factors and ergonomics discipline and its scientific credibility. • Opposing counsel challenges that human factors and ergonomics on “accident causation” is based on opinions of human behavior and will “invade the province” of the jury for finding fault.
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• In addition, the opposing counsel may challenge (as discussed previously) the qualifications of the human factors and ergonomics expert. The expert must be prepared to establish qualifications as a credible expert. For further discussion of these challenges and specific arguments supporting human factors and ergonomics testimony, see the “Position Paper Supporting Human Factors and Ergonomics Practitioners in Forensics,” produced by the Forensic Professional Group of the Human Factors and Ergonomics Society (Forensic Professional Group, 1996). The following general topics and activities should be considered in preparing for providing testimony in deposition and/or trial: • The three most important words in providing testimony are: preparation, preparation, and preparation. This activity cannot be overstressed. Remember that each accident litigation, regardless of its similarity to prior cases or the expert’s past experience, is uniquely different because the facts are never the same. The people are always different, and the law is probably different. Thus, each case involves new analysis, evaluation, and preparation. • Ensure a thorough understanding of, and basis for, the precise human factors and ergonomic issues in the accident and the case. • When giving testimony, an expert witness should: • Be honest, impartial, and always tell the truth. • Not speculate but, rather, be certain; avoid guessing (saying “I don’t know” if he does not know). • Work within the legal process, its practices, and procedures. • Look and act the part of a qualified professional. Remember that the expert is representing himself, possibly a company, the plaintiff or defense or court, and the profession of human factors and ergonomics. • In trial, face and talk to the jury. • Be articulate and not use sophisticated technical jargon. • Not be an advocate. An expert’s testimony is not intended to win a case or sell a point of view. Its purpose is to help the court reach a just decision. • Control his emotions. Remember that opposing counsel can be very challenging and emotional. This is his job, and if he can get the witness flustered or defensive, he will try to do it. It is all part of the system. • Answer questions responsively. As a general rule, do not volunteer information. Listen closely to the questions and answer what is asked to the best of his ability. If he does not fully hear or understand the question, he should say so and ask for the question to be repeated. • Always stay within his area of expertise. • The Human Factors and Ergonomics Society adopted in 1989 and amended in 1998 a code of ethics to promote and sustain the highest levels of professional and scientific performance by its members (Anonymous, annually). The seven basic principles of the forensic practice section of the code are particularly relevant during deposition and trial testimony. These principles are:
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• Provide objective, unbiased testimony that is based on credible data and/or scientific principles. • Avoid impugning the integrity of other expert witnesses. • Do not accept fees on a basis contingent on the outcome of the litigation. • Accept that the client is the attorney who engaged you and not the client of that attorney. • Except when required by the Federal Rules of Evidence, avoid discussing litigation with others in a way that would disclose the caption of the suit or the parties involved without the permission of the engaging attorney, until the litigation is resolved. • Do not make public statements likely to influence or prejudice the proceedings. • After suit resolution, do not reveal information detrimental to the parties involved, except when there is evidence of a greater duty of protecting public health and safety. • The following is a general line of direct examination questions that an expert should be prepared to answer when giving testimony in a deposition and/or trial: • Introduction: name, title, age. How long have you been an expert witness? Have you worked for either counsel in this case before? If so, how many times? How much are you paid for giving testimony? • What is your specific field of expertise? • What is human factors and ergonomics and how does it relate to this accident/litigation? • Review of the expert’s resume: education, work experience, present job and daily duties and responsibility, honors, certifications, publications, professional societies, etc. • State your specific experience (including design) regarding the subject matter involved in the specific accident/litigation (to establish why the expert is qualified and credible to be an expert in the case). • How many times have you testified in depositions and trials for plaintiffs and for defendants? • What case materials have you reviewed regarding this accident/litigation? • What general reference documents (e.g., standards, recommended practices) have you reviewed? • What specific analyses have been performed during the investigation of the accident? • Was an accident scene investigation conducted? • Have you inspected the subject product/equipment/process and/or analyzed an exemplar? • Based upon your review of the case materials, reference documentation, and the analyses and inspections that have been conducted, do you have any opinions: yes or no? (If yes, the opinions are then stated, followed by the specific basis for each opinion.) • After case completion:
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• Retain case file material until the case is settled plus one additional year allowing for appeal or other legal procedures. • Ask the engaging counsel for a critique of performance: testimony and effectiveness of the evidence and exhibits developed. This will help the expert to be a better expert witness in the future.
5.4 Example Cases Illustrating the Road Map This section presents two litigation cases—one plaintiff and one defense—that illustrate the phases of the road map. Plaintiff: Medical Equipment Phase I. Case Initiation A human factors and ergonomics expert was contacted by a plaintiff’s counsel with whom he had worked before on plaintiff and defendant accident litigations. Because of the previous experiences, the expert was very comfortable working with this attorney again. An updated resume and fee schedule were forwarded to the attorney. The initial conversation included a brief description of the accident scenario, activities of the persons involved, medical equipment (product) involved, and accident scene layout. Also discussed were: the case time schedule and critical dates, that the expert did not have any conflicts of interest, the basic role within the field of human factors and ergonomics that the expert would serve, and the general accident and case documentation available. The expert agreed to review the available documentation, begin an investigation of the accident, and set up a file. Phase II. Understanding the Accident Scenario The expert received and reviewed during the discovery phase the following documents from the plaintiff’s attorney • Photographs of the subject medical equipment, including the foot-operated controls • The plaintiff’s deposition • The defendant’s answers to the plaintiff’s interrogatories and motions to produce • The “Installation and Operation Manual” for the subject model equipment • Photographs of an older style of foot control and equipment from the same manufacturer • The defendant’s accident investigation report • The defendant’s sales brochures for the subject equipment • Underwriters Laboratory report on the subject equipment • Diagrams of the on-product labels • The defendant’s engineering change orders for the subject equipment from the older to the newer style • The defendant’s service manual and service bulletins for the subject equipment
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• Depositions of the defendant’s manager of engineering and the manager of quality assurance • Deposition of the plaintiff’s supervising physician • The design manufacture drawings of the subject equipment The expert did not visit the accident scene or inspect the subject equipment. However, he did inspect and take measurements of the defendant’s exemplar equipment and a competitor’s similar equipment. No witnesses were interviewed. The following accident scenario was developed and used by the expert. While he was operating medical equipment, the technician received a crushing foot injury. The equipment employs a multiswitch foot control to control various functions, including equipment position. The foot control is tethered to the equipment and can be moved to any number of positions for operation. While he was assisting the physician in performing a medical procedure on a patient, the technician was operating the equipment using the foot control. The foot control was in a position under the equipment, so when the equipment was lowered to a set position, it made contact and trapped the operator’s foot on the continuing-to-function control. The weight and continuous force of the equipment on top of the operator’s trapped foot caused the injury. Phase III. Analysis, Findings, and Opinions Analyses included the following activities: • Review of all the documents listed in Phase II and summarization of the relevant information • Application of the forensic accident analysis model to the accident scenario and determination of potential human factors and ergonomics issues • Search for and review of evaluation criteria documents such as medical equipment industry and government regulations, standards, recommended practices and guidelines, human factors and ergonomics design principles, data, and methods from human factors and ergonomics handbooks and guides • Search for similar accidents • Review of defendant’s previous subject equipment designs and similar equipment designs • Competitors’ designs Based upon the expert’s analysis of the accident, the following findings and basic human factors and ergonomics opinions were reached. The first basic opinion was that the medical equipment and its foot-operated control were unreasonably dangerous based upon inadequate human factors and ergonomics design. Inadequate design and guarding issues included the unguarded, movable foot control and the single, two-function pedal built into the unshielded foot control. Inadequate warnings were found on the product and in the accompanying operator’s manual with regard to the accident scenario’s identified hazard and risk. Alternative designs were available on similar medical equipment that exemplified good human factors design criteria and principles. The second basic opinion was that if the design and manufacture of the subject medical equipment and foot control had been consistent with sound human factors and
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ergonomics principles, the plaintiff would not have experienced the accident and corresponding injuries. Phase IV. Report No report was requested by the plaintiff’s attorney. Phase V. Deposition and Trial Testimony The human factors and ergonomics expert provided a 2-hour deposition based upon his investigation, findings, and opinions. The case settled prior to trial. Defense: Farm Equipment Phase I. Case Initiation A human factors and ergonomics expert was contacted by a defense counsel with whom he had worked before. During the conversation, the attorney provided: a brief description of the accident scenario, the activities of the persons involved, a description of the farm equipment involved and the defendant manufacturer, and the accident scene layout. Also discussed were: the case timeline, that no conflicts of interest existed for the expert, the basic human factors and ergonomics role that the expert would play, identities of the other defense experts and their expertise, and the availability of case documentation. The expert agreed to review the available documentation, begin an investigation of the accident, and set up a file. An updated resume and fee schedule were sent to the attorney. Phase II. Understanding the Accident Scenario The expert received and reviewed the following documents from the defense attorney: • Depositions of the plaintiff, the farm owner, the plaintiff’s supervisor, the equipment’s installer, and the plaintiff’s experts • The plaintiff’s medical records, including photographs of the foot and leg injuries • Photographs of the subject equipment and accident scene • The plaintiff’s answers to defendant’s interrogatories • Equipment “Assembly and Operating Instruction Manual” • The employer’s accident report of injury (signed by plaintiff) • The plaintiff’s notice to produce to defendant and the answers • The defendant manufacturer’s design and manufacture drawings of subject equipment • The defendant’s sales brochures • Competitors’ sales brochures The expert did not visit the scene of the accident or inspect the subject farm equipment. The expert did, however, rely on accident scene photographs taken by three different sources, as well as measurements of equipment sizes and distances made by plaintiff and defense investigators. The measurements proved to be particularly useful throughout the
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investigation and during trial testimony. These measurements were also made into a scaled drawing of the equipment and accident scene. The expert requested and received, through defense counsel, certain anthropometric measurements of the plaintiff, such as foot and shoe size, ankle height, knee height, arm length, and stature. No witnesses were interviewed. Phase III. Analysis, Findings, and Opinions The following analyses were performed: • Review of all the documents listed in Phase II • Summaries of relevant information • The forensic accident analysis model applied to the accident scenario for evaluation of the human factors and ergonomics inadequacies identified by plaintiff’s experts • Biomechanical/anthropometric analysis of the plaintiff’s size in relation to the equipment size and operational characteristics • Review of the evaluation criteria documents identified by the plaintiff’s experts, such as American Society of Agricultural Engineers Standards. • Evaluation of the subject equipment’s warning labels and manuals for adequacy with regard to the specific accident scenario’s hazards and risks and the plaintiff’s training and experience • Evaluation of the alleged need for a remote control Based upon the expert’s analysis of the accident, the following findings and opinions were reached. The first opinion was that the accident did not happen in the way in which the plaintiff testified. Instead, the evidence and the expert’s analyses led to the conclusion that a different scenario had probably occurred. The second opinion was that the warnings on the subject equipment were adequate to advise anyone of the hazards and risks presented, especially someone with the plaintiff’s years of experience, awareness, and training in working with this type of equipment. The third opinion was that providing a remote control switch would not have prevented this accident.
TABLE 5.1 Checklist of Main Considerations by Phase Phases I. Case initiation
Considerations
Nature of case/time schedule Yes/no work on case Financial arrangements Available information/data II. Understand accident scenario Environmental Equipment Human Process Organizational III. Analysis, findings, and opinions Forensic accident analysis model Adapt model to accident scenario Analysis using model (five elements)
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Evaluate findings by criteria hierarchy Develop opinions Proper format Short length Timely Discoverable evidence Thorough preparation Examination questions Behavior during testimony Code of ethics
Phase IV. Reports No report was requested by the defense attorney. Phase V. Deposition and Trial Testimony The human factors and ergonomics defense expert gave a 2-hour deposition and testified at trial. The expert’s exhibits, including the equipment’s scale drawing and articulated anthropometric model of the plaintiff, were especially effective in demonstrating that the accident scenario did not occur in the way in which the plaintiff had testified. The trial resulted in a verdict for the defendant manufacturer. 5.5 Checklist of Main Considerations by Phase A summary checklist of the main considerations for the five phases is given in Table 5.1. 5.6 Technical Approach to Analysis, Findings, and Opinions An aid to performing an analysis and developing findings and opinions is a three-part technical procedure. The procedure includes: (1) a forensic accident analysis model, (2) applying the model to the specific type of accident and litigation, and (3) evaluating results of the analysis and developing findings and opinions about the human factors and ergonomics conditions of the accident scenario. Each of these topics is discussed in this section. Forensic Accident Analysis Model A product safety model advocated and used by Christensen (1981) served as the basis for the forensic accident analysis model. The evolved model has five steps that lead the analyst through the procedure to determine the adequacy or inadequacy of preaccident considerations of the human factors and ergonomics parameters relevant to the accident scenario. The preaccident concept is crucial because the analyst is attempting to
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determine if efforts were made before the accident to provide for human performance and safety. The five steps of the analysis are: • Step 1: Design. Evaluate the design of the product, equipment, or process for its adequacy to have provided for effective and safe human interfaces such as installation, use, and maintenance. • Step 2: Remove. Assess the feasibility of having removed the human from a potentially unsafe condition, for example, a remote control station. • Step 3: Guard. Evaluate the adequacy of guarding to protect the human from potential hazards. • Step 4: Warn. Evaluate the adequacy of warnings to have informed the human about potential hazards and risks, to reinforce prior knowledge about hazards and risks, and to provide the steps to take to avoid the hazards. • Step 5: Train. Evaluate the adequacy of training about potential hazards and risks and the proper procedures to avoid the potential hazards and reduce the risks. This general forensic accident analysis model must now be applied to the specific type of accident under investigation and the unique litigation. Applying the Forensic Accident Analysis Model to the Accident Scenario All five elements of the analysis model might not necessarily apply to a given accident litigation. Therefore, the model needs to be used selectively, based on the characteristics of a given litigation accident. The tailoring generally would be of the type to select which one or more of the five elements apply to the specific accident case. This would be followed by an analysis and evaluation of the adequacy or inadequacy of the human factors and ergonomics considerations for the selected model elements. Information and data that can be used as criteria for the evaluations of the results of the analyses will be discussed later. For the remainder of this section, suggestions are provided for the usefulness of the five steps of the model for different types of accident cases. Potential usefulness of the five steps of the model is illustrated with four different types of cases: consumer product accidents; motor vehicle accidents; industrial machine or process accidents; and slip, trip, and fall accidents. Consumer Product Accidents Accidents of this type cover a wide range, from simple cans of spray paint or insect spray purchased off the shelf in stores to complex products such as pleasure boats and allterrain vehicles (ATV) purchased from dealers. The Consumer Product Safety Commission directory lists hundreds of consumer products, which have a great variety of human factors and ergonomics interface issues. The following suggestions are general information about applying the product safety model to consumer product accident cases; in no way can they reflect the full range and diversity of consumer products. Other chapters in this handbook provide additional information about consumer product accidents.
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• Design. Design can certainly apply to consumer products. However, there is no single statement as to. the human factors and ergonomics design parameters for consumer products, given that such a broad range of product types is available. Design parameters can be as simple as the location and coding of a pushbutton on a spray can to the full range of operator and maintainer interface topics for a pleasure boat or an ATV. The intent during analysis is to understand the adequacy or inadequacy of the design as related to the accident. This may be quickly determined or may require extensive analysis. • Remove. The remove topic generally would not apply to consumer products, although it might be relevant to human tasks for some types of products. A historic example is the handle control start for lawn mowers, which reduces the risk of contact with the rotating blade while an individual is starting the mower and reduces the strain on the user’s body. • Guard. The guard topic would generally apply to the more complex consumer products that have mechanical or electrical hazards—for example, guards over switches to prevent inadvertent activation of a power source, or guards over moving parts to prevent accidental contact by a body part. • Warn. Warnings apply to all types of consumer products and have become one of the primary human factors and ergonomics issues in litigation. The simplest spray cans might require information about the hazardous nature of the propellant. The more complex products might need to warn about hazards for a variety of operating and maintenance procedures. Warnings can have many forms for consumer products, such as on-product labeling or on-packaging labeling, an information insert in the product packaging, information in the user manual, and information in advertising literature such as catalogues and brochures. Warnings may be appropriate for assembly, installation, operation, maintenance, and disposal of the product. Details on the subject of warnings may be found in other chapters in this handbook, as well as in Laughery et al. (1994) and Wogalter et al. (2001). • Train. For consumer products, the train topic applies to a wide range of situations, e.g., instruction labels on products, user guides accompanying the product, and customer training courses for the more elaborate products, such as pleasure boats or ATVs. Motor Vehicle Accidents The concern here is primarily with roadway vehicles under the regulation of the National Highway Traffic Safety Administration (NHTSA) and the Federal Highway Administration (FHA). Other chapters in this book provide additional information about motor vehicle accidents. • Design. Design is obviously very relevant to safe use of motor vehicles, but this is an extremely complicated topic involving the vehicle and the roadway and is best understood by reading publications produced by the SAE, FHA, NHTSA, and Peters and Peters (1993). The best that can be said here is that design, as it interfaces with human factors and ergonomics capabilities and limitations, can play an important part in proximal causes of motor vehicle accidents. • Remove. The remove factor is relevant and could apply to motor vehicles and to roadways. It generally is most relevant to roadway design, e.g., roadway overpasses to
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avoid vehicle collisions at intersections and at railroad crossings. Useful references on this topic include publications provided by FHA and state Departments of Transportation. However, in some instances, vehicle design may remove the user from a hazard, e.g., the historical electric starter to replace the hand crank with its potential injury to the body. In the future, “removal” may become more intellectual by “removing” the driver from certain decisions regarding braking, steering, accelerating, etc. • Guard. Guarding is certainly relevant. Examples of the guard factor in vehicle design are seat belts, air bags, occupant interior padding, and guarding of the fan in the engine compartment. The guard factor is relevant also to roadway design, e.g., guardrails and slow-compressing containers on concrete posts. • Warn. Warnings would have a variety of applications, such as vehicle operator manuals, labels mounted on the vehicle (particularly in the occupant compartment), and roadway signs of potentially hazardous conditions, e.g., falling rocks and ice on bridges. • Train. Training could have a wide range of implications, from vehicle operator instruction manuals to formalized training programs for commercial drivers. Industrial Machine or Process Accidents The focus here is on the industrial manufacturing arena. There is a wide range of application of the accident analysis model in this area, from simple punch press and manual lathe equipment to very complex computer numerical control machines and automated assembly operations. Publications by OSHA, ANSI, NSC, and NIOSH are instructive on this topic. Other chapters in this book provide additional information about industrial accidents. • Design. Design for safety can range across the spectrum of industrial machines and processes, such as location of controls on basic machines to the layout and arrangement of work stations for complex process operations comprising many machines, conveyors, and workers. • Remove. Removing the human from contact with hazards by such techniques as remote manipulators, robots, and remote control panels is becoming an increasingly useful procedure for worker safety; see, for example, a NIOSH publication on the subject of robotic workstations (Etherton, 1988). When an industrial accident is investigated, the expert should ask, “Could the process have been designed to remove the worker from the hazard?” Certainly, economics and technical feasibility must be considered, but the question should be explored. • Guard. Guarding to prevent injury to workers is certainly relevant and has a long history of technical achievement with a variety of guarding techniques. A useful reference is Blundell (1983). The human factors and ergonomics expert should definitely look at the adequate use, or non-use, of guards for the specific accident. • Warn. There is a long history of the use of warnings in the industrial world, ranging from workplace signs and placards and on-machine labels to more elaborate auditory and visual signals. The use or non-use of warning should definitely be examined for a specific accident.
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• Train. Training is certainly an important element in the industrial world. Generally, most industries provide training for their employees. For a specific accident case, questions should be asked about whether any training was provided and, if provided, whether it instructed about avoiding the conditions that led to the specific accident. Slip, Trip, and Fall Accidents Slip, trip, and fall accidents occur frequently, and the forensic accident analysis model also can be a useful approach for these types of accidents. Useful references to understanding the dynamics of slip, trip, and fall accidents are publications by NSC and ANSI. Other chapters in this book provide additional information about these types of accidents. • Design. Design is relevant, e.g., geometry of steps, slip resistance of the walking surface, handholds, and defects in the walking surface due to failure to maintain an adequate design. • Remove. The remove element is not really relevant, unless we visualize removing the plaintiff from the necessity of walking on a surface. • Guard. Guarding is certainly important, for example, the adequacy of railings, handholds, fences, grates, and temporary barricades. • Warn. Warning about hazards on or near a walkway is relevant, for example, signs about repairs in progress, water or ice on the surface, and edge drop-offs. A fairly recent type of warning is the auditory warning on moving walkways in airports that alerts the traveler that the end of the automated walkway is approaching. • Train. The train element is not generally applicable to slip, trip, and fall accidents. Evaluating Analysis Results and Developing Findings and Opinions Assuming that one or more of the accident analysis model elements were found relevant to the specific accident and litigation and that human factors and ergonomics information and data were compiled for the relevant model elements, the next step is to evaluate the adequacy or inadequacy of these findings as related to human performance and safety. Therefore, this section deals with the types of information and data that can provide the criteria against which to determine the adequacy or inadequacy of the design/remove/guard/warn/train findings for a given accident scenario and to develop opinions as to their effect on the accident. The information and data are grouped into categories, which are listed in a hierarchy that reflects the general legal acceptance of the information and data to support the development of opinions for forensic cases. The categories, in descending order of generally acceptable information and data, are: • Government codes, regulations, and law, e.g., OSHA, CPSC • Voluntary industry and association standards, e.g., ANSI, ASTM • Industry customs, guidelines, and recommended practices, e.g., SAE, ASAE • Professional handbooks, e.g., Human Factors Design Handbook • Historical accident databases, e.g., CPSC, NHTSA • Scientific literature, e.g., professional journals
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• Empirical study, e.g., consumer use test, user surveys • Professional judgment, e.g., safety analysis of a tool or procedure As stated earlier, the significance of this hierarchy is that an evaluation of findings, as well as the development of opinions based on the information and data obtained from categories near the top of this hierarchy, generally carries more weight in the legal system. This is not to repute the lower-ranking categories because sometimes a wellconstructed empirical study focused on the accident case scenario in the absence of documented human factors and ergonomics data can provide powerful opinion data. Also, the opinions of a nationally recognized professional may be well received in the legal system. The opinions about the adequacy or inadequacy of the human factors and ergonomics parameters of the specific accident scenario to provide for safe human performance generally emerge during the course of the analysis and evaluation of the findings. As the analysis progresses through the five steps of the accident analysis model and the findings are tested against the evaluation criteria, the opinions often become self-evident. It should be remembered that this is an evolving, iterative procedure, with opinions gradually developed and refined over time before their presentation in the form of a written report or orally in deposition and/or trial. Defining Terms ANSI—American National Standards Institute ASAE—American Society of Agricultural Engineers ASTM—American Society of Testing and Materials ATV—All-terrain vehicle CPSC—Consumer Product Safety Commission CV—Curriculum vitae (aka resume) FAAM—Forensic Accident Analysis Model FHA—Federal Highway Administration NHTSA—National Highway Transportation Safety Administration NIOSH—National Institute of Occupational Safety and Health NSC—National Safety Council OSHA—Occupational Safety and Health Administration SAE—Society of Automotive Engineers References Anonymous, Annually, Code of ethics, Article V, forensic practice, in Directory and Yearbook , Santa Monica, CA: Human Factors and Ergonomics Society. Blundell, J.K., 1983, Machine Guarding Accidents , Columbia, MD: Hanrow Press, Inc. Christensen, J.M., 1981, Forensic human factors psychology, in ASME-ASNT-NBS Symposium on Non-destructive Evaluation: Reliability and Human Factors , Washington, D.C.: National Bureau of Standards. chap. 3.
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Etherton, J.R., 1988, Safe maintenance guidelines for robotic workstations, Morgantown, WV: NIOSH Technical Report. Forensic Professional Group, 1996, Position paper supporting human factors and ergonomics practitioners in forensics, Santa Monica, CA: Human Factors and Ergonomics Society. Laughery, Sr., K.R., Wogalter, M.S., and Young, S.L., 1994, Human Factors Perspectives on Warnings , Santa Monica, CA: Human Factors and Ergonomics Society. Peters, G.A., 1971, Product Liability and Safety , Washington, D.C.: Coiner. Peters, G.A. and Peters, B.J., 1993, Automotive Engineering and Litigation , Vols. 1–6, New York: John Wiley & Sons. Poyntrer, D., 1987, Expert Witness Handbook , Santa Barbara, CA: Para Publishing Company. Weinstein, A.S., Twerski, A.D., Piehler, H.R., and Donaher, W.A., 1978, Product Liability and the Reasonably Safe Product , New York: John Wiley & Sons. Wolgalter, M.S., Young, S.L., and Laughery, Sr., K.R., 2001, Human Factors Perspectives on Warnings , Volume 2 , Santa Monica, CA: Human Factors and Ergonomics Society.
6 Can Training for Safe Practices Reduce the Risk of Organizational Liability? Katherine A.Wilson University of Central Florida Heather A.Priest University of Central Florida Eduardo Salas University of Central Florida C.Shawn Burke University of Central Florida 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
6.1 Introduction to Human Factors Principles It has been well documented that human error contributes to accidents and incidents more than two thirds of the time (see Decker, 2001; Freeman and Simmon, 1991; Helmreich, in press; Kletz, 1985), leading to liability issues for the individual and even the organization. In an effort to reduce accidents, the Occupational Safety and Health Administration (OSHA) was created in 1970 and has since reduced the number of workplace deaths by 50%. However, the incidence of workplace accidents remains high. For example, it has been estimated that approximately 5.7 million worker-related injuries/illnesses and almost 6000 deaths occurred in private-sector firms in 2000 (http://www.osha.gov/). In other words, despite safety laws and regulations for organizations, a significant number of injuries continue to occur each year. Because many of these accidents and incidents are due to human error, organizations have turned to training as a way to teach employees how to mitigate and capture errors before they become detrimental. Training in today’s organizations is “big business” and is estimated to grow as organizational complexity increases the propensity for human error. It is estimated that organizations spend between $55.3 billion and $200 billion each year on training employees (Salas and Cannon-Bowers, 2001; Bassi and Van Buren, 1998). Although the purpose of training in organizations varies (e.g., improve safety, increase human capital, increase competencies, better product quality, error reduction), the overarching theme is to create a more productive and safe work environment for employees as well as for consumers.
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Many organizations believe that by providing individual training as a means of reducing human error and improving safety will minimize the organization’s threat of legal liability. However, often the training provided by the organization is inadequate, thus opening the door to litigation against the organization. The most likely cause of inadequate training is its improper design, delivery, implementation (i.e., transfer of training), and evaluation. Training research has been around for several decades (see Campbell, 1971; Goldstein, 1980). Over the past decade, there has been an explosion in the science of training. The research conducted on training in the 1990s led to the expansion of theoretical frameworks, concepts, and constructs (Salas and Cannon-Bowers, 2001). The training field can now offer principles and guidelines based on sound theories to practitioners and instructional designers. In addition, new models to design training and better tools to evaluate it have been developed. Yet, despite this research, its impact on organizational practice has not been seen. Salas and colleagues (1999; in press) argue that the reason for this is the many myths and misconceptions about the science of training and its practice to which many designers fall prey. Thus, training is often designed based on assumptions that cannot be supported, and it is not always effective. Effective training, therefore, relies on incorporating sound principles of learning in the design and delivery, systematic evaluation of what was taught, and ensuring the transfer of the newly acquired skills to the job. In sum, when not designed and delivered correctly, training can represent an organizational liability. 6.2 Objective and Scope The purpose of this chapter is threefold. First, we provide an understanding of the principal issues that influence safe behaviors in organizations. Next, we discuss how training can be used to improve safe behaviors and the factors that must be considered when designing, delivering, evaluating, and ensuring transfer of training. Finally, we offer guidance (i.e., checklists) for organizations and training developers to help in the design, delivery, implementation, and evaluation of training to reduce the potential risk of organizational liability. 6.3 Discussion of Principal Issues What Is Human Error? Although often forgotten, human capabilities are limited. This, in turn with organizational and environmental complexity, makes error practically inevitable. Human error has been defined as any “occasion in which a planned sequence of mental or physical activities fails to achieve its intended outcome” as a result of an inadequate plan or of intended actions not going as planned (Reason, 1990, p. 9). Errors can originate from many different sources, including inadequate training and inadequate procedures (Helmreich and Merritt, 2000).
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Reason (1990) has classified errors into three basic types: slips, lapses, and mistakes. Slips and lapses are unintentional actions that result when the execution and/or storage stage of an action plan breaks down (Reason, 1990; Shappell and Wiegmann, 1997). More specifically, a slip is a failure that can be observed (e.g., slip of tongue or action), whereas a lapse is typically not observable (e.g., lapse of memory) and thus may only be detected by the person who errs. Finally, a mistake is an inappropriate action that results when one’s judgment and/or inferential processes fail. Mistakes, like lapses, are often more difficult to detect because they are usually more complex, subtler, and less understood than other types of errors. Kletz (1985) and Reason (1990) argue that errors, specifically slips, can be minimized through improved training, instructions, and/or procedures. Reason (1994) argues that humans do not intentionally commit the acts that lead to errors; even highly qualified individuals commit them. On the other hand, some acts— violations—are not errors because they are intentional. Violations involve consciously bending the rules for something that at the time seemed reasonable and/or an acceptable risk. Yet, if organizations are not careful, these violations can become a normalization of deviance in which risk becomes the norm (i.e., maladaptive norms; Vaughan, 1996). Normalization of deviance can be characterized by a five-step process: (1) awareness of a problem, (2) unsafe behaviors seen deviating from the norm, (3) problem investigated, (4) working norm revised to “normalize” the problem, and (5) risk now deemed acceptable. An example of a seemingly harmless violation that led to a maladaptive norm and disastrous consequence involved the space shuttle Challenger (Pidgeon, 1998; Vaughan, 1996). In this case, erosion problems were identified with the rocket booster O-rings (steps 1 and 2). A work group was established to investigate the concerns (step 3). They estimated the probability that a hazardous condition would result to be unlikely and thus expanded the “normal” boundaries for the erosion (step 4). As a result, additional erosion incidents were deemed an acceptable risk (step 5). This deviance was also influenced by the organizational culture within NASA’s shuttle program, which was characterized by features such as interpretive flexibility, cost/safety compromises, and lack of appropriate guidelines. Who Is to Blame? Once an error has been committed and realized, typically the next question concerns where to place the blame. Using the Challenger explosion as an example, the following scenarios are possible. First, the equipment could be blamed because ultimately it was the equipment that failed and resulted in the accident. Next, the work group that investigated the erosion problems could be blamed because it created and enforced the deviant norms. Finally, the organization could be blamed because it provided a culture for its employees that tolerated behaviors that deviated from the norm. Ultimately, all three sources (i.e., equipment, individuals, and the organization) could potentially be to blame. The society in which we live today is one filled with blame, especially of the “fallible” human. It is argued that placing blame on the individual is a universal phenomenon that is emotionally satisfying (because it is human nature to want someone to blame) (Reason, 1994), and it may even be politically and legally convenient. In other words, it is easier,
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natural, and more satisfying to blame a single individual than an entire organization. Although, from a legal perspective, it may be easiest to place the blame on an individual (Reason, 1994), all of the blame cannot be placed there. People and organizations are generally quick to place blame on the human and fail to recognize the important role that the organization may have played in the events leading up to an error (e.g., inadequate training, lack of safety culture, lack of safety procedures). However, this trend is beginning to change. Organizations are now being held accountable for improper training and unsafe behaviors of their workforce. For example, many law enforcement organizations are now held accountable for officers’ less-than-adequate performance on the job. In the case of Sampson v. City of Schenectady, two officers were charged with violating the defendant’s Constitutional rights when the officers took him to a remote location without justifiable reason. The officers claimed that they were not trained properly for their encounter with the defendant and that the organization (or city of Schenectady) had an “unofficial relocation” policy of individuals. This unofficial policy could ultimately put those being “relocated” in an unsafe situation. As such, the officers sought immunity by shifting some, if not all, of the liability to the city of Schenectady (also see Dunton v. County of Suffolk, 1984). This example shows how improper training and maladaptive procedures can lead to legal liability for the organization. (Refer to Section 6.4 for information on similar cases.) How Can Training Help? Training can be defined as the systematic acquisition of knowledge (i.e., what we think), skills (i.e., what we do), and attitudes (i.e., what we feel) (KSAs) that lead to improved performance in a particular environment (Salas et al, 1992). We recognize that much of the literature refers to the “A” as abilities (e.g., Goldstein, 1993); however, for the purpose of this chapter, we will refer to the “A” as attitudes. In addition, training is influenced by multiple factors prior to, during, and following training—all of which should be considered to ensure a training program’s effectiveness. When human error is combined with failures within the organization, such as training deficiencies and lack of safety culture, an accident or incident is likely to become imminent (Isaac, 1997). The previous example set in the law enforcement community stresses the importance of creating a training program that follows sound theoretical principles and guidelines. When designed and implemented correctly, training can help organizational members mitigate errors and increase safety (see aviation example, Section 6.4). However, improperly designed training can lead not only to unsafe organizational practices, but also legal liability for the organization (Goldman, 2000). Furthermore, simply providing an off-the-shelf, generic training program does not guarantee its effectiveness or protection from the law. Therefore, we will next present the steps that one would take to design a sound training program that targets safety, as well as additional factors to consider outside the training to help ensure desired outcomes and overall effectiveness. The development of a theoretically based and defensible training system should be done systematically (Salas and Cannon-Bowers, 2000b). Using sound theoretical underpinnings, instructional strategies are developed using available tools (e.g., needs analysis), and by incorporating delivery methods (e.g., simulation) and focused content
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(i.e., competencies) specific to the needs of an organization (Salas and Cannon-Bowers, 1997, 2001). In other words, training creates an environment in which trainees learn necessary competencies (i.e., knowledge, skills, and attitudes—KSAs); to practice using the learned KSAs; and to receive constructive feedback on their performance. The steps for systematically developing a training program will be described next (see also Checklist 6.1). Training-Needs Analysis To deliver a defendable training system, training designers must first understand the tasks to be performed, the competencies that will be required of the worker, and worker/trainee characteristics (Salas and Cannon-Bowers, 2000b). Therefore, one of the earliest and most crucial steps is to conduct a training-needs analysis (Goldstein and Ford, 2002). The purpose of this analysis is to determine who needs to be trained for which tasks, and which KSAs need to be trained; this ultimately leads to the development of learning objectives. Three types of analyses need to be conducted: organizational analysis, job/task analysis, and person analysis. Organizational Analysis An organizational analysis is conducted to establish the organizational components (e.g., climate, norms), resources, and constraints that may affect how the training program is delivered (Salas and Cannon-Bowers, 2001; Goldstein, 1993). In addition, this analysis focuses on determining how well the training objectives (described later) fit with organizational factors (e.g., resources, goals, strategic focus, constraints). For example, an organization whose goal is safety should develop a training program that supports an environment for safe practices (e.g., error management). Finally, this analysis determines characteristics within the organization that will support the transfer of training. For instance, in order for the newly acquired skills to be transferred to the working environment, it is important that the organization provide a positive transfer climate that supports the behaviors that trainees learn (Rouiller and Goldstein, 1993; Tracy et al., 1995). Because we argue that transfer of training is an important factor influencing the outcomes of training, this will be described in more detail later (see “External Factors”). As such, it is important that organizations pay close attention to the organizational characteristics that may influence training because they may have a significant impact on the outcomes of training. Job/Task Analysis Another tool of the training needs analysis is the job/task analysis, the purpose of which is to analyze the job/task of those who are to be trained. More specifically, this analysis seeks to uncover the job description, task specifications, and task requirements (Goldstein, 1993). The first step is to determine the job/task description that needs to be trained, which generally consists of essential work functions of the job and the resources needed (e.g., materials, equipment). The next step is to determine the task specifications, which include the specific tasks to be performed and the conditions under which the job
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is to be completed. Finally, the requirements of the task are determined. The requirements describe the competencies needed to perform the specific tasks effectively. Although it is relatively easy to determine the job description and task specifications, it is often more difficult to determine the needed KSAs. Training designers tend to focus on readily observable competencies (i.e., skills) and pay less attention to those that cannot be observed (i.e., knowledge and attitudes). However, as tasks become increasingly complex and require greater cognitive demands for decision-making and problem-solving skills, the need to understand the competencies required for the task can be seen. As such, one tool to help accomplish this is cognitive task analysis. Cognitive Task Analysis To determine these KSAs, training designers can use cognitive task analysis techniques (e.g., knowledge elicitation) to gain insight from subject matter experts (SMEs) on their cognitive processes and requirements (Cooke, 1999). Cognitive task analysis (CTA) has been defined as “a set of methods to elicit, explain, and represent the mental processes involved in performing a task” (Klein and Militello, 2001, p. 168). Some argue that CTA is most appropriate for analyzing tasks that are cognitively demanding in complex, dynamic environments (such as those in which safety is of concern) (Gordon and Gill, 1997). Using CTA, training designers attempt to construct a model of what the expert knows (i.e., his knowledge) (Cooke, 1999). This helps designers to determine not only which KSAs are needed to perform a task, but also the cues and cognitions that facilitate a trainee’s decision to apply the appropriate skills (Salas and Cannon-Bowers, 2001). Several knowledge elicitation methods can be used to obtain information from experts (e.g., interviews, verbal protocols, observation, and conceptual methods; see Cooke, 1999). Guidelines for conducting a cognitive task analysis are presented in Checklist 6.2. Klein and Militello (2001) argue that three criteria must be met for CTA to be successful: • An important discovery needs to be made. More specifically, the CTA should identify something new regarding judgments (e.g., patterns), decisions (e.g., strategies), and/or other cognitive demands (e.g., cue patterns). • Effective communication needs to take place. Success of this criterion means that those conducting the CTA must effectively communicate the findings in the discovery phase to the training designers so that the information may be utilized in training development. • The CTA must have impact, which is achieved when the findings of the CTA are successfully put into action (e.g., safety interventions). Person Analysis The third type of analysis that should be conducted as a part of the training-needs analysis is a person analysis, the purpose of which is to determine who needs to be trained and the training that each person needs (Tannenbaum and Yukl, 1992). This analysis ensures that the right people get the right training. For example, training for new employees has different needs and requirements than those of recurrent training for existing employees (Feldman, 1988). Additional research suggests that different-level managers require different skills; specifically, more administrative skills are needed by
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lower-level managers (Ford and Noe, 1987). Therefore, an effective analysis must be conducted to determine the level of difficulty and job specificity needed for training to be adequate. The person analysis also determines whether trainees have the necessary KSAs and motivation to be trained. If trainees do not meet the training prerequisites, the training will not be as effective as it could be and may require additional training in the future; legal liability for the organization may result. Designing Training The information gained from the training needs analysis phase drives the objectives of the training, which should be specific, measurable, and task relevant so that they can be evaluated when training is completed. The training objectives, which serve to help guide training, have three general characteristics (Goldstein, 1993). Training objectives: • State what the trainee should be able to do as a result of the training (i.e., performance) • Describe the conditions during which the performance, stated previously, should occur • Provide a description of acceptable performance criterion, i.e., how the trainee should perform (at what level) to be judged acceptable In sum, training objectives state the competencies that trainees are expected to acquire and demonstrate once the training is complete. Once the objectives have been clearly defined, they are used to guide the training strategies that need to be implemented. The strategies are selected based on their effectiveness on promoting the task-relevant behaviors and competencies determined in the objectives. Instructional Strategies Once the training objectives have been established, the next step is to determine the instructional strategies to be used during training (i.e., how to train the requisite safe behaviors). Numerous instructional strategies have been developed over the last several decades that can prepare individuals and teams to increase their KSAs, reduce errors, and increase their expertise in performing their tasks—ultimately leading to safe behaviors. When individuals are trained to perform safe behaviors, we argue that there are three important issues. • Trainees should learn to be adaptable to changing situations and to recognize when things go wrong. By training flexible knowledge structures (i.e., cognitive representations), trainees can adjust their behavior to compensate for any changes. Rigid knowledge structures in a changing environment could lead to errors. • All training strategies must provide trainees with constructive feedback that focuses on the task. This feedback allows trainees to compensate for incorrect behaviors and readjust or correct their strategy to be more appropriate for a given situation. • Training needs to be dynamic (i.e., interactive). A recent report suggests that almost 84% of all companies use classroom-based and instructor-led training (Bassi and Van Buren, 1998). In addition, it was discovered that the most commonly used delivery methods (approximately 90% of the time) were videotapes and workbooks, compared to only 10% that used interactive, digital technologies. Computer-based or other technology-based training was used less than 35% of the time. Therefore, we argue
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that training for safe practices must involve the trainees through practice (e.g., roleplay, simulations). Table 6.1 presents some frequently used instructional strategies that may be used to improve safe practices in the workplace. We focus on four: scenario-based training, error training, stress-exposure training, and team training. Scenario-Based Training Scenario-based training (SBT), also known as event-based training, is unique and especially helpful in training individuals and teams to exhibit safe behaviors (Fowlkes et al., 1998). This type of training provides the opportunity to embed learning events into scenarios (determined from critical incidents data), thus giving trainees a meaningful framework by which to learn (Salas and Cannon-Bowers, 2000a; Fowlkes et al., 1998). SBT provides trainers with valuable tools, including guidelines and steps to achieve training objectives, trigger events, measures of performance, scenario generation, exercise conduct and control, data collection, and feedback. Figure 6.1 provides a graphical representation of the components or cycle of SBT (Cannon-Bowers et al., 1998). The cycle begins with determining the tasks and competencies that the training will focus on (circle 1), followed by the development of training objectives (circle 2). Steps 1 and 2 serve to drive the development of the scenarios (i.e., events, exercises, curriculum) to be embedded into the training (circle 3). Next, performance measures must be developed (circle 4) to evaluate if the trained skills are being applied. Once performance data have been collected, feedback must be provided to trainees (circle 5). Finally, information pertaining to trainee performance (i.e., skill inventory, performance history) must be incorporated into future training programs so that it can build upon previous training (circle 6). A key reason why this method, when applied appropriately, is effective in improving safety is because it is practice-based. Trainees are able to practice in preplanned scenarios while their performance is evaluated. The embedded events serve as cues that trigger behaviors and competencies, which can then be observed, evaluated, and incorporated into feedback. Feedback can be given to trainees immediately and corrections in performance can be made if necessary. In addition, SET supplies trainees with instructional strategies that allow them to practice the trained skills in order to perform effectively on the job.
TABLE 6.1 Training Strategies Strategy Event-based training (EBAT) or Scenario-based Training (SET)
Definition
Level
Individual Provides trainees with a structure in dynamic, complex environments by embedding scenarios and team in work environments that trigger targeted behaviors in complex environments. Instructional strategy designed to structure training in complex, distributed environments. Provides guidelines and steps for training objectives, trigger events, measures of performance, scenario generation, exercise conduct and control, data collection, and feedback. Provides a
Sources Fowlkes et al, 1998; Oser et al., 1999; Salas and Cannon-Bowers, 2000a
Can training for safe practices reduce the risk of organizational liability? meaningful framework that supplies the opportunity to embed learning events into scenarios. Assertiveness Practice and feedback help create and reinforce Individual training assertiveness in trainees. Provides opportunities for practice and supplies feedback. Metacognitive Training that develops and reinforces cognitive Individual training skills, such as inductive and deductive reasoning, problem solving. Stress-exposure Provides information regarding links between Individual training (set) stressors, trainee affect, and performance. and team Provides coping strategies for trainees in dealing with stressors. Team training Team training provides trainees with the Team necessary competencies at individual and team levels to complete their assigned tasks safely and effectively, by providing interventions that facilitate: (1) information presentation, (2) demonstration of teamwork behaviors and skills, (3) opportunities to practice, and (4) diagnostic feedback. Cross training Team members receive practice in performing Team other team members’ roles and tasks. Leads to a better understanding of other team members’ responsibilities and taskwork. Leads to enhanced shared mental models and interpositional knowledge. Improves team coordination and communication Team Team (explicit and implicit), encourages backup coordination behavior, and provides practice opportunities for training other KSAs that lead to effective coordination. Individual On-the-job Provides an opportunity to practice actual and team training required behaviors needed to do task. Targets team members’ procedurally based cognitive skills and psychomotor development. Training is provided in the same environment in which they will be working. Self-correction Helps individuals correct and evaluate their own Individual and team training behavior to assess its effectiveness. Team members learn to assess other team members. Allows constructive feedback and correction of discrepancies. Simulation-based Provides opportunities for trainees to operate in a Individual training and realistic setting with lifelike terrain, interaction, and team games and dynamic situations. Range in fidelity, immersion, and cost. Widely used in business, the military, and research. Behavior Targets concrete behaviors that are optimal for a Individual modeling particular task. and team
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Smith-Jentsch et al. 1996 Jentsch, 1997
Driskell and Johnston, 1998
Salas and CannonBowers, 2000a; Salas et al., 1997
Salas et al, 1997; Volpe et al., 2001
Entin and Serfaty, 1999; Bowers et al., 1998 Goldstein, 1993; Ford et al., 1997
Smith-Jentsch et al., 1998; Blickensderfer et al., 1997 Tannenbaum and Yukl, 1992; Marks, 2000
Tannenbaum and Yukl, 1992
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FIGURE 6.1 Components of scenariobased training. (Adapted from CannonBowers, J.A. et al, 1998, in J.A. Cannon-Bowers and E.Salas, Eds., Making Decisions under Stress: Implications for Individual and Team Training, Washington, D.C.: American Psychological Association, 365–374.) Another benefit of SET is that scenarios can be varied in that they require different responses from trainees. This in turn creates templates for trainees of what to expect and how to react to many different situations (Richman et al., 1995). It is argued that these templates will allow for rapid recall from memory and the ability to make decisions quickly (Klein, 1997), which may be necessary in environments in which errors can have catastrophic consequences if not rectified promptly. This should ultimately affect the transfer of the training to the actual environment (more discussion on this later). A final benefit of SET is that it is a broad instructional strategy within which many competencies can be framed. SET has been used extensively in the military, especially with aircrews in simulators (Smith– Jentsch et al., 1998) and others who are required to operate in complex decision-making environments. An example of a situation in which SET could be used appropriately to encourage safe practices is through assertiveness training. It has been found in past accidents (e.g., 1978, United Airlines Flight 173 in Portland, OR; 1982, Air Florida Flight 90 in Washington, D.C.) that some lower-ranking individuals did not assert themselves to higher-ranking individuals (e.g., copilot to pilot) when they became concerned about their situation. Many of these situations have resulted in disastrous consequences. If SET were used, events could be embedded in a training scenario that would require a low-ranking individual to assert himself to a high-ranking individual. This training would serve to train lower ranking individuals to voice their concerns and also to make higher ranking individuals aware (e.g., attitudes) of the consequences of not listening to the concerns of others, regardless of rank. Additionally, metacognitive training could be trained using SET strategies. This type of training
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improves trainees’ cognitive skills so as to optimize the decision-making and judgment processes (Jentsch, 1997) necessary for exhibiting safe practices. SET could be used to embed a dynamic, ambiguous situation into a training practice scenario requiring trainees to recognize, react, and continuously reevaluate the situation and their decisions. Error Training A second type of training that might be used to improve safe behaviors is error training, the purpose of which is to use errors as an information function that provides feedback to trainees (Frese and Altman, 1989; Lorenzet et al., 2003). This feedback then serves to help develop improved learning and strategies to transfer the learned knowledge to the actual task environment. Trainees are able to experience errors and thus see the consequences of such actions (Karl et al., 1993). Trainees are then taught strategies to correct these errors and are able to practice them. Research suggests that individuals given error training performed better than those who were given error-free training (e.g., Dormann and Frese, 1994; Ivancic and Hesketh, 1995). Error training is, however, more complex than it may appear. Two components must be considered when developing an error training program: error occurrence and error correction (see Lorenzet et al., 2003, for more detail). Error occurrence can be (1) avoided (i.e., training is designed to prevent errors), (2) allowed (i.e., training is designed to allow errors to occur but they are not triggered; Gully et al., 2002), (3) induced (i.e., training is designed so as to evoke errors; Dormann and Frese, 1994), or (4) guided (i.e., training is designed intentionally to guide trainees to errors to encourage learning). The second component to error training, error correction, has two subcomponents: (1) selfcorrection (i.e., trainees work through errors alone; Frese et al., 1991), or (2) supported correction (i.e., trainees are offered support to help them correct errors; Carlson et al., 1992). Based on the training literature available and research conducted using error training, Lorenzet and co-workers suggest that guided error training may improve the skill development of trainees best (2003). A brief description of their work is next. In a recent study by Lorenzet and colleagues (2003), error training utilizing a guided error occurrence and a supported correction approach was compared to an error-free training approach to determine its impact on trainee skill development and self-efficacy. The results of this study suggest that trainees who were given guided-error training performed better (i.e., more accurately) and faster than those given error-free training. We submit that providing trainees with an opportunity to make errors during training so that they can learn corrective strategies and practice them may improve safe practices on the actual job. Therefore, improving safe practices in employees will reduce the likelihood of errors on the job, resulting in fewer accidents and less chance of legal liability. Stress Exposure Training (SET) Stress exposure training (SET) is an instructional strategy for training individuals that seeks to give the trainee the tools and ability to maintain effective performance in environments with high stress (Driskell and Johnston, 1998). Because stress increases the likelihood of error, SET training is particularly important for maintaining safe behaviors on the job. SET has three phases of training: information provision, skill acquisition, and application and practice.
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• Phase 1—information provision: trainees are provided with information regarding the types of stressors that may be encountered and the effects of stressors on performance. • Phase 2—skill acquisition: provides trainees with the opportunity to acquire the specific behavioral and cognitive skills necessary to manage and adapt to stressors. • Phase 3—application and practice: the knowledge and skills learned in earlier phases are applied and practiced within an environment that gradually approximates a highstress situation. At the end of this phase, trainees receive feedback on their performance. Two recent studies were conducted (see Driskell et al., 2001) to determine if stress training would generalize (1) from exposure to a specific stressor in training to a novel stressor after training (study 1) and (2) from exposure to stress while performing a specific task during training to a novel task after training (study 2). The results of these studies suggest that stress exposure training was beneficial and did generalize from stressor to stressor and task to task. Although these results are encouraging, additional research is needed to determine whether stress training would generalize to stressors and tasks dissimilar to those who were trained. Team Training The fourth instructional strategy that we argue to be effective for training safe behaviors is team training. Teams are increasingly used by organizations to perform in complex, ambiguous environments in which human error can have catastrophic consequences (e.g., aviation), so the need to understand the research involving teams is important. Whereas asking a group of qualified individuals to work together as a team will likely be ineffective, team training provides trainees with the necessary competencies at the individual and team levels to complete their assigned tasks safely and effectively (Salas et al., 1997). At the individual level, team members must possess the KSAs needed to perform their specific task roles within the framework of the team, while incorporating the individual competencies into an interdependent, coordinated unit at the team level. Research conducted in the aviation community concluded that errors were more likely to be based on failures in team communication and coordination, rather than the individual crewmember’s inability to fly the airplane or perform his duties (Murphy, 1980, as cited in Helmreich and Foushee, 1996). Team training seeks to provide team members with interventions that facilitate: (1) information presentation, (2) demonstration of teamwork behaviors and skills, (3) opportunities to practice, and (4) diagnostic feedback (Salas and Cannon-Bowers, 2000a). Additionally, Kozlowski (1998) proposed three conditions that may be necessary to promote effective team training: (1) training that involves knowledge and skill acquisition (i.e., instructions that link related concepts and goals that must be acquired), (2) the promotion of transfer and adaptation, and (3) training that involves maintenance (e.g., monitoring) and enhancement of the KSAs that the team learned during training. Finally, through the use of “team” instructional strategies (see Table 6.1), training can encourage and facilitate specific team competencies such as shared knowledge structures (e.g., cross training; see Salas et al., 1997) and coordination and communication (e.g., team coordination training; see Entin and Serfaty, 1999). These two instructional strategies will be described next.
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Examples of Team Training Cross training, most effectively used in team training, involves exposing trainees to goals, roles, tasks, and responsibilities of other employees within the organization (Salas and Cannon-Bowers, 2000a). There are two advantages to this type of training. First, this strategy involves trainees learning and practicing the tasks required of others’ jobs, allowing them to gain some degree of proficiency needed by the organization. This is extremely helpful when an employee is unable to perform his job adequately—a “crosstrained” employee could provide assistance. The second advantage of this training strategy is that it creates and reinforces a common understanding (i.e., shared mental model) of the roles and responsibilities of others. In situations such as an emergency, this shared understanding will reduce the amount of explicit communication needed because each team members will know what his task is as well as that of others. In short, crosstraining not only improves a trainee’s ability to predict what others are doing, but also allows him to step into that role if needed. However, in training these shared cognitive frameworks, it is necessary to ensure that they are not rigid and therefore are flexible to change. Another example of an instructional strategy focused at the team level is team coordination training, shown in Table 6.1. In order to perform effectively in situations of high stress, teams must switch from explicit to implicit coordination (Entin and Serfaty, 1999; Kleinmen and Serfaty, 1989). Team coordination training has been found to be necessary to make this switch (Serfaty et al., 1998). Entin and Serfaty (1999) examined the effectiveness of team adaptation and coordination training (TACT). The first step in TACT involves teaching team members to recognize changes due to varying stress levels in order to give them the tools needed to become aware of increasing stress. Next, team members are given a set of coordination strategies to use in stressful situations. Last, they are given information regarding the conditions under which these strategies should be applied. The theoretical basis supporting coordination training is that when teams face increased stress, teams that have received coordination training will minimize their communication and coordination overhead while maintaining the level of their performance. The communication used will likely be necessary and effective for a safer performance. On-the-Job Training One final type of training that we argue might help to improve safe behaviors in the actual work environment is on-the-job training (OJT). OJT is one of the most widely used types of training in organizations and can be used in conjunction with an off-the-job instructional strategy (such as those mentioned earlier) or as the sole strategy (Goldstein, 1993). In this instructional strategy, an expert or supervisor trains specific skills related to the job (e.g., what to do, how to do it) to an employee in the actual physical and social environment in which the task is to be performed (Sacks, 1994; Wehrenberg, 1987; De Jong and Versloot, 1999). Many benefits of OJT may serve to improve safe practices. For example, transfer of the learned skills to the job will be more likely because trainees are trained in the actual physical and social environment to which the skills must be transferred. In addition, trainees are able to practice the actual behaviors that they will be expected to perform
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under the supervision of an expert. As such, trainees can practice the behaviors necessary to conduct the task in a safe manner, thus making it more likely that these safe behaviors will be used when the training is completed. It should be mentioned, however, that often OJT programs are not designed and developed properly and are not as successful as they could be (Goldstein, 1993). Therefore, like any training program being implemented, sound principles of training design should be followed to ensure its effectiveness. We will next briefly discuss two types of OJT programs that might improve safe practices in organizations: apprenticeship training and mentoring. Examples of OJT When a task is performed, thinking about, knowing, and understanding the task are very important (Hendricks, 2001). One way to accomplish this is through apprenticeship training. Although apprenticeship training has most often been used to train trade skills, other nontraditional trade organizations are beginning to show an interest in it (Goldstein, 1993). A typical apprenticeship training program consists of classroom-based instruction followed by supervision on the job from an experienced employee. Following a predetermined time and if the necessary skills are met, the apprentice is promoted to a “journeyman” (Goldstein, 1993; Hendricks, 2001; Lewis, 1998) and is able to perform the duties on his own. The importance of this type of training for safety is that the trainee is provided first with the basic KSAs needed for the job (i.e., in the classroom) followed by the opportunity to practice the learned skills on the job. If safe behaviors are not demonstrated, the experienced supervisor can correct the behavior before it becomes a habit. In addition, a new employee will not be allowed to perform a task alone until the supervisor is certain that he can perform it safely. A second type of OJT, which is very similar to apprenticeship training, is mentoring— the process of creating a relationship between a less experienced individual and a more experienced one (Wilson and Johnson, 2001). As a part of this relationship, the more experienced worker will train and develop the trainee to perform his job properly. Research suggests that mentoring improves communication, job satisfaction, and success in an organization, which will likely influence safety (Mobley et al., 1994; Forret et al., 1996). Additionally, this type of training might benefit safety in that the trainee is guided by the mentor as to which behaviors are appropriate and which are not (Scandura et al., 1996). Therefore, it is important that the mentor be an individual who values and respects the cultures (e.g., safety), policies, and procedures within the organization and will encourage the trainee to do so also. Finally, mentoring may be beneficial not only to the trainee but also to the mentor by improving skills that may have diminished over time (Forret et al., 1996). Evaluating Training Once the instructional strategy has been chosen and the training program has been implemented, it is imperative that the training be evaluated. Few organizations conduct systematic evaluations of their training programs. We acknowledge that evaluation can be resource intensive; however, it is the only way to truly assess training’s effectiveness. Numerous methods of assessment can be applied to training. We argue for the use of a multilevel approach such as that suggested by Kirkpatrick (1976).
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Kirkpatrick (1976) proposed a method of training evaluation that constituted a multilevel approach to evaluating the outcomes of training programs. He argued that training evaluation should include assessment at four levels: (1) reactions (i.e., what trainees think of the training), (2) learning (i.e., what trainees learned), (3) behavior (i.e., how trainees’ behavior changes), and (4) results (i.e., impact on the organization). Building on Kirkpatrick’s framework, Kraiger and colleagues (1993) outlined three similar outcomes: (1) affective (i.e., reactions), (2) cognitive (i.e., learning), and (3) skillbased (i.e., behavior) outcomes. The first level, reactions, evaluates how well trainees liked the program (i.e., affect), as well as how useful they think it is (i.e., utility). Similarly, Kraiger et al. referred to affective outcomes as attitudinal outcomes and motivational states (i.e., motivational disposition, self-efficacy, and goal setting) that training has produced.
TABLE 6.2 Kirkpatrick’s Multilevel Evaluation (1976) Step
Guidelines/requirements
Measurement
1. Determine what you want to know. Use a Self-report Reaction written survey to get at what you want to know. survey The form should be quantifiable. The forms should be anonymous to get honest reactions. Additional written comments by trainees should be allowed. 2. Each trainee should be measured. Pre- and post- Self-report Learning test evaluations should be used. Measurement survey should be as objective as possible. A control group should be used, if possible. Measurement of learning should be analyzed statistically.
3. Trainees must want to improve. Trainees must Observation Behavior be aware of their own weaknesses. The work environment must be permissive. Someone who is skilled and interested must provide help. An opportunity to try out ideas must be provided. 4. Although results may appear to be Longitudinal Results straightforward, it is difficult to determine how data much is due to training.
Example survey questions How well did the trainer state the objectives? How helpful and friendly was the trainer? Did you like the training? T/F. Well trained employees are a reflection of a large training department. T/F. The supervisor is closer to his employees than management is. Is employee more observant? Is employee more patient? Does employee demonstrate learned behaviors? What changes have been observed since training in the following areas: quantity of production; safety; employee attitudes; employee turnover?
The next level, learning, evaluates the principles, skills, and knowledge that the trainees gained from the training. This level seeks to determine if the trainees learned the KSAs presented in the training (i.e., training validity) and not whether the trainees exhibit the trained behaviors. The third level of evaluation, behavioral, determines the changes in behavior of employees after the training intervention. The behavioral level evaluates how
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the learned KSAs transfer to the actual work environment (i.e., transfer validity). Finally, the last and highest level, results, evaluates the organizational outcomes of the training program (e.g., improved safety, reduced costs, improved quality). Evaluation at this level can help determine intraorganizational validity (i.e., are the performances of multiple groups of trainees consistent?) and interorganizational validity (i.e., will the training program in one organization or department be effective in another?). Unfortunately, due to the necessity of and difficulty in collecting longitudinal data, this level is not often evaluated. See Table 6.2 for more information on utilizing Kirkpatrick’s (1976) multilevel approach (e.g., guidelines, measurement). This multilevel approach has been shown to be effective and is still used in a number of studies (Cohen and Ledford, 1994; Field, 1995). For example, Salas and colleagues (2001b) examined the success of crew resource management (CRM) training in aviation using this approach by examining the literature available (58 studies total). Although 41% of the studies collected information at multiple levels of Kirkpatrick’s framework, a majority of those only collected information pertaining to two of the levels—usually, reaction/learning or reaction/behavior. Although research generally suggests that CRM has been successful in improving safety in the aviation community, the results are still unclear. As such, the results of this review further emphasize the importance of organizations evaluating their training programs at all levels. However, regardless of an organization’s goal of training (for our purposes, improving safe behaviors), any multilevel evaluation should revolve around two central issues: (1) establishing
TABLE 6.3 Augmented Kirkpatrick Training Taxonomy Augmented framework 1. Reactions
2. Learning
3. Transfer
Components
Definitions
Affective Emotionally based opinions given immediately with little, if any, reactions forethought Utility judgments Trainees’ opinions about the transferability and utility of training; more behaviorally evaluative Immediate Trainees required to indicate how much they know about what knowledge they were trained in (i.e., multiple-choice tests, open-ended questions, listing of facts) Knowledge Essentially the same tests as immediate knowledge, but retention administered much later; can be used instead of or in combination with immediate knowledge Behavior/skill Indicators of behavioral proficiency exhibited within training, as demonstration opposed to on the job; measures include simulations, behavioral role-plays, behavioral reproduction, scores in performancecentered classes, and ratings of training performance Includes measures that indicate on-the-job performance taken some time after training that seeks to assess a measurable aspect of job performance; measures on-the-job performance, outputs, outcomes, and work samples
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4. Organizational impact of training assessed, typically by measuring productivity gains, Results customer satisfaction, any change in cost, an improvement in employee morale, and profit margin; results often difficult to measure because of organizational limitations and because they are the most distal from training; results often regarded as the basis for judging training success, but judgments are often based on false expectations Source: Alliger, G.M. et al., 1997, Personnel Psychol., 50, 341–358.
measures of success and (2) using experimental and nonexperimental methods to determine what has changed due to training (Goldstein, 1993). Although Kirkpatrick’s approach was a breakthrough for training evaluation and is still widely used (see Cohen and Ledford, 1994; Field, 1995), the original multilevel framework has also been revised or modified based on more recent research (Alliger et al., 1997; Kraiger et al., 1993). Alliger and colleagues (1997) reviewed Kirkpatrick’s approach through meta-analysis of 34 articles used in an earlier study (Alliger and Januck, 1989). The authors suggested an augmented framework, shown in Table 6.3, based on their analysis of the results. Their framework further clarified Kirkpatrick’s original method of evaluation by classifying different types of reactions and learning and by focusing on transfer of training to the work environment, instead of the more vague behavior. A significant problem with training evaluation is that it is often conducted using selfreport measures of trainees’ reactions to the training. Although these measures are an easy method of evaluation, they fail to provide evaluators with valuable information regarding the training’s effectiveness. Whether a trainee “likes” the training intervention generally does not reflect how well the training was conducted or if the training addressed the appropriate competencies. Ultimately, researchers found that “liking does not equate to learning or to performing” (Alliger et al., 1997, p. 344). In part to combat this fallacy, another dimension of reactions, similar to that suggested by Kraiger and colleagues (1993), was added to the framework: utility judgments, which refer to trainees’ opinions of whether what they learned will help them in their jobs. Affective reactions continue to measure how much the trainees liked the training. As noted earlier, liking does not translate into desired outcomes, but the trainees’ feelings toward training can tell researchers about organizational factors (i.e., organizational support of training programs). Alliger and colleagues (1997) divided the learning phase into three categories: • Immediate knowledge involves trainees indicating how much they know about the training content (i.e., what they were taught during training). Immediate knowledge assessment, under Alliger and colleagues’ (1997) framework, consists of multiple methods of evaluation (i.e., multiple-choice tests, open-ended questions, listing of facts). • Knowledge retention involves the same types of tests given in immediate knowledge assessment, except that they are given after more time has elapsed between training and testing. Knowledge retention can be used alone or in combination with immediate knowledge assessment. • Behavior/skill demonstration involves the trainees’ performances within training, as opposed to their performances on the job. Measures of behavioral and skill
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demonstration include simulations, behavioral role plays, and ratings of training performance by SMEs. All three components are designed to evaluate what trainees learn. When combined with a trainee’s reactions, they strengthen the reactions’ predictive power of performance, but even alone, learning assessment is a strong indicator of performance (Alliger et al., 1997). The last two steps in the augmented framework are transfer and results. Transfer measures seek to evaluate on-the-job performance and are taken some time after training. Transfer differs from knowledge retention because transfer assessment is more behaviorally based. Transfer measures focus on on-the-job performance, outputs, outcomes, and work samples. Finally, results refer to the “bottom line” variables or what management typically assesses for training outcomes. Results include measurement of productivity gains, customer satisfaction, changes in cost of production, employee morale, and profits. These variables can be difficult to measure and may be misleading because they are not always directly related to training. Additionally, problems are often encountered when evaluating results due to falsified or inflated expectations of training’s impact on organizational results by management. Researchers recommend caution when dealing with result variables. We will next present a tool that can be utilized to evaluate performance following training. Line Operations Safety Audit (LOSA) One tool that can be adapted to help evaluate an organization’s training program is based on the line operational safety audit (LOSA) developed for the aviation industry. LOSA was developed by Helmreich in 1995 as a way to evaluate how CRM was working in the cockpit (Croft, 2001). This audit provides training and performance evaluation with a framework for collecting data. Although used primarily with flight crews, the framework can be applied to evaluate the performance of trainees in a variety of settings. Traditionally, LOSA uses nonintrusive, trained observers who ride in the cockpit jumpseat and examine how pilots respond to threats (i.e., weather, airway congestion, or unexpected events resulting from errors). The observers complete a questionnaire regarding the crew’s performance during a flight and assign one of four ratings: (1) poor (observed performance had safety implications), (2) marginal (observed performance was barely adequate), (3) good (observed performance was effective), or (4) outstanding (observed performance was truly noteworthy). The observers also interview the pilots to gain more insight into what happened and what their thought process was in the course of making decisions. One of the most important features of LOSA is that, in addition to recording errors, it evaluates how crews deal with or adapt to the consequences of the errors. See Checklist 6.4 for an example of a training evaluation form adapted from the LOSA program. The implementation of LOSA ideally results in the discovery of weaknesses or critical incidents that may exist within the training structure that, in turn, can be incorporated into future training programs. Croft (2001) provides an example of LOSA’s success. Pilots at a major airline were found to have difficulty flying according to company standards. The LOSA program found that, during training, pilots were provided with ambiguous guidelines as to how to fly within company standards; this led to their difficulties. The
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error was corrected for the future training interventions and the pilots showed a 59% improvement in that area of performance. External Factors Until this point, we have provided a brief methodology by which to develop and evaluate an effective program for training safe behaviors systematically. Although this may ensure a training program that produces desired learning outcomes, it may not guarantee exclusion from legal liability. Factors outside training also need to be considered because they will impact the program’s outcomes over and above the content and strategies used (see Table 6.4). A few of these—specifically, the pretraining environment, organizational and individual characteristics, training motivation, and post-training environment—will be briefly described next.
TABLE 6.4 Components of Training Effectiveness
Source: Adapted from Salas, E. et al., 1999, Personnel Hum. Resour. Manage., 17, 123–161.
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Pretraining Environment An additional key to training’s success is the pretraining environment, of which two main characteristics need to be considered: (1) prepractice conditions and (2) pretraining climate (Salas and Cannon-Bowers, 2001). Prepractice conditions are elements in the pretraining environment that help prepare trainees for practice during training. Research suggests that practice is more than mere repetition of a task; rather, it is a complex process that leads to skill acquisition (Ehrenstein et al., 1997; Shute and Gawlick, 1995). Cannon-Bowers and colleagues (1998) suggest that trainees can be prepared by using such interventions as preparatory information and advance organizers; however, this is just beginning to be investigated empirically. The second characteristic of the pretraining environment to be considered is the pretraining climate. Characteristics of the climate that will influence the outcomes of training include framing of the training, attendance policies, and previous training experience. More specifically, research has shown that whether the training is framed as remedial or advanced will influence trainees’ motivation and learning (see Quinones, 1995, 1997). In addition, the attendance policy of the training program (i.e., voluntary vs. mandatory) is also believed to influence the outcomes of training (Baldwin and Magjuka, 1997). This research suggests that the ability of trainees to choose whether or not to attend training will influence the training outcomes. Finally, it is suggested that trainees with previous training experience, whether positive or negative, will influence the trainees’ learning and retention (see Smith-Jentsch et al., 1996). Organizational Characteristics In addition to characteristics of the pretraining environment, organizational characteristics (i.e., those present within the organization to which the newly acquired KSAs must be performed) may also influence the outcomes of training. Examples of these characteristics are selection and notification, situational constraints (e.g., improper equipment), organizational climate (e.g., perceived organizational support, safety culture, and policies), and opportunities to practice (see Salas et al., 1995, for more detail). We do, however, want to expand on two organizational characteristics that greatly influence the transfer of safe behaviors from training to the actual work environment—safety culture and policies. Safety Culture An important factor influencing training within an organization is its culture. The necessity of a positive organizational culture has been argued to be of importance for the effectiveness and transfer of a training program (Rouiller and Goldstein, 1993). More importantly—especially when designing training for safe behaviors—is the organization’s safety culture. A safety culture can be defined as the end result of the values, beliefs, attitudes, behaviors, perceptions, and competencies of individuals and groups within an organization that determine the proficiency and style of, and commitment to, the organization’s safety management (HSC, 1993, as cited in Glendon, 2001). Pidgeon (1991) and others (Turner, 1991; Pigeon and O’Leary, 1994) suggest that a positive safety culture is encouraged through four factors: (1) commitment to safety from upper-level management, (2) shared attitudes regarding hazards and safety, (3)
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flexible norms and rules to deal with hazardous situations, and (4) practice and organizational learning. Others also argue that a positive safety culture is characterized by effective communications, mutual trust, and efficacy (Glendon, 2001). Hofmann and colleagues (1995) addressed a related issue. Specifically, the authors emphasized the need for management in organizations to make safety an observable issue. Management must, as they say, “talk the talk and walk the walk” when safety is concerned. In order for the four factors (presented here) to translate into a positive safety culture (see Pidgeon, 1991; Pidgeon and O’Leary, 1994; Turner, 1991), it is argued that the organization, through management, must promote them through actions and words. In order to accomplish this, some researchers recommended two guidelines gleaned from research with coal miners and their managers (Fiedler et al., 1984). First, in order to promote a positive safety climate, employees must perceive management as devoting time, energy, and attention to safety issues and training interventions. This will reinforce the support of the organization and the importance of safety within the work environment. Second, it is argued that positive safety cultures develop when employees are allowed to take an active role in the safety training intervention. By giving workers a degree of control over the interventions, their investment in and dedication to the maintenance of a positive safety culture will increase. In sum, research suggests that organizational support and encouragement of employee involvement are necessary for success of a safety culture. Safety Policies and Procedures Underlying the safety culture philosophy within an organization are its safety policies and procedures. Policies can be described as broad requirements that management has set to let employees know about what is expected of them (Degani and Wiener, 1997). For example, a safety policy may encourage employees to demonstrate safe behaviors and procedures and then provide guidance to employees on how to meet these expectations. Thus, in order for employees to demonstrate safe behaviors, management may require that checklists be used for certain tasks or following standard operating procedures. Trainees can be made aware of these policies and procedures through a well-designed training program. According to Hofmann and Stetzer (1996), however, a problem develops when social pressures are more influential than the formalized rules and procedures. These authors argue that, regardless of an organization’s established safety policies and procedures, if employees perceive that deviations from them are appropriate and encouraged (i.e., normalization of deviance), the rules and procedures will be less influential. For example, if the organizational climate promotes faster production at all costs, the rules promoting safety will likely be ignored. Wright (as cited in Hofmann et al, 1995) observed this phenomenon in his examination of workers on oil rigs, which are expensive to build, are expensive to maintain, and depend heavily on interdependence. In addition, this is a dangerous job in which small errors could lead to significant consequences. Due to the expense and resources used, management often focuses on increasing production times at the cost of sacrificing worker safety. Wright’s research uncovered an underlying theme for a majority of the accidents examined (which were in the thousands): an attitude of “get the job done, while placing less emphasis on safety issues” (Hofmann et al., 1995, p. 134). Therefore, safety rules and procedures must be developed and promoted with
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consideration of the powerful effect of the organizational climate on adherence to policies and procedures by employees. Error Reporting Some argue that underlying organizational issues (i.e., culture) influence errors and even implicitly encourage and support individuals to commit unsafe acts (Hoffman et al., 1995). Error reporting is one tool that can help organizations to organize and learn from these errors. Reason (1998) argues that error reporting is an essential element of a safety culture because it allows the organization to be informed about unsafe practices in the workplace. Therefore, a positive safety culture that encourages safe behaviors, adheres to safety policies and procedures, and encourages error reporting will likely reduce human error. Although many of the human errors that occur do not result in an accident, numerous “near misses” (i.e., incidents) do result. As a part of creating a positive safety culture, organizations need to realize that great lessons can be learned from these incidents (Klair, 2000) and should encourage employees to report them. By taking a proactive approach to promoting safe behaviors, organizations may be able to correct these errors (e.g., through an effective training program) and prevent an accident from occurring in the future (Helmreich and Merritt, 2000). Error reporting can be organized in two ways: (1) critical incidents technique and (2) voluntary reporting systems. Critical incidents technique. This technique, now often used as a job analysis tool (i.e., a trained analyst interviews workers about their work duties and responsibilities), began as a technique to gather information to help develop training needs and performance appraisal (Gatewood and Field, 1998). The critical incidents technique involves the observation of good and bad examples of behavior performed on the job. In essence, it consists of a description of the task, the behaviors observed, and the consequences of those behaviors. Although it does not illustrate every possible dimension of a job, the report provides a range of behaviors providing examples of what not to do, what should be done, and what results either elicited. For an example of the critical incidents technique, see Prince and Salas (1993). Voluntary reporting systems. Most individuals are not likely to report errors due to fear of retribution; thus, anonymous, voluntary reporting systems are a viable alternative. The aviation safety reporting system (ASRS) was developed by the National Aeronautics and Space Administration (NASA) for the aviation industry. Using the ASRS database, pilots and/or crewmembers are able to report errors and unsafe acts that occurred during the flight without providing discernible information about themselves. The aviation industry has been extremely successful since its inception and receives more than 32,000 reports each year (Orlady and Orlady, 1999). The data collected from ASRS have allowed the aviation community to react to errors proactively (Sexton et al., 2000) by incorporating critical incidents that occur frequently into training. The data not only are useful for training purposes but also provide an awareness to other aviation professions via publication in periodicals and on the Internet. The success of ASRS has led to the development of similar systems in other organizations, for example, the medical, nuclear, and petrochemical domains (see Köhn et al., 1999; Helmreich, 2000). Köhn and colleagues (1999) offer some guidance for developing an error-reporting system. First, it is suggested that the system be overseen (if possible) by an organization
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separate from that at which those reporting the errors work. This will likely improve the participation rate by employees because they will have less fear of retribution. It is understandable that organizations may not have the resources to work with another organization to oversee their reporting system. We advocate that an error-reporting system can be a valuable tool for obtaining information regarding safe behaviors, and therefore encourage organizations to implement the system regardless of which organization may oversee it. Next, employees need to be confident that the information they provide to the system will remain anonymous and that they will not be punished. If employees fear retribution from the organization for unsafe behaviors, they will be less likely to report an error that went “undetected” by the organization. Finally, it is suggested that the data be accessible so that it can be analyzed. Based on the data, critical incidents can be identified and incorporated into the organization’s training programs. Individual Trainee Characteristics Training outcomes are also influenced by characteristics beyond the organization. Characteristics that the trainee brings to the training program will influence its outcomes and may do so before it begins or after it is completed (i.e., transfer). Individual characteristics reported to influence the outcomes of training are • Cognitive abilities (i.e., “g” or general intelligence). Cognitive ability has been shown to influence trainees’ attainment of knowledge about the job (see Ree et al., 1995; Colquitt et al., 2000). In addition, cognitive ability has been shown to be a strong determinant of success in training (Ree and Earles, 1991). • Self-efficacy. Research that has looked at self-efficacy (i.e., belief in one’s own ability) indicates that high self-efficacy leads to better performance (see Quinones, 1995; Ford et al., 1997; Martocchio and Webster, 1992). In addition, it is suggested that selfefficacy is influenced by cognitive ability (see Hunter, 1986). • Expectations. Trainees’ expectations regarding training will influence training outcomes. In a study conducted by Tannenbaum and associates (1991), it was found that trainees’ whose expectations were met demonstrated better post-training commitment, greater motivation, and higher self-efficacy. • Goal orientation (i.e., mastery vs. performance). Goal orientation will influence training outcomes (Dweck, 1986; Dweck and Leggett, 1988). Individuals high in mastery orientation aim to acquire new skills and master novel situations, and research suggests that this is positively related to metacognitive activity and self-efficacy (Ford et al., 1997; Phillips and Gully, 1997). On the other hand, those high in performance orientation aim to achieve high performance ratings and to avoid negative ones. See Salas and colleagues (1995, 2001b) for more detail as to how these factors may influence training. Trainee Motivation Trainee motivation is influenced by individual (e.g., self-efficacy) and organizational (e.g., notification) characteristics. It consists of variables that influence trainees’ willingness to participate in and learn from the training. As with individual trainee characteristics, motivation may also influence the outcomes of training prior to or after
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training. Training motivation influences the amount of time and effort the trainee will invest and the behaviors the trainee will exhibit (Naylor et al., 1980, as cited in Goldstein, 1993). Research suggests that higher trainee motivation prior to training results in greater learning and positive training reactions (see Mathieu et al., 1992; Williams et al., 1991; Tannenbaum et al., 1991; Baldwin et al., 1991). Finally, it is suggested that training is more effective when trainees believe that the outcomes of the training are relevant to their job performance (Noe, 1986). For example, if the purpose of training is to promote safe behaviors, the trainee must believe that the behaviors will be applicable to and improve his performance on the job. Recently, Colquitt and colleagues (2000) conducted a meta-analysis of the literature related to training motivation. The results of their analysis suggest that individual and situational characteristics influence motivation to learn in training. Specifically, the individual characteristics related to motivation included self-efficacy, valence, anxiety, cognitive ability, and age. Situational characteristics included supervisor and peer support, positive climate, and organizational support. Although it was previously believed that cognitive ability alone influenced learning outcomes, the results of this meta-analysis suggest that training motivation explained additional variance beyond just cognitive ability. These results indicate the importance of including multiple individual differences when conducting the needs assessment because they will likely influence training outcomes. Post-Training Environment The post-training environment is important in determining whether the competencies learned during training will transfer to the job. Regardless of how well the training program was developed, without an environment that encourages the transfer of the learned competencies, it will not be effective. Research suggests that several characteristics of the work environment are essential for the transfer of training: (1) supervisor support, (2) organizational transfer climate, and (3) continuous-learning culture, although supporting empirical evidence is limited (see Baldwin and Ford, 1988; Rouiller and Goldstein, 1993; Tracy et al., 1995; Ford and Weissbein, 1997). Additionally, it is argued that some elements of the transfer climate may facilitate (e.g., rewards, positive transfer climate) or hinder (e.g., lack of peer or supervisor support, lack of resources) the transfer of training (Tannenbaum and Yukl, 1992; Rouiller and Goldstein, 1993). We will briefly discuss how supervisor support and organizational transfer climate can promote the transfer of training. Supervisor support has been argued to influence transfer of training. Research conducted suggests that discussions with supervisors prior to and following training, as well as supervisor sponsorship, result in transfer of learned skills to the job (Huczynski and Lewis, 1980; Brinkerhoff and Montesino, 1995). Additional research concluded that opportunities to perform learned skills provided by supervisors encourage transfer of training (Ford et al., 1991). However, Baldwin and Ford (1988) argue that there is a lack of understanding regarding the behaviors that lead trainees to perceive support. Tannenbaum and Yukl (1992) state that supervisor support could include goal-setting activities (e.g., minimize number of accidents), reinforcement (e.g., error reporting), and modeling of trained behaviors (e.g., safe behaviors). Although these results are
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encouraging, additional research is needed to determine the true impact of supervisor support on transfer of training. The research evidence supporting the role of the organizational transfer climate on transfer of training is slightly larger than that for supervisor support. Organizational climate can be defined as the interaction between observable elements within the organizational setting as well as those that are perceived by trainees (Hellreigel and Slocum, 1974; James and Jones, 1974). Research suggests that trainees who perceive a positive organizational climate (e.g., organizational support, rewards, safety policies, nonpunitive error-reporting systems) apply learned competencies on the job (Baumgartel et al., 1984; Rouiller and Goldstein, 1993; Tracy et al., 1995). In addition, we argue that a positive safety culture (a part of the organizational climate) that supports the demonstration of safe behaviors by trainees will encourage the transfer of these behaviors back to the work environment (see subsection on External Factors). Finally, a continuous-learning culture (i.e., work environment) is important for the transfer of learned competencies to the job. A continuous-learning work environment is one in which the acquisition of knowledge and skills is supported and opportunities are provided; achievement is reinforced; and innovation and competition are encouraged (Dubin, 1990; Rosow and Zager, 1988; Tracy et al., 1995). Members of organizations with these characteristics understand that learning is a part of their daily work environment. Research conducted by Tracy and colleagues (1995) suggests that trainees who perceived a continuous-learning environment demonstrated more post-training behaviors. In organizations in which errors are likely to occur, we argue that a continuous-learning environment may be necessary to encourage employees continuously to demonstrate safe behaviors learned during training and to learn from the errors that may occur. 6.4 Examples A number of liability cases have addressed training and the repercussions of inadequate training (i.e., resulting in unsafe behaviors) in deciding legal culpability. Going as far back as 1978, the courts have made landmark decisions regarding the responsibility of an organization or municipality in providing adequate training. Cases that have come before the courts cover numerous training issues, including the use of deadly force (Gilligan v. Morgan, 413 U.S. 1, 1973), training for high-stress situations such as a car chase (Springfield v. Kibbe, 480 U.S. 257, 1987), training to ensure safety for employees (Collins v. Harker Heights, 503 U.S. 115, 1992), and the need for single-sex environments with certain types of training (United States v. Virginia et al., 518 U.S. 515, 1996). One notable case was that of Monell v. Department of Social Services of the City of New York, 436 U.S. 658 (1978). As a result of this case, the Supreme Court justices upheld the decision that municipality officials could be held legally responsible for policy making, which has proved to be unfavorable for some organizations.
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Law Enforcement In Oklahoma City v. Tuttle, 471 U.S. 808 (1985), an innocent man was shot and killed by a police officer outside a bar where a robbery in progress had been reported. The city was held liable in the original trial due to negligence in training of the officer. The precedent had been set by Monell v. New York City Department of Social Services, and the court found that the training enforced through city policy had resulted in the inappropriate behavior of the officer and, ultimately, in one man’s death. Upon appeal, the court upheld the decision and indicated that even a single incident can represent negligence on the part of the policy makers (i.e., those making policies regarding training). Although the Supreme Court eventually overturned the decision, it was due to their disagreement with the lower courts that a single incident could represent negligence. The justices agreed with the culpability of the city in providing appropriate training. Industrial In 2002, a construction company was cited and ordered to pay more than $100,000 when a worker was electrocuted and killed while on the job (OSHA, 2002). The company was cited for improper procedures, inadequate training of workers, failure to conduct safety briefings, and improper equipment. In a similar instance, a trucking company was ordered to pay more than $70,000 when a worker was killed in an explosion. The company was cited for improper training, failure to follow safety precautions, improper equipment (e.g., lack of fire extinguishers), and failure to inspect the work environment. Aviation Beyond the examples presented earlier, the aviation industry has generally been successful in combating unsafe practices through the use of team training, specifically crew resource management (CRM) training (Helmreich and Merritt, 2000). It is argued that this industry is the number one advocate of team training (Helmreich et al., 1993). CRM was developed as a means to train aviation crewmembers to utilize all resources available to them (e.g., people, information, equipment) through coordination and communication (Wiener et al., 1993; Salas et al., 2001a). Although CRM’s focus has changed over the past two decades (i.e., from changing interpersonal style to assertiveness training for junior crewmembers), its current focus is on error management. Since the inception of CRM training, the aviation safety record has improved greatly. The risk of death when traveling by commercial airliners has dramatically decreased from 1 in 2 million to 1 in 8 million over the past two decades as a result of CRM training (Kohn et al., 1999). The most notable success of CRM training was demonstrated during the approach to landing of United Airlines Flight 232, which had suffered a catastrophic engine and hydraulic failure (Roberts and Bea, 2001; www.airdisaster.com). Crewmembers worked together as a team to maneuver the nearly uncontrollable aircraft to a crash landing in Sioux City, Iowa. Approximately 200 of the 300 passengers and crew on that flight survived as a result of the crew’s teamwork and CRM training. The overwhelming
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success of CRM training in aviation has led to its adaptation and implementation in many other organizations (e.g., medical, oil, nuclear power; see Salas et al., 200la). Medical For many years, the medical industry has ignored the role that human error has played in the field (Pietro et al., 2000), in part due to the risk of legal actions that could be brought against not only individual medical professionals but also medical organizations. It has been estimated that human error leads to approximately 100,000 patient deaths and many more injuries in U.S. hospitals each year and results in costs of up to $9 billion annually (Barach and Small, 2000). At least 50% of these errors are not reported and 70% of those reported were deemed preventable (Leape, 1994). However, medical errors are often justified and rationalized in this domain due to the complex and subjective nature of medicine (Pietro et al., 2000). To further complicate the issue, medical organizations and their personnel are not obligated to report errors. Reasons provided for not disclosing or further investigating errors are risk of negative publicity and legal actions, high costs, lack of standards to define an unacceptable error, and lack of justification to conduct such an investigation. The medical domain’s resistance to accepting human error makes it difficult to train for safe practices; however, there is some good news. Recently, the medical domain began taking advantage of the lessons learned from the aviation industry and implemented CRM training to medical teams (e.g., surgical; Helmreich, 2000). Specifically, surgical and anesthetic teams have been provided with CRM training to improve communication within the operating room (Helmreich, 1997). The training programs embed critical scenarios using a “dummy patient” that require the team members to make decisions together to perform the operation successfully. Following the training, the teams are provided feedback on their performance. Helmreich suggests that other medical domains (e.g., emergency rooms, ambulance teams) could also benefit from this training, as well as other complex, dynamic environments. 6.5 Conclusion Human error is unavoidable, and training employees to trap and mitigate the consequences of these errors and unsafe behaviors is a welcome start in the right direction. However, the threat of organizational liability for improper training resulting in an accident or incident exists. The purpose of this chapter was to provide an understanding of issues that influence safe practices in organizations as well as how training can be utilized to reduce errors and improve safe behaviors. We also offered guidance regarding factors to consider during the design, delivery, and evaluation/transfer of training. In this chapter, we have argued that training must be designed and delivered systematically by taking into consideration key factors such as the pretraining environment, organizational and trainee characteristics, trainee motivation, and the posttraining environment. We emphasized the importance for organizations to understand that training is more than just a program. The human factors field, as well as the
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industrial/organizational psychology field, has helped to develop a science behind it that needs to be exploited to better ensure its intended outcomes. Therefore, to minimize the risk of legal liability, organizations need to rely on the science of training when developing a training program. By incorporating sound learning principles; conducting systematic, multilevel evaluations; and ensuring the transfer of trained skills to the job, organizations can appropriately determine that the desired outcomes were produced and training’s overall effectiveness was achieved. Until then, inadequate training will lead to unsafe practices and the threat of legal liability will always be on the horizon. Can training for safe practices reduce the risk of organizational liability? Yes, when human factors principles are incorporated into the design, delivery, implementation, and evaluation of training as is suggested in this chapter. Although there is no guarantee that a training program that does not utilize human factors principles will lead to legal liability, the risks involved and potential consequences do not make this a chance worth taking.
CHECKLIST 6.1 Steps to Develop an Effective Training Program Systematically Primary factors
Considerations
1. Conduct training needs analysis Provides information used to develop instructional objectives and training criteria • Where is training needed? a. Organizational analysis • When is training needed? b. Task analysis (cognitive task • Task characteristics analysis—see Checklist 6.2) • Task competencies (KSAs) • Who needs to be trained? c. Person analysis • In what do they need to be trained? 2. Consider external factors Determine impact of organizational (e.g., safety culture), individual (e.g., self-efficacy), and motivation characteristics on training a. Organizational characteristics • Selection and notification • Situational constraints (e.g., improper equipment) • Organizational culture (e.g., perceived organizational support, safety culture, and policies) • Organizational resources and opportunities to practice b. Safety culture • Safety policies • Error reporting system c. Individual characteristics • Cognitive ability • Self-efficacy • Goal orientation d. Motivation • Direction • Effort • Intensity • Persistence 3. Establish training objectives (see Are objectives: Checklist 6.3) • Measurable? • Specific?
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5. Determine the strategies to use
6. Develop scenarios for training
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• Relevant to task? • Information based • Demonstration based • Practice based • Combination of above methods • Event-based training • Assertiveness training • Metacognitive training • Stress-exposure training • Cross training • Represent critical incidents? • Represent actual task environment?
Considerations Questions to answer: • Was training effective? • Were training objectives accomplished? Methods to use: • Multilevel evaluations (see Table 6.2 and Table 6.3) • Experimental methods • Nonexperimental methods • Supervisor support • Organizational climate • Continuous-learning culture
CHECKLIST 6.2 Development and Implementation of Cognitive Task Analysis Primary factors Select experts
Develop scenarios based on task analysis Choose a knowledge elicitation method: • Interviews • Verbal protocols • Observations • Conceptual methods Implement knowledge elicitation method chosen: • Interviews
Considerations • Experience with domain • Experience with task • Number to include • Develop relevant task scenario(s) with problem statement • Pretest scenarios to determine completeness • What information are you trying to elicit? • Ask experts about cognitive processes needed to complete task scenarios • Ask experts to think aloud while completing task scenarios • Observe experts completing task scenarios • Inferences made based on experts’ relatedness judgments • Decide the number of sessions to be recorded • Obtain consent and provide task scenario to expert • Ask experts questions, for example: – What rules/strategies used to complete scenario?
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• Observations
• Conceptual methods
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– What knowledge is needed to complete scenario? – What cognitive skills are needed to complete scenario? – If this happens, then what would you do? • Record comments provided by experts via video, audio, pen and paper • Repeat each scenario for each expert • Ask expert to “think aloud” while working through scenario • Record comments provided by experts via video, audio, pen and paper • Repeat each scenario for each expert • Be as unobtrusive as possible • Ask for clarification as necessary • Record comments via video, pen and paper • Repeat each scenario for each expert • Present pairs of tasks to experts • Ask experts to judge how related the tasks are • Present each pair of tasks to each expert • Record similarities between experts • Interview additional experts if questions arise from data • Identify rules and strategies applied to the scenario • Identify knowledge required • Identify cognitive skills required • Generate list of task requirements • Verify list with additional experts
CHECKLIST 6.3 Developing Training Objectives Primary factors Review existing documents to determine job tasks and competencies required
Translate identified competencies into training objectives
Considerations Sources to examine: • Essential task lists • Previous training objectives • Organization performance standards • Instructors, based on their knowledge and experience Objectives should include: • Specification of behavior to be observed – Use “action” verbs (e.g., “provide,” “prepare,” “locate,” and “decide”) – State the specific behavior(s) that demonstrates the skill or knowledge – State in a way that can be plainly understood by everyone • Conditions under which they are to be exhibited • Standards to which they will be performed or demonstrated – Are standards realistic?
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– Are standards clearly stated? – Do standards include completeness, accuracy, timeliness, and performance rates? Categorize: • General objectives specify the end state that trainee should attain • Specific objectives identify tasks that must be performed to meet the general objectives Use training objectives to: • Design exercise training events (e.g., scenarios) – Use events to provide opportunities to evaluate how well trainees performed training objectives • Develop performance measurement tools (e.g., checklists) • Brief trainees on training event
CHECKLIST 6.4 Evaluating Training (Metacognitive training example) Task being observed Narrative
Narrative should provide a context and justify the behavioral ratings assigned 1 2 3 4 Poor: observed Marginal: observed Good: observed Outstanding: observed performance had safety performance was performance was performance was truly implications barely adequate effective noteworthy Execution behavioral markers Behavior to be observed Definition of behavior Evaluator comments: to of behavior Rating: justify rating assigned 1–4 Problem Identified Problem to be solved and objectives to meet were correctly identified Communication Correct information was communicated to the appropriate individuals Tasks Delegated Tasks were delegated to appropriate individuals Monitor Individuals monitored own behaviors and those of others Task Completion Tasks were completed in the correct order and at the appropriate times Review/modify behavioral markers Behavior to be observed Definition of behavior Evaluator Rating: comments: to 1–4 justify rating assigned Evaluation of procedures Procedures were reviewed and modified when appropriate
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Inquiry Individuals sought help/information when uncertain Source: Adapted from University of Texas at Austin, 2002, LOSA Observation Form Example. Austin, TX: The University of Texas Human Factors Research Project.
Defining Terms Critical incidents technique—“A job analysis technique in which SMEs provide many specific behavioral descriptions of incidents resulting in effective or ineffective performance” (Chmiel, 2000, p. 441). Error reporting—Reporting of errors that resulted in unsafe behaviors but did not lead to an accident. Human error—“…Occasion in which a planned sequence of mental or physical activities fails to achieve its intended outcome” (Reason, 1990, p.9). Job/task analysis—“…Carried out by interview or questionnaire, with generic questions, relying on the incumbent, supervisor or subject matter expert to provide job specific information…[the worker] on answering the questions,…is drawing on an implicit analysis of the job and its knowledge and skill requirements, without which, training needs cannot be determined” (Lees and Cordery, 2000, p. 47). Motivation—“…Refers to psychological processes that cause arousal, direction, and persistence of behavior. Arousal and persistence focus on the time and effort that an individual invests, and direction refers directly to the behaviors in which the investment of time and effort are made” (Goldstein, 1993, p. 90). Organizational analysis—“…Begins with an examination of the short- and long-term goals of the organization, as well as of the trends that are likely to affect goals…focuses on training program and support systems—for example, selection, human-factors engineering, and work procedures” (Goldstein, 1993, pp. 20–21). Person analysis—“…To identify on an individual basis the skills to be learned by each trainee” (Patrick, 2000). “…concerned with how well a specific employee is carrying out the tasks that comprise the job” (Goldstein, 1993, p. 22). Safety climate—“…Can be determined by examining structural properties of organizations such as system complexity and leadership style…often measured by eliciting worker perceptions about organizational commitment to safety, such as the perceived importance of safety training, management’s attitude to safety and so on” (Chmiel, 2000, p. 270). Training—“The systematic acquisition of skills, rules, concepts, or attitudes that result in improved performance in another environment” (Goldstein, 1993, p. 3). Training effectiveness—“…Why training did or did not achieve its intended outcomes…identifying and measuring the effects of individual, organizational, and training-related factors on training outcomes such as learning and transfer of training” (Kraiger et al., 1993, p. 312). Training evaluation—“Refers to a system for measuring whether trainees have achieved learning outcomes…concerned with issues of measurement and design, the accomplishment of learning objectives, and the attainment of requisite knowledge and skills” (Kraiger et al., 1993, p. 312).
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Training objectives (instructional objectives)—“From information obtained in the assessment of instructional needs, a blueprint emerges that describes the objectives to be achieved by the trainee upon completing the training program” (Goldstein, 1993, p. 23). “…are vital ingredients in the development of training, and influence or determine the content, design and evaluation of training (Patrick, 2000, p. 110). Training outcomes—“Outcomes…are defined as their name implies, as the outcome of the various task processes” (Cannon-Bowers and Salas, 1997, p. 51). Outcomes “may be regarded as a combination of behavior and results criteria” (Kozlowski et al., 2000, p. 192) and/or as “changes in individual behavior” (p. 193). Examples of outcomes include: productivity, time, number of errors, and number of safety behaviors exhibited. References Alliger, G.M. and Januck, E.A. (1989). Kirkpatrick’s levels of training criteria: thirty years later. Personnel Psychol. , 42, 331–342. Alliger, G.M., Tannenbaum, S.I., and Bennett, W., Jr. (1997). A meta-analysis of the relations among training criteria. Personnel Psychol. , 50, 341–358. Baldwin, T.T. and Ford, J.K. (1988). Transfer of training: a review and directions for future research. Personnel Psychol. , 41, 63–105. Baldwin, T.T. and Magjuka, R.J. (1997). Training as an organizational episode: pretraining influences on trainee motivation. In J.K.Ford et al. (Eds.), Improving Training Effectiveness in Work Organizations (99–127). Mahwah, NJ: Lawrence Erlbaum Associates. Baldwin, T.T, Magjuka, R.J., and Loher, B.T. (1991). The perils of participation: effects of choice of training on trainee motivation and learning. Personnel Psychol. , 44, 51–65. Barach, P. and Small, S.D. (2000). Reporting and preventing medical mishaps: lessons from nonmedical near miss reporting systems. Br. Med. J. , 320, 759–763. Bassi, L.J. and Van Buren, M.E. (1998). The 1998 ASTD state of the industry report. Training Dev. , January, 21–43. Baumgartel, H., Reynolds, M., and Pathan, R. (1984). How personality and organizational-climate variables moderate the effectiveness of management development programs: a review and some recent research findings. Manage. Labour Stud. , 9, 1–16. Blickensderfer, E.L., Cannon-Bowers, J.A., and Salas, E. (1997). Theoretical bases for team selfcorrection: fostering shared mental models. In M.Beyerlein, D.Johnson, and S.Beyerlein (Eds.,), Advances in Interdisciplinary Studies in Work Teams Series (Vol. 4, 249–279). Greenwich, CT: JAI Press. Bowers, C.A., Blickensderfer, E.L., and Morgan, B.B. (1998). Air traffic control specialist team coordination. In M.W.Smolensky and E.S.Stein (Eds.), Human Factors in Air Traffic Control (215–236). San Diego, CA: Academic Press. Brinkerhoff, R.O. and Montesino, M.U. (1995). Partnership for training transfer: lessons from a corporate study. Hum. Resour. Dev. Q. , 6, 263–274. Campbell, J.P. (1971). Personnel training and development. Annu. Rev. Psychol. , 22, 565–602. Cannon-Bowers, J.A. and Salas, E. (1997). A framework for measuring team performance measures in training. In M.T.Brannick, E.Salas, and C.Prince (Eds.), Team Performance Assessment and Measurement: Theory, Methods, and Applications (45–62). Hillsdale, NJ: Lawrence Erlbaum Associates. Cannon-Bowers, J.A., Burns, J.J., Salas, E., and Pruitt, J.S. (1998). Advanced technology in scenario-based training. In J.A.Cannon-Bowers and E.Salas (Eds.), Making Decisions under Stress: Implications for Individual and Team Training (365–374). Washington, D.C.: American Psychological Association.
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Sexton, J.B., Thomas, E.J., and Helmreich, R.L. (2000). Error, stress, and teamwork in medicine and aviation: cross sectional surveys. Br. Manage.J. , 320 , 745–749. Shappell, S.A. and Wiegmann, D.A. (1997). A human error approach to accident investigation: the taxonomy of unsafe operations. Int. J. Aviation Psychol , 7(4), 269–291. Shute, V.J. and Gawlick, L.A. (1995). Practice effects on skill acquisition, learning outcome, retention, and sensitivity to relearning. Hum. Factors , 37, 781–803. Smith-Jentsch, K., Salas, E., and Baker, D.P. (1996). Training team performance-related assertiveness. Personnel Psychol , 49, 909–936. Smith-Jentsch, K.A., Zeisig, R.L., Acton, B., and McPherson, J.A. (1998). Team dimensional training: a strategy for guided team self-correction. In J.A.Cannon-Bowers and E.Salas (Eds.), Making Decisions under Stress: Implications for Individual and Team Training (271–297). Washington, D.C.: American Psychological Association. Springfield v. Kibbe (1987). Case No. 480 U.S. 257. Retrieved online May 31, 2002 from: http://case-law.lp.findlaw.com/scripts/getcase.pl?navby=case&court=US8cvol=480&invol=257. Tannenbaum, S.I., Mathieu, J.E., Salas, E., and Cannon-Bowers, J.A. (1991). Meeting trainees’ expectations: the influences of training fulfillment on the development of commitment, selfefficacy, and motivation. J. Appl. Psychol , 76, 759–769. Tannenbaum, S.I. and Yukl, G. (1992). Training and development in work organizations. Annu. Rev. Psychol , 43, 399–441. Tracy, B.J., Tannenbaum, S.I., and Kavanagh, M.J. (1995). Applying trained skills on the job: the importance of the work environment. J. Appl Psychol , 80, 239–252. Turner, B.A. (1991). The development of a safety culture. Chem. Ind. , 1, 241–243. United States v. Virginia et al (1996). Case No. 518 U.S. 515. Retrieved May 31, 2002, from http://%20supct.law.cornell.edu/supct/html/94–1941.ZS.html. University of Texas at Austin. (2002). LOSA observation form example. Austin, TX: The University of Texas Human Factors Research Project. Vaughan, D. (1996). The Challenger Launch Decision . Chicago: The University of Chicago Press. Volpe, C.E., Cannon-Bowers, J.A., Salas, E., and Spector, P.E. (2001). The impact of cross-training on team functioning: an empirical investigation. In R.W.Swezey and D.H.Andrews (Eds.), Readings in Training and Simulation: a 30-Year Perspective (115–128). Santa Monica, CA: Human Factors and Ergonomics Society. Wehrenberg, S.B. (1987). Supervisors as trainers: the long-term gains of OJT. Personnel I. , 66(4), 48–51. Wiener, E.L., Kanki, E.C., and Helmreich, R.L. (Eds.) (1993). Cockpit Resource Management . New York: Academic Press. Williams, T.C., Thayer, P.W., and Pond, S.B. (1991). Test of a model of motivational influences on reactions to training and learning. Paper presented at the meeting of the Society for Industrial and Organizational Psychology, St. Louis. Wilson, P.F. and Johnson, W.B. (2001). Core virtues for the practice of mentoring. J. Psychol Theol. , 29(2), 121–130.
Further Information Barling, J., Weber, T., and Kelloway, E.K. (1996). Effects of transformational leadership training on attitudinal and financial outcomes: a field experiment. J. Appl Psychol , 81(6), 827–832. Helmreich, R.L., Merritt, A.C., and Wilhelm, J.A. (1999). The evolution of crew resource management training in commercial aviation. Int. J. Aviation Psychol. , 9(1), 19–32. Reason, J. (1990). Human Error . New York: Cambridge University Press.
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Salas, E. and Cannon-Bowers, J.A. (2000). Designing training systems systematically. In E.A.Locke (Ed.), The Blackwell Handbook of Principles of Organizational Behavior (43–59). Maiden, MA: Blackwell Publisher. Salas, E. and Cannon-Bowers, J.A. (2001). The science of training: a decade of progress. Annu. Rev. Psychol. , 52, 471–499. Salas, E., Bowers, C.A., and Edens, E. (Eds.) (2001). Improving Teamwork in Organizations: Applications of Resource Management Training . Hillsdale, NJ: Lawrence Erlbaum Associates. Wiener, E.L., Kanki, B.C., and Helmreich, R.L. (Eds.) (1993). Cockpit Resource Management . San Diego, CA: Academic Press.
7 The Influence of Daubert on Expert Witness Testimony—The Human Factors Context Jone McFadden papinchock SHL Litigation Support Frank J.Landy SHL Litigation Support 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
The role of the human factors expert witness in Federal Court was dramatically changed with the United States Supreme Court decision in Daubert v. Merrell Dow Pharmaceuticals in 1993. 1 This chapter provides basic information about the general impact of Daubert on legal proceedings and illustrations as to the specific impact in human factors cases. In particular, it provides guidance for human factors experts in preparing for and delivering testimony in the litigation context. 7.1 Some Rationale The reason for providing “safeguards” in the case of expert testimony is to prevent the “finder of fact” (judge in the case of a bench trial, or jury in a nonbench trial) from being unduly swayed by the mantle of “expert” testimony. By definition, expert testimony deals with areas outside the knowledge domain of 1
Jason Daubert and Eric Schuller sued Merrell Dow, alleging that their birth defects were the result of their mothers’ use of a prescription antinausea drug (Bendectin) during pregnancy.the judge or jury. As a result, there may be an inclination simply to accept anything said by an expert as “truth” in a general sense. The purpose of guidelines such as those in Daubert is to prevent the finder of fact from even hearing expert testimony that lacks scientific foundation. In practice, many judges feel sufficiently confident to admit questionable testimony if the trial is a bench trial. When objections are raised by opposing counsel, they often respond by saying that they will admit the testimony but may not place much weight on it. 2
Judges tend to be more cautious, however, with what a jury may hear, believing that judges and attorneys are better able to discern flawed scientific findings than jurors (Kovera and McAuliff, 2000). When the testimony of an expert may be difficult for a jury to evaluate through common sense, the standard of admissibility maybe increased (Mark, 1999). The 11th Circuit Court of Appeals specifically addressed this issue in Allison v. McGhan Medical Corporation (1999) in the statement that
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while meticulous Daubert inquiries may bring judges under criticism for donning white coats and making determinations outside their field of expertise, the Supreme Court has obviously deemed this less objectionable than dumping a barrage of questionable scientific evidence on a jury, who would be even less equipped than the judge to make reliability 3 and relevance determinations and more likely than the judge to be awestruck by the expert’s mystique (at 1310). 4 Because human factors litigation invariably involves a jury as the finder of fact, the discussion that follows will assume a jury-trial scenario rather than a bench trial. 7.2 Superceding of Frye by Federal Rules of Evidence in Daubert The Supreme Court provided a ruling in Daubert that had a direct impact on the guidelines for admissibility of scientific evidence through expert testimony in federal courts. The ruling established that the Frye test 5 set in 1923 had been superceded by the Federal Rules of Evidence (U.S. House of Representatives, Committee on Judiciary, 2002), which were originally enacted in 1975 to direct the use of evidence in federal courts on civil as well as criminal cases. 6 It should be noted that as a result of Daubert, the Federal Rules of Evidence have also been accepted by some, but not all, state courts. The State of Florida, for example, still relies on the Frye test. The Frye test was stated in the following way: …just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs (at 1014). The Frye test had been criticized because of the de facto waiting period that it implied before the “general acceptance” of new theories and their impact on emerging science (Black et al., 1994; Miller et al., 1994; Price and Kelly, 1998; Sanders et al., 2002). 2
One trial judge has indicated that reserving a ruling during a bench trial occurs because it “buys time for study and reflection” that does not exist in a jury trial (Gless, 1995, p. 263). 3 The Court’s use of “reliability” is more commonly referred to as validity by scientists (Sanders, 1994). 4 It should be noted that the U.S. 11th Circuit Court of Appeals made these comments in the context of a case with a 3-day Daubert hearing by the district court. 5 Frye v. United States, 54 App. D.C. 46, 293 E 1013 (1923). 6 Available at www.house.gov/judiciary/Evid2002.pdf
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In contrast, the Federal Rules of Evidence (FRE) 402 states that “all relevant evidence is admissible, except as otherwise provided by the Constitution of the United States, by Act of Congress, by these rules, or by other rules prescribed by the Supreme Court pursuant to statutory authority. Evidence which is not relevant is not admissible” (U.S. House of Representatives, Committee on Judiciary, 2002) A refinement to the inclusion of “relevant evidence” is presented in 403, which states that, “although relevant, evidence may be excluded if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the jury, or by considerations of undue delay, waste of time, or needless presentation of cumulative evidence” (U.S. House of Representatives, Committee on Judiciary, 2002). Article VII of the Federal Rules of Evidence includes specific requirements for admissibility of expert testimony in FRE 702, which prescribes that 7
if scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skills, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case (U.S. House of Representatives, Committee on Judiciary, 2002). In Daubert, the U.S. District Court in California granted summary judgment for the defendant, specifically ruling that the testimony of the plaintiffs’ experts did not meet the “general acceptance” standards under Frye and that the studies performed by the plaintiffs’ experts were not published and had not been peer-reviewed. Specifically, the court excluded evidence provided by the plaintiffs’ experts in rebuttal of Merrill Dow’s experts about the association between Bendectin and birth defects in humans. When heard by the U.S. Court of Appeals (Ninth Circuit), the ruling was affirmed. The U.S. Supreme Court reversed and remanded the case, indicating that the lower courts had erroneously relied on the Frye test of “general acceptance.” The Court indicated that the Federal Rules of Evidence did not include reference to Frye or to a “general acceptance” standard. The Court assigned what has come to be known as “gatekeeping responsibility” (Daubert at 2800) to the trial judge by indicating that the “trial judge must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable” (at 2795). In his opinion, Judge Blackmun further indicated some of the important factors that have come to be recognized as “Daubert factors.” It should be noted that in his opinion, Judge Blackmun wrote that these were “general observations” and that the Court did “not presume to set out a definitive checklist or test” (at 2796). Furthermore, in Kumho Tire Co. v. Carmichael (1999) following the Daubert decision, Justice Breyer wrote, The conclusion in our view, is that we can neither rule out, nor rule in, for all cases and for all time the applicability of the factors mentioned in Daubert, nor can we now do so for a subset of cases categorized by
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category of expert or by kind of evidence. Too much depends upon the particular circumstances of the particular case at issue. Thus, the following factors should be interpreted in that light: Ordinarily, a key question to be answered in determining whether a theory or technique is scientific knowledge that will assist the trier of fact will be whether it can be (and has been) tested. Scientific methodology today is based on generating hypotheses and testing them to see if they can be falsified; indeed, this methodology is what distinguishes science from other fields of human inquiry (at 2796). 7
“Relevant evidence” is defined in 401 as “evidence having any tendency to make the existence of any fact that is of consequence to the determination of the action more probable or less probable than it would be without the evidence.”
Another pertinent consideration is whether the theory or technique has been subjected to peer review and publication. Publication (which is but one element of peer review) is not a sine qua non of admissibility; it does not necessarily correlate with reliability…and in some instances well grounded but innovative theories will not have been published…. Some propositions, moreover, are too particular, too new, or of too limited interest to be published. But submission to the scrutiny of the scientific community is a component of “good science,” in part because it decreases the likelihood that substantive flaws in methodology will be detected (at 2797). Additionally, in the case of a particular scientific technique, the court ordinarily should consider the known or potential rate of error…and the existence and maintenance of standards controlling the technique’s operation (at 2797). Finally, “general acceptance” can yet have a bearing on the inquiry. A reliability assessment does not require, although it does permit, explicit identification of a relevant scientific community and an express determination of a particular degree of acceptance within that community…. Widespread acceptance can be an important factor in ruling particular evidence admissible, and a known technique that has been able to attract only minimal support within the community…may properly be viewed with skepticism (at 2797).
7.3 Impact of Daubert More than 10 years have passed since the Daubert ruling and during that period dozens of articles have been written on the impact of the ruling. The popular press and many legal tomes have concentrated on the demise of “junk science” in the face of Daubert (Holden, 1998; Price and Kelly, 1998; Riley, 1996; Vondrak, 1998; Worthington et al., 2002). Junk science is commonly defined as “speech or information which claims to have scientific basis but, is false” (http://home.comcast.net/~bkrentzman/glossary.html). “Junk
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science is the mirror image of real science, with much of the same form but none of the substance. There is the astronomer on one hand, and the astrologist on the other. The chemist is compared with the alchemist…” (Huber, 1991, p. 2). Given this definition, the full impact and complexity of Daubert might be overlooked. The role of the judge is far more straightforward in making a decision on the exclusion of outright “junk science” compared to the nuances associated with determining whether scientific findings apply in a given case or whether expert opinions have been derived using the scientific method. This latter condition most often will affect human factors litigation. Within this type of litigation, “junk science” has probably been a lesser concern than the misapplication or misinterpretation of scientific findings intentionally or unintentionally by experts who lacked the necessary training, experience, or animus. Thus, substantial emphasis is placed on the judge’s role as an interpreter and gatekeeper in human factors cases. Daubert has provided a nomenclature (relevance, reliability, error rate, falsifiablity, peer review, scientific method) upon which judges can determine the appropriateness of expert witness testimony. However, it is unclear how well judges understand all of this nomenclature. The ability of judges to perform the gatekeeper role, regardless of their best efforts, has been a source of concern since the Daubert ruling. It is presumed that many do not have backgrounds necessary to provide the theoretical structure for evaluating the information needed to determine the reliability and relevance of scientific evidence (Dixon and Gill, 2002; Faigman, 1995a; Krauss and Sales, 1998; Saxe and BenShakhar, 1999). This issue was even voiced by Chief Justice Rehnquist and Justice Stevens in their partially dissenting opinion in Daubert when they cautioned against the role of judges as “amateur scientists” (Rehnquist at 2800). In a survey of state court judges, 48% (or 191 judges) reported they were not fully equipped through their education to evaluate the myriad of scientific issues in their courts (Gatowski et al., 2001). The vast majority of the survey respondents (241 of 251) indicated that they had not received training in general scientific methods and principles. Demonstrating this lack of foundation, only a fraction (6%) of the survey participants (23 of 400) gave accurate responses to a question written to assess their level of understanding of the scientific meaning of the term “falsifiability.” In fact, 35% gave responses that highlighted a complete lack of understanding such as “I would want to know if the evidence was falsified” or “I would look at the results and determine if they are false” (Gatowski et al., 2001, p. 445). These results are particularly striking in light of the fact that, in 1994, the Federal Judicial Center issued a copy of the Reference Manual on Scientific Evidence (Federal Judicial Center, 1994) to all federal judges (Walker and Monahan, 1996). This manual contains sections on the scientific method and falsification theory. On this point, in his introduction to the second edition to the Reference Manual on Scientific Evidence, Associate Justice Breyer wrote that “most judges lack the scientific training that might facilitate the evaluation of scientific claims or the evaluation of expert witnesses who make such claims. Judges typically are generalists, dealing with cases that vary widely in subject matter. Our primary objective is usually process related…” (Federal Judicial Center, 2000, p. 4).
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7.4 Affirmative Role of the Human Factors Expert after Daubert The survey data of Gatowski and colleagues (2001) reported in the preceding section might lead one to consider whether extensive changes in court decisions have occurred since Daubert and what, if any, impact they should have on the role of the human factors expert. In fact, there is some question as to how extensively the Daubert test is applied by judges (even in federal courts), particularly as relates to experts in the social sciences (Dixon and Gill, 2002; Lipton, 1999; Shuman and Sales, 1999; Tenopyr, 1999). In contrast, there seems to be more evidence of the impact of Daubert in the exclusion of experts in other areas of law such as toxic tort cases (Clark, 1996). Furthermore, it has been suggested that fewer Daubert proceedings will take place than expected for a number of reasons, including the possibility that a trial lawyer may not raise the issue of the opposing expert’s credibility because he does not recognize the technical weaknesses, his expert used similar methods and procedures, he recognizes the weaknesses but considers it a strategic advantage to bring the weaknesses directly to the jury’s attention through cross-examination, or he simply wants to control costs (Shuman and Sales, 2001). Any question about the applicability of Daubert to human factors testimony was clarified in Kumho Tire Company v. Carmichael (1999), when the U.S. Supreme Court ruled that the Federal Rules of Evidence govern all expert testimony. In Kumho, the Supreme Court found that the testimony of an expert in a tire failure case (opining about whether a tire failure on a minivan resulted from a defect in the tire’s manufacture or design) was subject to Daubert consideration. Specifically, the Court indicated that Federal Rules of Evidence 702 does not distinguish between scientific and nonscientific knowledge. In further support of the applicability of Daubert to human factors testimony, in a 1998 survey, of the 1281 expert witnesses identified in 297 federal civil trials, 21.8% were designated as “engineering/process/ safety”; these were further deconstructed into “accident reconstructionists” (2%), “products engineers” (2%), and “other engineering/process/safety” (8.3%) (Krafka et al., 2002). This 1998 survey also reported that experts addressed the cause of injury or damage in 63.5% of the cases, the reasonableness of the party’s actions in 34.1% of the cases, and industry standards or state of the art in 30.3%—all issues that human factors experts commonly handle. Moreover, some preliminary evidence suggests that Daubert is affecting case outcomes (Dixon and Gill, 2002). Of particular note is the finding that, since the Daubert ruling, challenges to the relevance and reliability of expert witness opinions have resulted in more summary judgments, with 90% of the judgments against the plaintiffs, “making it likely that challenges to plaintiffs’ evidence increasingly resulted in case dismissal” (Dixon and Gill, 2002, pp. 298–299). Also, review of opinions pre- and post-Daubert indicates a “rapid rise in the frequency with which judges addressed the clarity and coherence of the expert’s explanation of the theory, methods, and procedures underlying the evidence” (Dixon and Gill, 2002, p. 299). In their survey of judges, Krafka and colleagues (2002) reported that pretrial scrutiny of experts had increased between 1991 and 1998 and that judges were less likely to admit the testimony in 1998. There seems little doubt that human factors experts are, and will continue to be, challenged on Daubert standards.
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This means that the human factors expert should carefully consider his or her role in the context of expert testimony. Preparing one’s testimony as if it will be challenged on the basis of Daubert is never a waste of time for an expert. It ensures that he will locate relevant research, use a scientific approach to gathering and evaluating evidence (“through the methods and procedures of science”; Daubert at 2795), and be prepared for trial testimony and cross-examination (Shuman and Sales, 2001). Shuman and Sales liken preparing opinions as if there will be a Daubert challenge to “Pascal’s wager,” which recommends that little risk is attached to choosing to believe in God but greater potential risk is associated with not believing. Minimally, the expert will serve as an educator and resource to the judge in his or her gatekeeping capacity and as an interpreter of the applicability of technical or scientific research to a given case. The expert should carefully craft the expert report because a substantial proportion of judges (63%) have indicated that expert reports assist them in focusing on case issues (Krafka et al., 2002). From this perspective, it is clear that it is insufficient simply to present theories, particularly sophisticated or complex theories, without explaining them in lay terms and drawing parallels to the facts of the current case. This role of the testifying expert has been described as “assisted sense making” (Mark, 1999). In the role of educator, the human factors expert must competently present sophisticated concepts not only in his specialty area but also in basic scientific methods. The expert witness cannot assume that the judge or jury will have sufficient background in the scientific method to proceed immediately to more complex theories. The language of the expert should be easily understandable. The human factors expert must also demonstrate that he has relied on the scientific method in reviewing case information, performing tests, analyzing results, and arriving at conclusions. “One of the basic lessons of Daubert should not be lost: Daubert exhorts scientists to do good science and expects them to be scientists first and expert witnesses (and advocates) second” (Faigman, 1995b, p. 975). That is, the expert demonstrates that “through the use of proper methods we can know with some degree of certainty which of our judgments about the world are correct” (Sanders et al., 2002, p. 151). The human factors expert must also carefully explain the linkages between the theories presented and the facts of the case (Thornton and Wingate, in press). As described in the Daubert decision, “‘fit’ is not always obvious, and scientific validity for one purpose is not necessarily scientific validity for other, unrelated purposes Rule 702’s ‘helpfulness’ standard requires a valid scientific connection to the pertinent inquiry as a precondition to admissibility” (at 2796). It is insufficient simply to state that a particular theory has been published and is well grounded from a scientific basis. It must be tied to the facts of the case. One must demonstrate that the theory proposed is applicable to the facts of the case. Some preliminary research indicates that, particularly when testimony is nonscientific in nature, demonstrating the applicability of the Daubert factors may be less important than demonstrating the witness’s capacity to assist the trier of facts and that the testimony is relevant and nonprejudicial (Groscup et al., 2002).
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7.5 Rebuttal Role of the Human Factors Expert after Daubert Given the potential lack of skill among judges (and, to a greater extent, the jury) to evaluate the use of the scientific method and determine reliability and relevance, it is also important to recognize and describe clearly for them the flaws in the opposing expert’s arguments (Kovera et al., 2002). In fact, it has been recognized that the Daubert decision was predicated on the assumption that a safeguard is built into the judicial process by the use of opposing expert evidence that is part of the adversarial process. Specifically, Daubert assumes that “presentation of opposing expert testimony, which contradicts flawed expert testimony, will sensitize jurors to the unreliability of the original expert evidence” (Kovera et al., 2002, p. 184). Given this significant responsibility, it is essential that human factors experts carefully evaluate the testimony of the opposing expert and educate the court on flaws in design, analysis, or interpretation. There are at least four major methods of rebuttal based on flaws in the opposing expert opinions. Each of these will be described next. Rebuttal of Mischaracterization of the Literature Demonstration of the mischaracterization of literature addresses the reliability and relevance of the opposing experts’ opinions in addition to consideration of the known error rate of the published research upon which they rely. This can occur in an expert rebuttal report in several ways: • It is common to read in expert reports that “a scientific body of knowledge” supports a given opinion. Many times no references are provided to delineate the body of knowledge and often no such body of knowledge exists. In the educator role, the rebutting expert should explain such discrepancies. In United States v. Rincon (1994), the Ninth Circuit upheld the trial court’s decision to exclude the proposed testimony of an expert in eyewitness identification. The declaration provided by counsel indicated that “there is a wealth of research supporting this point,” “the research is clear,” and “the research suggests.” Initially, the district court excluded the proposed testimony, indicating that “no showing has been made that the testimony relates to an area that is recognized as a science.” The appellate court indicated that “none of the research was submitted or described so that the district court could determine if the studies were indeed scientific on the basis the Court explained in Daubert? thus providing an indication that Daubert is interpreted as meaning that simply indicating that research exists is insufficient support for an expert opinion. When an article “General Acceptance of Psychological Research on Eyewitness Testimony” (Kassin et al, 1989) 8 was submitted (during the hearing in district court, which was remanded by the Ninth Circuit on remand from the U.S. Supreme Court), the Ninth Circuit found insufficient detail for the district court to determine the scientific validity. Furthermore, the Court of Appeals indicated that it based its support of the district court’s ruling on the lack of information provided by this expert in this case and not a general predisposition against expert testimony on eyewitness identification. The Court of Appeals stated, “Our conclusion does not preclude the admission of such testimony when the proffering party satisfies the standard established in Daubert by showing that the
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expert opinion is based upon ‘scientific knowledge’ which is both reliable and helpful to the jury in any given case.” • Often, references are provided but inspection reveals that they are nonscientific sources (popular magazines, newspapers, or thought papers) that have not been peer-reviewed or subjected to scientific testing. Thus, such statements may be extremely misleading to judges and juries who assume that the expert is relying on scientific sources. It is important to highlight this factor. As the Supreme Court stated in Daubert, peer review is not a prerequisite but it should be considered, particularly if an expert is presenting concepts from popular sources as if they were based on empirical research. • Even when scientific literature is presented by the opposing expert, it should be carefully reviewed to determine whether it supports the interpretations and conclusions for which it is proffered. It is possible for an expert to “cherry pick” sections of an article or book (for use in an expert report) that are not at all representative of the totality of the source. For example, in a product liability case concerning breast implants, the testimony of the plaintiff’s expert was excluded because of the unreliability of the two published studies that were introduced. In one study of the relationship between breast implants and Sjogren’s syndrome, the statistical significance level was 0.067 and the authors indicated that further research was necessary to confirm conclusions; in the second study, the authors indicated that there were limitations on their findings because of possible bias in their sampling techniques (Kelley v. American Heyer-Schulte Corporation, 1997). These qualifications of results were not presented by the expert who cited the research. • It is also common for experts to overstate the reliability of findings in the research. For example, the research in a given area may be equivocal and as yet undetermined with findings both supporting and opposing a given theory. It is important that the rebutting expert present the 8
This article reported the survey of 63 experts’ opinions about scientific acceptance of research on various topics.
missing perspective from the literature and/or demonstrate the flaws in the studies presented by the opposing expert. One might consider presenting information about the number of times a particular study has been cited based on listing in the Social Science Citation Index. It may also be useful to search for meta-analytic studies that provide insight into differences across individual studies that establish scientific reliability in the face of equivocal findings (Penrod et al., 1995). This approach, of course, introduces its own complexity in terms of explaining the statistical methodology to the judge or jury; nevertheless, it is becoming more common. Rebuttal of Misapplication of Scientific Literature to Case Facts The most difficult rebuttal to prepare is often the explanation of why a body of scientific literature does or does not apply to the facts in a particular case. Clearly, this is an important aspect of the Daubert factors as visualized by the Daubert court. The trier of fact makes the determination of “whether the reasoning or methodology underlying the
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testimony is scientifically valid and of whether that reasoning or methodology properly can be applied to the facts at issue” (Daubert at 2796). An example of this might be an expert who references a “significant body of literature on the relationship between driver fatigue and accidents,” suggesting that this literature supports his or her opinion that the performance of a truck driver involved in an accident was affected by fatigue. One cannot simply apply a body of literature to a given case without careful consideration of the research base for the literature and the facts of a case. If, upon inspection, it is determined that the research base of the literature proposed by the expert was measurement of fatigue and vehicle accidents among long-distance drivers, this may not be appropriate for application to local-haul drivers. In this situation, for example, the literature on fatigue and vehicle accidents specifically references the impact on long-haul drivers of irregular hours of work, significant periods of night driving, interrupted sleep patterns from sleeping in the truck cab, and potential use of stimulants. The research postulates that any or all of these factors may have an impact on vehicle accidents. As such, the research would not apply in a case of an accident involving a local-haul driver who did not work irregular hours, who did not perform night driving, who slept in his or her own home and did not have signs of interrupted sleep patterns, and who had not used any forms of stimulants. No matter how strong the relationship in the literature is between fatigue and vehicle accidents, if the research has been performed on long-haul drivers, it is of little value in the case at hand. A finding in the literature (based on long-haul drivers) that illustrates the inappropriateness of application to local-haul drivers is that “most instances in which drivers were judged to be drowsy occurred during the nighttime hours (between 7:00 p.m. and 6:59 a.m.)” (Hanowski et al., 1999, p. 378). These are not hours commonly worked by local-haul drivers and, as such, these results would be meaningless if applied to localhaul drivers. According to Daubert, “scientific validity for one purpose is not necessarily scientific validity for other purposes…. (FRE) Rule 702’s ‘helpfulness’ standard requires a valid scientific connection to the pertinent inquiry as a precondition to admissibility” (at 591). This example might also be considered more generally from the perspective of whether this literature has a known error rate. To quote from a keynote address to the Association of Professional Sleep Societies relative to these studies: Although…we have investigated many accidents in which sleep loss, sleep disorders, fatigue and circadian factors are clearly implicated, I don’t think we have the foggiest notion of the true prevalence of these factors in transportation system accidents. One of the most perplexing problems our accident investigators face is how to determine what role, if any, fatigue played in a specific accident. Unlike metal fatigue, human fatigue generally leaves no telltale signs and we can only infer its presence from circumstantial evidence (Brown, 1994, p. 309). One might also consider the applicability of this literature more generally from the perspective of the adequacy of the scientific methodology:
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There is broad, consensual agreement among transport professionals and the driving public alike about what constitutes unsafe or undesirable driving. It is common sense to pronounce that sleepy, intoxicated or sick drivers constitute a safety hazard to themselves and to other road users. However, there are theoretical problems surrounding the diagnosis of driver impairment beyond this anecdotal level. In the simplest case, the diagnosis of impairment due to alcohol intoxication is relatively straightforward. The amount of alcohol consumed may be measured by the blood alcohol concentration (BAC); this variable has an exponential relationship with accident likelihood…. There is no equivalent index for other categories of driver impairment such as fatigue. This absence may simply be a conceptual limitation. The individual often spontaneously perceives and can report changes in energetic state from a purely phenomenological perspective. In the absence of an anchor scale (such as BAC in the case of alcohol…), the multidimensional character of driver impairment renders the concept susceptible to an undesirable level of indeterminancy [sic]. Ambiguity at the conceptual level inevitably creates practical problems of measurement and interpretation. The limitation is particularly striking when attempting to measure the impact of multivariate energetic states on a complex skill such as driving (Brookhuis et al., 2003, p. 434). Rebuttal of Testimony Provided by Experts Testifying outside Their Area of Expertise Testifying outside one’s area of expertise can occur in any field. Many judges (45% compared to 24% of attorneys) believe that expert reports discourage such testimony (Krafka et al., 2002). However, within human factors, many experts in accident cases, for example, testify without experience or training in areas such as employee training or employee compensation. They will make statements related to a workplace accident resulting in injury such as “the worker was not properly trained in lockout procedures” or the “worker was not adequately trained in driver safety.” Similarly, it is common for experts to make statements such as “if the company had trained the drivers on specific conditions on rural roads with farm equipment, the accident would not have occurred.” These statements are made on the basis of common sense or intuition and may go unnoticed by a judge or jury unless challenged. “Common sense, like science, provides knowledge about natural phenomena, but it does not systematically establish connections between occurrences that are not obviously related” (Black et al., 1994, p. 754). This is a situation in which the opposing expert should identify the qualifications that are required for this testimony, such as education and/or experience in developing, evaluating, researching, or modifying employee training programs. It may not otherwise occur to a judge or jury that a body of science surrounds such issues. It is also useful, again as an educator, for the opposing expert to present the research literature on the identified issues. The same types of statements as “the worker was not properly trained in lockout procedures” can also be rebutted on the basis of the expert’s not relying on a scientific
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approach to arrive at this conclusion. As the Daubert court indicated, “Science is not an encyclopedia body of knowledge about the universe. Instead it represents a process for proposing and refining theoretical explanations about the world that are subject to further testing and refinement.” However, in order to qualify as “scientific knowledge,” an inference or assertion must be derived by the scientific method. Proposed testimony must be supported by appropriate validation—i.e., “good grounds,” based on what is known. In short, the requirement that an expert’s testimony pertains to “…‘scientific knowledge’ establishes a standard of evidentiary reliability” (Daubert court). Often experts will not only opine that “the worker was not properly trained” but also conclude that the “company was negligent in its training practices.” This latter point should be, but is almost never, based on a scientific approach. One cannot conclude from the behavior of one employee in one incident that training practices were inadequate. One must consider how probable it is that any training program would be 100% effective. That probability would be low. Thus, the expert would not have employed the necessary scientific rigor to arrive at such a conclusion by only considering the actions of the employee involved in an accident. Rebuttal of Misinterpretation of Scientific Findings Again, often without reference to a particular body of literature, experts may misinterpret scientific findings based on common-sense interpretations instead of empirical evidence. These opinions may make intuitive sense to the lay person, so it is essential that the opposing expert present the correct interpretations and concrete examples to demonstrate the error. For example, estimating reaction time is often an element in reconstructing a vehicular accident. This is an area about which jurors may believe (based on a cursory understanding of reaction time gained from reading a driver’s handbook or some other brief exposure to the concept) that an expert is presenting an accurate recreation of some accident or event. From this exposure, the jurors may readily agree with an expert in a vehicle accident case who opines that it took several seconds for the driver to begin responding. The expert will often establish this by breaking a behavior like stopping a car into multiple steps such as noticing an oncoming train, making a decision on what action to take, deciding to stop the car, moving the foot to the brake, and applying the brake. Calculated in this way, the response time is often “estimated” to be 2 sec or more (before adding time for the car to come to a stop based on speed and distance after application of the brake). In terms of the scientific literature on reaction time, numerous studies indicate that traditional simple and choice reaction time estimates are far shorter than experts independently calculate. Sanders and McCormick (1987) offer information on the approximate reaction time for situations with from 1 to 10 choices. Even if there are 10 choices of what behavior to take, the approximate reaction time is 0.65 sec. The estimated reaction time is only 0.35 sec with two choices and 0.20 sec with go/no go choice. Furthermore, studies that specifically consider driver behavior provide even more direct rebuttal evidence. Hills (1980) found that the mean time for 215 subjects to “transfer their foot from the accelerator pedal to the brake in response to a large stop signal” was 0.63 sec. Approximately 85% of the drivers in that study accomplished this
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task within 0.70 sec (p. 207). These types of studies can be used to rebut such overestimates of reaction time. However, the opposing expert must take the initiative to locate the appropriate studies and present them. Another area often handled inappropriately by experts is motion detection. Specifically, an expert may erroneously indicate that a vehicle driver was not looking in the direction of the train so did not recognize that a train was approaching. The expert will then begin calculations of reaction time at the point at which the driver oriented to the train (when the engineer blew the whistle, for example), implying that motion detection is a complex information-processing task. In fact, the literature indicates that the process of motion detection is almost instantaneous and that motion perception is actually more sensitive in the periphery of the visual field than the central retina (McBurney and Collings, 1984). Thus, one does not need to be looking directly at the train in order to notice it and begin a response. 7.6 Conclusion Daubert provided the courts with criteria for considering whether an expert’s testimony should be admitted or excluded. At the same time, this ruling provided experts with notice of what aspects of their work would be reviewed and evaluated by the court. It also offered insight into how opposing experts could “debunk” the opinions of the first expert. As such, Daubert offers experts a road map for how to perform the duties of an expert witness. This direct link between court procedures and expert witness behavior might be problematic if the U.S. Supreme Court had chosen other parameters of evaluation. No scientist wants to be directed in his or her work by a legal system that is presumably a nonscientific institution. However, because the legal system specified that it would carefully consider good scientific method, reliability, and relevance, there should be relatively few conflicts between the work that the expert would perform based on the expectations of his or her specialty field and that expected by the court. In fact, the U.S. Supreme Court specified that the expert’s methods should mirror those he or she would use outside the context of litigation. An expert can rarely, if ever, go wrong by following good scientific method and relying on well-developed research and literature in his or her field. References Allison v. McGhan Medical Corp., 184 F.3d 1300 (11th Cir. 1999). Black, B., Ayala, F.J., and Saffran-Brinks, C., 1994, Science and the law in the wake of Daubert a new search for scientific knowledge. Tex. Law Rev. , 72, 715–802. Brookhuis, K.A., De Waard, D., and Fairclough, S.H., 2003, Criteria for driver impairment. Ergonomics , 46, 433–445. Brown, I.D., 1994, Driver fatigue. Hum. Factors , 36, 298–314. Clark, M.W., 1996, The impact of Daubert on the admissibility of expert opinion. Advocate , April, 10–17.
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Daubert v. Merrell Dow Pharmaceuticals, Inc., 951 F.2d 1128 (9th Cir. 1991), vacated, 113 S.Ct. 2786 (1993). Dixon, L. and Gill, B., 2002, Changes in the standards for admitting expert evidence in Federal civil cases since the Daubert decision. Psychol, Public Policy, Law , 8(3), 251–308. Faigman, D.L., 1995a, Mapping the labyrinth of scientific evidence. Hastings Law J. , 46, 555–579. Faigman, D.L., 1995b, The evidentiary status of social science under Daubert is it “scientific,” “technical,” or “other” knowledge? Psychol., Public Policy, Law , 1, 960–979. Federal Judicial Center, 1994, Reference Manual on Scientific Evidence , 1st ed., Washington, D.C.: Federal Judicial Center. Federal Judicial Center, 2000, Reference Manual on Scientific Evidence , 2nd ed., Washington, D.C.: Federal Judicial Center. Federal Rules of Evidence, H.R. Rep. No. 8, 107th Cong., 2d Sess. (2002), Washington, D.C.: U.S. Government Printing Office. Gatowski, S.I., Dobbin, S.A., Richardson, J.T., Ginsburg, G.P., Merlino, M.L., and Dahir, V., 2001, Asking the gatekeepers: a national survey of judges on judging expert evidence in a postDaubert world. Law Hum. Behav. , 25, 433–458. Gless, A.G., 1995, Some post-Daubert trial tribulations of a simple country judge: behavioral science evidence in trial courts. Behav. Sci. Law , 13, 261–291. Groscup, J.L., Penrod, S.D., Studebaker, C.A., Huss, M.T., and O’Neil, K.M., The effects of Daubert on the admissibility of expert testimony in state and federal criminal cases. Psychology, Public Policy, and Law , 8, 339–372. Hanowski, R.J., Wierwille, W.W., Gellatly, A.W., Dingus, T.A., Knipling, R.R., and Carrol, R., 1999, Safety concerns of local/short haul truck drivers. Transp. Hum. Factors , 1(4), 377–386. Hills, B.L.,1980, Vision, visibility, and perception in driving. Perception , 9 , 183–216. Holden, C., 1998, Supreme Court clarifies junk science stance. Science , 279, 35. Huber, P.W., 1991, Galileo’s Revenge: Junk Science in the Courtroom , New York: Basic Books. Kassin, S.M., Ellsworth, P.C., and Smith, V.L., 1989, The “general acceptance” of psychological research on eyewitness testimony. Am. Psychologist , August, 1089–1098. Kelley v. American Heyer-Schulte Corp., 957 F. Supp. 873 (W.D. Tex. 1997). Kovera, M.B. and McAuliff, B.D., 2000, The effects of peer review and evidence quality on judge evaluations of psychological science: are judges effective gatekeepers? J. Appl Psychol , 85, 574–586. Kovera, M.B., Russano, M.B., and McAuliff, B.D., 2002, Assessment of the common sense psychology underlying Daubert legal decision makers’ abilities to evaluate expert evidence in hostile work environment cases. Psychol, Public Policy, Law , 8, 180–200. Krafka, C., Dunn, M.A., Johnson, M.T., Cecil, J.S., and Miletich, D., 2002, Judge and attorney experiences, practices, and concerns regarding expert testimony in federal civil trials. Psychol, Public Policy, Law , 8, 309–332. Krauss, D.A. and Sales, B.D., 1998, The problem of “helpfulness” in applying Daubert to expert testimony: child custody determinations in family law as an exemplar. Psychol, Public Policy, Law , 5, 78–99. Kumho Tire Co. v. Carmichael, 526 U.S. 137 (11th Cir. 1999). Lipton, J.P., 1999, The use and acceptance of social science evidence in business litigation after Daubert . Psychology, Public Policy, and Law , 5, 59–77. Mark, M.M., 1999, Social science evidence in the courtroom: Daubert and beyond? Psychol., Public Policy, Law , 5, 175–193. McBurney, D.H. and Collings, V.B., 1984, Introduction to Sensation/Perception , 2nd ed., Englewood Cliffs, NJ: Prentice Hall. Miller, P.S., Rein, B.W., and Bailey, E.O., 1994, Daubert and the need for judicial scientific literacy. Judicature , 77, 254–260.
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Penrod, S.D., Fulero, S.M., and Cutler, B.L., 1995, Expert psychological testimony on eyewitness reliability before and after Daubert the state of the law and the science. Behav. Sci. Law , 13, 229–259. Price, J.M. and Kelly, G.G., 1998, Junk science in the courtroom: cause, effects and controls. Hamline Law Rev. , 19, 395–407. Riley, S.E., 1996, The end of an era: junk science departs product liability. Defense Counsel J., 63, 502–508. Sanders J., 1994, Scientific validity, admissibility, and mass torts after Daubert . Minn. Law Rev. , 78, 1387–1441. Sanders, M.S. and McCormick, E.J., 1987, Human Factors in Engineering and Design , 6th ed., New York: McGraw-Hill. Sanders, J., Diamond, S.S., and Vidmar, N., 2002, Legal perceptions of science and expert knowledge. Psychology, Public Policy, and Law , 8, 139–153. Saxe, L. and Ben-Shakhar, G., 1999, Admissibility of polygraph tests: the application of scientific standards post-Daubert . Psychol., Public Policy, Law , 5, 203–223. Shuman, D.W. and Sales, B.D., 1999, The impact of Daubert and its progeny on the admissibility of behavioral and social science evidence. Psychol., Public Policy, Law , 5, 3–15. Shuman, D.W. and Sales, B.D., 2001, Daubert’s wager. J. Forensic Psychol. Pract. , 1, 69–77. Tenopyr, J.L., 1999, A scientist-practitioner’s viewpoint on the admissibility of behavioral and social scientific information. Psychol., Public Policy, Law , 5, 194–202. Thornton, G.C. and Wingate, P.H., (in press), Industrial and organizational psychologists as expert witnesses: Employment discrimination litigation post Daubert . In Landy, F.J. (Ed.), Employment Discrimination Litigation , San Francisco: Jossey-Bass. United States v. Rincon, 921 F.3d 28 (9th Cir. 1994). Vondrak, A., 1998, Junk science finally gets slammed. The Washington Times , 18 October, B5. Walker, L. and Monahan, J., 1996, The future of science in law. Va. Law Rev ., 82, 837–857. Worthington, D.L., Stallard, M.J., Price, J.M., and Goss, P.J., 2002, Hindsight bias, Daubert, and the silicone breast implant litigation: Making the case for court-appointed experts in complex medical and scientific litigation. Psychology, Public Policy, and Law , 8, 154–179.
II Human Performance in the Legal Context
8 Reconstructing Situated Performance in Human Error Investigations Sidney W.A.Dekker Lund University 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
Every scripture is entitled to be read in the light of the circumstances that brought it forth. To understand the choices open to people of another time, one must limit oneself to what they knew; see the past in its own clothes, as it were, not in ours. Barbara Tuchman, Practicing History: Selected Essays, 1981 (p. 75)
8.1 Introduction: How to Make Sense out of Puzzling Performance How could it have made sense for the pilot to continue his approach despite (what we now know to have been) increasingly bad weather? How could the shift operator have missed the valve setting that, in hindsight, appeared so obviously necessary? How could it have made sense for the surgeon to revert to an open procedure despite (what we now know as) indications that this would be more dangerous for the patient than the laparoscopic one? Forensic human factors experts can be called on to make sense out of such puzzling performances. However, making sense out of other people’s puzzling performances is incredibly difficult. It is difficult, in fact, for two different reasons. The first is that whenever we look at past performance, all kinds of biases start to cloud our ability to understand the reasons for people’s behavior. Even the human factors expert is not immune to this. William James called it the “psychologist’s fallacy”: we easily mistake our own reality for the one that surrounded people at the time. “Standards of care” become difficult to assess objectively, even by experts, when one is faced with the rubble of human failure. Even the expert can see, in all retrospective clarity, the choices that were open to people at a different time and even the expert can feel befuddled at how these people ended up picking the wrong ones. This hindsight bias is persistent. It will confound anybody’s attempt at making sense of past puzzling performance if it is not recognized and controlled. This is discussed in the subsection “Recognizing and Controlling the Hindsight Bias.”
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The second reason why it is difficult to make sense of other people’s puzzling performance is a technical one. Technical, in this sense, refers to the human factors theories, issues, or concepts that could shed light on why people did what they did. Scientifically, it refers to the problem of how to make a credible, traceable connection between the behavioral sequence (which played out in a particular setting) and a human factors concept that covers what went on in there. Matching the context-specific particulars of an accident sequence with a human factors explanation may seem straightforward. For example, the human factors expert could note how, in a cockpit voice recording, pilots were asking each other questions about direction or the location of navigational way-points before crashing into a mountain. The expert then proclaims that the pilots “lost situation awareness.” Yet this only conveys the illusion of understanding. Large labels such as this may sound appealing in a courtroom, but if no verifiable connection is shown between the label and the data it supposedly covers, then it explains nothing. It amounts to folk- or pseudoscience and can easily be attacked by the opposite side on credibility issues alone. Folk modeling fools the advised team members into believing that they have learned something of value. The traps here are severe and deep and need to be discussed (see the subsection “Reconstructing Behavioral Sequences”). The two difficulties are not separate, nor are the ways to deal with each. In fact, much of what human factors calls protocol analysis, or process tracing, is aimed at reconstructing the situation as it evolved from the point of view of the people involved in it at the time. Reconstructing the situation provides a relatively unambiguous scaffolding upon which to hang people’s puzzling assessments and actions. People assessed and acted inside that situation: their performance was “situated.” Thus, if the situation is understood in detail, maybe their assessments and actions will be, too. Much recent human factors work and cognitive theory back this up (see subsection “Reconstructing Behavioral Sequences”). Such reconstruction also persuades the analyst not to judge the situation from a position as omniscient 20/20 retrospective outsider, but from the perpetually incomplete and unfolding perspective of the people caught up in the situation. Such reconstruction continually pulls the analyst away from the lofty hindsight outlook where he enjoys the vista of a completely evolving situation and its disastrous outcome. It compels the analyst back into the trenches where assessments and decisions were actually made with a restricted outlook, under time pressure, with limited knowledge, and under uncertainty— to see how the world looked from there and what it would have been like to assess, decide, and act under those circumstances. In the end, whether standards of care were adhered to can honestly be assessed only when the locally limited perspective of the protagonist is taken and any reference to outcome is erased. Indeed, the quality of decisions cannot be evaluated on the basis of their outcome because the people making those decisions at the time did not know the outcome. The subsection “Recognizing and Controlling the Hindsight Bias” is reserved for more discussion on this.
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8.2 Objective and Scope of the Chapter This chapter deals with the two difficulties mentioned previously. The subsection “Recognizing and Controlling the Hindsight Bias” shows human factors experts and those who consult them how to recognize and control the hindsight bias. The subsection “Reconstructing Behavioral Sequences” discusses how to reconstruct situated performance technically without getting trapped in pseudoscience. Section 8.4 offers some examples. The chapter then concludes with a checklist for quick reference, defining terms, and references. 8.3 Discussion of Principal Issues Recognizing and Controlling the Hindsight Bias Human factors experts and attorneys know more about the incident or accident than the people who were caught up in it, thanks to hindsight (Fischoff, 1975), which: • Means being able to look back, from the outside, on a sequence of events that led to an outcome they already know about • Provides almost unlimited access to the true nature of the situation that surrounded people at the time (where they actually were vs. where they thought they were or what state their system was in vs. what they thought it was in) • Allows them to pinpoint what people missed and should not have missed and what they did not do but should have done From the perspective of the outside and hindsight, people can oversee the entire sequence of events—the triggering conditions, its various twists and turns, the outcome, and the true nature of circumstances surrounding the route to trouble. This is in stark contrast with the perspective from the inside of the situation. To people inside, neither the outcome nor the entirety of surrounding circumstances was known. Time to decide and act was pressurized. Resources (to think, to ask around, to reflect) were limited. These people contributed to the direction of the sequence of events on the basis of what they knew and saw on the inside of the unfolding situation then, not on the basis of what the expert knows now, looking back from the outside. Any human factors expert who takes the retrospective position and pretends to explain people’s behavior from there is not a real human factors expert. However, although critical for determining whether standards of care were met, it is very difficult to attain the insider perspective. The mechanisms by which hindsight operates are powerful and mutually reinforcing. Together they continually pull in the direction of the position of the retrospective outsider. The ways in which even human factors experts retrieve performance evidence from the rubble of an accident, represent it, and retell it typically sponsor this migration of viewpoint. I discuss three of those mechanisms here so that the various stakeholders can be aware of how they operate.
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Making Tangled Histories Linear by Cherry-Picking and Regrouping Evidence One effect of hindsight is that “people who know the outcome of a complex prior history of tangled, indeterminate events, remember that history as being much more determinant, leading ‘inevitably’ to the outcome they already knew” (Weick, 1995, p. 28). Hindsight allows us to change past indeterminacy and complexity into order, structure, and oversimplified causality (Reason, 1990). In trying to make sense of past performance, it is always tempting to group individual fragments of human performance, rear-range them linearly, and then make them point to some prima facie condition or mindset. For example, “hurry” to land is a leitmotif extracted from the evidence in the following investigation, and that haste in turn is enlisted to explain the errors that were made: Investigators were able to identify a series of errors that initiated with the flightcrew’s acceptance of the controller’s offer to land on runway 19… The CVR indicates that the decision to accept the offer to land on runway 19 was made jointly by the captain and the first officer in a 4-second exchange that began at 2136:38. The captain asked, “Would you like to shoot the one nine straight in?” The first officer responded, “Yeah, we’ll have to scramble to get down. We can do it.” This interchange followed an earlier discussion in which the captain indicated to the first officer his desire to hurry the arrival into Cali, following the delay on departure from Miami, in an apparent [attempt] to minimize the effect of the delay on the flight attendants’ rest requirements. For example, at 2126:01, he asked the first officer to “keep the speed up in the descent”…[This is] evidence of the hurried nature of the tasks performed (Aeronautica Civil, 1996, p. 29). The fragments used to build the argument of haste come from over half an hour of extended performance. This excerpt treats the record as if it were a public quarry to pick stones from, and the accident explanation as the building that needs erecting. The problem is that each fragment is meaningless outside the context that produced it; each fragment has its own story, background, and reasons for being, and when it was produced it may have had nothing to do with the other fragments with which it is now lumped. Also, behavior takes place in between the fragments. These intermediary episodes contain changes and evolutions in perceptions and assessments that separate the excised fragments not only in time, but also in meaning. Thus, the condition and the constructed linearity in the story that binds these performance fragments arise not from the circumstances that brought each of the fragments forth; it is not a feature of those circumstances. It is an artifact of hindsight. In the case described here, “hurry” is a condition identified after the fact—one that plausibly couples the start of the flight (almost 2 hours behind schedule) with its fatal ending (on a mountainside rather than an airport). “Hurry” is a retrospectively invoked leitmotif that guides the search for evidence about itself. It produces a linear, plausible story that, nevertheless, is founded on tautologies, not findings.
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Finding What People Could Have Done to Avoid the Accident Tracing the sequence of events back from the outcome, which we already know about, we invariably come across junctures at which people had opportunities to revise their assessment of the situation but failed to do so; people were given the option to recover from their route to trouble, but did not take it. These are counterfactuals and are quite common in forensic analysis. For example, “The airplane could have overcome the windshear encounter if the pitch attitude of 15 degrees nose-up had been maintained, the thrust had been set to 1.93 EPR [engine pressure ratio] and the landing gear had been retracted on schedule” (NTSB, 1995, p. 119). Counterfactuals prove what could have happened if certain minute and often Utopian conditions had been met. However, saying what people could have done in order to prevent a particular outcome does not explain why they did what they did. Counterfactuals circumvent the human factors expert’s difficult problem: finding out why people actually did what they did. Counterfactuals are a powerful tributary to hindsight bias. They help impose structure mostly in the form of easy, binary choices. For example, people could have perfectly executed the go-around maneuver, but did not; they could have denied the runway change, but did not. As the sequence of events rewinds from its outcome, the story of missed opportunities and failed perceptions and wrong decisions rolls into time in reverse: all these options to do the right thing and they were ignored! Attorneys have a field day. How could they have been so stupid…so ignorant…so negligent? The role of the human factors expert here is to counsel caution: human work in complex, dynamic worlds is seldom about simple dichotomous choices (as in: to err or not to err). Bifurcations are rare—especially those that yield clear previews of the respective outcomes at each end. In reality, people’s choice moments (such as there are) typically offer multiple possible pathways that stretch out, like cracks in a window, into the ever-denser fog of futures that were not yet known. Their outcomes are indeterminate, hidden in what is still to come. In reality, actions need to be taken under uncertainty and under the pressure of limited time and other resources. What from the retrospective outside may look like a discrete, leisurely, two-choice opportunity not to fail is, from the inside, just one fragment caught up in a stream of surrounding actions and assessments. In fact, from the inside it may not look like a choice at all. These are often choices only in hindsight. To the people caught up in the sequence of events, there was perhaps not any compelling reason to reassess their situation or decide against anything (or else they probably would have) at the point that an attorney has now found significant or controversial. They were likely doing what they were doing because they thought they were right, given their understanding of the situation and their pressures. The challenge for the human factors expert becomes to understand how this may not have been a discrete event to the people whose actions are under investigation. The expert needs to make clear how other people’s “decisions” to continue were likely nothing more than continuous behavior—reinforced by their current understanding of the situation, confirmed by the cues on which they were focusing, and reaffirmed by their expectations of how things would develop.
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Judging People for What They Did Not Do but Should Have Done When counterfactuals are used, even as explanatory proxy, they often require explanations as well. After all, if an exit from the route to trouble stands out so clearly, how was it possible for other people to miss it? If there was an opportunity to recover, not to crash, kill, or die, then failing to grab that opportunity demands an explanation. The place where attorneys often look is the set of rules, professional standards, and available data that surrounded people’s operation at the time, and how people did not see or meet that which they should have seen or met. Mismatches between what the rules said and people did or available data that were not noticed are easily chalked up as negligence. For the human factors expert, it is important to recognize that pointing to such mismatches is merely judging people for not doing what they (in perfect hindsight) could or should have done. It does not explain anything. Procedures Were Not Followed When fragments of behavior are contrasted with written guidance found to have been applicable in hindsight, actual performance is often found wanting; it does not live up to procedures or regulations. For example, “One of the pilots…executed [a computer entry] without having verified that it was the correct selection and without having first obtained approval of the other pilot, contrary to procedures” (Aeronautica Civil, 1996; p. 31). Attorneys invest considerably in organizational archeology so that they can construct the regulatory or procedural framework within which the operations took place or should have taken place. Inconsistencies between existing procedures or regulations and actual behavior are easy to expose when organizational records are excavated after the fact and rules uncovered that would have fit a particular situation. This is not, however, very informative. There is virtually always a mismatch between actual behavior and written guidance that can be located in hindsight (Suchman, 1987; Woods et al., 1994). Pointing out that there is a mismatch sheds little light on the why of the behavior in question. For that matter, mismatches between procedures and practice are not unique to mishaps (Degani and Wiener, 1991), and some of the most dangerous, yet safest, work is carried out entirely without procedures (Rochlin, 1999). The role of the human factors expert is not to parrot that procedural guidance was not adhered to because this, again, explains nothing. The challenge is to elucidate how a procedure is never the job: that situated work requires the skillful application and sometimes adaptation of written guidance, which is substantive cognitive work. Available Data Were Not Noticed Another route to constructing a world against which attorneys hold individual performance fragments is to find all the cues in a situation that were not picked up by the practitioners, but that, in hindsight, proved critical. Take the turn toward the mountains on the left that was made just before an aircraft collided with one of them (Aeronautica Civil, 1996). What should the crew have seen in order to notice the turn? They had plenty of indications:
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Indications that the airplane was in a left turn would have included the following: the EHSI [electronic horizontal situation indicator] map display (if selected) with a curved path leading away from the intended direction of flight; the EHSI VOR display, with the GDI [course deviation indicator] displaced to the right, indicating the airplane was left of the direct Cali VOR course, the EaDI indicating approximately 16 degrees of bank, and all heading indicators moving to the right. Additionally the crew may have tuned Rozo in the ADF and may have had bearing pointer information to Rozo NDB on the RMDI (Boeing, 1996, p. 13). This is a standard response after mishaps: point to the data that would have revealed the true nature of the situation. Knowledge of the “critical” data comes only with the omniscience of hindsight, of course. However, if data can be shown to have been physically available, it is assumed that this information should have been picked up by the practitioners in the situation. The problem is that pointing out that it should have does not explain why it was not, or why it was interpreted differently back then (Weick, 1995). The role of the human factors expert here is to explain that in complex, dynamic work, cues and indications about the true nature of the situation emerged over time, in the midst of other, competing cues, tasks, priorities, and pressures. Attorneys can be fond of presenting a shopping bag full of epiphanies (“Look at all these indications! How could they have missed all of this?”), but this is far from how cues and indications reached people inside the situation at the time. Indeed, there is a dissociation between data availability and data observability (Woods et al., 1994)—between what can be shown to have been physically available and what would have been observable given the multiple interleaving tasks, goals, attentional focus, interests, and, as Vaughan (1996) shows, culture of the practitioner. The role of the human factors expert is to explain why there is a mismatch between data availability and data observability: how it would have made sense for people to see what they saw and to interpret it the way that they did. Professional Standards Were Not Met There are also less obvious or not-documented standards. These are often invoked when a controversial fragment (e.g., a decision to accept a runway change [Aeronautica Civil, 1996] or the decision to go around or not [NTSB; 1995]) knows no clear preordained guidance but relies on local, situated judgment. For these cases there are always “standards of good practice” based on convention and putatively practiced across an entire industry. One such standard in aviation is “good airmanship,” which will explain the variance in behavior not yet accounted for, if nothing else can. Judging Instead of Explaining Performance It is always easier to judge than to explain performance, even for human factors experts. A number of recent labels make it even easier to judge. They appear to be explanations of human error, but are just reinventions of it, stating what people should have done but did not do, or should not have done but did do, for example: • Loss of crew resource management (CRM)—judging people for failing to invest in common ground, to share data that proved operationally significant in hindsight
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• Loss of situation awareness—judging people for their failure to notice things that, in hindsight, turned out to be critical. Loss of situation awareness says only that you now know more about the situation than the people who were caught up in it at the time. This explains nothing, but only judges them for not knowing what you know now. • Complacency—a judgment of people’s failure to recognize the gravity of a situation as you now know it, or to follow procedures or standards of good practice that you match in hindsight with their circumstances Judgments, by whatever (modern) label, frame people’s past assessments and actions in a world that is invoked or built retrospectively. The problem is that this after-the-fact world has very little relevance to the actual world that produced the behavior in question. The behavior is contrasted against a retrospective, complete reality, not the unfolding, incomplete reality surrounding (and producing) the behavior at the time. Judging people for what they did not do relative to some rule or standard does not explain why they did what they did. Saying that people failed to take this or that pathway (only in hindsight the right one) judges other people from a position of outcome knowledge that they did not have. It does not explain a thing; it does not shed any light on why people did what they did given their surrounding circumstances. The professional commitment of the human factors expert is not to judge behavior (that should be left to others), but to explain behavior. Human factors experts should understand that human error by whatever label (“loss of SA”) is not an explanation. Instead, human error demands an explanation. Resisting the urge to judge instead of explain can be challenging. Most people, in order to explain failure, will seek failure. In order to explain dead bodies on a hillside (failure), they want to lay out the prior missed opportunities and bad choices (failures). In order to explain those, they in turn seek flawed analyses, inaccurate perceptions, violated rules, or negligence (failures), even if none of these was influential or obvious or flawed or even true at the time (Starbuck and Milliken, 1988). This search for people’s failures is another well-documented effect of the hindsight bias: knowledge of outcome fundamentally influences how people see a process. If people know the outcome was bad, they can no longer objectively look at the behavior leading up to it—it must also have been bad (Fischoff, 1975; Woods et al., 1994; Reason, 1997). Given this, the human factors expert must recognize that accuracy or, really, truthfulness is not a criterion for a successful legal forensic explanation; however, plausibility is, even if, in the words of Weick (1995), it all makes “lousy history.” Local Rationality: Nobody Comes to Work to Do a Bad Job What is striking about many accidents in complex systems is that people were doing exactly the sorts of things they would usually be doing—the things that usually lead to success and safety. Mishaps are more typically the result of everyday influences on everyday decision making than they are isolated cases of erratic individuals behaving unrepresentatively (e.g., Perrow, 1984; Woods et al., 1994; Reason, 1997; Amalberti, 2001). People are doing what makes sense given the situational indications, operational pressures, and organizational norms existing at the time. Accidents are seldom preceded by bizarre behavior. Because of the hindsight bias, this is very difficult to accept for most people. It is frightening, too. Rather than changing their beliefs about the system in which the
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accident took place (“Hey, it can actually happen and it is not that abnormal”), people will change their beliefs about the players who took part in creating the accident (“Look at how bad, how uncharacteristically negligent these operators were”). They will often embrace an account that singles out limited groups of people (departments, ethnic clans) or individuals (e.g., operators) for their responsibility because it is easier to grasp. This is called the fundamental surprise error (Lanir, 1986), which limits the need for any systemic doubt and changes the accident into a merely local “hiccup” (due to erratic, nonrepresentative individuals) that temporarily ruffled an otherwise smooth operation. The reassurance is that the system is basically safe and only some people or other parts in it are unreliable. In the end, it is not often that an existing view of a system gives in to the reality of failure. Instead, the event or the players in it are changed to fit existing assumptions and beliefs about the system, rather than the other way around. Good attorneys know this and capitalize on it. In reality, however, human errors are seldom just about the people who committed them. People’s errors and mistakes (such as can be found in any objective sense) are systematically coupled to their circumstances, tools, and tasks. Indeed, a most important empirical regularity of human factors research since the mid-1940s is the local rationality principle. What people do makes sense to them at the time; it must or they would not do it. People do not come to work to do a bad job; they are not out on crashing cars or airplanes or grounding ships. The local rationality principle says that people do things that are reasonable, or rational, based on their limited knowledge, goals, and understanding of the situation and their limited resources at the time (Woods et al., 1994). Avoiding the mechanisms of the hindsight bias means acknowledging that failures are baked into the nature of people’s work and organization and are symptoms of deeper trouble or by-products of systemic brittleness in the way business is done. It means needing to find out why the things people did at the time actually made sense, given the situation that surrounded them. Reconstructing Behavioral Sequences To understand what went on in people’s minds, we first must understand the situation in which those minds found operated. Basic findings from cognitive science and related fields keep stressing how human performance is fundamentally embedded in, and systematically connected to, the situation in which it takes place (Neisser, 1976; Gibson, 1979; Winograd and Flores, 1987; Varela et al., 1995; Clark, 1997). Human actions and assessments can be described meaningfully only in reference to the world in which they are made; they cannot be understood without intimately linking them to details of the context that produced and accompanied them (Orasanu and Connolly, 1993; Woods et al., 1994; Hutchins, 1995; Klein, 1998). Some human factors experts favor traditional information-processing approaches for explaining people’s performance difficulties. To understand what went on in the mind, they will try to look into the mind. For example, they will assert that particular data were not noticed because of an overloaded working memory (which can only contain seven plus or minus two chunks of information). This approach explains performance shortcomings by reference to constraints imposed by hypothesized internal mental mechanisms (like working memory). The problem is that such assertions are difficult to
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verify because we still do not know whether something like a working memory actually exists and, if it exists, how it really works. Looking into the mind is singularly difficult. The alternative approach, often called the ecological approach, tries to understand performance problems by reference to constraints imposed by the world on people’s goaldirected behavior. The commitment of the ecological approach is to look first at the evolving situation in which the mind found itself and then reconstruct how features of that situation shaped assessments and actions. There is a lot of merit in human factors experts taking this approach also for credibility reasons. Past situations can be objectively reconstructed to a great extent and are often documented in detail; there are tight and systematic connections between situations and behavior—between what people did and what happened in the world around them. These connections between situations and behavior work both ways. People change the situation by doing what they do, by managing their processes. However, the evolving situation also changes people’s behavior. An evolving situation provides changing and new evidence; it updates people’s understanding, presents more difficulties, and forecloses or opens pathways to recovery. Human factors experts can uncover the connections between situation and behavior; investigate, document, and describe them; and represent them graphically. Other people can look at the reconstructed situation and how they related it to the behavior that took place inside it. Other people can actually trace the explanations and conclusions. Starting with the situation brings a human error investigation out into the open. It does not rely on hidden psychological structures or processes, but instead allows verification and debate by those who understand the domain. When a human error investigation starts with the situation, it sponsors its own credibility. A large part of human factors analysis, then, is not at all about the human behind the error. It is about the situation in which the human was working, the tasks he or she was carrying out, and the tools that were used. It is about reestablishing the connections between: • How the process, the situation, changed over time • How people’s assessments and actions evolved in parallel with their changing situation • How features of people’s tools and tasks and their organizational and operational environment influenced their assessments and actions inside that situation This is what the following five steps discuss. Step 1: Lay Out the Sequence of Events in Context-Specific Language The record and other data about an incident typically reveal a sequence of activities— human observations, actions, assessments, and decisions—as well as changes in the state of the process or system. The goal is to examine how people’s mindsets unfolded in parallel with the situation evolving around them, and how people, in turn, helped influence the course of events. Cues and indications from the world influence people’s situation assessments, which in turn inform their actions; these, in turn, change the world and what it reveals about itself, and so forth. This means that if certain actions or assessments are difficult to interpret, the circumstances (and particularly what was observable about them) in which they appeared can hold the key to their sensibility. Indeed, the reconstruction of mindset often begins not with the mind, but with the situation in which the mind found itself.
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Similarly, if there is a lack of data from system or process sources, certain behaviors that are canonical in particular process states can help reconstruct the state of cues and indications observable at the time. There are various entries to scour the record for events and activities: • Shifts in behavior. There can be points at which people may have realized that the situation was different from what they believed it to be previously. One can see this in their remarks or their actions. These shifts are markers where later one will want to look for the indications unfolding around them that people may have used to come to a different realization. • Actions to influence the process. These may come from people’s own intentions. Depending on the kinds of data that the domain records or provides, evidence for these actions may not be found in the actions, but in process changes that follow from them. As a clue for a later step, such actions also form a nice little window on people’s understanding of the situation at that time. • Changes in the process. Any significant change in the process that people manage must serve as evidence. Not all changes in a process managed by people actually come from people. In fact, increasing automation in a variety of workplaces has led to the potential for autonomous process changes almost everywhere, for example: • Automatic shutdown sequences or other interventions • Alarms that go off because a parameter crossed a threshold • Uncommanded mode changes • Autonomous recovery from undesirable states or configurations However, even if they are autonomous, these process changes do not happen in a vacuum. They always point to human behavior around them, behavior that preceded it, and behavior that followed it. People may have helped to get the process into a configuration in which autonomous changes were triggered. When changes happen, people may or may not notice or respond to them. Such actions, or the lack of them, again give a strong clue about people’s knowledge and current understanding. The way to capture these events and activities during this stage is in context-specific language, which means a minimum of psychological diction; instead, a version of what happened in terms that domain people use to talk about their own work is created. The goal is to miss as few details as possible. Skipping to higher-level descriptions of human performance is seductive, even at this stage, but should be avoided. Seemingly low-level concepts, such as decision making or diagnosis, already are large (meaning they contain a lot of behavior) and are easily mistaken for detailed insight into psychological issues (Woods, 1993; Hollnagel, 1998). Time (and/or space) can be a powerful organizing principle to help lay out the activities and events. Behavior, and the process in which it took place, unfolded over time and, probably, in some space. By organizing data spatially and temporally (e.g., through drawing maps or timelines or both), actions and assessments can become more clearly coupled to the process state and location in which they took place; they can recover their spot in the flow of events of which they were part and that helped bring them forth. Such
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organization likely yields further clues about why actions and assessments made sense to people back there and then. Step 2: Divide the Sequence of Events into Episodes, If Necessary Accidents do not simply happen; they evolve over a period of time. Sometimes this time may be long and, when it is, it may be fruitful to divide the sequence of events into separate episodes that each deserve their own further human performance analysis. Cues about where to “chunk up” the sequence of events can mostly come from the domain description arrived at earlier, especially at discontinuities in human assessments or actions or process states. There is, of course, inherent difficulty in deciding what counts as the overall beginning of a sequence of events (especially the beginning; the end often speaks for itself). Because, philosophically, there is no such thing as a root cause, there is technically no such thing as the beginning of a mishap. Yet the investigation needs to start somewhere. Making clear where it starts and explaining this choice is a good step toward a structured, well-engineered human performance investigation. Here is one option: take as the beginning of the first episode the first assessment, decision, or action by people or the system close to the mishap—the one that, according to you, set the sequence of events in motion. This assessment or action can be seen as a trigger for the events that unfold from there. Of course, the trigger has a reason, a background, that extends back beyond the mishap sequence in time and in place. The whole point of taking a proximal action or event as the starting point is not to ignore this background, but to identify concrete points to begin the investigation into it. Step 3: Discover How the World Looked or Changed during Each Episode This step is about reconstructing the unfolding world that people inhabited: find out what their process was doing and the data available. This is the first step toward coupling behavior and situation—toward putting the observed behavior back into the situation that produced and accompanied it. Laying out how some of the critical parameters changed over time is nothing new to investigations. Many accident report appendices contain read-outs from data recorders that show the graphs of known and relevant process parameters. However, building these pictures is often the point at which investigations stop today. Tentative references about connections between known parameters and people’s assessments and actions are sometimes made, but never in a systematic or graphic way. The point here is to marry all the events that have been identified with the unfolding process—to begin to see the two in parallel as an inextricable, causal dance-adeux. The point of this step is to build a picture that shows these connections. The record will most likely contain some kind of data about how process parameters were changing over time (e.g., speed until impact, but also traces of changing pressures, ratios, settings, quantities, automation or computer modes, rates, and so forth) and how these were presented to the people in question. Considerable domain knowledge (from the human factors expert or from outside) may be necessary to determine which of the parameters could have counted as a stimulus for the behavior under investigation. The
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difficulty (reflected in the next step) will be to move from merely showing that certain data were physically available to arguing which of these data were actually observable and made a difference in people’s assessments and actions and why this made sense to them back then. Step 4: Identify People’s Goals, Focus of Attention, and Knowledge Active at the Time What, out of all the data available, did people actually see and how did they interpret it? Given that human behavior is goal directed and governed by knowledge activated in situ, clues are available from looking at people’s goals at the time, and at the knowledge activated to help pursue them. Finding the goals on which people were working does not need to be difficult. It often connects directly to how the process was unfolding around them: • What was canonical or normal at this time in the operation? Tasks (and the goals they represent) relate in systematic ways to stages in a process. • What was happening in the process managed by the people? Systems were set or inputs were made—changes that connect to the tasks people were carrying out. • What were other people in the operating environment doing? People who work together on common goals often divide the necessary tasks among them in predictable or complementary ways. There may be standard role divisions, for example, between pilot flying and pilot not flying, that specify the work for each. It is seldom the case, however, that only one goal governs what people do. Most complex work is characterized by multiple goals, all of which are active or must be pursued at the same time (on-time performance and safety, for example). Depending on the circumstances, some of these goals may be at odds with one another, producing goal conflicts. Any analysis of human performance must take the potential for goal conflicts into account. Goal trade-offs can be generated by the nature of the work. For example, anesthesiologists need to maximize preoperative workup time with a patient to guard patient safety and quell liability concerns, while their schedules interlock with other professions that exercise pressure with respect to timing. Goal conflicts can also precipitate from the organizational level. In this case, not all goals (or their respective priorities) are written down in guidance or procedures or job descriptions. In fact, most are probably not. This makes it difficult to trace or prove their contribution to particular assessments or actions. However, previous occurrences in similar circumstances or in the same organization may yield powerful clues. They can substantially influence people’s criterion setting with respect to a goal conflict. For example, a decision to take off or not to take off in bad weather may be precluded by earlier incidents or, conversely, encouraged by organizational reactions to lack of on-time performance. When it comes to knowledge, not all knowledge that people once possessed is necessarily available when called for. In fact, the problem of knowledge organization (is it structured so that it can be applied effectively in operational circumstances?) and inert knowledge (even if it is there, does it get activated in context?) should attune human factors experts to mismatches between how knowledge was acquired and how it is to be
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applied in practice. For example, if material is learned in neat chunks and static ways (books and most computer-based training) but needs to be applied in dynamic situations that call for novel and complex combinations, inert knowledge is a risk (Woods et al., 1994). What people know and what they try to accomplish jointly determine where they will look and direct their attention and, consequently, which data will be observable to them (Neisser, 1976). Recognize that this is, once again, the local rationality principle. People are not unlimited cognitive processors (there are no unlimited cognitive processors in the universe). People do not know and see everything all the time, so their rationality is limited, or bounded. What people do, where they focus, and how they interpret cues make sense from their point of view: their knowledge, objectives, and limited resources (e.g., time, processing capacity, workload). Re-establishing people’s local rationality will help one to understand the gap between data availability and what people actually saw or used. In dynamic situations, people direct their attention as a joint result of: • Their current understanding of the situation, which in turn is determined partly by their knowledge and goals. Current understanding helps people form expectations about what should happen next (as a result of their own actions or as a result of changes in the world). • What happens in the world. Particularly salient or intrusive cues will draw attention even if they fall outside people’s current interpretation of what is going on. Keeping up with a dynamic world, in which situations evolve and change, is a demanding part of much operational work and implies two different kinds of “errors.” People may fall behind during rapidly changing conditions and update their interpretation of what is happening constantly, trying to follow every little change in the world. Conversely, people may become locked in one interpretation, even while evidence around them suggests that the situation has changed (see De Keyser and Woods, 1990). Step 5: Step Up to a Conceptual Description The goal here is to build an account of human performance that runs parallel to the one created in the first step. This time, however, the language that describes the same sequence of events is not one of domain terms; it is one of human factors or psychological concepts. One reason for the importance of this step perhaps goes beyond the mandate of an individual investigation. Getting away from the context-specific details—in a language that may not communicate well with other context-specific sequences of events—opens a crucial way to learn from failure: discovering similarities between seemingly disparate events. Instead, if people stress the differences between sequences of events, learning anything of value beyond the one event becomes difficult (Rochlin, 1999). Similarities between accounts of different occurrences can point to common conditions that helped produce the problem under investigation. The Risk of Pseudoscience in Human Factors Testimony The challenge for the human factors expert is to build up an account that moves from the context-specific to the concept-dependent gradually, leaving a clear trace for others to
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follow, verify, and debate. However, given that the audience of a human factors expert often consists of lay people (e.g., juries and judges), there is a huge risk of human factors pseudoscience slipping into the testimony. Pseudoscience here refers to human factors experts drawing grand conclusions (that sound good) without making a strong theorybased or analytical connection between those conclusions and the actual data about which they speak. In pseudoscience, there is an empty space between the context-specific data and the conceptual description of those data—between the modeled and the model. For example, one cockpit voice recording captured pilots asking questions about the direction of a particular waypoint. The grand conclusion is that “deficient situation awareness is evident” (Aeronautica Civil, 1996, p. 34) and that “the CRM (crew resource management) of the crew was deficient” (Aeronautica Civil, 1996, p. 47). Such “explanations” frequently make it into conclusions and statements of cause and even into human factors testimony. For example, “Aeronautica Civil determines that the probable causes of this accident were:…(3) the lack of situational awareness of the flightcrew…” (1996, p. 57). None of this explains anything. The labels used (e.g., loss of situation awareness or loss of CRM) are theory-begging folk models that do little more than parrot popular contemporary consensus between experts and nonexperts on the nature of an everyday phenomenon, for example, getting lost or confused (Hollnagel, 1998). Juries and judges can understand it, but that does not mean that it technically explains anything. Human factors is more in vogue than it was (this volume is one testimony to that), and, as a result, researchers and others have introduced, loaned, or overgeneralized concepts that try to capture critical features of individual or coordinative behavior and make for accessible lay labels, for example, workload, complacency, stress, and situation awareness. Although easily mistaken for deeper insight into human factors issues by those who do not know any better, these concepts can create more confusion than clarity. The problem is that folk models typically lack the human performance measures or probes that would be necessary to reach down into the context-specific details because they postulate no underlying psychological theory that could deliver any (Hollnagel, 1998). A credible and detailed mapping between the context-dependent (and measurable) particulars of an accident sequence and pertinent conceptual models is often lacking. The jump from accident details to conceptual conclusions is typically a single and large one, which immunizes it against critique or verification. For example, when one pilot asks the other, “Where are we?” (Aeronautica Civil, 1996, p. 33), this may be a clear instance of a loss of situation awareness to a lay observer. However, there is nothing in models of situation awareness (e.g., Endsley, 1999) that dictates that this would be so. The model proposes no performance measurement based on an underlying psychological theory, i.e., that asking a question involving direction indicates a loss of situation awareness. This is similar to the issue faced by psychological field studies, in which the translation from context to concept needs to go through various steps or levels in order for those without access to the original situation to trace and appreciate the conceptual description (Woods, 1993). In other words, by drawing such a grand conclusion in one grand leap, the human factors expert leaves no trace for others to critique or follow. It is unverifiable and nonanalytic and, by definition, pseudoscience.
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The steps presented earlier are one way to establish a more verifiable mapping between the particulars of context-specific behavior in an accident episode on the one hand and models or descriptions of human performance on the other. Starting with the situation and how it unfolded in parallel with people’s assessments and actions is a good way to leave a trace and a credible human factors analysis (see Woods, 1993; Klein, 1998; and Dekker, 2002, for more achievement in this respect). To be sure, any explanation of past performance that the human factors expert arrives at remains a fictional story, an approximation or tentative match open to revision as new evidence may come in or as other interpretations cover and explain more of the data. In the words of Woods (1993, p. 238): A critical factor is identifying and resolving all anomalies in a potential interpretation. We have more confidence in, or are more willing to pretend that, the story may in fact have some relation to reality if all currently known data about the sequence of events and background are coherently accounted for by the reconstruction. Explaining vs. Excusing Human Behavior To some attorneys or opposing experts, the human factors work described here may seem like a ploy to excuse defective operators, similar to an apologist scheme to let erratic people off the hook and allow them to plod on as uncorrected unreliable elements in an otherwise safe system. Human factors experts, however, should aim to help explain the riddle of puzzling human performance, not to explain it away. There is a difference between explaining and excusing human performance. Human factors expertise is about explaining behavior, not excusing it. The latter is not within its purview, but rather is something for legal proceedings to decide that hinges on the norms and laws that govern practice and is shaped by reactions to failure within the organization or profession. The commitment of a human factors expert is neither to excuse nor to judge people for what they did—that is the job of the legal people who hire the expert—but rather to explain why people did what they did. The bottom line is this: people’s actions and assessments must make sense when viewed from their position inside the situation. If, despite the human factors expert’s best efforts, people’s actions and assessments still make no sense, then human factors is probably not the field that needs to be engaged for guidance on how to explain their behavior. Attorneys may need to go to psychiatry or clinical psychology if they really cannot make sense out of certain decisions or actions. Those fields could help them explain behavior on the basis of suicidal tendencies or sabotage, for example. As long as human performance can be made to make sense using human factors concepts (and most performances in complex dynamic worlds can be), attorneys should be safe with a human factors expert. Human factors experts should push on performance until it makes sense, because it probably will.
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8.4 Example: Two Perspectives on an Accident Sequence Taking the perspective of a person caught up inside a situation is difficult technically and because of the hindsight bias. It is easier to retain the position of retrospective outsider and judge people for what they did or did not do; however, that explains nothing. The example here shows the tension between the two perspectives, even within one account of one accident by one set of authors (Rodgers et al., 2000). The two perspectives struggle into view alternately; the accident account oscillates between the normative/ judgmental and the insightful. Here the two perspectives will be reviewed for their contribution to understanding the grounds for people’s performance in this particular situation. As expected, the retrospective outsider position contributes little or nothing to understanding; it only judges from a rationalist point of view. In contrast, the insider perspective (to the extent that it is reconstructed) can carry the interpretative load. The accident occurred to a DC-9 airliner in 1994 (NTSB, 1995). It crashed next to the Charlotte, North Carolina, airport during a severe thunderstorm. While trying to break off its approach and go around, the crew got caught in a severe downdraft and microburst (a huge parcel of air coming down and exploding in all directions when it hits the ground that is akin to a water balloon dropping on the floor and bursting open, except for no balloon and more air than water). The microburst pushed the aircraft toward the ground and slowed it down below safe flying speed. This is a typical accident for a human factors expert in the sense that, in hindsight, there appeared to be two possible interpretations of the situation. In one, there was going to be a microburst; in the other there was not. The crew chose the wrong one and people wondered how they could have missed all the critical cues that were, after all, available to them. Rodgers et al. write how they aimed at “understanding the crew’s attempt to continue the flight into the adverse weather because no rational pilot would deliberately endanger the safety of the flight by attempting to traverse such weather” (2000, p. 104). This is the local rationality principle: the starting point for trying to make sense of people’s behavior. Crashing is generally not deliberate; therefore, the behavior must have made sense to people at the time. The point is not to find out what people missed, but to understand why it made sense for them to continue based on their incomplete, continually unfolding interpretation of the situation at the time. Indeed, continuing did make sense; Charlotte Air Traffic Control (ATC) had told the crew to expect a visual approach and, later, that there was only some rain south of the field. It indicated that the weather was basically good. Not much later, however, ATC changed the crew’s approach into an instrument one (used in clouds or bad visibility). Rodgers and colleagues’ perspective is pulled outside the sequence of events, looking back onto the total situation and its outcome when they say, “There was no indication, either from their conversations on the CVR or with ATC, that they understood its implications” (2000, p. 105). These “implications,” however, would only become clear with the full benefit of hindsight, with the rubble of the aircraft scattered next to the airport. In reality, nobody (including ATC) knew that a microburst was going to hit or that it would be so severe. Crews make instrument approaches all the time; it is no indication of abnormality. Rain and thunderstorms occur in the South (and elsewhere) all the time, especially in the summer; they are not abnormal. Thus, the judgment that “implications” were not understood is made from the outside and from hindsight. The crew’s understanding (or
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lack thereof) is contrasted against an after-the-fact world that is rich, filled with data, completely certain, and with an outcome about which we now know. However, this explains nothing about why the crew did what they did on the inside of their uncertain, incomplete, and unfolding world at the time, for which they did not yet have an outcome. Rodgers et al. then continue from the normative, judgmental stance and indicate that “although they addressed the possibility of a go-around, the CVR conversation described their attempt to avoid the storm cell…rather than a formal review of the missed approach procedure…as was required” (2000, p. 105). Actual behavior (attempts at storm avoidance) is contrasted against “required” written guidance (formal missed-approach procedure). No explanation is given about why the crew may have wanted to adapt their practice in the face of the conditions ahead or why the formal plan may in fact have been a bad idea at the time. (As Chapman [1987, p. 91] put it, “No plan survives contact with the enemy”) All that is said is that there was a mismatch between procedures and practice. This explains nothing. Yet, then there is another shift, away from the normative outsider perspective, back into the cockpit at the time: …the crew repeatedly discussed the weather conditions during the approach to Charlotte. They observed and commented on the heavy rain over the field. They identified the storm cell on their airborne radar and attempted to locate it. They even discussed the potential presence of windshear and were prepared to execute a go-around if the weather conditions so warranted. Finally they requested the tower controller to provide them with the airport surface winds and the ride conditions experienced by the pilots of the aircraft just ahead of them…it was clear by both their statements and by their initiation of apparently routine goaround procedures that, until just prior to impact, they were unaware of the magnitude of the microburst they were encountering (2000, p. 106). Concrete crew actions are employed as probes into their possible awareness inside their situation. This is critical for reconstructing sensemaking; any claims about what other people were aware of can, of necessity, only be made from their local perspective at the time. From inside the situation, there was not going to be a microburst and certainly not one of this magnitude. Rodgers et al. do not stay inside the situation for long, though. Pulling themselves out once again and looking back onto the entire sequence of events, where it is clear that the crew should have zigged instead of zagged, they judge: The fact that the crew had attempted to traverse a severe microburst in itself demonstrates that their SA regarding the weather conditions along the final approach path was deficient and this deficiency led to their decision to continue the approach…the evidence also indicated that the crew had obtained, but did not perceive or comprehend, considerable information that would have supported an alternative assessment regarding the severity of the weather (2000, p. 106).
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The nonperception and noncomprehension of information that can only in hindsight be construed as “considerable” is simply an outsider’s judgment of crew performance, not an explanation from within the unfolding, uncertain situation at the time. It judges people for not seeing or understanding what can be seen or understood only with full knowledge and hindsight. “Considerable information,” in addition, is that typical shopping bag full of epiphanies (“Look at all the information available to them! And they still didn’t get the message!”). It does injustice to how cues and indications about the nature of the situation emerged in reality: over time and in the midst of all kinds of other tasks and indications. The assertion is also pseudoscientific because it claims that “deficient SA” caused something (to continue an approach and subsequently to crash); however, nothing in theories of situation awareness endows it with such causal power. “Deficient SA” is merely an after-the-fact judgment about a past situation (saying we now know more than people did at the time). It cannot logically have caused anything in that situation. As Billings (1996, p. 3) put it: The most serious shortcoming of the situation awareness construct as we have thought about it to date, however, is that it’s too neat, too holistic and too seductive. We heard here that deficient SA was a causal factor in many airline accidents associated with human error. We must avoid this trap: deficient situation awareness doesn’t “cause” anything. Faulty spatial perception, diverted attention, inability to acquire data in the time available, deficient decision-making, perhaps, but not a deficient abstraction! Even if this were resolved, Rodgers and colleagues (2000) offer no criteria (nor do other authors) by which SA can be measured to have been “deficient” (other than the rubble of an aircraft next to the airport). Its deficiency is an appealing and easy judgment in hindsight, not the outcome of anything resembling scientific analysis. In addition, no underlying theory or model is presented that links deficient situation awareness to the decisions and the outcome that followed. It is all folk modeling—an appeal to smoothsounding labels that lack any deconstruction or traceable connection to the data about which they pretend to speak. Then, from the lofty perspective looking down on the errors of others and judging them for their deficiencies in modern human factors labels, Rodgers and colleagues once again descend into the situation and discover that: It is likely that the ride report from the aircraft crew just ahead was most influential in the crew’s SA regarding the weather. As a crew from the same airline as the accident crew and flying turbojet aircraft, the crew of the plane ahead was well versed in the kind of weather that would exceed the capabilities of the accident airplane and was knowledgeable on the company’s guidance regarding weather conditions its pilots could not safely traverse. Further, because they were just ahead of the accident crew and closest to the airspace conditions the accident crew was about to enter, their report contained the most timely information on weather (2000, p. 107).
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From the point of view of the people inside the unfolding situation, who did not have knowledge of the outcome, it made sense to continue with the information at hand. Lots of information about the weather was in fact not at hand (e.g., ATC did not communicate everything that it could have; an onboard windshear warning system was momentarily deactivated because of its logic; the crew had to switch radio frequencies, just missing important announcements about the weather). Yet, in the tugging of perspectives, the retrospective outsider still wins in the end, apparently making for a quicker, cleaner, more holistic conclusion. As the hindsight bias would predict, it is failure explaining failure. Unfortunately, it explains nothing and is short on scientific credibility: “the incorrect SA of the pilots led them, in addition to continuing an approach beyond the point that it should have been discontinued, to fail to anticipate a microburst of the severity that they encountered.” This is counterfactual, judgmental, and pseudoscientific. It is counterfactual because it says the pilots continued with an approach that should have been discontinued. Saying that which should have been done but what was not does not explain why people did what they did. Furthermore, claiming that the pilots failed to anticipate the weather for what it (in hindsight) turned out to be is a judgment from outside the situation. It identifies an alternative pathway that the people inside did not take and calls it their failure. It is not an explanation from people’s point of view within. Finally, “incorrect SA” is, of course, a judgment and a pseudoscientific one at that. If human factors experts want to reconstruct sensemaking, they must avoid pseudoscience, counter-factuals, and judgments. One way to do this for the preceding case is to reconstruct a detailed timeline to see when, and in which context, the various competing cues about the equivocal nature of the situation emerged, and what these would have meant in domain semantics. This rebuilds, per second or minute, the continually evolving situation in which the crew found itself and can be the scaffolding for beginning to understand how the crew’s assessment evolved in parallel. When it comes to mapping these context-specific data into a larger human factors concept, various options, other than reverting to normative outsider judgments such as “incorrect SA,” are open to the expert. One is to use the concept of plan continuation (rather well specified and deconstructed; see Orasanu et al., in press), which describes how people continue with their original plan of action if the cues and indications in favor of the plan are consistently more compelling, numerous, and stronger than cues that (in hindsight) would have suggested the plan should be discontinued. Another way to see the Charlotte accident conceptually is as an adaptive control problem (which overlaps in some sense with the plan continuation concept), in which the situation is initially too uncertain and incomplete for effective feedforward (ambiguous cues about the weather situation, smooth rides by company aircraft in front), but then quickly becomes too dynamic for effective feedback (the wind speeds changing so rapidly that they outrun the aircraft’s performance capabilities). Here, too, using control theory, there is plenty of opportunity for detailed decomposition making verifiable links between the specifics of the data trace and the model that explains what went on inside.
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8.5 Checklists for Reconstructing Behavioral Sequences The following three checklists remind human factors experts what to consider and do (and not do) when reconstructing behavioral sequences. The first is about rules to follow in the analysis, the second is about typical errors made in human factors analysis, and the third is about the steps necessary to reconstruct a behavioral sequence. Checklist 8.1: Rules for Human Factors Analysis of Behavior Sequences 1. Do not use the outcome of a sequence of events to assess the quality of the decisions and actions that led up to it. 2. Do not mix elements from your own reality now into the reality that surrounded people at the time. Put performance back into the circumstances that brought it forth. 3. Do not create shopping bags full of epiphanies (“Look at all this! It should have been so clear!”) because evidence about the unfolding situation did not reach people that way at the time. 4. To understand and evaluate human performance, it is necessary to understand how the situation unfolded around people at the time and to take on the view from inside that situation. From there, try to understand how actions and assessments could have made sense. 5. Recognize that consistencies, certainties, and clarities are products of hindsight and not data available to people inside the situation. That situation was most likely marked by ambiguity, uncertainty, and various pressures. 6. Remember that the point of a human error investigation is to understand why people did what they did, not to judge them for what they did not do. 7. At all times, remember the local rationality principle. People are not unlimited cognitive processors (in fact, there is not a single unlimited cognitive processor, machine or human, in the entire world). They cannot know everything at all times. What people did made sense from their point of view, their knowledge at the time, their objectives, and their limited resources. Checklist 8.2: Typical Errors Made in Human Factors Analysis of Behavioral Sequences • The counterfactual reasoning error. You make this error when you say what people could or should have done to avoid the mishap. (“If only they…”). Saying what people did not do but could have done does not explain why they did what they did. • The data availability-observability error. You make this error when you highlight the data available in the world surrounding people and wonder how they could have possibly missed them. Pointing out the data that would or could have revealed the true nature of the situation does not explain people’s interpretation of the situation at the time. For that you need to understand which data were observed or used and how and why. • The micromatching error. You make this error when you try to match fragments of people’s performance with all kinds of rules and procedures that you excavate from
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written documentation afterward. Of course, you will find gaps where people did not follow procedures. This mismatch, however, does not at all explain why they did what they did. For that matter, it is probably not even unique to the sequence of events that you are investigating. • The cherry-picking error. You make this error when you identify an overarching condition in hindsight (“they were in a hurry”), based on the outcome, and trace back through the sequence of events to prove yourself right. This violates rule 2: leave performance in the context that brought it forth. Do not lift disconnected fragments out to prove a point you can really only make in hindsight. Checklist 8.3: Steps to Take in the Reconstruction of a Behavioral Sequence 1. Lay out the sequence of events based on the data gathered. You can use language of the domain in which the mishap occurred (a context-specific language) to structure the events and use time and space as principles along which to organize them. 2. Divide the sequence of events into episodes that you can study separately for now. Each of these episodes may fit a different human factors explanation, but you may also find that you must readjust the boundaries of your episodes later. 3. Reconstruct critical features of the situation around each of these events. What did the world look like; what was the process doing at the time? What data were available to people? 4. Identify what people were doing or trying to accomplish during each episode. Reconstruct which data were actually observable. See what goals people were pursuing, what knowledge they used, and where, as a consequence, their attention was focused. Be relentless; press on their behavior until it makes sense to you. 5. Link the details of your sequence of events to human factors concepts. In other words, build an account of the sequence of events that runs parallel to the account in step 1 but is instead cast in concept-dependent, or human factors, terms. This will help you synthesize across mishaps and understand broader patterns of failure.
Defining Terms Cherry picking—Selecting disparate performance fragments from an accident record to prove a point that can only be made in hindsight. Counterfactual reasoning—Saying what did not happen, but if it happened, it would have avoided the accident. Counterfactual reasoning does not explain why people did what they did. Ecological approach—The approach in human factors that tries to understand performance difficulties with reference to constraints imposed by the world on people’s goal-oriented behavior. Hindsight bias—Bias in looking at past performance of which one already knows the outcome. If the outcome was bad, then people’s performance must have been bad, too.
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Local rationality principle—Principle based on cognitive science that says that people are limited cognitive processors; what they were doing had to make sense from their local perspective: their knowledge, objectives, and focus of attention at the time. Micromatching—Picking fragments from the accident record and holding them against an after-the-fact world now known to be true (e.g., procedures or available data). This does not explain why people did what they did at the time. Pseudoscience—Putting large labels on a behavioral sequence (e.g., “loss of situation awareness”) without leaving an analytic trace for others to follow or verify. Retrospective outsider—One looking back onto a sequence of events and overlooking it in its entirety (including outcome). From this perspective, it is possible only to judge people for not doing what they should have done (or vice versa). One cannot understand why people did what they did; for that, it is necessary to attain the incomplete, unfolding perspective of the people inside the situation at the time. Situated performance—Behavior that took place in a complex, dynamic situation and that can only be understood in parallel and connection with the unfolding situation. Fragments of performance considered outside that situation are robbed of their meaning. References Aeronautica Civil (1996). Aircraft accident report: controlled flight into terrain, American Airlines flight 965, Boeing 757–223, N651AA near Cali, Colombia, December 20, 1995. Bogota, Colombia: Aeronautica Civil. Amalberti, R. (2001). The paradoxes of almost totally safe transportation systems. Safety Sci. , 37(2001), 109–126. Billings, C.E. (1996). Situation awareness measurement and analysis: a commentary. In D.J.Garland and M.R.Endsley (Eds.), Experimental Analysis and Measurement of Situation Awareness , Daytona Beach, FL: Embry-Riddle Aeronautical University Press, 1–5. Boeing Commercial Airplane Group (1996). Boeing submission to the American Airlines Flight 965 Accident Investigation Board. Seattle, WA: Boeing. Chapman, G. (1987). The new generation of high-technology weapons. In D.Bellin and G.Chapman (Eds.), Computers in Battle: Will They Work? New York: Harcourt Brace Jovanovich, 61–100. Clark, A. (1997). Being There: Putting Brain, Body and World Together Again . Cambridge, MA: MIT Press. De Keyser, V. and Woods, D.D. (1990). Fixation errors: failures to revise situation assessment in dynamic and risky systems. In A.G.Colombo and A.Saiz de Bustamante (Eds.), System Reliability Assessment , The Netherlands: Kluwer Academic, 231–251. Dekker, S.W.A. (2002). The Field Guide to Human Error Investigations . Bedford U.K.: Cranfield University Press (also Aldershot, U.K.: Ashgate Publishing Co.). Degani, A. and Wiener, E.L. (1991). Philosophy, policies and procedures: the three Ps of flightdeck operations. Paper presented at the 6th International Symposium on Aviation Psychology, Columbus, OH, April. Endsley, M.R. (1999). Situation awareness in aviation systems. In D.J.Garland, J.A.Wise, and V.D.Hopkin (Eds.), Handbook of Aviation Human Factors , Mahwah, NJ: Erlbaum, 257–276. Fischoff, B. (1975). Hindsight is not foresight: the effect of outcome knowledge on judgment under uncertainty. J. Exp. Psychol: Hum. Perception Performance , 1(3), 288–299. Gibson, J.J. (1979). The Ecological Approach to Visual Perception . Boston, MA: HoughtonMifflin.
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Hollnagel, E. (1998). Measurements and models, models and measurements: You can’t have one without the other. In Proceedings of NATO AGARD Conference , Edinburgh, U.K. Hutchins, E. (1995). Cognition in the Wild . Cambridge, MA: MIT Press. Klein, G. (1998). Sources of Power: How People Make Decisions. Cambridge, MA: MIT Press. Lanir, Z. (1986). Fundamental Surprise . Eugene, OR: Decision Research. National Transportation Safety Board (1995). Flight into terrain during missed approach. USAir Flight 1016, DC-9–31, Charlotte/Douglas International Airport, Charlotte, NC, 7/2/94 (NTSB Rep. No. AAR/95/03). Washington, D.C.: NTSB. Neisser, U. (1976). Cognition and Reality . San Francisco, CA: Freeman. Orasanu, J. and Connolly, T. (1993). The reinvention of decision making. In G.A.Klein, J.Orasanu, R. Calderwood, and C.E.Zsambok (Eds.), Decision Making in Action: Models and Methods , Norwood, NJ: Ablex, 3–20. Orasanu, J., Martin, D., and Davison, J. (in press). Sources of decision error in aviation. In G.Klein and E.Salas (Eds.), Applications of Naturalistic Decision Making , Mahwah, NJ: Lawrence Erlbaum Associates. Perrow, C. (1984). Normal Accidents . New York: Basic Books. Reason, J. (1990). Human Error . Cambridge, U.K.: Cambridge University Press. Reason, J. (1997). Managing the Risks of Organizational Accidents . Aldershot, U.K.: Ashgate. Rochlin, G.I. (1999). Safe operation as a social construct. Ergonomics , 42(11), 1549–1560. Rodgers, M.D., Mogford, R.H., and Strauch, B. (2000). Post hoc assessment of situation awareness in air traffic control incidents and major aircraft accidents. In M.R.Endsley and D.J.Garland (Eds.), Situation Awareness Analysis and Measurement , Mahwah, NJ: Lawrence Erlbaum Publishers, 73–112. Starbuck, W.H. and Milliken, R.J. (1988). Challenger, fine-tuning the odds until something breaks. J. Manage. Stud. , 25, 319–340. Suchman, L.A. (1987). Plans and Situated Actions: The Problem of Human-Machine Communication . Cambridge, U.K.: Cambridge University Press. Tuchman, B.W. (1981). Practicing History: Selected Essays . New York: Norton. Varela, F.J., Thompson, E., and Rosch, E. (1995). The Embodied Mind: Cognitive Science and Human Experience . Cambridge, MA: MIT Press. Vaughan, D. (1996). The Challenger Launch Decision . Chicago, IL: University of Chicago Press. Weick, K. (1995). Sensemaking in Organizations . London: Sage. Winograd, T. and Flores, E (1987). Understanding Computers and Cognition . Reading, MA: Addison-Wesley. Woods, D.D. (1993). Process-tracing methods for the study of cognition outside of the experimental laboratory. In G.A.Klein, J.Orasanu, R.Calderwood, and C.E.Zsambok (Eds.), Decision Making in Action: Models and Methods , Norwood, NJ: Ablex, 228–251. Woods, D.D., Johannesen, L.J., Cook, R.I., and Sarter, N.B. (1994). Behind Human Error: Cognitive Systems, Computers and Hindsight . Dayton, OH: CSERIAC.
Further Information A very concrete guide on how to conduct human error investigations and how to reconstruct situated performance is Sidney Dekker’s The Field Guide to Human Error Investigations (Cranfield University Press, Bedford, U.K., and also Ashgate Publishing Co., Aldershot, U.K., in 2002). Gary Klein’s Sources of Power: How People Make Decisions is an excellent treatise on how people make decisions in actual complex, dynamic situations (1998, MIT Press, Cambridge, MA). David Woods’ chapter on process-tracing methods for the study of cognition
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outside the experimental laboratory was one of the first to pull together the issues associated with reconstructing situated performance (in G.A.Klein, J.Orasanu, R.Calderwood, and C.E.Zsambok [Eds.], Decision Making in Action: Models and Methods , Norwood, NJ: Ablex, 1993, 228–251).
9 Causation Issues in Workers’ Compensation Roger C.Jensen Montana Tech Francisco J.Bricio The Bricio Law Firm 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
9.1 Introduction Ergonomics experts occasionally serve as experts in workers’ compensation (WC) cases. These cases typically involve a causation issue for disorders such as cumulative trauma disorders of the upper extremities, low back troubles, vibration-induced white finger, or heat disorders. This article provides ergonomists with an overview of various WC systems, explains legal issues most relevant to ergonomics, and provides an example. 9.2 Objectives and Scope The objective of this chapter is to explain the WC legal issues that an ergonomics expert may help resolve. Such cases involve cumulative trauma disorders, low back injuries, vibration disorders, and heat disorders. An ergonomist asked to provide expert testimony in a WC case should understand which WC system applies because there are many WC systems and each has its unique features. Of particular concern are different tests for causation—the issue most likely the focus of the ergonomist’s testimony. Thus, it is necessary to understand the specific legal requirement for an employee’s injury or disease to qualify as having been caused by employment. This chapter begins with a brief history of WC laws. A section is included to educate the ergonomist on the unique distinction made in WC systems between injury and disease. A section discusses the common causation tests used in WC systems. Following this are sections on ergonomic principles and the potential contribution of an ergonomics expert in WC cases. A case involving a heat disorder is used to illustrate the principles and the role of the ergonomist in this kind of case.
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9.3 Discussion of Principal Issues Historical Perspective A concise history of workers’ compensation laws is provided in an annual publication by the U.S. Chamber of Commerce (2002). Some key aspects are summarized in this chapter. Before WC laws, a worker injured on the job received nothing unless the employer felt generous. Families of dead and disabled workers had to seek charity. The charities were using much of their resources to take care of families who had no income due to the temporary or permanent loss of their breadwinner. The injured workers, or the families of deceased workers, could sue the employer. However, they had to prove the employer was negligent. The employer, of course, would contest the negligence allegations as his core defense. In addition to denying negligence, the employer could assert other defenses. The three defenses most used were known as “three witches” or “unholy trinity” because they acted as three nasty hurdles to a successful suit. The three witches were: • Contributory negligence (the employee contributed to the accident) • Fellow servant (another employee contributed to the accident) • Assumption of risk (the employee knew of the hazards and still chose to work) The employer could win by proving any one of the three defenses. The law was so stacked in favor of business that few workers could win. Stories about injustices from this law began to affect public sentiment in the early 1900s. Employers began to recognize that a change was going to take place. The charitable institutions also favored a change, reasoning that business caused the problem so business should pay for it. In 1908 the U.S. government enacted the Federal Employers’ Liability Act. It provided a system for compensating railroad employees who were injured on the job. Subsequent legislation brought merchant seamen under this same compensation system. Under these systems, injured workers must sue their employer for compensation and prove that their employer’s negligence was, at least, partially responsible for the injury. Between 1910 and 1949, all U.S states enacted a workman’s compensation law. Some states later renamed the laws “Workers’ Compensation” to be gender neutral. Canadian provinces and Australian states enacted similar compensation laws. A WC law for civilian employees of the U.S government, the Federal Employees’ Compensation Act, was enacted by the federal government. Another federal act established a compensation system for longshore and harbor workers. In these “no fault” systems, the majority of claims are handled as ordinary insurance claims. Disputed claims are handled through adversarial litigation. Today, jurisdictions differ in the specifics of their WC laws, but many commonalities exist. Lencsis (1998, pp. 14–17) provides a concise comparison of the WC systems in U.S. states, Canadian provinces, Australian states, Japan, the United Kingdom, France, and New Zealand.
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Many jurisdictions made WC the exclusive remedy for an injured employee against his employer. Recently, some U.S. states have opened a narrow pathway around the exclusive remedy provision that allows an employee to collect WC benefits and sue his employer. An ergonomist may be asked to testify in such a case, so an understanding of the burden of proof is essential. In his suit, the employee must prove that his injury was caused by the employer knowingly engaging in some form of very bad conduct. Jurisdictions differ somewhat on the specific standard for defining very bad conduct, using terms like egregious conduct, grossly negligent conduct, or wanton disregard for employee safety. These cases are not WC cases, and this chapter does not address them. Injury or Disease WC laws were originally established to compensate workers for work-related injuries. Gradually, certain work-related diseases were brought within the scope of coverage. Today, many jurisdictions have different statutory provisions for injuries and diseases regarding the test of causation, the statutory time limit for
TABLE 9.1 Common Causes of Occupational Disease Covered by WC Exposure peculiar to work Extended exposure to airborne particulates or hazardous chemicals
Examples Byssinosis resulting from years of breathing cotton dust in a cotton mill Leukemia resulting from years of exposure to benzene Hepatitis contracted by a nurse from infected blood
Exposure to an infectious agent by a healthcare worker Exposure to a hazard having a latency Radiation technician develops cancer 6 years after period between exposure and onset of the receiving a high exposure disorder Assembly line worker diagnosed with carpal tunnel syndrome after 10 months of performing highly repetitive work
filing a claim, and the amount of benefits. Thus, determining the proper classification of an employee’s disorder is important and not always easy. The plaintiff’s attorney will certainly want to avoid a situation in which, for example, the claim is filed as a disease and his or her expert calls it an injury. The following discussion aims to help the ergonomist understand the basis for the WC distinction between an injury and a disease. The first thing to recognize is that the distinction between an injury and a disease is based on the statute. For example, the U.S. Supreme Court ruled that the hearing loss of a retired harbor worker was an injury because hearing loss is a “scheduled injury” in the Longshore and Harbor Workers’ Act (Bath Iron Works v. Director, Office of Workers’ Compensation Programs, 1993). Thus, the specific WC statute is the principal source of law for making the classification. If the statute is not crystal clear, the classification may be made by consulting case law based on the statute or similar statutes. Research into statutes and case law is a job for the attorney, not the ergonomist. If the statute and case law are unclear, expert opinion and logic may be helpful.
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Covered injuries are traditionally those resulting from accidents. However, the definition of accident is imprecise. It clearly includes an event not expected by the employee, such as falling, being struck by something, overexertion, or contacting a very hot object. It also appears to include a single exposure to a hazard lasting anywhere from seconds to a few hours. The duration of the event does not appear to be the controlling factor. For example, the amputation of a press operator’s finger takes less than 1 second, drowning takes several minutes, and death from carbon monoxide poisoning may occur in an hour or two. The harmful effects of such “accidents” and exposures are generally classified as injuries, but the laws of each jurisdiction should be consulted. Most covered diseases are adverse medical conditions resulting from one of the exposures listed in Table 9.1. In addition to those listed, some WC laws cover cases of mental stress caused by employment. Again, the duration of exposure does not determine if the harm is a disease or an injury. The nurse who contacted hepatitis may have been in contact with the infected blood for only a few seconds, but the harm is still classified as a disease. The radiation technician who developed cancer 25 years after being exposed to a very high level of radiation for a short period would have her cancer classified as a disease under most WC systems. Ergonomists serving as experts in WC cases are advised to have the attorney explain the classification system of the applicable WC law. It is very possible that a particular disorder may be referred to as a disease or illness in the ergonomics literature, but be classified as an injury in the WC system. This may be illustrated by some familiar types of disorders. Historically, the occupational safety and health literature has referred to gradual, noise-induced hearing loss as an occupational disease. However, in the WC systems, hearing loss is classified as an injury. The rationale is that each single exposure to loud noise may result in irreversible damage to hearing. Future single exposures may add to the damage. The cumulative effect over years of exposure is the end result of many injuries. Eventually, damage becomes detectible by audiometric testing. In essence, occupational hearing loss is the result of many single exposures, each causing irreversible injury to the hearing mechanisms. Categorizing vibration-induced white finger is challenging. On the one hand, it is similar to noise-induced hearing loss in that the disorder gradually builds up as a result of many single exposures to the stressors. On the other hand, the disorder differs from noiseinduced hearing loss in that the damage caused by single exposures, at least during the early stages of the disease progression, is reversible. Another difference is that vibrationinduced white finger has a latency period between exposure and onset. This latter characteristic favors classification as a disease. Occupational carpal tunnel syndrome also seems to fit better into the disease category. It typically develops from extended repetition of stressful exertions over time. There is a latency period during which resting the affected tendons will allow their return to normal health. There is also a point at which the disorder is no longer reversible by rest alone. Therefore, these two disorders would seem to belong in the WC classification of disease, but the laws of each jurisdiction should be consulted. Low-back sprains/strains are classified as an injury in WC systems. At first blush, this might seem in conflict with biomechanical theories of cumulative low-back deterioration resulting from repeated biomechanical stressors. The rationale behind the WC
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classification is that, even if the individual’s low back may have deteriorated over the years to a point at which it could handle little biomechanical stress, the incident that triggered the pain was a single event, which is typical of an accident, as defined in WC laws. Under these laws, it does not matter if the employee’s back was sturdy or fragile immediately before the incident. Also deserving some discussion are disorders resulting from exposure to extremes of heat or cold. Cases of hypothermia and frostbite result from exposure to extremes of cold. The time from onset of exposure to the disorder may range from less than 1 minute (in the case of frostbite from touching a very cold piece of metal) to several hours of being in a cold environment with inadequate clothing. Cases of heat exhaustion and heat stroke result from exposure to excessive heat from environmental and metabolic sources. The time from initial exposure to onset of the disorder depends on the rate of heat transfer and the individual’s acclimatization and health. A relatively short onset time would be 1 hour, and a long onset would be an entire work shift of 8 to 10 hours. In the heat stroke case discussed in this chapter, the applicable WC law was not crystal clear on whether to classify heat stroke as an injury or a disease. If the jurisdiction defines an injury as an unexpected event or a single exposure to a hazard, then these thermal stress cases fit best within the injury classification. An ergonomist consulting on a WC case should be sure to ask the attorney about the possible significance of the injury vs. disease classification. Causation in WC Systems All jurisdictions require some causal relationship between an employee’s disorder and his work. The general requirements for U.S. states are summarized next. Nearly all work-related injuries are covered. Covered injuries are traditionally those resulting from “accidents” or single exposures. Injuries resulting from assaults have generated some jurisdictional differences. Generally, an injury resulting from a workrelated assault is covered, but an injury resulting from an assault of a personal nature is not. Some work-related diseases are covered. Those most widely authorized by WC laws are noted in Table 9.1. WC laws generally exclude ordinary diseases of life (e.g., common cold, flu) and diseases that are not peculiar to or characteristic of the employee’s occupation. Some infectious diseases that anyone can get are compensible if the working conditions exposed the worker to significantly greater risk than that of other work places or public places, e.g., a nurse who contracts tuberculosis from a patient. The basic WC test of causation for an injury or disease is: did it arise out of and occur in the course of employment? Application of these tests to specific cases has generated an extensive body of case law. An ergonomist is most likely to be involved in the “arising out of” issue. This test is clearly met if the risks for the injury were distinctly associated with the employment. An example is the power press operator who amputated a finger while operating a press as part of her employment. The test is not met if the risks were entirely personal to the individual, for example, if a bank teller suffers a heart attack while working on a routine day. In many situations the risks are not exclusively tied to the work or to the individual.
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These are sometimes referred to as neutral risks. Jurisdictions tend to follow one of three doctrines for neutral risk cases (Lencsis, 1998, pp. 35–37). • Jurisdictions that follow the actual risk doctrine find for compensation if the risk was actually part of the employment. This is the most liberal doctrine. • Jurisdictions that follow the positional risk doctrine find the injury or disease arose out of employment if the incident occurred while the employee was in a position appropriate for his job. There is no need to prove the employee was at increased risk because of the job. Another way of looking at this test is to ask whether it would not have occurred but for the conditions and obligations of employment. For example, suppose a janitor cleaning a building gets crushed when the building collapses. His case would meet this test because, had it not been for his employment, he would have been somewhere else when the building collapsed. His attorney would not need to prove that janitors are at increased risk of death by building collapse compared to people in other occupations or the general public. • Jurisdictions that follow the increased risk doctrine find the injury or disease arose out of employment if the claimant proves his risk of the injury or disease was increased by (or peculiar to) the employment. The plaintiff needs to prove that employment put him at an increased risk of the injury or disease compared to the general public. This is when testimony of an appropriate expert may be helpful. Examples include an employee who develops carpal tunnel syndrome, sciatica, or heat stroke. The expert may help identify the risk factors and determine if workplace risk factors made this individual’s risk greater than that of the general public. With this brief summary of WC systems, we turn to the principles of ergonomics that apply to certain litigated WC cases. Ergonomic Principles Ergonomists work to match task demands to mental as well as physical human capabilities (Kroemer and Grandjean, 1997). Throughout the mental-physical continuum, a distinction is made between stress and strain. Stress is some form of load on the person and may be a physical, mental, or mixed load. Strain refers to the person’s response to the stress. Ergonomists are asked to assist with WC cases when a question arises about the occupational stress level’s being sufficiently intense to overstrain an individual and/or cause a disorder. The ergonomics community has devoted considerable effort toward techniques to assess workplace stress levels and define the limits of safe levels. Thus, ergonomists are well suited to serve as experts on these issues. Thermal stress provides an excellent example. Humans function well and maintain a constant body temperature in a broad range of climatic conditions (Bernard, 1996; Bishop, 1997). Figure 9.1 illustrates the concept. At the lower end of this region are conditions referred to a cold stress, in which the human body responds by shifting blood flow to protect vital organs and by shivering to increase metabolic heat production. When the body’s ability to adapt to cold stress is exceeded, body temperature decreases. At the upper end of the region are conditions referred to as heat stress, in which the human body responds by shifting blood flow toward the skin and sweating to increase
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evaporative cooling. In this region, when the body’s ability to adapt is exceeded, body temperature increases. In a WC case, an ergonomist might be asked to determine if the heat exposure of an individual was sufficient to cause a rise in body temperature and/or a heat stroke. The Ergonomics Expert in WC Litigation In WC litigation, the injured employee is characterized as the plaintiff. In the case of a deceased employee, the plaintiff is the spouse or other lawful heirs. The employer is the defendant. Often the case also names the employer’s WC insurance company as a defendant. The plaintiff bears the burden of introducing evidence to prove entitlement to compensation. The defendant will try to discredit the plaintiff’s evidence and may introduce evidence to refute his case. The plaintiff needs evidence to establish that an employer-employee relationship existed, the employment was within the scope of the jurisdiction’s WC law, and the injury or disease developed in the course
FIGURE 9.1 Body core temperature related to environmental heat level for a person doing light work. of employment. These elements of a WC claim are outside the scope of this chapter. For a more complete explanation suitable for nonattorneys, see Lencsis (1998). For a comprehensive treatise on the subject suitable for attorneys, see Larson and Larson (1996). The focus of this chapter is the element involving proof that the disorder arose out of employment. In jurisdictions following the increased risk doctrine, a part of this burden involves proving that the plaintiff’s risk for the injury was increased by (or peculiar to) the employment. This chapter explores this legal concept as it applies to WC claims for heat-related disorders and cumulative trauma disorders because these are types of cases, for which ergonomists are most likely to contribute. The major heat-related disorders are heat cramps, heat exhaustion, and heat stroke. Heat exhaustion is a moderately serious disorder sometimes resulting in a WC claim. Heat stroke is a very serious disorder that requires immediate medical treatment; and if it occurs at work, it will involve a WC claim.
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Some disorders associated with cumulative trauma are carpal tunnel syndrome, hearing loss, and white-finger disease. All of these disorders may be developed on or off the job. Thus, an employee who develops one of these disorders does not automatically qualify for WC. To do so requires evidence to establish that the disorder arose out of the job. What sort of evidence can a plaintiff introduce to support his position that the disorder arose from a job? The following types of testimonial evidence should be helpful whether the disorder is classified as an injury or a disease. • What are the known personal and work-related risk factors for the disorder? • Did the work performed by the plaintiff involve exposure to the work-related risk factors? • Was the plaintiff’s exposure to the work-related risk factors of sufficient intensity and duration to cause or contribute to the disorder? • Was the plaintiff’s occupational exposure to the work-related risk factors considerably greater than that of the general public? • Do employees who perform jobs similar to the plaintiff’s tend to have higher prevalence or incidence rates of the disorder than employees in other jobs or the general public? • Were the plaintiff’s symptoms consistent with those known to be associated with the hazardous exposure according to authoritative scientific literature? A plaintiff may need more than one expert to address all these questions. The trier of fact (e.g., judge or hearing examiner) needs to determine the qualifications of the proposed expert and decide on the scope of his or her testimony based on the individual’s credentials. There may be legal precedence in the jurisdiction specifying the credentials of the expert for specific issues. For example, the North Carolina Supreme Court declared that the expertise of a medical expert is appropriate for testimony on risk factors for heat disorders (Dillingham v. Yeargin Construction Co., 1987). In some jurisdictions, a qualified ergonomist may be permitted to testify about work-related risk factors. If not, he or she can provide copies of important literature to the attorney, who can share it with a medical expert for testimony. Testimony regarding studies involving prevalence and incidence rates should be offered by a qualified individual who knows and understands the studies. These concepts are illustrated with the following example. 9.4 Example A Mexican farm laborer was working in North Carolina. He had a proper work visa and his employer had WC insurance to cover him and his fellow employees. During the middle of the summer, he was working long hours harvesting crops. On the 19th straight work day, he started work at 6:30 a.m., had a half-hour lunch break, and continued working, but in the late afternoon he was unable to continue working. His foreman had two fellow laborers take him to an area to rest. They took him to an outdoor location beside the trailers where they resided while working at the farm. Sadly, the employer had a walk-in cooler where the worker could have been placed. About an hour later, he was found completely unconscious and unresponsive by a fellow laborer. Someone called for an ambulance, which arrived 40 minutes later after getting lost on the way to the farm. It
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took 30 minutes to get the laborer to the hospital. His diagnosis was coma resulting from exertional heat stroke, from which he never recovered. The employer reported the incident to the North Carolina Industrial Commission. The Commission appointed a guardian, who then retained an attorney to represent the worker. He filed a WC claim with the employer’s WC insurance company. The company denied the claim. When the hospital learned of the denial, they had the worker flown back to Mexico rather than continue providing charitable care. The attorney challenged the denial of the claim. The case was handled by the North Carolina Industrial Commission, Court Division. The WC insurance company took the position that heat stroke was not peculiar to a farm laborer’s job (an earlier version of the increased risk doctrine). Thus, the plaintiff’s attorney had the burden of proving that the employee’s job involved exposure to risk factors for heat disorders peculiar to his employment. After conducting a literature search, he found an article comparing risk of heat disorders for different occupational groups and different industries. The attorney contacted the author and explained the case. After some discussion, the author agreed to serve as an expert for the case. The author’s testimony was taken in a deposition, which began with testimony about his qualifications to serve as an expert for the case. After this testimony, the plaintiff’s attorney moved to tender the author as an expert in the area of occupational safety and, in particular, on the area of heat stress in work environments. Defense counsel objected but offered no basis for the objection. The plaintiff’s attorney continued with the deposition. In response to a series of questions by plaintiff and defense attorneys, the expert provided the following testimony. On the day of the incident, the weather was hot. The conditions were mostly sunny with air temperatures in the range of 32.8 to 33.9°C (91 to 93°F) all afternoon. The humidity level was moderate, about 35% relative humidity. According to the expert and both physicians, this level of heat is enough to cause a heat disorder in a worker doing physical labor for several hours in the sun. The expert mentioned a study of Nebraska WC claims finding that when the maximum daily temperature was in this range, the rate of WC claims for heat disorders was noticeably increased (Jensen, 1987). The relationship is shown in Figure 9.2. Two physicians who treated the plaintiff were deposed, and both stated the risk factors for heat-related injuries. The safety and health expert’s testimony regarding risk factors for heat disorders was only to supplement the testimony of the physicians. His testimony was that risk factors for heat stroke include personal factors and occupational factors. The expert expressed no opinions on personal risk factors. On the subject of occupational risk factors, he explained that sources of heat load are primarily metabolic heat from performing manual labor and radiant heat from the sun. The air temperature was similar to that of the skin; therefore, little heat was transferred between the plaintiff’s body and the air through convection. The principal mechanism for transferring heat from the plaintiff’s body was through evaporation of sweat from his skin. The plaintiff performed physical labor outdoors all day, beginning at 6:30 a.m. His extended exposure to a significant heat load substantially increased the risk of a heat disorder.
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FIGURE 9.2 Relationship between daily incidence of heat disorder WC claims and population-weighted daily maximum temperature during a hot summer in Nebraska. Adapted from Jensen, 1987. Another key topic of testimony concerned comparison of different occupational groups for heat disorders. This testimony was based on a paper by the expert (Jensen, 1983). Occupational groups were compared on their annual incidence rate of workers’ compensation claims for heat-related disorders. A comparison based on occupational classification indicated that the rate for farm laborers was 13 cases per 100,000 employees, whereas all occupations combined had a rate of 2 cases per 100,000 employees. This testimony helped support the plaintiff’s burden of proving that the job of farm laborer involves greater risk of a heat disorder than that of the broad spectrum of all employees in diverse occupations. The decision in the case was for the plaintiff. As a result, testimony on the issue of damages was needed. Medical experts testified on the likelihood of the plaintiff coming out of the coma, how long he would likely live, and what types of care would be needed. This case also illustrates the no-fault character of WC laws. Here, the plaintiff suffered a serious heat disorder and the employer failed to provide prompt and proper first aid. The employer had a walk-in cooler where the plaintiff could have been placed while waiting for the ambulance. Instead of applying this basic form of first aid, the plaintiff was left lying outdoors in hot weather for over an hour. Thus, the employer was at fault for failing to provide proper care; however, that is not relevant to the issue of qualifying for WC. Remember that WC is a no-fault system. However, the lack of proper first aid did become an issue in the plaintiff’s claim for an extra 10% monetary award based on North Carolina’s WC law allowing extra compensation if the injury was caused by the employer’s violation of a statutory safety duty.
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9.5 Checklist Table 9.2 is a checklist for use by an ergonomics expert who is asked to assist with a WC case. The checklist emphasizes the causation issues. Defining Terms Arising out of—A phrase expressing a causation-related requirement for an injury or disease to qualify for workers’ compensation. Basically, the cause of the injury or disease must be related to employment. Jurisdictions differ on rules for applying this requirement. Heat stress—A condition in which the thermal demands placed on a human (or animal) due to metabolic heat plus environmental heat exchange invoke a physiological cooling response, such as sweating. In the course of employment—A phrase expressing a causation-related requirement for a workers’ compensation claim to qualify for compensation. Part of the employee’s burden of proof is to
TABLE 9.2 Checklist of Primary Factors for the Causation Issue in a WC Case Primary factor Was employment within workers’ compensation coverage? Arose out of employment
Considerations
Check law of the jurisdiction The responsible employer is identified The risk for the injury/disease was distinctly associated with the employment. If not, which doctrine applies in the jurisdiction? Not if the risk factors for the injury/disease were entirely personal, unrelated to the employment Generally, not commuting between home and workplace unless performing a task of employment Not an intentional injury of a personal nature Occurred in the course of Occurred at the employee’s place of work, including the employment parking lot Occurred during a time when employee had a work-related reason to be there Occurred while the employee was engaged in an employment-related activity, and not during unreasonable horseplay or while on a curiosity venture Workplace stressors were related to the type of strain known Cumulative trauma disorders in jurisdictions following the increased to cause or contribute to the disorder risk doctrine Employee’s exposure to work-related risk factors was great enough in duration and intensity to cause the employee’s symptoms Time of exposure to onset of symptoms is consistent with known scientific knowledge Symptoms were consistent with the workplace stressors or exposures. Can inconsistent symptoms be explained?
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Job involved increased risk of the disorder compared to risks faced by the general public Is there epidemiological documentation that the employee’s job involved greater risk of the CTD than most other jobs did? Heat disorders in jurisdictions Heat stress experienced by employee was enough to exceed following the increased risk doctrine ability to regulate body temperature Employee’s occupational exposure to heat stress was greater than that of the general public The job involved greater risk of a heat disorder than that of the general public and/or employees in most other jobs Is there epidemiological documentation that the employee’s job involved greater risk of a heat disorder than most other jobs?
offer evidence indicating the injury or disease occurred while he or she was engaged in employment activities rather than in personal activities. No-fault system—A phrase used to indicate that WC systems were intended to compensate injured workers without regard for fault. In a no-fault system, the employee does not need to prove the employer was negligent or otherwise at fault, and the employer cannot deny the claim because the employee was at fault. Today, a few exceptions are recognized, depending on the jurisdiction. Stress—A form of load on an object, person, or body part. It may be a physical load, mental load, or a combination load. Strain—A response to stress. Engineers and physicists define strain as a deformation in response to a physical stress. The occupational safety and health community uses the term to describe an injury or impairment of a tendon or muscle caused by overstretching, overexerting, overusing, or wrenching. The various human responses to thermal stress are referred to as strain responses. References Bath Iron Works v. Director, Office of Workers’ Compensation Programs, 506 U.S. 153 (1993). Bernard, T.E., 1996, Occupational heat stress. In Bhattacharya, A. and McGlothlin, J.D. (Eds.) Occupational Ergonomics; Theory and Applications . New York: Marcel Dekker, 195–218. Bishop, P.A., 1997, Applied physiology of thermoregulation and exposure control. In DiNardi, S.R. (Ed.) The Occupational Environment—Its Evaluation and Control Fairfax, VA: American Industrial Hygiene Association, 629–658. Dillingham v. Yeargin Construction Co., 320 N.C. 499 (1987). Jensen, R.C., 1987, Incidence of workers’ compensation claims for heat illness as a measure of the effects of a heat wave. In Asfour, S.S. (Ed.) Trends in Ergonomics/Human Factors IV . Amsterdam: North-Holland, 341–348. Jensen, R.C., 1983, Workers’ compensation claims relating to heat and cold exposure. Prof. Safety , 28(9), 19–24. Kroemer, K.H.E. and Grandjean, E., 1997, Fitting the Task to the Human: a Textbook of Occupational Ergonomics . London: Taylor & Francis, 230–231.
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Larson, A. and Larson, L.K., 1996, Larson’s Workers’ Compensation Law . New York: Matthew Bender. Lencsis, F.M., 1998, Workers’ Compensation: A Reference and Guide . Westport, CN: Quorum Books. U.S. Chamber of Commerce, 2002,2002 Analysis of Workers’ Compensation Laws . Washington, D.C.: U.S. Chamber of Commerce.
10 Legal Issues in Work-Related Musculoskeletal Disorders: a European Perspective from the U.K. Vincent Kelly University of Surrey Jason Devereux University of Surrey 0–415–2887–3/05/$0.00+$1.50 © 2005 by CRC Press
10.1 Introduction to Human Factors Principles and Relevance to Standard of Care Ergonomics is concerned with understanding the interactions between the work system and individual capacities in order to minimize worker ill health, improve comfort and safety, and increase production. The work system is formed by the technology, organization, task, environment, and the person (Smith and Sainfort, 1989; Carayon et al., 1999). An imbalance between the work system demands and individual capacity can result in musculoskeletal disorders (MSDs). Such an outcome as a result of this imbalance has been referred to as an ergonomic injury (Pheasant, 1996). There is substantial evidence that some musculoskeletal disorders are a significant problem within the European Union in terms of a major ill-health and financial burden (Buckle and Devereux, 2002). In the U.K., a four-tier hierarchy sets the standard of care: statutory requirements, approved code of practice, guidance, and general and approved practice. For example, in relation to MSDs in the U.K., there are statutory regulations and guidance on manual handling and VDU work. Work-related upper-limb disorders are currently covered by guidance issued by the Health and Safety Executive (HSE). The ergonomic approach is central to the European Directive on manual handling (90/269/EEC) and to the U.K. Manual Handling Operations Regulations 1992 (HSE, 1998). The Health and Safety Display Screen Equipment Regulations 1992 also take into account ergonomic principles in the design, selection, and installation of display screen equipment; the design of the workplace; and the organization of the task and software particular to human data processing (HSE, 2001). The HSE guidance on upper-limb disorders in the workplace, HSG60 (HSE, 2002), states that an ergonomic approach is the most effective way of dealing with work-related upper-limb disorder problems. General and approved practice in industry is the primary guide in determining the standard of care, but it is not inflexible and it may be departed from when there is a
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failure to take account of some danger (de Navarro et al., 2001). The prevention of ergonomic injuries is based on the application of ergonomic knowledge to work practice. An approved work practice is one that takes account of current ergonomic knowledge. According to the U.K. Health and Safety Commission (HSC, 2000), authoritative sources of good practice are prescriptive legislation, approved codes of practice, and guidance produced by government and HSE inspectors. Other sources include standards produced by standard-making organizations and guidance agreed upon by a body representing an industrial or occupational sector, provided the guidance has gained general acceptance. Consequently, ergonomic and human factors principles underpin the standard of care required in musculoskeletal disorders litigation. Ergonomics is the science that bridges the gap between the generality of the law and the specifics of each individual case (Kelly, 1998). 10.2 Objective and Scope A report by the European Agency for Safety and Health at Work (2000) highlighted that six of the fifteen member states of the European Union use legal proceedings as a means of compensating employees for MSDs, in particular upper-limb disorders. The U.K. is the member state in which litigation is most frequently used. In the U.K., claims for damages are based on the tort of negligence or on breach of statutory duty (Barrett and Howells, 1997). The definition of negligence is set out in the judgment of Alderson B in Blyth v Bermingham Water Works Company (1856): “Negligence is the omission to do something which a reasonable man, guided upon those considerations which ordinarily regulate the conduct of human affairs, would do, or doing something which a prudent and reasonable man would not do.” To succeed in a legal action in negligence, the claimant must show that: • He has been injured. • The injury was a direct consequence of risks to which he had been exposed in the course of his work. • The employer was in breach of his duty of care, that is, the claimant must prove (i) the risk to which he was exposed was reasonably foreseeable (ii) it would have been reasonably practicable to circumvent the risk (Pheasant, 1991). In order to succeed on a breach of statutory duty, the claimant must prove: • He belongs to the class of persons the statute is designed to protect. • The defendant was the person on whom the duty was imposed. • The defendant was in breach of the duty. • The breach caused the damage (Barrett and Howells, 1997). The remainder of this chapter provides a description of the legal issues concerning the tort of negligence and breach of statutory duty in relation to claims for musculoskeletal disorder compensation. These legal issues are exemplified through case law concerning work-related musculoskeletal disorders affecting the back and upper limbs. Finally,
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criteria that need to be addressed in a legal action are provided as a checklist for use by ergonomists and other professionals involved in litigation. 10.3 The Legal System in the U.K. The English legal system is based on Common Law, which developed from the decisions of judges whose rulings over the centuries have created precedents for other courts to follow; these decisions were based on “custom and practice of the realm” (Carter and Howard, 1995). Statute Law is passed by Parliament and in recent times, in relation to safety, health, and welfare at work, originates increasingly from the European Union, has an accident prevention focus, and is rooted in scientific knowledge. An injured employee is entitled to sue the employer for damages for injury resulting from a breach of a duty at common law and a statutory duty. This has led to the emergence of a “double-barreled” action against the employer. In such cases, an injured employee sues separately, though simultaneously, for breach of both duties on the part of the employer (Stranks, 1999). When considering an action brought in negligence, a number of issues must be addressed: causation; foreseeability; knowledge; reasonable practicability; contributory negligence; vicarious liability; and the duty of the employer. Causation A claimant must show the relationship between the injury for which compensation is being claimed and the breach of duty that is said to give rise to this injury, thus establishing a causal link between a breach of duty and the injury. It is particularly important in cases of alleged work-related upper-limb disorders to relate the injury caused to the breach alleged, as opposed to the work in general. If the absence of a warning is to be relied upon as a breach, then the claimant must be able to say that the warning would have made a difference (Scott and Langstaff, 2001). Reasonable Foreseeability What can be foreseen depends on knowledge: what the defendant actually knows or what a reasonable man in his position should know (Munkman, 1990). In relation to the reasonable man, Lord McMillan in Glasgow Corporation v Muir (1943) said: “The standard of foresight of the reasonable man is in one sense an impersonal test. It eliminates the personal equation and is independent of idiosyncrasies of the particular person whose conduct is in question. The reasonable man is presumed to be free of over apprehension and over confidence.” Of course, a strict correlation exists between the extent of the duty on the one hand and negligence (the breach of duty) on the other. Both depend on the degree of risk foreseeability (Munkman, 1990). What is foreseeable depends largely on technical knowledge available at the time when the claimant was injured. Advances in technical and scientific knowledge make occurrences in the present foreseeable which would not
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have been foreseeable in the past. Most accident investigations disclose the cause of accidents and enable others to learn from the experience (Barrett and Howells, 1997). Knowledge The issue of knowledge in a legal action is complex and important for determining what is reasonably foreseeable. In Stokes v Guest, Keen and Nettlefold (Bolts and Nuts Ltd.) [1968], Swanwick J considered the case law and said: From these authorities I deduced the principles, that the overall test is still the conduct of the reasonable and prudent employer, taking positive thought for the safety of his workers in the light of what he knows or ought to know; where there is a recognised and general practice which has been followed for a substantial period in similar circumstances without mishap, he is entitled to follow it, unless in the light of common sense or newer knowledge it is clearly bad; but, where there is developing knowledge, he must keep reasonably abreast of it and not be too slow to apply it; and where he has in fact greater than average knowledge of the risks, he may be thereby obliged to take more than the average or standard precautions. He must weigh up the risk in terms of the likelihood of injury occurring and the potential consequences if it does; and he must balance against this the probable effectiveness of the precautions that can be taken to meet it and the expense and inconvenience they involve. If he is found to have fallen below the standard to be properly expected of a reasonable and prudent employer in these respects, he is negligent. This passage of Swanwick J was cited with approval in two Court of Appeal cases, Joseph v Ministry of Defence (1980) and White v Hallbrook Precision Castings Limited [1985]. It was further endorsed by the Court of Appeal in Hayes v Pilkington Glass Limited [1998]. In general, an employer is expected to keep reasonably abreast of current knowledge concerning dangers arising in trade processes and should be acquainted with pamphlets issued by the HSE and other safety organizations drawing attention to risks that have come to light and the means of avoiding them (Wright v Dunlop Rubber Co. Ltd and ICI Ltd., 1972). The issue of warning pamphlets by the HSE may be decisive: Cartwright v G.K.N. Sankey Ltd (1973) shows that the courts expect these pamphlets to be read carefully by a person with authority and not skimmed over quickly. Depending on the size of the employer, these may well fix the date from which liability arises (Thompson v Smiths Ship Repairers Northshields Limited, 1984). In McSherry v British Telecommunications PLC [1992], it was held that an organization like British Telecom should have been aware by 1985 of the risks of upperlimb injuries from repetitive keyboard use. However, the mere mention of the possibility of a risk in an HSE publication will not necessarily be sufficient to find liability (Walker v Wabco Automotive U.K. Limited, 1999).
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The influence of advancing knowledge and what is considered to be reasonable care is shown in the judgment in Bankstown Foundry Pty Ltd. v Braistini (1986) per Brennan and Dean J.J: Contemporary decisions about what constitutes reasonable care on the part of an employer towards an employee in the running of a modern factory are in sharp conflict with what would have been considered reasonable in the 19th century workshop and, for that matter, reflect more demanding standards than those of 20 or 30 years ago. While it is true that that has come, in part, being the consequence of the elucidation and development of legal principle, it has, to a greater extent, reflected the impact, upon decisions of fact, of increased appreciation of the likely causes of injury to the body, of the more general availability of the means and methods of avoiding such injury and of the contemporary tendency to reject the discounting of any real risk of injury to an employee in the assessment of what is reasonable in the pursuit by an employer of pecuniary profit. Changing standards in the community also have an impact on what is considered reasonable care. The judgment by Mason, Wilson, and Dawnson J.J in Bankstown Foundry Pty Ltd. v Braistini (1986) said: What reasonable care requires will vary with the advent of new methods and machines and with changing ideas of justice and increasing concern with safety in the community. This must be so, because in every case the tribunal of fact, be it a judge sitting alone or a jury must determine whether or not in the circumstances of the particular case the employer failed to take those precautions, which an employer acting reasonably could be expected to take. What is considered to be reasonable in the circumstances of a case must be influenced by current community standards. In so far as legislative requirements touching industrial safety have become more demanding upon employers, this must have its impact on community expectations of the reasonably prudent employer. Therefore, as new standards emerge and more knowledge becomes available, the employer is expected to keep up to date and take reasonable action to ensure compliance. Reasonable Practicability A statutory requirement is qualified by the phrase “so far as is practicable” when it implies that if, in the light of current knowledge and invention, it is feasible to comply with this requirement, then, irrespective of the cost or sacrifice involved, such a requirement must be complied with (Schwalb v. H.Fass & Son Ltd, 1946). “Practicable” is equivalent to physically possible and implies a higher duty of care than a duty qualified by the phrase “so far as is reasonably practicable” (Stranks, 1999). “Reasonably
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practicable” was defined by Lord Justice Asquith in Edwards v. National Coal Board [1949] when he said: Reasonably practicable is a narrower term than “physically possible” and seems to me to imply that a computation must be made in which the quantum of risk is placed on one side of the scale and the sacrifice involved in measures necessary for averting that risk (whether in money, time or trouble) is placed on the other, and that if it be shown that there is a gross disproportion between them, the risk been insignificant in relation to the sacrifice—the employer discharges the onus which is upon them. The Approved Code of Practice (HSC, 2000) in the Management of Health and Safety at Work Regulations 1999 deals with risk assessment. In this approved code: • A hazard is something with the potential to cause harm (this can include articles, substances, plant or machines, methods of work, the working environment, and other aspects of work organization). • A risk is the likelihood of potential harm from the hazard being realized. The extent of the risk will depend on: • The likelihood of that harm occurring • The potential severity of that harm, i.e., of any resultant injury or adverse health effect • The population which might be affected by the hazard, i.e., the number of people who might be exposed Risk reflects the likelihood that harm will occur and its severity (HSC, 1998). Lord Reed said, in Morris v West Hartlepool Steam Navigation Co. Ltd. [1956]: It is the duty of an employer, considering whether some precaution should be taken against the foreseeable risk, to weigh, on one hand, the magnitude of the risk, the likelihood of an accident happening and the possible seriousness of the consequences if an accident does happen, and, on the other hand, the difficulty and the expense and any other disadvantage of taking the precaution. Consequently, in manual handling situations an understanding of what is reasonably practicable can only be arrived at on the basis of ergonomic knowledge concerning likelihood of injury, the extent of injury, and the measures necessary to avert the risk. In Bolton v Stone [1951], the decision of the House of Lords was that because of the slightness of the risk, there was no negligence in failing to take measures that would involve great sacrifice at a cost; however, Lord Reed pointed out, referring to Bolton v Stone [1951] in The Wagon Mould (2) [1967], that it is negligent to allow even a small risk to arise if it can easily be avoided. The first authoritative decision from the Court of Appeal on the Manual Handling Operations Regulations 1992 is Hawkes v London Borough of Southwark (1998). In relation to the concept of reasonable practicability, the Court of Appeal made it clear that the traditional interpretation should be given to this concept: “I believe it is proper to
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conclude that Parliament had in mind, when they enacted the regulations, the construction of words ‘reasonably practicable’ which has been accepted by the court since 1938” (per Aldous L.J). In this case, the balancing approach was considered in the context of whether or not additional help should have been provided to the claimant, who was injured lifting a heavy door in a block of flats, as follows: In my view the risk was slight as was the sacrifice. There was no evidence to suggest that the defendants, with their workforce, could not have made available a second man to help carry the door upstairs. How many extra man hours would have been needed over a year was not clear and I do not believe it appropriate to assume, in the defendants’ favour, that they would be other than minimal in the context of the total number of hours worked by the relevant personnel employed by the respondent. If so, the risk was not in my view insignificant in relation to the sacrifice (per Aldous L.J). Contributory Negligence The Law Reform (Contributory Negligence) Act 1945 s(l) provides that: Where any person suffers damage as a result partly of his own fault and partly of the fault of any other person or persons, a claim in respect of that damage shall not be defeated by reason of the fault of the person suffering the damage, but the damages recoverable in respect thereof shall be reduced to such an extent as the court thinks equitable having regard to the claimant’s share in the responsibility for the damage. That is to say, the damages awarded would be affected by the claimant’s contribution to the injury through his own negligence. In considering contributory negligence in Jones v Livox Quarries Limited [1952], Denning LJ said: “…although contributory negligence does not depend on a duty of care it does depend on foreseeability. Just as actionable requires the foreseeability of harm to others, so contributory negligence requires the foreseeability of harm to oneself.” In practice, this means that a person whose injury is caused in part by his own negligence will receive damages reduced proportionately at the discretion of the court. Vicarious Liability Under the doctrine of vicarious liability, an employer is liable for the negligence of an employee when it is committed in the course of that employee’s employment (Hendy and Ford, 2001). Vicarious liability rests on the employer simply as a result of the fact that he is the employer and is deemed to have ultimate control over the employee in what is known as a “master and servant” relationship. This liability must be insured against under the Employer’s Liability Compulsory Insurance Act, 1969 (Stranks, 1999).
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Duty of the Employer The concept of personal nondelegable duty in the context of an employer’s duty of care and negligence to his servants received recognition from the House of Lords in Wilsons and Clyde Coal Co. Ltd. v English [1938]—a Scottish appeal that marked the development of the modern law of employers’ liability and negligence (White, 1993). Exposition of the employer’s personal duty to his servants is found in particular in the judgment of Lord Wright, who said, “The obligation is threefold—the provision of a competent staff of men, adequate material and a proper system and effective supervision.” Lord Wright further broke down the element of “material” into plant and appliances. It has become customary to separate the place of work from the other element of “plant and appliances” with the result that the obligation is usually spoken of today as being fourfold, as set out by Streatfield J in Hudson v Ridge Manufacturing Company Ltd [1957]—namely, to exercise reasonable care in: • Provision of a safe system of work • Provision of a safe place of work • Provision of proper equipment • Provision of competent staff These are not four separate duties but, as Pierce L.J said in Wilson v Tyneside Window Cleaning Co. [1958], are “ultimately only manifestations of the same duty of the master to take reasonable care to so carry out his operations so as not to subject those employed by him to unnecessary risk.” Provision of a Safe System of Work A very important branch of the employer’s duty is that he must take reasonable care to establish and enforce a proper system or method of work. The importance of “safe system” is that it stresses the obligation to plan the work in advance with due regard to safety (Munkman, 1990). The organization or “system” is a broad term including such matters as set out by Hendy and Ford (2001): • Order of the work • Coordination of different departments, workers, and activities • Numbers and roles of workers • Layout of plant and appliances for special tasks • Methods for using particular machines or carrying out particular processes • Instruction and supervision of workers, especially of trainees and inexperienced workers • Precautions to be taken against risk In Colfar v Coggins and Griffiths (Liverpool) Ltd [1945], Lord Greene said that “the safety of a system must be considered in relation to the particular circumstances of each particular job.” He expressed the opinion that the system may include the physical layout of the job, the sequence in which the work is to be carried out, the provision in proper cases of warnings and notices, and the issue of special instructions.
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In General Cleaning Contractors v Christmas [1953], Lord Oaksey said, “It is the duty of the employer to give such general safety instructions as a reasonably careful employer who has considered the problem presented by the work would give to the workman.” In planning the system of work, the employer must take into account the fact that workmen become careless about the risks involved in their daily work (Munkman, 1990). In General Cleaning Contractors Ltd v Christmas [1953], Lord Reid and Lord Oaksey considered this issue: Where a practice of ignoring an obvious danger has grown up I do not think it is reasonable to expect an individual workman to take the initiative in devising and using precautions. It is the duty of the employer to consider the situation, to devise a suitable system, to instruct his men what they must do and to supply any implements that may be required (Lord Reid). It is well known to employers that their work people are very frequently, if not habitually, careless about the risks which their work may involve. It is for that very reason that the common law demands that the employer should take reasonable care to lay down a reasonably safe system of work. Employers are not exempted from this duty by the fact that their men are experienced and might be, if they were in the position of an employer, able to lay down a reasonably safe system of work themselves. Workmen are not in the position of employers. Their duties are not performed in a calm atmosphere of a boardroom with the advice of experts. They have to make their decisions on narrow sills and other places of danger and circumstances where the dangers are obscured by repetition (Lord Oaksey). On the question of supervision in Clifford v Charles H.Challen and Son Ltd. (1951), Denning L.J said: The standard which the law requires is that they should take reasonable care for the safety of their workmen. To discharge that duty properly an employer must make allowance for the imperfections of human nature. When he asks his men to work with dangerous substances he must provide proper appliances to safeguard them. He must then set in force a proper system by which they use the appliances and take the necessary precautions; he must do his best to see that they adhere to it. He must remember that men doing a routine task and often heedless of their own safety may become careless about taking precautions. He must, therefore, by his foreman do his best to keep them up to the mark and not tolerate any slackness. He cannot throw all the blame on them if he has not shown good example himself.
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Consequently, in sofaras a safe system of work is concerned, it is the duty of the employer to consider the situation with regard to the state of knowledge at that time and take reasonable precautions deemed necessary for the safety of his employees. Provision of a Safe Place of Work Since Wilsons and Clyde Coal Co. Ltd. v English [1938], it is the duty of the employer to take reasonable care, by himself or by his servants or agents, to provide a safe place of work (Munkman, 1990). In Cole v De Trafford (2) [1918], Scrutton L.J had already said that “the master is bound to use reasonable care to provide safe premises and appliances for his servants to work in and with, and to use reasonable care to keep them safe.” Workplaces must be adequately lit: Garcia v Hartland and Wolfe Limited [1943], but it must not be so excessive as to be dangerous: Russel v Criterian Film Productions Limited [1936]. The employer must take reasonable care to make and keep floors safe to prevent slipping and tripping: Davidson v Handley Page Limited [1945]. In the case of known dangers, it is a question of fact whether a defendant ought to have taken a special precaution or whether those in fact taken were sufficient (Hendy and Ford, 2001). The duty of an employer is to take reasonable care for the safety of his workmen throughout the course of their employment. This duty does not come to an end because the workmen are sent to work on premises that do not belong to the employer. In McQuilter v Gouldandris Bros. Ltd. [1951], Lord Guthre said: The fact that the work had to be carried out in the premises of a third party did not absolve the employer from his duty of exercising reasonable care for the safety of his workmen. The duty must still be fulfilled, although scope is circumscribed by the fact that the work was been done on premises not in the possession and control of the employer. But he was still under the duty of exercising reasonable care to safeguard him against dangers which he should anticipate and which he had the power to avert. This duty to provide a safe place of work is of particular importance when a manual handling job must be carried out in crouched or confined spaces or when the footing is insecure or the foot placement is limited. Provision of Equipment In Wilsons and Clyde Coal Co. Ltd. v English [1938], the duty as laid down by Lord Wright was to provide suitable plant; however, it was also indicated in his judgment that the plant must be kept in good order: “The obligation to provide and maintain proper plant and appliances is a continuing obligation.” An employer is bound to keep reasonably abreast of safety developments within his type of business, and this may require the adoption and provision of new or improved equipment in the interest of safety. In Toronto Power Co. Ltd. v Paskwan [1915], the defendants were found to have been negligent in circumstances in which the deceased had been killed by a falling block from a traveling crane; evidence indicated that a safety
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device was in existence at the time of the accident and would have prevented the overwinding of the chain that caused the accident. The duty concerning new and improved equipment is set out clearly in the Canadian case Reed v Ellis (1916): “A master is not bound to provide all the latest devises for the care or benefit of those he employs; he is bound to take reasonable means to protect them from injury in his service.” In Munrow v Plymouth Health Authority (1991), a case involving the lifting of a very heavy female patient, the judge said “one does not look for perfection, one looks for reasonable steps that are practicable. A hoist is a reasonable step that is practicable.” Provision of Staff The employer is now liable for the negligence of a worker’s fellow employees (or even other workers under their control). However, in some cases a claimant will need to rely on breach of the primary duty on the part of the employer to select competent staff (Hendy and Ford, 2001). Vicarious liability requires original negligence on the part of a fellow worker and, if the employer requires an inexperienced workman to do a job outside his competence, the workman may not be negligent when he fails to do the job properly with resulting injury to the claimant. In such cases, therefore, the injured employee, if he is to succeed in his claim, must rely upon a breach of the employer’s duty to provide competent staff by proving that the employer initially employed an incompetent person or failed to ensure the employee’s competence by instruction, training, warning, and supervision. The standard of care required from workmen is that appropriate to their status and duties, and it is not correct to say that an everyday act of carelessness or inadvertence in a factory cannot amount to negligence (Munkman, 1990), or to apply an especially lenient standard of conduct in a case in which workmen are collaborating and working in a team: Staveley Iron and Chemical Co. Ltd. v Jones [1956]. In McCann v J.R.McKeller (Alloys) Ltd. (1969), the House of Lords sustained the verdict of a Scottish jury that it was negligent for a workman to drop his end of a heavy steel ingot, although he excused himself by saying that his hand was suddenly “jagged” or “pricked” by a sharp edge. A proper system of work requires that, when the job cannot be safely carried out by the claimant on his own, he should be provided with sufficient helpers to enable the work to be safely carried out. An employer must exercise reasonable care to ensure that the exertions that he requires from his workers will not be such, by reason of the physical and mental strain that they produce, as to result in injury to workers (White, 1993). The duty is owed to the individual worker. In Paris v Stepney Borough Council [1951], Lord McDermot said, “It is no less clear that the duty is owed to the workman as an individual and that it must be considered in relation to the facts of each particular case.” He further added: It seems to me to follow that in the known circumstances that a particular workman is likely to suffer a graver injury than his fellows then that happening of a given event is one which must be taken into consideration in assessing the nature of the employer’s obligation to that workman.
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On the issue of suitability for a specific job and the workload involved in Wilsons and Clyde Coal Co. Ltd v English [1938], Lord Thankerton said that “if the employer knows or ought to know that the workman has a vulnerable back they are in breach of duty in requiring him to lift and move weights which are likely to cause him injury even if a normal man can carry them without risk.” The individual worker’s stamina and fatigue were considered by Stuart-Smith LJ in Johnstone v Bloomsbury Health Authority [1992] when he said: Take the case of a man whose contract requires him to work a certain number of basic hours and overtime in addition if required. If he is required to work such long hours that he is exhausted and his attention or concentration fails so that he suffers an accident it is no defence for the employer to say that the workman expressly agreed to work such hours. It must be remembered that the duty of care is owed to the individual employee and different employees may have different stamina. If the authority in this case knew or ought to have known that by requiring him to work the hours which they did, that they exposed him to risk of injury to his health, then they should not have required him to work in excess of those hours that he could safely have done. These cases highlight the duty of the employer to take steps to become aware of each employee’s condition and suitability for the job, in effect indicating the requirement for proper selection procedures and ongoing health surveillance. It is well established at Common Law that a defendant must take the claimant as he finds him; this is commonly called “the eggshell skull principle.” Lord Parker, in Smith v Leech Brain and Co. Limited [1962], said, “It has always been the law in this country that a tortfeasor takes his victim as he finds him.” In relation to musculoskeletal disorders, Judge Byrt, QC, said in McSherry v British Telecommunications PLC [1992]: It is sufficient in law if the tortfeasor should reasonably have foreseen that his breach of duty was likely to cause injury within a broad category of the injury that was in fact caused. I am satisfied that the defendants should have been aware that bad posture could cause musculoskeletal problems. The fact that the injuries sustained were more extensive than those they might have envisaged is of no consequence in law. Statutory Duty All statutory duties are of relevance in criminal proceedings, but only those that carry civil liability can be relied on in civil actions for a breach of statutory duty. Regulations introduced under the Health and Safety at Work etc. Act 1974 give rise to civil liability, unless otherwise stated, under section 47(2) of that Act, which reads: “Breach of a duty imposed by health and safety regulations shall, so far as it causes damage, be actionable except in so far as the regulations provide otherwise.” Health and safety regulations are made under section 15 of the act.
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Statutory duties may influence the common law standard of care (de Navarro et al., 2001). Statutory duties maybe evidence of good practice that a reasonable employer should adopt (Franklin v Gramophone Company Limited [1948]; National Coal Board v England [1954]; Hewett v Alf Brown’s Transport Limited [1991]). In Bux v Slough Metals Limited [1974], Stephenson L.J, in considering the relevance of statutory regulations to a liability in negligence, said that “the employer must try and make the law of the land the rule of the factory.” Breach of Statutory Duty Whatever an act requires to be done must be done, although it is always a matter of construction precisely what is the nature of the obligation. It is in this sense that, subject to causation, every statutory duty is absolute (Ford and de Navarro, 2001). As Lord Akin said in Smith v Cammell Laird and Company Limited [1940]: “It is precisely the absolute obligation imposed by statute to perform or forbear from performing a specified activity that a breach of statutory duty differs from the obligation imposed by common law, which is to take reasonable care to avoid injuring another.” Ford and de Navarro (2001) consider that in this sense, statutory duty is absolute even though it is qualified by the words “as far as is reasonably practicable” because it is a question of fact whether a thing is reasonably practicable or not and unless, on the facts, it is not reasonably practicable, the requirement must be carried out: Marshal v Gotham Company Limited [1954]. Management of Health and Safety at Work Regulations 1999 The Management of Health and Safety at Work Regulations 1999 contains the principle methods of implementing the EEC Framework Directive (89/391/EEC). These regulations carry civil liability in actions brought by employees under regulation 6 of the Management of Health and Safety at Work and Fire Precautions (Workplace) (Amendment) Regulations 2003. The directive may be useful as evidence of approved employer practice for the purpose of establishing negligence (Smith and Ford, 2001). The regulations are accompanied by an approved code of practice (ACOP) and guidance (L21). In relation to the code, HSC (2000) says, “If you follow the advice you will be doing enough to comply with the law in respect of those specific matters on which the code gives advice” and, in relation to guidance, “Health and safety inspectors seek to secure compliance with the law and may refer to this guidance as illustrating good practice.” Regulation 3 deals with risk assessment and reads: “(1) Every employer shall make a suitable and sufficient assessment of: (a) The risks to the health and safety of his employees to which they are exposed while they are at work; and (b) The risks to the health and safety of persons not in his employment arising out of or in connection with the conduct of his undertaking.”
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The ACOP gives a general indication as to “suitable and sufficient risk assessment”; this requires a systematic general examination of the effect of the work activities and the condition of the premises, the hazards present, the likelihood of these hazards materializing, and the damage likely to arise. The extent of the sophistication of the risk assessment will depend on the complexity of the processes. All employers and selfemployed people are required to make a risk assessment. The regulation also provides that employers with five or more employees must record the significant findings of their risk assessment. Regulation 4 says that when an employer implements any preventive and protective measures, he should do so on the basis of the principles specified in schedule 1 to the regulations. These are the general principles of prevention set out in article 6(2) of Council Directive 89/391/EEC. The general principles of prevention are “(a) Avoiding risk (b) Evaluating risks that cannot be avoided (c) Combating the risks at source (d) Adapting the work to the individual—especially as regards the design of work places, choice of work equipment, and choice of working and production methods—with a view, in particular, to alleviating monotonous work and work at predetermined work rate and reducing their effect on health (e) Adapting to technical progress (f) Replacing the danger by no danger or less danger (g) Developing a coherent overall prevention policy that covers technology; organization of work; working conditions; social relationships; and the influence of factors relating to the working environment (h) Giving collective protective measures priority over individual protective measures (i) Giving appropriate instructions to employees” Regulation 6 deals with health surveillance and reads: “Every employer shall ensure that his employees are provided with such health surveillance as is appropriate having regard to the risks to their health and safety which are identified by the assessment.” The primary benefit, and therefore objective of health surveillance, should be to detect adverse health effects at an early stage, thereby enabling further harm to be prevented (HSC, 2000). Regulation 10 provides that every employer shall provide his employees with comprehensible and relevant information on the risks to health and safety identified by the assessment and the preventive and protective measures. Regulation 13 deals with capabilities and training. Regulation 13(1) reads: “Every employer shall entrust a task to his employees taking into account their capabilities as regards health and safety.” Regulation 13(2) deals with the issue of training and says that every employer shall ensure that his employees are provided with adequate health and safety training when they are recruited into the employer undertaking and when they are exposed to a new or increased risk. The training shall
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“(a) Be repeated periodically when appropriate (b) Be adapted to account for any new or changed risks to the health and safety of employees concerned (c) Take place during working hours” (regulation 13(3)) Under regulation 14, employees have a duty to cooperate with the employer to enable him to comply with statutory duties for health and safety and to notify him of any shortcomings in the health and safety arrangements so that he can take remedial action if needed. Manual Handling Regulations The Manual Handling Operations Regulations 1992 made under the Health and Safety at Work etc. Act 1974 implement Council Directive 90/269/EEC on the manual handling of loads and supplement the general duties placed on employers and others by the Health and Safety at Work etc. Act 1974 and the broader requirements of the Management Regulations (HSE, 1998). The Court of Appeal in Koonjul v Thameslink Health Care Trust [2000] considered that the purpose of the regulations was to place an obligation on the employers to look after the safety of their employees who might not behave with proper and full concern for their own safety. The Manual Handling Regulations carry civil liability and are qualified by reasonable practicability. Regulation 2(1) defines manual handling operations: “‘Manual handling operations’ means any transporting or supporting of a load (including the lifting, putting down, pushing, pulling, carrying or moving thereof) by hand or by bodily force.” “Load” includes any person or any animal. By way of definition, the directive says: For the purposes of this Directive, “manual handling of loads” means any transporting or supporting of a load, by one or more workers, including lifting, putting down, pushing, pulling, carrying, or moving of a load, which, by reason of its characteristics or of unfavourable ergonomic conditions, involves a risk particularly of back injury to workers. The various parts of regulation 4(1) establish a clear hierarchy of measures, avoidance, assessment, and reduction of risk. Regulation 4(1)(a) reads: “(1) each employer shall—so far as is reasonably practicable, avoid the need for his employees to undertake any manual handling operations at work which involve a risk to their being injured.” This is the primary duty on the employer. If the general risk assessment carried out under the Management of Health and Safety at Work Regulations 1999 indicates the possibility of injury from manual handling, then the first issue to consider is whether the manual handling operation can be avoided. Manual handling of loads can be avoided by elimination of the handling operation or, alternatively, automation or mechanization. Regulation 4(1)(b)(i) deals with assessment of risk when it is not reasonably practicable to avoid the need for manual handling operations that involve a risk of injury. In these circumstances, employers “shall make a suitable and sufficient assessment of all such manual handling operations to be undertaken by them.” This assessment must have
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regard to the factors set out in schedule 1 attached to the regulations. This schedule sets out five issues: the task, the load, the working environment, individual capability, and other factors. Questions that the employer must consider in the assessment of manual handling operations are provided on each of these issues. As an appendix to the guidance on the regulations (L23), the HSE published a filter to screen out more straightforward cases and identify manual handling operations in which a more detailed risk assessment is necessary. The filter is based on a set of numerical guidelines developed from data published in scientific literature and on practical experience of assessing risks for manual handling. They are pragmatic, tried, and tested; they are not based on any precise scientific formula. The intention is to set out an approximate boundary within which the load is unlikely to create a risk of injury sufficient to warrant a detailed assessment (HSE, 1998). This filter indicates a maximum weight of 25 kg for men and 16 kg for women in operations involving lifting a load. Regulation 4(1)(b)(ii) deals with reducing the risk of injury when the manual handling operation cannot be avoided and the obligation on the employer is to “take appropriate steps to reduce the risk of injury to those employees arising out of their undertaking any such manual handling operation to the lowest level reasonably practicable.” Health, safety, and productivity are most likely to be optimized if an ergonomic approach is used to design the manual handling operations as a whole. Wherever possible, consideration should be given to the task, load, working environment, and individual capacity, as well as the relationship among them, with a view to fitting the operations to the individual rather than the other way around (HSE, 1998). Reduction of risk can be brought about through work place or job design; mechanical assistance; improving work routine; lightening the load and making it easier to manage; improving space constraints and footing; improving thermal environment, ventilation, and lighting; and providing information and training. Regulation 4(1)(b)(iii) deals with the provision of additional information in relation to the load. This says that precise information, in situations in which it is reasonably practicable to do so, should be given on the weight of each load and the heaviest side of any load where the center of gravity is not positioned centrally. Regulation 5 deals with duties of employees and reads: “Each employee while at work shall make full and proper use of any system of work provided for use by his employer in compliance with regulation 4(1)(b)(ii) of these regulations.” Employees are already under a duty under section 7 of the Health and Safety at Work etc. Act 1974 to take reasonable care for their own health and safety and that of others and to cooperate with their employers to enable them to comply with their duties. Application of Manual Handling Regulations Application of the regulations is not confined to injuries arising from carrying excessive loads, as illustrated by the following cases. In King v RCO Support Services Limited [2001], Kay LJ accepted that the regulations applied in circumstances in which the claimant sustained personal injuries when he slipped on ice while shoveling grit because the operation fell within the definition of “manual handling operations” in regulation 2. The fact that the primary cause of the accident was ice rather than the manual handling was irrelevant; the possibility of an icy
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surface was a factor that should have been considered when assessing the risk of the manual handling operation (Hermer and Ford, 2001). The plaintiff in Hawkes v London Borough of Southwark (1998) was injured when he fell down stairs while carrying a door. Also, it was accepted in Purves v Buckingham County Council (1998) that a teacher grabbing an unruly child could fall within the regulations (Hermer and Ford, 2001). Work Equipment Regulations The Provision and Use of Work Equipment Regulations 1998 are intended to implement the Work Equipment Directive, 89/655/EEC, and amendments to the directives. The regulations adopt a wide definition of “equipment” and impose general obligations in relation to its safety. These regulations carry civil liability. Two regulations are of specific interest in relation to musculoskeletal disorders. Regulation 4(2) states “in selecting work equipment, every employer shall have regard to the working conditions and to the risks to the health and safety of persons which exist in the premises or undertakings in which that work equipment is to be used and any additional risk posed by the use of that work equipment.” The Approved Code of Practice (HSC, 1998), which accompanies the Provision and Use of Work Equipment Regulations 1998, says that the employer should take account of ergonomic risks in selecting the equipment. Regulation 5(1) requires every employer to ensure that work equipment is maintained in an efficient state, efficient working order, and good repair. The guidance accompanying the regulations warns that ergonomic design must take into account the size and shape of the whole body and should ensure that the design is compatible with human dimensions. Operators should not be expected to exert undue force or stretch or reach beyond their normal strength or physical reach limitation to carry out tasks. This is particularly important for highly repetitive work such as working on supermarket checkouts or high-speed “pick and place” operations. Thus, it can be seen that the ambit of regulation 5(1) is of very real significance in that it gives rise to strict liability if injury has been caused by a malfunctioning machine, irrespective of the system of maintenance and repair imposed by a conscientious employer. In Cadger v Vauxhall Motors (2000), regulation 5 was breached when pneumatic work equipment malfunctioned; arguments about the rea sonableness of the system of inspection and maintenance were irrelevant (Ford and Hermer, 2001). Display Screen Equipment (or Visual Display Unit [VDU]) The Health and Safety (Display Screen Equipment) Regulations 1992 give rise to civil liability and are not supported by an approved code of practice. However, there is guidance on the regulations (HSE, 2001). The regulations define a work station and set out the duties of the employer in relation to assessment of risks, requirements for
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workstations, daily work routine of users, provision of eye and eye-sight tests, training, and information. Regulation 1(2) (a) says that “display screen equipment” means any alphanumeric or graphic display screen, regardless of the display process involved. A “user” means an employee who habitually uses display screen equipment as a significant part of his normal work (regulation 1(2)(d)). In regulation 1(2)(e), “work station” means an assembly comprising: • Display screen equipment • Any optional accessories to the display screen equipment • Any disk drive, telephone, modem, printer, document holder, work chair, work desk, work surface, or other items peripheral to the display screen equipment • The immediate work environment around display screen equipment Regulation 2 deals with risk assessment of work stations and the updating of the assessment. The obligation of the employer under regulation 2(3) is to “reduce the risks identified in consequence of an assessment to the lowest extent reasonably practicable.” The guidance note at paragraph 21 says a suitable and sufficient analysis should be systematic; be appropriate to the likely degree of risk; be comprehensive, covering organization, job, work place, and individual factors; and incorporate information provided by employer and worker. Possible risks that have been associated with display screen equipment workers are summarized at Annex B to the Guidance on the Display Screen Regulations. Paragraph 1, Annex B reads: “The introduction of VDUs and other display screen equipment has been associated with a range of symptoms related to the visual system and working posture. These often reflect bodily fatigue. They can readily be prevented by applying ergonomic principles to the design, selection and installation of display screen equipment, the design of the work place and the organisation of the task.” The main conditions are upper-limb pains and discomfort, eye and eyesight effects, fatigue, and stress. Other concerns are epilepsy, facial dermatitis, electromagnetic radiation, and effects on pregnant women (HSE, 2001). Regulation 3 sets out the duty of the employer to ensure that work stations meet the requirements laid down in the Schedule to the Regulations. This schedule sets out the minimum requirements for work stations, which are contained in the annex to Council Directive 90/270/EEC on the minimum safety and health requirements for work with display screen equipment. An employer should ensure that a work station meets the requirements laid down in the schedule to the extent that: • These requirements relate to the component present in the work station concerned • These requirements have an effect with a view to securing the health, safety, and welfare of persons at work • The inherent characteristics of a given task make compliance with these requirements appropriate with respect to work station concerned
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The requirements deal with equipment (display screen, keyboard, work desk or work surface, work chair); environment; space requirements; lighting; reflections and glare; noise; heat; radiation; humidity; and the interface between the computer and the operator/user where the general principles of software ergonomics should be taken into account (HSE, 2001). Regulation 4, dealing with daily work routine of users, reads: “Every employer shall so plan the activities of users at work in his undertaking that their daily work on display screen equipment is periodically interrupted by such breaks or changes of the activity as to reduce their work load at the equipment.” The guidance on the regulations states that when the display screen work involves intensive use of the keyboard, any activity that would demand broadly similar use of the arms or hands should be avoided during breaks. Similarly, if the display screen work is visually demanding, any activities during breaks should be of a different visual character. Breaks must also allow users to vary their posture. Exercise routines that include blinking, stretching, and focusing eyes at distant objects can be helpful and could be covered in training programs (HSE, 2001). Regulation 6 deals with the provision of training and says that the employer should ensure that users are provided with adequate health and safety training in the use of any work station upon which they are required to work. Health and safety training should be aimed at reducing or minimizing the risk areas set out in Annex B for each individual user and take account of guidance in Annex A. Information provided under regulation 7 must deal with all aspects of health and safety relating to work stations and the measures taken by the employer under the regulations that relate to the workers and their work. Minor amendments have been made by the Health and Safety Executive (Miscellaneous) (Amendments) Regulations 2002 to regulations 3, 5 and 6 relating to workstations, eye testing and training. Additional guidance on the regulations (L26, 2nd ed., HSE 2003) has been issued. Consultation The Safety Representative and Safety Committee’s Regulations 1977 and the Health and Safety (Consultation with Employees) Regulations 1996 deal with consultation with employees and their representatives. These regulations do not carry a civil right of action. These regulations ensure that all employees, whether represented by a trade union or not, must be consulted on the introduction of measures in the place of work that may substantially affect the health and safety of employees, the planning and organization of any health and safety training as required to be provided, and the health and safety consequences for employees of the introduction of new technology into the work place (HSE, 1996). There is also a duty on the employer’s part to make available all relevant information to enable employees to participate fully and effectively in the consultation process; these should cover the provision of accident reports and risk assessments that have been carried out (Zindani, 1998). The Guidance (HSE, 1998) accompanying the Manual Handling Regulations stresses the importance of consultation and the contribution that workers can make:
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…the views of staff can be particularly valuable in identifying manual handling problems and practical solutions to them. Encourage employees, their safety representatives and safety committees to play a positive part in the assessment process. They can assist the employer by highlighting difficulties from such things as the size or shape of loads, how often they are handled, or the circumstances in which the handling operations are carried out. European Union Directives A claimant can bring an action against an emanation of the state based on a directive. In the leading case of Foster v British Gas Plc (1991), the European Court of Justice stated that direct effect could be relied upon against: “A body, whatever its legal form, which has been made responsible, pursuant to a measure adopted by the state, for providing a public service under the control of the state and has for that purpose special powers beyond those which result from the normal rules applicable in relations between individuals.” Under this ruling, an independent police authority is an emanation of the state, as are public health bodies; local and regional authorities; tax authorities; a nationalized corporation; a privatized water company; and the governing body of a voluntary aided school (Meade and Langstaff, 2001). Meade and Langstaff (2001) suggest that European jurisprudence has no obvious counterpart to that of the U.K. requirement of “reasonable practicability” as a qualification to the performance of an employer’s duty in many regulations. However, in the Court of Appeal referring to the Manual Handling Directive (90/269/EEC), which includes the terms “appropriate organizational measures” and “appropriate means,” Hale L.J, in King v Sussex Ambulance NHS Trust (2002), said, “The Directive does not refer to what is ‘reasonably practicable’ but that must be what it means by taking ‘appropriate measures’ or using ‘appropriate means’ to ‘reduce’ the risk.” 10.4 Examples of Case Law In a personal injury civil action, the claimant must show that he is injured and that the injury was caused, wholly or partly, by risks to which he was exposed at his work. If the action is brought in negligence, the claimant must show that the defendant was in breach of his duty of care in that the risk to which he was exposed was reasonably foreseeable and that it would have been reasonably practicable to circumvent the risk. If the action is brought under a breach of statutory duty, the claimant must show that he was protected by the statute, which placed the duty on the defendant and was breached by the defendant causing the injury. How the courts approach these issues is illustrated by the following examples of case law.
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In relation to the existence or not of an injury, Mughal v Reuters Ltd. (1993) is a much-publicized case concerning musculoskeletal disorders. In this case, Judge Prosser said, “I believe that the main stream view is that there is no pathology, no clinical symptoms that can be pointed to as confirming a patient having RSI,” and he agreed with the view “that RSI has no place in the medical books.” An injury must be shown to be related to work. In Alexander v Midland Bank PLC (1999), the judge accepted that the condition from which the claimants suffered, fibromyalgia, was physical and caused by factors of repetitive work under intense pressure with insufficient work breaks and sustained bad posture. The Court of Appeal found that the judge had a choice between two alternative explanations. The five claimants had to prove that the physical explanation for their upper-limb disorders was more probable than the psychogenic cause suggested by the defendants. On the evidence, the judge had been entitled to conclude that the fibromyalgia was physically based and arising from the work conditions. In McPherson v London Borough of Camden (1999), it was held that De Quervain’s syndrome could be caused occupationally by repeated movements of the wrist or the thumb. The use of keyboards, on occasion, could cause the necessary stenosis and inflammation. The claimant had used her thumb excessively and her condition had been caused by the continual use of the keyboard in the poor ergonomic and working-time conditions that prevailed from June 1993 to January 1994. On the issue of foreseeability, the Court of Appeal in Koonjul v Thameslink Health Care Trust (2000) held that there must be a real risk—a foreseeable possibility of injury—and certainly nothing approaching a probability. Furthermore, Hale LJ stated that, in making such assessments, an element of realism must be present. The Court of Appeal in Alsop v Sheffield City Council (2002) adopted this reasoning. The facts of this case were that the claimant, a refuse collector, was injured pulling a wheelie bin up a concrete ramp with a gradient of 30°. There were no complaints by dustmen or refuse collectors and there were no recorded accidents of the type suffered by the claimant. The Court held that the council could do no more than to tell experienced dustmen to use their common sense. The claimant should have made use of the options open to him, which included the possibility of wheeling the bin to the end of the gradient where the road met the pavement at an even level. The Court of Appeal in Koonjul v Thameslink Health Care Trust (2000) considered the issue of reasonable practicability in making an assessment of manual handling operations under regulation 4(1) (b). The question of what involved a risk of injury was context-based and, accordingly, it was necessary to look at the particular operation in context; this included the context of the particular place of employment and also the particular employees involved. This case involved an employee in a small residential home with a small number of employees injuring her back pulling a bed out from a wall. The bed was against the wall to prevent children falling out of the bed. The Court held that the employer was entitled to take the fact that the employee had been carrying out the task for a very long time into account in assessing the risk of injury. In considering the duties of the employer, the court found that the first obligation was to prevent the risk but, in this case, there was good reason for having the bed against the wall to prevent the children falling out.
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In these circumstances, the employer’s second obligation was to reduce the risk of injury to the lowest level reasonably practicable. In this case, the employment involved a number of everyday tasks and the Court considered the idea that the level of risk involved should be met by a precise evaluation of each of those tasks and precise warnings to each employee as to how each was to be carried out took the case way beyond the realms of practicability. In these circumstances, the Court held that there was no breach of the regulations. In O’Neill v DSG Retail Limited (2002), the claimant was supporting a microwave oven when he was called by a colleague; he turned by twisting his body toward the direction of the call without moving his feet. It was conceded by the defendants that, in breach of their own policy, the claimant had not been given practical training, nor had he been shown a video. The purpose of the training was to highlight the risks involved in lifting and to make employees aware of them by watching demonstrations of safe lifting and then practicing such techniques. The video contained demonstrations of safe lifting and also material designed to train people out of the instinct to twist when carrying a load. It was held by the Court of Appeal that the defendants’ failure to give the claimant the desired practical training and video gave rise to a foreseeable possibility of injury in relation to the particular task he had been carrying out and that failure to provide training was a cause of the claimant’s injury. By not giving the claimant training and not showing him the training video, the defendants failed to reduce the risk of injury to the lowest level reasonably practicable and were in breach of regulation 4(1)(b)(ii) of the Manual Handling Operation Regulations 1992. The 36-year-old claimant in Knott v Newham Health Care NHS Trust (2002) suffered a back injury and alleged that the defendants had no adequate or proper system for manually handling patients, which meant that she was exposed to risk of back injury. The Court held that, on the evidence, there was only one hoist for use in two wards and that hoist was often inoperable. The consequence of the inadequacy of mechanical aids was that the claimant would habitually use a drag lift to move heavy patients. The drag lift was an inherently unsafe method that carried with it a real risk of injury. The defendants did not operate an appropriate system for lifting patients and no real steps had been taken to reduce the risk of injury to its employees to the lowest level reasonably practicable during the relevant period; the defendants were therefore in breach of the regulations. It was also held that the claimant’s degenerative disease rendered her particularly vulnerable to disc prolapse, and the lifting of patients during the period of her employment with the defendants was likely to have damaged the annulus of the claimant’s disc posteriorily. The disc prolapse and neural damage were the eventual result of the process. It followed that the defendants’ breach of duty caused (and, at the very least, materially contributed to) the claimant’s injury. In King v Sussex Ambulance Health Trust (2002), the claimant was injured while carrying a patient in a carry-chair with a fellow worker down a stairway that was narrow, steep, and had a bend in it. The Court of Appeal judgment referred to it as an awkward lift with a not particularly heavy patient who needed a response within an hour. The only alternative was to call the fire brigade and have the patient taken out through a window.
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The claimant’s case was brought on the basis of a breach of the Manual Handling Directive, a breach of the Manual Handling Regulations, and in negligence. In the County Court, the judge held that there was a breach of article 3.2 of the directive and said that calling the fire brigade should have been given more serious consideration than it was. The Court of Appeal held against the claimant on all grounds. Lady Justice Hale said that it was clear that if there were no liability under the directive then there was no liability under the regulations and, in her view, there was no liability under either. There was nothing to suggest that calling the fire brigade would have been an appropriate measure in this case to avoid the need for carrying patients down the stairs or to reduce risk of injury in so doing. If calling the fire brigade was not appropriate or reasonably practicable for the purposes of the directive or the regulations, it cannot be a lack of reasonable care to fail to do so. In practice, the claimant’s damages are reduced by a percentage comparable to the degree of fault that the court finds against the claimant (Barrett and Howells, 1997). The courts can impose substantial reductions on claimant damages due to contributory negligence. In Mearns v Lothian Regional Council (1991), the worker’s damages were reduced by 50% because help was available even though not readily available. In McCaffery v Datta (1997), a finding of one-third contributory negligence was upheld by the Court of Appeal. The Court considered that, given the claimant’s previous history of back problems, she could have arranged the patient’s bed to minimize the risk. However, a court will be slow to criticize mere inadvertence or inattention on the part of a worker (Zindani, 1998). In Caswell v Powell Duffryn Associated Collieries Ltd. [1940], Lord Porter said: The skill gained by a workman may enable him to take risks and do acts which in an unskilled man would be negligence, and on the other hand the fatigue and repetition of the same work may make a man incapable of the same care, and therefore not guilty of negligence, in doing or failing to do an act which a man less fatigued would do or leave undone. In a patient-lifting case, Munrow v Plymouth Health Authority (1991), the judge said, I think if one looks at the facts of this case in the light of the training which she received, this plaintiff could have chosen a hoist, but that she received nothing in the way of training nor assistance from any nursing plan which would have steered her towards a hoist and though I think she made the wrong decision I do not think that the wrong decision would be sound by way of contributory negligence. The cases show that the courts consider that the application of regulations and the principles of negligence must involve common sense and an element of realism while taking into account the particular circumstances of each individual case.
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10.5 Checklist of Main Factors to Consider in a Legal Action in Relation to Work-Related Musculoskeletal Injury Primary factors Considerations Personal details
Age Previous injury Work history Gender Medication Out-of-work activities Selection Evidence of selection procedures Medical examination Suitability for the task Instruction and Evidence of instruction and training training Job-specific instruction and training Warning of the hazards, including unfavorable ergonomic conditions Evaluation of training effectiveness Revision of training Supervision Extent of supervision Extent of supervisory support for training Health surveillance Provision of health surveillance Methods of health surveillance Action on the results of health surveillance Consultation and Evidence of the consultation process complaints Evidence of complaints procedure Evidence of action on consultation or complaints Activity Description of the work system Description of the incident/injury Amplitude, frequency, and duration of exposure Subjective assessment Employee’s involvement in determining the workload Capacity to meet workload requirements Avoidance Possible avoidance of the injury-related task by job redesign or automation, work organization, or layout measures
Primary factors Risk assessment
Risk reduction
Considerations Generic risk assessments Can risk be avoided Detailed risk assessment Update of risk assessments and evaluation of interventions Use of an ergonomic approach including consideration of the task, equipment, job rotation, rest breaks, environment, work organization, job design, and the individual
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References Barrett, B. and Howells, R. (1997). Occupational Health and Safety Law . London: Financial Times Pitman Publishing. Buckle, P.W. and Devereux, J.J. (2002). Work-related neck and upper limb musculoskeletal disorders: reaching a consensus view across the European Union. Appl. Ergonomics 33:207– 217. Carayon, P., Smith, M.J., and Haims, M.C. (1999). Work organization, job stress, and work-related musculoskeletal disorders. Hum. Factors 41:644–663. Carter, G.T. and Howard, J.S. (1995). Legal aspects on services for the disabled. In: R.A.F.Cox, F.C. Edwards, and R.I.M.McCallun (Eds.) Fitness for Work Medical Aspects , 2nd ed. Oxford: Oxford University Press, de Navarro, M., Ford, M., and Hendy, J. (2001). The general principles of negligence. In J.Hendy and M.Ford (Eds.) Munkman on Employer’s Liability , 13th ed. London: Butterworth, 33–65. European Agency for Safety and Health at Work (2000). Repetitive Strain Injuries in the Member States of the European Union: the Results of an Information Request . Luxembourg: Office for Official Publications of the European Communities. Ford, M. and de Navarro, M. (2001). Breach of statutory duty. In: J.Hendy and M.Ford (Eds.) Munkman on Employer’s Liability , 13th ed. London: Butterworth, 229–255. Ford, M. and Hermer, R. (2001). Machinery and equipment. In: J.Hendy and M.Ford (Eds.) Munkman on Employer’s Liability , 13th ed. London: Butterworth, 317–332. Health and Safety Commission (1998). Safe Use of Work Equipment: Approved Code of Practice and Guidance . London: HMSO. Health and Safety Commission (2000). Management of Health and Safety at Work: Approved Code of Practice and Guidance . London: HMSO. Health and Safety Executive (1996). A Guide to the Health and Safety (Consultation with Employees) Regulations . Norwich: HMSO. Health and Safety Executive (1998). Manual Handling: Guidance on Regulations . London: HMSO. Health and Safety Executive (2001). Display Screen Equipment Work: Guidance on Regulations . London: HMSO. Health and Safety Executive (2002). Upper Limb Disorders in the Workplace HSG60 (rev) . Sudbury: HSE Books. Hendy, J. and Ford, M. (2001). The employer’s duty of care. In: J.Hendy and M.Ford (Eds.) Munkman on Employer’s Liability , 13th ed. London: Butterworth, 91–116. Hermer, R. and Ford, M. (2001). Manual handling. In: J.Hendy and M.Ford (Eds.) Munkman on Employer’s Liability , 13th ed. London: Butterworth, 333–344. Kelly, V. (1998). Development of a tool for use in civil action involving a cumulative back injury. Unpublished M.Sc. thesis, University of Surrey. Meade, P. and Langstaff, B. (2001). European law. In: J.Hendy and M.Ford (Eds.) M unkman on Employer’s Liability , 13th ed. London: Butterworth, 257–283. Munkman, J. (1990). Employer’s Liability at Common Law , 11th ed. London: Butterworth. Pheasant, S. (1991). Ergonomics, Work and Health . London: Macmillan. Pheasant, S. (1996). Bodyspace—Anthropometry, Ergonomics and the Design of Work . London: Taylor & Francis. Scott, I. and Langstaff, B. (2001). Industrial diseases. In: J.Hendy and M.Ford (Eds.) Munkman on Employer’s Liability , 13th ed. London: Butterworth, 193–221.
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Smith, I. and Ford, M. (2001). The general legislation: the Framework Directive, the Temporary Workers Directives and the Management of Health and Safety at Work Regulations. In: J.Hendy and M. Ford (Eds.) Munkman on Employer’s Liability , 13th ed. London: Butterworth, 285–301. Smith, M.J. and Sainforth, P.C. (1989). A balance theory of job design for stress reduction. Int. J. Ind. Ergonomics 4:67–79. Stranks, J. (1999). Health and Safety Law , 3rd ed. London: Financial Times Pitman Publishing. White, J. (1993). Civil Liability of Industrial Accidents . Dublin: Oaktree Press. Zindani, J. (1998). Manual Handling: Law and Litigation . Birmingham, England: CLT Professional Publishing.
Cases Alexander v Midland Bank PLC (1999) IRLR 723. Allsop v Sheffield City Council (2002) EWCA civ429, LTL 05/03/2002. Bankstown Foundry Pty Limited v Braistina (1986) 160 CLR 301. Blyth v Bermingham Water Works Company (1856), (1843/60) All ER Rep 478. Bolton v Stone [1951] AC 850, (1951) 1 All ER 1078. Bux v Slough Metals Ltd [1947] 1 All ER 262, CA. Cadger v Vauxhall Motors (2000) 6 CLD. Cartwright v G.K.N. Sankley Ltd (1973), 14 KIR 349, CA. Caswell v Powell Duffryn Associated Collieries Ltd [1940] AC 152, (1939) 3 All ER722. Clifford v Charles H. Challen & Son Limited (1951) 1 KB 495, (1951) 1 All ER 72. Cole v De Trafford (No 2) [1918] 2 KB 523, (1918/19) All ER Rep 290. Colfar v Coggins and Griffiths (Liverpool) Ltd. [1945] AC 197, (1945) 1 All ER 326. Davidson v Handley Page Limited [1945] 1 All ER 235. Edwards v National Coal Board [1949] 1 KB 704, (1949) 1 All ER 743. Foster v British Gas PLC (1991) FCR 84. Franklin v Gramophone Co. Ltd. [1948] 1 KB 542, (1948) 1 All ER 353. Garcia v Hartland and Wolfe Limited [1943] 1 KB 731, (1943) 2 All ER 477. General Cleaning Contractors v Christmas [1953] AC 180, (1952) 2 All ER 1110. Glasgow Corporation v Muir (1943) AC 448, (1943) 2 All ER 44. Hawkes v London Borough of Southwark (20 February 1998, unreported), CA. Hayes v Pilkington Glass Limited [1998] PIQR P 313, CA. Hewett v Alf Brown’s Transport Ltd. [1991] ICR 471, (1992) 15 LS Gaz R33, AC Hudson v Ridge Manufacturing Company Limited [1957] 2 QB 348, (1957) 2 All ER 299. Johnstone v Bloomsbury Health Authority (1992) QB 333, (1991) 2 All ER 293. Jones v Livox Quarries Limited [1952] 2 QB 608, 96 Sol Jo 344. Joseph v Ministry of Defence (1980) Times, 4 March, CA. King v RCO Support Services Ltd. [2001], ICR 608, AC. King v Sussex Ambulance NHS Trust (2002) EWCA civ 953, LTL 05/07/2002. Knott v Newham Health Care NHS Trust (2002), (2002) EWHC2091 (QB), LTL 16/10/2002. Koonjul v Thameslink Healthcare Services NHS Trust [2000] LTL 28/03/2000. Marshall v Golham Co. Ltd. [1954] AC360. McCaffery v Datta (1997) CLR 142.
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McCann v J.R. McKeller (Alloys) Limited [1969] SC (HL) 1. McPherson v London Borough of Camden (1999) QBD, Itl 24/05/1999. McQuilter v Goulandris Bros. Limited [1951] SLT (notes) 75. McSherry v British Telecommunications PLC [1992] 3 Med LR 129. Mearns v Lothian Regional Council (1991) SLT 338. Morris v West Hartlepool Steam Navigation Company Limited [1956] AC 552, (1956) 1 All ER 385. Mughal v Reuters Ltd. (1993) IRLR 571, 16 BMLR 127. Munrow v Plymouth Health Authority (1991) (unreported 5/12/91) H.C. Exeter. National Coal Board v England [1954] AC 403, (1954) 1 All ER 546. O’Neill v DSG Retail Ltd. (2002), LTL 31/07/2002. Paris v Stepney Borough Council [1951] AC 367, (1951) 1 All ER 42. Purves v Buckingham County Council, (20 Nov. 1998, unreported) QBD. Reed v Ellis (1916) 38 OLR 123. Russell v Criterion Film Productions Limited [1936] 3 All ER 627. Schwalb v H. Fass and Son Limited (1946) 90 Sol Jo 394. Smith v Cammell Laird & Co. Ltd. [1940] AC 242. Smith v Leech Brain & Company Limited [1962] 2 QB 405, (1961) 3 All ER 1159. Staveley Iron and Chemical Company Limited v Jones [1956] AC 627, (1956) 1 All ER 403. Stokes v Guest Keane Nettlefold (Bolts and Nuts) Limited [1968] 1 WLR 1776, 5 KIR 401. Thompson v Smith Ship Repairers (Northshields) Limited [1984] QB 405, (1984) 1 All ER 881. Toronto Power Co. Ltd. v Paskwan [1915] AC 734. Wagon Mould (no 2) [1967]—Overseas Tankership (U.K.) Ltd. v Miller SS Co. Pty. (1967) 1 AC 617, (1967) ALR 97. Walker v Wabco Automotive U.K. Limited (1999, unreported), CA. White v Hallbrooke Precision Castings Limited [1985] IRLR 215, CA. Wilson v Tyneside Window Cleaning Company [1958] 2 QB 110, () 2 All ER 265. Wilsons and Clyde Coal Company Limited v English [1938] AC 57, (1937) 3 All ER 628. Wright v Dunlop Rubber Company Limited and ICI Limited (1972) 11 KIR 311, 115 Sol Jo 366.
11 Age and Functioning in the Legal System: Victims, Witnesses, and Jurors Deborah Davis University of Nevada, Reno Elizabeth F.Loftus University of California, Irvine 0–415–28870–3/05/$0.00+$ 1.50 © 2005 by CRC Press
11.1 Objectives and Organization of the Chapter As the population of elderly citizens continues to increase in the United States, greater numbers of older adults will become victims of crimes and later report their experiences to police, attorneys, and juries, and perhaps attempt to identify the perpetrators (National Institute on Aging, 1996). In fact, already we know that roughly 2 million elderly individuals become victims of crime each year (U.S. Bureau of Justice Statistics, 2002). Likewise, older Americans will become disproportionately represented among accident victims, witnesses in civil and criminal trials, and juries. Thus, aging has an impact upon the legal system in myriad ways, from its role in generating situations subsequently litigated in the courts, to the vagaries of memory among aging witnesses, to the role of age in juror judgments. To provide context for understanding age-related declines in cognitive functioning, we begin this chapter with a brief review of changes in the brain and their consequences for basic mechanisms of cognitive processing. Subsequently, we consider specific agerelated deficits in cognitive functioning that (1) cause or contribute to incidents generating torts; (2) impair accuracy of testimony regarding these incidents; and (3) affect jurors’ processing of evidence and, thus, verdicts. 11.2 Sources of Age-Related Declines in Cognitive Functioning The Aging Brain Modern cognitive neuroscience has begun to identify changes in the brain that in turn appear to cause changes in fundamental cognitive processes such as information processing, memory, performance, and judgment (for reviews of the following, see Glisky, 2001; Grady, 2001; Raz, 2000; Reuter-Lorenz, 2000; Schacter, 1996; and the
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special 2002 issue of Neuroscience & Biobehavioral Reviews Vol. 6, Issue 7, on the aging brain). Structurally, for example, there is widespread shrinkage of brain matter volume (and thus enhanced volume of cerebrospinal fluid) stemming from such underlying causes as shrinkage of the brain tissue, cell loss in some regions, and reduced dendritic branching. Enhanced atrophy is one of the hallmarks of Alzheimer’s disease, but is also characteristic of older adults without such a diagnosis. Atrophy is also greater in those with high blood pressure or declining diastolic blood pressure (de Heijer et al., 2003). Brain mass steadily shrinks after the 50s at the rate of roughly 5 to 10% per decade, and brain volume is related to cognitive performance and dementia (Anstey and Maller, 2003; Mingus et al., 2002; Pantel et al., 2003; Scahill et al., 2003; Sullivan and Ruffman, 2004). Indeed, those who begin with smaller volume (i.e., smaller head circumference) and have less education are four times as likely to suffer dementia as others (Mortimer et al., 2003). Perhaps related to atrophy of tissues and cell volume, brain metabolism also changes so that cerebral blood volume and flow and cerebral metabolic rate of oxygen utilization decline. Age is negatively related to cerebral blood flow, which in turn predicts memory performance (Santens et al., 2003). Neuropathology also tends to escalate with age. A yellowish-brown lipid lipofuscin, called “wear and tear pigment,” accumulates in cells throughout the cerebellum and cerebral cortex, typically accompanied by decrease in myelination of nerve axons and increased numbers of vascular lesions. In Alzheimer’s patients, the brain accumulates neuritic amyloid plaques and tau protein tangles, which hamper neuronal function and eventually kill the cells. The extent of these plaques and tangles in neural tissue (although the extent of tau tangles is more predictive), combined with the number of areas of the brain in which they are present and the presence of stroke damage, directly predicts cognitive symptoms (Schneider et al., 2003; Snowdon, 2001; Guillozet et al., 2003). Neuronal communication is impaired by reduced dendritic branching and demyelination of axons (Bartzokis, 2004), as well as decline in neurotransmitters such as dopamine (which contributes to frontal lobe functions) and acetylcholine (which plays a role in learning and memory). One of the most prominent changes in the white matter of the brain (myelinated axons connecting nerve cells) is known as white matter hyper intensities (WMHs), which can be observed in MR images (or called leukoaraiosis when seen on CT scans). These WMH changes are assumed to reflect damage from vascular as well as neuronal causes and, particularly in some regions, they predict cognitive impairment (Bigler et al., 2003; Deary et al., 2003; de Groot et al., 2000). The effects of these abonormalities can be attenuated in those with greater education, however (Dufouil et al., 2003). The preceding changes in brain structure and pathology are not uniformly distributed throughout the brain. Some structures atrophy at greater rates, such as the hippocampal formation; the frontal, temporal, and parietal convexities; and the parasagittal region, whereas others, such as the occipital lobe, remain relatively spared. Changes in neuropathology are also somewhat region specific. Given this situation, it is not surprising that consensus exists among cognitive-aging researchers that although mental processes generally slow and become less efficient—and thereby become, in some cases, less accurate—arenas exist in which performance is age invariant or even positively
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related to age (see reviews of age-related changes in a variety of cognitive processes in Craik and Salthouse, 2000; Salthouse, 2004; Verhaeghen and Salthouse, 1997). Generally, memory researchers have found greater declines in memory tasks that require a great deal of self-initiated or effortful processing (such as complex reasoning) but age invariance on memory tasks that require less effortful processing (such as word recognition) (see reviews in Craik and Salthouse, 2000; Light, 1991; Park and Schwartz, 2000). Generally, speed of processing, reasoning, and episodic memory (memory for events) appear to decline most rapidly (Salthouse, 2004; Verhaeghen and Salthouse, 1997). Selective decline in cognitive functioning appears to be related to selective decline in the brain. Unfortunately, some of the most vulnerable structures are also those most important for cognitive functioning. For example, the hippocampus (which contributes to formation and maintenance of memories) and the amygdala (considered particularly important for emotional memories) exhibit loss of number and volume of neurons, as well as synaptic loss. Medial-temporal dysfunction has been related to losses in long-term memory. Furthermore, the frontal lobes, and particularly the prefrontal cortex, are widely thought to suffer decline sooner and more extensively than other regions. Losses in volume, cells, and blood flow are greater in frontal regions, and some evidence indicates selectively greater decline in neurotransmitters and myelin (see the review in Rabbitt et al., 2001). Frontal lobe function has been shown to predict performance on a variety of tests of memory, cognitive functioning, and executive functions such as planning, initiating, and carrying out goal-directed behaviors—and inhibition of inappropriate behaviors. Age-related deficits in frontal functioning are related to a variety of failures of perception, memory, and decision making in forensic contexts. These will be reviewed in subsequent sections. Finally, the corpus callosum, which connects the various regions of the brain, suffers enhanced atrophy relative to some other regions of the brain, thus suggesting that it may be particularly susceptible to the effects of aging. Because a variety of processing and memory functions require communication between regions, dysfunction of the corpus callosum will contribute to age-related cognitive deficits. Indeed, age-related differences in processing efficiency have been shown to be greater for tasks requiring communication through the corpus callosum (see the review in Reuter-Lorenz, 2000). Indeed, some have argued that neural networks and larger systems of interconnected brain regions and the functional activity in these circuits may be generally more important than specific cortical regions in predicting cognitive functioning (Tisserand and Jolles, 2003) and that the frontal cortex may exert its effect upon executive functioning in combination with processes involving links between different brain regions (Andres, 2003). Raz (2000) noted that the magnitude of dysfunction is related to the order of appearance of structures in mammalian history such that “last in is first out” (p. 37). Those that evolved in more ancient species and those that appear earlier in human development are less affected by age than those that evolved or appear later. Thus, structures such as the prefrontal cortex, which evolved last and is presumed to be the seat of the intelligence that separates humans from lower animals, suffers the earliest and greatest decline with age. Structures that evolved earlier, such as the pons or occipital cortex, suffer much less damage with age. It should be noted, however, that even though
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these regions maintain greater structural integrity, functioning may decline. For example, the primary visual cortex exhibits decline in sensitivity and increases in response time (Crognale et al., 2001). In apparent response to increasing decline in structure and function, the brains of older adults appear to accomplish cognitive functions somewhat differently than those of younger adults, as indicated by brain imaging during task performance. Thus, the aging brain appears to compensate for changing physiology and structure by rerouting or reorganizing functions, sometimes recruiting more of the brain to accomplish tasks that, in younger years, required fewer regions. The multitude of changes in the underlying structure, neuropathology, and function of the brain are presumed to cause changes in four general cognitive mechanisms widely considered responsible for age-related declines in a wide range of specific cognitive tasks. These are (1) sensory function, (2) speed of information processing, (3) working memory functioning, and (4) inhibitory processes. Each of these is conceptualized as a form of “cognitive resource” or “processing resource,” with the combination viewed by some as the best index of overall cognitive resources (Salthouse, 1991). The nature of these changes is reviewed in the following sections. Perception and the Aging Senses As the preceding section made clear, age-related changes in cognitive functioning are clearly linked to underlying changes in brain physiology. Among the most fundamental of these functions is sensory perception. External information can only enter the brain for further processing through the gateway of the senses. When these senses fail, so will the accuracy of perception and, in turn, that of memories and judgments based on the flawed perceptions. To the extent that information is encoded poorly or incorrectly, it cannot later be remembered completely and accurately or used appropriately. In this sense, then, perception may be regarded as the most fundamental sense in which cognitive processing fails with age. Clinically significant and subclinical reductions in hearing and vision increase markedly with age, beginning in the 40s (see reviews in Kline and Scialfa, 1996; Schneider and Pichora-Fuller, 2000). Of particular importance, whereas loss in visual acuity can often be compensated for through corrective lenses, in most cases hearing aids are limited in effectiveness for correction of hearing loss (Lubinski and Higginbotham, 1997). Even so, uncorrectable losses in vision and hearing become more common with increasing age. Some have argued that sensory functioning is a crude proxy for brain integrity and suggested that sensory function should therefore mediate all remaining cognitive abilities (Lindenberger and Baltes, 1994, 1997). In two studies, the authors tested subjects ranging from 25 to 103 years of age. Simple tests of auditory and visual acuity were strongly correlated with a wide range of other cognitive abilities, such as speed of processing, reasoning, memory, world knowledge, and verbal fluency. Furthermore, sensory functioning appeared to function as a more fundamental cognitive resource, and/or as a better indicator of underlying brain functioning, than the other cognitive mechanisms to be discussed later, in that the sensory tests mediated age-related variance in the other measures of cognitive function. Taken together, vision and hearing accounted for 49.2%
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of the total variance in the overall index of cognitive functioning and 93.1% of the agerelated variance. Other researchers (Mariske et al., 1997; Salthouse et al., 1996) have since obtained similar findings (see the review in Schneider and Pichor a-Fuller, 2000). Dulay and Murphy (2002) argued that such effects should obtain for all senses if the common cause hypothesis is valid. Consistent with this supposition, brain reactivity to olfactory stimuli declines (Cerf-Ducastel and Murphy, 2003), olfactory threshold rises, and odor detection and identification and odor memory decline across the lifespan (Lehrner et al., 1999; Larsson et al., 2000), and the quality of olfactory functioning predicts general cognitive decline (Dulay and Murphy, 2002). Although such correlational results do not indicate that decrements in cognitive functioning are caused by losses in sensory function, they do indicate that decrements in sensory functioning are powerfully predictive of decrements in other cognitive functions—most likely, as Lindenberger and Baltes (1994) suggested, because sensory function is a better proxy for underlying brain function than the other measures. Not surprisingly, other variables related to physical (and thus brain) decline have been related to cognitive performance. Interestingly, balance-gait accounted for as much variance in cognitive functioning as hearing/vision in the Lindenberger and Baltes studies and may be thus taken as another excellent predictor of cognitive function. Other studies have found a link between grip and lower-limb strength and cognitive performance (see Schneider and Pichora-Fuller, 2000, for review). Recent evidence has also begun to link metabolic processes such as glucoregulation (Messier et al., 2003) to cognitive performance. Hearing Older listeners tend to suffer decline in processing of auditory information (labeled “presbycusis”), the hallmark of which is elevated thresholds for detection of highfrequency (higher-pitched) sounds, due to damage to hair cells at the base of the cochlea (cells on the basilar membrane in the inner ear where high-frequency sounds are coded). In addition, the elderly tend to suffer difficulties in detection of simple, high- and lowintensity stimuli, discrimination of small changes in frequency (pitch) or intensity (loudness), temporal resolution abilities (detecting when one sound stops and another begins), filtering out of background noise, and precision in location of the source of sounds—and thereby to suffer deficits in correct encoding of auditory information in many everyday situations (see Pichora-Fuller and Carson, 2001, for review of physical causes of these declines). In practical terms, perhaps the greatest deficit resulting from hearing loss is accuracy in speech perception. Discrimination between consonants becomes difficult for the elderly, particularly the higher frequency consonants such as “f,” “g,” “s,” “t,” and “z” (Sataloff and Vassallo, 1966). Generally, speech begins to sound “fuzzy,” with words appearing to run together even when the speech is loud enough to hear. These problems are exacerbated by general decline in cognitive processing efficiency that slows processing of speech, sometimes to the point that earlier words or sentences have dropped from working memory before the rest are fully understood (see Nussbaum et al., 2000). Speech processing also becomes more difficult when others speak at a fast rate; when
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there is external noise, distortion, or reverberation in the target speech; and when the listener is under stress (see Kline and Scialfa, 1996, for review). Problems with hearing in conversation require a louder and slower conversational style and can result in such poor outcomes as inaccuracy and misunderstanding, stress in both parties, inefficiency, slowness and repetition, and avoidance of further conversation on the part of both parties. Finally, because we also rely on hearing to produce our own speech sounds, hearing loss can result in declining clarity in production of speech (Nussbaum et al., 2000). Despite these problems, three quarters of those who might benefit from hearing aids fail to use them, and among those who do, many problems remain unsolved. Hearing aids function to aid in hearing low-intensity sounds, such as consonants in speech, but also tend to amplify irrelevant and unwanted background sounds that interfere with hearing of the target sounds. This leads users to experience difficulties processing specific sounds— such as speech—in auditorily complex situations involving multiple simultaneous sources of sound (see the review in Schneider and Pichora-Fuller, 2000). Even those who show hearing sensitivity within normal limits and hear well in quiet conditions may suffer age-related inability to hear well in noisier circumstances (see reviews in CHBB, 1988; Willott, 1991). Individuals suffering from cochlear pathologies may also find speech discrimination difficult even in quiet circumstances (see Humes, 1996, for a review); in addition, they have enhanced difficulties with frequency selectivity (ability to detect smaller differences in pitch) and abnormal growth of loudness as signal intensity increases (see reviews in Moore, 1989; Pickles, 1988; Schneider, 1997). Of particular importance, even when speech is understood under noisy or other perceptually difficult conditions, it is remembered less well (see Schneider and PichoraFuller, 2000, for review) by older as well as younger adults. Thus, it is important to consider the external context in which conversation was heard, along with the internal processing difficulties created by the age of the listener, when attempting to assess accuracy of processing of, and memory for, speech. As suggested by Rabbitt (1991), difficulty in hearing may affect memory because the more resources one must devote to decoding the speech signals, the fewer are available to think about what is heard—i.e., to rehearse the material or to process it deeply and elaboratively—which would otherwise facilitate memory (see below). Specific hearing deficits may derive from degeneration of the ear (such as losses in threshold sensitivity to various frequencies and the cochlear pathologies noted earlier) or brain functioning. Even when a person has a normal audiogram assessing threshold sensitivities primarily determined by the ear, age-related deficits detected by auditory brainstem responses (ABRs) may independently cause decline in auditory functioning under more difficult circumstances. For example, deficits of synchrony in neural firing may cause problems with frequency discrimination, temporal discrimination, localization, binaural unmasking (ability to focus on a particular sound when multiple sounds enter each ear from multiple but different origins), or speech perception (see Hellstrom and Schmiedt, 1990) Again, such losses may be independent of threshold sensitivity. For example, difficulty in temporal discrimination (e.g., detecting when a sound has stopped and another begun) may cause difficulties in speech perception, even though the person hears loudness adequately. Older adults experience greater difficulty with gap detection
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and with detection of differences in duration of sounds (see Fozard and Gordon-Salant, 2001; Schneider, 1997; Schneider and Pichora-Fuller, 2000; Strouse et al., 1998). Finally, difficulties in speech perception can be compensated for in some degree by lip-reading and general use of nonverbal cues to clarify meaning. However, because vision also tends to decline with age, the older person is often further hampered by inability to read and employ nonverbal information effectively (Nussbaum et al., 2000). Some have argued that difficulties in comprehension of speech and conversation are caused by the increased load imposed on working memory by the enhanced effort that older listeners must devote to accurate hearing (Rabbitt, 1991). The more working memory resources must be devoted to detection and identification of the sounds, the less working memory capacity is available for processing and storage of meaning. If so, removing the burden of sound detection and identification should improve cognitive processing of the speech. Therefore, several researchers have addressed the question of whether age-related declines in word recognition, immediate recall of verbal materials, and discourse comprehension can be eliminated or reduced by improvements in hearing. These studies addressed this issue by adjusting volume to exceed the threshold sensitivities of young and old adults by a constant amount—in quiet and noisy conditions—so that each person could recognize the words accurately, or by hampering the hearing of younger adults to simulate the sensory difficulty of older adults. Generally, these results indicate that when the sheer difficulty of hearing the words adequately is equated between young and old, age-related differences in comprehension and memory are minimized or eliminated (see the review in Schneider and Pichora-Fuller, 2000). Summary Clearly, age is associated with a variety of hear ing-related losses. Perhaps most important for the forensic arena are losses in accuracy of speech perception, elevation of thresholds for sound detection, and increasing difficulty in sound localization. However, when the possible role of hearing in forensic circumstances is considered, it is vital to remember that the specific deficit of interest must be directly tested. As shown by a host of studies (see reviews in Moore, 1989; Pickles, 1988; Schneider, 1997; Schneider and Pichor a-Fuller, 2000; Hellstrom and Schmiedt, 1990; Humes, 1996), a person may have normal or reasonably normal threshold sensitivity as measured by standard hearing tests while suffering several serious losses in other auditory functions or, indeed, in threshold sensitivity under circumstances more complex than those presented by a standard hearing test. Of particular interest would be the effects of aging on speech perception. Although the person possessing normal threshold sensitivity may hear the speech as loud enough, some of the fine detail encoded at higher frequencies would be lost even in quiet circumstances. In louder circumstances, low frequencies tend to be masked by the background noise, and gap perception becomes more difficult, thereby blurring distinctions between words. Gap perception also becomes more difficult for older listeners with faster speakers. Difficulties with binaural processing can impair ability to localize the source of sound and to focus clearly on one speaker amid a crowded noisy room. Thus, for any given older person of normal threshold sensitivity or not, specific deficits of relevance to the situation in question must be individually established.
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Vision Correctable refractive errors constitute the most commonly recognized age-related form of decline in visual functioning. However, even with such correction and among those with both good and bad general health of the eyes, visual acuity (per the “Snellen” measure in which subjects must identify letters of varying size at a specified distance) begins to decline after 45 years of age. Moreover, declines occur in other aspects of visual functioning, such as contrast sensitivity (ability to discern luminance differences for targets of various sizes) and contrast discrimination (ability to discern differences between objects in amount of contrast to background). Older adults may need two to three times more contrast to be able to see small- or medium-sized targets (such as the characters that comprise most text). Other aspects of visual functioning decline as well, including dark adaptation (speed with which rod-based black-and-white vision functions clearly after light is reduced or eliminated), perimetric fields (gradient of differential ability to see (threshold sensitivity) in the foveal vs. peripheral regions of the retina), color vision, and stereopsis (use of both eyes for depth perception). Pathologies of the eye also increase with age, including cataracts, glaucoma, and macular degeneration (see Michaels, 1993, for a review). Overall, visual representations tend to become less precise or accurate—more so under conditions of poor lighting or poor stimulus contrast (for a review, see Faubert, 2002; Schneider and Pichora-Fuller, 2000; Pichora-Fuller and Carson, 2001; also see Enoch et al., 1999, for discussion of some visual functions that do not decline with age). Visual perception also becomes slower, so longer viewing times are necessary for older adults to perceive and recognize a visual image (Jacoby and Debner [2001], discussed in Jacoby et al., 2001). As with hearing, some age-related changes in vision are the result of changes in the eye: • Retinal image quality (visual acuity) is reduced and hence vision is blurred by changes in light diffraction through the cornea. • Thresholds for rod (low light level) and cone (high light level) vision are raised as less light passes through yellowed and more opaque lenses and narrowed pupils. • Poorer rod vision (including poorer vision under low illumination and restricted effective field of view) results from decreasing numbers of rods (Curcio, 2001). • Poorer cone (high light level) vision results from decreased sensitivity of the cones to the light that does pass through to the retina (Werner, 1998). • Presbyopic difficulties in adjusting focus to accommodate distance follow from increases in stiffness of the lenses. • Inefficient transduction of light to neural impulses results from narrowing of the arteries of the retina. • Decrease in retinal contrast is caused by increased light scatter by the cornea (resulting in decreased ability to detect and recognize common objects, including traffic signs). • Blue-yellow color confusions are caused by greater absorption of and therefore reduced sensitivity to shorter (blue) wavelengths (and discrimination of colors of the same hue and desaturated colors such as pastels becomes more difficult).
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Generally, less efficiency and precision in processing visual input results. (See Faubert, 2002; Fozard and Gordon-Salant, 2001; Kline and Scialfa, 1996, 1997; Schneider and Pichora-Fuller, 2000; Scialfa, 2002; Spear, 1993.) Essentially every structure in the primary visual pathway changes with age. Density in the retinal ganglion cell layer decreases, particularly outside the macular region. Similarly, cell and synapse density, number of synapses, and myelin sheath integrity decrease in the visual cortex. Similar changes occur throughout the brain and predict a variety of specific indices of cognitive decline (Faubert, 2002; Peters et al., 1996, 2000; Nielsen and Peters, 2000; Scialfa, 2002). Great individual differences exist within age groups, with poorer vision associated with greater exposure to sunlight, which is associated with aging of the lens and the retina (see Werner, 1998, for review). There is substantial evidence of the practical effects of declining visual functioning of the eye on activities of daily living. Difficulties with visual acuity, depth perception, motion perception, and vision in low illumination or shadowed areas cause difficulty in managing daily routines. We illustrate a number of these effects in the context of driving. Visual Acuity Visual acuity (the clarity of an image) is especially important for night driving (Eby et al., 1998; Panek et al., 1977), but declines substantially with age, particularly in conditions of low illumination. Thus, visual acuity—at least for drivers (and especially older drivers)—tends to be worst when it is most needed. The previously referenced changes in lens color and opaqueness, combined with narrowing of the iris and often cataracts on the corneas, reduce the amount of light entering the eye. Because the sharpness of an image is dependent upon illumination and, to some degree, on color and because color vision drops out with sufficient drop in illumination, overall visual acuity will decline with decline in illumination entering the eye. Furthermore, neural processing mechanisms adapt to lower illumination by, in essence, trading temporal and spatial acuity for sensitivity. The aging eye causes some degree of reduction in illumination under all circumstances. However, this essential reduction renders the aging person more vulnerable to loss of acuity in external conditions of low illumination, such as nighttime. Indeed, older persons have substantially greater difficulty with night vision (and night driving), as well as more difficulty (time needed) in recovering from glare (see Klavora and Heslegrave, 2002). Motion Perception Motion perception is dependent upon a variety of visual factors, including • Ocular musculature adequate to track objects smoothly • Contrast sensitivity (ability to see differences in luminance between target and background) • Stereopsis (use of both eyes for depth perception) • Temporal contrast sensitivity (ability of the eye to see changes occurring over time at different rates, such as fast vs. slow flickering patterns) • Backward masking (the ability of new stimuli to obscure the afterimage of previously seen objects)
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These factors, as well as others, decline with age. Thus, not surprisingly, motion perception (dynamic vision) tends to be impaired in the elderly (Tran et al, 1998; Willis and Anderson, 2000; Wist et al, 2000, Wojciechowski et al., 1995) in foveal and peripheral vision, although more so in the foveal area (see reviews in Schneider and Pichora-Fuller, 2000; Faubert, 2002; Scialfa, 2002). Because the oculomotor system (eye movement) is slowed with age, older adults suffer impairments of tracking speed—i.e., greater difficulty tracking objects moving at high speeds and when there is a high degree of relative motion between the target and observer (Scialfa et al., 1988). Furthermore, older adults suffer deficits in visual marking for moving stimuli. Visual marking refers to the top-down inhibition of attention to or processing of old stimuli already in the visual field (such as cars already in the stream of traffic) so that processing of new visual information (such as a car entering the traffic stream) can be facilitated (Watson and Humphreys, 1997). This visual marking is assumed to be advantageous, in that it facilitates the observer’s ability to maintain an upto-date representation of the world, which in turn would provide the most useful basis for action decisions. As we shortly review, older adults suffer deficits in attentional control, particularly in controlled inhibition of attention to undesirable or irrelevant stimuli. Consistent with this general deficit, older adults manifest deficits in visual marking for moving stimuli (although they do so less consistently for stationary stimuli; see Kramer and Atchley, 2000; Watson and Maylor, 2002). That is, they show greater difficulty locating new stimuli amid a constellation of already present stimuli. Age-related declines in marking ability are relevant for a variety of everyday human factors issues (see Rogers and Fisk, 2000), such as driving, instrument monitoring, air traffic control, and so on). In practical terms, deficits in motion perception play a substantial role in automobile accidents among the elderly (Staplin and Lyles, 1991). Difficulties in motion perception render the elderly subject to errors in speed, distance, time-to-collision, and gapacceptability judgments, which tend to result in misjudgments in complex traffic situations, including failure to yield the right of way. Such failures, in combination with generally slower responses, are responsible, for example, for the tendency of the elderly to be involved in accidents in which they turn left in front of an oncoming vehicle (see Klavora and Heslegrave, 2002, for review). Older persons also become less sensitive to (less likely to notice changes in) temporally modulated (changing across time) stationary patterns such as flickering lights, as well as to spatial movement of objects (see Schneider and Pichora-Fuller, 2000). While a person is driving, for example, this insensitivity can result in failure to notice a vehicle begin to move, changes in traffic lights, or other important changes in position. Visual Search Visual search refers to the ability to identify a target object or objects in a field of distractors. Depending upon the complexity of the scene, the number of distractors, the nature of features distinguishing the target from distractors, and features of the context such as fog, mist, or poor illumination, accuracy and speed with which the target is located can be compromised. Correct discrimination between stimuli requires comparing a given stimulus with internal models of correctness and incorrectness. Reduction in
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short-term visual memory capacity will limit ability to discriminate accurately and rapidly. Generally, age is associated with poorer overall performance and greater reactivity to features that tend to compromise performance (Burton-Danner et al., 2001; Scialfa and Joffe, 1997; Madden et al, 2002; Speranza et al., 2001). Indeed, older adults report difficulties with everyday activities relying on visual search, including such problems as distracting objects and events, cluttered visual scenes, and insufficient time to find target objects (Kosnik et al., 1988; Kline et al., 1992). Safe driving often requires the ability to search complex traffic scenes rapidly in order to locate critical objects—such as signs, traffic lights, pedestrians, turnoffs, and address markers—and respond appropriately. Therefore, age-related slowing and increased susceptibility to distractors render older drivers less able to locate critical objects. For example, older drivers are less able to locate traffic signs successfully, particularly in visually cluttered scenes (Ho et al., 2001; Schieber and Goodspeed, 1997) and less able to read them successfully, particularly at night (Sivak et al., 1981). Older adults tend to scan traffic scenes differently, using more fixations, less evenly distributed fixations, and more repeat fixations to a specific target (Maltz and Shinar, 1999) and require more eye movements to find a target such as a sign (Ho et al., 2001). Thus, older adults are less efficient and less accurate in traffic-related visual searches. Peripheral Vision Peripheral vision declines with age, resulting in less likelihood of detection of objects in the peripheral field, less accurate discrimination between objects in the peripheral field, and less accurate motion detection. One study (Johnson, 1986; see also Panek et al., 1977) showed that the range of the visual field declined from 180° among younger adults to 140° beyond age 70. A related index of peripheral vision, the “useful field of view,” or UFV, comprises the limits at which the observer can no longer locate or identify objects or targets in the visual field (tested under conditions in which eye movement is prohibited). (Coeckelbergh and colleagues [2004] discuss age differences for an alternate measure, AFOV, or attended field of view, which tests for target search in circumstances permitting eye movement.) UFV has become popular among many investigators, particularly those concerned with predicting driving performance and accidents (Owsley et al., 1991; Sekuler et al., 2000). Useful field of view is assumed to decrease with age as a function of the three underlying cognitive processes of decreased ability to divide attention, decreased ability to ignore distractors, and reduced processing speed (Ball et al., 1990). UFV has proven to be a strong predictor of accident involvement. Those with poor peripheral vision are believed to have two to six times the accident rate of those with normal peripheral vision (Morgan and King, 1995; Ball et al., 1993; see reviews in De Raedt and PonjaertKristoffersen, 2001; Klavora and Heslegrave, 2002; Park and Gutchess, 2000). However, this predictive value appears to be due to the divided attention component and is unrelated to the other two (Owsley et al., 1998). In light of the role of capacity for divided attention in determining UFV, it is not surprising that the presence of distractors effectively reduces UFV (Sekuler et al., 2000), particularly for older adults in whom capacity for divided attention is reduced (see below). Such distractors can include irrelevant objects in the peripheral field, greater
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similarity between relevant and irrelevant objects, and engagement in multitasking (such as eating or talking on the phone while driving). Depending upon circumstances, older adults’ UFV can become restricted to only one third of that of younger adults in similar circumstances (see Schneider and Pichora-Fuller, 2000, for review), with obvious consequences for detection of pertinent traffic signs, obstructions, and approaching vehicles. Fortunately, declines in UFV can be successfully decreased with normal elderly clients and stroke victims with a program called “visual-motor useful field of view” (VM-UFOV) using the “Dynavision” apparatus (a device used for training athletes and others to enhance dynamic vision, reaction time, movement time, hand-eye coordination, peripheral vision, and the ability to divide attention and make decisions under stress). The device is in use in a number of rehabilitation and medical centers across the country (see the review in Klavora and Heslegrave, 2002). Summary As with hearing, a number of age-related declines occur in the visual system. Also, as with hearing, in forensic contexts it is vital to test the specific suspected deficits relevant to the situation at hand. The most common vision test is the Snellen test of visual acuity (identification of letters of varying sizes from fixed distances). However, Snellen acuity is measured in conditions involving no motion but full illumination. For this reason, it is a poor predictor of other aspects of processing, including impaired processing of motion, tracking of high-speed objects, vision in low illumination, and the UFV index that is so predictive of peripheral vision performance and automobile crashes. For traffic accidents involving the elderly, impairment in one or more visual skills may well play a causal role. The elderly appear to be aware of visual deficits to some degree. They drive shorter distances; drive more slowly; and decrease their night, highway, and rush-hour driving. However, they are still at greater risk of accidents, per mile driven, at a level comparable to that of 15- to 25-year-olds (see Klavora and Heslegrave, 2002; De Raedt and Ponjaert-Kristoffersen, 2001). Although thus far we have illustrated with examples regarding driving, impairments in vision contribute widely to a variety of accidents and are relevant for ergonomic design in a number of situations (see Echt, 2002, for an excellent review of the effects of agerelated declines in vision on reading and the use of computer screens) and to issues of perception and memory in forensic contexts involving witnesses and jurors (explored later). Processing Speed Substantial evidence exists in support of the proposition that decreased speed of processing accounts for age-related decline in performance of all cognitive tasks. Salthouse (1991,1996) proposed that two general mechanisms underlie the relationship between speed of processing and cognitive performance. First, Salthouse suggested that “the time to perform later operations is greatly restricted when a large proportion of the available time is occupied by the execution of earlier operations” (p. 404), which he referred to as “the limited time mechanism.” Second, he suggested that “the products of
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earlier processing may be lost by the time that later processing is completed” (p. 405); he referred to this as the “simultaneity mechanism.” These two mechanisms can together result in slower, but still accurate, performance or performance failures. Earlier stages of processing may be slowed but accurate, but can result in performance failure if this slowing causes the person to fail to reach later stages. Salthouse (1991, 1996) believed the effects of slow processing to affect all cognitive tasks, including those with no obvious speed component. Salthouse (1996) reviewed an impressive array of evidence that performance on “perceptual speed tasks” is an excellent predictor of performance on a wide range of other specific cognitive tasks. Perceptual speed tasks require the person to make rapid perceptual same-different judgments about pairs of digit or letter strings, or two similar symbols. Speed of processing is measured by the number of correct same-different comparisons made in a fixed period of time. Generally, Salthouse (1996) demonstrated that age-related variance on other specific cognitive tasks is reduced or eliminated when controlling for variance in processing speed. Despite the success of perceptual speed tasks as predictors of performance on other, even apparently non-speed-related, cognitive tasks, the processing speed theory of agerelated decline has not been universally accepted, as suggested by Bashore et al. (1997), Fisk and Fisher (1994), Hartley (1992), and Perfect (1994). These authors suggest that no strong tests have been conducted regarding the issue of whether age differences on the wide range of specific tasks are attributable to the general factor of processing speed vs. process- or task-specific factors and no agreement on how best to test the relative influences of general vs. specific factors has been reached. Notwithstanding such unresolved issues, however, it is clear that speed of processing does decline with age (Salthouse, 1996). Processing Speed and Older Drivers A person trying to follow directions or a map can often be required to make quick choices and execute them in a complex and rapidly moving traffic situation—frequently in the midst of complex and rapidly changing contexts such as shopping districts replete with shops, pedestrians, and cyclists. Thus, impairments of processing and response speed can seriously compromise the driving safety of older adults, who tend to perform best under simple conditions, when not rushed. Increased difficulties of older adults in perception, choosing responses, preparing and executing responses, and so on tend to result in slower reaction times that, in turn, can cause accidents. Stelmach and Nahom (1992) reviewed changes in all aspects of motor performance, including selection, preparation, and execution of responses, among others. Consistent with a large body of research showing stronger age-related declines of all kinds under more complex or demanding conditions, decrements in speed were particularly strong under conditions of task complexity and complex arrays of stimuli—for example, during complex driving situations or responding to pending collisions. Increased decrements under demanding conditions are presumably due to increased demands upon working memory (see below). In this light, not surprisingly, response selection (which presumably places the greatest demands upon working memory) was the most age-sensitive factor studied.
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In addition to slowing of cognitive processing with age, physical behaviors and reactions are slowed as well. Older drivers exhibit slower movements, due in part to reduced joint flexibility, joint deterioration, arthritis, etc. The U.S. Department of Transportation maintains a web site with a variety of materials related to how physical condition and cognitive functioning are related to driving safety (http://www.nhtsa.dot.gov/people/injury/olddrive/), which includes an excellent research report (April, 1999) of the data documenting these relationships (http://www.nhtsa.dot.gov/people/injury/olddrive/safe/). Also see a recent meta-analysis of the relationship between neuropsychological functioning and driving ability by Reger and colleagues (2004). Working Memory Craik and Byrd (1982) suggested that age-related deficits in processing resources are best measured by working memory tasks, rather than perceptual speed tasks. Working memory is conceptualized as the total processing resources available at any given moment to perform online cognitive operations (Baddeley, 1986) and is measured through tasks in which the subject must store and process information simultaneously. For example, a person might be asked to perform a computational span task, in which he or she must solve a series of equations while remembering the second number in each equation. Working memory is measured by how many equations the subject solves correctly while accurately remembering the target number. Well-documented age-related declines in working memory reflect decreasing ability to hold multiple items of information in mind while performing one or more cognitive tasks (see a recent meta-analysis by Verhaeghen et al., 2003) Age-related deficits appear most strongly in cognitive tasks imposing stronger processing demands on working memory, such as tasks requiring simultaneous consideration of multiple items of information, difficult manipulation of information (e.g., reasoning, problem-solving, mathematics), multitasking requiring divided attention, or working in distracting conditions that require filtering of irrelevant information. These deficits are negligible for those requiring less effortful processing (Craik and Jennings, 1992; Light, 1991). Furthermore, effective processing load or capacity is affected by age-related physical conditions. For example, chronic pain (e.g., Grigsby et al., 1995) is related to deficits in information processing, as are such conditions as hypertension, diabetes, impaired thyroid function, and others (see the review in Nilsson and Soderlund, 2001). In practical terms, declining capacity of working memory is reflected in age-related declines in performance of more processing-intensive tasks, in multitasking (see the review in Kemper et al., 2003), and in memory for information encountered during processing-intensive tasks or in complex or distracting circumstances. Of particular pertinence in legal settings, deficits in working memory are widely considered to result in failures of “associative learning” or “binding” (learning associations between items such as between word pairs or, more practically, between a person’s face and the context in which that person was encountered). Failures of this kind are considered to contribute to such dramatic memory errors as mistaken eyewitness identifications (Wells et al., 1998) or development of false memories of sexual abuse (Loftus and Ketcham, 1994). Furthermore, failures of working memory can compromise the ability of older jurors to
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process trial input and to remember it and reason adequately to arrive at an appropriate verdict. Fortunately, declining working memory can be compensated for through “environmental supports” (Cherry et al., 1996; Craik and Byrd, 1982; Park et al., 1990). Essentially, such supports reduce the load on working memory by providing external cues (such as pictures or lists) to make it unnecessary to hold all information in working memory in order to use it for processing or judgment. Working Memory and Older Drivers Decline in working memory capacity is widely considered to contribute substantially to age-related accidents. As working memory declines, the person cannot manage the demands for divided attention and complex decision making that tend to characterize complex driving situations. Therefore, as noted earlier, speed of response slows most dramatically for the elderly under complex, stimulus-intensive driving conditions. In these conditions, many distractors place demands on allocation of attention, and rapid responses to multiple moving stimuli must be selected, planned, and executed rapidly. Older drivers are prone to experiencing cognitive overload on the road and fail to divide attention successfully in order to process the full range of relevant stimuli such as other vehicles, pedestrians, traffic lights and signs, road hazards, and so on. They encounter problems in discriminating between relevant and irrelevant stimuli in complex situations and have difficulty ignoring irrelevant or meaningless information in favor of focus on relevant and important objects. Thus, older drivers have difficulty changing lanes, turning, passing, driving in reverse, and comprehending traffic sign symbols. They tend to commit such attention-related errors as running red lights or stop signs, failure to yield right-of-way, and committing traffic violations during turning maneuvers. Perhaps because the driving situation is more complex at intersections, older drivers are more likely to experience multivehicle, side-impact collisions at intersections, particularly when turning left. They also experience accidents due to tendencies to turn mistakenly prior to the intersection, commit illegal turns, disregard traffic signals, and rear-end others, due to failure to notice change in motion (Stamatiadis et al., 1991). Finally, all of the consequences of limitations in working memory are enhanced by anxiety and stress, which further limit working memory capacity, narrow the focus of attention, and thereby enhance accident potential (see De Raedt and PonjaertKristoffersen, 2001; Klavora and Heslegrave, 2002; Preusser et al., 1998). Generally, Hakamies-Blomqvist (1994) found errors of attention to be the most important cause of fatal accidents involving older drivers. Reflecting failures of attention and processing,. 44% of older drivers in another of this author’s studies (Hakamies-Blomqvist, 1993) had not noticed any danger prior to their accident, whereas only 26% of younger drivers failed to notice danger. Inhibitory Functions A particularly interesting proposition was introduced by Hasher and Zacks (1988; see also Lustig et al., 2001; Persad et al., 2002), who argued that optimal performance requires control over attention to irrelevant information. Furthermore, they provided
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evidence that age is associated with declining ability to focus on target information while inhibiting attention to irrelevant information. Others have since provided neuroimaging and neuropsychological evidence to suggest that age-related declines in attentional control may be the result of age-related changes in the frontal lobes of the brain (Moscovitch and Winocur, 1995; Shimamura and Jurica, 1994; West, 2000). Successful inhibition in older adults is associated with activation of areas of the brain beyond those activated by younger adults, suggesting that older adults must compensate for age-related difficulties in inhibition with supplementary recruitment of brain resources (Nielson et al., 2002). In contrast to theorists emphasizing age-related reductions in speed of processing, the inhibitory control framework emphasizes changes in efficiency of processing. Efficient processing is presumed to require strong attentional control so that attention is occupied only by goal-relevant information. Inefficient inhibitory processes are assumed to permit goal-irrelevant information to command attention and enter working memory, thereby detracting from processing of goal-relevant information. Moreover, impaired inhibitory processes allow the irrelevant information to persist in inhabiting working memory, thereby affecting cognitive performance for some time after exposure. As the attentional draw of the irrelevant information becomes stronger, so does impairment of the focal task (Zacks and Hasher, 1997), particularly when inhibitory processes are compromised by age or other factors. Hasher and colleagues suggest that failures of inhibitory control affect present performance and future memory. Present performance depends upon the ability to concentrate attention on task-relevant information and to ignore irrelevant distractions. Furthermore, memory is dependent upon attention (Schacter, 2001). Memory follows the focus of attention and depends upon the amount and quality of attention. Thus, to the extent that failing inhibitory processes alter the nature of attentional processes, they will alter performance and memory. Proponents of the inhibitory deficit framework view a wide variety of age-related declines in cognitive processing as the result of failing inhibitory processes. Although substantial debate exists regarding whether these deficits are the result of generalized age-related slowing vs. specific deficits in inhibitory capacity (McDowd et al., 1995; Verhaeghen and Meersman, 1998), strong evidence exists of age-related decline in ability to control attention and to engage more generally in controlled rather than automatic processing strategies (see reviews by McDowd and Shaw, 2000; Rogers, 2000). Older adults are less able to sustain attention or maintain focus on relevant information. Problems of this nature are reflected in poorer performance on “vigilance tasks,” such as those of air traffic controllers, radar monitors, or product defect screeners, in which the person must sustain attention for long periods and successfully focus on relevant targets only. Older adults are also more distracted by irrelevant information (current distractors or irrelevant information from long-term memory). This age-related susceptibility to current distractors results in poor immediate performance, as well as shallow encoding and later poorer memory. Memory and performance are further impaired by age-related failures to inhibit attention to irrelevant past information. For example, Lustig and colleagues (2001; see also Bowles and Salthouse, 2003) reviewed evidence that older adults are more susceptible to “proactive interference” effects. That is, previously learned information is
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more likely to interfere with learning (memory for) new information. Presumably, this difficulty in learning the new information is caused by the age-related inability to suppress activation of (and therefore interference from) the old information (see Hedden and Park, 2001, for similar age-related enhancement of “retroactive interference” effects). Similarly, failure to inhibit attention to irrelevant information hampers problemsolving and decision making. Finally, similar inhibition deficits are reflected in agerelated differences in automatic vs. controlled processing in that older adults are more susceptible to the effects of positive priming and more likely to engage in schematic and automatic processing (see reviews by McDowd and Shaw, 2000; Rogers, 2000). In later sections, we explore the implications of these processes for older witnesses and jurors. Circadian Patterns and Inhibitory Capacity Hasher and her colleagues have shown that inhibitory abilities vary with the time of day in older and younger adults. However, whereas younger adults’ abilities are lowest in the morning and peak in late afternoon, those of older adults peak in the morning and wane throughout the day (May and Hasher, 1998; May et al., 1993, Yoon et al., 2000b). May (1999), for example, showed that distractors had greater effects on performance for young and old adults who were tested at their own nonoptimal time of day, compared to those tested at their optimal time. These established differences in circadian arousal patterns can contribute to hourly variation in accidents, performance in job-related settings, or memory and information processing in witnesses and jurors. Stereotype Vulnerability, Stereotype Threat, and Enactment of AgeStereotyped Behaviors A final explanation for age-related decrements in memory and performance has proposed that age differences may be caused in some degree by age stereotypes. Research examining stereotypes of age has revealed positive as well as negative attitudes toward aging and the old. However, in contexts in which cognitive competence is at issue, the stereotypes tend to be overwhelmingly negative (Hertzog et al, 1999; Kite and Johnson, 1988; Levy, 2003), including expectations of declining cognitive performance and memory (see reviews in Levy and Langer, 1994; Nelson, 2002; Stone and Stone, 1997). Ryan (1992) suggested that these stereotype-based expectations of poor cognitive performance may become a self-fulfilling prophecy through indirect impact on decreased effort, lesser use of adaptive strategies, avoidance of challenging situations, or failure to seek medical help as a result of improper attribution of cognitive failures to age, rather than to underlying disease or drug side effects. Similar processes may cause other stereotype-based self-fulfilling prophecies (see Wheeler and Petty, 2001, for review of mechanisms by which stereotypes affect performance). Indeed, research has suggested that childhood exposure to the negative images of old age present in fairy tales, television, and everyday conversations in America can influence one’s level of activity and alertness in old age (Langer et al., 1988; Rodin and Langer, 1980). A series of subsequent studies has supported Ryan’s (1992) reasoning. Levy and Langer (1994) reasoned that age-related deficits in memory performance would be
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predicted by beliefs in age-related memory stereotypes. Therefore, they compared the performance of Chinese mainland participants to that of hearing and deaf Americans. Based on research indicating that those from the Chinese mainland and deaf Americans would have less exposure to negative age stereotypes, they predicted (and found) that, although younger participants from all groups performed equivalently, older American hearing participants performed more poorly than older American deaf or older Chinese participants. In China, no age differences were found on any of the four separate memory tests that commonly show age-related deficits in American participants. Overall, positive views of age also predicted better memory performance, and path analyses indicated that memory performance across cultures was mediated by views of aging. In a subsequent conceptual replication, Yoon and colleagues (2000a) found a difference on two of four memory tasks between Anglophone Canadians and Chinese Canadians who had recently emigrated from Hong Kong. However, younger adults outperformed older adults on all tasks. This age difference was reduced for Chinese Canadians on two tasks, but not eliminated. Moreover, unlike Levy and Langer (1994), views of aging did not mediate memory performance. The authors concluded on the basis of these findings, as well as various methodological issues in their own and the Levy and Langer work, that cultural differences in age-related stereotypes cannot yet be considered a clear contributor to age-related decline in memory. Levy (1996) later employed a subliminal priming methodology to examine the effects of activation of age-related stereotypes on four memory tasks. Older adults consistently performed worse than younger adults. However, exposure of older participants to negative age-related stereotype primes (e.g., senile) resulted in poorer memory performance, whereas exposure to positive (e.g., wise) primes enhanced performance. This difference was not obtained with younger adults, for whom such stereotypes presumably did not seem personally relevant. In a later conceptual replication of Levy’s priming research, Stein and colleagues (2002) found that, although priming negative stereotypes impaired performance of older adults who were unaware of the primes, priming positive age stereotypes did not enhance performance. Like Levy (1996), the authors found no priming effects in younger adults. Levy et al. (2000) argued that exposure to negative age stereotypes can cause cardiovascular stress (which could in turn affect cognitive functioning). The authors exposed older individuals to subliminal presentations of positive or negative age stereotypes, followed by mathematical and verbal challenging tasks (stressors). Those exposed to negative primes exhibited increased physiological responses to stress— including skin conductance, systolic and diastolic blood pressure, and heart rate— compared to those exposed to positive primes; these effects persisted at a second measurement one half-hour after the interventions. Negative primes also induced poorer performance on the math test than positive primes did. Levy and her colleagues went on to explore the effects of subliminal positive and negative age-related stereotypical primes on other age-related behaviors such as measures of walking performance of gait speed and swing time (time with one foot in the air during walking; Hausdorff et al., 1999; see also Bargh et al., 1996, for effects of negative age stereotype primes on walking speed of young adults) and handwriting (Levy, 2000). In each study, performance was shown to conform to the nature of the primes (but in varying degree).
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In perhaps the most dramatic of her studies, Levy et al. (1999–2000) examined whether aging self-stereotypes could influence the will to live. The authors exposed young and old participants to positive or negative age-stereotype primes presented subliminally. They then asked participants to read a series of hypothetical medical situations involving fatal conditions and interventions that could prolong life. The scenarios included presentations of disadvantages of the treatment involving financial cost or care-giving responsibilities of family members. Older persons who were exposed to positive aging stereotypes tended to accept the life-prolonging medical interventions, regardless of financial or caregiving costs, whereas those exposed to negative aging primes tended to reject such interventions although no effects of the primes were observed among younger participants. Levy subsequently demonstrated that positive self-stereotypes of aging measured earlier in life appear to predict the will to live and actual health and mortality in older age (Levy et al., 2002a, b). Finally, borrowing on the stereotype threat paradigm (Steele, 1997), Rahhal and Hasher (1998) examined age-related differences in performance of tasks that participants had been led to believe were memory related (i.e., relevant to the negative age-cognitive functioning stereotypes) or memory unrelated (unrelated to negative age-related stereotypes). Presumably, older adults perform worse when they believe the task reflects abilities (i.e., memory) for which negative age-related stereotypes exist than if it reflects one for which there are no such stereotypes. Indeed, although the tasks were held constant, with memory instructions, younger adults outperformed older adults, whereas with “knowledge” instructions, there were no age differences. Similarly, Earles and Kersten (1998) found that younger adults performing a series of memory tasks tended to remember the items they found most difficult, whereas older adults tended to remember those they found relatively easy. Unfortunately, the effects of memory-related stereotype threat appear to be strongest for older persons who place more value on their memory abilities. Hess and his colleagues (2003) had older and younger adults perform memory tasks under high or low conditions of stereotype threat. High threat affected the performance of older more than that of younger subjects, and this effect was strongest for older adults who valued memory performance the most. In part, stereotype threat appears to impair performance through its effects upon working memory. Although this has not yet been shown with respect to age stereotypes, Schmader and Johns (2003) demonstrated that stereotype threat regarding gender and ethnicity impaired working memory capacity, and that reduction in working memory capacity mediated the effect of stereotype threat on women’s math performance. Overall, the results of these stereotyping studies suggest that older adults can react to salient age-related stereotypes by behaving in stereotype-consistent ways (see the review in Levy, 2003). Thus, negative age-related stereotypes appear to contribute to, but not to explain fully, age-related performance deficits. Although salient positive age-related stereotypes may sometimes reduce age-related performance decrements, it is clear that they cannot eliminate them. It is also clear that older adults can suffer greatly from exposure to (or belief in) negative age stereotypes.
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11.3 Applications to Aging Victims and Witnesses Age-related problems with forensic implications occur at all stages of cognitive processing. We review some of these next. We emphasize the aging witnesses but also discuss implications for generation of accidents. Problems of Perception In order to process and remember information accurately and therefore use it appropriately, the perceiver must first perceive it correctly. Age exerts a major influence at this stage. We have previously reviewed the nature of decline in auditory, visual, and olfactory processes with age and noted some of their effects for aging drivers. We now review several areas of perception that rely on these senses and, therefore, suffer agerelated declines as well. We focus on those that are relevant in forensic contexts. Estimating Time Time estimation is central to everyday life. One must prospectively project time to schedule work and leisure activities such as time to arrive at a destination, cook dinner, perform tasks at work (write a chapter), see a movie, and so on. One must also prospectively estimate much shorter time intervals, such as in those involved in drivingrelated judgments such as time to impact, gap-acceptability judgments, and so on, correctly. Such short-interval judgments are also important for sports-related abilities such as catching a ball. Witnesses are most often confronted with the task of estimating actual time passed— the duration of a particular sound or event (e.g., “How long were you able to observe the perpetrator?”) or the elapsed time between two events (e.g., “How long was the defendant out of the room?” or “How long between when he left and when you heard the scream?”). Generally, estimates of duration tend to be inaccurate and to overestimate actual duration, particularly when the observer is under stress (Loftus et al., 1987; see Block and Rakay for a review). Aging is associated with enhanced inaccuracy (McCormack et al., 2002) and enhanced verbal overestimation of duration (see a meta-analysis by Block et al., 1998). Witnesses are also frequently asked to report the order in which events occurred across short and long intervals. Again, memory for order is often poor across the lifespan, but older adults suffer enhanced impairment (Schmitter-Edgecombe and Simpson, 2001), perhaps because memory for order is dependent upon frontal region functioning (Schacter, 1996). Visuospatial Processing Processing of visuospatial information appears to be particularly susceptible to agerelated decline. Converging evidence indicates that visuospatial cognition is more age sensitive than verbal cognition (Craik, 2000; Jenkins et al., 2000; Lawrence et al., 1998; Myerson et al., 2003a, b; Park et al., 2002; Verhaeghen, 2002). Furthermore, like all aspects of information processing, visuospatial deficits are manifest more strongly as
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demands upon working memory increase (e.g., Chen et al., 2003), for example, in complex visual environments or when multitasking. This decline is reflected in a number of age-related deficits in driving skills, as we outlined in the earlier sections on visual decline. However, visuospatial processing is central to a wide variety of additional daily living skills, as well as in forensic contexts. First, elderly witnesses suffer the same difficulties in processing of speed, motion, distance, time to impact, and so on as elderly drivers. Thus, whether they are the parties involved in an accident or those witnessing it, older persons are less likely to encode such information accurately or to report it accurately later as witnesses. Second, processing of spatial information is central to object identification, including face identification, as we discuss shortly. In addition to facial identification, object identification is crucial to many professions, from military personnel attempting to distinguish friend from foe to medical personnel reading x-rays or slides. Age-related declines in visual marking, target detection, or visual matching are reflected in performance of these and other identification tasks. For example, Dollinger and Hoyer (1996) found age-related declines between younger (mean age 26.5 years) and middle-aged (mean age 45.7 years) matched novices and medical technologists on domain-specific and general visual recognition performance. Younger participants were faster than older participants on both tasks. Moreover, those tested under dual task conditions were slower and less accurate than those tested under single task conditions—a difference that was greater for older adults. However, expertise compensated to some degree for age-related declines, in that medical technologists suffered fewer age-related deficits for the domain-specific tasks. Other studies have similarly indicated that performance differences between young and older experts are substantially smaller than those between young and older novices (Rogers and Fisk, 1996; Salthouse, 1991). Poor identification of shapes and objects is associated with poor memory for them. Thus, in addition to declines in facial identification and recognition, similar age-related declines occur in object recognition (Park et al, 2002)—which would in turn be reflected in witness failures to identify accurately such objects as vehicles, clothes, guns, and other items relevant in forensic contexts. Older adults also experience greater difficulty with memory for the location of objects. Older persons cite difficulties in remembering object locations in everyday life among their memory concerns (Reese et al., 1999), and substantial evidence exists to support the beliefs that spatial location memory declines with age (see the review in Cherry and Jones, 1999). Caldwell and Masson (2001), for example, had subjects work with drawings of household objects and rooms of a house depicted on a computer monitor to simulate placing objects in various places. Older subjects demonstrated poorer memory for object locations. In a real-life study of memory for spatial layout, Uttl and Graf (1993) tested museum visitors of ages 15 to 74 on memory for the spatial layout of recently visited museum displays. Those over age 55 showed reduced accuracy. Finally, even when reporting on familiar well-known spatial locations, older adults perform more poorly (see the review in Lipman and Caplan, 1992). For example, Evans and colleagues (1984) found that older adults were less able to recall, or place accurately on a map, buildings from a familiar part of their city. These results and others suggest that older witnesses may suffer a disadvantage when asked to testify regarding spatial
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layout or object location. Furthermore, evidence demonstrating that older adults tend to overestimate their ability to recall object location (West et al., 2002) suggests that they will not be aware of their inaccuracy, perhaps becoming very confident, but inaccurate, eyewitnesses. Spatial processing is also important for encoding location or relative location and for navigation from one point to another, as well as for memory for that route. In a creative use of virtual environment (VE) technology, Moffat and colleagues (2001) examined the navigation skills of adults from 22 to 91 years of age. The VE included a richly textured series of interconnected maze-like hallways, complete with dead ends and others leading to the goal. Older participants took longer to solve each trial, traveled longer distances, and made significantly more spatial memory errors. More of the younger (86%) than older (24%) adults achieved error-free performance after five trials. Furthermore, performance was related to standard measures of verbal and visual processing. Similar results for place navigation have also been obtained using a virtual Morris water maze (Moffat and Resnick, 2002; see also Shukitt-Hale et al., 2004). The navigation skills that depend upon spatial processing are reflected in everyday use of the environment. For example, Simon and colleagues (1992) examined the relationship between spatial processing and neighborhood use among older adults. Spatial memory was related to neighborhood knowledge, which in turn was predictive of neighborhood use (e.g., visits to shops, services, restaurants) and more predictive than mobility or years living in the neighborhood. Finally, such skills are also reflected in memory for routes taken, which also has been shown to decline with age (see the review in Lipman and Caplan, 1992). Problems of Attention and Encoding Successful encoding of information is dependent upon adequate attention (Craik and Lockhart, 1972). Memory is, in turn, dependent upon adequate encoding, such that inadequate attention and depth of processing at encoding may cause a person later to commit errors of omission (failure to remember things that did happen) and errors of commission (“remembering” things that did not happen, or remembering inaccurately what did happen; Schacter, 1999). Age-related decline in attentional control and resources renders older adults more susceptible to both errors, such that they remember less, and less accurately, than younger adults (see reviews in Craik, 2000; Koutstaall and Schacter, 2001). These age-related limitations also render older adults more susceptible to disruption of attentional capacities at encoding. For example, encoding is more impaired by distraction for older than younger adults. Therefore, although complex events are encoded more poorly than simpler events for those of all ages, complexity will cause greater encoding deficits in older adults. Thus, across a variety of tasks, undistracted older adults often perform similarly to distracted younger adults, and distracted older adults perform more poorly than distracted younger adults (see Zacks et al., 2000).
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Bias in Interpretation Information may be perceived accurately by the senses and nevertheless be encoded incorrectly due to failures of interpretation. One source of such failures is “schematic processing.” The influence of schemas on information processing is pervasive (for reviews of the following, see Fisk and Taylor, 1991; Hastie, 1981; Kunda, 1999). They allow us to recognize and categorize objects, people, events, situations, and other features of the environment. They form the basis of expectations that tell us what to do with objects or persons, or how to behave in specific circumstances. They offer standards for evaluation for what we witness or experience, direct attention to schema relevant features of what we witness, and direct interpretation of it. Schemas generally direct attention and information processing so that attention is selectively focused on schema-relevant aspects of the situation. Thus, memory for schema relevant information is generally better than for schema-irrelevant information. Schema-inconsistent information is often processed more carefully, in order to try to integrate it into the schema-driven impression and, hence, this enhanced processing leads to better memory. Schemas exert a biasing effect on initial interpretation and later memory. Information is interpreted in light of salient schemas. Hence, interpretation is often distorted toward consistency with the schema, e.g., when activation of a racial stereotype can lead to interpretation of success as luck rather than ability. Furthermore, memory is distorted so that schema-relevant information is retained at the expense of schema-irrelevant information. In addition, schema-based “constructive” memory processes can cause a person to fill in additional schema-consistent information. Generally, memory is biased toward retention of true schema-relevant information and addition of false, but schemaconsistent, information. Older adults are more susceptible to the biasing effects of schematic processing with respect to social information (Hess, 1999) and memory for nonsocial objects (Hess and Slaughter, 1990). We discuss this in greater detail in the section on jury decision making. Failure of Retention Age is related to more rapid forgetting in a variety of specific domains, including spatial location (Rutledge et al., 1997). When tested for recall immediately, older adults show substantially less impairment relative to younger adults than when tested after delay (see reviews in Craik, 2000; Zacks et al., 2000). Thus, it is particularly important to interview older witnesses as soon as possible after the event in question. This differential slope of forgetting over time also has implications for the performance of older jurors, particularly in long trials in which evidence and witness testimony must be remembered for weeks or months before the jurors reach a verdict. Accuracy of Retrieval Generally, older adults are unable to remember events as completely or as accurately as younger adults (see reviews in Craik, 2000; Rubin, 2000). “Episodic memory,” or memory for autobiographical events that have happened comparatively recently (see reviews in Craik, 2000; Wingfield and Kahana, 2002), is among the cognitive abilities
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shown to decline most sharply with age. Thus, older adults will, on average, be less able to retrieve elements of events they have witnessed, whether peripheral details or the core of the event. However, a particular deficit of episodic memory—memory for the context of an event (often referred to as “source monitoring”)—has been of interest in legal settings. Therefore, we will focus our discussion on this problem. Age and General Problems of Source Monitoring Older persons experience greater difficulty in “associative learning”—that is, in forming and maintaining connections between mental events. This is referred to as a deficit in “binding,” or integration of the various elements of an event, or of the event with the context in which it occurs (see reviews in Craik, 2000; Glisky, 2001; Koutstaal and Schacter, 2001). “Source memory” or “source monitoring” refers to the latter instance of associative learning (or binding), in which the memory of the core or gist of an event is bound successfully with the memory of the context in which it occurred. Substantial evidence has indicated that source or contextual memory is particularly dependent upon frontal lobe function and that the frontal lobes are preferentially affected by aging (see Glisky, 2001; Koutstaal and Schacter, 2001; Raz, 2000). Memory for context is considered to be more difficult than simple memory for the core of an event, as well as more susceptible to age-related decline, in that it requires greater attention (and divided attention) and processing of content and the spatiotemporal link between elements at encoding—capacities known to decline with age. Older adults may have problems dividing attention to encode the core event, along with the contextual cues and links between them, and therefore narrow attention to the core at the expense of context. Schacter and his colleagues (see Koustaal and Schacter, 2001) have suggested that elderly adults tend to encode information in a less elaborative and distinct manner (such that cues that would distinguish the target information from other potentially similar information are encoded and bound with the target), which tends to render them more susceptible to source-monitoring errors. Indeed, a number of studies have shown that fact memory is substantially less affected by aging than source memory (see the review in Glisky, 2001). Furthermore, although source errors can be reduced for younger and older adults through use of more elaborative encoding strategies that increase the distinctiveness of target information, age differences still remain (see Koustaal and Schacter, 2001). Difficulty with adequate encoding of contextual cues has been shown to result in a disadvantage for older adults in memory for, among others, • Perceptual details such as color, case, or font of written stimuli • Locations • Temporal sequence • The sex or specific identity of a speaker • Whether an item was presented in video or photo format • Whether something was presented auditorily or visually • Whether the individual personally simply said something or actually did it • Whether something was seen or heard vs. simply inferred on the basis of other things that were seen or heard
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• Whether something was imagined or actually happened • Why a face seems familiar (i.e., where it is known from) • Which person did or said something • Things one is supposed to do at a particular time or place (termed “prospective memory”) • The source of medical information See reviews in Glisky (2001); Zacks et al. (2000); and Koutstaal and Schacter (2001). Furthermore, older adults tend to rely more on schematic knowledge in attempts at source memory, which may enhance their source-monitoring errors when the actual source is inconsistent with their schemas (Mather et al., 1999). In part, these deficits in source monitoring are reflected in problems we have already reviewed, such as less detail and poor memory for time and spatial features such as durations, sequence, location, layout, or route. However, of particular interest in forensic settings, problems in source memory have been implicated as the cause of inaccuracy in witness testimony. Three general arenas of source confusion in witness testimony have been extensively studied: • The “misinformation effect” (Loftus, 1979), in which information suggested during an interview replaces or becomes integrated with the memory of the actual event • Confusion between ideas or “memories” developed in therapeutic procedures and actual events (Loftus and Ketcham, 1994) • Misidentification of an innocent suspect due to misunderstanding of the source of the sense of familiarity of the face We review research relevant to age differences in susceptibility to these three forms of source monitoring errors in the following subsections. Later, we consider the implications of age-related decline in source monitoring for jurors. The Misinformation Effect A popular paradigm for studying memory distortion that is applicable to the forensic arena has been the “misinformation” paradigm developed by Loftus and her colleagues (Loftus, 1979; 1992; Loftus and Hoffman, 1989; Loftus et al., 1978). Participants are exposed to pictures or films depicting objects or action sequences and, subsequently, experience misleading information regarding the contents. For example, the experimenter may ask a question that presumes the existence of a fact or object not depicted in the original materials (e.g., “Did another car pass the red Datsun while it was at the stop sign?”). When later asked whether the nonpresented object (the stop sign) was present in the original depiction, many participants will nonetheless report that it was and proceed to describe it in detail. Older subjects have reliably shown greater susceptibility to this misinformation effect (Cohen and Faulkner, 1989; Karpel et al., 2001; Loftus et al., 1992; Searcy et al., 2000; see Coxon and Valentine, 1997, for less clear differences) and greater confidence in their false memories (Cohen and Faulkner, 1989; Karpel et al., 2001; Mitchell et al., 2003). Underwood and Pezdek (1998) investigated relative susceptibility to misinformation provided by credible vs. incredible sources. Although misinformation from a credible source induced more errors immediately after the misinformation, 1 month later errors consistent with the misinformation were high for both high- and low-credibility sources.
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Presumably, as memory for the source of information decreased, discounting of information from a low-credibility source also decreased. Greater susceptibility to source forgetting in the elderly would be expected to render them relatively more susceptible to misinformation from low-credibility sources—particularly as the delay between the misinformation and retrieval increases. Multhaup and colleagues (1999) investigated the potential of a “source-monitoring” retrieval procedure to reduce the misinformation effect in older adults. This procedure had previously been shown to eliminate the misinformation effect in younger adults (Lindsay and Johnson, 1989). Lindsay and Johnson gave half of the participants in a misinformation experiment a yes/no recognition test for items in the original event. The other half was given a source-monitoring test, in which they were asked to identify the origin of each item as the original picture, the (misleading) text, neither, or both. The authors found the standard misinformation effect with the yes/no procedure, but not for the source-monitoring procedure. Multhaup et al. (1999) replicated this design with older adults and, again, the source-monitoring test format eliminated the misinformation effect. At least in their sample, instructions requiring conscious effort to retrieve the contextual source of information were effective for the older adults. A conceptually similar pattern of results was obtained by Multhaup (1995), who showed that the “false fame” effect was eliminated by a similar source-monitoring retrieval task. Subjects in the false-fame task pronounce a list of nonfamous names. Later, they judge as famous or nonfamous a list of names including famous names, pronounced nonfamous names, and new nonfamous names. During the fame judgment task, the pronounced nonfamous names seem familiar. If the person fails to monitor the source of that feeling of familiarity accurately as the previous pronunciation, he may falsely conclude the name is famous. As a result, previously pronounced nonfamous names will more often be judged famous than those not previously pronounced. Multhaup’s (1995) source-monitoring retrieval task led participants to indicate whether each test name was a famous name, a nonfamous name pronounced earlier, or a new nonfamous name. Although older adults were more susceptible to the false fame effect than younger adults in a standard famous/nonfamous recognition task, the false-fame effect was eliminated for both groups in the sourcemonitoring retrieval task. For the misinformation and false-fame studies, the authors attributed their results to the adoption of stricter decision criteria for assigning a particular item to a particular source to perform the source-monitoring task. In the absence of such strict criteria, the person may rely on a sense of familiarity to decide whether the item was present in the picture, whereas the stricter criterion presumably requires reliance on memory for more specific perceptual and spatial details to establish context. Multhaup et al. (1999) suggested that older adults may benefit from listing possible sources when they are trying to retrieve the context of events or information. (See Zacks et al., 2000, for other factors and strategies that moderate age differences in source monitoring failures.) A promising line of research showing that elderly people can learn to reduce source monitoring errors involves the use of a procedure known as the DRM paradigm. Here, subjects study lists of semantically related words (such as dream, tired, bed, snore) and then try to recall or to recognize what they previously heard. A central finding is that all adults, regardless of age, are prone to remember nonpresented but associated words (e.g.,
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sleep). However, older adults are more likely than younger adults to falsely recognize the critical nonpresented lures. This increase in false recognition has been seen in a number of paradigms (Dodson and Schacter, 2002). On a more positive note, older adults were able to learn to use a retrieval strategy called the “distinctiveness heuristic” to reduce their rate of error. If pictures accompanied the words, an especially large reduction in error rate occurred for the elderly, making their performance more comparable to that of young adults. Source Confusion and Therapeutic Process Recent years have witnessed an explosion of interest in the extent to which common therapeutic techniques such as hypnosis, guided imagery, dream interpretation, and participation in “survivor groups” might lead a patient to develop false memories—in particular, false memories of sexual abuse (see Loftus and Ketcham, 1994). A wealth of data has now accumulated to demonstrate that these techniques can, indeed, produce false memories (see reviews in Davis and Follette, 2001; Loftus and Ketcham, 1994). Essentially, the person is exposed to suggestions from the therapist that a particular event may have happened, followed by a variety of procedures designed to uncover the memories that are at first allegedly inaccessible. These procedures involve continuing suggestion during such activities as dream interpretation, guided imagery, or hypnosis. For example, the person may be asked to imagine the event in question, try to remember it, or expose himself to situations that might trigger the memory (such as survivor group discussions). In this context, the person may develop vivid images or dreams of the presumed events, even though they never occurred. The combination of suggestion and imagery results in what feels like a “memory.” However, the person mistakenly believes the source of this memory to be an actual event, rather than the mental processes and images generated by the therapeutic process. Empirical research has demonstrated the capacity of suggestion, guided imagery, hypnosis, and other procedures to generate false memories. However, although there is not a great deal of research on aging and the potential of such procedures to induce false memories, we did locate some work using imagination with older participants. A number of studies have shown that older adults more easily mistake events they have imagined as memories for actual events. This difference applies with respect to confusion between imagining and actually doing something, and imagining vs. seeing or hearing something done or presented by others (see reviews in Koustaal and Schacter, 2001; Zacks et al., 2000). Given these specific results in combination with the general literature showing age-related decline in accurate source monitoring, it is reasonable to hypothesize that older adults will be more susceptible to development of false memories through common therapeutic procedures. Face Perception and Eyewitness Identification Cognitive researchers have identified age-related declines in fundamental face perception processes, which ultimately result in greater rates of inaccurate eyewitness identification and, in particular, higher rates of false identification. We first consider age-related changes in basic face perception processes and then turn to research specifically on eyewitness identification.
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Age-Related Declines in Face Perception and Face Memory. Aging is generally associated with decline in spatial/nonverbal ability (see reviews in Chalfonte and Johnson, 1996; Jenkins et al., 2000). Consistent with this general decline in visuospatial abilities, research on face recognition has documented age-related declines in recognition performance for unfamiliar (once before seen) faces (Bartlett, 1993; Bartlett and Leslie, 1986; Bartlett et al., 1989; Crook and Larrabee, 1992; Ferris et al., 1980; Smith and Winograd, 1978). Older adults exhibit greater susceptibility to false recognition of faces not actually previously seen (Koustaal et al., 2001), although consistent age differences in accurate recognition of once-seen faces has not been observed (see Searcy et al., 1999, for review). In addition, older adults report less confidence when they do correctly reject foils (Yarmey, 1984; Yarmey and Kent, 1980). Older adults seem generally more susceptible to false recognition because they exhibit greater tendency to select false information when recognizing details of a previously seen event as well. Several processes appear to underlie age-related differences in facial recognition performance. First, many face recognition tasks rely at least in part on long term episodic memory—for example, in the standard eyewitness identification paradigm to be discussed later. Because episodic memory shows one of the steepest declines with age, age-related declines in facial memory may reflect general deterioration of long-term episodic memory. Consistent with problems with long-term episodic memory, Memon and colleagues (2003) found the effect of age on perpetrator lineup identification to be greater after 1 week than after 35 minutes. Second, face recognition relies in part on accurate source-monitoring capabilities. The person must recognize that the face is known and retrieve the context in which it was encountered. Some have suggested that older adults rely more on heuristic strategies such as “familiarity,” “feeling of knowing,” or “availability,” in the absence of more consciously controlled processes such as contextual recollection and source monitoring (Bartlett and Fulton, 1991; Jacoby, 1991; Searcy et al., 1999, 2000). Thus, they will tend to choose faces that seem familiar, whether or not the source of familiarity is correct. Indeed, Memon et al. (2003) showed that correct perpetrator lineup identifications were related to an independent measure of source recollection ability, which in turn was negatively related to age. Third, advancing age may result in declining face perception abilities. Indeed, evidence from the standard Benton Facial Recognition Test (Benton et al., 1994) has indicated that older adults become less able to match a target face to the correct alternative among six candidates shown immediately below (and simultaneously with) the target. This non-memory-dependent task has been shown to predict time-delayed memory-dependent witness lineup performance (Searcy et al., 1999). Therefore, age appears to be related to decline in perceptual feature matching, which is in turn related to poorer recognition performance. Furthermore, Memon and Bartlett (2002) have offered evidence that older witnesses reported greater reliance on feature matching as a strategy for identification of culprits from a lineup and, in turn, those who reported relying on feature matching were less accurate (13%) than those who reported other strategies (44%). Interestingly, the reverse was true for younger witnesses (38 vs. 15%) Thus, it appears that older adults may be more reliant on feature matching as a strategy for recognition and less accurate in using their preferred strategy.
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These and other potential mechanisms underlying decline in face perception and memory are the likely results of age-related changes in brain structure and function. For example, Schretlen and his colleagues (2001) examined the influence of age, sex, education, perceptual comparison speed, frontal lobe volume, nonfrontal volume, and ventricle-to-brain ratio (VBR) to Benton Facial Recognition Test performance. Age was the strongest negative predictor of performance. However, VBR and processing speed alone accounted for almost 34% of the variance, with age in the equation. Frontal and nonfrontal lobe volume also contributed significantly to the equation, but added only slightly more than 1% to the explained variance. Such results are consistent with longstanding findings that lesions, injuries, or lobectomies to the frontal lobes create impairment in face processing and recognition (see the summary in Schretlen et al, 2001). Others have directly examined brain function during facial processing tasks through use of event-related brain potentials (ERP) (Grady, 2002; Pfutze et al., 2002) or PET (positron emission tomography; Grady et al., 2002) in attempts to identify the location and nature of age-related differences in brain function and their relationship to deficits in specific stages of face processing and retrieval under varying task conditions. A detailed review of these results is beyond the scope of this chapter. However, Grady et al. (2002) and Pfutze et al. (2002) provide excellent summaries of recent relevant literature. Generally, such studies of brain function have shown some age-invariant functions but a greater variety of age-related changes in brain functions, which can be empirically linked to face processing/recognition performance. Furthermore, they have shown that older adults appear to use different areas of the brain than younger adults for face processing under some conditions, indicating that loss of function in some areas of the brain may be compensated for by alternative processing routes. Together with studies linking structural changes in the brain to performance, the ERP and imaging studies clearly demonstrate that brain changes underlie age-related declines in face processing. Finally, several studies have shown that older adults less accurately identify facial displays of emotion in photographs and video clips (Sullivan and Ruffman, 2004; McDowell et al., 1994). As with other visual skills, older adults appear to use different areas of the brain for emotion identification than younger adults (Gunning-Dixon et al., 2003). Although not directly relevant to eyewitness identification, these results suggest that older adults may be less accurate in reporting the emotional tone of interchanges and thus less accurate in their reports of the meaning of the exchange. Specific Studies of Age and Eyewitness Identification. Compared to the enormous number of studies that have been done on children as eyewitnesses, there is a relative paucity of research involving older eyewitnesses. A few studies have shown that elderly eyewitnesses are more prone to inaccuracy in eyewitness identifications (List, 1986; Memon and Bartlett, 2002; Memon and Gabbert, 2003a, b; Memon et al, 2002; O’Rourke et al., 1989; Yarmey, 1985, 1993, 1996; Yarmey et al., 1984), with elderly witnesses making from 25 to 50% more identifications than their younger counterparts—most of them false. A few studies have failed to replicate this age difference (Memon et al., 2003; Wright and Stroud, 2002; Yarmey and Kent, 1980). However, Yarmey and Kent (1980) did find poorer recognition of bystanders among older participants. Also, Memon et al. (2003) found no age differences on the Benton Facial Recognition Test in their sample. Thus, the lack of differences in false identifications in their study may be explained by their relatively high-functioning older sample.
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As with basic face recognition studies, eyewitness identification studies have shown that older adults are particularly prone to false identifications of innocent foils, whereas there are often smaller or no age differences in accurate identification of the perpetrator in target-present lineups (Adams-Price, 1992a, b; Searcy et al., 1999,2000; Memon and Bartlett, 2002; Memon et al., 2003; Memon and Gabbert, 2003a, b), although Searcy et al. (2001) found the opposite pattern and, in another study, found an age-related reduction in hit rates (Searcy et al., 1999, lineup 3). Generally, the tendency of older adults to make false identifications in target-present, as well as in target-absent, lineups is robust and widely interpreted as the result of older adults’ greater use of “gist-like” encoding and failures of source memory (Koutstaall and Schacter, 1997; Schacter et al., 1998; Tun et al., 1998). The Own-Age Effect. An unfortunate characteristic of much of the research on age and eyewitness memory is that, although witness age is varied systematically, perpetrator age is often held constant within younger age groups, thereby confounding witness age with witness-perpetrator relative age. This presents a problem of potential significance. That is, just as eyewitness researchers have documented a “cross-race” effect in eyewitness identification (Sporer, 2001), there appears to be a “cross-age” effect, such that witnesses are better able to identify targets of their own age group. In two experiments, Wright and Stroud (2002) found that participants from two age groups (18 to 25 vs. 35 to 55), who had previously viewed videos of a car or a television theft, were more accurate at identifying the culprit when viewing culprit-present lineups of people their own age. (This effect occurred in those making the identification after only 1 day, but was very weak in those making the identification after 1 week and was weaker in older than in young adults.) No same-age effect was found for misidentification of innocent suspects in target-absent lineups. Similarly, an earlier study by List (1986) had 10-year-olds, college-age students, and adults 65 to 70 view shoplifting videos. Culprits were college-age or middle-age females. Older adults exhibited poorer recognition memory for the college-age culprits than either of the two other groups but better memory for the middle-age culprit. Memon et al. (2003) investigated accuracy in identification of perpetrators who were old or young among old and young participants. Younger participants generally outperformed older participants. Older participants made more false identifications in perpetrator-present and perpetrator-absent lineups, particularly for younger perpetrators and after delays of 1 week rather than 35 minutes. Younger participants were also more prone to misidentify someone in older lineups, but were not less likely to identify the perpetrator. Finally, own-age recognition biases have been observed outside the eyewitness identification paradigm. Several studies using standard face recognition paradigms, for example, have found superior performance for own-age targets (Bartlett and Leslie, 1986; Fulton and Bartlett, 1991; Mason, 1986). Furthermore, in their initial demonstration of the “change-blindness” phenomenon, Simons and Levin (1998) obtained what was apparently an own-age effect. College-aged experimenters approached an unsuspecting pedestrian on campus, asking for directions to a campus building. While the pedestrian attempted to provide directions, two other confederates appeared to interrupt rudely by passing between the experimenter and pedestrian, carrying a large door. As the door passed between them, the first
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experimenter changed places with a second, who emerged from behind the door and continued the exchange with the pedestrian as if he had been in the conversation all along. The second experimenter wore different clothing and differed in height and voice. Yet, less than half of participants noticed the change and older adults were less likely to notice than younger adults. Simons and Levin interpreted this age difference as an instance of the broader owngroup bias in face processing. A replication of the door experiment revealed that even younger people are more likely to notice the change for members of their own social group (other college students) than for those of a different social group (the same persons, but dressed as construction workers; Simons and Levin, 1998, experiment 2), perhaps due to greater specificity in processing for in-group members. The growing evidence of an own-age bias in face recognition suggests that the results of many earlier studies of eyewitness accuracy might be due not to age-related general decline in accuracy but rather to the particular age combinations used in the study. Further research is needed to examine the relationship between witness and culprit age that employs adults throughout the age span, including into old age. Meanwhile, the results are nonetheless useful in practice for a wide variety of witnessing situations. Because crime is much more prevalent among the young, elderly witnesses will often be in the position of attempting identification of a younger culprit. Interaction of Age with Conditions of Encoding or Retrieval. To the extent that age renders the witness, more susceptible to failures of encoding, storage, or retrieval, it is relevant to ask whether the aging witness will suffer enhanced impairment as a result of poor witnessing conditions, longer retention intervals, or biasing influences at retrieval. To date, however, only a few studies have addressed these issues. Witnessing Conditions. Two studies examined the effects of “weapons focus,” violence of the crime, perpetrator disguise (O’Rourke et al., 1989), and “cross-race” targets (Brigham and Williamson, 1979) as a function of age, but found no interaction of these variables with age. Memon et al. (2003) examined the effect of duration of exposure to the perpetrator’s face, and whether the lineup was target present or target absent, on accuracy in young and old adults. They also found no interactions with age (although as noted earlier, the sample of older adults scored equivalently to the young adults on the Benton Facial Recognition Test). We were unable to locate other studies examining the interaction of age with effects of such variables as lighting, arousal, and so on, even though the documented declines in perceptual processes would suggest such age-related interactions. Thus, a number of issues remain open for future research to pursue. Attention at Encoding. The Negative Relationship between Memory for Detail and Eyewitness Accuracy. Some previous research has indicated that memory for details of some aspects of an event is negatively associated with memory for others (Wells and Leippe, 1981). If attention is focused on some things, attention to others will suffer. To the extent that older adults suffer decrements in capacity for divided attention (as reviewed earlier), they might be expected to show enhanced negative relationships between recall of peripheral detail and identification accuracy. Indeed, Searcy et al. (2000) found that higher levels of recall of the target event and of other nonfacial features of the target were associated with higher levels of false identifications for seniors, but not for younger adults.
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Lineup Procedures. Several studies have attempted to assess the differential impact of variations in identification procedures for younger and older witnesses. Eyewitness researchers have adopted the position that witness identification accuracy is enhanced through use of sequential lineups in which one potential culprit is present at a time, as opposed to simultaneous lineups in which (usually) six potential suspects are presented simultaneously (Steblay et al., 2001). More specifically, as shown by Steblay’s (Steblay et al., 2001) meta-analysis of these effects, sequential lineups appear to reduce the overall likelihood of any choice, correct or incorrect. Thus, although the procedure reduces the proportion of false identifications of innocent suspects, it also reduces true identifications of the perpetrator (hits). Self-reports of those tested with a sequential lineup suggest they tend to use an “absolute”—as opposed to a “relative”—judgment strategy, whereby the target is judged for absolute fit to the witness’s memory of the culprit rather than for the relative fit of the target to the memory (i.e., the fit relative to other members of the lineup) (Dysart and Lindsay, 2001; Wells et al., 1998). This stricter decision criterion would naturally have the effect of reducing witness willingness to make any choice, whether correct or incorrect. Memon and her colleagues have investigated the potential interaction of age with lineup procedure in a series of studies. Using a target-present lineup only, Memon and Bartlett (2002) investigated the effects of simultaneous vs. sequential procedures for young (18 to 30 years) vs. old (60 to 80 years) adults. Generally, older adults made more false identifications, but lineup procedure did not interact with age. Instead, sequential lineups decreased accurate identifications (hits) for both age groups. Similar results were obtained by Memon and Gabbert (2003b) for target-present lineups. However, these researchers (2003a) did find an interaction between age and lineup procedure in target-present lineups (but not target-absent lineups), such that sequential testing reduced false alarm rates for younger but not for older adults. For target-absent lineups, the authors found main effects for both age and testing conditions, such that both groups made fewer false identifications under sequential testing conditions, but older adults made more false identifications than their younger counterparts in sequential and simultaneous target-absent lineups Memon and Gabbert (2003b) further investigated the effects of lineup procedure specifically for TP (target-present) lineups. However, in this study, they also varied whether the appearance (hairstyle) of the perpetrator had changed subsequent to the crime. This variation was expected to have a greater effect under conditions in which the witness adopts stricter criteria of absolute fit for identification (i.e., the sequential procedure) than under those in which he might adopt a more lenient criterion of best fit (i.e., the simultaneous procedure). Younger (17 to 33 years) and older (58 to 80 years) adults viewed a short film depicting a female target stealing money from a car. Later, participants described the perpetrator and subsequently viewed a lineup, in either simultaneous or sequential format, in which the perpetrator’s hairstyle had or had not changed. Across conditions, younger adults recalled more details of the target’s appearance correctly and fewer incorrectly. Older adults made fewer hits and more false identifications than younger adults. Across age groups, fewer choices of all kinds were made under sequential (58%)
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than under simultaneous (75%) lineup procedures. This drop was due to a drop in hit rates in the sequential lineups because there was no drop in false identifications. Interestingly, although the rate of misses increased dramatically for perpetrators whose appearance had changed, it did so particularly for sequential lineups, and particularly for younger adults. For older adults, although the pattern was similar, no significant main effects or interactions were found. Memon and Gabbert suggested that change in appearance was particularly detrimental to younger adults, who they presumed would be relying on attempts to remember the face in context specifically, whereas it would be less detrimental to older adults, who they presumed would be more likely to rely on a contextfree sense of familiarity. Memon and Gabbert’s (2003b) results suggest that, in practical circumstances, older adults may suffer a lesser drop in hit rates when viewing sequential, as opposed to simultaneous, lineups, specifically under conditions in which the perpetrator’s appearance may have changed. Changes in clothing, hair, facial hair, the presence of a hat, removal of elements of a disguise, and so on are arguably quite common between the crime and arrest. To summarize, for target-present lineups, age effects are somewhat inconsistent. For simultaneous lineups, some have found reduced hit rates among older adults (Searcy et al., 1999, lineup 3; 2001), and some have found no age differences (Searcy et al., 1999, lineup 1; Memon et al., 2003). Older adults have been consistently more susceptible to false alarms in target-present and target-absent lineups, whether administered simultaneously or sequentially. Sequential vs. simultaneous testing did not eliminate agerelated declines in eyewitness performance. Instead, under conditions in which the perpetrator’s appearance (hairstyle) was different in the lineup than when he or she had committed the crime, the hit rate of younger adults was selectively impaired by the sequential procedure, whereas the rate of false identifications of older adults was not improved. Overall, then, there appear to be no reliable age by lineup procedure interactions. Source Monitoring and Exposure to Mugshots. In some cases, the witness is asked to examine mug books to attempt identification of a suspect. This exposure can lead to a sense of familiarity, which forms the basis of a source-monitoring error that can produce a false identification when the witness later sees the same person in a lineup. If the witness actually identifies the innocent person in the mugbook, he may become committed to that identification in a way that further encourages him later to identify the innocent falsely in a lineup (see the review in Memon et al., 2002). Memon and colleagues (2002) exposed participants to a videotaped car theft. Subsequently, they were asked to examine a target-absent mug book to attempt identification of the suspect (although control subjects did not inspect the book). All participants were given a target-absent lineup 48 hours later. Older adults were significantly more likely to identify someone from the mug book falsely and to choose a foil from the lineup. However, although all subjects who viewed a mug book were more likely to pick the foil who appeared in both the mug book and lineup, there was no age difference in this tendency. The Verbal Overshadowing Effect. Memon and Bartlett (2002) also attempted to assess age-related susceptibility to the “verbal overshadowing” effect (Schooler and Engstler-Schooler, 1990). Verbal over-shadowing refers to a situation in which verbal
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descriptions of a target interfere with later target recognition. However, the authors reported only a small effect of verbal descriptions prior to attempted identification of a culprit, and no evidence of greater susceptibility in older jurors was found. Interviewing Procedure: Effects of Context Reinstatement. Because false identifications are considered to result in part from inaccurate source monitoring, a number of investigators have examined the effects of context reinstatement on identification accuracy (see the review in Searcy et al., 2001). The results of these investigations have been mixed. Nevertheless, Searcy and colleagues (2001) tested the effects of context reinstatement on identification accuracy of young and old adults, 1 month after a personal interaction with the target. No beneficial effects were obtained in either population. Similarly, Memon and colleagues (2002) found no benefit from verbal reinstatement of the context of a previously viewed crime on identification accuracy. Although other procedures for context reinstatement may prove more effective, there is currently no overall support for the effectiveness of context reinstatement. The “cognitive interview” (Fisher and Geiselman, 1992) includes such techniques as context reinstatement, minimizing background noise, asking open-ended questions, and encouraging use of nonverbal responding. This interview method has been shown to enhance the amount of correct information recalled. Although they did not examine accuracy of eyewitness identification, Mello and Fisher (1996) found that, whereas the cognitive interview enhanced accuracy for young and old adult witnesses to a videotaped crime, enhanced recall was greater for older adults. However, McMahon (2000) found no overall or age-specific effects of the cognitive interview (vs. a structured interview) but did find a significant age effect on amount of true (but not false) information recalled. Overall, research investigating remedies for age-related declines in eyewitness accuracy has been disappointing, yielding conflicting findings that make firm conclusions premature. Given the importance of accuracy in eyewitness testimony, this search for improvements should not be abandoned. Eyewitness Metamemory: Are Aging Eyewitnesses Aware of Their Inaccuracy? Eyewitness researchers have shown that the relationship between confidence in accuracy and actual accuracy is often weak (Bornstein and Zickafoose, 1999; Brewer et al., 2002; Olsson, 2000). Some researchers have examined the relative strength and direction of this relationship in older and younger witnesses. Yarmey (1985) reported that, although elderly witnesses were less confident than younger witnesses, there were no age differences in the relationship between confidence and accuracy. In contrast, although replicating the main effect of age on accuracy, four studies found positive relationships between confidence and accuracy in young adults, and no significant relationships among older adults (Memon and Bartlett, 2002; Memon et al., 2002, 2003; Searcy et al., 2000). Searcy and colleagues (2001) further found that seniors’ self-rated memory self-efficacy was positively associated with false identifications in target-absent lineups. It appears, then, that seniors may less accurately monitor the quality of their identification performances. A New Area for Expert Testimony? Stereotypes of older eyewitness are mixed. That is, although older witnesses are seen as less accurate (Groth, 1979; Kwong See et al., 2001), they are also seen as more honest (Brimacombe et al., 1997; Kwong See et al., 2001). Thus, juror intuition is consistent with actual overall age differences—at least with
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respect to accuracy. Even so, aging witnesses are not always seen as less credible. Nunez and colleagues (1999) presented a case involving an aggravated assault, in which the victim identified the defendant. The victim was described as a generic adult victim or as one of five variations of older adults varying in apparent abilities. Ratings of believability were not significantly lower for older witnesses. Thus, in some cases, jurors may not be sensitive to age-related inaccuracies. It is also important to remember that age does not exert uniform effects on all measures of accuracy (e.g., hits in target-present lineups are comparable, whereas false identifications are greater), and age-related decline is widely variable across individuals. Thus, jurors would benefit from some mechanism for distinguishing between impaired and relatively unimpaired older witnesses. Reflecting this need, Geiselman and his colleagues (2001) examined the effects of disclosing the results of a witness’s Benton Facial Recognition Test scores on juror verdicts. Witnesses described as scoring lower on the BERT were seen as less credible. When the testimony included an explanation of the conditions under which BERT scores are most predictive of accuracy, jurors correctly placed more weight on the BERT scores when witnessing conditions for the reported crime were poor. These results indicate that testimony regarding individual witness abilities (including age-related abilities) can significantly affect witness credibility. Voice Perception and Earwitness Identification Forensic research addressing “earwitness identification” is far less extensive than that on eyewitness identification but has received increasing attention in recent years (see the review by Yarmey, 1995). Like eyewitness identification, evidence suggests that earwitness identification accuracy will decline with age. In line with the general agerelated decline in auditory acuity, pitch discrimination, and so on, older adults suffer declining ability to recognize specific speakers (Bull and Clifford, 1984; Maylor, 1997). In part, this difference is due to encoding difficulties. For example, older adults are less accurate at initial discrimination between male and female voices (Kausler and Puckett, 1981). Furthermore, older adults—particularly those with relatively poor frontal lobe functioning—show poorer source memory for voices (Glisky et al., 1995). After hearing several sentences spoken in one of two voices, those with poor frontal function showed impaired memory for the voice, but not for the sentences. Although there is a burgeoning literature on earwitness identification (Yarmey, 1995), we were unable to locate any studies of the relationship between speaker identification and age conducted within a witness identification paradigm. Therefore, much remains to be investigated regarding the elderly earwitness. 11.4 Age-Related Judgment and Decision-Making Processes in Jurors Stereotypes of the cognitive status of older adults appear to be both realistic and overly optimistic. Several studies of beliefs regarding age and cognitive function among German adults (Heckhausen et al., 1989; Heckhausen and Krueger, 1993; Hummert et al., 1994) found that, although age is viewed as associated with memory problems (e.g., slow, forgetful, absentminded) and inflexibility (e.g., moralistic, overcautious, obstinate, headstrong, stubborn, inflexible), it is also viewed as associated with knowledge (e.g.,
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knowledgeable, smart, experienced, well read, educated, well informed, etc.) and wisdom (e.g., open minded, reasonable, levelheaded, wise, intelligent, etc.). Thus, stereotypes of aged thinkers do include forgetfulness, but also appear to include confidence in more rational and wise decision making. How, if at all, do such stereotypes reflect actual differences in juror decision-making processes? Thus far, we have summarized a number of differences in cognitive/informationprocessing abilities between younger and older persons. In this section, we first consider some implications of age-related declines in perception and memory for jury information processing. Second, we briefly review what is known about age-related differences in judgment and decision processes that would affect how jurors use the information they acquire to come to verdict/sentencing/damage decisions. As we consider these issues, we offer recommendations for effective presentation of information to older jurors if they are seated on the trial jury. Age-Related Differences in Information Processing Perhaps most relevant for aging jurors are age-related declines in perceptual abilities (see Faubert, 2002; Scialfa, 2002) that will compromise ability to process speech, nonverbal cues to meaning and deceit, and visual and auditory exhibits successfully. The most central of these, of course, are speech and discourse processing/understanding, which unquestionably decline with age. However, much of this decline is due to simple perceptual difficulty, and can be reduced by slower and louder speech (see the review in Schneider et al., 2002). Thus, attorneys facing older jurors should take care not to speak too quickly, to face jurors and have witnesses face jurors when possible (to allow the jurors to clarify unclear speech through lip reading and nonverbal cues), and to maintain adequate volume at all times. Unfortunately, even when aging jurors do understand the content and the point of the presented evidence, they will (on the average) retain less of that information, particularly across the long retention intervals required in lengthy trials. For example, Fitzgerald (2000) examined memory for evidence among younger vs. older jurors. In a measure of free recall, jurors were asked to write an account of a 2-hour toxic tort trial they had just witnessed, written “so that someone who had not watched the trial would know what had taken place.” Overall, the accounts of older jurors were judged as significantly less “cohesive” than those of younger jurors. Older jurors’ accounts also included fewer statements of probative facts, but more evaluative statements regarding parties to the case or lines of argument (although these differences were attenuated when legal instructions were provided before, rather than after, the evidence). Older jurors did not, however, include more erroneous statements or reports of evidence that was not actually presented. Recognition measures of memory for evidentiary statements and testimony were similarly influenced by age, in that older jurors recognized fewer actual statements, but did not show greater false recognition for nonpresented statements. Clearly, older jurors will be at greater risk of failure to understand and remember evidence. Thus, these jurors may benefit more than younger ones from standard presentation tactics designed to enhance memory, such as redundancy, vividness in language and visual exhibits, exhibits designed to reinforce points, enumeration of points
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of evidence and drawing connections between them and trial issues, and so on. Fitzgerald (2000) also varied whether jurors were permitted to take notes, showing that older and younger jurors benefited. Thus, note-taking may be another valuable support for older jurors. Implications of Age-Related Failures in Source Monitoring We have already documented the age-related relative inability to monitor the contextual source of information or events accurately. In jurors, failures of source monitoring would be expected to result in failure to track the source of testimony and evidence accurately, as well as to track the association between information and other cues relevant to the accuracy of that information. Indeed, older persons are less able to remember accurately which person gave them specific items of information (Ferguson et al., 1992; Hashtroudi et al., 1989; Schacter et al., 1991) and less able to remember the source of conversational contributions accurately (Brown et al., 1995; see Davis et al. [Chapter 12 in this volume], Davis and Friedman, in press for reviews). This failure to track the source of information accurately may contribute to failure to discount low-credibility evidence or testimony properly. For example, research on the “sleeper effect” (Priester et al., 1999; Underwood and Pezdek, 1998) has shown that although information associated with a source lacking in credibility may be initially discounted, as time passes the information becomes more credible. As the low-credibility source is forgotten or becomes dissociated from the information, the information ceases to be discounted, becomes more credible, and thus exerts greater influence on judgment. As noted earlier, using the misinformation paradigm, Underwood and Pezdek (1998) found that subjects became relatively more influenced by misinformation from a lowcredibility source over time. To the extent that aging jurors will be more susceptible to confusion regarding the source of evidence, the testimony of witnesses who have been discredited may likewise become more influential with older jurors because they fail to connect the discrediting information with the discredited witness’s testimony. Although the effects of the passage of time have not been directly tested, Chen and Blanchard-Fields (2000) studied age differences in reactions to true and false information, using the “false information paradigm” developed by Gilbert and his colleagues (1990, 1993). Participants read police reports containing true statements printed in black and false statements printed in red. They were told that the red statements had gotten into the report by accident and actually belonged to another crime report or an unrelated incident. Presumably, source-monitoring errors would be more prevalent among older adults—and among younger adults subject to distraction during their review of the report—and later cause them to include the discredited information in their judgments. As expected, undistracted older adults and distracted younger adults were more influenced by the false statements. Thus, even when judgment immediately followed the presentation of information, older adults were more likely to lose the link between a fact and the credibility of the fact than younger adults. A related failure may occur with respect to attorney claims or arguments. People tend to rate repeated statements or claims as more valid and believable than those presented less often—an effect known in the marketing and advertising literature as the “truth effect.” Older persons are more susceptible to this effect (Law et al., 1998), suggesting
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that older jurors may be more persuaded by oft-repeated claims, whether backed by good evidence or not. This tendency is assumed to result from the increasing sense of familiarity resulting from repetition, combined with failure of source memory. Although we know of no direct tests of our suggestion that source forgetting may selectively enhance the credibility of discredited witnesses or attorney arguments in aging jurors, one study directly tested source memory for plaintiff, defense, and neutral facts (i.e., correct linking of statements to witnesses and other participants in the trial). Older jurors made fewer correct links than younger jurors (Fitzgerald, 2000). (See also Davis et al. [Chapter 12 in this volume] and Davis and Friedman, in press for reviews of age differences in source monitoring in conversation.) A final kind of source monitoring is potentially more important that those we have cited thus far; that is, maintaining the mental link between an item of evidence and the implications of that evidence for the central issues of the case. Such links are often a problem for jurors because attorneys do not always take care to tell jurors why a particular fact is important and to link it to the case issues—often because they believe it is so obvious as not to need connection. In both senses, however, older jurors may be at a disadvantage. Cohen (1979) suggested that even when elderly people are able to understand what was said, they are less able to draw inferences from the literal content, so others often view them as failing to “get the point.” This point has been supported in studies of comprehension of medical information. Older patients answer questions concerning the literal content of drug information somewhat more inaccurately than younger adults (e.g., “What are the side effects of this drug?”), but perform much more poorly when answering inferential questions requiring searching for information in several places and putting it together sensibly (e.g., “How long will this medication last?”—which requires use of information concerning number of times daily the medication is to be taken, along with the number of pills in the bottle). The age difference became even stronger for more complex inferential questions, although both groups performed more poorly on more complex questions (Finucane et al., 2002; Park et al., 1994). This age-related deficit in inferential processes would suggest that attorneys must go to greater lengths to connect the information they provide to the inferences and conclusions they wish the jurors to draw. Furthermore, given that older jurors may also be more susceptible to forgetting such connections, attorneys should reinforce these connections more frequently for them. Age-Related Differences in Judgment/Decision Processes Once the evidence is in, jurors must consider the nature and weight of the evidence for each side, compare that evidence to legal standards for verdict and damage decisions, and arrive at their final decision. Again, some evidence suggests that older adults face greater difficulties in reasoning, judgment, and decision making. For example, Salthouse (1993; Verhaeghen and Salthouse, 1997) found that younger adults outperformed older adults on a variety of tests of reasoning ability. In fact, age-related declines in matrix reasoning and analytical reasoning (which test such abilities as perception of relationships between information, integration of information to reach a conclusion, abstraction, verification, and so on) have shown some of the largest correlations with age of any behavioral
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variable (Salthouse, 2001). Such deficits present a clear challenge for jurors faced with the lengthy presentations, substantial processing demands, and complex decisions necessitated by their role. Gathering and Combining Information In part, older adults seem to shortchange the information-gathering stage of decision making, relying on less complete evidence gathering and comparisons between fewer alternatives prior to making a decision. Some have suggested (Cole and Balasubramanian, 1993) that restrictions on working memory capacity may lead aging decision-makers to reach a point of information overload with less information than their younger counterpoints. Beyond this point, additional search can yield dysfunctional consequences and incorrect decisions (Malhotra, 1982). Zwahr and colleagues (1999) studied the implications of limitations in working memory for information use in medical decisions. Younger and older women studied detailed information regarding the pros and cons of hormone replacement therapy (HRT) for menopause and recommended a decision for a hypothetical woman in a vignette. Although age was unrelated to the recommended decision to take HRT, the manner in which the participants arrived at their decisions did vary with age. Older women sought out less information, made fewer comparative judgments, and considered fewer alternatives to HRT prior to arriving at their decisions (see also Meyer et al., 1995, for age and decisions regarding breast cancer). Path analyses indicated that cognitive abilities (including text memory, vocabulary, working memory, and perceptual speed) directly affected decision-making processes, whereas age exerted only indirect effects due to its strong negative association with cognitive abilities. Studies of decision making in arenas such as product choice (Beatty and Smith, 1987; Cole and Balasubramanian, 1993; Furse et al., 1984; Johnson, 1990, 1993; Schaninger and Sciglimpaglia, 1981) have shown a similar age-related restriction in information search and review of alternatives prior to a decision, and/or poorer final choices. Although not directly analogous to information processing in court, studies of computer search and retrieval tasks, such as searches for information on the Internet, library, or customer service databases, have shown that older adults have less efficient search strategies and greater difficulty remembering previously followed links or information on previously viewed pages (see the review in Czaja et al., 2001). In a particularly elaborate design, Streufert and colleagues (1990) studied decision making among four-person young, middle-aged, and older teams. Participants studied background materials about a fictitious nation and simulated the performance of a “national security council” required to manage the nation over a simulated compressed time scale of events across several months. The simulation posed management, governance, diplomatic, and emergency problems. As with the individual decisionmaking research reviewed previously, older teams considered less information, came to fewer decisions, and were less responsive to incoming information. Furthermore, whereas younger and middle-aged teams had more focused discussions and reached decisions more quickly, older teams talked more but were more diffuse and less task oriented and “engaged in many seemingly endless discussions or arguments, often about minor details” (Streufert et al., 1990, p. 556). However, they did respond to
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unexpected positive and negative (emergency) information as well as the younger teams. Older teams also expressed satisfaction with their performance, apparently unaware of their failure to handle a wide range of events unsuccessfully. The literature on aging and decision making appears to converge in indicating that older jurors are likely to give less complete consideration to the evidence before arriving at an individual verdict. To the extent that the jury contains mostly older people, the Streufert et al. (1990) study suggests that the entire group may collectively review the evidence less completely. At this point, however, it is premature to conclude that older jurors will ultimately vote differently than younger jurors because they will, perforce, be exposed to the full jury’s deliberations. Schematic Processing Evidence also suggests that older jurors may use the information they acquire differently because they are more susceptible to biases due to personal attitudes and values and, more generally, to schematic processing (see the review in Hess, 1999). Hess (1999) suggested that aging will affect judgment through three components. The first, a processing component, refers to the cognitive resources brought to bear, including such components as speed, working memory, and inhibition that are known to decline with age. This decline should result in fewer resource-consuming modes of processing, including greater use of more automatic and effortless “top-down,” or schematic, processing, and less use of more effortful “bottom-up,” or systematic, piecemeal processing. Hess (1999) explicated the implications of greater use of schematic processing for construction of mental models. Generally, mental models refer to representations of specific situations constructed by individuals to reflect their current level of understanding (Johnson-Laird, 1983; 1989). They include an integrated view of the available information regarding the situation at hand, in the context of the person’s general world knowledge and world view, which results in a coherent conceptual representation independent of the surface structure of incoming information. In the trial context, construction of mental models may include those of specific individuals, products, situations, etc., or of the juror’s overall trial story. It is well known within the social cognition literature that more automatic and schematic processing occurs under conditions of limited attentional resources or heavy processing load (Bargh, 1994). Thus, in line with reduced processing capacity views of aging, studies of the relationship of age to construction of mental models have shown that age-related resource limitations posed by working memory and reduced efficiency due to failing inhibitory capacity combine to impair construction, updating, and access to mental models (see the review in Hess, 1999). Essentially, schematic, top-down-driven processing results in more rapid categorization, less systematic review of new information, and therefore less updating and revision of impressions as new input comes in. Along with increased schematicity, age-related enhanced susceptibility to the effects of priming on judgment (Hess et al., 1998) is consistent with the notion that the initial impression a person forms becomes, in effect, the schema that controls further processing. Information relevant to that schema
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(or initial trial story) will be noticed and remembered better and will later become more influential in the final impression. To the extent that older adults are more susceptible to schematic processing, for example, they should also show greater selective memory for schema-relevant information. Consistent with this expectation, Hess and his colleagues (see the review in Hess, 1999) showed that older adults attempting to remember a narrative showed poorer memory for items that were atypical for, or irrelevant to, the type of situation depicted than younger adults. Essentially, script-inconsistent or -irrelevant information that could not be linked to the operative script was simply not processed sufficiently to promote memory. Generally, research on reproduction of recently learned stories has shown that older adults remember less information and are more likely to impose schematic narrative themes, morals, or lessons on their recall of story elements, thus remembering more highly integrative and succinct representations of the story’s essential meanings than younger adults (Adams et al., 1990, 1997; Pratt et al., 1989; Mergler et al., 1984/1985— see the review in Isaacowitz et al., 2000). Hess and his colleagues also showed that older adults are less likely to process apparently schema-inconsistent information carefully in order to try to understand the inconsistency. In research with younger adults, schema-inconsistent information is typically remembered better than consistent information (Hastie, 1984). Presumably, the effort to understand how the inconsistent information can be explained in light of the overall mental model causes it to be processed more deeply, leading to superior memory for it. However, Hess (1999) showed that this effect occurred for younger but not older adults. In line with Craik’s (2000) argument that self-initiated, effortful processing becomes less likely with age, the author interpreted these results to mean that older adults simply did not choose to engage in the effort to try to integrate the apparently contradictory information and therefore did not remember it better (or sometimes at all). In turn, failure to process apparently contradictory information carefully renders it less influential—hence, the lesser tendency of older adults to update and revise mental models as indicated by incoming information. In addition to its effects on memory for information that is presented, as noted earlier, schematic processing can lead to pseudomemories for information that is not presented, but consistent with (or implied by) the information that was presented. For example, in the false recognition paradigm developed by Roediger and McDermott (1995), participants study a list of words (such as symphony, song, lyrics, piano, jazz, etc.) semantically connected to a particular theme (e.g., music). Although the theme word (music, in this example) is implied by the other words, it is never presented. Nevertheless, many participants falsely recognize “music” as a word they previously learned. Older adults are reliably more susceptible to this effect (see the review in Koutstaal and Schacter, 2001). Thus, older adults may be susceptible to developing pseudomemories for nonpresented evidence or testimony implied by or consistent with the trial stories they have developed based on the actual presentation. Schematic processing can also influence the nature of source monitoring errors. For example, Mather and colleagues (1999) found that those who had previously watched a videotaped discussion tended to misattribute a liberal statement to a Democrat (rather than to the Republican who actually made it) or a statement regarding working out to an
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athlete (rather than to the writer who actual made it) and that older adults were more susceptible to such schema-driven misattributions. In other words, source memory was reconstructed so that the statements matched the person from the social category schematically associated with the behavior or attitude reflected in the statement. Similar results have been obtained by others (Bayen et al., 2000; Sherman and Bessenoff, 1999). Generally, schematic influences on memory tend to be greater when veridical memory is poorer, when processing demands are high in comparison to processing resources, or when processing capacity is restricted in some way (Bayen et al., 2000; Sherman and Bessenoff, 1999; Spaniol and Bayen, 2002)—all conditions more likely to occur for older adults. Such schematic influences can include, among other processing biases: • Selective attention • Biased interpretation of evidence • Selective memory for evidence • Schema-consistent source misattributions and other schema-driven memory distortions • False memories for nonpresented evidence Thus, memory is trimmed of schema-irrelevant material and shaped by schema-driven distortions and additions to form a generally schema-consistent account of what has occurred. Finally, Hess and his colleagues (Hess, 1999) found that when coming to a judgment based on information in memory (such as would be the case for jurors arriving at a verdict at the end of trial), older jurors were less systematic in their use of that information. It should be noted that a particularly unfortunate result of schematic processing and failing inhibitory control is increased prejudice among older adults. In an influential model of prejudice, Devine (1989) proposed that what differentiates prejudiced from nonprejudiced people is their voluntary inhibition of negative and stereotype-related thoughts. She argued that because our culture is suffused with negative stereotypes concerning race, social class, sexual orientation, gender, age, and other social categories, we cannot fail to think of them when confronted with a member of such a category. The unprejudiced person is presumed to reject and inhibit such thoughts voluntarily, whereas the prejudiced person willingly accepts them. Von Hippel and colleagues (2000) proposed that older people may become more prejudiced unwillingly, due to failing capacity to inhibit stereotype-based thinking and response. In support of their hypothesis, the authors found that older adults were more prejudiced, even though they reported stronger desire than younger adults to control these reactions. Furthermore, their judgments relied on stereotypes even when instructed not to, whereas those of younger adults did not. Finally, age differences in stereotyping and prejudice were mediated by age differences in inhibitory capacity. Thus, older jurors are likely to suffer stronger effects of stereotype-based processing and to reflect greater impact of prejudice in their verdicts. Hess (1999) also pointed to a second “knowledge-based” age-related influence on processing. That is, he suggested that the nature of the person’s experiential and knowledge base changes with age and that older persons tend to rely more on their own experience to arrive at judgments. For example, Erber and colleagues (2001) found that, although younger adults were equally forgiving of a younger and older target who forgot
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she was wearing a hat and left the store without paying, older adults were more forgiving of the older target. Arguably, the older adults’ experiences told them the older target had a better excuse for forgetting. Older persons also employ different social rules than younger persons when attributing blame or causality to a person’s behavior or to a social outcome (see the review in Blanchard-Fields, 1999). To the extent that social or other domain-specific knowledge increases or becomes more accurate, age may lead to greater accuracy in judgment. Hess and Auman (2001), for example, reviewed evidence suggesting that older adults may become more sophisticated in judgments of people and their behavior. In two studies, the authors found that relative to younger adults, older adults tended to give greater relative weight to more diagnostic information regarding a person than to less diagnostic information. Thus, at least when the evidence is primarily social, older adults may suffer less disadvantage in processing trial input. In this vein, Yates and Patalano (1999) suggested that aging jurors may develop more and more strongly held story schemas for a wide variety of circumstances that they may bring to bear on judgments of a particular case. If accurate, these strongly held schemas and stories among older jurors may facilitate accurate decision making. However, it should also be noted that relatively automatic application of this social knowledge base can become problematic if the juror fails to consider all information that might suggest an exception to general social-behavioral rules. Indeed, impaired executive function in younger adults has been shown to result in a pervasive memory bias favoring schema-consistent over schema-inconsistent material, whereas in unimpaired persons the bias is exactly the opposite (Macrae et al., 1999).The authors suggest that executive function is necessary to facilitate enhanced processing of (and thus better memory for) unexpected or schema-inconsistent material, and that failing executive function renders the mind less Firmly established personal opinions and values can also bias the manner in which a person processes evidence. For example, Klaczynski and Robinson (2001) illustrated the importance of Hess’s (1999) third age-related change in processing—that of motivation. The authors examined age differences in use of analytical vs. heuristic reasoning to support personal beliefs. Participants read vignettes with arguments supporting or attacking the value of their social groups (e.g., religion, social class). Both age groups tended to use heuristic reasoning to support belief-consistent arguments or evidence, whereas they tended to use scientific reasoning to support rejection of arguments contradicting their beliefs. Biased reasoning, however, was more common among middle-aged and older participants than among younger ones. Thus, particularly among older adults, motivation to discredit a particular point of view led to more systematic processing. A final relevant line of research has concerned the “theory of mind” (TOM) performance of older adults (reasoning about mental states and how they predict and explain behavior). Participants read stories requiring an inference about the characters’ thoughts and feelings and how they drive behavior. For example, in one story developed by Happe and colleagues (1998), a burglar has just robbed a shop. As he leaves the scene of the crime, a policeman sees him drop his glove. Not knowing of the burglary, the policeman wants to tell the burglar he has dropped his glove; however, when the policeman shouts out, the burglar gives himself up.
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The participant is asked to explain why the burglar does this and thus must judge what the burglar thought about the policeman’s shout. Two of three studies on this issue have found poorer performance among older adults (Sullivan and Ruffman, 2004, and Maylor et al., 2002, vs. Happe et al, 1998). Sullivan and Ruffman further found that performance in older (but not younger) adults was predicted by fluid as well as crystallized abilities, and that when these abilities were controlled for, age differences were eliminated. The latter authors also found poorer memory for the stories among older adults. Both findings would suggest poorer memory and judgment among older jurors. Summary The literature reviewed here suggests several preliminary conclusions regarding differences that might be expected between younger and older jurors. On the average, older jurors will experience greater difficulty with hearing, seeing, understanding, and integrating trial input to form their judgments. These jurors are likely to engage in more schematic processing of trial input, using existing knowledge structures to guide processing and using less detail in specific testimony and evidence to guide their judgments. Once an initial impression is formed, it may exert greater influence on subsequent information processing for older than for younger jurors, causing them to use less critical judgment for evaluation of later evidence or to be more biased in processing that evidence. Throughout, older jurors will exert less effort to process and integrate apparently contradictory information carefully. In addition to general schematic processing, older jurors are specifically more prone to stereotype-based judgments. Thus, race and other heavily stereotyped social categories and issues can be expected to bias the judgments of older jurors to a greater degree than those of younger jurors. Furthermore, the specific stereotypes and social beliefs possessed by older adults are in many instances different from those of younger adults, so efforts to identify and take into account these strongly held values and beliefs will be important. Older jurors will also tend to remember less trial input overall and will be more likely to make source-monitoring errors regarding the source or credibility of statements or evidence and the difference between evidence actually presented and schema-related and other inferences they have drawn from it. In particular, older adults may be less likely to correctly remember false or discredited information as false rather than true, and thereby more likely to be influenced by poor-quality evidence. Moreover, because of failing inhibitory capacities, older adults may be less able to follow judicial instructions to ignore inappropriate statements or evidence. Perhaps in light of these difficulties, older persons report less confidence in their ability to serve well as jurors than younger persons do (Boatright, 2001). Despite at least some relative disadvantages in quality of processing of trial input, older jurors may be more committed to their judgments via choice-supportive biases in memory for choice-relevant evidence (Mather and Johnson, 2000; Mather et al, 2000) and more resistant to influence from other jurors (Pasupathi, 1999). Thus, their decisions may be relatively unresponsive to correction in deliberation. These conclusions must be considered in light of considerable individual variability in processing capacity among older jurors. Within older jurors, schematicity and reductions
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in range of information use are related to working memory capacity and other measures of cognitive functioning. Also, even in the context of these limitations on processing capacity, older jurors may possess enhanced ability to recognize more diagnostic information—particularly regarding domains (such as human behavior) in which their life experiences have provided them with greater expertise than their younger counterparts. Finally, older adults can engage in deeper processing when highly motivated and in possession of sufficient cognitive resources. Thus, many older adults will behave very comparably to their younger counterparts. The study of age-related differences in juror behavior is still in its infancy. The cognitive aging literature provides evidence of age-related differences in cognitive processing and is a rich source of hypotheses regarding differences to be expected in juror behavior. However, it remains to conduct further research specifically with relevant trial-related stimulus materials and judgment tasks. Meanwhile, the consumer literature is also a rich source of findings of potentially great relevance to juror behavior. The arena of advertising effectiveness bears at least superficial resemblance to persuasion in trial because, in both cases, the recipient of persuasive messages must evaluate the relative credibility of competing claims for validity. 11.5 Overall Conclusions The literature reviewed herein reveals that age is crucial to functioning in the legal system. Age-related declines in cognitive functioning can cause, or contribute to causing, incidents that are later litigated in the legal system and can affect the performance of witnesses and jurors. However, although substantial empirical evidence has directly linked age-related decline in cognitive functions to accidents, such as those related to driving, very little research has directly examined the influence of age on witness testimony or juror decision making. The basic research on memory and decision making clearly documents age-related changes in these processes that would predict a number of specific interactions of age with particular witnessing variables and with variations in evidence, trial procedures, etc. that might affect jury decision making. Eyewitness researchers have begun to examine the effects of age on eyewitness identification and on susceptibility to the misinformation effect. However, other aspects of witness memory remain largely unaddressed. Moreover, the general area of age and juror decision making remains completely unexplored, with perhaps the single exception of the Fitzgerald (2000) study cited earlier. Finally, few studies of reactions to aging perpetrators or other case parties exist. Given the rapid aging of America, there is a clear and present need to develop better understanding of the many and varied ways in which aging victims, witnesses, and jurors can be expected to function differently than their younger counterparts. 11.6 Checklist: Relationships among Underlying Causes, Effects on Cognitive Processing, and Consequences for Victims, Witnesses, and Jurors Causes of Effects on cognitive processing Examples of
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impaired processing
practical difficulties
Brain structure Reduced efficiency of neuronal transmission; impaired and pathology perceptual abilities; impaired formation and retention of memories; impaired efficiency and complexity of cognitive processing; impaired self-control and executive capacity
Causes of impaired processing Hearing
Effects on cognitive processing
Victims: Failure to smell leaking gas Witnesses: Reduced capacity to form long-term memories Jurors: Less accurate memory and failure to remember until deliberation
Examples of practical difficulties
Elevated sound detection thresholds; failure to Victims: understand speech; difficulty in localization Failure to understand instructions of sound leads to accident Witnesses: Inaccurate report of witnessed conversations Jurors: Failure to understand courtroom instructions, arguments, and testimony Vision Failure to see clearly, particularly in poor Victims: light; restriction in range of peripheral vision; Failure to see cars approaching difficulty in motion perception, tracking from side at intersection, failure to objects, visual marking, etc.; difficulty estimate speed of oncoming reading nonverbal cues during conversation vehicles Witnesses: Failure to report accurately on things seen accurately; failure to report correct object locations, failure to identify persons or objects correctly Jurors: Difficulty seeing courtroom exhibits, reading nonverbal cues to interpret speech or reading cues to deception Victims: Reduced speed Slowed performance overall; impaired of cognitive performance of complex tasks Slowed reaction times in processes emergency situations Witnesses: Enhanced impairment of perception and memory in complex circumstances Jurors: Reduction in elaborative
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Failures of inhibition
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processing of trial input Victims: Victimization by scam artists due to failing ability to reason and critically evaluate proposals Witnesses: Less complete memory; failure of source monitoring such as susceptibility to misinformation effect Jurors: Greater use of relatively effortless schematic processing; failure to track source and credibility of testimony Inability to control attention; greater Victims: distractibility; reduced ability to divide Accidents due to enhanced attention; greater susceptibility to priming distractibility; failure to focus attention on most important tasks of driving Witnesses: Less memory for peripheral detail due to inability to divide attention between core event and context Jurors: Stronger effects of racial prejudice on judgment of minority defendant; inability to follow instructions to ignore inadmissible evidence Greater anxiety when stereotype salient; Victims: belief in applicability of negative stereotypes Elderly victim believes claims that to self; self-fulfilling prophecy he promised to send check to scam artist because of belief in fallibility of own memory Witnesses: Witness loses confidence in own testimony under cross examination because of belief in age-related memory impairment suggested by attorney Jurors: Failure to offer memories of evidence due to low confidence Reduced ability to hold multiple items of information in mind; reduced ability to carry out complex cognitive operations such as reasoning, math, etc.; reduced ability to multitask; failures of binding and source memory
Acknowledgment The authors would like to thank Michael Webster, Michael Crognale, and William P.Wallace for their helpful comments on previous drafts of this chapter.
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Defining Terms Episodic memory—Memory for recently experienced events. Inhibitory processes—The ability to control attention so that attention is focused on important or task-relevant information while attention to irrelevant information is inhibited. Presbycusis—Decline in processing of auditory information. Processing speed—The speed at which basic cognitive operations occur. Source memory (source monitoring)—Memory for the context in which a core event occurred (such as memory for where a person was encountered, where or from whom information was obtained, where a conversation took place, etc.). Stereotype vulnerability—The tendency to act in stereotype consistent manner when relevant stereo-types are salient. Visual acuity—Ability to see clearly. Visuospatial processing—Processing of spatial location and relationships through vision; includes object identification and perception of location and motion. Working memory—The ability to hold information in short-term memory while simultaneously using that information to form judgments or solve problems. References Adams, C., Labouvie-Vief, G., Hobart, C.J., and Dorosz, M. (1990). Adult age group differences in story recall style. J. Gerontol: Psychol Sci. , 45, 17–27. Adams, C., Smith, M.C., Nyquist, L., and Perlmutter, M. (1997). Adult age-group differences in recall for the literal and interpretive meanings of narrative text. J. Gerontol. Series B: Psychol. Sci. Social Sci. , 4, 187–195. Adams-Price, C. (1992a). Eyewitness memory and aging research: a case study in everyday memory. In R.L.West and Sinnott, J.D. (Eds.), Everyday Memory and Aging: Current Research and Methodology (246–258). New York: Springer-Verlag. Adams-Price, C. (1992b). Eyewitness memory and aging: predictors of accuracy in recall and person recognition. Psychol Aging , 7, 602–608. Andres, P. (2003). Frontal cortex as the central executive of working memory: time to revise our view. Cortex , 39, 871–895. Anstey, K.J. and Maller, J.J. (2003). The role of volumetric MRI in understanding mild cognitive impairment and similar classifications. Aging Mental Health , 7, 238–250. Baddeley, A. (1986). Working Memory . Oxford, England: Clarendon Press. Ball, K., Owsley, C., Sloane, M.E., Roenker, D.L., and Bruni, J.R. (1993). Visual attention problems as a predictor of vehicle crashes in older drivers. Invest. Opthalmol. Visual Sci. , 34, 3110–3123. Ball, K., Roenker, D.L., and Bruni, J.R. (1990). Developmental changes in attention and visual search throughout adulthood. In J.Enns (Ed.), Advances in Psychology (Vol. 69, 489–508). Amsterdam: North-Holland-Elsevier Science. Baltes, P.B. and Smith, J. (1997). Emergence of powerful connection between sensory and cognitive functions across the adult life span: a new window to the study of cognitive aging? Psychol. Aging , 12, 12–21. Bargh, J.A. (1994). The four horsemen of automaticity: awareness, intention, efficiency, and control in social cognition. In R.S.Wyer and T.K.Srull (Eds.), Handbook of Social Cognition (1– 40). Hillsdale, NJ: Erlbaum.
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Stone, M.J. and Stone, L. (1997). Ageism: the quiet epidemic. Can. J. Public Health , 88, 293–294. Streufert, S., Pogash, R., Piasecki, M., and Post, G.M. (1990). Age and management team performance. Psychol. Aging , 5, 551–559. Strouse, A., Ashmead, D.H., Ohde, R.N., and Grantham, D.W. (1998). Temporal processing in the aging auditory system. J. Acoustical Soc. Am. , 104, 2385–2399. Sullivan, E.V., Rosenbloom, M., Serventi, K.L., and Pfefferbaum, A. (2004). Effects of age and sex on volumes of the thalamus, pons, and cortex. Neurobiol. Aging , 25, 185–192. Sullivan, S. and Ruffman, T. (2004). Social understanding: how does it fare with advancing age? Br. J. Psychol , 95, 1–18. Tisserand, D.J. and Jolles, J. (2003). On the involvement of prefrontal networks in cognitive aging. Cortex , 39, 1107–1128. Tran, D.B., Silverman, S.E., Zimmerman, K., and Feldon, S.E. (1998). Age-related deterioration of motion perception and detection. Graefes Arch. Clin. Exp. Ophthalmol , 236, 269–273. Tun, P.A., Wingfield, A., Rosen, M.J., and Blanchard, L. (1998). Response latencies for false memories: gist-based processes in normal aging. Psychol. Aging , 13, 230–241. U.S. Bureau of Justice Statistics. (2002). Victim characteristics: summary findings. Washington, D.C.: U.S. Government Printing Office. Underwood, J. and Pezdek, K. (1998). Memory suggestibility as an example of the sleeper effect. Psychonomic Bull. Rev. , 5, 449–453. Uttl, B. and Graf, P. (1993). Episodic spatial memory in adulthood. Psychol. Aging , 8, 257–273. Verhaeghen, P. (2002). Age differences in efficiency and effectiveness of encoding for visual search and memory search: a time-accuracy study. Aging, Neuropsychol Cognit ., 9, 114–126. Verhaeghen, P. and Meersman, L.D. (1998). Aging and the Stroop effect: a meta-analysis. Psychol Aging , 13, 120–126. Verhaeghen, P. and Salthouse, T.A. (1997). Meta-analyses of age-cognition relations in adulthood: estimates of linear and nonlinear age effects and structural models. Psychological Bull , 122, 231–249. Verhaeghen, P., Steitz, D.W., Sliwinski, M.J., and Cerella, J. (2003). Aging and dual-task performance: a meta-analysis. Psychol Aging , 18, 443–460. Villaume, W.A., Brown, M.H., and Darling, R. (1994). Presbycusis, cummunication, and older adults. In M.L.Hummert, J.M.Wiemann, and J.F.Nussbaum (Eds.), Interpersonal Communication in Older Adulthood: Interdisciplinary Theory and Research (83–106). Thousand Oaks, CA: Sage, von Hippel, W., Silver, L.A., and Lynch, M.E. (2000). Stereotyping against your will: the role of inhibitory ability in stereotyping and prejudice among the elderly. Personality Social Psychol Bull , 26, 523–532. Watson, D.G. and Humphreys, G.W. (1997). Visual marking: prioritizing selection for new objects by top-down attentional inhibition. Psychol Rev. , 104, 90–122. Watson, D.G. and Maylor, E.A. (2002). Aging and visual marking: selective deficits for moving stimuli. Psychol Aging , 17, 321–339. Wells, G.L. and Leippe, M.R. (1981). How do triers of fact infer the accuracy of eyewitness identifications? Using memory for peripheral detail can be misleading. J. Appl. Psychol , 66, 682–687. Wells, G.L., Small, M., Penrod, S., Malpass, R., Fulero, S.M., and Brimacombe, C.A.E. (1998). Eyewitness identification procedures: recommendations for lineups and photospreads. Law Hum. Behav. , 22, 603–647. Werner, J.S. (1998). Aging through the eyes of Monet. In W.G.K.Backhaus, R.Kliegl, and J.S.Werner (Eds.), Color Vision: Perspectives from Different Disciplines (3–41). New York: Walter de Gruyter. West, R. (2000). In defense of the frontal lobe hypothesis of cognitive aging. J. Int. Neuropsychol. Soc. , 6, 727–729.
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Yoon, C., May, C.P., and Hasher, L. (2000b). Aging, circadian arousal patterns, and cognition. In D.C. Park and N.Schwarz (Eds.), Cognitive Aging: a Primer (151–171). Philadelphia, PA: Psychology Press. Zacks, R. and Hasher, L. (1997). Cognitive gerontology and attentional inhibition: a reply to Burke and McDowd. J. Gerontol: Psychol. Sci. , 52, 274–283. Zacks, R.T., Hasher, L., and Li, K.A.H. (2000). Human memory. In F.I.M.Craik and T.A.Salthouse (Eds.), Handbook of Aging and Cognition (2nd ed., 293–358). Mahwah, NJ: Erlbaum. Zwahr, M.D. (1999). Cognitive processes and medical decisions. In D.C.Park and R.W.Morrell (Eds.), Processing of Medical Information in Aging Patients: Cognitive and Human Factors Perspectives (pp. 55–68). Mahwah, NJ: Erlbaum. Zwahr, M.D., Park, D.C., and Shifren, K. (1999). Judgments about estrogen replacement therapy: the role of age, cognitive abilities, and beliefs. Psychology and Aging , 14, 179–191.
Further Information Birren, J.E. and Schaie, K.W. (1996). Handbook of the Psychology of Aging . San Diego: Academic Press. Craik, F.I.M. and Salthouse, T.A. (Eds.) (2000). The Handbook of Aging and Cognition . Mahwah, NJ: Erlbaum. (2nd ed.). Dixon, R.A. and Backman, L. (Eds.) (1995). Compensating for Psychological Deficits and Declines . Mahwah, NJ: Erlbaum. Fisk, A.D. and Rogers, W.A. (Eds.) (1997). Handbook of Human Factors and the Older Adult . San Diego, CA: Academic Press. Hess, T.M. and Blanchard-Fields, F. (Eds.) (1999). Social Cognition and Aging . San Diego, CA: Academic Press. Hummert, M.L. and Nussbaum, J.F. (Eds.) (2001). Aging, Communication and Health . Mahwah, NJ: Erlbaum. Mayr, U., Spieler, D.H., and Kliegl, R. (Eds.) (2001). Ageing and Executive Control . New York: Psychology Press. Morrell, R.W. (Ed.) (2002). Older Adults, Health Information, and the World Wide Web . Mahwah, NJ: Erlbaum. Naveh-Benjamin, M., Moscovitch, M., and Roediger, H.L., III (Eds.) (2001). Perspectives on Human Memory and Cognitive Aging . New York: Psychology Press. Nussbaum, J.E, Pecchioni, L.L., Robinson, J.D., and Thompson, T.L. (2000). Communication and Aging (2nd ed.). Mahwah, NJ: Erlbaum. Park, D.C., Morrell, R.W., and Shifren, K. (Eds.) (1999). Processing of Medical Information in Aging Patients . Mahwah, NJ: Erlbaum. Park, D.C. and Schwarz, N. (Eds.) (2000). Cognitive Aging: a Primer . New York: Psychology Press. Rogers, W.A. and Fisk, A.D. (Eds.) (2001). Human Factors Interventions for the Health Care of Older Adults . Mahwah, NJ: Erlbaum. Schacter, D.L. (2001). The Seven Sins of Memory . New York: Houghton-Mifflin. Schacter, D.L. (1996). Searching for Memory . New York: Basic Books. Snowdon, D. (2001). Aging with Grace: What the Nun Study Teaches Us about Leading Longer, Healthier, and More Meaningful Lives . New York: Basic Books.
12 Memory for Conversation on Trial Deborah Davis University of Nevada Markus Kemmelmeier University of Nevada William C.Follette University of Nevada 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
12.1 Introduction Testimony regarding conversation is central to the vast majority of criminal and civil cases litigated in the courts. In some cases, testimony may concern relatively public group discussions such as those that might take place in a corporate boardroom. Witnesses to such group interactions must attempt to remember what was said, as well as which member of the group said it and, perhaps, to whom it was said. Some are relatively more private, such as the famous small group conversations among President Richard Nixon, John Dean, and others that became central to the Watergate hearings (Gold, 1974). Others are more private still, occurring between a rape victim and her attacker or between a doctor and patient. Across a variety of circumstances, testimony regarding the specific details of these conversations becomes central to the decisions of the jurors who decide the cases. When an employee sues for wrongful termination, discussions held in the corporate boardroom (or university committee meeting) can become central evidence of the reasons underlying the termination. Discussions between doctor and patient of issues such as the nature of the patient’s symptoms, possible diagnoses, risks and benefits of alternative treatments, or instructions for medication or other treatments become central to cases of malpractice—as do discussions between other professionals and their clients. Criminal defendants are convicted based in part on testimony from witnesses to threats, verbal fights, and other conversational indicators of hostile intentions or the conflictual status of the relationship between the defendant and victim. Such witnesses sometimes overhear the conversations of others and sometimes are central participants. However, in all cases, the quality of jury decisions based on this testimony depends upon the accuracy of witness memories. Like other witnesses, those reporting memories for conversation can voluntarily choose to lie. Perhaps more commonly, however, their memories are subject to the same
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honest failures and distortions that plague witness memories for specific persons, locations, objects, and events. It is this latter source of inaccuracy that we will address in this chapter. Modern scientific theories of memory suggest that human memory systems operate in three general stages: (1) acquisition (or encoding), when information is first transferred into our memory system; (2) storage, when information is maintained in memory over a period of time; and (3) retrieval, when information is located and retrieved from storage. At each stage, memory may be compromised by failure or inaccuracy. Comprehensive reviews of principles of human memory have been written and we refer the reader to them for an introduction to the basics (Baddeley, 1999; Schacter, 2001; Spear and Riccio, 1994). Similarly, excellent treatments of eyewitness memory (Davis and Follette, 2001; Thompson et al., 1998) or the role of memory in the forensic interview (Eisen et al., 2002) are also available. Consequently, this chapter’s review focuses on aspects of memory that are particularly important to, or even peculiar to, conversational memory. Furthermore, we focus our discussion on memory for conversational features that are commonly the subject of testimony in trial. First and foremost of these are, of course, who said something and what was said. However, in addition to the identity of the speaker and other participants, and the specific content of a conversation, witnesses must often report on such contextual features as where and when the conversation took place, who else might have been present, in which of many conversations a particular exchange took place, and so on. We will identify the many issues witnesses to conversations are asked to address and review relevant research when it is available. 12.2 Failures of Encoding Information must first be successfully encoded in order to be remembered. Three primary factors may cause memory to fail at the stage of encoding: (1) failure to perceive (or in this instance to hear) and to see relevant face and body language, (2) failure to devote sufficient attention to the target information, and (3) failure to understand it correctly. Perception Accurate understanding of conversation requires accurate speech perception, as well as accurate perception of facial expressions and body language that may affect interpretation of what is said. A person may fail to encode the nature of a conversational contribution accurately due to personal sensory impairments in hearing or vision (see Davis and Loftus, Chapter 11, this volume, for review) or to environmental interference through such factors as background noise, distance, or blocked vision. Visual cues, such as gestures or lip movements, can compensate for an impaired auditory channel and make message transmission more resilient to the presence of background noise and other auditory disturbances (Argyle and Graham, 1975; Rogers, 1978). This is particularly important for the hearing impaired, who tend to compensate by lip reading (Davis and Loftus, this volume; Nussbaum and Coupland, 2004; Nussbaum et al., 2000; Villaume et al., 1994).
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However, even for unimpaired listeners, nonverbal cues such as gestures, facial expressions, or body movement and posture help the hearer to understand what the speaker is trying to convey and how it is to be understood. Thus, failure to see the speaker is likely to undermine the adequacy of encoding utterances such as those that, for example, use sarcasm, irony, and similar rhetorical means that often come with nonverbal signals indicating that the utterance is not to be interpreted literally. Finally, multichannel perception is important for evaluation of the emotional underpinnings of the message and its veracity (see DePaulo et al., 2003). Interpretations of conversational contributions based on the availability of, or attention to, a limited number of channels may be completely erroneous. Therefore, when an attempt is made to evaluate the accuracy of memory for conversation, it is of crucial importance to consider the sensory abilities of the witnesses, as well as the environmental challenges to vision and hearing present at the time of the conversation (see Davis and Loftus, Chapter 11, this volume; Davis and Friedman, in press, for reviews). Attention The success with which information is encoded is determined by the amount of attention devoted to it, as well as the depth with which it is processed. The more that one attends to something and the more that one thinks about it while attending to it, the more likely it is to be remembered later (see reviews in Davis and Follette, 2001; Schacter, 1999, 2001). Conversational involvement, for example, enhances overall memory for ideas mentioned in the interaction, presumably because it increases attention (Cegala, 1984). Thus, to understand the conditions under which a particular conversation, part of a conversation, or particular person participating in the conversation will be best remembered, one must first consider what determines the amount and direction of attention paid by the observer to the conversation and its participants. Davis and Follette (2001) reviewed in detail the way in which attention is determined by personal characteristics and states, and contextual features of a target event. First, attention is vulnerable, so it may be impaired by internal or external distractions. The person’s internal processing resources may be diminished by such factors as illness, fatigue, old age, intoxication, pressing personal concerns, anxiety, and so on, which would limit attention devoted to external events of most kinds, including conversation. External distractions such as noise, complexity in the environment, interruptions, etc. can also compromise attention to conversation partners and their utterances. Second, because attention is selective, greater attention is devoted to aspects of the environment or of a conversation that (see the review in Davis and Follette, 2001) • Are salient (i.e., stand out and draw attention) • Are threatening (including physical and emotional threats) • Are distinctive, unexpected, or unique • Are interesting • Are relevant to personal interests, goals, or current concerns • Are relevant to activated schemas, stereotypes, or expectations • Elicit powerful emotions
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Furthermore, attention tends to go toward what is deemed the essential “core” of the event—or to what is deemed the central point of a conversation (see the review in Davis and Friedman, in press). Attention may be selectively devoted to topics and to people. Therefore, people deemed most important, interesting, distinctive, etc. tend to draw more attention than others. Among the interpersonal features most extensively investigated is status. Persons of high status are typically relatively novel and relatively important. They are novel because access to higher status persons is often restricted, and thus interaction occurs less frequently; they are more important because higher status persons are often in possession of desired resources or in control of one’s outcomes. Typically, lower status individuals tend to be highly vigilant with regard to the behavior and utterances of higher status individuals, in particular when their own outcomes are dependent on the higher status persons (Berscheid et al., 1976; Fiske and Depret, 1996; cf. Erber and Fiske, 1984). Attention is also affected by expectations associated with conversational norms. One such expectation, for example, derives from the conversational maxim “be relevant” (Grice, 1975), which dictates that conversational contributions should be relevant to the previous content of others’ remarks and to the general content and context of the interaction. Davis and Holtgraves (1984) demonstrated that such an expectation of relevance can result in poor memory for irrelevant (or tangential) contributions. The authors had participants read a supposed debate between two Nevada politicians. Each was asked four questions regarding the deployment of an “MX” missile system in Nevada. The replies of one politician were directly relevant to the questions asked, whereas those of the other were only tangentially relevant. Two sets of questions were used so that the first politician’s answers were directly relevant to the first set and tangentially relevant to the second, whereas the reverse was true for the second politician. Memory (recognition and recall) was clearly impaired for the tangentially relevant replies. In fact, when asked to recall each reply verbatim, subjects often simply wrote “did not answer the question” for tangential replies. Presumably, schematic processing directing attention to material relevant to the question led to superficial processing of the irrelevant content and thus poor memory. Generally, violations of social norms or strongly held expectations are attention grabbing, and people remember such instances better, primarily because they are trying to resolve the discrepancy between expectation and reality (see Graesser et al., 1979). For example, one of the implicit expectations in many conversations is that participants follow norms of politeness and modesty, i.e., that they do not engage in unfavorable comments about each other, inappropriate sexual innuendo, or excessive self-praise. To the extent that certain statements violate these norms, their content becomes more memorable than the remainder of the conversation (Pezdek and Prull, 1993; Wyer et al., 1994). Role-based expectations also guide social perception and memory. Status differences, often associated with social roles, give rise to expectations with regard to how high- and low-status individuals will behave in conversation. Typically, lower status individuals are more polite to higher status individuals, who often command the resources upon which the other is dependent (Lee, 1993). Consistent with the idea that social status induces politeness-related expectations, Kemper and Thissen (1981) found that impolite requests by low-status speakers (which do not fit our expectations) are more likely to be
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remembered, whereas such requests by high-status speakers are more likely to be forgotten or distorted. Conversely, polite requests by high-status speakers were more memorable than the same requests by low-status speakers (but see Holtgraves, 1997, experiments 1 and 2, for more ambiguous results). Similarly, when speakers state a request in ways that are not appropriate for the specific context, the wording of the request is more likely to be remembered compared to when the request is made in an appropriate way (Gibbs, 1987). Whereas discrepancy between expectation and reality is generally attention grabbing, in other instances expectations may actually facilitate memory for information that is consistent with them. This is primarily true when a person possesses expectations concerning the organization or structure of a particular conversational event. For instance, Gamst (1982; study 2) tested the notion that people have expectations with regard to the structure of a dialogue and have better memory for conversations that conform to a generic script. When participants heard a dialogue that did not conform to the script, their memories were poorer compared to those for a dialogue that conformed to their expectations. The Role of Anxiety and Emotion Many of the circumstances giving rise to litigation involve intense emotion among participants and witnesses alike. Thus, it is of interest to understand how anxiety and emotion might affect memory for conversation. Christianson and his colleagues have suggested a two-stage process by which stress or arousal affects memory (Christianson and Safer, 1996). First, in the “preattentive” stage, emotion-eliciting stimuli, such as blood or personal threat, trigger an orienting response drawing attention to the emotion-eliciting stimuli. In the second stage, active attentional mechanisms engage elaborative encoding focused on the emotional material. This selective attention and elaboration limit processing capacity for peripheral information not central to the emotional aspects of the event. In cases of very strong emotion, the person may become preoccupied by intrusive thoughts regarding the threatening event, further narrowing the focus of attention/processing. Safer and colleagues (1993) refer to the outcome of the narrowed attention and heightened psychological focus on the source of the emotional arousal as “tunnel memory.” Events witnessed under this narrow processing mode will tend to promote better memory for central information—that is, the details of the emotion-provoking part of the event. In contrast, it will tend to inhibit processing of and memory for peripheral details, or details that are irrelevant or spatially peripheral to the core source of arousal (Easterbrook, 1959; see reviews in Brown, 2003; Christianson, 1992a, b; Christianson and Safer, 1996; Heuer and Reisberg, 1992). This dynamic of selective attention and selective recall is powerfully illustrated with regard to the so-called “weapon focus effect” (Kramer et al., 1990). To the extent that a weapon is present in the situation, individuals tend to focus their attention on this potentially threatening object, but are less attentive and have a poorer memory of other characteristics of the situation. Beyond the general instance of threat, emotional arousal has often been linked to decreased memory for conversation (Goss et al., 1985; Sillars et al., 1990; Singer, 1969; Stafford and Daly, 1984). However, it appears that in these studies emotion was
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peripheral with regard to the conversation, so research participants did have a poor memory for aspects of the conversation that did not produce their emotional state. Arousal often facilitates the formation of detailed and personally meaningful event memories. That is, the person may be particularly likely to retain a memory (though not necessarily accurate) of the event and peripheral details associated with it. Indeed, MacWhinney and colleagues (1982) showed that episodes causing physiological arousal were more likely to be remembered than episodes that were less arousing (see also Bools et al., 2001). It appears that emotional arousal generally promotes long-term retention of the emotion-arousing event or message (Parkin et al., 1982). This may also explain why jokes and other emotion-eliciting utterances tend to be retained better than neutral utterances (Schmidt, 1994; cf. Keenan et al., 1977). However, as Brown and Kulik (1977) and others have shown with their research on “flashbulb memories,” these very vivid memories can be quite inaccurate. In particular, although the core features of the events can be well retained, memories for peripheral detail (such as where or when it happened) are often quite mistaken. Notwithstanding the potential of emotion to facilitate memory, it may also be expected to impair memory in some circumstances. Anxiety and other unpleasant emotions, for example, maybe responsible for the well-known failure of patients to remember the content of their conversations with physicians (DiMatteo, 1985; Ley, 1966, 1979, 1986; Ley and Spelman, 1967). During aspects of physical examinations, for example, patients may invoke distracting strategies to avoid thinking about the unpleasant aspects of the examination. Although these strategies may have the intended benefit, they are likely to prevent patients from paying attention to aspects of their environment. Thus, it would not be wise to present important information to patients during aversive components of examinations. That is not to say that the physician cannot do and say things to reduce anxiety such as explaining the purpose of the examination, what to expect in terms of physical sensations, and so forth. Engaging in conversation for the purpose of relaxing the patient is also warranted. However, the doctor should not assume that those are optimal times to try to impart important information to the patient, especially information upon which the patient needs to act at a later time. Furthermore, anxiety is known to interfere with successful communication and memory. Physicians and patients are under special stress during discussions of serious or life-threatening diseases. However, physicians appear to have anticipatory anxiety that peaks early in interactions with patients (though it may persist for some time afterward) and patients’ anxiety increases later in the consultation and even after an initial consultation about serious news has concluded (Ptacek and Eberhardt, 1996). Physician anxiety may interfere with clear expression, attention to content, and noticing cues of confusion that may be presented by the patient as the conversation proceeds and the patient becomes more anxious. Summary. The effects of emotion on memory for events have been widely studied within psychology; however, little research has addressed the relationship of emotion to memory for conversation. Research that has addressed these issues has been correlational in nature and is open to alternative explanations. This dearth of research is particularly unfortunate because emotions are high during incidents such as sexual harassment or rape and fights that degenerate into violence, and in a variety of stressful professional interactions—all situations commonly giving rise to litigation of some form.
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Interpretation Difficulty of Perception The presence of noise, distraction, personal sensory impairments, or other factors that cause difficulty in simple perception of words has the additional effect of compromising comprehension. That is, even though individuals may understand all the words spoken, they are less likely to understand the overall meaning, draw appropriate inferences from utterances, and integrate the new information with their existing knowledge. The result of this is frequently diminished comprehension and retention (Schneider et al., 2000). Those who have tried to learn a foreign language may have experienced the analogous effect when attempting to process rapid speech in the new language: one must try so hard to understand the words that the meaning of the entire sentence is lost. This problem often plagues older listeners, partic ularly in the presence of background noise (see Davis and Loftus, Chapter 11, this volume). Meaning Depends upon Context Language comprehension inherently depends on context. Initial understanding of conversational utterances requires integration of verbal and nonverbal cues, as well as background, situational, and relationship contexts (Argyle and Graham, 1975; Cohen, 1977; Rogers, 1978). For example, the English language is full of words that carry different meanings dependent on the context in which they are used (“nut” as fruit vs. “nut” as counterpart of a screw vs. “nut” as deranged individual). Similarly, phrases and utterances need to be considered within the social and physical context in which they are made in order for a hearer to infer a speaker’s intention accurately (Sperber and Wilson, 1995). For adequate understanding to occur, hearers and speakers must share a common understanding of the exact context. Speakers routinely make assumptions about the kind of information shared between speaker and hearer (Clark and Haviland, 1977). These assumptions are often warranted, perhaps because interactants are in the same room, have had similar experiences, or have communicated before about a particular subject. From this perspective, a speaker’s utterances carry with them assumptions about what he thinks a hearer knows already. It is easy to see that in cases in which a speaker’s assumptions are incorrect, misunderstandings will occur. Frequently, these misunderstandings are detected and eliminated. However, in other cases, interactants may not notice that they are making different assumptions. To the extent that an utterance is interpretable to them, two people can agree on what was said, yet encode very different interpretations (cf. Fletcher, 1994; see Davis and Friedman, in press, for review). Features of Speech That Create Difficulty in Understanding As we are all aware, some speakers are much more difficult to understand than others. Of course, failure initially to understand an utterance correctly will cause memory to fail as well. Thus, it is important to consider the aspects of speech that affect initial understanding.
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Generally, linguistically simple statements are understood more easily. Long sentences that include numerous clauses and subordinate clauses require more effort and put great processing demands on the individual. In order to understand such a sentence, a hearer must hold all information extracted from different clauses in working memory long enough to be able to integrate all parts and extract an overall meaning. Thus, listeners— especially older listeners, distracted listeners, and those with otherwise impaired processing capacity—are particularly likely to fail to comprehend complex utterances (see Davis and Loftus, Chapter 11, this volume). Hearers generally find it easy to understand statements that involve concepts, vocabulary, and information with which they are familiar but struggle if statements take an unfamiliar form or convey new content. This is a common reason why conversations between professionals and their clients often fail. A specific problem in the medical realm is the use of a sophisticated and highly specialized vocabulary that is inaccessible to the layperson. The physician has a special responsibility to communicate in a language that is comprehensible to the patient. If patients have a particularly acquiescent response style, it may be difficult for the doctor to discern that the patient does not understand what he has been told. Under these circumstances, it is useful for the doctor to ask the patient to repeat what he was just told. The physician then must ascertain that the patient actually understands the concepts and does not merely parrot what was said without really understand its meaning. In general, it is desirable if patients para-phrase the information using language meaningful to them rather than incorporating ambiguous jargon. High-stakes medical conversations are likely to be about complex topics about which the physician uses terms familiar to the medical community but less so to the lay community. For instance, one study indicated that 73% of women informed about breast cancer did not understand the meaning of the word “median” as in median survival time (Lobb et al., 1999). If the patient does not understand such a term during a high-stress interaction, it is easy to see how physicians could correctly claim they informed patients of the likely survival time of a particular treatment option but the patient could claim that no such discussion occurred. Ambiguity about the meaning of important words in medical decision making and communication is not limited to statistical terms. Considering that many documents intended for public consumption are written at the sixth-grade level, it is easy to see how terms like “prognosis” and “morbidity” can be misunderstood, not encoded, and therefore not recalled. Even terms that fall within everyday language become salient and misunderstood in medical interactions. Physicians and patients use terms relating to frequency (frequently, rarely, likely, probably, often, etc.) quite differently (Girgis and Sanson-Fisher, 1995). This means, of course, that a complication experienced following a conversation with a physician could take a patient very much by surprise if he and the doctor had different subjective understanding of what was meant by “occasionally.” Attempts have been made to quantify the probabilities implied by adjectives used in the medical literature (Kong et al., 1986), but ambiguities still remain. There is no single best way to be sure that patients and physicians mean or understand words or probability estimates of risk, treatment options, or side effects the same way (Mazur and Hickam, 1991; Nakao and Axelrod, 1983; Ohnishi et al., 2002; Robertson, 1983; Woloshin et al., 1994). What is clear is that professionals need to engage in extra effort to ensure understanding—as well as to help patients remember vital information and instructions.
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In addition to knowing how to disclose high-stakes information, it is important for physicians to anticipate what patients want to know. Because of the high level of affect likely to be present for the patients, they may not be as good at communicating their desires for information. In a study of cancer patients’ experiences at receiving news of a cancer diagnosis, patients were less interested in the diagnosis than the prognosis. Although 14% of patients felt diagnosis was the most important part of cancer disclosure, more (18%) felt treatment options were most important and fully 52% wanted prognostic information. More than half the patients wanted to discuss life expectancy, though only 27% of physicians actually did so. Certainly, recall of these conversations would more likely be reported as unsatisfying, and the possibility of the patient inserting his understanding of what the prognosis is (even if it is incorrect) would be higher than if the physician supplied the information initially. Schematic Processing Schemas refer to units of knowledge that people have about recurring objects, situations, social categories, persons, or topics. Whether ordering a meal at a restaurant or going to the doctor, people have a clear conception of the kinds of people involved and the way in which these interactions typically proceed. This knowledge not only gives rise to specific expectations but also helps people to understand the events and people that they encounter. Ambiguous events are usually interpreted so that they are consistent with the schema for a particular situation (Bransford and Johnson, 1972). Similarly, schemas help to fill in the gaps (Bower et al., 1979) in what is directly perceived with schema-based assumptions about what is also likely to be true (see the review by Davis and Loftus, in press). People often compensate for lost words (missed or not clearly understood), for example, by filling in words they expect would typically fill such a spot. This is particularly likely to occur when the person has very strong expectations, when he is distracted and not processing carefully, or when his hearing is poor. This is particularly characteristic of elderly listeners, who rely on expectations for content as well as knowledge of syntax and semantics to fill in gaps (Nussbaum et al., 2000). Specific schemas for other persons or the circumstances of an interaction also affect expectations, which in turn determine which elements of an interaction are most likely to be noticed and how they will be interpreted when ambiguity exists. Consider a new mother whose 10-month-old child is just beginning to walk and is heading toward a toy he clearly does not see. The mother, noting the child is about to trip, grabs the child by the hand just as the child falls. The child cries out in pain and is unable to move his arm. Upon taking the child to the pediatrician, the new mother worries that the physician will think she abused the child, although all she did was stop him from falling. During the conversation with the physician, she is tense, nervous, and defensive when the doctor asks her if the child is meeting his developmental milestones, a routine question. The doctor also tells the mother that one must be very careful when placing pressure on the arm of children under the age of six because they can become easily dislocated. Though the physician never overtly questions about child abuse, the new mother feels a dislike for the doctor and ultimately tells her friends that the doctor is suspicious and condescending during interactions with her. From the doctor’s point of
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view, a mild dislocation (radial head subluxation) of the elbow is common. He was never suspicious of child abuse and simply provided information to a new mother about an action and condition commonly referred to as “nursemaid elbow.” The mother’s expectation created a confirmatory bias in her assessment of the doctor’s suspicion. In recalling the conversation to others, she then highlights the “evidence” that the doctor was suspicious. In this case of nursemaid elbow, one can just as easily see how a physician with an expectation of abuse based on a stereotype or pre-existing suspicion could read the nervous new mother’s body language and verbal defensiveness as evidence for the abuse hypothesis. Research supports the possibility that the physician could selectively recall evidence from the conversation to support his hypothesis that there was reason for concern about possible abuse (Sande et al., 1986). Personal Determinants of Understanding Personal difficulties may exist that compromise understanding in conversation, many of which have been studied in the context of medical interactions. For example, beyond patients suffering age-related cognitive impairments or dementias, people who are acutely or subclinically cognitively impaired tend to encode or retrieve information improperly. Acute impairment may be due to such factors as mild disorientation secondary to illness or even medication toxicity. Medication-induced acute impairments may come from drug interactions or may have developed because the patient is taking drugs improperly. The patient may also inadequately metabolize the drugs, resulting in toxicities due to higher than anticipated blood levels of medications. In both instances, patients often try to cover up early signs of cognitive decline by being overly acquiescent. It is easy to understand how a doctor could report informing such a patient about the side effects of a drug while the patient denies being told of any such effects. 12.3 Failures of Retention Memory of the Fact of the Conversation Perhaps the most fundamental aspect of memory for conversation is memory for whether the conversation took place at all. Like memory for all information, memory for the very fact of a conversation can fail. Unfortunately, this form of failure of memory for conversation plays an integral role in a common crime against the elderly known as the “where’s the check?” scam (Schacter, 2001). Essentially, perpetrators of this scam convince elderly targets that they have already agreed in some way to give the perpetrator a check. In some cases, the perpetrator may simply claim that the elderly target promised to send the check in an earlier conversation, say it has not arrived as agreed, and remind the person to send it. In others, the perpetrator may say he has received the agreed-upon check, but that it was written for more than necessary. He then asks the elderly target to send a replacement check for the lesser amount. Perpetrators of such scams often pretest their elderly targets to assess their memory by calling in advance to collect personal information. When the perpetrator later calls back
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to initiate the scam, he first determines whether the older targets remember the previous conversation and thus whether they would be likely to remember other events. If not, the perpetrator proceeds to make his false claim. Many older people expect their memories to be poor and would not be surprised to hear that they had forgotten a phone call or conversation or the details of past financial agreements or transactions. Thus, they are easily convinced that they had previously written (and then forgotten writing) a check or that they had agreed to donate to a particular cause. Memory of What Is Said How Much Is Remembered? Most of what is said in conversation is lost. Stafford and colleagues (1987) found that immediately after a mundane conversation, participants could recall only about 10%. After 1 month, this number dropped to 4%. What we retain from a conversation is primarily the gist of what was perceived as its core. Such poor retention of what is said contributes to poor outcomes of professional interactions that are later litigated in the courts—prominently, those between doctors and patients. It has long been noted, for example, that patients are unable to recall about half of what they have been told by their physicians (DiMatteo, 1985; Ley, 1966, 1979, 1986; Ley and Spelman, 1967). Gender effects have also been noted to affect recall of medical information. One should be cautious about how changing cultural influences could alter these findings over time; however, it appears that, especially for women, medical information presented by a female physician with high degrees of expressiveness produces the most recall of information (Bush, 1985). Similar effects were present for males, but to a lesser degree. High degrees of nonverbal expressiveness in opposite sex dyads may actually interfere with recall for both sexes. Memory of Exact Content vs. Inferred Meaning Often the exact wording of a statement is crucially important in forensic contexts. For example, the statement “I’m going to kill the son of a bitch!” may constitute a clear threat, whereas “The son of a bitch doesn’t deserve to live!” might be taken as a statement of opinion. The two, however, would often be understood as equivalent and consequently remembered equivalently later—particularly if the person in question ended up dead. Memory for exact wording is often poor. That is, only minutes after an utterance is made, a conversation partner may be unable to recall its exact wording. Hearers routinely extract the basic idea underlying an utterance and forget the linguistic surface form (Bock and Brewer, 1974; Brewer and Hay, 1984; Graesser and Mandler, 1975; see Fletcher, 1994, for a review). They process “between the lines,” remembering not precisely what was said but, rather, what was pragmatically implied or what appears to make most sense in a given situation (Harris and Monaco, 1978; Hilton, 1995). For practical purposes, specific wording is often irrelevant because the same prepositional content (or meaning) can be expressed in a variety of different ways and because hearers primarily care about the message that is conveyed. Language
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comprehension and, ultimately, memory for utterances are geared toward inferences hearers draw from speakers’ utterances, not the utterances alone. As is readily apparent, this may cause problems in contexts in which the specific wording used has great legal relevance or when the hearer has inferred and remembered the wrong meaning (see Davis and Friedman, in press, for review). This meaning-driven or gist-based memory applies not only to individual utterances, but also to the entire episode of a conversation. People may not recall any details of what was said or even who said what, but rather may remember the gist of what the conversation was about. Specifically, individuals may recall the general kinds of opinions or beliefs that the participants in a conversation expressed but no longer remember any specific statements. This type of memory is much more abstract and primarily a reflection of how a person interpreted and experienced a situation. For example, a witness may report hearing a “fight” between two persons, one of whom is later found dead, but the witness may be unable to report any of the content. This interpretation could have resulted from other cues such as tone of voice, volume, body language, and so on, perhaps in the absence of ever having heard the actual content. More dangerously, the label “fight” may be the result of “reconstructive” memory processes (or “hindsight” biases) resulting from the witness’s post hoc discovery of the death. Unfortunately, listeners may later confidently report that they remember exactly what the speaker said when in fact they remember only the gist of their interpretation of what was said (for example, see Neisser, 1981). This situation arose for a local instructor, whose students accused her of calling them stupid in class. As is characteristic of any qualified college instructor, she was very careful to avoid any insults or inappropriate language in her interactions with students. One day, she dismissed the class early because students had quite obviously failed to do the readings and were unprepared for the scheduled in-class discussion. The instructor, who had expressed her dissatisfaction with this situation before dismissing the class, later was astonished to find out that students reported she had called them “stupid.” In hindsight, however, one can understand this disagreement in terms of interpretation-based or gist-based processing on the part of the students. They interpreted the instructor’s behavior to mean she thought they were stupid and, later, confidently “remembered” that stupid was exactly what she said. This example illustrates the principle that subsequent memory for an utterance can only be as accurate as the inference initially drawn by the hearer. It is easy to see how the combination of loss of linguistic form combined with inference drawing or interpretation can create a number of problems so that the hearer does not interpret an utterance in line with what the speaker intended to say or remembers primarily what the speaker only implied but did not say. The prevalence and importance of such inferences was illustrated by Fulero and Finkel (1991), who found that juror inferences from the actual content of expert testimony strongly affected verdicts. The authors presented three versions of a trial in which expert testimony regarding insanity was presented. In one version, the expert presented only diagnostic information that the patient suffered from delusional paranoid disorder. In the second version, the expert testified regarding the diagnosis and, in addition, testified that because of the delusions associated with the disorder, the patient would be unable to consider the consequences of his behavior or to appreciate the wrongfulness of his acts. Finally, for the third version, the expert testified to the preceding facts and further stated
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the conclusion that the defendant was insane at the time of the crime. No differences in verdict were obtained among the three levels of testimony, in part because jurors tended to infer the final determination of insanity in all conditions and/ or to remember falsely that the expert had stated that conclusion even when he had not. The importance of conversation-based inferences has also been extensively discussed in the literature on false confessions. Kassin (1997) noted that judges typically exclude confessions elicited through explicit threats and promises, but they commonly admit confessions elicited through implied threats and promises. Kassin and McNall (1991) directly tested whether certain interrogation practices were interpreted as threats or promises of leniency. The interrogation techniques they focused on were “maximization” (in which the interrogator overstates the seriousness of the offense and the magnitude of charges, and makes false or exaggerated claims regarding the strength of evidence against the defendant) and “minimization” (in which the interrogator offers sympathy or excuses for the accused, perhaps blaming the victim or someone else, and thus minimizes the seriousness of the crime). Participants read one of five versions of an interrogation. The interrogator (1) explicitly promised leniency if the defendant confessed, (2) explicitly threatened harshness if he did not confess, (3) used minimization techniques, (4) used maximization techniques, or (5) did none of these. Participants then estimated the likely sentence to be imposed on the suspect. Results indicated that (1) minimization and actual promises of leniency led to equivalently lenient expectations of punishment and (2) maximization and explicit threats of harshness led to equivalently harsh expectations of punishment. That is, observers inferred the promises or threats that were never explicitly made. Thus, Kassin (1997) concluded that common interrogation tactics essentially violate the intent of the law by using pragmatic implication to accomplish what they are forbidden to do explicitly. Which Contributions Are Remembered? Which conversational contributions will be remembered depends on a complex web of factors. To illustrate this point, Hirst and Gluck (1999) conducted a study comparing the testimony of John Dean before the Senate subcommittee on the Watergate affair in 1973 with transcripts of White House recordings of 1972 conversations among Richard Nixon, H.R.Haldeman, and John Dean. The tapes of the conversations were an unpublished transcription prepared by the impeachment inquiry staff for the House Judiciary Committee at the time of the Watergate Hearings (National Archives, 1996), which contained a more complete transcription than the previously published White House Transcripts (Gold, 1974). From these, the authors selected the transcription of the September 15 meeting of Nixon, Haldeman, and Dean involving a review of events related to Watergate. Each person’s contributions to the original conversation were coded as narration, facilitating remarks (mentoring), or monitoring (evaluating and correcting). The authors found a number of interesting relationships between conversational role and the content of Dean’s statement to the Watergate subcommittee. Although there are many potential explanations of the results, the authors suggest that the observed patterns may reflect the influences of schematic-processing and conversational roles (Hirst and Gluck, 1999).
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Perhaps the largest observed difference was in memory for Dean’s contributions versus those of others. Whereas Dean offered 58% of the narrations in the meeting, 71% of the narratives offered in his statement to the subcommittee were his own. The authors attributed this difference to the greater relevance of Dean’s contributions to his preexisting knowledge and beliefs regarding the Watergate events, along with personal motivations such as a need for self-importance. The authors also predicted that because Dean’s schematic organization would dictate what he chose to tell the others and what he attempted to elicit from them, Dean would be more likely later to recall and report these schema-consistent narratives than those reflected in answers to others’ less schema-relevant questions and narratives. Indeed, Dean’s memory for conversational contributions due to his own initiatives was superior to that resulting from the initiatives of others. The narratives elicited from Dean by Haldeman and Nixon were more likely to remain unstated than to appear in Dean’s statement. On the other hand, the narratives elicited by Dean from Haldeman and Nixon were more likely to make it into the statement than remain unstated. Hirst and Gluck (1999) concluded that narrative responses to others’ questions make it into subsequent recollections only if they can be assimilated into existing schemata. Presumably, Dean thought his responses to questions from Nixon and Haldeman were relatively unimportant and thus failed to assimilate them into his preexisting schema. In contrast, their answers to Dean’s chosen questions, which he undoubtedly considered relevant, were easily assimilated: he probably knew the details about the events following Watergate extremely well. Thus, nothing Nixon or Haldeman could do—narrating the events or asking Dean questions—could alter Dean’s perspective on the events. One might have expected that power relationships would have an effect on memory such that Dean would be more likely to remember something said by a powerful person than a less powerful individual. In contrast, Dean’s memory appeared to be affected by a combination of perceived expertise and authority. That is, he correctly believed he possessed the greatest expertise about the events that had transpired since the Watergate break-in. However, Dean realized that Nixon had the authority to decide future actions concerning Watergate and that Nixon’s beliefs concerning how the Watergate situation would unfold in the future would affect those decisions. From this perspective, it is not surprising that Dean remembered his own narratives better than those offered by Nixon, but that he remembered Nixon’s prognostications and plans for the future better than his own. Thus, a complex interplay between one’s goals, existing knowledge structures, schematic perceptions of the issues and persons involved, the relationship between parties, and much more determines the focus of attention within a given conversational interaction and therefore determines what is later remembered. Beyond the factors described here, conversational memory for specific utterances is highly affected by the function that these utterances play in a conversation. Studies show that utterances high in interactional content are highly memorable in the sense that individuals are highly successful in recognizing the exact surface form of the utterances (Keenan et al., 1977; MacWhinney et al., 1982). In this research, interactional content was defined as pragmatic information that conveyed a great deal about the communicative situation as well as the speaker and his “intentions, beliefs, and his relations to the listener” (Keenan et al., 1977, p. 550). Concretely, this category includes,
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but is not limited to, statements of personal opinions, evaluations, jokes, profanity, and sexually suggestive language (see also Bates et al., 1978; Pezdek and Prull, 1993). Consistent with our review of the role of attention for conversational memory, Kintsch and Bates (1977) hold that the specific wording of utterances is encoded and remembered to the extent that it draws attention to itself. Source Monitoring in Memory for Conversations: Who Said What to Whom, under What Circumstances? Memory researchers have examined errors in source memory or source monitoring across a number of domains. Source memory refers to memory for the context in which a target object or item of information was encountered, whereas source misattribution (i.e., failure of source monitoring) occurs when a person has some form of memory that is misattributed to an incorrect time, place, person, or other context. Such errors are considered to result from failure to bind the contextual and target information together successfully during encoding, as well as from lack of careful attempts to monitor the source of information accurately at retrieval (see reviews in Davis and Follette, 2001; Johnson et al, 1993; Koutstaal and Schacter, 2001; Meiser and Broder, 2002; Schacter, 2001). In the context of conversation, several kinds of source memory are of interest, including: • Who said what? • To whom was something said? • Did one actually say what one had considered, imagined, or planned to say? • In which conversation (of a number of possible conversations) did a particular exchange take place? • When or where did a particular exchange take place? • In what order within a conversation or interaction did a particular exchange take place? • What other participants or witnesses were present, if any? • What other features of the context or previous utterances would alter the meaning of the target utterance? • Was information acquired from a particular conversational source or from some other medium? • When planning a particular conversational contribution, has one said these things to this person before? The last of these is simply a problem of source monitoring that can create negative reactions to a speaker who repeats information all too often. However, the remaining nine are relevant in legal settings. Of these, some have been investigated empirically, whereas others remain unexplored. We will discuss each, however, pointing to its relevance in forensic contexts and reviewing empirical research when it is available. Memory of Who Said What On June 8th, 2002, a drug dealer named Jack Costos was shot and killed by a masked intruder in his home. As part of the investigation, police interviewed a group of Costos’
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customers who had recently spent an evening together playing cards and using drugs and alcohol. The group included three Caucasians, two Hispanics, and four African Americans. Tyler Jackson—one of the African Americans—was identified as a suspect by police. Generally, the group members disliked Costos and were prone to criticizing him in their discussions. Upon questioning the group members, police focused their questions on Tyler. Two Caucasian members of the group told police that they remembered hearing Tyler say that he wanted to “waste” Costos on the night of the recent party, which was only 2 days before the murder. Did Tyler indeed make such a threat, or could this testimony have been an honest mistake of memory? Several aspects of the situation suggest that it might have been. We explore them as we consider some of the documented influences on memory for who said what in conversations. Social Categorization and Source Confusion One factor of considerable potential importance for Tyler Jackson’s case is the fact that he was one of a group of four African Americans present at the party, whereas his two accusers were Caucasian. A large body of literature has shown that when we try to remember which specific person in a group conversation has said something, we are particularly likely to attribute one person’s statement mistakenly to another member of the same social category. In this case, the two Caucasian witnesses could have confused Tyler with one of the other three African American participants. According to the source-monitoring framework proposed by Johnson and her colleagues (Johnson et al., 1993), source monitoring is more likely to be accurate when the original memory is highly elaborated and differentiated (or distinct) from other memories (see also Koutstaal and Schacter, 2001). Thus, source differentiation is encouraged by encoding conditions that encourage deep and elaborative processing and impaired by those making it more difficult to distinguish information associated with one source from that associated with another (such as two sources that are similar rather than different). Regarding conversational partners, one factor that can impair this ability to distinguish source-information connections is similarity in speaker characteristics and, in particular, similarity in the social category membership of the speaker—and, in Tyler Jackson’s case, similarity of race. The popular “who said what?” paradigm in social psychology has been widely used to demonstrate this phenomenon (Taylor et al., 1978). This line of research has shown that when asked to remember which of several speakers contributed a particular statement to a discussion, participants are more likely to misattribute the statements of one member of a social category (race, gender, age, physical attractiveness, hometown, clothing color, educational status, and many more) to another person from the same category than to someone from a different category (see the review in Klauer and Wegener, 1998). Justice Ruth Bader Ginsburg recognized this tendency to confuse members of the same social category in her complaint that attorneys arguing before the Supreme Court commonly confuse her with the other female justice, Sandra Day O’Connor (The New York Times, October 5, 1997). Although misattributions of statements between members of the same social category are common, the incidence of such confusions is affected by personal and situational factors that influence (1) the depth with which the characteristics of the speakers and their
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statements are originally processed, (2) the salience of social categories at encoding, or (3) use of heuristic versus controlled decision criteria at retrieval. Thus, for example, category-based source confusions are more common when the person is faced with distraction or heavy processing demands at encoding than when he is encouraged to use elaborative encoding strategies. Source confusions are more common among persons for whom the social category in question is salient and who tend to think in stereotypical terms regarding the category, as well as in situations that encourage category-based thinking (such as when one’s own category is in competition with the other). Finally, source confusions are encouraged by heuristic strategies at retrieval (such as guesses based on which statement would be most likely to fit a member of a specific category, rather than careful, controlled attempts to retrieve associations between source and content; see reviews in Brewer et al., 1995; Gawronski et al., 2003; Klauer and Wegener, 1998; Klauer et al., 2002). With respect to the Costos case, source confusion between members of Tyler Jackson’s (the defendant’s) race would have been made more likely by several factors, including (1) widespread use of drugs and alcohol, which would have rendered deep and elaborate encoding more difficult, and (2) the fact that Costos was discussed (and “dissed”) by other members of the group, which would have rendered any threat made against him similar to other negative statements and complaints. The impact of age. Older persons are generally more susceptible to failures of source memory (see reviews in Davis and Loftus, Chapter 11, this volume; Glisky, 2001; Koutstaal and Schacter, 2001). Thus, it is not surprising that they are similarly more susceptible to source misattributions in conversation. This has been demonstrated in straight learning paradigms in which the person is tested on which of two speakers presented each word or item of information (Bayen and Murnane, 1996; Ferguson et al., 1992; Hashtroudi et al., 1994; McIntyre and Craik, 1987; Schacter et al., 1991), as well as in memory for who says what in conversation (Brown et al., 1995; Mather et al., 1999), and for which witness offers which testimony in a videotaped mock trial (Fitzgerald, 2000). Furthermore, older adults have more difficulty remembering whether an item was merely thought about or spoken out loud (Hashtroudi et al., 1989), although this has not yet been demonstrated in a conversational context. One thing that appears to enhance source-monitoring difficulties for older adults is similarity between sources. Thus, older persons are more susceptible to category-based source confusion than younger adults. For example, Ferguson and colleagues (1992) showed that, although older adults had poorer source memory than younger adults for information offered by two female speakers, they did not differ from young adults in source memory for those offered by a male and a female speaker. The Influence of Schematic Processing Conversational source misattributions are often the result of our expectations regarding what a person is, or is not, likely to say. Just as our schemas for particular persons, social categories, or social situations lead us to expect specific characteristics, appearance, behaviors, sequences of events, and so on, they also lead us to expect certain kinds of conversational contributions from particular sources under particular circumstances. Mather and colleagues (1999) examined the extent to which older and younger people rely on schematic knowledge to attribute statements to sources. Participants watched a
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videotaped discussion and later attempted to remember which persons made which statements. These researchers also investigated the extent to which focusing upon oneself rather than on the speaker during encoding (thereby inducing shallow processing of speaker content) led to more schema-based source errors. Indeed, older as well as younger participants made source errors and both were particularly likely to attribute statements mistakenly to a source who, based on his category membership, would be expected to make such a statement. For example, the statement “I work out almost every day” was disproportionately misattributed to a person described as an athlete when it was actually made by a different speaker (i.e., a speakerinconsistent statement was reattributed to render it speaker consistent). Older participants made more stereotype-consistent errors in misattributing speaker-inconsistent statements than younger adults (but not more errors attributing speaker-consistent statements). The extent to which they did so was related to scores on neurological tests assessing frontal and medial-temporal area functioning of the brain (see Davis and Loftus, this volume, for further discussion of the relationship of brain functioning to source monitoring failures). Furthermore, self-focused participants made more schema-consistent source misattributions—an effect that was stronger for older participants. Similar schematic influences on speaker source memory were obtained by Spaniol and Bayen (2002), who showed that schematic effects were most likely among those with poorer overall memory, and by Gawronski et al. (2003), who showed that persons with stronger stereotyped associations (as measured by the implicit attitudes test; Greenwald et al., 1998) made more stereotype-consistent source errors. Generally, schematic influences on memory tend to be greater under conditions that encourage shallow or heuristic processing, including when veridical memory is poorer, when processing demands are high in comparison to processing resources, or when processing capacity is restricted in some way—all conditions more likely to occur for older adults, who are more likely to engage in schematic processing of a wide variety of stimuli (Bayen et al. 2000; Davis and Loftus, Chapter 11, this volume; Davis and Loftus, in press; Hess, 1999; Hess and Slaughter, 1990; Sherman and Bessenoff, 1999; Spaniol and Bayen, 2002). Tyler Jackson’s accusers may well have been affected by schematic processing when trying to recall whether, and by whom, any threats against Costos were made. Tyler was a large and muscular man who was known to anger easily and start fights. Thus, he would have seemed like the type of person who would make a threat (and even carry it out). In addition, because the police seemed to be targeting Jackson in their interviews, he would readily come to mind as a potential source of threat—thus creating the perfect conditions for misattribution to him of any threats that may have occurred. Differential Source Monitoring for Varying Conversational Roles Several investigators have asked the question of whether a person is better able to distinguish between (1) what he has said versus what another has said or (2) things two other sources have said. Raye and Johnson (1980), for example, had individuals play the role of speaker (one of two speakers alternating contributions), recorder (a person matched with each speaker who was to write down that speaker’s contributions), or listener. When later asked to identify which contributions came from which speaker, speakers did better than recorders or listeners (who did not differ). In a second
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experiment, the authors added the role of director, which involved requesting information from each speaker. Again, speakers did better than recorders or listeners—and directors did worst of all! Apparently, the additional processing demands for the director impaired encoding. In an elaboration of the Ray and Johnson (1980) design, Brown and colleagues (1995) attempted to examine the full range of source judgments relevant to a more naturalistic conversation, including which speaker asked a question and which answered the question (oneself or one of three other participants). The exchange was structured so that each person played each role (inquirer, respondent, listener) an equal number of times. Generally, source memory was best for the respondent role—primarily due to greater success at self-identifications by responders. Strangely, for the other active role of inquirer, source memory was poor and was no better among the inquirers than among the respondents or listeners. Similarly, responders were no better than listeners at identifying who the inquirer had been. After 1 week, memory for the inquirer role had dropped to chance. Apparently, people are not good at remembering who asked questions but do better than chance at memory for who answered them. Finally, as in other arenas, source memory among older participants was poorer than among younger participants. Unconscious Plagiarism (Cryptomnesia) One of the most frequently studied conversational source misattributions has been the phenomenon dubbed unconscious plagiarism or cryptomnesia, whereby another’s ideas are mistakenly remembered as one’s own. Although deliberate instances of plagiarism are common (particularly in academic settings, for example), far more common are instances in which people in everyday life encounter ideas that later occur to them in a different context, but with no memory of the original source. The issue of plagiarism is often adjudicated in formal academic contexts—as well as in the press—when scientists or authors are accused of plagiarizing the work of others. Witness the recent flood of discussion in the press and on the Internet regarding historian Doris Kearns Goodwin’s book, The Fitzgeralds and the Kennedys, as a plagiarism of Lynne McTaggart’s previous work, Kathleen Kennedy: Her Life and Times. (A brief Google search as of 2/23/2003 produced 239 entries.) Although Goodwin claimed her plagiarism was “inadvertent” in that she simply forgot to footnote correctly, other wellknown authors have responded to accusations of plagiarism with claims of lack of awareness of the source of the material—in other words, with claims of unconscious plagiarism. For example, George H.Daniels, in his published explanation of plagiarized passages in his book, Science in American Society, explained that he had an unusually good memory and must have unconsciously memorized passages from other sources, which he later included in his book with (ironically) no memory of where they had come from (Daniels, 1972). Although this phenomenon initially appeared difficult to study in the laboratory, Brown and Murphy (1989) developed just such a procedure for studying cryptomnesia in group discussions. Groups of four people were asked to produce examples of a particular concept or category, taking turns announcing their contributions. Even while working in this initial group context, many subjects offered contributions already stated by another group member. Then, on a delayed test, subjects were asked to offer new examples of the original categories, but were very explicitly told not to use any previously offered by any
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member of the group. Despite such instructions, many subjects nevertheless offered “plagiarized” responses from the group session, even though they truly believed them to be new (as reflected in ratings of confidence that the new contribution was a novel contribution of their own invention). Plagiarism was greater under conditions that would tend to reduce overall memory (including successful binding of source and content), including situations in which the original generation sequences were more complex, the items came from the presumably more difficult orthographic (e.g., “name a word beginning with BE”) rather than semantic (e.g., “name a fruit”) categories, and for responses generated by the person responding immediately prior to the subject (presumably self-focused concern regarding one’s own turn would be greatest at this point and reduce “binding” of the source and content of the contribution). Subsequent work has further documented this tendency toward unconscious plagiarism and has also shown that such cryptomnesia tends to become greater (Bink et al., 1999; Brown and Halliday, 1991; Brown et al., 1995; Macrae et al., 1999; Marsh and Bower, 1993; Marsh and Landau, 1995): • With increasing delay between the original group interaction and the subsequent attempt to generate novel contributions • When the original information comes from a high- rather than low-credibility source • For contributions from a member of one’s own sex (presumably a more similar and therefore more easily confused source) • When participants are distracted during the original generation of ideas • When retrieval occurs in a context different from that of the original task • For older participants Cryptomnesia is less under conditions encouraging deeper processing. Essentially, with the addition of source credibility as a factor, unconscious plagiarism tends to be most likely under the same conditions that promote other source memory errors. Foley and her colleagues (Foley and Ratner, 1998; Foley et al, 2002; Ratner et al, 2002) studied children’s source-monitoring errors for collaborative activities. Children commonly suffered from source memory errors, in that they often remembered actions performed by others as if they had performed them themselves. These researchers offered evidence that the processes of imagining or planning activities that are actually performed by others simultaneously induce false memories of performing the action oneself and facilitate learning of the activity. Memory for Medium: Did You Tell Me This or Did I Read It Somewhere? Closely related to the issue of who told us something is that of whether information came from a conversational source or from another medium such as television, radio, or printed material. This was the central issue in a malpractice case against Dr. Randolf Hicks. Mr. James Ball alleged that Dr. Hicks prescribed an aspirin daily to reduce Mr. Ball’s high risk of cardiovascular incidents such as stroke or heart attack. Mr. Ball was obese and diabetic, with an unfavorable lipid profile and a history of blood clots in his leg. However, Mr. Ball also had a history of bleeding stomach ulcers. Mr. Ball began taking a
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full 325-mg aspirin daily and, within 2 months, suffered a near-fatal stomach bleed requiring resectioning of his stomach. Dr. Hicks denied that he had recommended aspirin to Mr. Ball. His office notes for the visit in question indicated that he had discussed options for controlling risk with Mr. Ball, and that he had prescribed Lipitor™ (a statin)—not aspirin. Mr. Ball agreed that he had been given the prescription for Lipitor™, but insisted that he had also been told to take an aspirin daily, as well as to make lifestyle and diet changes. Thus, clearly in this situation, the potential for failures of memory exist on each side. Recommendations for use of aspirin are offered in multiple sources in our culture, ranging from television ads to printed media such as health magazines to conversations with friends and professionals. Therefore, a primary concern for this case was the potential for Mr. Ball to have confused the source of the aspirin recommendation. He could have heard such a recommendation from friends or family aware of his risk profile or read it in any number of printed sources. Mr. Ball also accurately remembered that he and the doctor had discussed a number of measures for reducing his risks. Would it not seem reasonable—and even likely—that they would have discussed such a widely known measure as taking aspirin? Dr. Hicks, on the other hand, would clearly believe that he would never prescribe aspirin to a patient with a history of bleeding stomach ulcers. That is, his knowledge of what he should not do and what he routinely does not do would make it difficult for him to believe that he had done it in a specific instance. However, was the history of bleeding ulcers salient for him at the time of his discussion with Mr. Ball? Dr. Hicks is a cardiologist and was not the treating physician for the ulcers. Thus, although the information was in Mr. Ball’s records, these records were extensive, and the ulcer was not specifically the focus of discussion on the day in question. Therefore, an issue arose concerning whether Dr. Hicks in fact remembered the ulcer at the time at which he discussed measures Mr. Ball should take. If not, he might well have mentioned the possibility of aspirin (although most likely a smaller dose than Mr. Ball actually took). Memory for Target: To Whom Was It Said? Failure to remember to whom one has said something is commonly the source of interpersonal as well as legal difficulties. We may get in trouble with our spouses, parents, or close friends for failure to convey important gossip—even as we clearly remember having told them. Often, such difficulties are generated by failure to remember whom we actually did tell. Perhaps remembering that we have already told several people, we mistakenly remember that our spouse was one of them. This problem is compounded by the fact that we have often planned to tell the persons in question, perhaps even planning how and when to tell them. As we will discuss in the next subsection, it is common to remember falsely that one said something that one had actually only planned to say. In legal settings, the issue of to whom one has said something most commonly becomes relevant with respect to delivery of instructions, warnings, or information crucial to an impending decision. As noted earlier, accurate source monitoring is much more difficult when attempting to distinguish between very similar incidents than when attempting to do so for those that are dissimilar. Unfortunately, across a wide range of
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circumstances, professionals are faced with a series of interactions that are very similar in nature. For example, doctors, lawyers, therapists, financial consultants, real estate agents, professors, military officers, salespersons and countless others interact with a large number of clients and co-workers each day. The kinds of information, instructions, orders, and so on exchanged with others are often quite similar for many (if not most) of their conversational partners across the days, weeks, months, or even years of their professional lives. This sometimes extreme similarity across interactions with many parties presents a formidable challenge for memory of to whom one has given what information (as well as, when, where, or under what circumstances it may have been given). Nonetheless, the content of a specific professional interaction with a specific person is often crucial for cases such as those involving malpractice, fraud, wrongful termination, and others. The case of Larry Wilkes illustrated just such a difficulty. Larry Wilkes was a stockbroker employed by his brokerage for 5 years before he was fired for failure to execute a sell order allegedly given by his boss, Carlton Stackerton. Less than 1 week before the incident in question, Stackerton had been transferred to Larry’s office; he supervised 20 employees, including Larry and 15 other male employees within roughly 5 years of Larry’s age. Larry was of average height, with brown hair cut in a short professional style, and thus looked similar to a number of his co-workers. Stackerton claimed to have come to Larry’s desk and given him a verbal order to sell 10,000 shares of Microsoft stock for one of the firm’s clients. This sell order was never carried out, and within the weeks that followed Microsoft fell sharply in value, leaving the client with a considerable loss. When the failure to sell was discovered by the client about 3 months later, Larry was fired for failure to carry out the sell order, which his boss confidently remembered giving to him. Larry, of course, denied having received such an order and filed suit for wrongful termination. This situation highlights several important common issues of memory. Most relevant for our current point is the issue of to whom Stackerton actually gave the sell order (assuming that he did give it to someone). Stackerton had no need to remember the target of the specific sell order in question until approximately 3 months later. Thus, in the period between when he came to the brokerage and when he needed to remember the specific Microsoft sell order for the specific client, countless orders had been given to all of the 20 brokers whom he supervised. This similarity between incidents, combined with the passage of considerable time, would have seriously compromised his ability to remember the one in question accurately. However, another issue was of considerable importance in considering the accuracy of Stackerton’s memory for the target of his sell order. That is, he had been in that office for less than 1 week and was only beginning to become acquainted with the individual brokers. Larry Wilkes was similar in appearance, age, style of dress, and hairstyle to several other brokers. Therefore, a question arose concerning whether Stackerton could have confused which of the young men to whom he had actually given the order (and, of course, no others were likely to admit voluntarily to the mistake and be fired instead). Indeed, research on eyewitness identification would suggest that similarity between innocent foils and the target suspect will tend to enhance the likelihood of a false identification.
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Finally, the complexity of the daily activities at the brokerage presented a further barrier to accurate memory for a particular order. The brokerage was a highly active and successful business, involving a high rate of client interactions and processing of orders. The records for the day in question indicated that over 100 orders were processed on that day. Memory research would suggest that the greater the complexity of the environment in which the alleged specific order took place, the more difficult it would have been for Stackerton to bind the memory of that order successfully with memory of to whom it had been directed. The overall similarity of many instances of sell orders combined with the fast rate at which they occurred, in the context of generally complex circumstances, would present a particularly powerful mix of forces known to impair source memory. Similar issues of similarity between many instances of interactions with clients or coworkers and similarities in appearance or other features of the clients or co-workers commonly arise in memory-based litigation across many contexts. For example, a traffic cop might be asked such questions as “How many traffic tickets have you given in the 2 months since you issued this one to my client?” “So how is it that you specifically remember the exact words my client said to you that you think meant he was resisting arrest?” “Are you sure that it wasn’t Mr.___, whom you arrested that same day, who said this?” Similarly, specific instructions or warnings to a particular patient on a particular occasion become crucial to medical malpractice litigation; whether or not specific positive and negative information regarding potential investments was conveyed to a particular client becomes crucial to litigation against financial advisors; or whether or not all pertinent information was conveyed to a specific investor, buyer, or other becomes pertinent to allegations of fraud. In all such cases, if notes or other records are not available, the professional must rely on the specific memory for a specific instance of a type of conversation that occurs on a regular basis—a situation in which accurate source monitoring is notoriously difficult. Faced with such a task, the professional often falls back on script-based knowledge of what he typically does in such a situation. The doctor, for example, may commonly issue standardized instructions for specific ailments, drugs, or postprocedure care, and thus assume (and perhaps falsely remember) that he did so for the particular patient in question. In most instances, the “memory” that one performed a highly routine behavior in a specific instance will be accurate simply because the established routine makes it likely that the behavior occurred in the specific instance. However, behavior is rarely fully uniform. The doctor can plan to give an instruction or warning but forget to do so. He can be interrupted by a nurse or the patient and fail to return to the interrupted goal. In some instances, he can simply forget to provide the information to the specific patient. By the time the omission causes injury and the issue is raised with the doctor, he has seen countless other similar patients with similar problems. Without notes specifying the content of the interaction in question, it is highly unlikely that the doctor can accurately remember the conversation in question and whether he actually said the particular thing to the particular patient.
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Reality Monitoring: Did I Say It or Just Think about Saying It? In many contexts, ranging from household conversations to professional interactions with clients, trouble arises when one party claims to have said something the other swears never to have heard. Larry Wilkes’ case of wrongful termination against his brokerage is one instance of such trouble. However, in addition to the issues of memory raised for his case, yet another issue is relevant. That is, did Stackerton actually issue the sell order, or did he simply plan to, only to become distracted by other events and forget? A similar issue arose for a local psychologist, Dr. Barkley, recently sued by the wife of a client, Mr. Bremmer, who became violent and almost killed her. Unlike many such cases in which the therapist agrees that no warning was given but disputes the contention that evidence from therapy supported the prediction of dangerousness, the therapist in this case claimed that he did warn the wife. Mrs. Bremmer, on the other hand, adamantly denied that she was ever given any warning. Did he actually warn her? Did he intend to warn her and later falsely remember that he actually did? Although we can never know what actually happened, several interesting aspects of the case parallel factors known to promote false memories of having said the (in reality) unsaid. Parks (1997) conducted a series of very clever studies designed to study false memories of having “said the unsaid.” He began with a study in which participants were shown a series of phrases. Each phrase was followed by a command to say it out loud or not. For the second study, participants were asked a series of questions, which they were asked to answer out loud or not. For the third study, subjects were asked a series of questions in a public polling situation, but for some questions the participant was interrupted before having a chance to answer. Finally, for the fourth study, subjects participated in a debate. They were led to plan to use a particular point, but ultimately were prevented from doing so. Thus, in each experiment subjects were led to think of a particular phrase, answer, or debate point; however, they were prevented from saying some, but allowed to say others. The question of interest was whether subjects would later “remember” having said the things that they had actually only thought of saying. Indeed, participants often reported with great confidence that they had actually said things which they actually had only thought. Just as in these research examples, participants in real-life conversations routinely think of things to say that may never actually be said. Perhaps most often, failure to carry out conversational intentions is the result of some form of distraction or diversion. The phone rings, another person appears and interrupts, or one’s conversation partner changes the flow of the conversation away from the topic that one had planned. For one reason or another, the statements that one has imagined never come about. Each of the participants in the preceding two example cases was faced with exactly the kinds of interruptions that could have prevented them from carrying out their intentions. The stockbroker, Mr. Stackerton, lived in the epitome of a multitasking environment in which he was fielding questions from clients and subordinates, keeping track of the markets and the office transactions, giving instructions to subordinates, and receiving their reports. In that context, he could well lose track of which things he had said or done and which he had planned but had not yet carried out. The therapist, Dr. Barkley, reported that Mrs. Bremmer (his client’s wife) was extremely agitated during his discussion with her and that he had trouble getting his points across due to her constant interruptions and topic shifts. In such a case, either
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party’s memory could easily fail. Mrs. Bremmer, who was obviously very upset and full of anxiety, could well have failed to pay sufficient attention to what she was told to remember accurately later. On the other hand, Dr. Barkley was continually foiled in his attempts to tell Mrs. Bremmer the information he intended to convey. Just like the debate participants in Parks’ (1997) study who were prevented from making the points they planned, Dr. Barkley may well have falsely remembered giving his intended warning to Mrs. Bremmer, but was never allowed to deliver. Interruptions pose a substantial problem for professional interactions such as those between doctors and their patients. Indeed, Beckman and Frankel (1984) showed that doctors interrupted their patients within the first 18 seconds of the start of an interview. More recent findings indicate that interruptions are still a problem but that physicians in the newer study waited until 23 seconds to interrupt (Marvel et al., 1999). One result of interruptions is that, like Mr. Stackerton or Dr. Barkley, the patients failed to tell the doctor the things that they had planned. They did not get to explain their complaints fully and when the patients were able to raise them, these topics emerged late in visits with less time available to assess the concerns. If patients present with an explicit agenda but are interrupted before completing their story, it is easy to understand why there might be confusion about whether an important clinical topic was or was not actually covered. Later, the patient may complain of a misdiagnosis, fully believing that he had informed the doctor of all relevant symptoms, when in reality his plans had been disrupted by the doctor’s interruptions or by time pressures that prevented much of the discussion the patient had planned (Liang et al., 2002). Memory of Time and Space: Where, When, and in Which Conversation Did This Exchange Take Place? Studies of autobiographical memory have shown that memory for when something happened is far less accurate than memory for what happened (Larsen et al., 1996; Wagenaar, 1986, 1996). Nevertheless, memory for when something (in this case a conversation) happened is often crucial—as illustrated by the case of John Shinn. John Shinn was accused of embezzling over $200,000 from the manufacturer for whom he had worked for the last 6 years. John was identified as a likely suspect because he had access to company computers and financial transactions and was among the employees suffering the most obvious financial problems. The theft remained undiscovered for 6 months. When it was discovered, the investigation quickly focused upon six employees who had the means to commit the crime, and in short order narrowed to John. In large part, the investigation turned to focus on John due to the testimony of a single witness who reported a conversation with John that was alleged to have taken place prior to the theft. John’s co-worker, Lilly Baker, testified that John had discussed his financial problems with her on several occasions and that he had told her within a few weeks prior to the theft that he had a plan that would solve all of his financial problems. Lilly alleged that when she asked what it was, John had refused to tell her, saying that he did not want to talk about it until it actually worked out. John agreed that he had had such a conversation with Lilly Baker, but disagreed about the timing. He testified that the conversation took place approximately 3 months after the theft and that it referred to a real estate transaction he was attempting to arrange with a
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friend. This transaction was expected to result in substantial profit for both but failed to materialize. John’s friend verified their joint attempts to arrange the transaction and the time frame in which they were working on it. Eventually, the charges against John were dropped because the police were unable to prove he had taken the money. Meanwhile, however, John lost his job, and his reputation in the community suffered permanent damage as a result of media coverage and widespread knowledge of the accusation. Lilly Baker sincerely believed she remembered the timing of her conversation with John accurately. She was a highly credible witness, one who led the police to devote considerable energy to their investigation of John as their primary suspect. What could have caused Lilly Baker’s memory for the timing of their conversation to fail? We suggest that in this case, poor general memory for timing, combined with schema-based reconstructive memory processes, might account for her failure. Generally, memory for exactly when events take place is poor—particularly when they are in the relatively distant past (in this case several months past), and when there is nothing distinctive about the timing that associates the target event with others that can clearly be placed in time (such as an event taking place on one’s wedding anniversary). Furthermore, memory for past events can be distorted by knowledge acquired after the fact. In other words, memory is reconstructed so that it seems consistent with what is currently known to be true (see the review in Davis and Follette, 2001). Studies concerned with the retrospective bias have shown that reports of past attitudes or behaviors are biased by current attitudes or recently acquired information (Dawes, 1991; Levine, 1997). In this case, Lilly’s discovery in hindsight that the crime had been committed could have led her to reconstruct the timing of her conversation with John to be consistent with her crime-relevant stereotypical knowledge of motives. Commonly held crime schemas dictate that among the most likely motives for embezzlement is being in debt (Vanous and Davis, 2001). By the time that Lilly learned of the crime, she knew that John was severely in debt and that he clearly fit the prototypical model of an embezzler in her mind. When she was questioned by the police about who among those who could have committed the crime might have a motive, John immediately leapt to mind. For her story to fit, however, the conversation in which John told her he had a plan for solving his financial problems would have had to take place before the crime, not several months after. Both parties agreed that the conversations they had regarding John’s financial problems occurred in the context of casual on-the-job coffee break chats. Thus, no distinctive events associated with the conversations existed to help locate them clearly in time. Given an unclear memory for the real timing of the conversation, Lilly may well have unwittingly reconstructed her memory for the timing of the conversation to fit her current knowledge of the crime and her hypothesis regarding who might have committed it. Memory of Order: Which of These Things Was Said When? What Was the Last Thing We Decided Upon? Memory for the sequence of events is often poor (see, for example, SchmitterEdgecombe and Simpson, 2001). This problem is found in memory for single events, in
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which the sequence of specific actions within the event may be an issue (who hit whom first, for example). However, the problem can become particularly acute for sequences of events ranging over longer time spans, such as those typically involved in complex civil litigation. A particular problem of memory for order arises when one fails to remember which of a number of alternatives discussed in a conversation was the final choice. For example, two friends may each end up in a different restaurant (or in the same restaurant but at a different time) because several alternatives were discussed, and one person remembered the final choice differently than the other. The first author experienced an unfortunate incident in a musical performance in which musicians’ memories for the final outcome of a discussion of whether to take a particular repeat in the music differed. This problem involves two failures of source monitoring: one for the sequence of the discussion (in which minds may be repeatedly changed and changed back again) and one for the association of a particular alternative with the final decision to choose it. Both create the potential for serious misunderstanding and, perhaps, unfortunate outcomes—such as failure to meet for dinner or the cacophony created by musicians’ divergent memories for the final performance decision. This problem arose in a more serious manner in another case involving a stockbroker, Jesse Chandris, who bought 150,000 shares of a stock that his client claimed he was not authorized to buy. The stock later plummeted, resulting in a loss of over half a million dollars for the client. Chandris and his client, William Stokes, agreed that they had discussed the potential purchase, but their memories for the final decision of whether to purchase diverged. Stokes insisted his final instruction was not to buy, but Chandris insisted it was to buy. Why would their memories diverge so completely? Both agreed that they had discussed the purchase extensively, and both agreed that the pros and cons were closely balanced, making the decision difficult. Both also agreed that Stokes had changed his mind several times during the course of the conversation, instructing Chandris to buy and not to buy at various points. The sole disagreement was over the direction of the final decision. Clearly, each person’s memory was colored by motivation and self-interest, as many memories are. Furthermore, at least Stokes’ memory may have been affected by the hindsight bias (Arkes et al., 1981). Once an outcome is known, victims of this hindsight bias tend to overestimate, in retrospect, how likely that particular outcome was to occur. Blissfully ignorant of their own hindsight biases, they also fail accurately to remember their own judgments or behavior before the outcome was known. Instead, they recall that they were wiser (“I knew it would fall in value all along!”) and more confident (“…and I was sure of it!”) and that their behavior was more consistent with that knowledge (“I told you not to buy that stock.”) before the event than was actually the case (see reviews by Davis, 1991; Hawkins and Hastie, 1990). Thus, Stokes may well have fallen victim to the hindsight bias in his memory for his final instructions to Chandris. Memory of Other Participants: Who Else Was There? The case of Lydia Barnes and her sexual harassment claim against her boss, Tony Simpson, illustrates the importance of memory for other witnesses and/or participants in conversation. Ms. Barnes claimed that her boss harassed her over a period of many
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months, through continual sexual innuendo, requests for dates and sexual favors, and implied linkage of her compliance with job advancement. Prominent among the evidence she claimed to support her allegation was a statement Mr. Barnes allegedly made in front of witnesses to the effect that she should remember “who buttered [her] bread” as she walked away from him after rebuffing a whispered advance. This alleged witnessed incident was crucial because the other reported incidents were not witnessed and boiled down to “he said” versus “she said.” Ms. Barnes claimed that two co-workers had been working nearby and turned their heads as Mr. Simpson yelled his bread-buttering threat after her as she walked away from him. Although neither had reason to fear for their jobs at the time of their testimony, each co-worker claimed to have no memory of this incident. How, in this instance, can we assume that memory failed? Other people who witness or participate in a conversation are, in source-monitoring terms, part of the context in which the focal event takes place. In order for such contextual features to be successfully “bound” to memory of the focal event, they must receive adequate encoding and processing. Ms. Barnes may well have been so focused upon Mr. Simpson and her emotional reactions to his advances and threat that she failed to adequately attend to the identities of the coworkers who witnessed the exchange. As noted earlier, highly emotional events may lead to tunnel memory in which memory for the central core of the event is enhanced, but at the expense of more peripheral aspects of the context in which it occurs (cf. Safer et al., 1993). Unfortunately for Ms. Barnes, the conspicuous failure of her two co-workers to verify her report of this crucial threatening exchange undermined her credibility with the jury. Memory of Context: What Else Happened that Would Define What Was Meant? A final sense in which memory for context can be crucial is memory for contextual features of an interaction that in essence determine the actual meaning of an utterance or conversational exchange. As noted earlier, the full meaning of a conversational contribution is revealed not only in the words, but in the tone of voice, body language, and facial expression of the speaker, as well as the immediate and historical context of each person and the dyad, and the external circumstances of the encounter. Therefore, full and accurate memory for the meaning of a verbal conversational exchange must reflect awareness of the complete personal and situational context in which it occurred. This problem was exemplified in testimony surrounding an accusation of sexual harassment against Professor Janice Hill. A female student accused Dr. Hill of sexual harassment via the content of her course in that Dr. Hill covered sexual topics in her seminar, which was required of students in the graduate program. The student further testified that she had witnessed Dr. Hill making “rude and demeaning” comments regarding a male student’s body. When asked for the details of this commentary, the student testified that she had seen the professor touch the hair on the student’s chest and sideburns and make insulting statements regarding the rapidity with which he was aging. The student was unable to offer any testimony regarding the general context of these alleged remarks other than that they occurred at a department party at a faculty home.
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Further investigation revealed that the student in question had graduated 3 years earlier and was 5 years older than the professor. The two had become friends and worked together on consulting jobs outside academia. The student initiated the exchange of agerelated insults, whereupon the professor responded by asking whether he should be talking, given the amount of gray in his sideburns and the hair protruding from his shirt and touching the gray hair to illustrate. The entire exchange was part of a general teasing and bantering session among the student in question, the professor, and other students. Given this relational and situational context, which was verified by other student participants, the professor’s behavior took on quite a different meaning from that originally alleged by the complaining student. Clearly, responses must be interpreted in light of what they are responses to, as illustrated in the previous example. However, this issue can be relevant in a variety of ways in forensic contexts. For example, Bruck and colleagues (1999) recently explored the way in which a target utterance may be shaped by previous conversational contributions of others, who fail to remember the manner in which they triggered their partner’s responses. Specifically, they explored mother’s memories for interviews they conducted with their own preschool children. As expected, mothers’ memories for meaning were superior to those for exact wording or structure. However, they had difficulty with two forms of source monitoring: (1) whether the child’s statements had been spontaneous or prompted and (2) whether they or their child had offered particular utterances. Both of these issues are crucial to understanding testimony regarding such issues as child sexual abuse, when mothers can be expected to question their children repeatedly about the events in question. Failure to remember the way in which their own questions and suggestions may have prompted the child’s reports can contribute to their own certainty of the existence of foul play as well as increase belief in the crime by police or jurors. 12.4 Summary and Overall Conclusions As we have illustrated with a variety of case examples, testimony regarding the content of conversations is central to a vast array of criminal and civil cases litigated in our judicial system. Notwithstanding this centrality of memory for conversation, memory researchers have largely neglected basic research in this area and memory experts have rarely been asked to testify regarding the determinants of accuracy in memory for conversation. Although basic memory research offers a rich source of hypotheses regarding the determinants of memory for conversation, it remains for future research to explore the ways in which the principles governing memory for conversation converge (or not) with those governing memory for other events. Meanwhile, it is clear that memory for conversation can and does fail for most, if not all, of the reasons that memory for other events fails. Thus, memory experts can be helpful to trial attorneys faced with potentially inaccurate witness testimony regarding the contents or context of conversation.
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Checklist of Sources of Failure of Memory for Conversation Primary factor Considerations Encoding of conversation Perception
Attention
Interpretation
Retention
Source monitoring
Impairments of hearing or vision Complex or distracting circumstances Insufficient loudness Blocked vision Distracting environment Internal states impairing attention Salience, distinctiveness; interest value of conversation Perceived threat Goals; current concerns of hearer Presence of emotion Relevance of utterance Expectations • Expectancy-consistent events • Expectancy-inconsistent events Situational circumstances interfering with processing Biasing context Difficulty of speech or language use Reliance on schemas in interpretation and filling in gaps Person characteristics interfering with understanding Use of multiple channels (facial expression, body language, words, tone of voice, etc.) Memory for meaning better than wording Recall of inferred rather than stated meaning Passage of time Misattributing utterances to speakers • Misattribution of utterances to individuals similar to the original speaker • Stereotypical attribution of utterances to speakers • Inattention to sources of utterances • Forgetting sources of utterances Misattributing utterances to other sources Misattributing the intended recipient of a message Misremembering imagined events as actual events Misremembering for time and space of conversations Misremembering for sequence and order in conversations Misremembering one’s audience Misremembering context
References Anderson, R.C. and Pichert, J.W. (1978). Recall of previously unrecallable information following a shift in perspective. J. Verbal Learning Verbal Behav. , 17, 1–12. Argyle, M. and Graham, J. (1975). A cross-cultural study of the communication of extra-verbal meanings in gestures. Int. J. Psychol. , 1, 21–28. Arkes, H.R., Wortmann, R.L., Saville, P.D., and Harkness, A.R. (1981). Hindsight bias among physicians weighing the likelihood of diagnoses. J. Appl Psychol. , 66, 252–254. Baddeley, A.D. (1999). Essentials of Human Memory . Hove, UK: Psychology Press.
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III Driving Environments
13 Human Factors in Traffic Crashes Rudolf G.Mortimer Human Factors Engineering Richard D.Blomberg Dunlap and Associates, Inc. Gerson J.Alexander Positive Guidance Applications Evelyn Vingilis University of Western Ontario 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
13.1 Introduction to Human Factors Principles and Standards of Care Traffic crashes are the most frequent cause of unintended fatal injuries in the U.S. when compared with accidents occurring in public places, in homes, or at work places (National Safety Council, 2001). They accounted for about 41,821 deaths and 3.2 million injuries that resulted from about 6.4 million crashes in 2000 (USDOT, 2001). Though these numbers are staggering and involve huge personal, emotional, and financial losses, the fatality rate per distance traveled has been steadily declining. If the fatality rate per vehicle kilometer in 2000 had remained the same as it was in 1970 at 2.9 fatalities per 100 million km, there would have been about 131,000 fatalities in 2000. Therefore, it is evident that highway safety has improved significantly over the years. This trend has also been found in most other countries. The rates/distance traveled in Finland, Sweden, and the Netherlands are somewhat lower than in the U.S., while those in France and Israel, for example, are about 60% greater. Some countries, such as Morocco and Turkey, have rates about 20 and 10 times greater, respectively, than many European countries (National Safety Council, 2002). It has been estimated that road traffic crashes result in about 22 deaths per 100,000 population worldwide and are about 40% of unintended deaths. Among the factors that have contributed to the reduction in fatalities are improvements in the protection afforded to occupants of cars and trucks, such as air bags, seat belt systems, child restraints and interior packaging; stepped-up enforcement and educational campaigns to reduce impaired driving, especially targeted against drinking drivers; restricted licenses for young drivers, etc. At the same time, other events have increased the toll of injuries and fatalities, such as the allowable duty time of truck
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drivers (which can lead to fatigue); elimination of helmet laws for motorcyclists in many states or requiring helmets to be worn only by the young; inadequate lighting and marking of bicycles and cyclists at night; proliferation of jogging as a health measure with its attendant hazards when joggers use the roadway or cross it (especially at night); the historical difficulty of seeing pedestrians in darkness; and continued problems of visibility and glare in night driving, among many others. The vehicle, the environment, and the human all contribute variables that need to be considered in any analysis of traffic collisions. The emphasis in this chapter is on the human as a participant in the traffic system as a pedestrian, cyclist, or an operator of a vehicle, a perceiver of the environment, a decision maker, and a responder. The environment includes that within the vehicle and outside it. The vehicle and its relevant characteristics are those assimilated by the human so that the operator’s input and the vehicle’s output relationships have been learned. However, the vehicle also includes input-output relationships that are not well learned or understood by the operator, such as car drivers braking on a slippery road surface or maximum braking of motorcycles. The highway-traffic-environment-human system is dynamic and complex. There are no simple solutions to increasing safety and no simple reasons for crashes. As Haddon (1970) pointed out, the system is multidimensional and requires an epidemiological approach to unearth the underlying causes of crashes. The human as driver, pedestrian, motorcyclist, cyclist, and other participant in the traffic system is at the center of it and has been assigned a large proportion of the causes of crashes, as the principal cause or as one cause in association with other parts of the system. In almost all cases, it would be inappropriate to allocate cause only to the human element, independently of the other components. It is important that those involved in forensic work have a systems orientation so that the performance of the human is considered in the context of the overall situation. Forensic Data Gathering Traffic collisions result from a failure in one or more parts of the traffic system. The forensic analysis starts with the collection of the basic factual data that may include a police report; an accident reconstruction; statements of witnesses and the actors directly involved; photographs or video pictures of the scene and vehicles; and a survey of the area drawn to scale. These data are usually supplemented by depositions of persons having some knowledge that may be of relevance. An examination of the location of the scene is useful or imperative to allow observations and measurements of distances, lighting, or sound features, assuming that the scene has not been significantly altered in the interim. Based on such background information, the human factors investigator applies fundamental principles of psychology, physics, and other sciences to discern and evaluate the underlying failures that were causally related to the event and the means by which those failures may have been avoided. In evaluating the standards of care that may have been breached and that contributed to the event, it is not unusual for the human factors person to work with an accident reconstructionist or specialist in another discipline; thus, the combined effort results in a realistic appraisal of the contributing factors to the failure
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and the standards of care that should have been in place that could realistically, practically, and economically have been expected to be employed. 13.2 Objective and Scope The subject matter of this chapter is extensive and books have treated various aspects of it. The chapter must be incomplete in some respects but will attempt to deal with some of the major areas of forensic human factors in the most common or lethal traffic collisions. The major topics of this chapter include human factors aspects of: • Vehicles, such as marking and signaling systems and their role in rear-end crashes; headlighting for night-driving visibility and its effects on drivers’ visibility and night crashes; motorcycle braking systems and rider performance in crash avoidance; and railroad crossing safety factors in drivers’ information processing (Section 13.3, prepared by R.Mortimer) • Pedestrian and bicyclist safety (Section 13.4, prepared by R.Blomberg) • Highway signing and driver information systems (Section 13.5, prepared by G.Alexander) • Effects of alcohol and drugs on traffic safety and human performance (Section 13.6, prepared by E.Vingilis)
13.3 Human Factors Engineering Affecting Visibility and Perception, and Performance of Drivers, Motorcyclists, and Other Road Users Visibility in Night Driving The rate of crashes at night is about four times that in daytime (National Safety Council, 2002). Although other factors are at play, such as a greater incidence of alcohol use in hours of darkness, reduced visibility must be a major factor in the elevated risk in night driving. One way this is demonstrated is by the expected 30% reduction in crashes that occurs when street lighting is installed where none was before (Rowan and Walton, 1976). Drivers must rely on the illumination provided by headlights when other lighting is not provided. Motor vehicles are normally equipped with headlamps that provide a high beam and a low beam. The requirements for the performance of headlamps in the U.S. is set forth in Federal Motor Vehicle Safety Standard 108, “Lamps, Reflective Devices, and Associated Equipment,” which first became effective in 1968. The headlamp performance standard was essentially based on the Society of Automotive Engineers Standard J579a. The federal standard was amended in 1978 to adopt the revised SAE J579c Standard, which allowed a doubling of the total intensity of the high beam to 150,000 cd and an increase of 5000 cd (to 20,000 cd) in the maximum permitted intensity at the 0.5° down to 1.5° right seeing point. The change in the maximum intensity of the U.S. high beam brought it closer to the intensities permitted in Europe. The change in the low beam has meant an increase in direct glaring intensities from oncoming vehicles and
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indirectly by headlights of following vehicles reflected in rearview mirrors with some increase in visibility. The High Beam The high beam can only be appropriately used when there is no oncoming traffic and no traffic close ahead so as to avoid excessive glare to other drivers; it provides a wide swath of light with its greatest intensities aimed about parallel to the road surface. The intent is to provide visibility of the road at substantial distances ahead of the vehicle and to the sides of the traveled lane. Those goals can be readily achieved with high-intensity light sources. The Low Beam The low beam is designed to be used when meeting other traffic or when another vehicle is ahead and nearby. Low beams are now also used in urban areas in most countries with or without street lighting, although they have not been designed specifically to be used in that environment. The design of the low beam has been undergoing slow evolution over many years in order to try to compromise the need to maximize visibility while minimizing discomfort and disability glare. In a situation in which two cars drive toward each other on a straight, unlighted, level road at night, with both using the low beam, the visibility of the drivers will gradually decrease as the cars come closer due to the glare from the opposing car’s headlamps. Recovery from glare in this case will occur before the cars meet because the glare effect is an inverse exponential function of the angle between the glare source and the driver’s direction of gaze. At large separation distances between the vehicles, that angle is small and the glare effect is potentially large because it is then mainly a function of the glare illumination at the driver’s eyes from the oncoming car. When the cars are approximately 100 m apart and drawing closer, the glare angle becomes much larger, reducing the glare effect so that the visibility can increase. The eye’s sensitivity is rapidly affected by glare or any bright source; when it is adapted to the usual mesopic levels found in night driving, the readaptation of the eye to lower levels of glare and illumination is relatively slow and can take a number of seconds. Up to 10 seconds may be needed for approximately full recovery from headlight glare (Mortimer and Becker, 1973). Figure 13.1 shows an example of the visibility distance to a 12% reflectance object at the right edge of the road for car drivers at 30 mph approaching each other with low- and high-beam headlamps on a level, two-lane road. In this example, the visibility is a minimum at about 400 ft for the high beam meeting and at about 300 ft for the low beam before the cars meet and pass each other. Then recovery from the glare allows the visibility to increase. Figure 13.1 also shows that the curves cross when the cars are about 2400 ft (731 m) apart, indicating the separation distance when dimming from the high beam to the low beam should occur to best maintain visibility. However, many variables affect this general process, such as the geometry of the highway; reflectivity of the pavement; lateral separation between the vehicles; location of the object to be detected (pedestrian, parked vehicle, bicyclist, sign, delineation stripe, etc.); reflective properties of the object; approaching vehicles; following vehicles;
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properties of interior and exterior mirrors; mounting location of headlamps and the properties and aim of their beams; street lighting; environmental conditions such as fog, rain, and snow; and driver variables such as age, workload, and attention.
FIGURE 13.1 Visibility of car drivers meeting on two-lane road with low and high beams. Because of the many variables to consider that can affect the ability of a driver to detect and recognize an object, it is evident that no simple methodology can be reasonably applied to predict a driver’s visibility. In a human factors recreation of a collision, it is essential to know as many of the important variables as possible. Some of those will be detailed in the police report, photographs, and scaled diagrams of the scene. The paths traveled by vehicles, cyclists, or pedestrians may be determined from skid marks, postimpact trajectories, marks on the pavement, and other features normally provided in the accident reconstructionist’s report. The statements of witnesses may also provide useful information, although they are sometimes inconsistent with physical evidence and need to be treated with due respect. Night Photography Photographs taken at night will show limited information. Also, those photos will normally be taken with a flash device in order to show as much of the scene as the camera and film are capable of capturing. Retroreflective materials will be highlighted in such night photography. It is important to remember that the scene as shown in those photos will be different from what was visible to a driver who was relying on the illumination provided by headlamps. One important reason is that flash strobes have a much wider field of illumination and also are usually at greater intensities than headlamps. Photographs are sometimes made in a recreation of the scene at night in an attempt to simulate the view available to a driver. Attempts to reproduce what was seen by a driver
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at night using photos, film, or digital media most often cannot do this fairly, even when an effort is made to use a control object with which to compare the scene, such as varying shades of gray that are part of the picture. The photos are then made at various exposures so that the gray that is just at threshold in the actual scene and in a photo is taken as an estimate of the apparent visibility of other objects of interest in the photo to replicate a driver’s view (Holohan et al., 1989). That process may have some limited value in a very bare night scene, but if other lights than the headlights of the driver’s vehicle are present—and particularly if there is an approaching vehicle whose headlights will produce glare at the eyes of the observer—the photographic method is fraught with error and cannot be used as a representation of the visibility. The recording medium, film or tape, only has about 1/10,000 of the range of sensitivity of the eye, so true gradations of light and darkness are not reproducible as seen by the eye. In a case in which glare sources are in the scene, such as from the headlights of vehicles or from street lighting or extraneous sources such as store fronts or parking lot lighting, photographic or video methods are incapable of providing a fair rendition of the visibility. In addition, still photographs can present a false impression on those who view them, such as the jury, because they provide an unrealistic amount of time for the scene to be viewed and because the jury has already been alerted to the location and nature of the object of relevance (Hyzer, 1993). On the other hand, the driver had a limited time to view the scene and did not have advance information of the nature or location of the object. Because crashes occur in a dynamic context, still photos can create a false presentation. Another reason that night photography, whether still or motion, is not able to reproduce the scene viewed by the eye is that the driver’s eyes are subject to changing levels of adaptation, which directly affect the sensitivity of the eyes and the thresholds at which objects can be detected. Cameras have no such characteristic. Visibility Reconstruction In order to try to estimate what was discernable to a driver before a night crash, a type of visibility reconstruction may be undertaken. This is not the same as an accident reconstruction whose objective is to determine the paths taken by the vehicles and pedestrians, as well as their speeds and trajectories, shortly before, during, and after the crash. Based on the accident reconstruction, the vehicles and other relevant objects can be inserted into the scene, assuming that the environmental factors are still the same. In a simple case, such as one involving a vehicle on a two-lane road and a pedestrian who was struck while walking on the pavement, the recreation can be done reasonably easily. This assumes that the road has not been repaved; lighting has not been inserted or removed; other traffic can be controlled; weather conditions are similar; and the moon phase is the same, particularly if it was a clear night without clouds. The pedestrian must be simulated with a person of similar stature, wearing the same types of clothing. The original clothing from the victim, including shoes, socks, lower and upper body outer clothing, and headwear, must be measured for reflectance. The clothing to be used in the reconstruction must be of similar reflectance. If the original clothing is no longer available, the best estimate of the reflectance must be used. For example, in one such case, the pedestrian was known to have worn blue jeans but none of
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the actual material was available. Therefore, a survey was made of 20 randomly selected persons wearing blue jeans and the reflectance of their pants was measured. The minimum reflectance was 2% and the maximum 23% with a median of 9.5%. The range of reflectances is quite large and shows that knowledge of the actual reflectance is important and affects the visibility of the blue jeans in darkness. Knowing the distribution of the reflectances can allow the effects to be taken into consideration. The vehicle should be the same type as or similar to the one in the crash and be equipped with the same types of headlamps and auxiliary lamps if such were used. The headlamps should be correctly aimed, unless there is some reason to assume otherwise. Headlamp alignment can be affected by the loading of the vehicle, so that needs to be considered. The driver/observer in the vehicle should have normal eyesight unless the driver in the crash had known deficiencies, such as color blindness or monocular vision, in which case those would need to be taken into account then or later. The approximate location of the collision usually will be known from the police report or accident reconstruction. That point of impact acts as a reference point from which known distances can be measured and marked with paint or by small traffic cones. For example, in making the visibility reconstruction, the distance at which an object, such as a pedestrian, becomes just detectable may be sought. By having markers at the side of the road that show the distance from the point of impact, the distance at which the pedestrian becomes detectable, for example, can be readily obtained by noting the position of the car with respect to the nearest marker when detection occurs. To allow the markers or cones to be easily seen at night by a car’s headlights, it is useful to apply reflective tape to each and to number them. The forensic expert can make actual measurements of visibility by driving the car toward the pedestrian at a slow or moderate speed, not necessarily at the speed of the vehicle in the collision, so that the reaction time of the driver is not a factor. The position of the car when the pedestrian becomes just detectable is noted and is the detection distance. A number of such trials should be made to ensure that the data are reliable. Alternatively, another person of similar characteristics as the driver in the crash can be used to make the visibility observations. The disadvantage is that the person may be requested to appear at a deposition to describe what was done. It is important that good notes are kept of the procedure and the data. Photos should be made in daylight to show the vehicle and the test location and setup, which may become useful exhibits for later use in court to demonstrate to the jury. Although the use of night photography has its limitations, such still or motion photography can be used to illustrate the general scene to the jury. In the present example, a video made during the approach to the pedestrian could have a narrative simultaneously describing what can be seen by the observer and when the pedestrian becomes detectable by the eye. This would provide a foundation for use of the video recording as a support of the actual observations. It is not unusual that, very correctly, opposing counsel makes strong objections to the introduction of video or other photography. The underlying purpose of the photography or video needs to be made clear: namely, it represents an approximation of the visual scene and not a rendition of it as would be seen by the eye. In these kinds of tests, it will usually be noted that the pedestrian will be detectable at a certain distance and then will become much more clearly visible a short distance later. The detection criterion adopted by the observer can introduce variability, so it needs to be
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specified clearly. The detection phase is usually the one with the greatest variability, but the objective of the visibility reconstruction is to determine the distance at which the pedestrian would be at threshold of detection, given an observer who is looking in the appropriate location. This set will reduce the variability in the measurements. It is also helpful to obtain the distance at which the pedestrian is clearly detectable, which is often also when he is recognizable. This will provide an endpoint to the detection distance, when almost all observers looking in the direction of the pedestrian would detect it. The example just presented of a nighttime collision with a pedestrian on an unlighted road with no other traffic is relatively simple to examine in the general fashion described. However, if street lighting is present, the scene is more complex because of the relationship of the location of the pedestrian with respect to the luminaire. This can result in direct visibility of the pedestrian by illumination from the street lamp and the headlights of the car. Alternatively, if the pedestrian is between the street lamp and the driver of the vehicle, the pedestrian may be visible to the driver initially in silhouette as a dark object against the road. As the car gets closer, the headlamps increasingly illuminate the pedestrian, who will be more difficult to detect because of the reduction of the contrast of the pedestrian against the lighted road behind the pedestrian. At a certain point, the pedestrian or a part of the pedestrian may be momentarily lost to view when the luminance of the pedestrian is equal to that of the pavement that is the background of the pedestrian as viewed by the driver of the car. Then, as the car gets closer and the headlights provide more illumination, the pedestrian can be seen as a brighter object against the pavement. Therefore, the location of the pedestrian over time can be very important in affecting the illumination from street lighting and car headlighting; the effects on the resulting contrast of the pedestrian against the pavement are important determiners of visibility. For an example of the procedures in an analysis of the night visibility aspects of a pedestrian collision, see Mortimer (2001). Glare Another complicating factor often involved in night crashes is the glare from oncoming vehicles and from vehicles to the rear. The latter glare levels can often be greater than those from oncoming vehicles (Miller et al., 1974). Glare from headlights and other sources can have the effect of reducing the ability to see and causing discomfort, thus leading to fatigue and other responses. Although drivers are told not to look directly at the headlights of oncoming vehicles to reduce the deleterious effects of glare, eye fixation data (Mortimer, 1975) show that drivers do look at oncoming vehicles at night, at least on two-lane highways. Probably the reason is that drivers have a concern for the lateral position of those vehicles to ensure they are not encroaching into their lane of travel. Glare reduces visibility because the light entering the eyes of the driver from the source, such as headlights of an oncoming vehicle, effectively reduces the contrast of the object’s image on the driver’s retina. The glare effect is a veiling brightness added to the background brightness, thereby effectively raising the denominator in the contrast equation and reducing the contrast between the object and its background. The result is that the object is less detectable than if the glare was not present.
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The veiling brightness is a function of the illumination produced at the eyes by the glare source and the inverse of the glare angle (the angle of the glare source from the driver’s line of gaze) raised to a power. For example, using the equation of Fry (1954), the veiling glare is shown as: VG=KI/D 2θ (θ+1.5), where I is the glare intensity in candelas at the eye; D is the distance, in feet, from the glare source; θ is the glare angle in degrees; and K is a constant determined by the age of the observer. It should be evident that the effect of the glare drops off sharply as the glare angle increases. When two vehicles approach each other at night, the angle between the forward line of sight of the drivers and the oncoming vehicle will increase rapidly as the separation distance between the vehicles becomes small. This is a reason that the visibility will usually begin to increase before the vehicles pass each other, as shown in Figure 13.1. Another major factor is the illumination (I/D 2 ) at the eyes of the driver from the oncoming headlamps, which will be a function of the distribution of light from the headlamps. Age is also related to disability glare (Wolf, 1960), and older drivers can attest to the impairing and discomforting effects of glare, which become increasingly pronounced after about 40 years of age. In one series of experiments (Olson and Sivak, 1983), drivers aged 18 to 30 and 65 or more recognized low-reflectance typical pedestrians standing at the right and left side of the road when there was no oncoming car (no glare) and with an oncoming car at 300 ft (91 m) behind the location of the pedestrian. The older drivers recognized the pedestrian on the right side at about 38% of the distance compared with the drivers aged 18 to 30 when using conventional low-beam headlamps without glare from an oncoming vehicle. When there was an oncoming vehicle, the visibility of the young drivers was about 78% of the no-glare case. The oncoming vehicle reduced the visibility distance of the pedestrian for the older drivers to about 75% of their no-glare case.
TABLE 13.1 Recognition Distancesa in Darkness of Dark Pedestrian at Right and Left Sides of Road by Young (18 to 30) and Older (65+) Drivers Pedestrian location
No glare Young Older
Low-beam glare Young Older
Right side 50 19 39 14 Left side 27 15 a Meters. Source: Adapted from Olson, P.L. and Sivak, M., 1983. University of Michigan, Report UMTRI 83–9, Ann Arbor, MI.
Table 13.1 also shows that the location of the object has a substantial effect on its visibility by low-beam headlamps. The pedestrian on the left side of the road was recognized by the young and older drivers at about 53 and 79%, respectively, of the distances he was seen when on the right side of the road. The data shown in the table can be used as a general indication of the trends in recognition distances of a pedestrian wearing dark clothing with low-beam headlamps to show the effect of the location of the object, an opposing vehicle, and age of the driver. The data also demonstrate that older drivers need more illumination than younger drivers to see objects at night as well as young drivers do. However, the mean visibility
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distance of the younger drivers in this test was also far from what is needed even when there was no glare. At a speed of 88 km/h (55 mph), a vehicle will cover 50 m in 2.04 sec, which will not allow a driver not previously alerted to the pedestrian enough time to react to stop within that distance. Because of the design of the low beam to limit light in the locations of the eyes of approaching drivers, minimal light is distributed to the left side of the road in the lanes used by oncoming traffic. This means that a pedestrian crossing from the left to the right at night will be particularly difficult to see until he enters the lane used by the driver and moves into the part of the beam that includes higher intensities of light. Drivers will have less warning of the pedestrian crossing from the left than of one crossing their path from the right. Computational Analysis It should be evident that it is a complex task for a driver to estimate the detectability of an object, such as a vehicle, retroreflective device, or pedestrian, at night due to the many variables involved. One approach is the site examination and visibility reconstruction already described. Another approach is to use calculations or computer simulations. A few simulations to estimate detectability of objects in night driving have been developed, but the accessibility of most appears to be limited. Among the earliest is the one developed at the University of Michigan (Mortimer and Becker, 1973; Becker and Mortimer, 1974) that extended the work of Jehu (1955) of the Road Research Laboratory in England. That model simulates the approach of two vehicles on straight or curved roads at night and calculates the distance at which a simple characteristic of a specific test object is recognized as the vehicles approach and after the vehicles pass each other, as visibility is regained. The output of the program can be generalized in a limited way to objects other than the kind used in the validation studies. Mortimer (1974) offers an example of the extensive way in which the program can be used. The Ford Motor Company developed a program (Bhise et al., 1976; Farber and Matle, 1989) based on the visual target detection data of Blackwell (1952). This program is more versatile with respect to the kinds of objects that are to be detected and also incorporates age-related functions. Although probably not enough research has been done to validate the model, it is a useful program. Like all programs, it needs to be used judiciously and requires a fundamental understanding of factors affecting visibility. Although other simulation programs have been reported in the literature, their details are unclear and do not appear to be publicly available. Hand calculations can also be made, relying on the contrast threshold data of Blackwell, some of which are summarized by the Illuminating Engineering Society (1972). In any computational method, the characteristics of the headlamps and street lights will need to be known, usually in the form of iso-candela diagrams. When the locations of the target object (e.g., pedestrian) and the vehicle at a given point in time or distance from the collision are known, the illumination from the light source can be calculated. Using the reflectance of the clothing and the illumination on it, its luminance (B t ) is calculated (B t = illumination×reflectance).
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FIGURE 13.2 Photo looking south. The tractor-trailer pulled out from the right leg of the intersection and turned to go north. For an object seen against the road, the luminance of the road at the object can be used as the background luminance. However, it may be more appropriate to use the driver’s adaptation level, which is determined by the general illumination in the driver’s vicinity; this is often a function of the foreground illumination provided by the headlamps and the reflectance of the pavement or perhaps by street lighting. The available contrast can then be calculated and compared with Blackwell’s data of the contrast needed for a given probability of detection. The veiling glare caused by one or more approaching vehicles and by street lights can also be incorporated into the contrast equation. Example of a Forensic Examination of a Nighttime Car-Truck Collision The photo in Figure 13.2 shows a view to the south of a rural unsignalized intersection. At about 11 p.m. in December, 1992, a tractor and flat-bed trailer pulled out from the right (eastbound) leg of the intersection. The tractor crossed the southbound lane and turned left to head north. A few seconds later a southbound car struck the truck’s trailer just ahead of the rear tandem axles. The speed limit was 55 mph. As the car approached the intersection, it was descending around a left and then a right curve that led to the intersection. Prior to the crash, a truck traveling north had passed the southbound car about 122 m from the intersection. It will be noted that a street light was on the northeast corner and some lamps were also on the porch of the white building (a restaurant) and in some of the windows. In addition, on the east side of the road was a gas station that had just closed. A dynamic analysis of the truck’s acceleration into the intersection and its path of travel was made to enable the position of the truck and the car to be fixed by time to crash. Analyses were made of the visibility of the trailer’s side rail, retroreflectors in the
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center and rear side of the trailer, and the side-marker lamps that were standard, required equipment at the time and with which the trailer was equipped. Those analyses were made at intervals of 30 m starting at 122 m before the crash. Further analyses were made in which the trailer was assumed to have a continuous strip of retroreflective red/white alternating striped tape on the side such as that now required on all large trailers. The analyses included the effects of the street lamp in illuminating the trailer and also the effect of the glare of the low-beam headlamps of the tractor. Photometric measurements were made of the retroreflective performance of the standard yellow and red retroreflectors, the retroreflective tape, and the side-marker lamps as a function of their angle to the light source (“entrance angle”). This was done because the amount of light returned from retroreflective devices decreases rapidly at entrance angles greater than about 40° and the specifications for the performance of side-marker lamps do not go beyond 45° (FMVSS-108) (SAE J-592). The basic results of the analyses showed that the side-marker lights were detectable at 50% probability or better between 122 to 30 m from the trailer; the yellow retroreflector in the center of the side of the trailer was detectable at 122 to 91 m and the red at 91 m; the side of the trailer body was detectable at 15m; and the retroreflective tape was detectable at 122 to 61 m. (The analysis of the visibility of the tape was not done at 30 m.) The basic scene was recreated at the site of the crash and night observations were made of the visibility of the trailer at positions of the car and trailer equivalent to 1-sec intervals starting at 10 sec before the crash. With the trailer in the same condition as it was in at the time of the crash, the center yellow side marker was detectable at 78 m, but the trailer only became faintly visible at about 1 sec to crash. With tape on the side of the trailer, it became quite visible at about 205 m and clearly visible at 130 m; at 78 m, it was clearly noticeable that the tape went across the southbound lane. When additional sidemarker lamps were added to the side of the trailer with a separation of 1.5 m between them, they could be seen at more than 244 m. It was clear that an object was across the road at 104 m or 4 sec to crash, although the trailer was not visible. In the last condition, the reflective tape and additional side-marker lamps were used. At more than 244 m, the side-marker lamps were visible and, at 206 m, it was noticeable that they all moved as one unit, providing a good cue that the object was moving across the driver’s lane. The tape also became clearly visible at 130 m, and at 104 m it was clear that an object was across the road lane, although the body of the trailer could not be seen. In all cases, the tractor’s headlights and other front lighting gave the appearance of a truck traveling in the northbound lane toward the car. It was concluded that the truck that had passed the car before the crash exposed the driver to glare and would have attracted the attention of the driver away from the activity at the intersection as the truck involved in the crash began to pull into the intersection. After the first truck had passed, the driver would be in a right curve and should have noticed the headlights of another truck approaching. Although the center yellow, and later the red rearmost, side-marker lamps would be visible to the car driver, they would be faint and a long distance from the tractor: about 6 and 12 m, respectively. They may not have been readily associated as a part of the trailer, but may have been seen as ambiguous lights in the distance or driveway reflectors.
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The addition of retroreflective tape, additional side-marker lamps spaced about 1.5 m apart, and, especially, the combination of these methods provided greatly improved visibility and recognition of the trailer across the lane. The driver had little expectation of a trailer across the lane and was unable to see or recognize it in time to avoid it when it was provided only with the reflectors and side-marker lamps that were then required. The retroreflective tape along the side would have aided the driver substantially. The use of additional side-marker lamps, with or without the retroreflective tape, would have provided the driver with even better information that a continuous object was across the lane of travel (Figure 13.3). It would be expected that most drivers would infer that this was the truck’s trailer even though they could not see the body of the trailer. The use of the extra lighting and marking would have allowed the driver to avoid the crash or at least to reduce the speed and severity of the impact. Such aids to the visibility and recognition of trailers were readily available at the time of this crash and could have been implemented by the manufacturer or operator. Rear-End Collisions Rear-end collisions are about 25% of all crashes, approximately 27% of crashes causing injuries, and 5% of the fatalities (USDOT, 1998). It has been found that, in more than half of rear-end crashes, the struck vehicle was stopped or moving very slowly (Mortimer, 1981), which suggests that drivers do not perceive the speed of the lead car or perhaps the relative speed.
FIGURE 13.3 Driver’s view of turning truck at 76 m: (top left) standard lighting/marking; (top right) retroreflective tape; (bottom left)
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added side-marker lamps; (bottom right) tape and added side-marker lamps on the trailer. Drivers are reasonably sensitive to changes in headway between their vehicle and a vehicle ahead of them. The basis for this performance is the change in the visual angle subtended by the leading vehicle at the eyes of the following driver. For small angles, this can be represented also as the change in the headway. The driver’s ability can then be described most intuitively by a simple Weber function, ∆H/H =0.12, in which H is the initial headway distance (Hoffman, 1968). This means that alert drivers can be expected to notice a change in headway of about 12% and infer that the gap between their vehicle and one in front has changed. Unless the headway is very small, the detection of change in headway is normally adequate to alert drivers to a potential need to pay attention to the vehicle ahead of them and to be ready to respond. If the initial headway is small and closure is detected, the driver may need to react immediately. However, in most rear-end crashes, the vehicles are not in a close-coupled state (Perchonok, 1972) so there is usually time after the change in headway has been detected. The question then is: why do the crashes occur? Having detected closure by a change in headway, the driver still must determine how much time remains to the crash to determine the appropriate response. The time remaining is a function of the headway and the relative speed. Although headway can be estimated moderately well, drivers are decidedly limited in their ability to detect relative speed. The major cue to spacing changes is the change in the visual angle of the rear of the vehicle. At night, in particular, this will be the angle at the driver’s eyes subtended by the rear lighting. The rate of change of this angle provides the cue to relative velocity. Research has shown that the threshold for detection of relative velocity is about 0.003 rad/sec (Hoffmann and Mortimer, 1996). Table 13.2 shows the relative speed, time to crash, and distance between the vehicles at the relative velocity threshold for a lead vehicle 5 ft wide or for a vehicle whose rear lamps are set 5 ft apart, if viewed in darkness.
TABLE 13.2 Relative Speed, Time, and Distance between Vehicles at Threshold of Relative Velocitya Relative Time to crash Distance to crash speed (mph) (km/h) (sec) (ft) (m) 70 113 60 97 50 80 40 64 30 48 20 32 a 0.003 rad/sec.
4.0 4.3 4.8 5.3 6.1 7.5
414 380 350 312 270 220
126 116 107 95 82 67
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The amount of time remaining to crash after the threshold of detection of relative velocity is attained is inversely related to the relative speed but directly related to the distance between the vehicles (Table 13.2). It also needs to be remembered that the braking distance is directly related to the square of the initial speed. Consider the case of a car driver traveling at 113 km/h approaching a stopped car. If the driver has not slowed based on the cues provided by the change of visual angle or headway, the cue to relative velocity will be at threshold at about 126 m from the stopped car. Assume that the driver has a lag time of 1 sec in detecting the relative velocity. The driver will be 95 m from the stopped car. The driver will still need to process the information, decide on a response, and implement it, so assume that in another 1.5 sec the brakes are applied to achieve a deceleration of 0.8 g, assuming the pavement is dry. The distance remaining is 48 m. However, the braking distance to stop is about 63 m, so a crash results. Consider the same situation with a relative speed of 48 km/h. Braking again is assumed to start at 2.5 sec after the threshold of relative velocity detection is achieved. The distance then remaining to crash is 49 m. To stop from 48 km/h at 0.8 g requires 11 m, so the crash is averted. The driver’s ability to scale the perceived relative velocity is limited to a few categorical values such as low, medium, and high, which are nevertheless adequate to allow the driver to determine the urgency of the response that is needed. The relatively poor ability of drivers in estimating relative speed results in a short time remaining to crash, especially at the higher relative speeds. When combined with the other tasks involved in driving, complex driving situations, glare, and other visual degrading conditions, drivers’ relative velocity detection thresholds can often be further degraded and increase the probability of rear-end crashes. Overtaking and Passing It is worth noting that the same process just described for detection of relative velocity in the approach to the rear of a vehicle applies to determining the time available to pass another vehicle when there is an oncoming vehicle. However, because the distance when a passing maneuver is initiated is necessarily much larger than that involved in approaching a vehicle from the rear, the threshold for relative velocity perception will normally not have been exceeded when the decision to pass must be made. This means that drivers have no way of estimating the speed of the approaching vehicle. As Rumar and Berggrund (1973) stated, “Drivers cannot estimate the speed of the oncoming car. Being in that vague position they assume that the speed of the oncoming car is the same as their own speed and consequently base their decision mainly on the estimated distance to the oncoming car.” Farber and Silver (1967), in their studies of overtaking behavior, reported that “the threshold passing distance adopted by drivers tends to remain constant regardless of oncoming car speed”—again confirming that the drivers were not able to assess the relative speed due to the small visual angle subtended by the oncoming car and its small, subthreshold rate of change at the large distances involved.
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Expectancy Elsewhere in this chapter there is a discussion of driver positive guidance which has as a central tenet that systems should be designed to ensure that the expectations of drivers are met as much as possible. This will reduce ambiguities and reduce the time drivers need to make decisions. There are expectancies that are not easy to design in or out. An example would be a stalled vehicle in the travel lane of an interstate highway or a pedestrian on an unlighted rural road at night. Drivers do not expect either of these kinds of events. A driver approaching the stalled vehicle will initially assume that it is moving at normal highway speed. Even as the driver receives information about closure with the vehicle, the lack of expectancy that the vehicle is stationary will reduce the salience of the information as well as the driver’s attention to the vehicle, thus increasing the driver’s response time to the hazard. At night, if the stalled vehicle has an inoperative electrical system and the vehicle is unlighted, the hazard is extreme and almost inevitably will result in a crash. If the vehicle has operating tail lamps, the approaching driver will again assume that the stalled vehicle is moving and a crash is likely. Even the use of hazard flashers on a stopped vehicle, while aiding in detecting the vehicle and suggesting that it is stopped or moving at a speed less than the normal highway speed, is still an unexpected condition that may override the value of the hazard signal and delay the oncoming driver’s response. Few studies have tried to quantify the effect of a lack of expectancy on drivers’ reactions. One reason is that such studies are not easy to conduct because of the difficulty of introducing the unexpected condition without alerting the driver and the necessity of not creating an unsafe situation. In one early study (Roper and Howard, 1938), the observer drove the test car at night and was told that the task was to evaluate some aspect of the car such as the headlights. On the way to the test area, the driver encountered a pedestrian object in his lane. The distance driven from release of the accelerator to coming adjacent to the pedestrian was measured and taken as the detection-response distance in the “unexpected” condition. The task was repeated, but this time the observer knew that a pedestrian object would be encountered. These detection-response distances were taken as the observer’s response in the “expected” condition. It was found that the pedestrian was detected at about half the distance in the unexpected as in the expected condition. Some have assumed that this implies that drivers require twice the distance to detect an unexpected object as for one that is expected. That assumption is not appropriate, even in a situation similar to the one in which the data were obtained, for numerous reasons (Mortimer, 1996). However, there is no question that an unexpected event will require a longer time for the observer to respond, even in simple situations (Johansson and Rumar, 1971; Summala, 1981). In practice, the effect of a lack of expectancy will be difficult to quantify because of the paucity of current data. However, it is clear that drivers who are confronted with an unexpected situation will respond with great variability. For example, Summala (1981) found that some drivers needed up to 4 sec to respond by steering their car away from the side of the road when someone opened the driver’s door of a car on the road’s shoulder; the 50th percentile was about 2.5 sec. The extent of the variability will likely be greater in more complex tasks such as detecting an unexpected object in darkness. In one study of the detection of an unexpected stop sign at night (Olson, 1988), the ratios of the unexpected to expected response distances of the 10 subjects were between a low of
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approximately 1:08 to a high of about 1:2.6; thus, the intersubject variation was so great that it would be inappropriate to take any fixed value to represent the effect of expectancy. Even though these subjects knew they were in a test and can be assumed to have been attentive to the task, the variation among the subjects was large. Familiarity with an environment can reduce the negative effects of expectancy if prior exposure has created a heightened awareness of an event occurring. A driver who often drives through a residential area and has noted children playing near the road has an expectation of seeing children in that area and should be more ready to respond than if a child appears near the road in an area where children were not seen before. However, familiarity with an area can also have a negative transfer effect. A driver who comes upon a truck-trailer that is being backed across the road where this had not been seen before will have a response lag due to lack of expecting such an event. As Deese (1959) noted, the observer’s expectancy is a function of prior experience with the task, and the level of expectancy of the event determines the observer’s level of vigilance and the probability of detection. Stress When a small amount of time is available for a response to try to avoid a crash, the individual will experience stress. Although a low level of stress can lead to boredom and poor performance, a moderate
TABLE 13.3 Change in Probability of Response Error Associated with Stress and Operator Skill Level Stress level
Change in probability of error Skilled Novice
Very low ×2 ×2 Optimum ×1 ×1 Moderately high ×2 ×4 Extremely high ×5 ×10 Source: Adapted from Swain and Guttman, 1983.
level is usually beneficial to arousal and to maintain performance on a task. A high level of stress degrades performance. The familiar U-shaped relationship between stress and performance defines the Yerkes-Dodson law (Welford, 1973). For example, as a driver nears an unguarded railroad crossing where a train was not previously seen and suddenly detects a train close and at high speed, the driver will almost certainly experience high stress. In such a situation, the driver will tend to sample the most salient cues, such as the approaching locomotive, and neglect other cues that may be important in reaching a decision on how to avoid a collision. Under high stress, fewer cues are sampled and attention narrows (Broadbent, 1978). That behavior can lead to errors in selecting a response and also to a lag time in responding. In the extreme situation, drivers may “freeze” on the controls and fail to respond at all or fail to modify a response. In many precrash situations, drivers will use
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only the brakes to slow the vehicle, even when the stopping distance is insufficient and it may have been possible to steer around the hazard. Swain and Guttman (1983) developed a model to act as a guide of the effects of stress and operator level of experience on the increase in the probability of errors in routine tasks, which can include driving (Table 13.3). According to Table 13.3, novices are more affected by moderate or high levels of stress, as would be expected, because of lower spare information-processing capacity before the added workload imposed by stress. Although a good deal of research on the general topic of stress has been conducted, like expectancy, it is a difficult area to study and to generalize the results. Stress has an impact on working memory, attention, perceptual-motor skills, and communication skills (Stokes and Kite, 1999), but the studies provide little guidance on the extent of the effects in a given situation. In spite of this lack of guidance and quantification, the effects of stress on response-time lag and response errors should be given consideration. Response Time There is no such thing as a fixed response time for people. Nevertheless, statements that a driver’s response time is a fixed value, such as 0.75 or 2.5 sec, have often been made. Traffic and highway engineers, for example, do need a value of response time that they can incorporate into their everyday design decisions, such as determining stopping distance sight lines that drivers will need for various driving maneuvers. In the approach to a railroad grade crossing, adequate sight lines must be provided to enable the driver to detect and respond to a train in time to avoid a collision or to determine the distance that a stop sign needs to be visible to allow drivers sufficient time to come to a stop safely. Based on research, a value of 2.5 sec is often used for some of these purposes, but the complexity of deriving a useful figure of merit is exemplified by Olson et al. (1984), who found that other factors need to be considered. The detection and subsequent information-processing tasks involved have a great impact on the time needed to reach a decision and make a response. Detection of a relevant stimulus in traffic can very often be done quickly, such as in less than 1 sec; however, in some situations the time needed can be much longer due to weather, lighting, workload, and salience of the stimulus. The state of the driver or pedestrian is also a factor. Once the stimulus has been detected, the information processing, in terms of recognition of the stimulus and the decision-making task, can also vary greatly in time due to the complexity of the situation, ambiguity of the stimulus, expectancy, and stress. Response times to simple, easily detectable situations, such as a brake signal on a car ahead, can be about 0.8 to 1.2 sec. What if the driver of the following car is considering passing the car ahead and is looking in the outside rearview mirror when the brake signal appears? Then the time to detect the brake signal will be increased, perhaps by up to 2 sec. Detection time is the time from a stimulus being at threshold of detectability and its detection. A pedestrian on a straight, level road in daytime is detectable at a much greater distance than at night if illumination is only provided by headlamps. However, the pedestrian in the daytime may be detected after a longer time has elapsed from the threshold than the pedestrian at night would be. This may be because the pedestrian will present as a stimulus at a large distance, but not be detected as a relevant stimulus that gets the attention of the driver until he is much closer. If the threshold is at
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300 m from the pedestrian but he is detected at 200 m, the elapsed time for detection at 97 km/h is 3.4 sec. If, at night, the pedestrian is just detectable at 91 m and is detected at 61 m at 97 km/h, the elapsed time is 1.1 sec. The time remaining after detection is for recognizing the object, deciding on a response, and executing the response. Time to move the foot to the brake or to move the steering wheel in an evasive maneuver is about 0.5 sec in a quick response. There is also a short lag time for the brakes to take hold or the car to yaw. Although brake system lags are less than 0.25 sec in automobiles, they are about 0.5 sec in large trucks with air brakes. In measuring the time for drivers to swerve out of the way of the driver’s door being opened of a car stopped on a road’s shoulder (Summala, 1981), the mean time to initiate a steering response was about 1.5 sec while the longest time to execute the swerve was about 4 sec. This means that, even in a clear-cut situation in which some expectation exists that a driver may open the door of the car stopped on the shoulder, as much as 4 sec may be needed to accomplish a lateral movement of only about 25 cm. Another study of unobtrusive measurements of the response times of drivers (Triggs and Harris, 1982) found 85th-percentile times of 1.2 to 3.6 sec in a variety of situations. Driver response times of up to 4 sec are not necessarily unusual and need not indicate that the driver’s performance is impaired or shows a lack of alertness. Each situation must be evaluated in consideration of the variables that may affect performance. Motorcycles In 2000, about 2862 occupants of motorcycles were fatally injured and about 58,000 were injured in crashes in the U.S. (USDOT, 2001). The fatality rate of motorcyclists is estimated at about 27 per 100 million miles or about 21 times the rate for occupants of passenger cars. More than any other group of drivers, motorcyclists involved in 38% of fatal crashes had consumed some alcohol; in 27% of their crashes, the operator’s bloodalcohol concentration was at or more than 0.10%. Because of the nature of the vehicle, many motorcycle crashes are not reported to the police and do not enter the official records. This will be most true of property damage and minor injury crashes when no other person or vehicle is involved. In spite of that, almost half of motorcycle crashes involving injuries were reported to be single-vehicle crashes. This is much greater than the 15% of automobiles in single-vehicle crashes and illustrates the problems of motorcycle riders in maintaining safe control of the machines. In crashes involving another vehicle, most of which occur at intersections, the driver of the other vehicle was reported to have turned or crossed in front of the motorcycle in about 70% of the cases (Hurt et al, 1981). Most often the motorcyclist was proceeding straight and the other vehicle driver, approaching from the opposite direction, was turning left across the motorcyclist’s path. The drivers of the other vehicles often stated that they did not see the motorcycle in time. It is apparent that at least three basic factors contribute to motorcycle crashes: motorcyclists’ use of alcohol, lack of ability to control the motorcycle; and violation of the right of way by other drivers. The effects of alcohol and other drugs are described elsewhere in this chapter. Lateral (steering) control of motorcycles is much more complex than that of four-wheeled vehicles. Braking control is also much more complex and most motorcyclists are unable
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to achieve maximum braking performance (Ecker et al., 2000), especially in emergency situations (Hurt et al., 1981). The reason for this poor performance is the design of most motorcycles’ brake systems, which have separate brake controls for the front and rear
FIGURE 13.4 Visual angle of car and motorcycle by distance. wheels. The right foot can operate a brake lever for the rear wheel and the right hand can operate a lever on the handlebars that operates the brake on the front wheel. To exert maximum braking, the rider must activate both these controls and modulate them to achieve braking forces that do not quite lock either wheel. Because of the convenience of operation of the foot brake, riders favor it in everyday braking, and in emergencies they often fail to also use the front brake. Use of the foot-operated rear brake permits a maximum of only about 40% of the braking force of which the motorcycle is capable to be obtained. A brake system in which a single control operates the rear and front wheel brakes would lead to greatly improved braking performance (Mortimer, 1998), especially if combined with antilocking capability. Another factor in motorcycle crashes concerns the detectability of motorcycles and the ability of other motorists to judge their distance and speed. In many countries as well as states in the U.S., motorcycles are required to have the headlight on at all times, which should help to allow the motorcycle to be more readily detected by others in daytime. However, the narrow aspect of the motorcycle and its operator makes it less easy to estimate its distance, to notice a change in distance, and to estimate its relative speed. Figure 13.4 shows how the visual angle, based on the widths of a car and a motorcycle, changes with distance from the observer. A car at 1000 ft (304 m) subtends a similar angle as a motorcycle at 300 ft (91 m), which would lead to overestimations of the distance of a motorcycle. Other factors, such as size constancy and the surroundings of the motorcycle, help to correct partly for this error. The sensitivity of other drivers to changes in distance of the motorcycle will also be less than to the car, and their ability to estimate relative velocity will reach threshold when the motorcycle is closer to them than
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the car for the same actual relative speed. At night, compared with daytime, those estimations will be even more affected if the motorcycle is depicted only by its headlight(s). The performance of other drivers in turning and crossing across the path of a motorcycle can be made safer if the motorcycle has auxiliary lamps spaced as far apart as practicable, such as at least the width of the handlebars, on each side of the headlamp (Mortimer and Schuldt, 1980). Recently, some manufacturers of automobiles and light trucks have begun incorporating headlights that are lighted in daytime. As a result, it seems likely that the headlights of motorcycles will become a less prominent signal in daytime so that they will be more difficult to detect among those other lights, as is already the case in darkness. This will make the use of auxiliary lamps important also in daytime. Railroad Crossings Collisions between motor vehicles and trains have been significantly reduced in the past 20 years in the U.S. In 1980, about 739 fatalities in collisions with trains occurred and in 2000 there were about 400 fatalities. Motor vehicle collisions with trains are very severe in that fatalities occur in about 10% of them compared with about 0.3% in other crashes. Some caution needs to be exercised in interpreting crashes reported to have occurred at grade crossings because only about 25% involve a train. The others are mainly rear-end crashes involving vehicles that are stopping or stopped at the crossing. The two basic human factors considerations in evaluating vehicle-train collisions or those involving pedestrians or cyclists and trains are (1) those that affect the visibility or audibility of the train, and (2) the warning signs and signals at the crossing. The road user must take the initiative to avoid the collision with the train because the only options available to the train engineer are to provide a timely warning by lights and the train’s horn. In most cases, there is no reasonable opportunity to slow the train to avoid a crash because of its poor braking deceleration (Bentley, 2002) compared with road vehicles. Visibility Factors In the U.S., grade crossings are announced by a “railroad crossing ahead” sign, placed about 229 m before the crossing in rural areas and about 76 m in urban areas. The sign provides no indication of the level of protection at the crossing. In other countries, such as Australia and in Europe, the advance warning sign indicates if the crossing is passive or has some form of active signals or gates. This advance information can be used by drivers to plan their speed as they approach the crossing. At unguarded (passive) crossings, drivers must be able to see along the tracks to detect the train in time to stop or to cross before it reaches the crossing. This would also be desirable when crossing signals and even gates are present at active crossings because, even if the signal indicates that a train is in the vicinity, drivers may cross if they do not see the train. Minimum lines of sight have been suggested based on the speeds of the road vehicles and trains (USDOT, 1978). These lines of sight must take account of obstructions such as buildings and vegetation, although the actual lines of sight may be further impeded by parked vehicles on the road and train cars in sidings and adjacent tracks. When minimum lines of sight cannot be achieved because of fixed structures or the road or track
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alignment, or if the amount of road and train traffic exceeds some adopted criterion, active warnings must be employed to alert drivers to trains. These normally consist of flashing red signal lamps mounted at the side of the road before the tracks and sometimes on overhead gantries. Newer lamps produce about 3000 cd toward oncoming drivers. Most recently, conventional tungsten filament lamps are being replaced with lightemitting diodes, which offer greater reliability and resistance to vandalism. Although the signal lamps are usually easy to detect at night, depending on the other lights and their background, they are sometimes difficult to detect in daytime, especially when the sun is at a low angle behind the lamp, causing glare, or when it illuminates the lamp directly and dilutes the signal (Mortimer, 1991). Locomotives have lighting equipment in the form of headlights and sometimes ditch lights; those used in suburban service in the U.S. sometimes also have a strobe lamp above the cab. One or two headlights are mounted high up on the centerline of the locomotive and are aimed straight ahead to illuminate the tracks. The lower of the two headlamps may oscillate up to 30° to either side on older locomotives. The central intensity of these lamps is about 200,000 cd, with the major intensities concentrated in a narrow beam of about 10°. The ditch lamps—one on each side, mounted low—are aimed to the sides by up to 45°. A purpose of these lamps is to provide a stronger light signal to motorists approaching the tracks who may be out of the beam of the main headlamps. However, the triangular pattern of the main headlamps and the ditch lamps should aid drivers in assessing the distance and speed of the train if all three are visible. Auditory Factors The primary auditory signal to warn of the approach of a train is its horn. The Federal Railroad Administration requires the horn to have a minimum intensity of 96 dB at 100 ft (30 m). Many train horns provide about 115 dB. Because the intensity of the horn is attenuated by about 6 dB for each doubling of the distance, the horn may provide about 91 dB at 488 m. Although that is a good signal strength for a pedestrian or bicyclist, it is inadequate for the driver of a closed car because of the 20- to 30-dB reduction in intensity of the sound inside the vehicle. When the train is about 183 m distant, the horn may be detectable inside a quiet car, but that allows only about 6 sec before the arrival of a 113km/h train. Locomotives also operate a bell when approaching crossings, stations, or work crews on the tracks. The bell provides 70 to 80 dB (at 30 m) and is a relatively weak signal. There are also bells at crossings that have active signals with or without gates. They have an intensity of about 65 dB (at 30 m) and are intended to warn pedestrians or cyclists and can be a warning to drivers if a window of the vehicle is open (Mortimer, 1994). The audibility of these warning signals is affected by any hearing loss of the observer; such losses usually start beyond about 30 years of age and, by age 50, may be about 5 dB in the frequency range of 500 to 1000 Hz. Train horns have fundamental frequencies in the 300- to 600-Hz range. Using the low end of the sound spectrum ensures that the sound of the horn will travel a maximum distance. The ability to hear the train horn will also be affected by the frequency composition and intensity of the sounds surrounding the observer. Masking of the horn in a vehicle can be due to the radio, speech, wind, and engine and road noises. Low-frequency sounds can mask those of higher frequency but
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they have little effect on those of lesser frequency. In general, an auditory signal such as a train horn or the siren of an emergency vehicle needs to be about 10 dB more intense than the sound level in the vehicle to be reasonably detectable. To ensure that train horns are detectable, drivers should open the windows of the vehicle when approaching a crossing; otherwise, auditory signals are not much of an advance warning of a train. Other Factors Affecting Driver and Pedestrian Behavior at Railroad Crossings The lines of sight along the tracks available to a driver determine maximum potential visibility. Actual visibility is affected by vertical and horizontal alignment of the road and tracks, ambient lighting, weather factors, artificial lighting, other light sources that can be distractions or mask the crossing’s or locomotive’s signals, color of locomotives and trains, and the background against which they are seen. The behavior of drivers approaching crossings has been studied and indications are that drivers often fail to scan the tracks for trains or look in one direction only, sometimes ignore crossing signals, and have a low expectation that a train may be approaching. Drivers are at particular risk at crossings with more than one track. After waiting for a train to pass through the crossing, drivers have pulled onto the tracks while the warning signals are still activated only to be hit by another train, usually moving in the opposite direction. Signals that warn that more than one train is approaching and show the direction of the train are in use in some European locations and provide important information. Passengers and pedestrians are also at risk when crossing tracks at road crossings or in stations because they misjudge the speed of trains. Passengers in stations have been known to assume that a train approaching the station is stopping. They walk across the tracks to reach another platform only to find, too late, that the train is an express that is not stopping at that station. For this reason, signals are in place at some stations that warn passengers of the approach of a train and alert them not to cross the tracks. The Law and Visibility The Uniform Vehicle Codes of most states in the U.S. have statements concerning the visibility of marker lamps at night, signal lamps in the daytime, and the ability of high and low beams of headlamps to reveal persons and vehicles at certain distances (Chapter 316, sections 237, 238, etc.). For example, the Georgia vehicle code states that the turn signals of vehicles more than 80 in. (203 cm) wide should be visible in normal sunlight at 500 ft (152 m) to the front and rear. It also states that the high-beam headlight should reveal persons and vehicles at 450 ft (137 m) and on low beam at 150 ft (46 m); the low beam “shall be deemed to avoid glare at all times regardless of road contour and loading.” Can the law dictate nighttime visibility? Obviously it cannot. Visibility depends on many factors such as those already discussed. Pedestrians and other low-reflectance objects are often not detectable at the distances specified and there is some exposure to and effect of glare whenever vehicles oppose each other at night, especially on curves and hills.
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These statements in the vehicle codes are used to support legal arguments that an object should have been detectable at such distances, thus possibly allowing time for a driver to take avoidance action. In that case, the human factors expert must be able to explain the factors that affect visibility that may dispute the codes. An additional attack can come in the form of the “assured clear distance ahead” rule, which holds the driver responsible for ensuring that a speed is maintained that allows obstacles to be seen and avoided. Inherent in that rule is the assumption that drivers are aware of available visibility of hypothetical objects. However, it has been repeatedly demonstrated that drivers routinely “overdrive” their headlights. Drivers tend to base the maximum speed they drive upon the ability to control the vehicle on the road, which is a very different task from being able to see all manner of objects in time to avoid them. The preview distance required for tracking the road lane can be as short as 1 sec of travel time, but that is quite inadequate to avoid an obstacle. At 2 sec of preview distance at 97 km/h, drivers feel quite comfortable in lane tracking, having about 53 m of road in view, but they would not be able to stop before an object that is detectable at that distance. The incongruence between the road-tracking task and the object-detection task is ignored in the assured clear distance ahead rule, which fails to acknowledge normal driver behavior. Suggestions for alleviation of some of these problems have been made by Liebowitz et al. (1998), who have indicated that responsibility for avoiding obscure hazards at night should not rest solely on the driver but also on other road users. Drivers should be educated about their limitations in night driving, make more use of the high beams, and reduce speeds, and other road users should take measures to enhance their own visibility, such as use of retroreflective materials and lighting. 13.4 Pedestrian and Bicycle Crashes The human factors analysis of pedestrian and bicycle collisions with motor vehicles, although similar in many ways to the assessment of vehicle-to-vehicle crashes, differs in at least two important aspects. One difference is that the characteristics of pedestrian and bicycle crashes have been documented in great detail, and excellent taxonomies of crash types exist for both. The existence of crash types provides a normative standard against which to compare the circumstances of any crash analyzed. Once an analyst has concluded that a pedestrian or bicycle crash fits a known type, missing details can often be inferred from knowledge of the modal values associated with the specific type. This is fortunate because the other difference is that police crash reports on pedestrian and bicycle crashes tend to be less complete and insightful than those for crashes involving only motor vehicles. This is not due to any dereliction of duty on the part of the investigating officers. Rather, it is an outgrowth of the lack of in-depth training in the investigation of pedestrian and bicycle crashes that is given to police officers. In light of the foregoing, an understanding of the etiology of pedestrian and bicycle crash types and the limitations of the police crash report (PCR) is essential to the successful human factors analysis of these events.
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Crash Types Pedestrian and bicycle crashes have likely been studied for as long as there has been an interest in traffic safety. However, knowledge of the causes of these crashes took a quantum jump in the 1970s with the publication of studies by Snyder and Knoblauch (1971) and Cross and Fisher (1977) that identified specific crash types and their main causal factors for pedestrians and bicyclists, respectively. A taxonomy of crash types is a useful analytical tool in the assessment of pedestrian or bicycle crashes. The development of effective countermeasures to crashes is assisted by the ability to disaggregate these collisions into occurrences with similar causal elements, including human factors. In addition to aiding countermeasure development, the existence of crash types can also be a useful tool in the analysis of individual crash events, whether for forensic or research purposes. We rarely have a complete picture of a crash even when specialists have investigated it. Reliable, trained eyewitnesses are present at few crashes. Crash scenes are often disturbed before investigators arrive, frequently as part of
FIGURE 13.5 Function/event sequence as defined by Snyder and Knoblauch. (Snyder, M.H. and Knoblauch, R.L., 1971. Operations Research, Inc., final report U.S. Department of Transportation, National Highway Traffic Safety Administration, report no. DOT HS800 403.) the efforts to render assistance to victims. These and other factors produce gaps in the information available about the causes of the collision. Estimating what may have occurred in the absence of concrete information is greatly facilitated when a crash closely fits one of the predefined and well-researched crash types. This author has successfully argued as an expert witness for the most likely sequence of events in a crash at issue
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based on a good fit of that crash’s circumstances to one of the defined pedestrian or bicycle crash types. The Function/Event Sequence In order to develop their pedestrian crash types, Snyder and Knoblauch (1971) defined a model of how crashes are generated. The model (shown in Figure 13.5) consists of the following sequence of functions or events that drivers and pedestrians perform in the traffic environment: • Search—scanning the environment for threats • Detection—determining that something is there • Evaluation—assessing whether the detected object is a potential threat • Decision—determining what to do to avoid a collision • Action—executing the selected avoidance maneuver (human and/or vehicle as appropriate) The sequence begins when the driver and pedestrian or bicyclist commence a collision course, thus making a crash inevitable unless some avoidance is taken. If either party to a potential crash performs the sequence successfully, the crash is avoided. Thus, by definition, both parties must suffer a failure of their portion of the sequence for a crash to occur. Cross and Fisher (1977) adopted a virtually identical model in their work to define bicycle crash types. It is also important to note in Figure 13.5 that this sequence is a dependent sequential process. When a participant fails to complete a function successfully (a “no” exit from any of the functions in Figure 13.5), all subsequent functions must also fail. For example, if a motorist fails to detect a bicyclist, the motorist cannot properly perform evaluation, decision, and action. In this example, avoidance of a crash will therefore depend solely on the successful performance of the sequence by the bicyclist. Precipitating Factors The functions in the sequence are generic activities. For example, “search” is actually the process of information gathering and can be accomplished through visual, auditory, or tactile cues. Detection can mean actually seeing the threat or successfully receiving a warning from an artificial detection system such as a radar collision warning device. As part of the process of defining specific crash types, it is necessary to describe how each function failure occurred. For example, a search for threats may never have been performed or the search undertaken may have been inadequate, e.g., because it was made only in one direction. Snyder and Knoblauch (1971) called these descriptions of the function failures precipitating factors. The primary precipitating factor for each party was the one that occurred earliest in the function/event sequence and made completion of the sequence impossible.
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FIGURE 13.6 Depiction of the backing pedestrian crash type. Defining Crash Types By examining recurring clusters of precipitating factors, Snyder and Knoblauch (1971) and Cross and Fisher (1977) were able to define specific crash types for pedestrian and bicycle crashes with motor vehicles, respectively. Because precipitating factors can be viewed as behavioral errors, whether willful or unintended, the resulting crash type taxonomy is a valuable human factors tool. It is interesting to note that none of the defined crash types for pedestrians or bicyclists is based on the crash-involved population, although some groups, e.g., children and the elderly, are over-represented in certain types of events. Some crash types are characterized by the particular action or maneuver taken by one of the parties. The “backing” type for pedestrians depicted in Figure 13.6 is an example. In this type, the motorist embarks upon a maneuver (backing up), on the street or in a parking lot, that has significant task demands and makes it difficult to conduct a successful search for a pedestrian. The roof pillars of the car may block rearward vision, thereby preventing detection even though a search is performed. Alternatively, the driver may back up without ever scanning for pedestrian threats. The pedestrian in this crash type typically fails to search for a driver in the backing vehicle or assumes that he or she has been seen and that the driver will yield. Other crash types represent combined clusters of location and a particular precipitating factor. The “dartout” type for pedestrians and the analogous “midblock rideout” involving bicyclists occur at non-intersection locations and are precipitated by the pedestrian or bicyclist presenting a short time exposure to the motorist. The driver cannot complete the function/event sequence successfully because time is too short once the pedestrian or bicyclist becomes a threat. The short time exposure can be generated because the victim was running or came out between parked cars that thwarted an effective search, as shown in the depictions in Figure 13.7. It can also occur when a
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pedestrian or bicyclist on a sidewalk and apparently not in the act of entering the street (e.g., a pedestrian with back to traffic) makes a sudden movement into the roadway. This action invalidates the motorist’s evaluation that the pedestrian or bicyclist is not a threat, but leaves inadequate time for the successful completion of the function/event sequence.
FIGURE 13.7 Depictions of the dartout pedestrian crash type and the midblock rideout bicycle crash type . A third group of crash types is characterized by unique but not necessarily infrequent circumstances. For example, Snyder and Knoblauch (1971) identified a type involving ice cream trucks. As shown in Figure 13.8, the typical situation in this “ice cream/vendor truck-related” type involves a young child leaving an ice cream truck after making a purchase and crossing in front of the truck. The child is concentrating on the ice cream and fails to search. The large truck screens the child from view, thereby preventing the motorist from detecting the child. This is a special variant of the dartout type discussed
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previously. The important difference is that the involvement of the ice cream vending vehicle provides a focus for countermeasures in addition to efforts to instill correct behaviors in the pedestrian (stop at the edge of the ice cream truck and look left-right-left for oncoming traffic) and driver (slow down, stop if necessary, and search under and in front of the truck). Snyder and Knoblauch (1971) only examined urban pedestrian crashes, whereas Cross and Fisher (1977) included suburban and rural collisions in their study. Additional research by Knoblauch (1977) and Knoblauch and colleagues (1976) augmented the pedestrian crash types with a few additional entries based on crashes occurring in suburban and rural areas and on freeways. The pedestrian and bicycle taxonomies were reexamined by Hunter et al. (1996) to see if they had changed markedly in the almost 20 years since their development. The conclusion was that the basic classification continued to be valid, although some small shifts had taken place in frequency of occurrence and involved populations. Also, some new subtypes were evident, mostly as a result of emerging societal trends, e.g., the use of in-line skates in the roadway.
FIGURE 13.8 Schematic depiction of the ice cream/vendor truck-related pedestrian crash type. The proved utility of crash types in analyzing crash problems, developing countermeasures, and evaluating interventions led to the development of a computer program to assist in the process. This software, entitled Pedestrian and Bicycle Crash Analysis Tool (PBCAT), is readily available and is gaining widespread use (Harkey et al., 1999). PBCAT is particularly helpful to a community in analyzing the nature of its pedestrian and bicycle crash problems. It can also assist in the investigation of a specific crash occurrence by helping the analyst determine the crash type rapidly and accurately. In turn, knowing the crash type provides a wealth of information to guide a more in-depth examination for causes and fault.
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Predisposing Factors From the foregoing, it is clear that crashes result when a pedestrian or bicyclist and the striking motorist fail to complete the function/event sequence successfully. The fact that these failures result in specific crash types that appear quite universal and recurring is of interest and can help to estimate missing crash details. However, when a particular collision is investigated in order to assign blame or as a guide to remedial actions, crash types and their associated precipitating factors are not sufficient. We need to know why each party failed. Why did that driver and pedestrian or bicyclist collide at that moment when tens, hundreds, or thousands of others under the same circumstances did not? The needed information concerns the predisposing factors for the crash—those situations or conditions that made the errors by the parties in the crash inevitable or at least highly likely. Predisposing factors can arise from the vehicle, the environment, or the condition/state of the involved humans. Few vehicle factors predispose pedestrian and bicycle crashes. In the example of the backing crash type discussed earlier, an extra wide roof pillar or a vehicle designed with poor rear visibility could predispose a detection failure on the part of a driver. A bicycle with a wobbly front wheel might prompt the bicyclist to look down when entering the roadway, thereby predisposing a search failure that could lead to a rideout bicycle crash. Overall, however, the vehicle, whether motor vehicle or bicycle, is not a major cause of pedestrian and bicycle crashes. The environment, on the other hand, predisposes many pedestrian and bicycle crashes. Poor roadway design, road surfaces in disrepair, and, particularly, visual screens are all frequent contributors to crashes. Safety researchers have long known that a visual screen is a major predisposing factor to pedestrian and bicycle crashes. When a driver and pedestrian or bicyclist have their views of each other fully or partially obstructed, detection becomes difficult or impossible even when search is attempted, thereby making a crash more likely. The dartout and rideout types discussed earlier as well as the ice cream/vendor truck-related involve a visual screen. A commercial bus at a bus stop can produce the same dynamics if a pedestrian crosses in front of it. Hedges, road signs, and street furniture are other examples of visual screens that can predispose pedestrian and bicycle crashes. It is worth noting that visual screens do not need to be complete or stationary to predispose a crash. Even when significant portions of a pedestrian can be seen, the interruption of the anthropomorphic shape cue presented to a driver can lead to inconspicuity or improper evaluations after the driver detects something. Research has clearly indicated that the perception of a human-like image greatly enhances the recognition of pedestrians at night (Blomberg et al., 1981). The state or condition of the humans involved in the crash can be a strong predisposing factor. Section 13.6 of this chapter presents significant detail on the effects of alcohol and drugs on human performance. It is well known that impaired drivers run a greatly increased crash risk. It is perhaps less well accepted that pedestrians’ and bicyclists’ use of impairing substances, particularly high doses of alcohol, can also predispose their crash involvement. For example, the relative risk of a pedestrian crash as a function of blood alcohol concentration (BAC) increases according to a function that is almost the same shape as that for motor vehicle drivers except at a higher BAC (Blomberg et al., 1979). This is intuitively reasonable because walking is a less complex
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task than driving. Although no definitive study has been conducted, evidence also exists that the use of impairing substances by bicyclists can be a significant causal factor in their crashes. Other human conditions and circumstances that can predispose crashes include fatigue, anger, inexperience, reduced visual acuity, and impaired hearing. In addition, a host of pathological conditions ranging from a simple cold to more serious illnesses can interfere with psychomotor performance. Decisions made prior to entering the function/event sequence can also have a profound effect on crash likelihood and therefore must be considered as predisposing factors. The most obvious of these are the speed at which a person chooses to drive, ride, or walk and the route chosen for the trip. With respect to speed, for example, consider a motorist speeding at 50 mph in a 25-mph neighborhood. Everything happens twice as fast for that individual. Thus, when the vehicle is on a collision path with a pedestrian or bicyclist and the function/event sequence begins, that speeding driver has half as much time to execute the functions as would a motorist traveling at the speed limit. The choice of the route to travel can also profoundly affect the likelihood of completing the function/ event sequence successfully and thereby avoiding a crash. Consider, for example, a pedestrian who chooses a route without sidewalks and street lighting at night when an alternative path that is lighted and has a sidewalk is available. That pedestrian is greatly increasing his or her workload in performing the function/ event sequence as well as the task of any motorists encountered. Conspicuity Search and detection are the first two functions in the function/event sequence. Obviously, if a driver fails to search for pedestrians and bicyclists or vice versa, the sequence will fail and a crash will become more likely. Even when a potentially effective search is performed, however, detection may fail if the threat is not conspicuous. Unlike visibility, which is the physical property of an object being viewed, conspicuity deals with the properties of the target and the characteristics of the viewer. Humans tend to exclude things for which they are not looking and be more attuned to detecting things they are expecting or actively seeking. Conspicuity is dealt with here in some detail because it is a major predisposing factor to pedestrian and bicycle crashes and, thus, must be an integral part of the human factors assessment of these crashes. Conspicuity can be simply defined as the attention-getting value of a particular object to a specific viewer. A conspicuous object is one with a high likelihood of being noticed by a viewer even if the viewer is not specifically searching for it. Conspicuity is, in essence, the opposite of camouflage. The objective of camouflage is to reduce the chance that a viewer will detect the treated item. The goal of conspicuity enhancement is to maximize the chance that the particular item will be noticed. Conspicuity is not the same as visibility, although visibility is a necessary condition for conspicuity. An object is visible if it emits sufficient light energy to stimulate a viewer’s eyes (i.e., is above the visual threshold). That object becomes conspicuous if a viewer notices it. For example, a white bed sheet against a snow bank in daylight is highly visible but likely not conspicuous. A black sheet under the same viewing circumstances will emit less light energy but be much more conspicuous because of its contrast with the background.
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Different colors and varying levels of brightness are two ways to generate contrast and improve conspicuity. Three types of inconspicuity are potentially relevant to pedestrian and bicycle crashes (Blomberg et al, 1984): • Type I—subthreshold targets. When the object in question is at or below the visual threshold for detection by a human, conspicuity is almost impossible and safety will be compromised. A countermeasure to a subthreshold situation would be to increase the level of visual signal that the item produces, e.g., by adding a light to it. For example, a pedestrian carrying a flashlight or a bicycle equipped with a flashing light at night becomes considerably easier to see because the active light source adds visibility. • Type II—suprathreshold targets not seen. When a pedestrian or bicyclist is above the visual threshold but is still not detected, a camouflage or inconspicuity situation exists. This can occur, for example, when the color of a pedestrian’s clothing does not create sufficient contrast with the environment or because a bicyclist is in an unusual or unexpected location, e.g., riding against traffic. Typical physical countermeasures for this type of inconspicuity involve wearing clothing of a strikingly different color from the surrounding environment or treating clothes or the bicycle with high-visibility materials (fluorescent for daytime, dawn, and dusk or retroreflective for night-time). Fire engines are painted bright red or fluorescent lime green to avoid this type of inconspicuity. Behavioral approaches such as promoting bicycling on the right side of the road with the flow of traffic can also help. • Type III—concealed targets. Conspicuity can be compromised by a visual screen that blocks an otherwise potentially detectable object from view. Hedges, mailboxes, or parked cars, as in the dartout and rideout crash types, are common visual screens. Removing the visual screen can cure this type of inconspicuity as can increasing the apparent size of the pedestrian or bicyclist through the attachment of a flag or other extension that can be seen above or around the visual screen. The Police Crash Report The foregoing structure for the categorization and analysis of pedestrian and bicycle crashes is extremely helpful in understanding root crash causes and in guiding an analyst’s search for the specific predisposing factors of any particular crash. Unfortunately, police crash reports (PCRs) are not typically formatted to collect the type of information needed to reach a confident pedestrian or bicycle crash type decision. This is particularly true of the computerized crash archives maintained by all states and some local jurisdictions. For example, information on the presence of visual screens such as ice cream trucks, commercial buses, and hedges is not systematically captured. This pertinent information may appear in the investigating officer’s narrative or on a crash diagram, but these PCR elements are typically not digitized and stored in crash archives. Anyone who has worked with police reports knows that their quality and comprehensiveness varies from extremely sketchy to moderately extensive. They generally focus on describing what happened and determining legal fault rather than assessing the true causal elements of the crash. This is not intended as a criticism of police crash reporting. In an era of reduced budgets and under the pressures of a litigious
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society, police officers do the best they can. It just is not usually enough to uncover fully the relevant human factors issues in a particular crash. Part of the problem can certainly be traced to the minimal (often nonexistent) training that police officers receive in pedestrian and bicycle crash causation. A better understanding of pedestrian and bicycle crash types almost surely would result in more insightful narratives and diagrams on the police report, if time pressures did not prevent the officer from examining and recording the additional factors. The major area that needs attention to improve the situation for the human factors analyst relates to predisposing factors. Detailed predisposing factor information is rarely available on a police report. This may be because the report was not prepared at the scene, because the investigating officer did not have enough time to examine the scene thoroughly, or simply because the officer was not sufficiently sensitive to the importance of the information. In spite of any of their shortcomings, police reports are usually a primary source document for any human factors investigation or reconstruction of a pedestrian or bicycle crash. It is therefore important to understand the strengths and limitations of these documents. It is this author’s judgment from reviewing thousands of pedestrian and bicycle police reports that superior report quality is associated with careful completion of all preceded information, inclusion of a detailed narrative describing the extent of the investigation and pertinent particulars of the crash generation sequence, and provision of a scene diagram with relevant details and little or no extraneous elements. A good police report can be an invaluable aid to the human factors analysis of a crash. On the other hand, a poor PCR can render some information irretrievable and/or necessitate significant additional data gathering in order to determine what happened. Fundamentals of Pedestrian and Bicycle Crash Analysis Crash types, precipitating factors, and predisposing factors provide an ideal human factors framework in which to analyze pedestrian and bicycle crashes. Many such analyses are conducted in the context of a legal action. Therefore, before turning to the specific analytical steps, it is important to understand the basic distinction between a legal and a causal analysis. Legal and Causal Analyses The vehicle and traffic law (VTL) in all states and many municipalities prescribes and proscribes behaviors for drivers, pedestrians, and bicyclists. For example, pedestrians must walk facing traffic while motorists and bicyclists must drive with the flow of traffic, and pedestrians must not leave a place of safety and move suddenly into the path of a vehicle that is so close as to preclude the driver from taking appropriate evasive action (i.e., successfully completing the function/event sequence). Law enforcement officers and attorneys involved in litigation arising from a crash are often most concerned with violations of the VTL that occurred as part of a pedestrian or bicycle crash sequence. That is their job. It is important to realize, however, that a violation of the VTL per se is not necessarily a causal factor in the crash. It may not even be a predisposing factor at all. Assume a crash in which a pedestrian is crossing in a
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crosswalk at an unsignalized location on a street with two or more lanes in each direction. A car in an inside lane (near the sidewalk) stops to yield to the pedestrian as required by the VTL in almost all jurisdictions. A car in the center (far) lane overtakes the stopped car and strikes the pedestrian. The driver of the striking vehicle never sees the pedestrian because he is screened from view by the car that stopped to yield to him. This common crash type, known as a “multiple threat,” is depicted in Figure 13.9. With respect to the VTL, the pedestrian and the car that stops for him in the multiple threat example shown in Figure 13.9 have not committed a violation. The striking driver has violated a widely held VTL provision modeled after Section 11–502(d) of the Uniform Vehicle Code, which says that “whenever any vehicle is stopped at a marked crosswalk or at any unmarked crosswalk at an intersection to permit a pedestrian to cross the roadway, the driver of any other vehicle approaching from the rear shall not overtake and pass such stopped vehicle” (National Committee on Uniform Traffic Laws and Ordinances, 2000). In an actual crash of this type, the striking driver would likely receive a citation for this violation. A causal analysis of this same situation in accordance with the function/event sequence described earlier yields a different picture. The multiple threat crash occurs because the pedestrian and the striking driver suffer a detection failure predisposed by the presence of the visual screen generated by the car that stopped to yield to the pedestrian. The striking driver cannot execute his or her duty to stop for a vehicle that is stopped to permit a pedestrian to cross because the critical presence of the pedestrian cannot be determined due to the visual screen. The pedestrian can avoid the crash by stopping at the edge of the stopped car and executing an effective search for overtaking traffic. This would also place the pedestrian in a stationary position in which he is protected by the stopped car and can be seen by the overtaking driver.
FIGURE 13.9 Depiction of the multiple threat pedestrian crash type. The multiple threat crash type is just one example of pedestrian and bicycle crashes in which violations of the VTL and human factors causes of the event are different. When
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analyzing these crashes, therefore, it is important not to rush to a judgment on causation based on apparent law violations or citations issued. Steps in the Analytical Process The function/event sequence, defined crash types, and associated predisposing factors can be used to structure a systematic process for the human factors analysis of pedestrian and bicycle crashes with motor vehicles. The recommended steps are detailed below. 1. Determine as much factual information about the crash as possible. The police crash report is a good starting point for the basic data such as date, time, location, involved parties, and vehicle types. The narrative and diagram of the PCR should be examined and assessed in the context of the type of examination undertaken by the investigating officer. Crashes with more serious outcomes are typically investigated more thoroughly and will therefore produce more useful PCR data. Routine on-scene investigations produce somewhat less information. PCRs completed at the station house or mailed in by the involved parties are often incomplete and inaccurate. 2. Determine the likely crash type from the PCR information. The PBCAT software discussed earlier can provide assistance in determining the crash type from particulars that can be found on the PCR. If the circumstances can fit more than one type, prepare a list of the alternatives and the additional data needed to select among them. Knowing the crash type accomplishes several important things. First, it serves as a guide to the types of precipitating and predisposing factors that might have played a role in the crash. Second, it provides modal or most likely values for behaviors that are not specifically known from the available data. 3. Run through the function/event sequence for each involved party and enumerate possible failure points. This will help provide an understanding concerning why the crash occurred (actually, why the crash was not avoided). 4. Enumerate potential predisposing factors for each of the possible function/event sequence failures. This list will be an important guide for data gathering. It can be used to: structure observations at the crash scene, interviews or depositions with involved parties, witnesses, and the investigating officer, and any manual or computerized reconstructions attempted. When examining predisposing factors, pay particular attention to factors such as conspicuity and visual screens, which can influence or interfere with search and detection, because they are fundamental to safety. Do not forget to consider environmental and temporal conditions such as the position of the sun and any resulting glare and weather. Be sure to determine if any post-crash changes may have taken place at the crash scene. 5. Gather as much data as possible. A thorough human factors pedestrian or bicycle crash analysis typically requires a visit to the crash scene, preferably under weather and light conditions similar to those at the time of the crash. Look for visual screens or visual clutter that might have prevented detection even if all involved had searched. It is important to examine the scene from the perspectives of all involved parties. Try to look through their eyes and determine what they may have been seeing and doing as they proceeded through the function/event sequence. Access immediate post-crash medical treatment records for involved parties to look for possible impairing substance use or pathology that might have resulted in a participant’s reduced ability to perform.
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Examine the roadway to see if its condition may have diverted the attention of one or both parties. For example, a broken or excessively high curb may prompt a pedestrian, particularly a senior citizen, to look down to avoid tripping and thus interrupt an adequate search for cars. Look at the striking vehicle in person or in police photos to determine if its design (e.g., extra wide roof pillars) or condition (e.g., dirty windshield) may have interfered with detection. If necessary, find an exemplar that matches the striking vehicle and examine it. Interview the participants (or request that specific questions be asked in depositions) to inquire how they handled each function in the sequence, including whether they attempted a search, what factors may have prevented detection, and so forth. 6. Match the data with the postulated crash types and information on predisposing factors to update the initial assumptions on how each party failed in performing the function/event sequence. Collect additional data as required. This will provide the most complete picture possible of the crash from a human factors perspective. Using the Results The types of analytical processes presented previously have three primary uses: research and development, countermeasure application, and litigation. The same basic approach applies to all three. An example from the author’s experience based on the ice cream/vendor truck-related pedestrian crash type can further illustrate how effective this approach can be. The ice cream/vendor truck-related crash type was initially identified by Snyder and Knoblauch (1971). Using a function/event sequence analysis as part of a research project, Blomberg and colleagues (1974) developed the Model Ice Cream Truck Ordinance (MICTO). Based on the analysis of a large number of ice cream/vendor truck-related crashes, the MICTO required ice cream vendors to install and use flashing lights and a stop swing arm similar to the ones on a school bus. Drivers coming upon an ice cream truck with its lights and swing arm in operation were required to stop, proceed with caution, and yield to any pedestrian going to or from the truck. The MICTO also restricted vending to those streets on which it did not present an unreasonable hazard and dictated other appropriate safety practices such as prohibiting backing the vehicle to make a sale or selling to a pedestrian standing in the roadway. In a subsequent countermeasure application effort, the city of Detroit passed the MICTO. Using the function/event sequence as a guide, Hale and colleagues (1978) evaluated the Detroit implementation and documented a 77% crash reduction in the ice cream/vendor truck-related crash type that was attributable to the new ordinance. More recently, this author has been involved as an expert witness in several lawsuits arising from ice cream/vendor truck-related crashes. Although the circumstances of each case varied, the function/event-based analytical approach proved effective in documenting the underlying causes of all the crashes and in providing a compelling picture to the jury and the litigants As with any analytic technique, the human factors analysis of pedestrian and bicycle crashes is only as good as the available data. Detailed physical evidence and reliable participant and witness statements cannot always be obtained. Even in the absence of complete information, however, the availability of a well-documented taxonomy of crash
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types for pedestrian and bicycle crashes with motor vehicles, together with the underlying function/event sequence model, is an invaluable aid that should be more widely employed. An Example An example of an actual crash analysis using the approach just outlined will help illustrate the benefits of viewing crashes in terms of a human factors model. The particular crash used in the demonstration
FIGURE 13.10 A replica of the actual crash diagram for the example pedestrian crash. is an actual crash selected because it is simple and fits one of the types discussed earlier. This crash was analyzed by the author as part of a research study, but it will be assumed here that it is of interest in a forensic setting from the perspective of a plaintiff’s attorney. The crash involved a 6-year-old pedestrian struck while crossing the street, not at an intersection, in mid-May at approximately 5:00 p.m. It occurred in full daylight on a residential street. The striking vehicle was a passenger car. Neither the driver of the striking vehicle nor the pedestrian victim was cited for a code violation by the
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investigating officer. A replica of the actual diagram drawn by the police officer at the scene is shown in Figure 13.10. A review of the diagram shows that the child crossed in front of a stopped vehicle that likely produced a visual screen. The striking driver overtook the screening vehicle and struck the child as his car cleared the front of the screening vehicle. This diagram and the age of the victim suggest a classic dartout situation in which the screening vehicle predisposes the crash by allowing only a short time exposure of the child to the striking driver. It might also fit a multiple threat crash type even though the pedestrian was not in a crosswalk. If the stopped vehicle had halted to yield to the pedestrian in spite of no legal requirement to do so, the collision by an overtaking vehicle would have constituted a multiple threat. In either case, the focus for liability would rest wholly or substantially on the striking driver. In reality, the crash situation was somewhat different, as indicated by the police officer’s narrative shown in Figure 13.11. The narrative indicates that the stopped vehicle was, in fact, an ice cream truck and the crash type is therefore ice cream/vendor truck related. This is of more than academic interest to a plaintiff’s attorney. The extensive research on this crash type has raised the standard of care in the industry as well as spawning implementations of the MICTO. Ice cream vending companies are generally well aware of this crash type and the steps they can take to prevent it. Given that the ice cream truck predisposed this crash, it would behoove a plaintiff’s attorney to examine factors such as the training of the truck driver and the safety equipment installed on the vehicle when creating a theory of liability and planning discovery.
FIGURE 13.11 Actual officer’s narrative for the example crash. Note also that the narrative indicates that the officer believes the pedestrian is at fault even though no citation was issued. Although the pedestrian most likely did not search adequately for vehicular threats, this function/event sequence failure was greatly predisposed by the visual screen presented by the ice cream truck. This visual screen also predisposed the striking motorist’s detection failure. Overall, therefore, the ice cream truck’s visual screen was the major “cause” of this crash. This same example crash can illustrate the assistance possible from PBCAT in determining a crash type. PBCAT leads the user through a series of screens that request
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specific input on the circumstances of the crash and uses this information to determine a crash type. For this ice cream/vendor truck-related crash, the screens would proceed as follows:
FIGURE 13.12 Opening PBCAT screen.
FIGURE 13.13 PBCAT screen for entering type of location for the example crash.
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1. The user selects “pedestrian crashes” to start the typing process (Figure 13.12). 2. The user selects “crash typing” from among the tasks PBCAT can perform and enters database identifying information, e.g., report number (screens not shown). 3. The user begins to answer questions about precipitating and predisposing factors leading to a type decision. The first decision concerns where the crash occurred. For this example, “non-intersection location” would be selected from the screen shown in Figure 13.13. 4. The user is asked if the crash involved any unusual circumstances such as a deliberate assault with a motor vehicle. In this example, the user would select “none of the above.” The user is then asked if the crash involved any unique vehicle type or action, including a backing vehicle, driverless vehicle, disabled vehicle, emergency vehicle, or play vehicle. In the example, “none of the above” would be selected (screens not shown). 5. The user is then asked if the crash involved any unique pedestrian actions, one of which is “ice cream/vendor truck related” (Figure 13.14). 6. PBCAT pops up an overlay on the preceding screen that gives the crash type number and name and seeks confirmation from the user. The user then selects “OK,” the data are stored in the database, and the process is complete (Figure 13.15). This simple example shows only part of the power of a crash type analysis. By identifying what would otherwise appear to be another midblock crash involving a young pedestrian as a specific type, a litigant, researcher, or public safety official gains significant additional insights. These insights, in turn, can lead to better and more appropriately focused lawsuits, richer information on which to base countermeasure development and evaluation, and more effective societal responses to pedestrian crashes. 13.5 Positive Guidance Principles 1 Introduction Positive guidance means giving drivers the information they need to avoid hazards, when and where they need it, in a form in which they can best use it. Because positive guidance can be achieved only through 1
© Copyright by Positive Guidance Applications, Inc. Permission is expressly granted to Taylor & Francis for any use within its purview. Permission is further granted to quote excerpts with customary attribution. Permission to reproduce or republish any substantial portion of text must come from Mr. Alexander.
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FIGURE 13.14 PBCAT screen on which “ice cream/vendor truck related” is selected
FIGURE 13.15 PBCAT type number determination screen.
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the understanding and integration of human factors and highway engineering technologies, some basic human factors principles are included in this section. The materials here are drawn from Federal Highway Administration’s series on positive guidance (1975) (Post et al., 1977, 1981; Lunenfeld and Alexander, 1990) as well as materials developed by the author for the State of Maryland (undated) and the Province of Ontario (Alexander and Lunenfeld, 1998). In terms of driver behavior, optimum highway design is achieved when drivers know what to expect from the highway and their attention is naturally attracted to the most important sources of information, and they have adequate time to respond to conditions and situations as they arise. To attain this objective, it should be evident that all elements of highway planning, design, construction, maintenance, and operations consider expectancy and primacy. Definition and Concept Any information carrier, including the highway, that helps or directs drivers in making speed and/or path decisions, transmits guidance information. Positive guidance is provided when that information is presented unequivocally, unambiguously, and conspicuously enough to meet decision sight distance criteria and enhances the probability of drivers making appropriate speed and path decisions. Control, Guidance, and Navigation Levels of Performance Control refers to task performance related to a driver’s interaction with the vehicle; vehicles are controlled in terms of speed, path, and direction. Drivers exercise control through the steering wheel, accelerator, and brake. Information about how well drivers perform at the control level comes from the vehicle and its displays as well as visual observation of changes in speed, path, and direction. Drivers receive continual feedback through vehicle response to various control manipulations. Overt response to hazards is part of the control level of performance. Guidance refers to task performance related to a driver’s selection and maintenance of a safe speed and path. Control subtasks require action by the driver. Guidance requires decisions involving judgments, estimates, and predictions. The driver must evaluate the immediate environment and translate changes in alignment, grade, and traffic into control actions needed to stay in the appropriate lane at an appropriate speed for the prevailing conditions. Information at this level comes from the highway—its alignment and grade, geometric features, hazards, shoulders, etc.; from traffic—speed, relative position, gaps, headway, etc.; and traffic control devices—regulatory and warning signs, signals, and markings. Navigation refers to the activities involved in planning and executing a trip from origin to destination. Drivers generally evaluate route numbers and/or names, street names, interchange or intersection designations, cardinal directions, and landmarks. They make guidance-level decisions at choice points and ultimately translate those decisions into control actions. Offline information sources include maps, verbal directions, and prior experience. Online information input comes from the full range of guide signs, verbal directions, and landmarks. Through the implementation of intelligent
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transportation systems (ITSs), map information is increasingly presented online in the vehicle. (Noy, 1997; Barfield and Dingus, 1998). Task Complexity Information and task performance associated with the three levels of performance form a hierarchy of complexity. At control, the lowest level, information processing and vehicle handling are relatively simple and so completely overlearned by experienced drivers that they are performed almost without conscious thought. At the guidance and navigation levels, information handling is increasingly complex and demanding, and drivers need more processing time to make decisions and respond to information inputs. The need for more time frequently occurs in urban locations, at intersections and interchanges and where traffic demand is heavy. The nature and number of hazards and of the available information displays also affect task complexity. The scale of complexity increases from control through navigation. Primacy It should be evident that at any given location on the highway, some information is more important than other information. Primacy refers to the relative priority of each level of the driving task and of the information associated with a particular activity within each level. Here, too, is a hierarchical scale. The major criterion upon which primacy is assessed is the consequence of driver performance error. Because loss of vehicle control, the results of which can be catastrophic, is of the greatest immediate concern to the driver, the control level is assigned the highest level of importance. A guidance level failure also is assigned a high primacy because errors in speed and path selection frequently result in accidents (Haworth et al., 1997). In navigation, where errors usually result in delayed, lost, or confused motorists, the lowest priority is assigned. The scale of primacy decreases from control through navigation. Primacy is a most important consideration when information competes for drivers’ attention. If there is inadequate time to process all the information at one location, high primacy needs should be satisfied first and lower primacy needs should be deferred. Information should be placed so as to spread the information challenge at locations where critical driver decisions and/or actions are required. Information Handling While driving, drivers do many things simultaneously or nearly so. They monitor traffic, follow the road, stay in the lane, read signs, listen to the radio, and accelerate and decelerate their vehicles. At any given point in time, drivers may have several overlapping needs associated with each level of performance. To handle this array of needed and available information, drivers must search the environment for information sources, detect their presence, recognize their message, make decisions, and perform control actions safely and efficiently. Thus, information must be available when and where needed, and in a form best suited for driver comprehension. In situations in which information competes for drivers’ attention, unneeded and low-primacy information is
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shed. Errors can occur when drivers process less important information and miss or shed more important information. Perception Reaction Time PRT includes the components of information processing, detection, recognition, and decision making plus action initiation. It not only varies from individual to individual but also is a function of decision complexity, information content, and driver expectancy. The more complex the decision is or the more information is needed to make a decision, the more time it takes. Clearly, long PRTs reduce the time available to load shed, attend to other information sources, and respond to other task requirements, increasing the probability of error. Although 2.5 sec is the constant used for PRT in design and sight distance calculations (AASHTO, 1994), it is hardly a constant. Even for something as simple as brake-reaction time, there are substantial ranges in PRT, with the range of responses to unexpected signals higher than the range of responses to expected signals. (See also section titled “Response Time.”) Driver Expectancies and Surprises The nature of the driving task and drivers’ information-handling characteristics emphasize the importance of expectancies. Reaction to an unexpected event takes longer than when the event is expected (Johannson and Rumar, 1971). Conversely, drivers are less likely to become confused or commit errors when their expectancies are reinforced. Because the key to safe, efficient driving-task performance is rapid, error-free information handling, what drivers expect and do not expect has a major influence on task performance, particularly under time pressures and high task loading. Expectancy relates to a driver’s readiness to respond to conditions, situations, events, and information. It influences the speed and accuracy of information processing and is one of the more important driver-related characteristics in the design and operation of highways. Configurations, geometric features, traffic operations, and traffic control devices that meet or reinforce expectancies help drivers to respond quickly, efficiently, and without error. Roadway Design The configuration of a fully directional freeway-to-freeway interchange is a good example of an unusual design configuration that may contribute to driver expectancy problems. In a fully directional interchange, the exit to go left, i.e., the north-to-west, the east-to-north, the south-to-east, and the west-to-south movements, are all left exits. Because in conventional interchanges almost all exits are on the right, unfamiliar motorists expect to exit from the right lane of the freeway. Without conspicuous, specific advance notice, motorists unfamiliar with the road who want to exit to “go left” at the exit will move to the right lane. Here, motorists will miss their exit or perform an erratic late lane change to get to it. When the left-lane exit movement is also a lane drop, there is double expectancy violation. More drivers are affected, interactions in the traffic stream are more turbulent, and the potential for driver error is greater. Wherever this geometric
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design feature has been located, from Maryland to California, it is usually a source of operational problems. Conventional guide signs have been shown to be ineffective for left exits and left exit lane drops, and diagrammatic advance guide signs are recommended by the Manual on Uniform Traffic Control Devices (MUTCD) (Federal Highway Administration, 2000). At most freeway exits, motorists must move into a deceleration lane to exit the facility. It is therefore an expectancy violation when a lane that had been a through lane exits the facility directly. Instead of needing to change lanes to leave the freeway, motorists are required to change lanes to stay on the freeway. The black-on-yellow “EXIT ONLY” panel has the needed conspicuity when placed on the white-on-green guide sign to gain drivers’ attention. The uniform application of the panel at interchange lane drops serves to structure the appropriate expectancy. Freeway tangential exit ramps create expectancy problems for drivers. Interchange exits with this configuration are the scenes of many unintentional erratic maneuvers and other errors. Drivers find themselves leaving the freeway by going straight ahead on the tangent while the freeway curves to the left. The tangential off movement is thus an unexpected feature and one that creates perceptual problems whether the tangential exiting movement is at the beginning of the curve or within it. No traffic control device has yet been found that can adequately warn drivers about tangential exit ramps. Lacking superior sight distance, tangential exit ramps are best treated by configuring the diverge area so that the off movement does not appear as the continuation of the main roadway. The desired effect could be achieved if the diverge area could be relocated as little as 100 ft up- or downstream of the curve or the divergence angle were no longer tangent to the curve, so that drivers would be required to make a steering adjustment to exit. Rural two-lane road situations function similarly to the freeway tangential exit ramp. Off-road features, such as a line of trees or railroad tracks that run parallel and adjacent to the highway, create drivers’ expectancy that the condition will continue straight. A similar situation occurs where a tangent roadway intersects at the point of curve of a turning roadway. A common freeway design feature with the potential for violating expectancies is a variant of the interchange lane drop: the split or bifurcation. Two kinds of split surprise drivers: any split in which the off-route movement is to the left of the through-route movement, and the optional lane split. The optional lane split creates expectancy problems for many drivers. Because it is a lane drop, drivers in the exiting lanes are affected. Additionally, drivers in the optional lane do not expect to be faced with a lane choice by staying in lane. This situation can be described as a classical dilemma—the choice between equal alternatives. When drivers make a late choice—or worse, no choice—it is foreseeable that something undesirable will happen, such as an erratic maneuver, a gore crossover, a fixed object struck in the gore, or a truck jackknife. Any reduction in width of the road represents an expectancy violation and a hazard to drivers. Situations such as mainline lane drops, work zones, and narrow bridges are common sources of pavement width reduction. Although all are expectancy violations, narrow bridges are particularly difficult because of the many configurations they take, from those that are short box culverts to long bridges with trusses. Their narrowness
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ranges from loss of shoulder to narrowing of a lane width to a one-lane bridge that handles two-way traffic. Narrow bridges occur on curves (horizontal and vertical) and in sags beyond the crest vertical, making them hard to see. Thus, not only are they unexpected, but they may also be difficult to detect, recognize, and negotiate in the presence of oncoming traffic. Positive guidance treatments for a variety of narrow bridge configurations are contained in Appendix A of the “Yellow Book” (AASHTO, 1974). Traffic Control Devices Traffic control devices serve to structure expectancies about downstream features and operations. They also structure expectancies about information treatments at similar locations. The key to effective expectancy structuring is uniformity and standardization. Inconsistently applied standard devices create expectancy problems for drivers. If upstream curve warning signs underestimate maximum safe speed, drivers will expect similar underestimations for similar curves downstream. When a downstream curve is more realistically signed, drivers may be unprepared or unable to respond properly. Traffic control devices not only serve to structure expectancies but also tend to violate expectancies if they are misapplied, inconsistently applied, absent when needed, present when unneeded, and/or ambiguous. Traffic signals often violate expectancies. At many signalized intersections, motorists who are stopped for the red can see the signal display for the crossing roadway. This is particularly true at intersections where the roadways cross at something other than a 90° angle. From the stopped position, the lenses on the signal face for the crossing movement are frequently clearly visible. Invariably, a nonlocal driver at the head of the queue will move into the intersection when the crossroad signal changes from yellow to red, expecting to get the green; all too frequently, however, his signal indication does not get the green. Lagging greens, protected turning movements, pedestrian phases, and even clearance intervals surprise the unfamiliar motorist. Local drivers know the condition and stay put until the light changes to green. However, visibility of the crossing movement signal induces inappropriate behavior of those unfamiliar with the signal operation. Another example of an unexpected traffic signal indication is the mid-block signal. In most instances, drivers do not expect a traffic signal anywhere but at an intersection. When a mid-block signal is used, they will not be prepared without conspicuous advance warning and may not react in time or may hit the rear end of another vehicle stopped at or in advance of the crosswalk. Signs that provide information at the guidance level (regulatory and warning signs) as well as at the navigational level (guide signs) have the potential to structure and to violate driver expectancies. These expectancies are, of course, based on the driver’s experience. For example, drivers generally expect to be able to exceed the advisory speed safely when one is posted beneath a curve warning sign. Advisory speed warning plates are usually conservative when it comes to a safe speed under most conditions. On overhead guide signs, down arrows generally mean one needs to be in the specific lane to get to the signed destination, but not always. In some locations, the warning message requires special emphasis. Curves where the advisory speed should be adhered to, even in dry weather, and unexpected situations beyond a curve or vertical crest that would surprise drivers are two examples in which
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such special emphasis is justified, i.e., something that says, “This time we really mean it.” Special display treatments such as chevron alignment signs, oversize warning signs, and flashing beacons are used to good effect at such locations. For the sake of continued credibility of these special emphasis devices, however, their use should be reserved for locations in which gaining drivers’ attention is important. Key Considerations The development of appropriate highway designs and traffic control devices that meet driver expectancies or that tell drivers what to expect is the principal way to aid performance and enhance safety and efficiency on all highways. Attention should be given to assure consistent design from one segment of highway to another. When drivers get the information they expect from the highway and its information system, driver response tends to be rapid and error free. When drivers get what they do not expect or do not get what they do expect, longer response times, inappropriate responses, confusion, and errors are the predictable result. Key considerations about expectancies include: • Expectancies are associated with all levels of the driving task and all phases of the driving situation. • Drivers experience problems and commit errors when they are surprised. • Drivers anticipate upcoming situations and events that are common to the route they are driving. • The more predictable the design, information display, or traffic operation is, the less likely will be the chance for driver error. • In the absence of information to the contrary, drivers assume they will need to react only to standard (expected) situations. • The roadway, the information system, and the environment upstream will structure expectancies of downstream conditions. The objective in helping drivers overcome the effects of expectancy violation is to structure the appropriate expectation through advance warning. When it is not possible to give drivers what they expect, it is imperative to tell them what they should expect. Failures at the Guidance Level A guidance-level failure occurs when the driver chooses an inappropriate speed and/or path. The failure translates to improper, inadequate, or inappropriate control actions and does not imply driver fault. When an accident occurs because of wrong control action, it may be caused by certain inadequacies in relevant information available to the driver. Such inadequacies include too much information, too little information, ambiguity, conflicting information, improper location of information, and information not visible under ambient conditions. It is the function of positive guidance to enhance safe driver performance by providing appropriate, usable information that would reduce failures that are not caused by the driver. Two limitations to the potential effectiveness of positive guidance are important here. First, driver failures due to driver impairment are not necessarily amenable to correction by providing improved highway information. Drivers who are drunk, drugged, or drowsy
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or whose normal performance is otherwise impaired have problems that are not usually solved by better signs and markings, although exceptions to this generality do exist. An example is the use of wider lane edge lines to aid drivers impaired by alcohol at night. Second, certain highway design features exceed driver response capabilities. When the design complexity is such that drivers do not have enough time to make all the judgments required, no solution short of redesign will eliminate frequent accidents. Information at the Guidance Level At the guidance level of performance, drivers select and process information with the objective of selecting and maintaining a speed and path they consider safe, efficient, and comfortable. Roadway Environment Drivers gather considerable information from the roadway itself. Drivers’ ability to select an appropriate speed and path depends on their ability to see the road. They must see the road directly in front and see enough of it at some distance ahead to predict its alignment, grade, width, and several other factors with a high degree of accuracy. Drivers’ view of the road includes a view of the immediate environment including the shoulder and any obstacles. This also includes shoulder surface and width, sign supports, bridge piers, abutments, guardrails, and median barriers. Information received from the roadway and its immediate environment is used continuously during performance at the guidance level. Traffic Control Devices Three kinds of devices directly affect guidance performance: pavement markings and delineators, regulatory and warning signs, and signals. Guide signs, associated with the navigation level, indirectly affect performance at the guidance level and, as such, are an important source, although lower in primacy. Traffic Maintenance of a safe speed and path in response to other vehicles in the traffic stream is a major activity at the guidance level. Drivers must process information received from other vehicles at the same time as other information related to the driving task. Traffic information may be intermittent or continuous, but in either case, it must be integrated with other guidance information to assure adequacy of speed and path decisions. Hazards at the Guidance Level A hazard is any object, condition, or situation that tends to produce an accident when drivers fail to respond successfully. Object hazards, of course, can be fixed or moving. Condition hazards refer to conditions of the major system elements: driver, vehicle, or roadway environment. Situation hazards are combinations of conditions and objects,
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usually with a temporal feature, e.g., a wet pavement or a train approaching a highwayrailroad grade crossing. It is well beyond the scope of positive guidance to deal with driver or vehicle condition hazards. Guidance-level condition hazards are only those of the roadway environments. Fixed Objects This type of hazard is the most obvious because it includes objects recognized as killers: bridge rails, piers and other bridge elements, sign supports that do not break away, large trees, etc. In general, any object that is stationary and accessible is included. The fact that some objects are protective devices, like guard rails and median barriers, does not mean they are without hazard to motorists. Moving Objects Anything that can move into a driver’s path falls into this category (e.g., other vehicles, pedestrians). Driver assessment of what is hazardous is relatively simple for the fixedobject hazard but somewhat more complex for the moving-object hazard. Furthermore, the decision process involved in avoiding a moving-object hazard is also more complex in that drivers are required to evaluate the speed and path of the moving object, make corrections in their own speed and path, and reevaluate. This iterative process is well within the capability of most drivers but can consume much processing time and information-handling capacity. When seen in time, the object hazard is the simplest hazard with which to deal. Although the decision-making process is complex under some situations, the identification of what is hazardous is usually rapid and error free. Unfortunately, perception of highway condition and situation hazards is neither simple nor without error. Highway Conditions The condition of the highway, its design features, and its state of maintenance or repair, irrespective of any obstacles, contribute to consideration of the roadway environment as a hazard. Included are: • Design features such as tangential off-ramps or lane drops and other expectancy violations as mentioned earlier • Accessible roadway features that make it difficult to maintain or regain control of an errant vehicle, such as potholes, pavement edge drops, and curves with inadequate superelevation All of these features create perceptual problems and expectancy violations for drivers. Without positive guidance, they can be expected to induce driver error. Any location in which the condition of the highway or its immediate environment needs to be interpreted as a cause for extra caution or a cause to modify speed or path significantly should be considered as a highway condition hazard.
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Situations This hazard category includes combinations of conditions with or without objects and may include a temporary condition such as darkness or rain. A situation hazard could include conditions that, taken individually, may be of only moderate concern but in combination are treacherous. Combining such elements as rain, a polished surface, a vehicle with bald tires, a curve with not quite enough superelevation, and an insufficient recovery area for errant vehicles leads to the kind of situation hazard responsible for many skidding and single-vehicle running-off-the-road-type-accidents. Highway-railroad grade crossings are good examples of the difference between highway condition and situation hazards. Many crossings have several hazards associated with them. Elevated tracks, crossings at angles other than 90°, and rough crossings are conditions that warrant extra driver caution. When they all exist at the same crossing, the problem is much more serious for drivers. It is the approach of a train, however infrequent, coming from the acute angle that takes the crossing to another level of hazard. Strategic Improvements Looking at the range of hazards, it is possible to define the obligation of any state or highway authority to motorists on its highways. First, if possible, practicable, and within the financial and programmatic ability of the relevant traffic authority, the hazard should be eliminated. If that cannot be done (and there are many valid reasons for that to be the case), then the hazard should be made inaccessible or forgiving (move it, screen it, or make it breakaway). If that cannot be done (again, there are many valid reasons for that to be the case, particularly with design features), motorists must be given enough information to avoid the hazard. It is that information that provides positive guidance. Short of closing the roadway to traffic, no other alternatives exist. A final word about the term hazard: increasingly in personal injury litigation, the term is used to imply negligence. As used here, however, that is not the case. Having a hazard on the highway does not make a cognizant agency negligent. Negligence accrues when there is knowledge of the hazard and little or nothing is done to ameliorate its effects. Drivers Avoiding Hazards Successful performance by drivers is dependent upon their ability to detect a hazard, recognize it or the threat it poses, decide on an appropriate speed and path, and act on that decision. The principles of positive guidance would require that drivers be given all the information needed to maximize the selection of appropriate speeds and paths. Detecting the Hazard Hazards range in detectability from very easy (seeing a fixed object in the road) to very difficult (seeing a 3-in. pavement edge drop-off at night). How seeable a hazard is depends on many factors, including the interaction among its visibility, its conspicuity, and the number of competing information sources. Also included are the driver’s scanning behavior, visual acuity, prior knowledge, and expectancy. This interaction defines how detectability of a hazard can be enhanced. In the case of a fixed object,
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making it more visible makes it more detectable. With objects and highway conditions, reducing the number of information sources competing for drivers’ attention gives drivers more time to detect the hazard. In the case of any hazard, increasing driver expectancy of seeing the hazard will improve its detectability. Here, signing and marking play an important role in the hazard detection task. Recognizing the Hazard Hazard recognition is a simple name for a complex mental process. Once something has been seen, the driver must decide what it is. Because recognition follows detection in time, the driver is closer to the hazard and can see it better (or more of it) and get more information from it. That information is compared with the driver’s store of prior knowledge. Prior driving experience becomes increasingly important in recognizing highway condition- and situation-type hazards, although some of the knowledge can be gained through driver training. Some knowledge is too situation specific to be taught in driver education, and in those cases hazards are recognized through personal experience, flagged with a device (usually a warning sign), or not recognized. Warning signs prepare motorists to detect and recognize hazards. When the hazard is present, the value of the warning is reinforced. However, when the hazard is not there or not apparent to drivers, the credibility of the warning or regulation is reduced. A typical example is work zone signing, including reduced speed warnings with no work or workers in sight. Deciding What to Do After the hazard is recognized, drivers need to determine if modification of speed and/or path is necessary and, if so, define alternative courses of action. If more than one course of action is considered, drivers evaluate the probability of success as well as the ease and comfort of implementation. Here, too, experience plays a big role; we all tend to repeat past behavior that has been successful. Finally, drivers select the speed and path they consider to be the most appropriate for the situation. These decisions are frequently made under great time pressure. Here, it can be seen that those who are inexperienced and those whose information-processing abilities have deteriorated through advanced age or impairment are at a disadvantage. Doing It Helping motorists to select the appropriate speed and path is as far as the positive guidance process can go. Vehicle control to implement the decisions is entirely in the hands of the driver. After taking an action, the driver evaluates its adequacy, applies a speed or path correction if required, and continues the process until the hazard no longer poses a threat or a higher primacy need intervenes. A great deal of information handling occurs in this process—some at the guidance level and much at the control level.
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Planning, Design, and Construction Although the positive guidance procedures in the literature are designed to be used by traffic operations personnel, the concept and principles, as defined here, are equally important in the planning, design, and construction phases of project development. Traffic control devices are usually considered the principal means of communicating with motorists. However, the highway itself conveys more information to its users than any other single source. Planners and designers whose job is to determine what the highway will look like play a key role in the development of highway-related information. In fact, any activity whose output conveys to highway users information related to the driving task is an activity with potential for providing positive guidance, whether or not information giving is its primary intent. For example, although the principal purpose of guardrail placement is the physical protection of motorists from fixed object hazards and the redirection of errant vehicles, its placement and appearance also give motorists important guidance information. The information imparted is positive guidance when it assists highway users in making correct speed and path decisions to avoid hazards. Here, it is no more or less of an example of positive guidance than a line of retroreflectorized barrels delineating the temporary edge of travel lane in a work zone. The alignment and profile relationships of any highway are crucial to the formulation of accurate driver expectancy. Together, and in combination with other features such as superelevation, signs, markings, and roadside grading, they provide the positive guidance drivers need to conduct the task safely and efficiently. It is essential, therefore, that all the elements act in concert. For example, an urban or suburban facility should not be planned or designed to give the impression of a higher type facility than the posted speed limit would warrant. The ambiguity created by an apparent high type facility and relatively low speed limit violates driver expectancy, creates credibility problems, and invites speeds higher than can safely be accommodated. Positive Guidance Analysis of Two Accident Locations A Passively Protected Railroad Grade Crossing The Uniform Vehicle Code specifies that drivers approaching a passively protected railroad grade crossing be required to yield to oncoming trains in hazardous proximity to the crossing. They are required to maintain a speed from which they can stop within 15 ft of the track if, at any point on their approach, they see an oncoming train that is or will be in hazardous proximity to the crossing by the time they get there. Because no warning sign is present to specify or even suggest an appropriate approach speed, it is essential that drivers know how much distance to the track they will have when conditions permit an approaching train from either direction to be seen so that they may select an appropriate approach speed. In many, if not most, rural grade crossings, long “corner sight distances” are available, providing early detectability of an oncoming train and making the selection of an appropriate approach speed simple for all but the most novice drivers. In the absence of very long sight distances, however, three conditions are necessary for drivers to make the
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approach speed decision reliably: familiarity with visibility conditions at the crossing, experience at making speed judgments relative to rates of closure, and good visibility conditions (daytime or high ambient lighting) in the vicinity of the crossing. At 10 p.m. on a cold Friday night in December of 1994, a 16-year-old driver and two friends went for a ride after work. They lived in a small town in a large midwestern state and drove to a neighboring town about 5 miles away. They had not driven there before, so they decided to look around. As she made a turn onto a quiet residential street, the driver saw a railroad advance sign and a crossbuck two blocks away. In the first block, homes were on both sides of the street. In the second block, buildings were on the right side and homes and a stand of trees on the left. These impediments to the corner sight distance did not permit an unobstructed view in either direction until the driver was about 50 ft from the crossing. The crossing had no external illumination; neither did the street nor any location in the vicinity of the track. There was a single track, skewed at a 75° angle to her right and 105° to her left. It was elevated 5 ft above the approach roadway with an 8% grade over the last 50 ft. Because of its elevation and the lack of illumination, the track was not visible. A passenger train, traveling about 80 mph, approached from the right, blowing its horn. There was no posted speed limit on the street. Clear visibility to the right for the approaching motorist does not occur until the driver’s eye position is within 50 ft of the track, and even then vision would be obscured by the vehicle’s B pillar. The vehicle speed at which 50 ft is an adequate stopping sight distance is about 5 mph. For vehicles traveling at the speed limit of 25 mph and trains traveling at 75 mph, a driver would need to be able to see an approaching train when they are no closer than 165 ft (or 4.5 sec) from the crossing in order to bring his vehicle comfortably to a safe stop 15 ft from the track. At 4.5 sec from the crossing, trains traveling at 75 mph (or 110 ft/sec) are still 500 ft from the crossing and completely hidden from view. Although the engineer was blowing the train’s horn, several factors mitigate against that as an effective or even adequate warning. Even when effective as a general warning, train whistles do not unequivocally identify the specific location, speed, or direction of the train. Seeing the train is the only way to get that information. Ambient temperature and radio use play a role in the ability to hear well enough to identify the train horn or whistle. In mid-December, it is probable that windows are rolled up and heater fans turned on as well as the vehicle occupants engaging in conversation. In all, seeing the train early enough to respond has been recognized as the only way to assure the adequacy of information at passively protected crossings. According to Lerner et al. (1990), “Given such factors as raised windows, noise from heaters or fans, wind noise, engine noise, radios or tape decks and other outside noise sources, acoustic train signals cannot be considered useful means of providing accurate information on dynamic aspects of trains.” The Lerner report further indicates that physical barriers may reflect or absorb sound, such as buildings, trees, and foliage, thus attenuating sound level at the ear of the listener. Insertion loss of the train’s horn sound into the vehicle would, under these conditions, completely mask the sound until the last few seconds of its approach to the crossing. (See also section titled “Railroad Crossings.”) Differences in elevation as well as smoothness of the crossing play a role in the driving task at railroad grade crossings in general. Because of the steep grade in the
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immediate vicinity of the railroad crossing, drivers must pay close heed to negotiating it. This makes the task more complex than at flat, smooth, and 90°crossings. Drivers must ascertain an appropriate speed and path to traverse the elevated crossing and determine whether there are any oncoming vehicles, in addition to searching left and right for train approach. Unless motorists come to a virtual stop at the crossing, in the last few seconds of this task attention must be paid to negotiating the crossing. In observing traffic operations at the crossing, it became evident that almost all motorists came to a virtual stop before entering the crossing. Given poor night visibility, such behavior requires prior knowledge of the conditions at the crossing. The train and the car arrived at the crossing at about the same time. There was no physical evidence of braking by the driver. She survived the collision but had no recollection of the event. The passenger in the right front seat was killed and the driver and rear seat passenger were seriously injured. To paraphrase a U.S. Senator asking questions at the Watergate Hearings, what information did the driver need in order to avoid the accident, and when did she need it? In other words, what information would have provided her with positive guidance? At some point in her approach to the crossing, what did she need to know? • That she was on a collision course with a train and, if she continued at the speed limit, her vehicle and the train would arrive at the crossing at the same time? • The approach speed and distance of the train from the crossing? • The approach speed at which she would have enough time to see a train, recognize its threat, decide on a course of action, and bring her vehicle safely to a stop? Did she need any of that information, or was this one of those locations where a simple STOP sign at the crossing would be the most appropriate guidance? It seems evident that the simpler and more unequivocal the information, the more likely it is to be the right answer. We need merely to turn to the Manual on Uniform Traffic Control Devices for guidance: To be effective, a traffic control device should meet five basic requirements: Fulfill a need. Command attention. Convey a clear, simple meaning. Command respect of road users. Give adequate time for proper response. However, none of this information was available to the driver that December evening. An Urban Intersection Work Zone Work zones are stress-inducing situations. Workers perform their tasks in proximity to the frequently high-speed and high-volume traffic stream, where one errant vehicle can cause injury and death. They rely on temporary traffic control devices to keep them safe by giving drivers a clear understanding of the appropriate speed and path through the work zone.
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For drivers, work zones are equally stressful, whether or not workers are present. Because temporary traffic control information is superimposed on the existing highway and traffic control information, the quantity and complexity of information available to process are increased. As such, drivers need more time to determine appropriate speed and path, particularly on approach and at decision points. However, operating speeds are usually not reduced significantly (if at all), giving drivers even less time to handle the increased complexity of information. Furthermore, because of the increase in complexity, potential ambiguities between the existing information and the superimposed work zone information are also increased. The layout of traffic control devices changes during the course of the work, sometimes frequently. The benefits of familiarity and driver expectancy are lost, and drivers are left to interpret a sometimes-ambiguous meaning of a different array as conveyed by the layout and spacing of channelizing devices and temporary signs. In Figure 13.16, a line of barricades closes the left-turn and adjacent lanes (lanes 1 and 2), although the protective/permissive signal controlling the left-turn movement has not been moved to the temporary left-turn lane (lane 3), two lanes to the right. For the driver who intends to turn left at the intersection, the decision is made more difficult by the presence of the barricades extending well beyond the intersection.
FIGURE 13.16 A line of barricades closes the left-turn and adjacent lanes; the protective/permissive signal controlling the left-turn movement has
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not been moved to the temporary leftturn lane. A driver familiar with the intersection shown in Figure 13.16 and Figure 13.17 attempted to make the left turn from lane 3 at night during the permissive signal phase—a green ball in the left-turn signal. She knew she was required to yield the right-of-way to any vehicle coming through the intersection in the opposite direction. In testimony, she stated that she had stopped twice in the intersection in an attempt to determine whether any vehicles were coming from the opposite direction. An eyewitness corroborated her testimony. As she got to the opposing traffic lane seen in Figure 13.17, her vehicle was struck broadside, killing her daughter in the front passenger seat and severely injuring her twin 3-year-old boys in car seats in the back. She further testified that when she had been there earlier in the day, the original left-turn lane was still open, so she had been surprised by the new configuration. It is evident that the line of barricades obscured her vision. However, other issues pertaining to highway engineering and human factors played a significant role in the litigation:
FIGURE 13.17 Line-up of the far-side barricades at night. • Is it reasonable to have the left-turn signal over lane 1 and the turn from lane 3? The arrangement is highly ambiguous and violates the MUTCD. From a positive guidance perspective, such ambiguity can lead to confusion, delayed decisions, and errors. Inasmuch as lane 3 was not an exclusive turn lane, drivers turning left needed to determine whether the left-turn signal still controlled the left-turn movement. For
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example, if the left green arrow is illuminated over lane 1, and the signal over lane 3 is red, is a left turn legal? Furthermore, would it be appropriate to wait at the stop line when the signal is green until the protected phase was activated? It is at least foreseeable that errors will be made in this decision process. • Is it reasonable to have a permissive green for a 7-sec turn? The left turn from lane 3 would take several seconds longer than the left turn from lane 1. What does this mean in terms of how much farther a driver would need to see to determine whether clearance was adequate to make the turn? If it takes 7 sec to initiate and complete the turn, at least 10 sec of visibility should be available to provide a comfortable safety margin. With an operating or 85th-percentile speed of 45 mph or 66 ft/sec, 660 ft of visibility distance would be necessary. Not only was that distance unavailable because of the barricades, but it is also considered unlikely, even given full visibility at the location, that drivers stopped at or approaching the intersection would appreciate how far they would need to see in order to make the judgment. • Is this one intersection or two? The original roadway was a four-lane divided arterial with exclusive left-turn lanes. Two new outside lanes were being added and the median was being modified. On the day of the accident, the four inside lanes were temporarily closed to traffic and the two new outside lanes were opened. The effect was to create a six-lane divided arterial with a 56-ft-wide median (four 12-ft lanes and the 8-ft median). Treating the temporarily reconfigured intersection as two, with appropriate striping and signing, would have eliminated the need for protecting the left turn; drivers who were turning left would have been required to stop at a red signal and stop line before crossing the opposing traffic lanes. The purpose of the positive guidance analysis in these two litigation examples was to assist the court in determining whether the roadway and the information-processing task improperly burdened the drivers and played a role in accident causation. Furthermore, the analysis was helpful in defining alternative designs that met relevant design or traffic control standards and provided drivers with clear, unequivocal information about appropriate speed and path decisions to avoid hazards. 13.6 Alcohol, Other Drugs, and Driving Traffic collisions are a major cause of morbidity and mortality in the world. Alcohol and, to a lesser extent, other drugs have been implicated as causal factors in crash involvement. The research on the relationship between alcohol and driving began in the 1930s; research interest in other drugs and driving appeared in the 1970s, initially with illicit drugs, particularly cannabis. Current research interest is focused on licit, medicinal drugs as an emerging problem. Interest in drugs 2 and driving is driven by two questions: • To what extent is it a problem? • If it is a problem, what can we do about it? Studies examining the extent of the problem have found that, despite the increased interest in medicinal and illicit drugs and driving, alcohol is still the most frequently found drug in fatally injured drivers, although polydrug use is common. For example, in a
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3-year sample of seriously injured drivers consecutively admitted to a regional trauma unit in which the drug screening rate was 90.0%, 59.3% of drivers tested positively for alcohol and/or other drugs, 16.5% tested positively for alcohol in combination with 2
The word drug will be used to connote alcohol and licit, medicinal, and illicit drugs unless otherwise indicated.
other drugs, 18% tested positively only for alcohol, and 24.8% tested positively for a variety of other drugs (Stoduto et al., 1993). The two most commonly found drugs after alcohol were cannabinoids (13.9%) and benzodiazepines (12.4%). The fact that almost 60% of all seriously injured drivers were positive for alcohol and/or other drugs would suggest that drugs could be a problem if evidence were found that drugs did indeed impair driving ability. Current evidence suggests that drugs can impair mental and physical functions and thus contribute to road crashes (Ferrara et al., 1994; Moskowitz et al., 2000). Although more information is available on the role of alcohol in motor vehicle collisions, most evidence suggests that other drugs have a less detrimental impact on traffic collisions than alcohol (Xie et al., 1996); however, other drugs may still have an effect. For example, de Gier (1993) has estimated that at least 10% of persons injured or killed in road crashes in the European Union were taking some type of psychotropic medication. Determining what to do about this problem inevitably leads to the issue of detection, adjudication, and sanctioning of drug-impaired drivers. To date, the issue of detection is most developed for alcohol. For other drugs, the problem is that effects are not fully understood, can be additive, and can interact with alcohol (Crowley and Courtney, 1999). Similarly for adjudication and sanctioning, legal codes for alcohol-impaired driving are the most developed. Industrialized countries have impaired-driving and per se laws, with the per se blood alcohol concentration (BAC) legal limit in most countries set below 0.10% per 100 ml of blood. Sweden has a limit of 0.02% BAC; Australia, Finland, France, the Netherlands, and Norway have set 0.05% as the legal limit; while Austria, Canada, Great Britain, Switzerland, and all U.S. states have 0.08% as the BAC limit. In addition, a number of countries have laws for refusing breath tests. Driving under the influence of drugs other than alcohol is more difficult to detect and prosecute. Drugs can be determined by chemical or behavioral methods: blood, urine, breath, saliva, sweat, hair, field sobriety tests, and drug recognition experts (although internationally and in the U.S., state variations exist for the legal admissibility of blood, breath, and urine samples; field sobriety tests; and drug recognition experts) (National Highway Traffic Safety Administration, 1999). Blood tests can correlate more closely with impairment depending on the drug; however, they are more invasive (Kapur, 1994) and are typically only used in fatal crashes/trauma in North America although commonly used evidentially in the E.U. (e.g., Maes et al., 2002; Willekins et al., 2002). Although many countries have impaired driving legislation that includes licit and illicit drugs and some countries have recently introduced new laws on driving under the influence of illegal drugs (Maes et al., 2002; Willekens et al., 2002), assessment of drug impairment and of accuracy of interpretation is still a challenge. The challenges for assessment and accuracy require three types of research studies to: (1) produce a drug dose-related impairment of skills associated with driving or related psychomotor
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functions, (2) link these drug-dose effects with driving ability, and (3) link driving skills and any impairment to the skills that result from taking drugs to actual road crashes (Crowley and Courtney, 1999; McBay, 2002). The objectives of this section are to • Describe methodological strengths and weaknesses of the three types of research studies used to assess drug impairment • Provide a simplified, therapeutic categorization of drugs in three groups depending on the ways in which they affect the central nervous system (CNS), with a particular focus on alcohol and other commonly used drugs of concern: benzodiazepines, methadone, cocaine, and cannabis • Review the extent of drug use, including alcohol, in collisions and violations • Provide current evidence on drug impairment and collision risk Methodological Approaches Used to Assess Drug Impairment The combination of laboratory/experimental and epidemiological studies provides the best information for understanding the causal connection between drugs and traffic crashes (Friedel and Staak, 1993; Simpson and Vingilis, 1992). Studies to Produce Drug Dose-Related Impairment of Skills Associated with Driving Experimental studies determine the precise nature of impairment produced by specific drugs and its impact on performance tasks. These studies usually require subjects to perform laboratory psychomotor tasks or driving tasks on simulators or on closed-road circuits or regular roadways. The best research design typically consists of a double-blind experimental approach in which subjects are randomly assigned to an active drug group or to a nonactive drug (placebo), which is replicated using varying drug dosages. Performance differences between these two groups are assessed. The strength of this method is in its internal validity in controlling for extraneous factors, like expectancy of alcoholic effects, that could inadvertently affect outcome (Cook and Campbell, 1979). Thus, the experiment is the method of choice for determining drug and dose response effects on skills performance. The main limitations of laboratory and simulator experiments relate to external validity or generalizability of the findings to the real world. Drug use and the driving environment in experimental designs may not reflect actual patterns of drug use and driving (Del Rió and Alvarez, 1995a; van Laar et al., 1993; Volkerts and van Laar, 1993). Therefore, experiments that assess a driver’s performance may not be applicable to real driving situations. Generalizability problems of experimental research to driving and road crashes (i.e., external validity) can also emerge in relation to the use of healthy volunteers (vs. heavy drinkers, drug users, or actual medication users with health conditions); types of control drugs used; duration and dosages of drugs; types of psychomotor tasks; and other statistical and methodological issues (de Gier and Laurell, 1992; Del Rió and Alvarez, 1995a).
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Studies to Link Drug Dose Effects with Driving Ability In recent years, a second type of experimental study has been developed to link these laboratory effects with driving ability. Experimental research on drugs and driving through the use of “on-the-road” driving experiments and drug-using individuals as subjects has reduced many of the problems described earlier (Ferrara and Giorgetti, 1992; van Laar et al., 1993; Vermeeren et al., 1994). Studies to Link Driving Skills and Drug Impairment to Actual Road Crashes Epidemiological studies address the issue of incidence/prevalence of drug use among various subpopulations of drivers in the real world. The two major epidemiological research goals are descriptive and analytic. Descriptive epidemiology provides an indication of the extent or magnitude of the problem and, as such, guides experimental research by detecting the substances in persons involved in collisions. If a particular drug is not detected in crash-involved drivers, studying the impairing properties of the drug in a laboratory may be of little practical value (Friedel and Staak, 1993; Simpson and Vingilis, 1992). Descriptive epidemiology can also provide important trend data on the changing patterns of drug use and driving (Simpson and Vingilis, 1992). Analytic epidemiology seeks to determine which drugs are over-represented in crashinvolved drivers. The more methodologically valid approach is the case-control study in which crash-involved drivers are compared to non-crash-involved drivers matched for age, sex, location, and time of crash. Another related approach most typically used for fatal crashes is through responsibility or culpability analysis. Within a group of fatally injured drivers, the proportion of those judged responsible for crashes in the drug-positive group is compared to the proportion responsible in the drug-negative group. The resulting odds ratio helps in understanding whether the specific drug in question was related to the crash. Both these methods have strengths in that they use a systematic and consistent approach to gather data and control for extraneous factors that could affect outcomes. Limitations also exist with the interpretation of causality because the relationship established is one of association (Friedel and Staak, 1993; Simpson and Vingilis, 1992). Thus, although the relative risk of crash involvement for drug-using drivers could be higher than for non-drug-using drivers, other factors, such as a sensation-seeking personality, may explain the drug use and the high-risk driving. A methodological problem with culpability analysis relates to the difficulty in assessing 100% culpability to one driver in multivehicle crashes. A major challenge for any drug studies of crash-involved drivers relates to the measurement of psychoactive drugs in the crash victim (Ferrara, 1992; Simpson and Vingilis, 1992; Staak et al., 1993). Drug tests detect psychoactive drugs as well as metabolites (waste products) of the drug. Blood tests are better able to detect psychoactive drugs than urine and other tests because blood tests measure the drug circulating throughout the body, which can affect the brain and other tissues and cause impairment (Morgan, 1988). When drugs are used, whether ingested, injected, inhaled, etc., they pass into the blood by absorption. The drug is then metabolized by the liver and the metabolites are excreted in urine. Urine tests measure these byproducts of the liver’s metabolic processes (NIAAA, 1997).
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The challenge is to link the presence or quantity of a particular drug to impairment because some drugs have long half-lives, meaning that metabolites can be found in the body well after initial use. For example, the half-life of THC carboxylic acid (cannabis metabolite) can range from 3 days to 20 days after ingestion (Dalén et al., 1997). Some exceptions exist, as with alcohol; most of the ingested alcohol is metabolized in the liver and turned into metabolites, but the small amount that remains unmetabolized permits alcohol concentration to be measured in breath and urine (NIAAA, 1997). An added challenge in establishing the link between drug use, impairment, and crash involvement relates to the growing evidence that longer term use of certain drugs can cause brain damage that could also impair driving ability. That is, the impairment may not be caused by the psychoactive properties of the drug per se, but rather by the brain damage and cognitive and other impairments that occur after longer use. The neurological damage associated with chronic alcohol abuse is well documented (NIAAA, 2001). Other drugs have also been associated with neurological damage. Recent animal studies have shown that methamphetamine damages brain cells involved in transport of dopamine, a chemical messenger involved in movement and cognition (Cadet et al., 1997; Deng et al., 1999; McCann et al., 1998). Research on long-term methamphetamine abusers who have abstained for 2 months have found reduction in dopamine transporters that appears to be linked to slowed motor skills and weakened memory (Volkow et al., 2001a, b)—two skills needed for safe driving (NIAAA, 1994). Thus, findings of increased crash rates of drivers who have consumed drugs compared to non-crashed control drivers are not able to disaggregate the cause of the increased crash risk because it could be due to the acute affect of the drug on the brain, the longterm effect of the drug causing neurological damage, or other factors, such as sensationseeking personality, that could cause drug use and risky driving. Another epidemiological approach involves survey research in which subjects are asked to report on drug use and driving. For example, they might be asked to indicate if they believe their drug use contributed to a traffic crash. Here again, any identified relationship between self-reported drug use and traffic collisions would be correlational and not causal. Survey methods are generally considered less valid than methods using drug tests because many people under-report or lie about their drug use. The pathogenesis of drug use may be helpful for understanding the impact of drugs on traffic crashes. The degree to which casual or infrequent use of drugs leads to dependence varies based on the type of drug (McKim, 1986). Also, withdrawal and hangover effects from these substances, which vary from drug to drug, may differentially affect the likelihood of adverse driving outcomes (Burns and Anderson, 1995; McKim, 1986). Another problem of determining crash risk associated with different drugs in epidemiological studies relates to multiple drug use, which is common among drug users. Multiple drug use makes it difficult to disentangle individual drug use risks and to assess possible additive affects. Long-term use can also affect personality characteristics, such as paranoia, which in turn could elevate accident risk (Coambs and McAndrew, 1994). A final element with regard to medicinal drugs relates to the therapeutic impact of the drug. Studies are needed in which the potential dangers of drugs, such as behavioral impairments, are weighed against the potential improvement in the condition for which the drug was prescribed (Moskowitz, 1985a). As Del Rió and Alvarez (1995a) summarize, drugs can cause deterioration of driving skills of varying degrees depending
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on factors such as drug taking, abuse and dependence issues, expectations and factors associated with drug taking, multiple drug taking, and issues of dependence related to withdrawal and overdose. All of this is exceedingly hard to measure in order to determine the causal link between drug use and motor vehicle collisions. Therapeutic Categorization of Drugs and Pharmacological Effects Psychoactive drugs affect the CNS and interfere to various degrees with the psychophysical conditions necessary for driving (Del Rió and Alvarez, 1995a). Drug effects can vary among individuals. The effects are influenced by history of drug use (chronic or naïve user), tolerance, overall health, individual sensitivity to the drug metabolism, and other factors. Many drugs, especially those that affect the central nervous system, can impair driving. These include alcohol and illicit drugs, as well as therapeutic and over-the-counter medications. Many therapeutic drugs that are available with or without a prescription can have unwanted side effects that can impair driving performance. The three simplified categories of psychoactive drugs are depressants, stimulants, and hallucinogens (see DeLong, 2002, for a comprehensive and detailed description of drug psychopharmacology and effects). Depressants Depressants, which include alcohol, tranquillizers (e.g., benzodiazepine derivatives, barbiturates), narcotics (e.g., opiates, methadone) and inhalants, produce the predominant effects of relaxation, sedation, and a sensation of well-being (Del Rió and Alvarez, 1995a). Use of depressants can cause confusion, poor divided attention, slowed reaction times, memory effects, mental clouding, poor psychomotor skills, poor coordination, slurred speech, ataxia, disorientation, and decreased pulse and blood pressure (New Mexico Department of Health, 2002). Stimulants Stimulants include drugs such as amphetamines, cocaine, caffeine, and nicotine. The main effect of these drugs is to stimulate transmission at the synapses that use epinephrine, norepinephrine, dopamine, or serotonin as a transmitter (McKim, 1986). Although the drugs in this category have similar neurochemical effects, their behavioral effects can differ considerably. Use of stimulants can cause hypervigilance, anxiety, agitation, paranoia, self-absorption, obsessive activity, and elevated pulse and blood pressure (New Mexico Department of Health, 2002). Hallucinogens Hallucinogens include a wide range of drugs such as cannabis, LSD, psilocybin, mescaline, and many designer drugs (McKim, 1986). The main characteristic of hallucinogens is that they produce a distorted perception of reality. Although other types of drugs can produce altered perceptions, hallucinogens are categorized as such because they can produce these effects at low doses, without toxic effects. Thus, their effects are a
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direct result of the drug and not an effect of drug poisoning (McKim, 1986). They can produce a sense of euphoria together with disturbances in perception and varying intensities of hallucinations, difficulties with paying attention, and a diminishing of reflexes and movement coordination (Del Rió and Alvarez, 1995a). Due to their CNS effects, all the drugs described here have the potential to impair skills needed for driving and, consequently, to be a causal factor in motor vehicle collisions. Various drugs can impair coordination, reaction time, judgment, tracking, divided attention, and perception. Extent of Drug Use in Collisions and Violations All three therapeutic drug categories—depressants, stimulants, and hallucinogens—have been found among drug-tested drivers. Depressants, particularly alcohol, are most prevalent. Although testing methods and rates differ among countries, the percentage of alcohol-related fatalities declined in the late 1980s and 1990s and ranged from 13.6% in 2000 in Germany (Kroj and Lerner, 2002) to 40% in 2000 in the U.S. (Sweedler, 2002). Studies on the proportion of drivers in traffic collisions testing positive for cannabinoids find prevalence rates between 2.7 and 13.9% (Stoduto et al, 1993; Soderstrom et al, 1995; Mercer and Jeffery, 1995). A review article reported rates of benzodiazepines generally ranging from 2 to 9.6% among arrested, injured, and fatally injured drivers (Woods et al., 1992). Studies in which drivers were tested for cocaine generally show that between 4 and 8% test positive (Stoduto et al., 1993; Soderstrom et al., 1995; Mercer and Jeffery, 1995). In his review of drugs and casualty driver studies, Lillsunde (1998) said that cannabinoids and benzodiazepines generally were the most frequently detected drugs, after alcohol, although in the U.S. benzodiazepines were less common and alcohol, cannabis, cocaine, PCP, and opiates were common. Amphetamines were most commonly detected in Nordic countries, while opiates were more frequent in central European countries (Vingilis and MacDonald, 2002). Similar patterns have been found for arrests for impaired driving. The challenges of drug testing (Verstraete, 2002) and the lack of per se legislation for drugs other than alcohol means that drugs other than alcohol were far less likely to be tested. The prevalence of drugs among suspected drug-impaired drivers is similar to that in the driver casualty studies. Cannabis or benzodiazepines (including tranquillizers) are typically the most commonly found drugs after alcohol (Dussault et al., 2002; Gerostamoulos et al., 2002). These studies of incidence of drug use among collision-involved drivers or violators do not provide information on the role that drugs may have had in the collision or violation. In order to determine whether the various drugs identified previously are causal factors in the collisions, it is necessary to review experimental studies that examine drug and dose response effects on skills performance, as well as analytic epidemiological casecontrol studies that examine the risk of crash involvement of various drugs. Current Evidence on Drug Impairment and Collision Risk Experimental psychopharmacological studies have shown adverse effects of many drugs on driving in controlled environments and driving-related performance variables (Del Rió
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and Alvarez, 1995a, b; Ferrara, 1992; Moskowitz, 1985a; Moskowitz and Fiorentino, 2002). Based on current knowledge, certain classes of drugs capable of producing impairment in experimental studies are (Burns, 1996; Chesher, 1990; Ellinwood and Heatherly, 1985; Gengo and Manning, 1990; Linnoila and Seppala, 1985; Moskowitz, 1985b; Moskowitz and Fiorentino, 2000; O’Hanlon and Ramaekers, 1995; Roth and Roehrs, 1985; Simpson, 1985): • Alcohol • Anesthetics • Antidepressants • Antihistamines • Cannabinoids • Cardiovasculars • Hallucinogens • Hypnotics • Narcotics • Psychosometics • Sedatives • Solvents • Stimulants • Volatiles Experimental studies have also shown that some drugs produce large performance deficits, while other drugs produce minor changes in performance or even performance improvements. Few analytic epidemiology studies have been conducted in recent years in which different drugs are examined in the same study, using either the case-control method (Dussault et al., 2002; Ferrara et al., 1990; Honkanen et al., 1980, Marquet et al., 1998; Meulemans et al., 1996) or methods used to ascribe crash responsibility (Drummer, 1995). Both types of studies have found increased odds ratios for a variety of crashrelated measures, such as crash involvement, injury severity, and fatality for some drugs. For example, a recent case-control study conducted in Quebec, Canada, obtained blood and urine samples from 354 fatally injured drivers that were compared to samples of drivers who were stopped in two roadside surveys. The odds ratios, which constituted the ratio of the two rates of drug use, indicated that the odds of alcohol-positive drivers being fatally injured were 9.2. times as great as the odds for a sober driver. Similarly, the odds of cannabis, cocaine, and benzodiazepine drivers being fatally injured were 4.6, 12.2, and 4.2 times as great, respectively, as the odds for a sober driver (Dussault et al., 2002). An example of a culpability analysis study was conducted by Drummer (1995), who examined blood samples of driver fatalities in Australia. He found those with positive tests for alcohol were about 6.8 times more likely to be judged to be responsible for the car crash than those who tested negative. Those with opiates were 2.4 times more likely to be judged to be responsible for crashes; however, this was not significant. Those with stimulants or benzodiazepines had odds ratios of 1.4 and 1.0, respectively; however, these odds ratios were not significant. Interestingly, those testing positive for cannabis were less likely than those without drugs to be judged to be responsible for crashes (odds ratio=0.6).
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Depressants, Impairment, and Risk of Collision Involvement Alcohol Numerous studies and reviews have been conducted examining the effects of alcohol on driving-related performance skills by different dosage amounts. Moskowitz and Robinson (1988) and Moskowitz and Fiorentino (2000, 2002) summarized more than 300 experimental studies from 1950 to 1997 that met acceptable scientific standards such as placebo treatments, statistical significance, and ability to determine BAC levels at performance skill testing periods. The results were indexed by BAC and performance skill and two analyses were conducted. The first analysis determined the lowest BAC at which impairment was reliably present for a particular performance skill and the second determined thresholds of impairment for different performance skills (Moskowitz and Fiorentino, 2000, 2002). The results of the three reviews found that critical flicker fusion and simple reaction time studies were most insensitive to the effects of alcohol, while tests of divided attention and of driving exhibited impairment by 0.01% BAC. The majority of studies measuring physiological sleep tendency found increased drowsiness by 0.02%; the majority of vigilance tests exhibited impairment by 0.04%. Moreover, the results of these different studies were congruent in that nearly all studies produced evidence showing impairment at nearly all of the BACs examined. However, greater variability of results was found for tracking, perception, visual function, cognitive task, psychomotor skill, and choice reaction time. This variability seemed to be due to the range of tasks tested within certain performance domains. Areas that remain to be explored are alcohol effects on risk taking, aggression, and motivation. However, Moskowitz and Fiorentino (2000, 2002) conclude that domains crucial to driving, such as vigilance, drowsiness, and divided attention, are impaired at BACs of 0.01% and higher. The studies linking alcohol use to crash involvement were conducted from the 1930s onward. Early culpability and case-control studies of alcohol crash risk compared the incidence of alcohol in collision and noncollision cases. For example, a study conducted in Toronto, Canada, in 1951 and 1952 had research assistants accompany special traffic police cruisers investigating collisions each week from Monday to Saturday (Lucas et al., 1955). For each driver involved in the collision, four or more noncollision drivers passing the scene of the crash in vehicles of the same vintage at approximately the same time provided breath samples with the understanding that such samples were for research purposes only. Their research showed an increasing exponential curve in which relative risk for crash involvement increased as BACs increased, with an accelerated rise at BACs above 0.08% (Lucas, 1955). Subsequent case-control studies have replicated this exponential curve (Borkenstein et al., 1964; Compton et al., 2002; Krüger et al., 1995; McLean and Kloeden, 2002). The relative risk of crash involvement at BACs of 0.05% is 1.4 times the risk of a sober driver, while at 0.10% the relative risk is 4.8 times. At a BAC of 0.16% (the average BACs of drivers arrested for driving under the influence or of crash-involved drivers), the relative risk of crash involvement is nearly 30 times the risk of a sober driver (Compton et al., 2002).
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Benzodiazepines The second most commonly studied subclass of depressants on psychomotor performance are benzodiazepine derivatives (Coambs and McAndrew, 1994; Ferrara, 1987; Woods et al., 1992). Woods and colleagues (1992) have noted more than 20,000 papers on benzodiazepines since the 1960s and concluded that the degree of effect depends on the type of benzodiazepine and the types of psychomotor tasks used. Also, Berghaus and Guo (1995) conducted a meta-analysis of more than 1000 experimental studies of druginduced performance problems for prescribed drugs and also concluded that performance varied, depending on the type of benzodiazepine. Laboratory psychomotor tasks find less impairment with anxiolytics, while the hypnotic sedatives show more performance impairment (Hobi and Gerhard, 1993). Friedel and Staak (1993) in their review also found simpler tasks such as reaction time showed mixed results, while real on-the-road performance studies all reported some impairment. Similarly, van Laar et al. (1993), in their comparison of on-the-road and simulated driving tasks, found greater sensitivity in measuring impairment for on-theroad tests of benzodiazepine use than for simulator driving. Additionally, different benzodiazepines show differing degrees of impairment, with older benzodiazepines showing more behavioral side effects than newer ones (Del Rió and Alvarez, 1995b; Friedel and Staak, 1993). For example, O’Hanlon et al. (1995) found significant impairment of driving performance tests for on-the-road tests of benzodiazepines (diazepam, lorazepam) and benzodiazepine-like anxiolytics (alpidem, suriclone). Moreover, these authors found no placebo or drug differences between clinically anxious patients and healthy volunteers. Driving impairment has been found to be significant and equivalent to impairment found for BACs over 0.10% for the most commonly used benzodiazepines of lorazepam, diazapam, and flurazepam (Giorgetti et al., 2000; McBay, 2002; O’Hanlon et al., 1995). Several case-control studies have been conducted in which traffic records of groups with prescriptions for tranquilizers were compared to those of nonprescribed groups. The majority of these studies found increased likelihood of crash involvement for persons taking tranquilizers compared to drivers not taking tranquilizers, particularly for long half-life drugs (Hemmelgarn et al., 1997; Neutel, 1995; Ray et al., 1992; Skegg et al., 1979), although Leveille et al. (1994) found no relationship between benzodiazepine use and crashes. Narcotics Another subclass of depressants is narcotics, which include a wide class of drugs, from natural substances such as opium, morphine, and codeine to synthetically produced substances such as methadone and meperidine. Opiates depress neurotransmitter functioning, yet low to moderate doses of opiates do not greatly affect human performance (McKim, 1986). Tolerance to these drugs develops quickly, and first-time doses are much more likely to produce cognitive impairments than subsequent doses (Coambs and McAndrew, 1994). Some studies have been conducted on the impact of methadone on driving performance and crashes. Berghaus et al. (1993), in a case-control laboratory study on methadone users and non-drug-using controls, found that the methadone group exhibited poor performance on all psychophysical performance tests compared to the age-, sex-,
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and education-matched controls. However, the study could not conclude whether the methadone or the personal characteristics of the users caused the poorer performance. Friedel and Berghaus (1995) concluded that heroin addicts treated with methadone are unfit to drive. By contrast, Chesher et al. (1995) found clients in a methadone maintenance program showed no evidence of performance deficits associated with driving. In another epidemiological study, driving records of treatment patients for opiates were compared to a matched control group (Blomberg and Preusser, 1974). The two groups did not differ significantly in terms of traffic citations; however, the opiate group had more equipment problems and documentation violations. In a literature review, Gordon (1976) found that narcotics by themselves were not a significant factor in poor driving. Stimulants Two commonly used stimulants are cocaine and amphetamines, but this category also includes such widely used substances as caffeine. Most laboratory studies have failed to find performance deficits associated with this class of drugs (Ferrara et al., 1994). In fact, performance improvements have been found in some studies for endurance tasks (Burns, 1993; Coambs and McAndrew, 1994; McKim, 1986). Laboratory evidence on the performance-enhancing effects of cocaine and other stimulants is inconclusive and researchers have suggested that subjects may perceive performance improvements while no real improvements have been noted (Fischman, 1987). Experiments have shown that five types of stimulants, including caffeine, did not differ in terms of their impact on performance (Mascord et al., 1997); however, as Burns (1993) states with regard to her research on cocaine, the effects are not unidimensional in direction in that the effects of overstimulation on performance may be qualitatively, as well as quantitatively, different from the effects of mild to moderate stimulation. Time of day, as well, appears to be a critical variable. Ellinwood and Nikaido (1987) write, “The realistic understanding of the nature of stimulant-induced effects requires the scientific perspective of all aspects of drug use, including acute and chronic dosing conditions, behavioral sensitization and tolerance and drug withdrawal.” No analytic epidemiological studies that tested only the role of stimulants in driving crashes were found. None of the analytic epidemiological studies previously reviewed found cocaine was associated with increased crash risk. Hallucinogens Hallucinogens include a wide array of drugs such as cannabis, LSD, psilocybin, and mescaline. Cannabis Cannabis is classified as an hallucinogen, but is often treated as a separate category because its effects are somewhat different and the prevalence of use is considerably higher than with the other drugs. A recent review of the experimental research on the immediate effects of cannabis use has been conducted by Schwenk (1998). Several
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components of performance, such as attention and psychomotor skills, were examined. Most of the research has shown that subjects’ ability to concentrate and learn is reduced when they are under the influence of cannabis; however, long-term memory appears to be unaffected. In terms of psychomotor skills, the findings from research are mixed, especially in relation to driving simulation tasks. For example, one study found that marijuana had little effect on subjects’ ability to control a car, but impaired their ability to attend to peripheral stimuli (Moskowitz et al., 1976). Coambs and McAndrew (1994) have noted that studies in which deficits were not found involved more experienced marijuana users. For specific tasks, such as reaction time or spatial and temporal judgments, the preponderance of evidence suggests cannabis intoxication impairs performance, particularly in more complex tasks. Berghaus and Guo (1995) conducted a meta-analysis of experimental studies on the effects of cannabis on psychomotor skills and driving performance. More than 120 studies were collected, of which 60 fulfilled their methodological inclusion criteria. Their meta-analysis revealed that Smoking of marijuana causes to a more or less obvious extent impairment of every performance area connected with safe driving of a vehicle. Thus, performance areas such as tracking, psychomotor skills, reaction time, visual functions, attention, en-/decoding and performance in simulated or real driving experiments are involved. In each of these performance areas significant deterioration in dependency on the post smoking interval—that is to say on the THC concentrations in plasma—is found after smoking marijuana. THC-related impairment is concentrated within the first two hours after the beginning of the smoking procedure. Attention, tracking and psychomotor skills reveal the highest percentage of significant deterioration (p. 405). A recent meta-analysis of the experimental research literature on the impact of cannabis on performance was conducted by Smiley (1999). She noted that marijuana does impair one’s ability; however, drivers are quite aware of this impairment, which prompts them to slow down and drive more cautiously to compensate. However, in their review, Del Rió and Alvarez (1995a) stated that some studies found that psychomotor functions were disturbed up to 24 h after cannabis preparations were smoked and that the smokers were not aware of these deficits. In another review, Robbe and O’Hanlon (1993) examined laboratory and epidemiological studies of cannabis and traffic crashes and concluded that no clear relationship has been shown between marijuana smoking and seriously impaired driving performance or the risk of accident involvement. Later, they indicated that marijuana may well be the least harmful of the many psychotropic drugs. LSD, Psilocybin, and Mescaline With respect to other hallucinogens such as LSD, psilocybin, and mescaline, although less experimental research is available on their impairing properties, research shows these drugs cause major performance deficits (see McKim, 1986, for a review of experimental studies). No epidemiological studies were located in which the impact of hallucinogens
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on crashes was examined. These drugs are particularly difficult to detect through urine analysis techniques. The prevalence of use of these drugs is generally restricted to youth and prevalence of its use is fairly low based on survey data. Conclusions One clear conclusion from a large number of laboratory and experimental studies is that the pharmacological properties and effects on psychomotor performance of the drugs examined in this chapter vary quite considerably. Laboratory studies have shown that alcohol, hallucinogens, and benzodiazepines impair performance, while the findings for methadone are mixed and stimulants may enhance performance. The adverse effects on driving skills of one drug, alcohol, have been well established. Impairment effects can be clearly demonstrated based on blood and breath concentrations in experimental and laboratory studies. Relative risk of crash involvement can also be determined based on blood and breath concentrations. The epidemiological evidence of other drugs as causal agents in collisions, however, is largely inconclusive; however, this evidence, along with experimental studies, allows one to draw tentative conclusions. Cannabis is typically the most commonly used illicit drug in most industrialized countries. Although experimental studies have shown that it moderately reduces performance, epidemiological research has failed to show it is a major contributor to traffic crashes. This conclusion was reached in several review articles on the topic and case—control studies have failed to find it a significant predictor of crashes. Two explanations for this finding are likely. First, drivers under the influence of marijuana may be reluctant to drive, thereby avoiding a risk of crashes. Second, if they do drive, they may pace their driving by driving more slowly and reducing the likelihood of collisions (Chesher, 1995). The research evidence on the role of benzodiazepines and traffic crashes is more extensive and more conclusive than that of cannabis research. Several studies have linked health records for benzodiazepine use and driving records (that show traffic crashes). Experimental studies show decreased performance with use and epidemiological studies generally show that benzodiazepine users are up to six times more likely than nonusers to be in crashes, although some studies failed to find it a significant risk factor. The risk of crashes likely varies, depending on the specific type of benzodiazepine, the half-life of the drug, and duration of use. The results of methadone studies are more variable and definitive conclusions cannot be drawn regarding the risks related to driving. Stimulants have not been shown to affect performance adversely in experimental studies and can actually enhance performance, particularly for endurance tasks. However, long-term use could affect personality characteristics, thus possibly increasing the likelihood of crashes. Also, these drugs can be addictive and withdrawal could enhance traffic risks. Epidemiological studies have not conclusively shown stimulant use to be a major contributor to crashes. Similar conclusions can be drawn for methadone, although performance deficits have been demonstrated in some experimental studies. Experimental studies show hallucinogens (i.e., LSD, mescaline) produce measurable reductions in performance; however, virtually no epidemiological research has been conducted to demonstrate that it represents a significant crash safety problem. Such
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research faces severe methodological challenges because urine tests typically are not used to detect these substances. This review has been restricted to three categories of drugs. Other types of drugs may also impair performance and pose a traffic safety hazard. Also, this review focused on the independent effects of each drug and the probable impact on driving. Synergistic and dangerous effects on performance can occur when some drugs are used in combination with each other, particularly with alcohol. Better and more methodologically sound research in this area is required in order to understand the role of drugs other than alcohol in motor vehicle collisions. 13.7 Concluding Remarks This chapter has tried to provide insights into factors that need to be considered in the forensic evaluation of traffic crashes. Just as in any epidemiological study, examination of traffic crashes must proceed with a multidisciplinary team orientation to ensure that the important variables are properly considered. Human factors professionals are key members of such a team and it is their task to use their knowledge to ensure that the relevant human behaviors are evaluated and their role discerned in the sequence of events that led to the failures in the system and to crashes. This approach is exemplified by crash analyses by multidisciplinary accident investigation teams, which can arrive at crash sites, often within a few minutes of the event, and photograph, measure, and document the scene as well as talk with witnesses while the material is still fresh and unspoiled. By the time the human factors professional is brought into a case, the opportunities for getting to the scene while it is still fresh are rare. Other, secondhand materials must be relied on. Although some large trucks and buses and most railroad locomotives have event recorders that provide a few parameters such as speed and time (and, in the case of locomotives, also the time of brake and horn application and throttle position), most vehicles have no such records available. Such data could be of great value to researchers and forensic investigators and proposals have been made to equip more classes of vehicles with recorders. Human factors has traditionally been the discipline that examines a system from end to end including its human operators, equipment, ambient environment, and operating rules. The typical role of the human factors specialist is to help integrate the various system components into a harmonious and productive entity. This role is particularly germane to the forensic analysis of traffic crashes. Using human factors principles such as those enumerated in this chapter will invariably provide a more complete picture of crash causation, including salient interactions among possible causal factors. Thus, for example, the human factors analyst will not only determine if a driver made an error but also assess vehicle, environmental, personal, and organizational elements that may have induced the error. This, in turn, can provide a plaintiff with new theories for a complaint or a defendant with improved arguments to deflect liability. The human element is the one about which expert and nonexpert witnesses have been allowed to make subjective evaluations, sometimes with little foundation. This is probably because less is known about the behavior of drivers and other road users in events that lead to crashes than about most of the other factors involved. For example,
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even though the effects of alcohol on many aspects of human performance and behavior have been studied extensively and there is a relatively good understanding of some doseresponse relationships for alcohol, many aspects of driving and the effects of alcohol are still not clear, particularly at low concentrations. Our best information probably comes from epidemiological studies and secondly from experimental studies. However, the latter bear the burden of generalization to a particular set of traffic circumstances and the former fail to pinpoint the nature of the performance affected. Although the information on alcohol and driving performance is far from complete, it is much more tenuous for other drugs such as cannabis, methadone, stimulants, and hallucinogens. Evidence of impairment for benzodiazepines, particularly for older and longer half-life drugs, is more conclusive. There is a great need for models of human performance to aid the forensic analyst. These may take the form of check lists or taxonomies of types of crashes, such as described for the evaluation and analysis of pedestrian and bicycle crashes or such as the concepts of positive guidance. Positive guidance has an interesting historical development because it arose as a result of two narrow-bridge crashes and the congressional hearings that followed to find solutions to “America’s narrow-bridge problem.” It soon became apparent that the principles being developed were not only appropriate for narrow bridges but equally applicable to the broad range of hazardous locations on the nation’s highways. Then Federal Highway Administrator Norbert T.Tiemann testified that, if we could not physically protect motorists at all hazardous locations, “we must give them enough information so that they can protect themselves.” Positive guidance is an integrated human factors/traffic engineering tool designed to enhance safety at hazardous locations. As an analytic tool, it enables forensic human factors and traffic engineering practitioners to determine whether highway-related information, i.e., the design and layout of the highway and its devices, plays any underlying role in contributing to crashes. At a higher level of analytical modeling and simulation of human performance are models such as night driving visibility models. They can at least be used as good first approximations of the ability of drivers to detect objects in darkness even when confronted by glare of other headlamps and street lamps. Models of driver headway change detection and relative velocity detection should also be useful tools in evaluating perceptual aspects of rear-end or head-on crashes. As the science of human factors continues to develop, more and better tools will become available that can aid the forensics human factors analyst and lead to a greater understanding of the numerous interactions among road users and their environment. The human factors professional will play a more important role in the future because of the growth in complexity of the traffic system and increasing demands on the human’s information processing. The need to understand these interactions and their positive and negative effects on driver and system safety performance, as well as the ability to explain them to a jury, will remain a continuing and growing challenge to human factors forensic practitioners.
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13.8 Checklist of Main Factors to Consider in Traffic Collisions Primary factor Considerations Line of sight
Visibility
Audibility
Detection
Perception
Decision
Primary factor Response
Expectancy
Stress
Drugs/alcohol
Obstructions external to the vehicle Buildings, trees, vegetation, signs, other vehicles Obstructions internal to the vehicle and vehicle structure Vertical and horizontal alignment of road Illumination, street lighting, vehicle lighting, sun, moon Visual adaptation Glare Contrast Reflectivity, fluorescence Horns, bells, emergency vehicle sirens Background sounds, masking Hearing loss Stimulus Threshold Differential threshold Alertness, workload Movement Salience Recognition, encoding Ambiguity Interpretation Comprehension Exposure, learning Evaluation of information Evaluation of alternative responses Costs/effectiveness, effort Determination of response
Considerations Slow, stop, accelerate, reverse Turn, swerve Walk, run, look, listen Modulate control, turn on or off Familiarity Exposure Mental model Assumption, publicity Training Maturity, risk level acceptance Behavior of others Design-induced conditions Experience Knowledge Risk evaluation, training Personal, psychological Exposure
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Time of consumption, time from end of consumption Type of drug Amount consumed Amount measured in body fluids, what and when measured Effects on performance and behavior Tolerance Driver/pedestrian characteristics Age, sex, height, weight Body fat Experience, prior driving record and violation record Training Hearing, vision and force/reach abilities Physical disabilities Familiarity with traffic regulations Fatigue Hours of service Sleep deprivation, sleep apnea Boredom, vigilance, attention External environment Rain, fog, snow, heat, cold, clear, dry, wet Available friction Road characteristics, horizontal and vertical alignment Speed limit Traffic density Traffic controls, signs, railroad crossing Road delineation Law enforcement, automated enforcement Signs and signals Guide signs, regulatory signs, warning signs Sign location, illumination, reflectorization, cleanliness Traffic signals, railroad crossing signals Pedestrian signals Construction zone signs Advance warning signs Warrants for signs and signals Roadway markings Edge line delineation, center line markings No-passing zones Construction zone markings Delineators Channelization devices, barricades Stop line, railroad crossing marking, turn lane
Primary factor
Considerations
In-vehicle Controls, displays Road noise, heater/air-conditioning blower Radio, cell phone, environment map displays, conversation, children, other passengers Temperature, fogged windows Insulation from outside warning-sound sources Isolation from road and other external conditions Ride conditions, vehicle loading Driver’s seated position Eye location Accessibility of controls/displays Vehicle Condition of windows, headlamps, other lamps, reflective devices Brake system: total or partial loss, wear Antilock brakes, air brake system lag Tire condition, inflation Steering system condition, free play, power-assist failure Control force requirements
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Meulemans, A., Hooft, P., Van Camp, L, De Vrieze, N., Buylaert, W., and Wenning R., 1996, Belgian toxicology and trauma study: une étude portant sur la presence d’alcool, de médicaments et de drogues illicites chez des conducteurs victimes d’accidents de la route. Toxicological Society of Belgium and Luxembourg. Miller, N.D., Baumgardner, D., and Mortimer, R.G., 1974, An evaluation of glare in nighttime driving caused by headlights reflected from rearview mirrors. Society of Automotive Engineers report 740962, Warrendale, PA. Morgan, J., 1988, The “scientific” justification for urine drug screening. Schaffer Library of Drug Policy. http://www.druglibrary.org/schaffer/MISC/sciurin2.htm. Mortimer, R.G. and Becker, J., 1973, Development of a computer simulation to predict the visibility distance provided by headlamp beams. University of Michigan, report UM-HSRI-HF73–15, Ann Arbor, MI. Mortimer, R.G., 1974, Some effects of road, truck and headlamp characteristics on visibility and glare in night driving. Society of Automotive Engineers, report 740615, Warrendale, PA. Mortimer, R.G., 1975, Eye fixations of drivers in night driving with three headlamp beams. Proc. Soc. Photo-Optic. Eng. , 57, 81–88. Mortimer, R.G., 1976, Implications of some characteristics of drivers for brake system performance. Proc. Int. Conf. Braking Road Vehicles , Institution of Mechanical Engineers (London), Loughborough University, 187–195. Mortimer, R.G., 1981, Car following evaluation of braking deceleration signals. Society of Automotive Engineers, report 810188, Warrendale, PA. Mortimer, R.G., 1991, Visual factors in rail-highway grade crossing accidents. Proc. Hum. Factors Soc. 35th Annu. Meeting , 600–602. Mortimer, R.G., 1994, Oh! say, can you hear that train coming to the crossing. Proc. Hum. Factors Ergonom. Soc. 38th Annu. Meeting , 898–853. Mortimer, R.G., 1996, The effect of expectancy on visibility in night driving. Proc. 40th Annu. Meeting Hum. Factors Ergonom. Soc. , 506–510. Mortimer, R.G., 1998, Motorcycle braking controls—an ergonomic dilemma, Proc. Silicon Valley Ergonom. Conf. Exposition , ErgoCon ‘98, 102–106. Mortimer, R.G., 2001, The nighttime pedestrian accident: human factors issues and a case study. Proc. 45th Annu. Conf. Hum. Factors Ergonomics Soc. , 833–837. Mortimer, R.G. and Schuldt, R.C., 1980, Field test evaluation of gap acceptance of drivers as a function of motorcycle front lighting. Proc. Int. Motorcycle Safety Conf. , Washington, D.C., May 18–23, 945–954. Moskowitz, H., 1985a, Guest editor’s introduction. Accident Anal. Prev. , 17(4), 281–282. Moskowitz, H., 1985b, Marijuana and driving. Accident Anal. Prev. , 17(4), 323–345. Moskowitz, H., Hulbert, S., and Mcglothin, W.H., 1976, Marijuana: effects on simulated driving performance. Accident Anal. Prev. , 8(1), 45–50. Moskowitz, H. and Robinson, C.D., 1988, Effects of low doses of alcohol on driving-related skills: a review of the evidence. Report no. DOT HS 807 280. Washington, D.C.: National Highway Traffic Safety Administration, SRA Technologies, Inc. Moskowitz, H., Burns, M., Fiorention, D., Smiley, A., and Zador, P., 2000, Driver characteristics and impairment at various BACs. National Highway Traffic Safety Administration, Washington, D.C., DOT HS 809 075. Moskowitz, H. and Fiorentino, D., 2000, Driver Characteristics and Impairment at Various BACs. U.S. Department of Transportation. National Highway Traffic Safety Administration, DOT HS 809 075, August. Moskowitz, H. and Fiorentino, D., 2002, A review of experimental studies of low BAC effects on skills performance. In Mayhew, D. and Dussault, C. (Eds.), Alcohol Drugs, and Traffic Safety— T’2002 , (Montreal, Canada, CD-ROM) National Committee on Uniform Traffic Laws and Ordinances, 2000. Uniform Vehicle Code . Alexandria, VA.
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National Highway Traffic Safety Administration (NHTSA), 1999, Horizontal gaze nystagmus state case law summary, http://www.nhtsa.dot.gov/. National Institute of Alcohol Abuse and Alcoholism (NIAAA), 1994, Alcohol-related impairment. Alcohol Alert , 25, PH 351, July 1994. NIAAA,1997, Alcohol metabolism. Alcohol Alert , 35, PH 371, January 1997. NIAAA, 2001, Cognitive impairment and recovery from alcoholism. Alcohol Alert , 53, July 2001. National Safety Council, 2001, Injury Accident Facts , 2001 ed. Chicago: NSC. National Safety Council, 2002, International Accident Facts , 3rd ed. Chicago: NSC. Neutel, C.I., 1995, Risk of traffic accident injury after a prescription for benzodiazepine. Ann. Epidemiol , 5(3), 239–244. New Mexico Department of Health, 2002, Toxicology bureau fact sheet: drug-impaired drving. www.sld.state.nm.us/drug. Noy, I.Y., 1997, Ergonomics and Safety in Intelligent Transportation Systems , Erlbaum: Mahwah, NJ. O’Hanlon, J.F., 1993, Ten ways for physicians to minimize the risk of patients causing traffic accidents while under the influence of prescribed psychoactive medication. Primary Care Psychiatry , 1,77–85. O’Hanlon, J.F. and Ramaekers, J.G., 1995, Antihistamine effects on actual driving performance in a standard test: a summary of Dutch experience, 1989–94. Allergy , 50, 234–242. O’Hanlon, J.F., Vermeeren, A., Uiterwijk, M.M.C., Van Veggel, L.M.A., and Swijgman, H.F., 1995, Anxiolytics’ effects on the actual driving performance of patients and healthy volunteers in a standardized test. Neuropsychobiology , 31, 81–88. Olson, P.L. and Sivak, M., 1983, Improved low beam photometries. University of Michigan, report UMTRI 83–9, Ann Arbor, Michigan. Olson, P.L., Cleveland, D.E., Fancher, P.S., Kostyniuk, and Schneider, L.W., 1984, Parameters affecting stopping sight distance, University of Michigan Transportation Research Institute Report UMTRI-84–15. Olson, P.L., 1988, Minimum requirements for adequate nighttime conspicuity of highway signs. University of Michigan report: UMTRI-88–8, Ann Arbor, MI. Perchonok, K., 1972. Accident Cause Analysis. Cornell Aeronautical Laboratories, Report ZM5010-V-3. Post, T, Alexander, G., and Lunenfeld, H., 1981, A users’ guide to positive guidance, 2nd ed., report no. FHWA-TO-81–1 Federal Highway Administration, Washington, D.C. Post, T, Robertson, D., Price, H., Alexander, G., and Lunenfeld, H., 1977, A users’ guide to positive guidance, Federal Highway Administration, Washington, D.C. Ray, W., Fought, R., and Decker, M., 1992, Psychoactive drugs and the risk of injurious motor vehicle crashes in elderly drivers. Am. J. Epidemiol , 136, 873–883. Robbe, H. and O’Hanlon, J., 1993, Marijuana and actual driving performance. U.S. Dept. Transportation, National Highway Traffic Safety Administration, 9. Roper, V.J. and Howard, E.A., 1938, Seeing with motorcar headlights. Trans. Illumination Eng. Soc. , 33, 417–427. Roth, T. and Roehrs, T, 1985, Determinants of residual effects of hypnotics. Accident Anal. Prev. , 17(4), 291–296. Rowan, NJ. and Walton, N.E., 1976, Lighting of traffic facilities. In Baerwald, J. (Ed.), Transportation and Traffic Engineering Handbook , (Englewood Cliffs, NJ: Prentice Hall), 912–943. Rumar, K. and Berggrund, V., 1973, Overtaking performance under controlled conditions, Proc. 1st Intl. Conf. on Driver Behavior Res. , Zurich, Switzerland. Schwenk, C., 1998, Marijuana and job performance: comparing the major streams of research. J. Drug Issues , 28(4), 941–970. Simpson, H.M., 1985, Polydrug effects and traffic safety. Alcohol Drugs Driving , 1(1–2), 27–44.
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Simpson, H.M. and Vingilis, E., 1992, Epidemiology and special population surveys, in Ferrara, S.D. and Giorgetti, R. (Eds.), Methodology in Man-Machine Interaction and Epidemiology on Drugs and Traffic Safety , Centre of Behavioural and Forensic Toxicology: Padova, Italy. Skegg, D.C.G., Richards, S.M., and Doll, R., 1979, Minor tranquillisers and road accidents. Br. Med. J. , 1, 97–919. Smiley, A., 1999, Marijuana: on-road and driving-simulator studies. In H.Kalant, W.Corrigall, W.Hall, and R.Smart (Eds.), The Health Effects of Cannabis (Toronto, Ontario Addiction Research Foundation), 173–191. Snyder, M.H. and Knoblauch, R.L., 1971, Pedestrian safety: the identification of precipitating factors and possible countermeasures. Operations Research, Inc., final report U.S. Department of Transportation, National Highway Traffic Safety Administration, report no. DOT HS-800 403. Soderstrom, C.A., Dischinger, PC., Kerns, T.J., and Trifillis, A.L., 1995, Marijuana and other drug use among automobile and motorcycle drivers treated at a trauma center. Accident Anal. Prev. , 27(1), 131–135. Staak, M., Kaferstein, H., and Sticht, G., 1993. Importance of quantitative estimation of opiates and cannabinoids for determination of driving performance. In Utzelmann, H.D., Berghaus, G., and Kroj, G. (Eds.), Alcohol, Drugs and Traffic Safety—T’92 . H-D. Verlag TÜV Rheinland GmbH, Köhn, 490–496. Stoduto, G., Vingilis, E., Kapur, B., Shen, W., McLellan, B., and Liban, C., 1993, Alcohol and drug use among motor vehicle collision victims admitted to a regional trauma unit: demographic, injury and crash characteristics. Accident Anal. Prev. , 25(4), 411–420. Stokes, A. and Kite, K., 1999, Grace under fire: the nature of stress and coping in general aviation. Chapter 4 in O’Hare (Ed.), Human Performance in General Aviation ,, Aldershot: Ashgate. Summala, H., 1981, Driver/vehicle steering response latencies. Hum. Factors , 23(6), 683–692. Swain, A.D. and Guttman, H.E., 1983, Handbook of Human Reliability Analysis with Emphasis on Nuclear Power Plant Applications , Sandia Laboratories, NUREG/CR-1278, U.S. Nuclear Regulatory Commission. Sweedler, B., 2002, Worldwide trends in drinking and driving: has the progress continued? In Mayhew and Dussault (Eds.) Alcohol, Drugs, and Traffic Safety—T’2002 (Montreal, Canada, CD-ROM). Triggs, T.J. and Harris, E.C., 1982, Reaction time of drivers to road stimuli. Monash University, report HFR-12. USDOT, 1978, Railroad-Highway Grade Crossing Handbook , Federal Highway Administration, FHWA-TS-78–214, U.S. Department of Transportation, Washington, D.C. USDOT, 1998, Traffic safety facts 1997, National Highway Traffic Safety Administration, U.S. Department of Transportation, Washington, D.C. USDOT, 2001, Traffic safety facts, 2000, National Highway Traffic Safety Administration, U.S. Department of Transportation, Washington, D.C. van Laar, M.W., van Willigenburg, A.P.P., and Volkerts, E.R., 1993, Over-the-road and simulated driving: Comparison of measures of the hangover effects of two benzodiazepine hypnotics. In Utzelmann, H.D., Berghaus, G., and Kroj, G. (Eds.), Alcohol, Drugs, and Traffic Safety—T’92 , Verlag TÜV Rheinland GmbH, Köhn, 672–677. Vermeeren, A., de Gier, J.J., and O’Hanlon, J.F., 1994, Methodological guidelines for experimental research on medicinal drugs affecting driving performance: an international expert survey. J. Traffic Med. , 22(4), 173–174. Verstraete, A.G., 2002, Roadside drug testing: the results of the ROSITA Project. In Mayhew and Dussault (Eds.), Alcohol, Drugs, and Traffic Safety—T’2002 (Montreal, Canada, CD-ROM). Vingilis, E.R. and MacDonald, S., 2002, Review: drugs and traffic collisions. Traffic Injury Prev. , 3(1), 1–11. Volkerts, E.R. and van Laar, M.W., 1993, A methodological comparative study of over-the-road and simulated driving performance after nocturnal treatment with lormetazepam 1 mg and
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oxazepam 50 mg. In Utzelmann, H.D., Berghaus, G., and Kroj, G. (Eds.), Alcohol, Drugs, and Traffic Safety—T’92 , Verlag TÜV Rheinland GmbH, Köhn, 664–671. Volkow, N.D., Chang, L, Wang, G.-J., Fowler, J.S., Leonido-Yee, M., Franceschi, D., Sedler, M.J., Gatley, S.J., Hitzemann, R., Ding, Y.-S., Logan, J., Wong, C., and Miller, E.N., 2001a, Association of dopamine transporter reduction with psychomotor impairment in methamphetamine abusers. Am. J. Psychiatry 158(3), 9414–9418. Volkow, N.D., Chang, L., Wang, G.-J., Fowler, J.S., Franceschi, D., Sedler, M.J., Gatley, S.J., Miller, E., Hitzemann, R., Ding, Y.-S., and Logan, J., 2001b, Loss of dopamine transports in methamphetamine abusers recovers with protracted abstinence. J. Neurosci. , 21(23), 9414– 9418. Welford, A.T., 1973, Stress and performance. Ergonomics , 16, 567–580. Willekens, M., Samyn, N., De Boeck, G., Maes, V., and Versraete, A., 2002, First experiences with the new law on DUID in Belgium: Field results and plasma levels of illicit drugs. In Mayhew, D. and Dussault, C. (Eds.), Alcohol Drugs, and Traffic Safety—T02. D , Quebec, CD-ROM. Wolf, E., 1960, Glare and age. Arch. Opthalmol , 64, 502–514. Woods, J.H., Kats, J.L., and Winger, G., 1992, Benzodiazepines: use, abuse and consequences. Pharmacol. Rev. , 44, 151–347. Worm, K., Steentoft, A., and Toft, J., 1996, Drugs and narcotics in Danish drivers, J. Traffic Med. , 24(1–2), 39–42. Xie, X., Rehm, J., Single, E., and Robson, L., 1996, The economic costs of alcohol. Tobacco and illicit drug abuse in Ontario: 1992. Toronto: Addiction Research Foundation.
Further Information Alexander, G.J. and Lunenfeld, H., 1986, Driver expectancy in highway design and traffic operations, U.S. Department of Transportation, report FHWA-TO-86–1. Deese, J., 1955, Some problems in the theory of vigilance. Psych. Rev ., 62(5), 359–368 Forbes, T.W. (Ed.), 1972, Human Factors in Highway Traffic Safety Research , New York: John Wiley & Sons. Green, D. and Swets, J.A., 1966, Signal Detection Theory and Psychophysics , New York: John Wiley & Sons. Henderson, R.L. (Ed.), 1987, Driver performance data book, Vector Enterprises, report DOT-HS807–121, U.S. Department of Transportation, NHTSA. Johansson, G. and Rumar, K., 1971, Drivers’ brake reaction times. Hum. Factors , 13(1), 23–27. Mace, D,. Garvey, P., Schwab, R., and Adrian, W., 2002, Countermeasures for reducing the effects of headlight glare. Washington, D.C.: AAA Foundation for Traffic Safety. National Safety Council, 2002, Injury Facts 2001 Edition . Chicago: Illinois. Olson, P.L., 1996, Forensic Aspects of Driver Perception and Response , Tucson, AZ: Lawyers and Judges Publishing Co. Peters, G.A. and Peters, B.J. (Eds.), 1988, Automotive Engineering and Litigation , New York: Garland Law. Sens, M.J., Cheng, P.H., Wiechel, J.F., and Guenther, D.A., 1989, Perception/reaction time values for accident reconstruction, Society of Automotive Engineers report 890732. Shinar, D., 1978, Psychology on the Road: the Human Factor in Traffic Safety , New York: John Wiley & Sons. Staplin, L., Lococo, K., Byington, S., and Hartley, D., 2001, Guidelines and recommendations to accommodate older drivers and pedestrians, Federal Highway Administration, report FHWARD-01–051. Wickens, C., 1984, Engineering Psychology and Human Performance , Columbus, OH: Merril.
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See Also (complete references are in reference list): Compton et al. (2002); Beirness and Simpson (2002); Chamberlain and Solomon (2002); Mann et al. (1998); and Moskowitz and Fiorentino (2000) for reviews on the effects of low doses of alcohol on driving-related skills Del Rió and Alvarez (1995a) for a general review on the influence of illegal drugs on driving within the context of European Community regulations Ferrara et al. (1994) for a review of laboratory and epidemiological studies of psychoactive substances and driving Home and Barrett (2001) for a review of over-the-counter medicines Hunter et al. (1998) for a detailed, tabulated review of samples, methods, and findings of epidemiological and experimental studies Krüger et al. (1995) and Compton et al. (2002) for alcohol dose-response crash risk Lillsunde (1998) for a review of epidemiological studies McBay (2002) and DeLong (2002) for a detailed review of drugs and their effects Woods et al. (1992) for a comprehensive review of benzodiazepines use and consequences, including averse driving outcomes
Additional Literature of Interest: Horizontal Gaze Nystagmus (HGN) Oct 2, 2002 Horizontal Gaze Nystagmus State Chart Summary http://www.nhtsa.dot.gov/people/injury/enforce/nystagmus/app_c.html Oct 2, 2002 Melethil S., Breath tests for blood determination ratio: partition ratio, http://www.forensicevidence.com/%20site/Biol_Evid/Breath_Tests.html, Oct 2, 2002 http://www.druglibrary.org/schaffer/MISC/sciurin2.htm http://www.druglibrary.org/schaffer/MISC/driving/ddimp.htm http://www.druglibrary.org/schaffer/Library/studies/dwda/staffl.htm http://www.toxicologyassociates.com/toxicsubreg3.htm
14 Estimating Driver Response Times Jeffrey W.Muttart Accident Dynamics Research 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
14.1 Introduction This chapter addresses automobile driver response times and the factors that influence them. Previous research has reported driver response times from 0.5 to 10 sec for various tasks. This chapter will offer reasons for different response time results. Muttart (2003a, b, 2004) found that different results can be explained and quantified by methodology and substantive variables. Thus, a mean response time for various scenarios can be estimated. The precision of such estimates will also be addressed. First, we must clarify and explain terms. Perception in the case of a driver’s response is something beyond simple visibility; it is the organization and interpretation of sensations (visual, tactile, or auditory). Before an investigator can estimate a driver’s “perception”—response time, he should understand the processes that may delay the organization and interpretation of what may be visible (or heard or felt). The terms driver response time, brake reaction time, perception—reaction time, and perception—response time have been used almost interchangeably at times. This inappropriate use of the terms could lead to confusion. The reader should understand that a driver’s response does not follow an orderly step-by-step process. Research has shown that even the response may influence the perception (Bekkering and Neggers, 2002) and that drivers experience response inertia when the perception complexity likely influences the motor response time (Muttart, 2004). However, as a means to compare responses, Figure 14.1 was prepared to show the traveling distance components of a driver’s response.
FIGURE 14.1 The distance components of a driver’s response. (Reprinted with permission from SAE paper 2003–01–0885. © 2003 SAE International.)
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Driver response is a generic term used to describe any portion of a driver response time. Driver response time encompasses from first visibility (“something” may be visible but nothing has been recognized as a hazard) to first vehicle response. Perceptionresponse time is from first perception of an immediate hazard until first vehicle response. Perception-reaction time is from first perception of a hazard until first reaction (foot off the accelerator) by the driver, and brake reaction time or brake response time is the time from first perception of a hazard until the foot touches the brake (there is no effective deceleration at that point). As Figure 14.1 shows, the investigator must assure that the estimated response time he is using is applicable to the particular situation. Furthermore, if relying upon a research study, the investigator should make sure that he knows how the response time was measured and should not rely upon the terminology used by an author. Also, in most situations, before a driver can perceive an object as an immediate hazard, he must attend to it. Therefore, we should address attention. 14.2 Attention vs. Inattention Police reports frequently cite “inattention” as a cause in many collisions without any support for such a conclusion. Some investigators have supported “inattention” based upon a lack of skid marks on the road or because the driver was not able to recall seeing traffic that the investigator (with hindsight bias) may believe is a salient object. An investigator must understand what “attention” is before being able to evaluate a driver’s response. In simple terms, attention is a narrowing of focus. If investigators use the word focus rather than the word attention, a great many misunderstandings may be avoided. Any driver who is conscious is attentive. The question that must be asked is what was the driver attentive to (focused upon)? There are appropriate and inappropriate causes for inattention to a road hazard. An example of an inappropriate attention is a driver talking on a cellular telephone, eating fast food, and steering with his legs. A driver focused upon a possible path-intruding vehicle to his left will not be focused upon a previously hidden pedestrian who emerges suddenly from between two vehicles on the right and is struck. Other examples of appropriate inattention would be the allocation of attention to a vehicle in the immediate area at the expense of a pedestrian or other traffic that is downstream and not an immediate hazard. Summala and colleagues (1998) performed a study of drivers who were required to respond to the sudden slowing of a lead vehicle when focused on the instrument panel or rear view mirror. These researchers found that drivers responded much more slowly to the lead vehicle when the driver’s attention was allocated to these areas. A safe driver must navigate, guide, and control his vehicle (Alexander and Lunenfeld, 1975) and monitor the environment and vehicles in the area. Therefore, instances of acceptable inattention will occur. It is up to the investigator to attempt to differentiate between acceptable and unacceptable inattention. Consequently, an investigator must consider several things before evaluating a driver’s response time or response choice—basically, 10 considerations that account for the differences between what the investigator sees and knows and what the driver saw and knew. These considerations can be recalled by the acronym IN CAR CREED
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(immediacy, neutralized, contrast, anticipation, recall, context and priming, relative velocity, eccentricity, expectancy, driving tasks). 1. Immediacy. Was there any immediate reason to respond before the driver perceived the hazard or was the object a secondary stimulus to one being mentally processed (Batchelder et al., 2003; Harrell, 1994)? A sight line of 1 km has no bearing upon a collision if the object was a hazard for only 25 m before the collision. 2. Neutralized. Was there reason to believe that the driver may have mentally “neutralized” the stimulus by an earlier corrective action (Fuller, 1984)? (For example, a driver slowed and moved away slightly in response to a roadside pedestrian, but the pedestrian suddenly ran into the road when there was no time to respond.) 3. Contrast. Does the object to be responded to contrast with its background when not being focused upon? Is the object easily identifiable and intense enough to grab a driver’s attention away from that to which he is already attending (Mack, 2003; Most et al., 2001; Simon and Chabris, 1999; Muttart, 2003)? This is particularly true in situations in which the driver may not be adapted to the ambient level of light or if the ability to discriminate between an object and its background is degraded significantly by glare. 4. Anticipation. Drivers come to expect certain things with time. Hole and Tyrell (1995) conducted a laboratory study and found that when slides depicting traffic were shown to subjects rapidly, their responses to a motorcycle without a headlight decreased as the likelihood of a motorcycle having a headlight turned on increased. The subjects developed a “set” to allow for a quicker search technique by looking for headlights rather than motorcycles in that laboratory study. Therefore, (right or wrong) if a driver learns that it is more efficient to look for headlights, he is more likely to miss an approaching vehicle without headlights. Furthermore, if he knows the stimulus and knows the appropriate response, response time will improve. 5. Recall. Do not evaluate the driver’s recall of traffic or signs but ask (through the investigation) if the driver’s response was appropriate (Fisher, 1992; Carpenter, 2001; Louma, 1988; Resnick, 2004). 6. Context and priming. When a driver is alerted to what he is going to experience and what it means to him, then performance will likely improve. Simply because there may have been a sign or the lack of a sign may not in and of itself be evidence that a driver will know what is coming and what to do about it. Additionally, a driver may not be able to determine that the stray light or flicker of movement seen today is relevant to safe driving because similar nondescript lights have never been a problem in the past. 7. Relative velocity detection threshold. Drivers will not be able to detect the rate of closure on a lead vehicle without other cues until the subtended arc angle of the object expands in the observer’s field of view at a rate exceeding 0.003 rad/sec (Hoffman and Mortimer, 1996; Todosiev, 1965). Also, most road lines are 4 in. (1.6 cm) wide. A person with 20/20 visual acuity can read a 4-in. (1.6 cm) letter from approximately 220 ft (70 m). Therefore, it may be difficult to determine exact tire positions relative to a center line from distances greater than this. 8. Eccentricity. Considering that his central vision is a very narrow cone reported to be no more than a few degrees in each direction from straight ahead, it is unlikely that a
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driver will be looking directly toward the hazard. Thus, the investigator should assume that the hazard had to be detected in the driver’s peripheral visual field. 9. Expectancy. This has been cited as a primary reason for slow or inappropriate responses (Alexander and Lunenfeld, 1986; Green, 2000; Dewar and Olson, 2002). “Unexpected” could mean needing to respond to a satellite falling from the sky or it could mean not knowing when a traffic signal will change. Investigators should not evaluate the subjective term of “expectancy,” but should address the manner in which expectancy influences a response in a more direct and objective way. A single correction factor (Dewar and Olson, 2002, p. 372; Roper and Howard, 1938) to account for expectancy is not scientifically justifiable. “Lack of expectation” may have a different influence in each case, based upon current research (Muttart, 2003a, b). If a driver does not expect a hazard, he may experience any or all of the following: • Eccentricity: looking in a different direction • Context: looking for or expecting a different hazard • Anticipation: may not know what to look for or where to look and may not be adapted to the necessary level of lighting • Operant conditioning: may be anticipating a different response and misinterpret the situation or pattern that he is seeing • Response complexity: may not have a conditioned response available (Bekkering and Neggers, 2002) or may interpret the traffic pattern as something that he has seen before when in fact it is not • Contrast: the target may not be easily distinguishable when compared to its background and other objects in the area • Number of stimuli: despite several things to look at, the driver who has expectancy can weed through all the visual noise and focus specifically upon the hazard, while most real-life drivers do not have this luxury 10. Driving task. Drivers do not view the scene as a stationary observer. They are viewing an ever-changing scene and typically do not gaze in any one direction. The typical river changes fixation location approximately one to two times per second (OCED, 1970; Lee et al., 2003). They also must devote mental resources to the tasks of navigation, guidance, and control of their vehicle (Alexander and Lunenfeld, 1975). Lassiter et al. (Lassiter, 2002; Lassiter et al., 2002) found that people attribute unwarranted influence to a stimulus simply because it is more noticeable (to them) than other available stimuli. They referred to this as the “illusory-causation phenomena,” which could cause prejudicial effects relative to how people evaluated certain types of evidence. Objects that stand out in the visual field or are the focus of attention are more likely to be judged as originators of the event, even when no objective basis for such a conclusion exists. Therefore, it is common for postcrash investigators to suffer from the illusory-causation phenomena. To avoid this, the investigator should understand and consider the 10 considerations listed earlier. More than a few expert witnesses have been known to use a rule-of-thumb estimate for expectancy based upon the research by Roper and Howard (1938). These researchers conducted a test in which they placed a mock pedestrian in the path of the subjects, noted their response time, backed up and again approached the “pedestrian,” and noted the time necessary to respond to the pedestrian when they knew he was there. Roper and Howard
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may not have measured the effects of “expectancy” but instead measured the effects of their methodology; they were measuring perception-response, so someone had to determine when the pedestrian was perceivable. Expectancy is not an on or off switch; rather, there are degrees of expectancy. Muttart (2004) found that as the complexity of the situation increased, braking latency (limb movement) increased, and brake force decreased. Therefore, at least part of Roper and Howard’s results can be explained by their methodology. Furthermore, their findings could not be corroborated in a literature review and the research by Muttart has shown that a single correction factor is not justifiable. Muttart (2000) indicated that the acronym of CASE CR might be used to understand the probability of detection. The acronym stands for contrast, anticipation (or bias toward that object), strength of sensory stimulus, eccentricity, cognition, and response complexity. Muttart based his acronym upon Bundensen’s theory of visual attention (1990) and Bailey’s probability of detection (Peterson and Dugas, 1972). Factors such as alcohol use and fatigue may influence a driver’s ability to detect hazards based upon how they influence each of the variables in CASE CR. If we look at the CASE CR acronym, we can see that even the anticipated response may influence the driver’s ability to detect an object. According to Bekkering and Neggers (2002), in general, we are better at finding objects to which we are prepared to respond. This selection for action mechanism has also been supported by the research of others (Airport, 1987; Deubel and Schneider, 1996).
FIGURE 14.2 Response times of drivers responding to different stimuli during daylight and darkness.
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If a driver is attentive toward the direction of a hazard, this does not guarantee that the object will be detected, as is the case with inattentional blindness research (Mack, 2003; Most et al., 2001; Simon and Chabris, 1999). Research regarding inattentional blindness suggests that drivers who are mentally engaged in a primary task may not identify a noncontrasting second object. The most common reasons for drivers’ failure to detect are due to lighting and contrast difficulties when responding to nonilluminated objects at night. Simply stated, if the hazard is not easily identifiable as an immediate hazard, then a driver is not likely to perceive and respond to it until it is. Delayed detections are more common at nighttime, but nighttime is not associated with much slower response times in all cases. Driver response times to illuminated objects such as traffic signals and illuminated vehicles within lighted intersections have not been much greater at night than during daylight (See Figure 14.2). Muttart (2003a, b) compiled the response times of subjects and real-life drivers by what they were responding to and day vs. darkness (dusk, dawn, and nighttime responses). In Figure 14.2, there is a significant difference in response times and range of responses to pedestrians and bicycles at night compared to daylight. Therefore, objects that are not illuminated (or objects that do not offer an easily identifiable pattern) usually offer the greatest difficulty for a driver at night. For investigation of a collision involving an easily identifiable hazard, proceed to Section 14.5; otherwise, read on. 14.3 Driver Response to Objects Not Easily Identified A forensic investigator may account for a delayed detection interval (a term used by Olson, 1996) depicted in Figure 14.1 in two ways. The first method is to determine a threshold discernibility distance to account for the detection interval (depicted in Figure 14.1) and to apply a perception—response time from that location. Threshold discernibility, also known as the detection interval, detection threshold, or the absolute threshold, is the distance at which 50% of subjects will be able to identify the object. The second method is “distance to impact” research. Distance to impact accounts for the detection interval and perception but does not account for the driver’s motor response and the vehicle latency. An assumed starting point (where perception occurs) is necessary when using perception-response times in scenarios involving a response to an object that is not easily identifiable. The perception starting point is most commonly based upon visibility distance models or illumination criteria, or by measuring the headlight beam illumination pattern of an exemplar vehicle. Each method has inherent flaws and is based upon assumptions that certain visibility or illumination levels are associated with a driver’s ability to perceive a hazard in a real-world setting. Most “visibility” models involve numerous specific measurements. Visibility models frequently require several lighting, contrast, and reflection measurements. Objective and accurate measurements should be utilized whenever possible. The investigator must also consider the tasks of driving relative to the manner in which the model is based.
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An example of an illumination model is the twilight distance method (Liebowitz and Owens, 1991; Owens et al., 1989), which is based upon the premise that the end of civil twilight is when there is a need
TABLE 14.1 Twilight Illumination Distance Applied to SAE Ground Vehicle Lighting Standard J1383 Candela Twilight distance 25″ Headlight height 10 to 90° up and 45° left to right= 125 20.4 ft 20.4 ft 1° up and 1.5° left= 700 48.3 ft 48.3 ft 1.5° up and 1° right= 1400 57.7 ft 57.7 ft 0.5° up and 1–1.5° left= 1000 68.3 ft 68.3 ft 0.5° up and 1–3° right= 2700 94.9 ft 94.9 ft 0.5° down and 1–1.5° left= 3000 100.0 ft 100.0 ft 4° down and 4° right= 8000 163.3 ft 29.8 ft Max: 0.5° down, 1.5° right= 20000 258.2 ft 239.5 ft Typical max output (2° down and 2° 30000 316.2 ft 59.7 ft right) Notes: Column three shows the minimum of the beam aim distance or the twilight distance if the headlight height is 25 in. (10 cm).
for greater lighting during outdoor activities and that the ambient illumination at civil twilight is 0.3 fc (3 lx). Thus, the conclusion was that a reasonable threshold for visibility is when objects ahead are illuminated to 0.3 fc (3 lx) or more by headlights. When testing various vehicles, this threshold distance varies due to the nonsymmetrical beam of vehicle headlights. It is recommended that an exemplar vehicle (with a similar load) be used to determine the headlight beam characteristics and to consider where within the asymmetrical beam pattern the hazard was at different times during the vehicle approach to the crash. The equation utilized in the twilight method is: TD=(cd/0.3)1/2 (14.1) where TD is the distance at which headlight illumination is equal to or greater than ambient lighting at twilight (0.3 fc) and cd is intensity in candela. As an example, Table 14.1 shows the twilight distances applied to Ground Vehicle Lighting Standard SAE J1383. With this type of model, contrast, glare, and adaptation should also be considered and accounted for if necessary. Visibility models are typically based upon the research by Blackwell (1971, 1980a, b). Blackwell had stationary observers make observations in l/30th of a second. When similar types of studies were conducted, it was noted that subjects could be responding to changes as well as visibility (VISCON, 1998). If subjects were stationary and viewing the same scene, it is not clear how Blackwell determined that they were responding to mentally seeing a target or detecting a change in the scene. Researchers from the Ford
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Motor Company (Bhise et al., 1976) attempted to validate the Blackwell data by conducting an experiment of their own. However, Farber (1988, p. 14) indicted that “we do not as yet have a complete working model [for object detection distance determination].” Farber and Matle (1988) indicated that additional work was needed to substantiate more thoroughly the field factors (environmental factors) and assumptions used in DETECT and PCDETECT computer detection distance programs. Neither the DETECT nor PCDETECT program has been released to the public. Therefore, this model is not recommended for use in a forensic setting until it is released to the public and analyzed well beyond 12 subjects. Visibility models generally account for many more variables than does an illumination model. Visibility models may consider glare, reflectivity, and contrasts luminance, and they may be used to meet the requirement for scientific support, but they usually involve a great deal of work to develop a credible estimate that has no assurance of being more or less accurate than the much simpler twilight distance model due to individual variance in low-light situations (at this time). Furthermore, visible does not equate to discernible in a real-life environment by an unsuspecting nonstationary driver. Therefore, any visibility model or method must account for the limitations of a person who is engaged in the task of driving.
TABLE 14.2 Relationship of Driver Identification Distance to Clothing Brightness Material
Feet SD Meters SD
Ref.
Red/Red-Or/Or. retroreflective Red retroreflective Yell-Grn/Yell/Flr.Yell/Grn retroreflective Lime retroreflective White retroreflective White vest
Right Left Right Left Left Right
258 267 226 184 143 180
110 138 289
79 81 69 56 44 49
White vest
Left
120 114
37
Yellow Shirt Beige pants-green plaid—more unexpected Beige pants-green plaid—more unexpected Gray pants-blue jean shirt Gray pants-blue jean shirt Denim
Left Right
110 84 139 101
33 42
Turner et al., 1997 49 Muttart, 2000 Turner et al., 1997 34 Muttart, 2000 42 Muttart, 2000 88 Olson and Sivak, 1983 44 Olson and Sivak, 1983 26 Muttart, 2000 31 Muttart et al., 2003 24 Muttart et al., 2003
162
Left
84
78
26
Right Left Right
160 117 80
95 18 85
49 36 24
29 Muttart et al., 2003 5 Muttart et al., 2003 26 Olson and Sivak, 1983 Denim Left 60 33 18 10 Olson and Sivak, 1983 Notes: Speed of the vehicle ranged from 42 to 50 km/h, low beams, and the drivers were told to look for pedestrians. Right refers to the curbside and left is the opposite side.
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As mentioned earlier, visibility and illumination methods are used to determine a “point of perception” from which a perception-response time can be used. The alternative method to this would be to utilize “distance-to-impact” research results. Distance-toimpact results can be obtained from studies involving subjects in moving vehicles identifying when they could identify an object. The distance-to-impact method accounts for the time necessary to perceive an object; it is not necessary to determine a starting point or a “point of perception.” However, distance-to-impact results are from subjects who responded to the presence of a pedestrian or object and knew what they were looking for. Distance-to-impact research involves a driver or observer responding verbally or by pressing a button in response to pedestrians or objects in the road. This methodology includes the time necessary for identification and a simplified response (verbal response or time to press a button). Therefore, only the time necessary for formulating a potentially more complex response, the motor response of the driver (limb-movement time), and the inherent delay of the vehicle are not accounted for in distance-to-impact research. Motor response and vehicle latency usually account for approximately 0.75 sec (Muttart, 2004); subjects in distance-to-impact research are specifically looking for objects (but do not know when or where they will appear). The formulation of a response in distance-to-impact research is likely to be more complicated than “press the button when you see a pedestrian.” Therefore, an adjustment time of 0.75 to 1.5 sec is added at the point of identification to account for mental processing, limb movement, and vehicle latency. The identification distance is the distance to impact of an object of similar contrast and lighting identified in research. Several researchers have collected data regarding visibility distances. Research collected on a stark closed course or research from stationary observers will likely overestimate the identification distance. Laboratory studies using videotape have reported much shorter identification distances than those conducted with moving observers in more realistic environments (Olson and Sivak, 1983, 1984; Muttart, 2000; Muttart et al., 2003; Turner et al., 1997; refer to Table 14.2). The distances listed in Table 14.2 were those of observers in vehicles that were traveling 42 to 50 km/h and who were told to identify when they could see pedestrians (they were alerted to the purpose of the test); however, they did not know when or where the pedestrian(s) would appear. The investigator must effectively account for the visual noise, dynamic viewing, cognitive factors, and sensory filter that are inherent when dealing with unexpected objects in a real-life response situation. Thus, a seeing-distance study will not be an effective tool to predict the distance or likelihood of detection in most cases if the cognitive factors involved in real-world driving are not accounted for. Once the detection interval is accounted for or if there is no measurable detection interval, an estimated response time may be utilized. This leads to the question of what an appropriate perception response time is for a given situation. 14.4 Influence of Research Methods on Previous Results Previous authors have incorrectly concluded that driver response times varied and therefore could not be predicted (Sohn and Stepleman, 1998; Dilich et al., 2002).
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However, these studies mixed several different stimulus-response situations—many involving different methodologies—and then claimed that because the results were so different, response times could not be predicted. Muttart (2001, 2003a, b, 2004) found that the different results could be accounted for if the methodology of the study and the stimulus (object or hazard) were accounted for. The response time results reported will not only change due to the stimulus (hazard) to which the subjects responded, but the methodology of the experiment could also explain and predict the different results obtained among studies. The methodology variables examined in the research by Muttart (2003a, b, 2004) include the driving task, anticipation, experiment type, response complexity, and the amount of the transition time (limb movement and vehicle latency) accounted for. In some studies, the subjects did not have the burdens of the driving task. Anticipation varied in that a few researchers told the subjects what to look for and what to do in response and others did not warn the subjects at all. In some studies, subjects were told to brake in response and in others the driver was allowed to select his or her response. The differences among laboratory, simulator, closed-course, and road testing were a significant factor, as was the method used to measure the response. Some studies stopped the clock when the foot came off the accelerator (perception-reaction time), some measured brake reaction time, and others measured the full response. Therefore, the methodology of the study was a significant factor in the results. Alexander and Lunenfeld (1975) indicated that the driving task was a significant factor to consider when evaluating the response of drivers. These researchers claimed that the task of driving involves navigation, guidance, and control tasks, all of which contribute to the workload on a driver. Driver response results (Cohn, 1987; Yoo et al., 1999; Fambro et al., 1998) have subsequently corroborated Alexander and Lunenfeld. Overall, drivers needed more than twice as much time to respond to a light stimulus when engaged in the task of driving than when seated in a stationary vehicle. Therefore, to address properly how drivers may respond, the workload involved in the task of driving must be accounted for. Other methodology variables that Muttart found to be statistically significant were experiment type, transition time, and anticipation. The manner in which Muttart defined his variables can be found in Appendix A at the end of this chapter. In general, as the methodology of the experiment became closer to that of real life, the response times increased. Therefore, if the subject knew the stimulus (“When you see the light go on…”) and knew the appropriate response (“…depress the brake pedal”), the response times were faster. Response times increased from laboratory to simulator to closed course and then to road studies. Lastly, if a study measured a perception—“reaction,” or a brake reaction time, it would underestimate a perception-response time. Muttart also examined substantive variables such as age, movement, response options, response choice, number of stimuli, contrast, eccentricity, speed, road type, topography, and others (a complete list can be seen in Appendix A) to determine which variables prove to be significant influences upon a driver’s response (using ANOVA) or have linear trends (using linear regression). ANOVA allows for the evaluation of interactions and is also a relatively robust experimental design. Linear trends were used to evaluate the amplitude of the influence
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of each variable. Therefore, a primary goal of the research was to determine which variables influence driver response time and to what extent. A few of the variables that Muttart (2001, 2003a) found were not significant predictors of change in response times were noteworthy. These variables include alcohol consumption, age, fatigue, and gender. The primary reason that alcohol did not reach significance was due to lack of data. To understand the influence of alcohol properly, it is necessary to consider the acronym DATT, which stands for dosage, absorption, tolerance, and task. As we have found, when the stimulus-response scenario changes, so does the response time and also the influence of each variable (see the adjustments to the response time in Table 14.3). Therefore, alcohol dosage will likely have a different influence in car following, nighttime response, path intrusions, and responding to vehicles changing lanes. One adjustment for DATT
TABLE 14.3 Amplitude of Adjustments for Response Times in Various Collision Configurations and Variablesa Vehicle following Contrast Natural lighting Driving Eccentricity Experiment location Headway Number of stimuli Response complexity Topography Transition
583 ms/unit 97.5 ms −740 ms 26 ms/degree 56.5 ms/unit
On lighted roads Day vs. night Add for driving, subtract for not driving Measured from directly ahead 1—lab; 2—simulator; 3—closed course; 4—road
279 ms/sec 509 ms −210 ms
On straight and level road One vs. multiple Button—brake only—brake when other options were available—brake and steer Straight vs. curves (horz/vert)/intersections/cues 1—throttle release; 2—brake appl.; 3—full braking Path intrusions
Anticipation Contrast Natural lighting Driving Eccentricity
24 ms/unit 743 ms/unit 224 ms/unit 350 ms 17.5 ms/degree
Experiment location Road Number of stimuli Topography Transition
79.5 ms/unit
Natural lighting Driving
303 ms/unit −91 ms/unit
−703 ms 375 ms
63 ms/unit 716 ms/stimulus −496 ms/unit 375 ms/unit
On lighted roads Day vs. night Driving vs. not driving One lane 3°, instruments 16°, rear-view 27°, side-view 35 to 45°, radio 50° 1—lab; 2—simulator; 3—closed course; 4—road 1—rural; 2—urban; 3—highway One vs. multiple Straight vs. curves (horz/vert)/intersections/cues 1—throttle release; 2—brake application; 3—full braking Vehicles changing lanes Day vs. night Driving vs. not driving
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13 ms/sec
One lane 3°, instruments 16°, rear-view 27°, side-view 35 to 45°, radio 50° Lanes crossed 340 ms/lane 1 or 2 (multiple) Number of stimuli 254 ms/stimulus Up to 2 Transition 375 ms/unit 1—throttle release; 2—brake application; 3—full braking a In milliseconds. Notes: The amplitude of the adjustment for a single variable may change in different collision configurations. These adjustments are designed to supplement a research study analogous to a reallife crash situation so that the investigator can directly compare the research with the real-life situation.
combination is not justifiable. Instead, the response of a driver suspected of being intoxicated should be compared with the manner in which drivers have responded in research and real-life situations in order to estimate the influence of alcohol. The same type of analysis may be done relative to fatigue. No research is available that can enumerate the response delay of a fatigued driver and it is unclear what the definition of a fatigued driver is. Again, it is best to compare the response of the driver against the manner in which drivers have responded to analogous circumstances in research to determine the influence of fatigue, if any. When all the data (more than 20,000 responses) involving men and women were compared, men responded slightly less than 1/10th of a second faster, but that difference was not significant. One study measured the response time of drivers responding to a known audible alarm when backing a vehicle at slow speeds in a parking lot (Lerner et al., 1997). This study reported very fast response times and involved only men. There was no similar study involving all women. When that study was removed from the database, response times of men and women showed virtually no difference. Many believe that younger drivers will respond faster than older drivers. Mourant and Rockwell (1972) showed that younger drivers have underdeveloped search patterns; the meta-analysis of the data and the research by Muttart (2000) have shown that they also have poor discrimination skills and underdeveloped conditioned responses (Muttart, 2004) when compared to more experienced drivers. Although younger drivers are capable of faster limb movements (Olson and Sivak, 1986), the underdeveloped search patterns, discrimination skills, and conditioned responses could cause response delays much greater than the 1/10th of a second that they may gain in the motor response portion of the response. Overall, response times relative to driver age followed a very shallow Ushaped curve, with younger and older drivers responding marginally more slowly, although this did not reach statistical significance. Again, this research primarily involved responses on lighted roads and in daylight. Even though experienced drivers may have better search skills and discrimination patterns, the results may be different when evaluating response times to dark objects on unlighted roads. Muttart (2003a) completed a meta-analysis of 145 studies that reported driver response results. This involved reading each study and entering reported response times, short comments, the type of response, the stimulus (car, light, pedestrian, etc.), and appropriate codes (as listed in Appendix A) into a database. Although Muttart found that several variables were statistically significant predictors of driver response time, no single variable accounted for more than 15% of the variance and most accounted for less than 5% of the variance of the response. Therefore, the question that Muttart attempted to
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answer was: “How do the variables fit together and is it possible to develop a mathematical equation to predict driver response times based upon the manner in which drivers have responded in research?” 14.5 Perception-Response Time Muttart (2001, 2003a, b, 2004) developed a model for estimating driver response times. A series of equations that mathematically estimate driver response times based upon a meta-analysis of previous research and real-life responses was developed. Also, a method for estimating driver response times using analogous research studies was developed (Muttart, 2003b). Multiple linear stepwise regression (MLSR) was used to develop the equations (Muttart, 2003a, b). MLSR has been referred to as the surest path to the best prediction equation (Tabachnick and Fidell, 1996). Furthermore, Muttart (2003b, 2004) offered the statistical distribution of real-life driver responses. This information is extremely valuable because it offers insight into what could be considered a reasonable (85th percentile) response time range. The 85th percentile response is the maximum response time at which 85% of the population will respond and provides a benchmark to which to compare driver responses. After developing the equations using MLSR using data from the meta-analysis of research studies that measured driver response, Muttart compared the estimates using the equations to real-life driver responses. The real-life drivers were video-recorded during responses to emergency traffic incidents in Kentucky (2000 to 2003) and Helsinki (1991 through 1999). There were 147 real-life traffic responses and a total of many more than 10,000 measured responses in research studies. Of the emergency responses, 75 involved crashes, while the remaining incidents involved emergency responses. If an emergency response was not necessary, then the data were not included in the analysis. Emergency response was defined as skidding, steering, or horn use in an attempt to avoid a collision that would most likely occur without an avoidance response. Researchers video recorded and analyzed 62 responses to vehicles changing lanes, 12 responses to a lead vehicle, and 58 responses to a path intrusion. In cross-street (broadside configuration) events, the perception-response time started when the intruding vehicle moved beyond the stop line. In the Helsinki path intrusions, the stop line was a significant distance from the intersection. Therefore, the starting point in these videos was when the vehicle crossed beyond the crosshatched crosswalk. When the response to vehicles changing lanes was measured, the time was started at the first frame that showed lateral movement toward the responder’s lane. In instances in which the response of the turning driver was measured, the time started when the vehicle first crossed the stop line (not all were starting from a stop). In the carfollowing situation, the time was started when the lead vehicle began to decelerate (when the brake lights of the lead vehicle went on). When a subject was responding to pedestrians, the time was started when the pedestrian first started to move deliberately toward the road (up to 1.5 steps from the road edge) or when the pedestrian first emerged from behind a parked vehicle.
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TABLE 14.4 Simplified Estimates of Full Braking Response Times in Path-Intrusion Situations Looking….
Ahead Day Night
Instruments Day Night
Rear view Day Night
Single hazard Intersection 1.3 1.6 1.8 2.0 2.0 2.2 Single hazard Midblock 1.8 2.1 2.3 2.5 2.5 2.7 Multiple stimuli Intersection 2.1 2.3 2.5 2.7 2.7 2.9 Multiple stimuli Midblock 2.6 2.8 3.0 3.2 3.2 3.4 Notes: For objects that are easily recognizable as an immediate hazard, ±40% has accounted for the middle 70% of drivers. The response time varies in different situations. This chart should not be used without consideration of other variables, corroboration by other means, and consideration of individual variability.
The first video frame to show lateral movement, noticeable slowing (vehicle pitch) with sound (braking), or brake light activation identified the end of the response. In two instances, there was lateral movement with horn activation or noticeable deceleration with horn activation. In all other instances, sound refers to brake application noises (the short grinding sound followed by tire squealing). In all such events, the response could be defined within one frame (.03 sec). With the Helsinki videos, a change in forward movement per frame that was closely followed by vehicle pitch was included. However, in most cases, braking was identified by the brake lights. Only if tire squealing was concurrent with lateral movement, vehicle pitch, or first noticeable deceleration was that event included in this analysis. To estimate a driver’s response accurately, Muttart found that analogous situations should be used and defined an analogous situation as a response to an object that emerged from the same general direction—for instance, in-line, path-intrusion, or sideswipe situations. A study that measures the response time to a red light or the response time to a lead vehicle will not be an effective tool for estimating the response to a path intrusion. Furthermore, even with a similar scenario (path-intrusion study to estimate a pathintrusion response), the investigator should make sure the study is measuring the same time period to which he is comparing it. For instance, if the study measured a perception—“reaction” time (up until the foot first moves from the throttle), then it should not be used as a perception—“response” time (up until full braking or start of skid marks or first lateral movement) without an appropriate adjustment. Most importantly, perception-response time is exactly that—it is not vision-response time. Therefore, the time period starts from when the hazard is easily identifiable as an immediate hazard until the vehicle first starts to respond due to driver response choice. Objects that cannot be easily identifiable as an immediate hazard should be analyzed further before perception-response times are utilized, if utilized at all. The stepwise equations have estimated the actual response time within 0.5 sec nearly 75% of the time to date. Based upon the manner in which drivers have responded in 145 research studies that measured driver response times and also upon how the 147 real-life drivers have responded, tables were made that show the manner in which driver response time fluctuates in different situations. The tables (Table 14.4 and Table 14.5) show the estimate and the range of the middle 70th percentile, which would mean that 85% of the
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driving population would be expected to respond faster than the estimate plus the estimate multiplied by the range percent. Table 14.4 shows the ranges in response times in a path-intrusion situation and Table 14.5 shows how the range of driver response times fluctuates in a car-following situation. The range of responses tightens considerably if the adjustment-to-baseline method of estimating response time is also considered. “Adjustment to baseline” (A2B) is a corroborative method of estimating driver response. Baseline refers to an analogous study. Therefore, the A2B method involves making adjustments to an analogous study. For a path-intrusion crash, we want to obtain studies that measure driver response to a path intrusion. The study may report perceptionreaction rather than perception-response time, or may be a daytime situation, although our case occurred at night. In such a case, we would apply an adjustment to the results of the analogous study so that the result would be applicable to the situation being investigated.
TABLE 14.5 Simplified Estimates of Full Braking Response Times in Vehicle-Following Situations Looking ahead
Looking at instrument Looking at rearview panel mirror Straight Curve/cue/ Straight Curve/cue/ Straight Curve/cue/ intersection intersection intersection 1 second 1.5 0.8 1.9 1.2 2.2 1.5 2 1.9 1.2 2.3 1.6 2.6 1.9 seconds 3 2.3 1.6 2.7 2 3 2.3 seconds 4 2.7 2 3.1 2.4 3.4 2.7 seconds 5 3.1 2.4 3.5 2.8 3.8 3.1 seconds Multiple 1 second 2 1.3 2.4 1.7 2.7 2 stimuli 2 2.4 1.7 2.8 2.1 3.1 2.4 seconds 3 2.8 2.1 3.2 2.5 3.5 2.8 seconds 4 3.2 2.5 3.6 2.9 3.9 3.2 seconds 5 3.6 2.9 4 3.3 4.3 3.6 seconds Notes: The response time varies in different situations. This chart should not be used without consideration of other variables, corroboration by other means, and consideration of individual variability. Single hazard
Muttart (2003b) analyzed analogous path-intrusion studies involving simulator and closed-course studies. Also, the analogous studies included responses to pedestrians and vehicles. Lastly, the goal was to select studies that reported data for a larger number of variables. The following six path-intrusion studies were selected: (1) Barrett et al. (1968);
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(2) Broen and Chiang (1996); (3) an unpublished study conducted by the Southwestern Association of Technical Accident Investigators (SATAI; 1999); (4, 5) Mazzae et al., 1999a, b; and (6) Hankey et al. (1996). Barrett et al. (1968) was a simulator study that involved driving on an oval course. On the 11th lap, a pedestrian emerged from a shed and toward the path of the car. Broen and Chiang (1996) involved a simulator study in which the subjects were told to brake as fast as possible for two pedestrians who emerged into the path of the vehicle. The SATAI study involved subjects driving in a mostly vacant lot of a sports stadium and responding to a “skateboarder” (a cutout mounted to a skateboard) after emerging from around the corner of a stadium. The two studies by Mazzae et al. (1999a, b) were conducted using a simulator and a closed course and involved a vehicle emerging from the passenger side of the road and stopping with the front near the center of the subject driver’s lane. Hankey et al. (1996) conducted a simulator study that involved vehicles emerging into the path of the subject’s vehicle slightly more than 3 sec before impact. Only two studies have recorded the times necessary for drivers to respond to vehicles changing lanes (Currie, 1969; Muttart, 2004). Currie reported an average response time of 588 ms when his subjects “drove” an electric car on a track and responded to the other vehicle changing from its original lane and into the subject’s lane. The driver response times to a vehicle changing lanes (originally in a sideswipe type configuration) can be seen in Table 14.6. In car-following research, an attempt was made to select research that addressed short and long headways as well as simulator and closed-course or road results. The analogous vehicle-following response studies were conducted by Summala et al. (1998), van Winsum (1998), Kane et al. (1999), and McGehee et al. (1998). Summala et al. produced a comprehensive study relative to driver response times. They examined the influences of headway, eccentricity, and taillights on or taillights off on the response times of drivers in a car-following situation. These researchers examined the response times when looking straight ahead, at the dashboard, at the rear view mirror, and at the center console. Kane et al. measured response times in a simulator study at short headways, while comparing athletes to nonathletes. van Winsum measured driver response times on curves and McGehee et al. (1998) measured the response times of drivers to stopped cars and involved a longer headway.
TABLE 14.6 Comparison of Average Estimated Response Time Using Stepwise Equations with Average Real-Life Response Times in Helsinki and Kentucky N Path intrusions Turning Path intrusion while turning left Path intrusion while turning right After starting from
Actual average
Standard deviation
Predicted Within N Hazard N Hazard average 40% to right to left
58 8
2225
680
2443
86% 2
1747 6
2384
3
1905
563
2760
50% 2
2133 1
1448
6
3000
1125
2425
67% 1
1935 5
3213
Estimating driver response times stop: violation of red traffic control signal No turning or red light violation Natural lighting Path intrusion day Path intrusion lighted road at night Eccentricity Path intrusion visible ahead Path intrusion visible out windshield Path intrusion visible out side or rear windows Distracters Path intrusion was the only stimulus Path intrusion while turning or with distracter stimulus Following
419
41
1638
695
1752
67% 16
32 26
1742 2035
913 730
1666 2383
58% 77%
25
1543
538
1524
72%
19
1877
942
2128
67%
14
2460
872
2696
73%
36
1706
874
1739
22
2147
723
2341
534
Within 52% 1122 67% Within 30% 928 50%
12
Following with short headway Vehicles changing lanes Vehicle changing one lane day Vehicle changing one lane night Vehicle changing two lanes day Vehicle changing two lanes night Green traffic signals
12
Response to green traffic signal TOTAL
16
1124
61 870
308
10
1328
455
1305
70%
18
1213
375
1257
83%
17
1430
415
1590
82%
753
Within 53% 1400 69%
147
1119
1566
70%
16
16
1751 25
Within 39% 70% of estimate Notes: Response times varied based upon collision configurations; eccentricity, lighting, distracters, and turning also influenced response times. Furthermore, the stepwise equations were versatile enough to account for those differences. Source: Muttart, J.W. (2004). DRIVE3: a simplified method for estimating driver response, Auckland, NZ: Australasian S. Pacific Assoc. Crash Investigators 2004 Conf. Proc.
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To obtain the amplitude of the adjustments, a series of 32 methodology and substantive variables were mathematically evaluated to determine if statistically significant linear or quadratic relationships existed between that variable and driver response times based upon the meta-analysis of 145 driver response studies (a complete listing of these references can be seen in the original research). In preliminary analysis, it was learned that the contribution of a variable to a driver’s response time is usually more accurate when considered in context with several other variables. Therefore, the adjustments were determined based upon how the individual variable was linearly associated with driver response and reduced by 50% to account for interaction effects. The 50% figure was obtained by comparing the linear relationship of the variables included in the stepwise regression equations with the slope for that same variable when considered individually.
TABLE 14.7 Rule-of-Thumb Perception-Response Time Estimates 1.5 D/2.5 N
2.5
1.6
0.75–1.5
Within range 42 27 47 43 Outside range 47 62 42 46 Percent accuracy 47.2% 30.3% 52.8% 48.3% Notes: These estimates performed poorly, were inconsistent, and offered no versatility as a method for estimating response times. No rule-of-thumb method estimated all response times within 33% of the estimate more than 53% of the time. Source: Muttgart, J.W. (2003). Evaluation of methods for estimating driver response times, Proceedings of the Sixth International Conference of Traffic Accident Investigators, Stratfordupon-Avon, England, pp. 1–29.
Therefore, the variables that were statistically significant predictors of response time if considered alone but that did not reach significance enough to be included in the stepwise regression equations can be accounted for in the A2B method. The amplitude of the adjustments from each variable that will most accurately estimate driver response time (based upon the current available research) is listed in Table 14.3. Note that the adjustment for the same variable may change in different accident scenarios (pathintrusion vs. car-following situations as an example). Therefore, just as a single response time will not likely predict response times for all situations, a single adjustment applied to all collision scenarios will not likely be effective. Please refer to the original research paper for the method for making each adjustment (Muttart, 2003b). Muttart (2003b) compared the stepwise equations, rule-of-thumb estimates, and adjustment-to-base-line estimates to the real-life responses. The rule-of-thumb estimates that were compared included the often-used “1.6 sec” figure, the 2.5 sec figure addressed in the Manual on Uniform Traffic Control Devices, a range of 0.75 to 1.5 sec, and 1.5 for daylight and 2.5 for nighttime. Rule-of-Thumb Estimates The rule-of-thumb estimates did not perform well at all (see Table 14.7). The “1.5 sec day-2.5 sec night rule” was accurate within 33% only 47% of the time. The “2.5 sec rule”
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proposed by the MUTCD (U.S. Department of Transportation, 2001) was accurate within 33% only 30% of the time. The “straightforward” range (Olson, 1996) of 0.75 to 1.5 sec, if used improperly (for all responses), would estimate the response time within 33% only 48% of the time, and the relatively popular 1.6 sec estimate is within 33% of the actual response time only 52% of the time (Muttart, 2003b). The stepwise regression equations and the adjustment to baseline estimate were averaged to produce an overall estimate which was within 33% of the actual response time more than 67% of the time. The average margin of error for all 147 real-life responses was 436 ms. Vehicles Changing Lanes Humans are relatively good at detecting lateral movement or movement across their visual field. Therefore it is not surprising the responses to sideswipe configurations and to vehicles changing lanes were relatively fast. A vehicle changing lanes is defined as a vehicle originally traveling in the same direction of the responder but that then changes lanes across or into the responder’s path. The range of responses to a vehicle changing lanes was relatively small. Drivers who responded to a vehicle changing from the next lane during daylight responded on average in approximately 0.9 sec, while a driver responding to a vehicle that started turning from two or more lanes from the responder at night needed closer to 1.5 sec to initiate a response maneuver. Path Intrusions For the 58 real-life path-intrusion situations evaluated, the stepwise equation method estimated the response time of the real-life driver within 40% for 67% of the time (Muttart, 2004). The precision improved to 35% for the middle two thirds of drivers if the average A2B estimate from the six analogous studies was averaged with the stepwise equation estimate. It is apparent that the more sources that were considered in the analysis, the more accurate the estimate became (up to this level of analysis). Therefore, Table 14.4 and Table 14.5 should be utilized as rough guidelines only and are not appropriate for use in forensic settings without further analysis, adjustment, and substantiation that the estimate offered is appropriate for that particular situation. Response time varied due to eccentricity, natural lighting, and distracters, after red traffic signal violations, and while turning (when compared to driving straight). The average response time for a driver who started into the intersection while facing a green signal and had to respond to a red light violator was 3 sec. Five of the drivers averaged 2.7 sec and one responded in 4.7 sec. Drivers making a right turn responded faster to hazards emerging from their left than right, while drivers making left turns responded faster to hazards emerging from the right than left. More data should be collected and individual case anomalies considered before making conclusive findings relative to response time while turning right or left. However, it is apparent that drivers typically need more time to respond when attempting a turn. This finding corroborates the research by Hancock and colleagues (1990), who found that turning maneuvers were associated with greater mental workload and head movements, which would increase the potential for detection failures and, as found in this research, delayed detection, when compared to drivers traveling straight.
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Driver response times at night were only about 0.3 sec longer during dawn, dusk, and night than during daylight, which is consistent with prior research shown in Figure 14.2. The limited difference between lighted and low-light response times may also be due to the fact that the real-life responses occurred on lighted roadways. Based upon these results and the results of others (Figure 14.2), response times may increase significantly in crash situations involving pedestrians and nonilluminated objects on unlighted roads in most cases. Green Traffic Signals and Gaps in Traffic Several studies have measured the time necessary for a driver to respond to a green traffic signal or a gap in traffic (Graham et al., 1995; Fugger et al., 2001; Lerner et al, 1996; Naylor and Graham, 1997; Wortman and Matthias, 1983). When the result from each study is averaged, it suggests that drivers will respond to a green traffic signal or a gap in traffic in approximately 1.4 sec (SD=0.5 sec). Muttart (2004) measured the response time of 16 subjects responding to a green traffic signal; the average response time was 1.1 sec (SD=0.5 sec). Therefore, most drivers can be expected to respond to a green traffic signal or a gap in traffic in 0.75 to 1.75 sec, which is very similar to the “straightforward” estimate offered by Olson (1996). Car Following When evaluating the adjusted studies by Summala and colleagues, van Winsum, and Kane and colleages (who all investigated response times at shorter headways), the average margin of error was 187 ms (Muttart, 2003b). The adjusted estimates of response times developed using McGehee et al. (1998) were typically underestimated. However, the McGehee study is still recommended as a baseline because it involved a long headway event and, when averaged in with the other adjusted studies, provided a relatively accurate estimated response time most of the time. When the stepwise equations and the A2B estimates were averaged, the precision of that overall estimate improved to within 40% for two thirds of the real-life drivers. The stepwise equation estimated the actual average response time nearly exactly. However, all of the real-life following situations to date involve headways of less than 2.5 sec. It is expected that range of responses will become larger as the complexity of the event increases. Because longer headway situations are typically more complex for a driver, it is recommended that a larger range of potential responses be used (50 to 55% until more data are collected) when evaluating the response of a driver to a slow-moving or stopped vehicle (with no warning) on a straight road. The stepwise regression equations yielded the most accurate predictors. The A2B method considers many more variables and is based directly upon an individual research study. Therefore, to reduce the effects of confounding variables in any one study, the average of several analogous studies offers a more accurate estimate of response time. Furthermore, if the A2B estimate and the stepwise equation estimate are averaged and an overall estimate developed, the accuracy of the estimate increases even further.
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14.6 Urgency Several theorists have claimed that driver PRT is based in large part upon the urgency required. They have based their opinions upon the fact that drivers respond faster to an object that they first discover within a shorter period before “impact.” Significant confounding variables exist in this theory, however. First, if an object is presented to a driver 3 sec before impact, then the greatest PRT that can be recorded is 3 sec. Therefore, when those time-to-contact data are compared to a response to a vehicle stopped on a highway several meters ahead, the end result is that researchers may inappropriately determine that the cause was due to urgency (when it was, in fact, due to much more complicated issues). Furthermore, the research by Muttart (2001, 2003a, b, 2004) has shown that as eccentricity increased, so did response time. Therefore, if an object is thrown in front of a car 1.5 sec before impact and from the same position when the vehicle is 3.5 sec before impact, the driver will likely respond marginally faster when 3.5 sec away because the barrel has a smaller eccentricity relative to straight ahead. In a vehicle-following research study (Sivak et al., 1981), the brake lights on the lead vehicle illuminated but the vehicle did not decelerate. Therefore, the true time to contact was infinite (they are both still traveling at the same speed). However, the drivers who followed reacted very much as they would when a lead car decelerates from the same headway. Green (2000) pointed out that a vehicle traveling head-on within a driver’s lane may have a very short time to contact, but a much longer perception-response time, due to the confusion created by that situation. Furthermore, if the speed of a vehicle approaching a stopped lead vehicle is doubled, the time to contact will decrease by 200%. However, no evidence indicates that response times will change significantly if all else is held constant. In fact, research has shown that those who drive faster may perform more efficiently (Alm and Nilsson, 1991; Triggs and Harris, 1982; Sidaway et al., 1996; Muttart, 2001) as long as they are not overloaded by a second object to which to respond (see Figure 14.3). The very nature of the scenarios that we are examining involves a great deal of urgency, which begins when a driver perceives something as a hazard to himself or others, to his property, or to his time. Therefore, we are usually examining the performance of drivers when they are at the far right of the Yerkes-Dodson (performance vs. stress) curve. Performance is usually optimal when stress levels are at a moderate level, but when stress is increased or decreased from a moderate level, performance will likely be degraded. However, urgency may play a role in the response of drivers in less threatening situations such as responses to yellow traffic signals. 14.7 Transition Time (Limb Movement and Vehicle Latency) Despite the fact that many refer to the process as “perception-reaction,” or simply call it “reaction time,” at times, it is the physical reaction component of the process that receives some of the least attention. Much driver response research neglected the response process by having subjects press a button, brake only, or give a verbal response. In the research involving simplified responses, there are no cognitive components to the
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response process, no decision to be made, and no possibilities to consider. Other studies cut the response process short by stopping the clock when the foot comes off the accelerator and still others stop the clock the moment that the foot touches the brake. Again, these scenarios do not account for mechanical latency or the time necessary for the physical response. When comparing driver responses, we must make sure we know what we are comparing. Research by van Winsum (1998) and
FIGURE 14.3 The influence of number of stimuli and speed upon the driver response time in vehiclefollowing situations. This type of relationship holds true in pathintrusion situations as well. Note that response time does not increase with increased speed when responding to a single object, but increases significantly if the driver is responding to two or more objects. Kane et al. (1999) has shown that the variability within the response phase of the perception-reaction process is affected by physical response time and driver cognition. When the data for 145 studies that reported driver response were compiled, they showed that it typically took passenger vehicle drivers 0.15 to 0.25 sec to get full braking after application of the brake. The braking latency for commercial vehicles is usually longer. It has taken a little more than 0.5 sec to move the foot from the throttle to the brake pedal. Glencros and Anderson (1976) found that it took approximately 0.4 sec for
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subjects to move their foot from the accelerator to the brake. Burkhardt (1985) (cited in Cohen, 1987) found an approximately 0.6-sec delay between accelerator release and full braking. Research has shown that a cognitive component in the response phase could delay full braking by approximately 2 sec from the time the brake is applied if there is confusion (or indecision) during that portion of the response (Mazzae et al., 1999b; Kane et al., 1999). Bartram and colleagues (1985) indicated that there was no difference in the time to respond when subjects were asked to respond with a foot or a hand. Much of the latency differences found between steering and braking responses can be attributed to the greater movement distance required to transfer the foot from accelerator to brake when compared to no transfer of hands when steering, minus the greater cognitive requirements of steering vs. braking. The end result is that braking takes only slightly longer than a steering response, but not enough to be statistically significant (Muttart, 2003a, b). Several researchers have measured response latency. There have been two types of studies in this regard: those that measured response latency using a light stimulus (Scott et al., 1996; Hoffman, 1991; Parkes and Hooijmeijer, 2000; Burkhardt, 1985; Koppa et al., 1996) and those that measured the response latency to a road hazard, whether on the road or when driving a simulator (Broen and Chiang, 1996; Otto et al., 1980; van Winsum, 1998; McGehee et al., 2000; Barrett et al., 1968). Studies by Burkhardt (1985) and Lieberman et al. (1995) involved drivers responding to the brake lights of a lead vehicle. However, there was no “hazard” and the subjects were told to brake when the light went on. Therefore, even though a lead vehicle was present, these studies are best categorized as studies that measured drivers responding to a known light stimulus. Subjects responding to a known stimulus (usually a light on the dashboard or a command to brake) had movement times and braking latencies much faster than those responding to a hazard. Therefore, in a real-life situation, drivers are likely to need a half-second or more to move their foot from the accelerator to the brake. There is also a delay due to vehicle latency. Vehicle latency delay refers to the time period from when the brakes are first applied to the moment at which the wheels begin to leave skid marks (or to full braking). In many simulator studies, full braking is defined as 200 N brake-pedal force. Visible skid marks begin to appear before the wheels are locked (Goudie et al., 1995; Reed and Keskin, 1989). Research that reports vehicle latencies from application to lock up may slightly overestimate the vehicle latency time, but that difference is usually not more than 100 ms. Simulator studies reported very long vehicle latencies (Mazzae et al., 1999b; van Winsum, 1998; Brown, 2000; Kane et al., 1999). Kane and colleagues (1999) surmised that the reason for this is that the subjects were responding to the perceived lack of vehicle response. Because driving simulators may not offer the driver the same vehicle pitch and perceptible feeling of slowing, subjects may respond to that perception of failing to slow fast enough by reapplying the brakes or attempting a different maneuver. Muttart’s research was from intersections that were well lighted and there were no casual responses. Therefore, the estimations assume that the object is easily discernible as an immidiate hazard (usually that means daylight, well-illuminated conditions or a distinctly shaped, self-illuminated object at night). If a situation involving an object that is not easily identified as a hazard is evaluated, the equations and adjustment-to-baseline method will likely underestimate the response time. Also, the analyst must understand
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that an object’s being within the driver’s sight line does not equate to the object’s being perceivable as a hazard in all cases. One particular case would involve vehicles on straight planes associated with relatively faster traffic speeds that are stopped without priming to the approaching drivers. The analyst must also understand that the driver is most likely not looking in the direction of the hazard initially. No significance relative to the side of the road of the hazard or the direction of steering was found. Therefore, there is no reason that this research should not apply to driver responses in countries that drive on the left. (An eccentricity difference may be present if the crash involves a right-side-drive vehicle on a right-side-drive road, or a leftside-drive vehicle driving on the left.) Furthermore, the data upon which the equations were based were multicultural and they were compared to responses in Helsinki and the U.S. Therefore, this research suggests that drivers faced with emergency response situations respond similarly in analogous situations. If the situation does not call for an emergency response maneuver, this research may not apply. 14.8 Summary An investigator should understand that estimating the response of an individual must be done with the consideration that individual variability exists. Variability does not necessarily come from driver age as some suggest, but can be better explained by driver expectancy and attention toward a particular hazard. Therefore, it would be inappropriate to claim that a single number could define a driver’s response time and the investigator should report the precision along with the estimate. Some situations are not accounted for in the research. If that is the case, then adjustments to the response time estimates should be considered. (Suggested adjustments can be found in Table 14.3.) If the scenario considered does not involve an easily identified hazard or a nonanalogous event, then additional and/or alternative methods must be employed. In two known situations the estimated response time may be overestimated or underestimated due to the interaction of two variables. These situations involve drivers traveling at high speeds and responding to multiple objects (two hazards that are spatially separated or a hazard and a distracter) or when there are long headways on straight roads (with no perceptual cues that the lead vehicle is stopped or traveling slowly). When a driver travels at high speeds and responds to multiple objects, the response time increases significantly, as can be seen in Figure 14.3. These finding are corroborated by the research of Johnson and colleagues (2004). With regard to rear-end collisions at intersections, the response time is usually relatively quick, while response times to stopped vehicles that are straight ahead on straight and level highways are usually much longer (see Figure 14.4).
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FIGURE 14.4 The influence of headway and topography on the driver response times in vehicle-following situations. Note that response time remains constant regardless of headway when responding to lead vehicles at intersections and road curvatures. 14.9 Discussion Although driver response estimates have been offered, it is recommended that analogous studies be obtained to corroborate the response time estimate. Also, this research has focused upon easily identifiable objects. If the object is not easily identifiable, additional analysis is necessary. The driver response methods explained in this chapter have been adopted by a computer program called Driver Response in Various Environments Estimated Empirically or DRIVE3 (a software program sold by REG-TEC, LLC.). DRIVE3 offers a method of estimating driver response times using the stepwise equation and A2B methods and also offers the user the precision of their estimates as well as time and distance relationships of each vehicle or object. The stepwise equations, A2B method, driver response estimates, and adjustments are based entirely upon how drivers have responded in research and in real-life incidents. There has been no difference in the response of drivers in the emergency response incidents that did not involve crashes and those that did. Therefore, DRIVE3 and the research discussed in this chapter offer methods that had been validated against real-life drivers and based upon research involving several thousand driver responses (in real life and research).
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Muttart, J.W., Northrop, J., Russell, G., Reynolds, M., Muir, B., and Muttart, M. (2003). Identification distances of pedestrians and objects at night, Can. Assoc. Tech. Accident Investigators Annu. Meeting . Naylor, D.W. and Graham, J.R. (1997). Intersection design and decision-reaction time for older drivers, In J.Overton (Ed.), Human Performance in Intelligent Transportation Systems, Information Systems, and Highway Design and Older Drivers , (Transportation Res. Rec. 1573, 68–71). Washington, D.C.: National Academy Press. OECD Research Group (1970). Driver behaviour, in Synopsis of the State-of-the-Art of Driver Behaviour Research , Department of Civil Engineering, Monash University. Olson, P.L. and Sivak, M. 1983. Comparison of headlamp visibility distance and stopping distance. Perceptual Motor Skills , 57, 1177–1178. Olsen, P.L. and Sivak, M. (1984). Glare and headlighting design. (SAE 840047). Warrendale, SAE, 1985. Olson, P.L. and Sivak, M. (1986). Perception-response time to unexpected roadway hazards, Human Factors , 28(1), 91–96. Olson, P.L. (1996). Forensic Aspects of Driver Perception and Response , Tucson, AZ: Lawyers and Judges Publishing, Inc. Otto, W.M., Otto, C.L., and Overton, R.K. (1980). Response characteristics of motorcycle riders to a complex emergency situation, Washington, D.C.: Int. Motorcycle Safety Conf. Proc. , IV, pp. 1489–1503. Owens, D.A, Francis, E.L., and Liebowitz, H.W. (1989). Visibility distance with headlights: a functional approach. (Technical paper No. 890684). Warrendale, PA: Society of Automotive Engineers. Parkes, A. and Hooijmeijer, V. (2000). The influence of the use of mobile phones on driver situation awareness, Cawthorne, England: Transport Research Laboratory. Petersen, H.E. and Dugas, D.J. (1972). The relative importance of contrast and motion in visual detection, Human Factors , 14(3), 207–216. Rasanen, M., and Summala, H. (1998). Attention and expectation problems in bicycle-car collisions: an in-depth study, Accident Anal Prev. , 30, 657–666. Reed, W.S., and Keskin, A.T. (1989). Vehicular deceleration and its relationship to friction. (Technical Paper # 890736). Warrendale, PA: Society of Automotive Engineers. Resnick, R.A. (2004). Visual sensing without seeing, Psycholog. Sci. , 15, 27–32. Roper, V.J. and Howard, E.A. (1938). Seeing with motor car headlamps, Illuminating Eng. Soc. , 33, 417–438. Scott, P.A., Candler, P.D., and Li, J.C. (1996). Stature and seat position as factors affecting fractionated response times in motor vehicle drivers, Appl Ergonomics , 27, 411–416. Sidaway, B., Fairweather, M., Sekiya, H., and McNitt-Gray, J. (1996). Time-to-collision estimation is a simulated driving task, Human Factors , 38, 101–113. Simon, D.J. and Chabris, C.R (1999). Gorillas in our midst: sustained inattentional blindness for dynamics events, Perception , 28, 1059–1074. Sivak, M., Post, D.V., Olson, P.L., and Donohue, R.J. (1981). Automobile rear lights: effects of the number, mounting height, and lateral position on reaction times of following drivers, Perceptual and Motor Skills , 52(3), 795–802. Sohn, S.Y. and Stepleman, R. (1998). Meta-analysis on total braking time, Ergonomics , 41, 1129– 1140. Southwestern Association of Technical Accident Investigators (1999). Research results for subjects who responded to mock skateboarders. (Unpublished data). Summala, H. (2000). Commentary: brake reaction times and driver behavior analysis, Transp. Hum. Factors , 2, 217–226. Summala, H., Lamble, D., and Laakso, M. (1998). Driving experience and perception of the lead car’s braking when looking at in-car targets, Accident Anal Prev ., 30(4), 401–407.
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Tabachnick, E.C. and Fidell, L.S. (1996). Using Multivariate Statistics , 3rd ed., New York: Harper Collins College Publishing. Todosiev, E.P. (1965). Velocity thresholds in car following, Columbus, OH: Ohio Department of High-ways. Triggs, T.J. and Harris, W.G. (1982). Reaction time of drivers to road stimuli, (HFR No. 12) Victoria, Australia: Monash University, Human Factors Group. Turner, J.D., Simmons, C.J., and Graham, J.R. (1997). High-visibility clothing for daytime use in work zones. (Paper No. 970430). Washington, D.C.: Transportation Research Board, van Winsum, W. (1998). Preferred time headway in car-following and individual differences in perceptual motor skills, Perceptual Motor Skills , 87, 863–873. Wortman, R.W. and Matthias, J.S. (1983). An evaluation of driver behavior at signalized intersections. (PB83 218560). Springfield, VA: FHWA. U.S. Department of Transportation (2001). Manual on Uniform Traffic Control Devices for Highways and Streets , Washington, D.C.: Federal Highway Administration. Vaughan, R. and Vaughan, P. (2001). Evaluation of the influence of several variables upon driver perception response times, Instit. Traffic Accident Investigators Int. Conf. Proc. , York, England, pp. 1–8. Yoo, H., Tsimhoni, O., Watanabe, H., Green, P., and Shah, R. (1999). Display of HUD warnings to drivers: Determining an optimal location. (Technical report number UMTRI-99–9). Ann Arbor, MI: University of Michigan, Transport Research Institute.
Appendix A: Operationalization of Terms A=Anticipation 1. Subject knows stimulus and response multiple exposures 2. Subject knows stimulus and response infrequent exposure (1 or 2) 3. Stimulus or response is unknown, multiple exposures 4. Stimulus or response is unknown, single exposure 5. Stimulus and response are unknown, single exposure Al=Alcohol (in BAC%) Age=Age (in years) C=Contrast (Luminance reflectivity) 1. Audible stimuli 2. Illuminated object (includes reflective objects) 3. High contrast (>25%) 4. Moderate contrast (10 to 25%) 5. Low contrast (<10%) Cr=Crash Did not involve a crash Involved a crash D=Driving task (1. Yes or 2. No) E=Eccentricity in degrees, 1 for straight ahead Ex=Experiment location 1. Laboratory 2. Simulator 3. Closed course 4. Road G=Gender (1=male; 2=female)
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H=Headway (seconds) HD=Hazard direction 1. Right 2. Left Hr=Horn use 0. No horn use 1. Horn use before or during avoidance 2. Horn use after situation settled Hz=Hazard movement 0. Stationary 1. Vehicle following 2. Vehicle changing lanes 3. Path intrusion IL=In lane −1. Left 0. Center 1. Right L=Lanes 1. From the next lane 2. From more than 1 lane away N=NASA TLX score (subjective stress scale) NL=Natural lighting 1. Day (dusk/dawn so far ~1.5) 2. Night R=Response complexity 1. Press button or verbal 2. Braking or steering was the only option 3. Braking or steering both options 4. Braking and steering Rc=Response choice −1. Steer left 0. Continue straight 1. Steer right Rd=Road type 1. Rural 2. Urban 3. Highway 4. Arterial S=Number of reported stimuli One stimulus Two or more stimuli that are spatially separate (exception would be nonspatially separate with one interfering with identification of other) TTC=Time to contact To=Topography
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1. Straight—level plane 2. Other (intersection, cuing, or curve) T=Transition time 1. Foot off accelerator/first reaction 2. Brake/accelerator application/steering wheel turned 3. Full brake/lateral or forward movement (start of vehicle response) V=Speed of the vehicle (in km/h) W=Weather (actually, road condition) 1. Sunny (shadows present) 2. Clear (no shadows) 3. Wet 4. Snow
15 Pedestrian Injury Issues in Litigation 1 Richard A.Olsen Human Performance: Limited 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
15.1 Introduction to Human Factors Principles and Relevance to the Standard of Care Although the portion of traffic fatalities and injuries that involve pedestrians in the U.S. has dropped somewhat in recent years, it still accounts for about 11% of the 42,000 people each year killed on our highways and streets (U.S. DOT, 2000). About 6% of the pedestrians involved in a collision are killed, while only about 1% of vehicle occupants die. Total cost of traffic crashes in the U.S. approaches $200 billion annually. Despite recent strides, pedestrians do not have the kinds of advocates other groups in the trafficloss community have, with each case relatively separate and countermeasures largely local. Because of the vulnerability of pedestrians in even low-speed collisions, care in preventing collisions must be emphasized. This chapter raises the issues that might apply in pedestrian collisions and discusses plaintiff and defense arguments and their criminal implications in detail. Rules of pedestrian safety are set by law and often enforced by the laws of physics (sometimes in spite of traffic laws). Pedestrians are considered capable of making judgments required to avoid putting themselves in imminently dangerous situations. It is generally assumed—in law and by most drivers—that those not capable will remain out of traffic situations unless supervised, so that the common rules are sufficient for reasonable safety. Children on sidewalk bikes are generally considered to be pedestrians and will also be discussed in specific cases. 1
This chapter and the chapter by Robert Dewar complement each other with different approaches. This discussion is related more to forensic investigation and presentation processes, while the other chapter emphasizes data and sources necessary for presenting arguments.
15.2 Objective and Scope of the Chapter Litigation is seldom a clear-cut search for the “truth” in a situation. Ideally, the fault finding and award or punishment are based on scientific and legal grounds that would also ring true to a jury or to the general public. Complications such as the realities of
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insurance, political pressures, and the styles and diligence of the attorneys color the process. Because juries seem to act as though the injured party deserves some award (“that’s what insurance is for”), the outcome in many civil cases seems to be less concerned with the avoidability of the loss and more with its consequences. It does not seem that our legal system should grant a large award to a family because the child was killed when that requires putting the onus on a driver who had no reasonable chance to avoid the collision. Nevertheless, that can be argued to be a common outcome, and it is accompanied by a judgment against a driver amounting to “murderer” in order to justify the award. A similar case can be made for some criminal vehicular manslaughter charges. Rather than the guilty/not guilty verdict in a criminal trial, the civil case depends on a verdict of liability and a comparative finding (varies with states). The defendant contributed to the loss event, but the plaintiff may also have contributed to the loss. The defendant in essence is found “partly guilty.” Books such as those of Shinar (1978) and Olson and Farber (2003) cover many of these issues in greater detail. In a few cases, the defendant is found liable, but the contribution of the plaintiff is so significant that the award is essentially (or exactly) $0. Both sides can claim victory in some sense, but both also lose. The great majority of cases filed, of course, are settled instead of going to trial. Whether justice is served in cases in which fault or blame can be assigned to two or more parties still rests on the extent to which the facts were discovered, presented, weighed, and evaluated in the trial or settlement negotiations. An outcome may have significant moral and financial effects as well as the lingering guilt, shame, and loss of reputation that go along with a negative finding. Balancing risk and convenience is at the heart of much litigation. Arguments pose “safe” and “normal” behavior against “unsafe” behavior. Drivers and pedestrians consciously play the odds of give and take, and they will take a chance on a car or person suddenly appearing out of nowhere. When the long shot occurs or when the risk taken is excessive, collisions may result. The definitions of and debates on the concepts in the preceding four sentences constitute much of our court records. They have emotional components; nevertheless, many are subject to analysis. This chapter will not change the realities of the processes in litigation, but it may lead to a more thorough look at the full range of issues in a case. From the initial filing of a complaint, questions arise as to design and law enforcement for the public facility, design and maintenance of the vehicle, and custodial care in injuries, as well as the behavior of the parties. If these are not considered at the start, the case may be unnecessarily limited. Attorneys, juries, and judges are not always able to appreciate the arguments presented by truly qualified experts, despite their best efforts, because of assumptions or misconceptions formulated through specific experiences, common sense, tradition, and even movies or television. Ensuring that some of these problems are addressed may help to separate Mark Twain’s (actually attributed to Artemis Ward) “things we don’t know” from “things we know that ain’t true.” It is much easier to address the former than the latter, but we should try to do both. The discussion, checklists, and case illustrations to follow are intended to do just that.
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15.3 Discussion of Principal Issues Although overlapping of topics and issues is unavoidable, the following discussions will each center on the mechanisms of pedestrian collision involvement; crossing and driving tactics; public traffic facilities; lighting, marking, and visibility; and driver and pedestrian behaviors and judgments. Other concerns, such as vehicle design and traffic laws, are mentioned briefly and intended to illustrate the problems in pedestrian and vehicle interactions. Arguments for and against various views of proper and improper, risky and prudent, or legal and illegal behaviors are included. Although there is no hope of being encyclopedic in the coverage, the discussion should serve to supplement checklists and provide better insight into the conflicts and their reasonable resolutions. A number of books and innumerable reports on traffic and pedestrian safety discuss the human factors or ergonomic issues involved. The quality of the work varies widely, and much of it appears shortly after the introduction of the automobile. The greatest impetus to better research began in the U.S. when Congress passed the Omnibus Safety Act of 1966 and created a safety agency (under Dr. William Haddon), now known as the National Highway Traffic Safety Administration in the U.S. Department of Transportation. Many interest groups followed, and the contributions of the rest of the world to behavior-related safety research have multiplied the total effort. The Transportation Research Board of the U.S. National Research Council alone has hundreds of committees, many on behavioral topics. Its annual meetings in Washington, D.C., bring together about 12,000 participants in all specialties of transport. Among the most useful and readable books on driver and road-user behavior are Allen (1970), Allen et al. (2001), Shinar (1978), Olson and Farber (2003), and Dewar and Olson (2002). The fact that some have been around for many years does not destroy their value. Many of the most basic concerns in human factors engineering have not been resolved in any final sense during the last few decades. Olsen (1981) also reviewed basic questions and problems that have yet to be resolved. Design of roads and vehicles has improved immensely. Freeways have made the flow of traffic much less likely to end in a crash on the average. Vehicles are more reliable and crashworthy, with belts and airbags and energy absorbers that save thousands of lives. However, crash avoidance has not been perfected, largely because the people involved are failing to see and do the right things at the right times or fast enough. The number of miles driven continues to rise. There is not enough emphasis on the systems aspects of safe transport. Vehicle capabilities and road designs have not fully recognized human limitations. The variety of vehicles causes mixes that are not compatible with each other or with the average driver, let alone the young, older, or impaired driver. Speed and power lead to road rage and intimidation instead of cooperation and courtesy. Road users do not always know what they might encounter next, even if they sometimes act as though nothing could happen. Into this mix and confusion, we also add the pedestrians—legitimate road users with everything stacked against them when a collision occurs. They are not helpless, but they have responsibilities like other road users. Some walk because they do not have the skill, maturity, or resources to drive. Most walk or run because they choose to. The purpose of this chapter is to expand the inspection of vehicle-pedestrian conflicts to clarify who had the choices and who exceeded the reasonable limits of an imperfect system. Litigation is
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largely aimed at discovering who was at fault in a loss. Human factors analyses are needed to show how we discover what went on to produce a conflict and to clarify who had or did not have choices at various points. Many crashes result when two or more errors coincide to cause loss of control. Coincidence remains a big factor in some crashes, but preventing that second error can reduce losses. Progress may not be rapid, but things are known that can help—if they are applied more widely. A brief introduction to elementary accident reconstruction approaches is provided in the first subsections in order to suggest the rigor that can be applied by qualified experts. It also may help to illustrate why a layman is likely to be wildly inaccurate in common sense impressions. The more significant issues in crash causation are discussed in the remaining sections. Pedestrian Collisions Types and Analysis—Parallel and Transverse A vehicle-pedestrian collision can be predicted by the geometry and relative speeds of the two objects. At some point in a developing situation, the collision is inevitable. If things do change, the change must take place before a critical point is reached. The two common types of pedestrian collision situations are parallel and transverse. In a parallel development, the vehicle and pedestrian are on overlapping paths, with the pedestrian facing the vehicle or headed away from it but within its projected path. This is contrasted with transverse collision, in which the vehicle and pedestrian paths cross and meet. Both types should impress the reader with the strong element of chance in these collisions. The timing is tight, and one could argue in many cases that chance or coincidence is the overwhelming cause of the loss. The width of the vehicle largely determines the exposure in a parallel development: a single sidestep by the pedestrian may prevent a collision with a two-wheel vehicle, but four or five steps might be required to evade an oncoming truck or bus. Walking speed is usually near the range of 1.0 to 1.7 m/s (3.5 to 5.5 ft/s), with running seldom beyond about twice that. Clearing a small sedan, 165 cm (5.5 ft) wide, thus takes three or four steps in about 1 or 2 s. Correspondingly, a vehicle path deviation of 60 to 275 cm (2 to 9 ft) might be required to prevent contact if the pedestrian does not move laterally off the collision course. When perception distance allows, it is possible for a driver to deviate left or right to avoid an object. At 97 km/h (60 mph), it takes about 27 m (90 ft) of travel for a vehicle to move laterally 1.5 m (5 ft) and 38 m (125 ft) of travel to move 3.0 m (10 ft) (see Fricke, 1990, pp. 72–50). That is 1.0 and 1.4 s of travel, respectively, which must be added to the distance traveled while the driver reacts (1.5 s @ 27 m/ s (88 ft/s)=40.2 m (132 ft)) more, for a range of 67.4 to 78.3 m (221 to 257 ft). During that 2.5 to 2.9 s, the pedestrian is probably clear. More likely, the detection distance is not that great and the driver can at best start to react while the pedestrian cannot get out of the way. In that same time, the pedestrian’s small inertia is more easily overcome to move out of the danger, if he or she is aware of the situation. Because of oncoming traffic, road width, the relative position, and other factors, the driver may not be able to choose the shorter distance when a pedestrian is not near the
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center of the vehicle’s path. At the center location, the choice is moot. If the pedestrian is walking facing the vehicle flow (as required by law when no sidewalks are provided, but hardly universally heeded), the driver may anticipate the pedestrian moving one way or the other. If the pedestrian is facing away, the driver may assume the pedestrian is not aware of the vehicle. Often, the driver cannot tell which way the pedestrian is facing, and if the vehicle is centered on the pedestrian, the ambiguity of the encounter increases the danger: if both deviate in opposite directions, there is a chance of evading, but if both choose the same direction, they will collide. A few variables favor the avoidance of a collision as it develops in a parallel situation over the transverse. One of these is the location of the pedestrian relative to the headlights. Because the pedestrian is already in the vehicle’s path, he or she is located in the brightest part of its headlight pattern and thus is where the driver is most likely to look and where light is most likely strong enough to allow detection. The driver may have several seconds to discover the person. For passenger vehicles set on low beam, the detection distance at night for a light-gray object (17% reflectance) directly in the beam varies from about 61 to 91 m (200 to 300 ft). Using the 91-m (300-ft) distance, this is sufficient for skidding to a stop at the pedestrian’s location (without impact) from a speed of about 97 km/h (60 mph), assuming a dry road surface and a perception-reaction time (PRT) of 1.5 s. In the U.S., the following convenient equation can be used: s=2.2×v+v 2/(30×µ) (15.1) where s is in feet v is in miles per hour µ (mu, the coefficient of tire road friction) is about 0.75 to 0.90 (dry) or 0.60 to 0.75 (wet) The first term in Equation (15.1) is distance traveled during PRT: v×1.4667×1.5 s or 132 ft (40.2 m); the second term is the stopping distance (µ=0.75) in an emergency braking mode or 160 ft (48.8 m). Because the driver is observing from about 6 ft (1.8 m) back of the bumper, the total, 132+160+ 6=298 ft (91 m), is from the point of first detection. Moving at 60 mph (multiply by 1.4667 to get 88 ft/s), the driver takes about 5.1 s to stop with visibility of 300 ft. (1.5 s PRT plus 160 ft÷44 ft/s, which is the average speed in stopping from 88 ft/s to 0, or 3.64 s, for a total of 5.1 s). The accuracy of data and assumptions seldom justifies several decimal points in final results, despite what a computer may print out. For PRT, 1.5 s is the value used most commonly as a first estimate. Some collision reconstructionists will use a PRT of 2.5 s in situations with a very low expectancy. Compared to the previous calculation, using the other extremes for a 200-ft (61 m) detection distance and assuming a wet road (µ=0.60) and a PRT of 2.5 s, one could skid to a stop in time from a speed of only about 35 mph (57 km/h). The stopping time is then 2.5 for PRT (covering 128 ft) plus 2.65 s (for braking 68 ft), totaling 5.1 s, which just happens to be about the same as the previous calculation. Simplified equations for SI units can also be derived.
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A detection distance barely sufficient for a panic stop for 97-km/h (60-mph) traffic in good conditions is not reassuring for pedestrians on freeways or many arterial roads. When conditions are not as good, the 57 kph (35 mph) value for safe speed illustrates the problem. The majority of drivers on major roads will not slow to this extent, and a small number do not slow at all for poor conditions. Average reductions of speed in fog or rain are only 2 to 10 mph. The assumed (17%) reflection is also not typical of pedestrian clothing (Shinar, 1985; Olson and Farber, 2003) that often varies around 2 to 10%, thus further reducing the detection distance. A transverse vehicle-pedestrian collision is one in which the vehicle and pedestrian paths cross at some angle. If the paths cross at a right angle (90°), there is the shortest exposure: the time it takes for the pedestrian to cross the width of the vehicle plus the pedestrian’s body depth. When the angle is less than 90°, the exposure time for a given pedestrian speed is greater because the diagonal path across the vehicle width is longer. The most important difference from the parallel path situation is that here the pedestrian appears in the headlight beam only for a short time just before impact. A typical stopping time for a vehicle is about 5 s (see examples in the last section). A pedestrian can walk from a shaded sidewalk or run across three or more lanes of roadway in less time. Headlight beam cutoff sharply reduces the illumination to the sides of the vehicle path, especially the left, thus reducing the chance of detection by the driver unless the pedestrian is showing retroreflectors. The driver’s eyes are adapted to the bright “hot spot” from the headlights on the road and he is looking mostly at the road and other traffic. Looking at the darkness and shadows of the sides is unproductive because, without reflectors, what is visible is too near for any reaction or too dim to see with the eyes’ adaptation level. If a pedestrian appears in the headlight beams at a distance great enough for the driver barely to react, i.e., 1.5 s or 33.5 m (110 ft) at 80 km/h (50 mph), and keeps moving across, chances are good that he or she will clear the path of the vehicle before it arrives (1.5 s @ 4 ft/s=6 ft or @ 1.22 m/s =1.83 m further across). Jet pilots do not have much need to look through the front windshield; if they see a plane ahead, they hit it (if it is coming at them) or they do not (if it is going in the same direction or crossing) because, at that point, it is too late to start a maneuver. Drivers do not (yet) have radar. Vision and Visibility Visibility and Perception Visibility has several components. First, a driver must detect that something that may require action is near the intended path. Then the identification of that object must be established as one that requires action. At that point, the driver must determine the relative motion between the object and the vehicle, decide on a tactic, and react to carry it out. Evasion tactics depend on whether the driver judges that there is a collision course or not and whether the relative motions are going to continue or change. A lamp or reflected light from a single device on an object provides only the first function, detection. Detection distance then depends on the lamp’s power or the reflectivity of the device, its size, orientation, any obstructions, and visibility conditions. For a reflector, the presence of water may be important.
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The identification function requires a pattern that suggests a person, and the decision regarding action depends on information regarding motion. Johansson (1973) and Owens and colleagues (1994) showed that a few bright spots attached to a human body in motion can reliably serve to suggest the presence as a person as well as gender, size, approximate age, and how the body is moving or what he or she is doing. Shoe-heel reflectors, now available, provide a motion pattern that, seen from the rear, is fairly clearly a person. The most practical simple display seems to be a pair of reflective stripes around the forearms or hands. Visible from most angles, the stripes (see section “Visibility Devices”) are in constant motion during walking or running and quickly portray their bearer as a person in a particular action. Because the height above the ground is almost ideal for reflection of the farthest reaches of headlight energy and the relatively dim illumination is still perceptible at many times the distance of a white surface, arm stripes are a practical and effective visibility aid. The availability of reflective tapes in colors (they also appear white when illuminated, though somewhat less intense), as well as the ease of donning and doffing an elastic band, reduce the need for displaying potentially unfashionable or garish combinations. Of course, the gray, black, or pastel band does not appear bright in normal viewing, but only when the observer is very near a projecting light source such as a driver will be. At this point, these bands have not been optimized and are not widely used. Two Aspects of the Visual Sense The two aspects of vision—focal (also sometimes called foveal) vision, which most know as the normal visual sense, and ambient vision, which is related to our perception of our own locomotion in space—have different functions and are affected by conditions in different ways (Leibowitz, 1983). The fewer objects visible in poor conditions occupy the focal aspects in a tunnel-vision mode, while the less demanding ambient aspect maintains the driver’s ability to steer a reasonable path at fairly high speed. This latter aspect has little need for corrective lenses and has very sensitive, mostly large-area responses, unlike the detailed focal vision. It operates essentially beneath our conscious awareness most of the time. The result is that drivers at night or in rain or fog do not feel compelled to reduce their speed even though they are not able to see objects that are potential pedestrians, vehicles, or obstacles. Eye Movements and Visual Search Studies of eye movements and visual search show that certain areas or objects are scanned with higher probabilities than others. Signs and markings normally are scanned, especially when the driver seeks destination information. Routine or frequently posted signs tend to be disregarded; in fact, they are often scanned, evaluated for relevance, and then discounted. The driver typically does not recall ever seeing any of a number of signs or markings and may deny that they were there. The scanning process is so rapid (often three glances per second), so automatic, and the information potential so great that it is no wonder that much of what one glances at is not absorbed in the form of a long-term memory (LTM). Much of what we see is lost, never converted from the temporary shortterm memory (STM). Drivers are asked, “Didn’t you see the sign?” and they may be
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reluctant to say they do not recall seeing any sign because it sounds as if they were not attentive. If they report seeing one, it may be described as being different or in a different location from the one the interrogator indicates, because it is a generic sign, the kind of sign a driver could see every day but would not memorize, not the specific one in question. Because of the nature of visual scanning, no one can look everywhere in a moving environment, even with the aid of peripheral vision. As in many tasks, priorities must be set and employed, allocating attention where it is most likely to be productive. Attending to various parts of the driving task means one can look in the rear view mirror, for example, only by looking away from the windshield view. Manipulating controls for lights, wipers, washers, and turn signals can be essential to driving. Each requires some visual monitoring. Searches of the windshield view ahead, the crossing streets and sidewalks, traffic signals, inside and outside mirrors, and the speedometer are necessary. When radios, air conditioning, navigation systems, tapes and CD players, and cell phones are added, it becomes a matter or degree as to whether they are “required” (see Case D). One cannot see everything—or even one thing all the time. A good driver cannot constantly stare straight ahead with both hands on the steering wheel. Mere driving is not a full-time occupation, but staying judiciously alert is. Peripheral Vision and Information Much of the automaticity of visual search is dictated by peripheral vision. Although details such as symbols, patterns, and color are seriously degraded in the periphery, the visual system is organized to respond to novel bright, contrasting, or moving objects appearing at the sides, by aiming the central vision at them in order to evaluate them more fully. Especially at night when visible objects are fewer, the eye may continue to return to the same item after it has been discounted as irrelevant (see Case E). The driver’s task is to look for specific sources of information, to evaluate whatever else presents itself, and to balance the search for information known to be required against that which could be relevant by chance, such as a developing emergency situation. The preponderance of routine (boring) driving is shown by the fact that relatively few drivers ever are involved in a serious collision, and many report having driven long stretches of highway with no memory of any details. When a sudden episode of high information flow (a collision or near miss) occurs or when there are many distracting inputs, the driver must rapidly set priorities and make decisions. These situations are relatively rare. Although this could explain why drivers seem inattentive, this attitude may be based on years or decades of experience that confirms that their behavior is adequate. Boredom with routine driving is certainly involved in speeding, especially in youthful drivers, who have the least data upon which to base their judgment but feel the need for something “happening.” High speeds can certainly cause that. Meanwhile, search for threshold level contrasts (a pedestrian in dark clothing in the shadows) is a more taxing and usually (statistically) unproductive task—even more boring. If they were detected, the vast majority of these pedestrians would not be at risk and their presence certainly would not justify maximal emergency braking. If someone should suddenly appear on a collision path, visibility conditions with only headlighting
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often preclude detection in time for evasive action (see the subsection on transverse collision). Pedestrian Populations Pedestrian Competency It is generally assumed—in the law and by most drivers—that those pedestrians not capable of knowing and observing the rules will remain out of traffic situations unless supervised; however, it is recognized that rare exceptions may be encountered. This ordinarily makes the commonly understood system sufficient for reasonable safety. Children walking or on sidewalk bikes (classed by the Consumer Products Safety Commission (CPSC) as toys rather than bicycles) are considered pedestrians, but with special limitations. When drivers have reason to expect exceptional situations, they can use special precautions. For example, school zones at morning, noon, and afternoon transit times may have crossing guards as well as signals and standing regulations on speed and yielding when children are present. Children and persons in wheelchairs or using walking aids, as well as visually handicapped persons using canes, also give notice of the fact that the ordinary considerations for pedestrians may not be sufficient. Problems arise when such limitations are not obvious, at least from a distance that allows reasonable evasive action. Children will appear at times not related to school schedules, or persons with physical or mental limitations may appear in traffic and not proceed in the time and manner ordinarily experienced. Dart-outs from behind vehicles or structures and sudden dashes by people walking normally—most common with children in elementary grades, especially boys ages 5 to 9 years—are also seen occasionally in older persons. In any case, unexpected, unusual, random, and rapid actions make it difficult or impossible for a driver to avoid contact if a coincidence of timing suddenly puts such a person in a collision course with his or her vehicle, even in good daylight conditions (see Case D). The alternative is to drive at the speed at which stopping is possible in the worst situations. Because this speed can be under 25 km/h (15 mph) and seldom exceeds 40 km/h (25 mph), it would not be tolerated in regular traffic. Even near active school zones, the indicated lower speed limit is not widely observed. In residential areas, the rolling ball may be followed by a running child; in business areas, an attractive person may be followed by a pedestrian’s eyes, which should be on traffic. Pedestrian Vulnerability The obvious vulnerability of pedestrians, even when a striking vehicle’s speed has been reduced to walking levels, argues that reflectors or other visibility enhancements be required for everyone exposed to high-speed traffic (i.e., over 55 km/h or 35 mph) when visibility is reduced. Even good hearing, vision, and mobility are not enough to ensure safe crossing in normal traffic when visibility and stopping distances for the vehicles present are not comparable. Certain advocacy groups have maintained that they will not promote the use of special reflectors, markers, lights, or signs for persons who have various handicaps because that would result in treating them differently from the
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population at large. If any of these abilities to stay out or get out of danger is compromised, the need for greater visibility should be obvious. Too often, the conditions even for the able-bodied pedestrian are already borderline (see Case F). Of course, there is logic in encouraging or requiring all pedestrians to make themselves visible whenever they are in the traffic environment. Ambiguity The previous discussions illustrate another important point: ambiguity in an apparent traffic conflict may be particularly difficult to handle. When the driver sees a dilemma, it can result in failure to choose either of the (equally bad) alternatives; rather than taking course A or B, he or she drives into the “gore” (divider) area between the two. The situation can also be paralyzing or merely delay any action well beyond the usual range of reaction times. Either way, it reduces the chance of a satisfactory outcome. If a pedestrian stops while crossing at the same time that the driver starts to deviate behind the path he or she assumes is intended, there may be time for the vehicle to move a small distance laterally; however, because the pedestrian did not continue, there is contact. On the other hand, a driver who decides the pedestrian is going to stop would try to deviate to pass in front of him or her. Now if the pedestrian does not stop, they will collide. The timing involved is not sufficient for second guessing; both decide what they will do at the same time and then do it. In either instance, there is no way to predict the actions. Although a post hoc analysis might show one set of decisions to be the most logical, startle and panic or mere time pressure can prevail and make the instantaneous behavior of both parties beyond their control in the time available. The Situation, Darkness, and Weather Situational Issues The main situational issues in a pedestrian injury or death collision case are the behaviors of the driver and the pedestrian and the circumstances under which the collision occurred, as they affect the outcome. Specifically, these include facility characteristics; lighting and visibility; speed, path, and control of the vehicle; and judgment, timing and path, and visibility choices by the pedestrian (see Case A). Although many of these topics are controlled by laws and ordinances, many are not, and pedestrian and driver behaviors may or may not be influenced by law, common decency, or even common sense. Those under the influence of any mind-altering substances—pedestrians or drivers driving under the influence (DUI) or driving while intoxicated (DWI)—add special problems because awareness, judgment, and expectancies are all involved (but see Case A). Darkness and Weather Darkness and rain or other weather make the interaction between pedestrians and drivers more difficult. Each of the several components of visibility is affected by night and poor driving conditions. Andre and Owens (2001) use a “twilight envelope” to determine visibility in headlights, though this is still somewhat controversial. Despite the obvious
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increase in risk because of reduced visibility and increased braking distances, neither drivers nor pedestrians seem to vary their behaviors enough to compensate. The number of pedestrians on the roads may be reduced, thus reducing exposure, but at the same time, the reduced likelihood of encountering a pedestrian makes drivers less likely to anticipate the rare occurrence. The effect of reduced visibility is to increase the tunnel vision seen in drivers when the visual environment is impoverished, without reducing their tendencies to drive at speeds that would be appropriate in clear daylight. An important but still essentially disregarded aspect of night vision is “night myopia” (Leibowitz and Owens, 1977; Owens, 1984) by which some people become markedly nearsighted in the dark. The extent of the effect is widely variable, so each person should be tested for driving at night (and those most affected should be given appropriate correction). No common test or legal recognition of this problem exists. A wet road can produce mist, splash, and higher noise; reduced traction and braking; wet brakes that are even less effective; possible hydroplaning (loss of contact with the road due to a water film); introduction of foreign matter (sand and gravel) to the surface; increased glare from all lights; and false images and reflections. Braking distance and turning ability are proportional to the friction (µ or mu) available between the road and tires. A new, rough, Portland concrete road surface may have a µ of 0.85 for sedan tires and about 0.70 for tires on large trucks, whether it is dry or wet. Similar values hold for dry asphaltic surfaces, but they may drop sharply when the surface is wet. Worn surfaces of all types have lower values, and the values always decrease further with higher speeds. Braking distance doubles when the friction factor goes from 0.8 to 0.4. Few drivers know, or behave as though they know, that driving a sedan on a wet, worn, asphaltic surface at 70 mph is equivalent to driving on ice. The facts do not seem to change behavior much; however, brought out in court, they can make the driver look very irresponsible. The presence of fog has been associated with a number of sensational chain-reaction crashes with dozens of vehicles involved and resulting in many injuries and deaths. When visibility is suddenly reduced drastically, each driver, from the second vehicle on, suddenly has proof that his or her usual following distance or speed was not good enough. Leibowitz and Owens (1977) suggested a principle of visual perception to explain the common use of excess speed in poor conditions. There is no evidence that those who survive such incidents increase their spacing or reduce their speed after the experience. However, a driving history that includes rear-ender accidents will be used against the driver if the prosecution/plaintiff can get it on the record. In inadvertently dropping the wrong phrase, the expert or a party can open the door to further discovery never intended by the attorneys. Facility Issues A facility may or may not have been designed for use by pedestrians, either by its nature (a rural freeway) or because it was assumed other facilities would be used (sidewalks, overpasses, crosswalks). Laws and ordinances may specifically prohibit pedestrians on some facilities, but they continue to appear there for a variety of reasons, even if enforcement is practiced. If an area has changed in its usage patterns, it could be argued that the governing body has not kept up with reasonable improvements that have
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gradually become necessary for pedestrian safety. For example, when traffic speeds exceed the set limits, or the limits are above those consistent with pedestrian usage, a lack of recent traffic engineering studies can suggest liability or a lack of sufficient notice to drivers. Sovereign immunity in cases against states and governments has been reduced steadily in many such claims. When pedestrian injuries or deaths occur, the facilities face the following issues. Provisions for Needs and Informing Parties Crossing the road is a universal pedestrian need and crossing as the crow flies is an almost universal tendency. When blocks are long, a midblock crossing can be much shorter than the indirect route via a crosswalk. There are fewer real needs to cross a freeway or an arterial. Those few users should be discouraged by the obvious dangers, but breakdowns, collisions, etc. do cause some to try to cross wide busy roads. The balance between meeting emergency needs and the low frequency of usage is not easy to achieve. Pedestrians get little practice at and are ill prepared for judgments and decisions required in high-speed traffic. They typically overestimate low speeds and underestimate high speeds; they are more accurate in the 40- to 50-mph range (about 75 kph). Signs alone are seldom effective in deterring the occasional crossing. Walls and fences, overpasses or underpasses, and similar provisions are expensive and obviously cannot be everywhere someone might feel the need to cross. When shops, parks, or playgrounds are across the street from dense residential or school areas, the needs become more obvious, although the costs and human tendency for shortcutting remain. At some point, the onus must be placed on the pedestrians: if they expose themselves to high potential risk, even unwittingly, drivers may have no opportunity to avoid hitting them. Reasonable provisions must be made to bar pedestrian access to the area or to inform them that they are trespassing and at risk. Pedestrians are predictably going to use shortcuts (Fruin, 1971), even to reduce distances by a matter of yards. Wherever a path has been established over time, there will be foot traffic. Barriers in areas where authorities have decided the threat is high must be effective barriers. It is better, of course, to make a safer alternative path more attractive. The traditional crosswalk is not the only treatment available, and marked crosswalks may lull pedestrians into a false sense of security compared to unmarked crosswalks (Hermes, 1972; Zegeer et al., 2002), despite their almost-identical treatment in law. Crosswalk visibility is a major issue. When designers shape an intersection for drainage, the result may depress the stop lines, limit lines, crosswalk markings, etc. so that they are not visible on approach at distances compatible with the prevailing vehicle speeds. Worn or obscured markings reduce the visibility further. Diagonal hatched lines are generally more visible than the usual double 30-cm (12-in.) transverse lines delineating crosswalks, and many variations are being evaluated worldwide. A trade-off exists when more paint for visibility reduces the friction for stopping and walking and adds cost. The use of yellow markings near schools is wasted on most drivers. They do not notice the difference, or else they do not know what it means or when it applies (class and after-school schedules). Laws indicate that special provisions apply when children “are present” rather than “can be seen.” If a child is present but
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cannot be seen with reasonable efforts, the driver can hardly be blamed automatically, much as in dart-out and dash collisions. The enforcement of school zone speeds is so unlikely and sporadic that few drivers get a message other than “be careful of cops near schools.” Drivers may be warned by signs indicating pedestrians or crossings where they would not otherwise be expected, such as specially marked midblock crosswalks. A sign at every intersection saying “crosswalk ahead” or “here” (actually two crosswalks) has no practical function if persons are never seen because of low usage or obstructions to the lines of sight. If the traffic moves at speeds for which visibility does not exceed the required stopping distance, the warning has little value. This does not prevent the plaintiff’s attorney from claiming that it should. Unfortunately, even flashing lights may not change driver behavior if no one is seen crossing, and pedestrian signals that require requests (i.e., demand pushbuttons) are not widely utilized even when provided. A common minor, but probably critical, problem is that the pushbuttons are installed at points convenient for the traffic engineers but not in the paths used by pedestrians. There is seldom feedback to the pedestrian that the button has already been pushed or that it is working at all. New “count-down” walk signals, which show the remaining seconds of time available, seem to be proving helpful and welcome. In high-incident or high-usage areas (see McMahon et al., 2002), pedestrian crossing times and provisions may need to be increased to the detriment of driver convenience. When pushbuttons are provided for pedestrians, the green light with the crossing times is usually longer when the button is pushed compared to when it is not. Persons familiar with the intersections may assume wrongly that the green time is always the same and start without pushing the button when they see a green as they approach. They may be caught in the intersection when cross traffic gets an early green. In all the preceding provisions, enforcement and education are required in order to get driver and pedestrian compliance and cooperation. Lighting for Warnings, Boundaries, and Alternative Facilities Signs with reflectorized surfaces are intended to aid in readability and guide users. These retroreflective devices direct a narrow cone of light back in the direction of the vehicle’s headlights (and include the driver’s line of sight). Ordinary reflective surfaces, such as a mirror, reflect light back to the source only when the surface is exactly perpendicular to the source line of sight (LOS); otherwise, they send it off at an equal (useless) side angle. Pedestrians and most cyclists have no light sources and must depend on local lighting. Fortunately, a pedestrian can spend more time, if necessary, reading a sign or finding the path, and the adaptation level of a pedestrian’s eyes is lower, compared to a driver’s. Therefore, the pedestrian can operate with the scattered light available in built-up areas. The problem often comes down to providing incentives to use the path and to locate the sign. Overpasses and underpasses are notoriously underutilized by pedestrians unless they offer another reason to change levels, such as access to a subway. One could argue that roads should be depressed to keep pedestrians from needing to go up, over, and down to
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cross. Even if feasible, costs are high unless planning integrates the two mode facilities from the start. Enforcement and Pedestrian and Driver Behavior Speed laws are based to some extent on the demand for speed. A common method is to survey traffic speeds in an area and set the posted limit to that exceeded only by the fastest 15% of vehicles measured. This 85th percentile speed presumably is tacit acknowledgement that most drivers are able to determine what speed is reasonable for those conditions and thus a limit set below that will be widely violated. Two problems arise: • Not all situations that increase risk are obvious to unfamiliar drivers, and drivers who know the problem areas still tend to depend on the probabilities of encountering a pedestrian or other concern. • No matter what drivers would like to do, the stopping distances set by speed are largely immutable, and the visibility distances provided by headlighting and most overhead lighting—or even daylight—are limited for detecting a pedestrian. The choice becomes one of heavy, obvious enforcement to reduce speed or of enhancing pedestrian visibility and predictability to better notify drivers of their presence. Lighting and Visibility Area Lighting and Low-Beam Headlights Besides the illumination from a driver’s vehicle headlights, other light sources may aid or interfere with detection of pedestrians. The most obvious of these is overhead streetlights. For drivers, low-beam headlights are the norm and often the sole source of light. The cost of overhead lighting is a controlling factor in their use, and compromises are made when it comes to their placement, number, type, height, spacing, size, and the color (spectrum) of the light, among other factors. A common practice on smaller roads is to place a single light over an intersection. This presumably is to help the driver see a pedestrian in or near the crosswalk. It may also be useful in warning drivers that an intersection is present and that a vehicle or other activity is more likely in that area. For pedestrian safety, however, the design may need to be more carefully thought out. If the person is dressed in dark clothing, there would be very little reflection from the clothing, but a bright area on the pavement underneath the street light might provide a good contrast, although small in size. Seen from the flat angle presented to a driver, such a spot may not be conspicuous, especially in a rough road surface. If the lamp is directly over the crosswalk, the person appears as a small dark spot (a shadow) on the lighted street. If the light is behind the pedestrian’s location, the illuminated street provides a larger screen for contrasting the entire profile of the pedestrian. Now, if the light is located closer, between the driver and the crosswalk, the bright area attracts the driver’s attention, but it raises the adaptation level of his or her eyes and does little to make the dark pedestrian in the shadow detectable.
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On the other hand, when the pedestrian is in (the recommended) white or light-colored clothing, the situation changes. The lamp closer to the driver illuminates the light clothing from the front, and the dark street beyond provides good contrast for detection. A lamp directly overhead may reflect a small amount of light from the light clothing, but it also makes the surface light for a poor overall contrast. The lamp positioned beyond the crosswalk provides neither reflected light from the clothing nor contrast as it makes a lighter surface. When the headlights approach and begin to reflect off the light clothing, it blends with the light background surface, thus reducing contrast. In fact, for a lightcolored object, the mixture of an overhead light and headlighting on its front will always produce a point at which the contrast between the object and the surface is essentially zero (Pinkney et al., 1975). Detection with High-Beam Headlights The pedestrian detection situation improves somewhat at night if high-beam headlights are used. Unfortunately, many drivers never use the high setting, even on freeways, and most do so very rarely. This common failure is based on the erroneous notion (Allen, 1970) that blinding an oncoming driver is a serious problem, even on wide, multilane roads. Concern for the apocryphal face-to-face encounter with an irate trucker may have driven this unfortunate point home to many drivers. Other than the fact that the idea is dangerous and untrue, the trucker’s high eye position makes it least likely that this is a real problem. It is true that a vehicle in a long right curve (for right-hand driving rules) puts a greater portion of the headlighting into the direction of the eyes of oncoming traffic, but it is seldom debilitating; in some cases, the light may even help those drivers by backlighting objects in the road. The situation is in flux with the advent of higher (e.g., SUVs) and brighter new designs (e.g., high-intensity discharge or HID) in lamps. Although viewing the direct beam may be painfully bright, the beam is so narrow that any encounter would be brief. The new (bluish) HID lights had detection distances 100 m (328 ft) shorter than halogen lamps in one comparison by Blanco and colleagues (2001). Current codes do limit the situations in which high beams maybe used (e.g., within 500 ft [150 m] of an oncoming vehicle or 300 ft [90 m] when following a vehicle (California, 2000, VC 24409)). The intent is to keep the beam from directly striking the eyes of another driver. The effect may be to reduce visibility for long periods of driving during which pedestrians and other objects may be overlooked unnecessarily. Sivak and colleagues (1997) showed that lights available on current vehicles vary widely in their pedestrian detection distances. Presumably, standards will be forthcoming to reduce the variation determined by the vehicle selected, while all drivers face the same problems of avoiding pedestrians. Other Light Sources and Effects Overhead illumination is cheaper when more efficient light sources are used. Incandescent lamps, familiar from most home usage, provide a warm, slightly golden glow from a fairly even distribution of colors that do not quite add up to white (sunlight). Other spectra produced by mercury, high- and low-pressure sodium, fluorescent, metal halide lamps, and others change color perception but provide visible light with less
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electrical energy—often by factors of five to ten—making them economically attractive. There is continued controversy on this trade-off, however. The pure yellow (single spectral line) of low-pressure sodium (LPS) produces a monochromatic world presumed to be equivalent to the black-gray-white one of monochromatic photography or low-level (rod only) vision (but see Lewis, 1999). Still, many people report areas of LPS illumination as unnatural, eerie, or strange, although they feel they can get by with it. The high-pressure sodium (HPS) lamp adds a second spectral line not found on LPS. It is perceived as somewhat less yellow, and it allows more colors to be distinguished. Public opinion generally is more favorable for HPS than LPS. Especially for LPS, the obvious confusion of the yellow streetlight and the yellow (amber) phase of traffic lights is one disadvantage claimed to be crucial in some traffic disputes. More importantly, not enough study of the perception of objects or the estimation of speed and distance has been conducted in order to ensure that LPS is a good solution. One study showed that the reaction time for drivers to determine whether a pedestrian was entering a crosswalk or leaving it (facing left or right) increased almost 60% (944 ms vs. 593 ms) under LPS compared to incandescent lighting when both were dim (0.1 cd/m2). At higher levels (3.0 cd/m2), the differences disappeared. Street lighting commonly varies in intensity between luminaires by a factor of at least five and by much greater values as distance increases across a crosswalk with only one lamp, for example. In one case involving a man crossing almost directly under one LPS streetlight in a series, the driver reported he first saw him as he struck the windshield. Conditions were good in all aspects and the driver was an alert, rested, respected educator with a perfect driving record. He described the area as dark. The pedestrian, who died, probably was confident that the streetlights and light-colored clothing made him plainly visible (see Case B). Special Lighting Problems In certain conditions at night, false targets can appear, potentially confusing drivers or pedestrians. The one-headlight vehicle can be seen as a motorcycle or bicycle, or it may be seen as a four-wheel vehicle but misperceived as having, say, the left light out when it is actually the right one, causing a last-minute swerve. A wet road can make a car appear to be a large truck by doubling the image of the headlights. Reflectors on a sign or mailbox can be seen as a person. There are also dynamic illusions, such as the pseudopedestrian perceived as headlights from an oncoming vehicle casting a moving shadow from a pole or tree across the roadway; it can look very much like a pedestrian running into the driver’s path. If pedestrians happen to be present, this distraction could cause the driver to fail to see them. These ideas illustrate the variety of reports made by individuals; not all can be dismissed as grabbing at straws. Driver Behavior and Knowledge Evasive Maneuvers When perception distance allows, it is possible for a driver to deviate left or right to avoid an object. The minimum distance for evasion (67 to 78 m or 221 to 257 ft in examples)
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means a pedestrian must be detected almost directly in front of the vehicle (to be seen in the headlight beam) and must not move into the new vehicle path. The detection of a typical pedestrian at this distance is by no means assured. As pointed out earlier, a pedestrian who keeps walking in that situation will escape contact if the vehicle keeps going straight. The driver may not realize that the best course of action is to do nothing. If the driver never sees the person—a common finding—no loss occurs. In fact, in many such near-misses drivers are never aware of the danger unless a passenger reports seeing the pedestrian or another vehicle’s headlights happen to aid in the detection. Choices and Cognitive Map Appropriate choices regarding vision, speed, path, and control of the vehicle are responsibilities of the driver. In normal “looking,” humans build a strong sense of a detailed visual world because their eyes are in constant motion. Although road feel and sound add to this perception, it is predominantly visual. Wherever one looks at a given instant, much as a spotlight illuminates a small area, the person is able to perceive that area clearly. Each look or fixation allows the brain to process and compile information. Added together, these samples provide a continuous perception of an apparently continuous and detailed world, even though, inevitably, some parts of the complete field have not been examined or spotlighted. The resulting concept may be called a cognitive map. Drivers have cognitive maps of varying fidelity and adequacy, depending on familiarity with the area; experience; motivation; other personal characteristics, such as intelligence and training; and the conditions under which they are operating. The broad topic of attention and vigilance also must be considered. Assessing diligence and skill in such gathering of information and using it is no trivial task, but mechanisms and findings from studies can help determine whether the driver performed as one would expect. Driver Lane Changes Lane changes by drivers can complicate the pedestrian’s assessment of a situation. Lane discipline can be suggested as a preventive measure. This consists of keeping right except to pass; avoiding passing on the right when possible, making gradual changes, staying within marked boundaries, signaling; etc. Signaling before a lane change is required by law but seen in a minority of instances. Such rules simplify the search and decision processes. When the pedestrian expects or is informed of a change, he or she can make allowances. If there is no signal or if the lanes are poorly defined, a pedestrian may walk into the path of a vehicle that he or she assumed was going to pass in another lane (see Case B). Memory and Recall The fact that a driver does not recall a specific sign or marking does not imply that it was not perceived; in fact, studies show that a driver may react to a sign by slowing or steering, as appropriate, but still not recall it a short time later. As with many eyewitness accounts, the degree of confidence or certainty with which a witness asserts the
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observation is often inversely related to the accuracy of that report (Loftus and Ketcham, 1991). Elaborating scant details into a coherent story is a common, largely uncontrollable distortion of memory. Although it does not necessarily imply intent to deceive (Loftus and Ketcham, 1994), it can be a source of inaccuracy. This, coupled with the confusion and shock or startle from a collision, even without head injury or severe pain, makes reconstruction of events from percipient witnesses unreliable unless several independent accounts are compared and weighed. If an event is followed immediately by a traumatic situation, the memory of the initial event may never be consolidated into a long-term memory and is lost as most STM information is. Loftus and Ketcham (1994) point out that this is a more reasonable explanation of lack of recall in many situations than some repression mechanism that supposedly hides facts from the conscious memory, lurking until some special process releases it. For a detailed discussion of the role of memory in accident reconstruction, see Haber and Haber (2002). Judgment and Choices by the Pedestrian The Pedestrian Advantage We are all pedestrians, even if only from the parking place to a school, shop, or home. We have a degree of choice in most situations, although clearly age, resources, and employment can dictate a person’s duration and conditions of exposure to traffic. Just as drivers choose their vehicle’s speed and course and the degree to which they obey rules and laws, pedestrians largely determine their own exposure. Some areas of conflict are predictable, however. At night, pedestrians have an advantage in that they can see vehicle headlights at a great distance, if not obscured by large objects or changes of vehicle travel direction. A person near the edge of a road is seldom prevented from observing approaching headlights (or even parking lights or the unfortunately wide variety of daytime running lights) from 90 m (300 ft) away—often much further. The reverse is not true for a driver looking for pedestrians. A pedestrian’s eyes are adapted to a lower ambient light level than a driver’s eyes, which are focused near the relatively bright, large, and close area on the road surface illuminated by the headlights. Pedestrians can spend more time looking and can see smaller objects with lower contrasts to their surroundings than a driver can. Pedestrians, including those who are witnesses to an incident, are not usually aware of these differences. Often they report the driver did not react when “I could clearly see the person in the road several seconds before the vehicle hit him.” In some circumstances, it is true that drivers would be better able to see pedestrians if they did not have their headlights on. This is not advocated, obviously, and is not practical unless overhead lighting recreates essentially an artificial daylight (as is done in a few places throughout the world). Pedestrian Expectancy Pedestrians may have unrealistic expectations of a driver’s ability to see and avoid them for several reasons. It is estimated that pedestrians, on the average, overestimate their own visibility by a factor of three (Shinar, 1984). That is, a pedestrian may feel it is safe
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to cross because a driver 90 m (300 ft) away “certainly can see me,” when the driver, in fact, cannot perceive a presence until the distance is 30 m (100 ft). Whether this misconception is based on misperceived experience or plain luck (“I’ve done it for years and never been hit”), or purely on the egocentric illusion of invulnerability, is not known. Blanco et al. (2001) suggest that pedestrian education may be effective in reducing this error. Clothing At night there is no way to get around the need for a pedestrian to be visible. White clothing, often touted in safety campaigns, is visible under headlighting alone at a distance sufficient for a driver to perceive and stop from about 55 km/h (35 mph) or less. Dark colors (tan and gray to flat black) reduce this speed, seldom allowing for average speeds even in residential and urban areas. Only reflectors provide sufficient stopping distance for speeds above about 55 km/h (35 mph). Pedestrians wearing white shoes, who are directly in the beam of headlights in or near the road at about 23 to 46 m (75 to 150 ft) away, are somewhat more detectable. The brightness, coupled with the walkingmotion patterns, makes a pedestrian’s presence readily discernible at slower speeds (up to about 30 mph). Shoes with reflectors installed can extend the detection distance considerably, especially from the rear. Here, too, the motion pattern identifies the pedestrian, distinguishing the object from a bicycle or a stationary marker (see Owens et al., 1994). The unfortunate practice of dressing in dark clothing (“Goth”) or faded jeans and dark jackets exacerbates the problem for drivers, although, ultimately, the pedestrian loses. Because reasonable options in defensive behavior and visibility enhancement lie with pedestrians, and only unrealistic speeds can help drivers avoid low-visibility pedestrians (but see Case F), the logical emphasis is obvious. When litigation arises, these arguments cannot be ignored. In contrast to the preceding argument (no pun intended), in a certain type of case a dark pedestrian is visible. It is not because the person is illuminated but because background lighting is present and the dark body passing a bright area or a succession of light sources shows a pattern of light interruptions that are clearly perceived as a person moving (see Case C). In mixed suburban areas, lighting sources may be numerous and the alert driver can use this phenomenon for detection. No special training is required, although experience helps. Night and Poor Weather The pedestrian is often faced with complex situations made more difficult at night or in poor weather. The judgment of vehicle speed and the estimation of time to collision and time needed to cross are difficult enough. If the vehicle deviates (see Case B) from an assumed path or speed or an obscured vehicle suddenly becomes evident, even the most accurate calculations no longer apply. Youth, age, or impairments can make judgments less accurate and performance less adequate. The argument “I’m moving as fast as I can” does not mitigate the injury when a driver, not seeing any obvious limitation, assumes an older person will clear as fast as other pedestrians do, but he does not.
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Midblock Crossing and J-Walking Many maintain (unofficially) that crossing midblock is safer than crossing at a corner. It cannot be denied that it is usually shorter (but see Case F). Although speed may be higher midblock, there are gaps in traffic and traffic midblock can be a threat from only one way on each lane of the road. At intersections, traffic threats can be from any of the four directions plus each of the left and right turns. Especially in older populations, the searching, scanning, and decision processes are more complex and take more time. This is compelling logic to many and undoubtedly explains part of the popularity of the practice. As streets become wider, the need for median sanctuaries becomes greater, allowing pedestrians to make adjustments when an initial judgment was not accurate. Rather than attempting to legislate behavior, recognizing and accommodating prevailing tendencies and reducing the risks involved may be more productive. Almost every roadway has painted centerlines or lane lines that can serve as (narrow) sanctuaries; in cases in which a pedestrian ran across the second half of the road and was hit, the argument can be made that waiting on a line would have been safer than proceeding. Although one’s hesitancy to stop in the middle of the road is understandable, the odds are often much better with the wait. With a defined sanctuary they are better yet. Vehicle Design When the design of vehicles is questioned, a whole new population of experts is likely to become involved. A few issues should be mentioned here for completeness, although the coverage will not be exhaustive. See also Olsen (1992) for more on design liability. Pedestrian-Friendly Front-End Design Studies have shown that certain vehicle designs do more or less damage to the human struck by the vehicle. For example, flat-nosed vans tend to accelerate the body immediately to full vehicle speed and then drop it, allowing it to be run over. Other shapes deflect the body, accelerating it more gradually, and allow it to move off the side. Smooth surfaces without projections do less damage in low-speed impacts. There has been very little more than a mention of “cow-catcher” devices that could retain the pedestrian after impact and prevent the subsequent impact with the roadway and running over that often do more serious damage than the initial strike. Other Vehicle Structures The A-pillar (between the windshield and sides, supporting the roof) is in a position to obscure the driver’s view of pedestrians or small vehicles in traffic. One manufacturer advertised that, in their vehicles, this member was narrower than the distance between the eyes of most persons, so the driver could see everything with at least one eye. That is no longer seen, probably because of increased structural strength requirements. It is assumed that drivers are aware of this limitation and will use head movements to compensate, looking around the pillar. That may not be possible or likely in every situation (see Case B), especially with high visual demands.
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The glare often seen on the inside of a windshield in bright sunlight or with internal light sources can be a serious limitation to vision when light-colored objects are placed on the dash. A design using light colors on the dash could cause this problem unnecessarily. Even a black surface can have enough sheen to reduce contrast on the windshield, and flat or flocked surfaces can be added to minimize this problem. A windshield placed closer to vertical would minimize distortion and some other problems, but the realities of wind resistance preclude this. Tinted Glass Windshields and front side windows are required to transmit 70% of the visible energy perpendicular to the surface. However, because the surface is not vertical, the actual path is longer, reducing the transmission. Some green tints can reduce the brightness of red traffic signals. Dark tinting of rear and side windows in vans and SUVs makes the entire vehicle an impediment to vision for other drivers. Pedestrians and bicycles, as well as larger vehicles and all types of signals, can be overlooked, and vehicles—especially smaller ones—are often seen riding a foot or two out of line in traffic so that the driver can see what is going on ahead. With following distances already too short, the lack of view of the second and third vehicles ahead makes rear-end collisions and erratic maneuvers more likely. The driver has some choice in vehicle selection, but these considerations seem to be trivialized. The after-market tinting of windows is especially unfortunate because standards, if any, are not enforced; thus, individuals who so choose can drive a “black box” that interferes with traffic communications and makes enforcement efforts more difficult and dangerous. Drivers using sunglasses or yellow “night-driving glasses” at night or dawn and dusk reduce their ability to see marginal contrasts. The intensity and blue cast of HID headlights may increase this harmful practice. Clear windows and eyeglasses make for better and quicker visual response in marginal conditions. Whether the foregoing concerns suggest targets of lawsuits or reasoning that can help defendant cases is unclear, but they are mentioned for completeness. Visibility Devices Pedestrian Responsibility and Conduct At some point it can be claimed that a pedestrian or driver showed disregard for safety and must be held responsible for creating a situation in which it was beyond the ability of the other party to avoid a collision. Because of the financial, social, and emotional implications—as well as for public safety—it seems advisable to set a standard for minimum acceptable pedestrian behavior as well as driver behavior. When the pedestrian does not achieve this minimum, clearly there should be no criminal charges or no civil liability for the driver and no civil recourse for a pedestrian who is hit. In routine reports, police seldom hold the driver fault free in pedestrian collisions, even when the driver had no chance to evade and the pedestrian took no action to avoid the collision. It appears that, at least in some jurisdictions, this is changing and fewer citations or criminal charges are filed for drivers caught in such circumstances. Litigation, presumably, goes deeper
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into causation and could come to this conclusion more regularly. Some cases are going to fall on one party and some will have shared responsibility. Visibility Aids Retroreflectors or lights. Lights require batteries and a single light source is not really enough to serve the function of identification. Retroflectors (or retroreflectors and, loosely, reflectors) seem the more viable choice. Both types must be available and be used when needed, of course. The average pedestrian may not have a good understanding of reflector use. However, education can quickly point out that the reflection is much brighter to a driver than to the wearer (see Owens et al., 1994); that it can be seen often thousands of feet away but is not necessarily obtrusive on clothing; that its use is necessary even for short walking trips; and that reflective materials are compact, easy to use, and inexpensive. Retroflective wrist stripes, perhaps 25 mm (1 in.) wide and about 30 cm (12 in.) long, with a short elastic section, tend to be the most practical. They are in constant motion during walking or running, and they quickly portray their bearer as a person in a particular motion. White shoes and hats. White hats or caps, especially coupled with white shoes, help drivers identify pedestrians, but their value is lost as the approach speed increases above approximately 40 km/h (25 mph). Also, hats are good locations for added retroflectors. Police and Citations The most likely factors cited in police reports of fault or criminal action are or could be: • The pedestrian: • Took no steps to make his or her presence visible • Took no steps to make his or her intentions predictable • Did not consider the driver’s opportunity to evade collision • Chose and pursued a path that intercepted the vehicle’s path • Moved in or into a collision path geometry • Did not use available devices or facilities • Failed to attempt reasonable evasive action • Proceeded while impaired • The driver: • Proceeded while impaired • Drove at a speed incompatible with conditions of visibility • Failed to pursue an effective visual search • Took no steps to make his or her intentions predictable • Failed to observe signals, controls, and markings • Failed to use turn signals • Failed to use headlights or proper beam • Failed to attempt reasonable evasive action
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Illustrative Cases The following are encapsulated, anonymous summaries of issues from cases in actual litigation. In most instances, the data are disguised for privacy or confidentiality agreements, but the essence is undistorted. The preceding text refers to these cases by “Case” with a letter. The outcomes, if noted, are not necessarily what the involved expert would have liked or that which the evidence seemed to support most strongly (objectively assessed). Some are merely to illustrate that certain issues did come up in the litigation process and may need to be addressed. Case A A male, 32, waited at a crosswalk at night until vehicles #1 and #2, in two SB (southbound) lanes, and vehicle #3, in a NB lane of a four-lane arterial, stopped or had almost stopped for him. Another NB vehicle (#4) approached as he started to cross EB. The pedestrian said he saw #4 come up behind the stopped vehicle #3 and suddenly change lanes and hit him. He felt the stopped traffic and their headlights made his presence and intentions clear. The driver said the #3 vehicle had cut him off and he never changed lanes and never saw the pedestrian. The pedestrian was moderately intoxicated and the defense said he was confused as to what was happening and was not able to cross safely. A plaintiff’s expert said the crosswalk was at an angle to the roadway that made the pedestrian perceive vehicle #4 was changing lanes although it was not, and driver #4 was distracted by #3 and failed to see the developing situation. The jury agreed that the pedestrian’s behavior was not due to intoxication and the driver was obligated to stop. The pedestrian received a moderate award for damages. Case B A male, 55, in light-tan clothing was crossing a wide roadway at night, coming from a bus stop toward his home. For a short section, the road was more than four lanes wide, but it was marked (with faded lines) into only two lanes and a right-turn lane because the area was in transition and a wider road would eventually be built extending in both directions. The road had a gentle right curve. The area had a series of low-pressure sodium (LPS) streetlights that have a strong yellow cast. A male driver, 58, in good condition with a good record and at moderate speed struck the pedestrian, killing him. He reported he saw him only as he hit the windshield. An expert felt the yellow light made it difficult to see light-colored clothing against the gray (light-yellow) asphalt surface. The pedestrian crossed at about a 45° angle, with a streetlight almost directly overhead. A plaintiff’s expert opined that the pedestrian saw the vehicle coming and judged it would continue near the center line path that it was on, so he timed his crossing (L to R) to clear that portion of the road in time. For no apparent reason, the driver moved right, crossing the edge line (which was still 6 m or 20 ft from the roadway edge) and essentially tracked the pedestrian as he crossed. The expert noted that the rightward motion of the vehicle kept the pedestrian lined up with the “A-pillar” (between the windshield and the driver’s side window). As the pedestrian moved across, the rightward road curve plus the driver’s rightward turning caused the car to rotate enough to keep the pedestrian obscured for a relatively long time. The parties agreed that the driver did not
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search sufficiently to detect the pedestrian and settled with the widow for a moderate sum. Case C A male, 36, was crossing four lanes of a two-way arterial in an area with mixed business and residential (apartment) buildings. The area had several streetlights and many lights from signs, businesses, traffic controls, windows, and vehicle headlights of moderate traffic. A male driver, 34, had his 4-year old son in a car seat next to him (RF seat). He admitted talking to the son and had been looking straight at him for 3 or 4 seconds when he struck the pedestrian, who survived but was permanently disabled. A defense expert claimed that “scientific” evaluation proved that not enough light was on the pedestrian to meet the minimum detectable contrast level required for detection. The plaintiff’s experts used state-of-the-art digital video (verified by several trained observers comparing the actual reenactment to the video version) to show that the pedestrian was clearly discernible as a darkly dressed person crossing in front of a densely packed series of light sources. The case was settled with a small support stipend for the injured man but no provisions for his family. Case D A male, 17, driving 48 km/h (30 mph) on a posted 56 km/h (35 mph) residential main road, midday, sunny, no traffic, saw a continuous white wall surrounding a large apartment complex. Seeing no one and no vehicles for about two blocks ahead, he reached over to adjust a tape player. Although the wall appeared to be continuous, at one point it was set back slightly to provide a walkway. A male child, 23 months old, dashed out through the opening, across the sidewalk, into the street. He was hit and suffered fatal injuries. Two minutes later the mother came to the scene. The driver was charged with vehicular manslaughter, but the jury agreed with the expert that, under the circumstances, the young driver was not inattentive in looking at the tape player and he was acquitted. Case E A female, 34, was driving at the speed limit of 48 km/h (30 mph) in a mostly residential area that she had driven twice in the previous year. Streetlights and various residential lights were on. It had just become dark and she had her headlights on low beam. Each intersection had two marked crosswalks and the blocks were 120 to 210 m (400 to 700 ft) long. After 10 minutes on this road, with two stop signs, the driver came to a park one block long on her right. It was dark with several large trees. A small building in the park had a single lighted sign visible part of the time between the trees. At the next intersection, a boy, age 5, had run playfully away from his grandfather and had crossed the street, his grandfather shouting at him to stop. Instead, the boy ran back across the street and was struck and killed. The driver first saw him about 10 ft ahead. A streetlight was on the far side of the road, but a tree shaded the boy on the curb. The plaintiff’s lawyers claimed that the driver did not heed the “pedestrian crossing ahead” signs and that driving the speed limit at night was too fast, even though the park
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was dark. The defendant’s expert said that the driver would have seen the single light in peripheral vision and that she needed to look at it to see if it might be a vehicle that would enter the roadway. The child’s dark clothing provided no contrast with the road surface. Because of the emotional aspects, the case was settled for an undisclosed, but large, amount. Case F A male, 27, turned right at a corner house in a residential area in the morning at 32 km/h (20 mph); he encountered a bright low sun for the first time, just as a male, 76, 5 ft 5 in., stepped out from behind a vehicle to cross the road midblock, as he did every morning. The prosecution said the driver should have removed the moisture on the inside of the windshield and that it prevented the driver from seeing the man; the driver was charged with vehicular manslaughter. A defense expert showed the area needed for detection at the minimum stopping distance was only a 5-in. circle near the center of the windshield, which was clear. The black-haired pedestrian was wearing a gold-colored sweater that blended in with the house immediately behind him, and he was obscured on approach by a dark vehicle only 2 in. shorter than the man. The driver was acquitted. 15.4 Checklist This checklist is an outline of the material presented in this chapter with the addition of “concerns” for most items that suggest questions to be asked for further elaboration. Many concerns are common among the items, but each item has its own point of view. Primary factor Considerations/concerns Pedestrian collisions (1) Parallel paths (2) Transverse (angled) paths Concerns: Obstructions Road geometry Road elevation
Primary factor Vision and visibility
Pedestrian
Considerations/concerns (1) Night visibility (2) Two aspects of the visual sense (3) Eye movements and visual search (4) Peripheral vision and information Concerns: Obstructions Road geometry Road elevation Buildings and vegetation Speed (1) Competency
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populations
(2) Vulnerability Concerns: Mental models, cognitive maps Training Ambiguity For driver and pedestrian Concerns: Familiarity, experience; road, area and traffic patterns Mental models, cognitive maps Training Situation, (1) Situational issues darkness and (2) Darkness, weather weather Concerns: Exposure Road and shoulder characteristics Opposing and crossing traffic Traffic density Other road users Relative location and speeds of vehicles Noise, distractions Night myopia Facility issues (1) Provisions for needs, informing parties (2) Lighting, warnings, boundaries, alternatives (3) Enforcement, driver and pedestrian Concerns: Crosswalk and other markings Location and design of traffic control devices and signals Preview Roadside signs Work zone treatments Lighting and (1) Area lighting, low-beam visibility headlights (2) Detection with high beams (3) Other light sources and effects (4) Special lighting problems Concerns: Roadside luminaries Other sources of illumination Sun angle, moon angle and brightness Reflections Luminance contrast, colors Glare
Primary
Considerations/concerns
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factor Driver behavior (1) Evasive maneuvers and knowledge (2) Choices and cognitive map (3) Driver lane changes (4) Memory and recall (5) Training and licensing Concerns: Competency, fatigue Visual search Distraction, in-vehicle activity High/low-beam selection Speed control Risk taking, alcohol, drugs Braking and evasion Perception-reaction time Vision and hearing Disability, age Circadian rhythms (1) The pedestrian advantage (2) Pedestrian expectancy (3) Clothing (4) Night and poor weather (5) Midblock crossing and Jwalking Concerns: Exposure Conspicuity Competency, fatigue Visual search Path control Risk taking, alcohol, drugs Evasion Speed estimation Perception-reaction time Clothing and marking Vision and hearing Night myopia Disability, age Vehicle design (1) Pedestrian-friendly front ends (2) Other vehicle structures (3) Tinted glass Concerns: Vehicle lamps (condition, light output) Maintenance Judgment, choices by pedestrian
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(1) Pedestrian responsibility and conduct (2) Visibility aids Concerns: Background Background lights Reflective material Marker lights Angles of view (1) The pedestrian (2) The driver Concerns: Witnesses Choices in citing Accuracy and completeness of reports
References Allen, M.J., 1970, Vision and Highway Safety . Philadelphia: Chilton Book Company, p. 207. (Also updated in Allen, M.J. et al., 2001, Tucson AZ: Lawyers & Judges Publishing Co.) Andre, J. and Owens, D.A., 2001, The twilight envelope: a user-centered approach to describing roadway illumination at night. Hum. Factors , 43, 4, 620–630. Blanco, M., Hankey, J.M., and Dingus, T.A., 2001, Evaluating new technologies to enhance night vision by looking at detection and recognition distances of nonmotorists and objects. Proc. Hum. Factors Ergonomics Soc. 45th Annu. Meeting . California, State of, 2000, The Vehicle Code . Dewer, R.E. and Olson, P.L., Eds., 2002, Human Factors in Automobile Accident Reconstruction . Tucson, AZ: Lawyers & Judges Publishing Co. Fricke, L.B., 1990, Traffic Accident Reconstruction , Vol. II. Northwestern University Traffic Institute, Evanston, IL. Fruin, J.J., 1971, Pedestrian Planning and Design . New York: Elevator World, Inc. Haber. R.N. and Haber, L., 2002. Why witnesses to accidents make mistakes: the cognitive psychology of human memory. In Dewar, R.E. and Olson, P.L., Eds., Human Factors in Automobile Accident Reconstruction . Tucson, AZ: Lawyers & Judges Publishing Co., pp. 663– 695. Hermes, B.F.Z., 1972, Pedestrian crosswalk study: accidents in painted and unpainted crosswalks. High-way Research Board, Highway Res. Rec. , 406, 1–13. Johansson, G., 1973, Visual perception of biological motion and a model for its analysis. Percept. Psychophys. , 14,201–211. Leibowitz, H.W., 1983, The two modes of visual processing: implications for spatial orientation. Proc. Peripheral Vision Horizontal Display Conf. , Edwards Air Force Base. Leibowitz, H.W. and Owens, D.A., 1977, Nighttime accidents and selective visual degradation. Science , 189, 646–648. Lewis, A.L., 1999, Visual performance as a function of spectral power distribution of light sources at luminances used for general outdoor lighting. J. Illum. Eng. Soc. , 28(1), 37–42. Loftus, E.F. and Ketcham, K., 1991, Witness for the Defense . New York: St. Martin’s Press. Loftus, E.F. and Ketcham, K., 1994, The Myth of Repressed Memory . New York: St. Martin’s Griffin.
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McMahon, P.J., Zegeer, C.V., Duncan, C., Knoblauch, R.L., and Khattak, A.J., 2002, An analysis of factors contributing to “walking along roadway” crashes: research study and guidelines for sidewalks and walkways. U.S. DOT, FHWA-RD-01–101 Report. Olsen, R.A., 1981, Human factors engineering and psychology in highway safety. In Transportation and Behavior , Vol. 5 of Human Behavior & Environment Advances in Theory and Research, I.Altman, J.F.Wohlwill, and P.B.Everett, Eds. New York: Plenum, chap. 5, 131– 167. Olsen, R.A., 1992, Human factors engineering and product design. Prod. Liability J. , 4(1), 23–41. Olson, P.L. and Farber, E., 2003, Forensic Aspects of Driver Perception and Response , 2nd ed. Tucson, AZ: Lawyers & Judges Publishing Co. Owens, D.A., 1984, The resting state of the eyes. Am. Sci. , 72(4), 378–385. Owens, D.A., Antonoff, R.J., and Francis, E.L., 1994, Biological motion and nighttime pedestrian visibility. Hum. Factors , 36(4), 718–732. Pinkney, H.F.L., Walker, A.C., and Ayad, A.A., 1976, Application of a photographic method to study the luminance distribution governing visibility in night driving. NEA Laboratory Technical Report 15350, National Research Council of Canada. Also presented at TRB, January 1975. Shinar, D., 1978, Psychology on the Road, the Human Factor in Traffic Safety . New York: John Wiley & Sons. Shinar, D., 1984, Actual versus estimated nighttime pedestrian visibility. Ergonomics , 27, 863– 871. Shinar, D., 1985, The effects of expectancy, clothing reflectance, and detection criterion on nighttime pedestrian visibility. Hum. Factors , 27(3), 327–333. Sivak, M., Flannagan, M., Kojima, S., and Traube, E.C., 1997, A market-weighted description of low-beam headlighting patterns in the U.S. Ann Arbor: The University of Michigan Transportation Research Institute UMTRI-97–37. U.S. DOT, 2000, Traffic safety facts 2000—pedestrians. DOT HS 809 331. Zegeer, C.V., Stewart, J.R., Huang, H.H., and Lagerwey, P.A., 2002, Safety effects of marked vs. unmarked crosswalks at uncontrolled locations: executive summary and recommended guidelines. U.S. DOT, FHWA-RD-01–75 Report.
16 Pedestrian Accidents in Traffic 1 Robert Dewar Western Ergonomics, Inc. 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
16.1 Introduction Because pedestrians and vehicles must share the same roadways, the result can be a conflict between the two. In such conflicts the pedestrian is typically the loser. Street crossing can be quite complex for some pedestrians in certain situations; for example, a task analysis for child pedestrians by van der Molen (1981) identified 26 subtasks. In the street-crossing task, the road is scanned, traffic is perceived, and judgments are made about the distance, speed, and movement of vehicles. This information is processed and stored and, on the basis of it, a decision is made about whether or where to cross the road. Various factors have an impact upon pedestrian behavior and safety: • Environment (road type, intersections, surfaces, lighting, regulations) • Traffic (volume, moving and stationary vehicles, communication) 1
This chapter and the chapter by Richard Olsen complement each other with different approaches. This discussion emphasizes the data and sources relevant to pedestrian and driver behavior, while the other is more related to the forensic investigation and presentation processes.
• Personal (physical, psychological, and personal characteristics; motivation; age; experience) • Social (presence of others, purpose of journey, play)
16.2 Pedestrian Accidents Pedestrian accidents have been classified in various ways. Snyder (1972) proposes the following types: • Dart-out, first half: a pedestrian, not at an intersection, appears suddenly from the roadside. • Dart-out, second half: a pedestrian, not at an intersection, appears suddenly from the roadside and covers half of the crossing before he is struck. • Intersection dash: similar to dart-outs, these occur in or near a crosswalk at an intersection.
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• Multiple threat: the pedestrian is struck by a vehicle after other vehicles have stopped for him and block the view of the driver of the striking vehicle. • Vehicle turn or merge with attention conflict: the driver is turning or merging with traffic and his attention is directed to the traffic to look for a gap to enter or turn when he hits a pedestrian who is crossing the roadway. • Bus stop related: pedestrian crosses in front of the bus, which is blocking the view of oncoming drivers. The most common of these is dart-out, first half. Since that classification scheme was first proposed, other types of “pedestrian” accidents, such as those involving people on in-line skates, skateboards, and nonmotorized scooters, have become common. Accidents involving pedestrians represent a significant proportion of traffic collisions (12 to 45%, depending on the country). Rates in North America are among the lowest (about 12% of road fatalities) and have been reduced in recent decades, possibly because of less pedestrian traffic and greater use of private motor vehicles than are found in most other areas of the world. For example, 4882 pedestrians were killed in the U.S. in 2001— a decrease of 51% per 100,000 population since 1975. However, care must be taken in interpreting statistics from different countries because the definition of a pedestrian fatality differs across nations. Death within 30, 7, 6, and even 3 days following a pedestrian collision has been classified as a traffic fatality. The number of pedestrians killed in traffic has dropped in recent decades; however, a problem still exists. For example, pedestrian deaths represent 13 to 17% of motor vehicle deaths in the U.S. over the past two decades and a higher proportion in many countries. Deaths are highest among pedestrians over the age of 65, with the highest rate for older men. Interstate highways are the site of more than 10% of pedestrian fatalities in the U.S. In a 3-year study of 394 police accident reports of fatal freeway crashes from three states, Johnson (1997) found that 80% occurred after dark and about 40% involved pedestrians crossing or entering the highway, usually taking the shortest route to their intended destinations. Another common scenario (18%) involved pedestrians working on or pushing their vehicles. 16.3 Turning Accidents A large number of pedestrian accidents involve vehicle-turning movements. In comparison with through maneuvers, the probability of a pedestrian accident during a left-turn maneuver is about four times as great, and the proportion of pedestrian collisions associated with left-turning vehicles is nearly double that for right-turning vehicles at intersections of two one-way streets. Among the contributing factors in left-turn accidents is poor visibility from within the vehicle. Pedestrians obscured by the vehicle’s A-pillar comprise a major factor in leftturning accidents. The extent of obstruction by the left A-pillar of the turning vehicle has been demonstrated by Abdulsattar and McCoy (1999a), who measured the visibility of the crosswalk as the vehicle was about to make a left turn. About one third of the time, a pedestrian in the crosswalk was blocked by the A-pillar during the left-turn maneuver. This obstruction was slightly greater when turning from a two-way street compared with
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a one-way street. No such blind zone area was created by the right A-pillar during right turns. Left-turning drivers experience much greater demands on their attention than do those turning right or traveling straight through because they must monitor traffic coming from two or three directions while preparing to negotiate the turn. Habib (1980) found that pedestrians and drivers failed to yield the right of way with about equal frequency during right-turning vehicle maneuvers. However, left-turning drivers failed to yield to the pedestrian 62% of the time and pedestrians did not yield 38% of the time. See Caird and Hancock (2002) for a detailed discussion of left-turn accidents. One of the conditions leading to a significant number of pedestrian accidents is the conflict created when vehicles turn right at an intersection on a red light. Turning drivers are supposed to stop and yield to pedestrians in this situation, but they often fail to do so. The right-turn-on-red (RTOR) rule was examined in a study by Preusser and colleagues (1984), who found a significant increase in pedestrian and bicyclist accidents after the introduction of the RTOR at signalized intersections. These increases for pedestrian accidents in four U.S. jurisdictions ranged from 43 to 107%. Drivers typically stop or slow for the red light, look left for a gap in the traffic, and fail to see pedestrians and cyclists coming from their right. On the other hand, pedestrians often fail to scan the traffic environment and, as a result, are hit by turning vehicles. A study of the interaction between pedestrians and turning vehicles by Lord (1996) revealed that left turns at T-inter sections involve about twice as many conflicts with pedestrians as left turns at cross intersections. Most conflicts at the former occurred closer to the beginning of the green phase, while the opposite was the case for cross intersections. It was also found that chances of a conflict are greater if a pedestrian starts crossing late at a cross intersection or early at a T-intersection. The cross intersections may be “safer” for pedestrians than T-intersections because drivers typically must wait for a gap in oncoming traffic, thus allowing pedestrians time to complete their crossing before the turn is made. Differences between left- and right-turn maneuvers might be explained in part by drivers’ eye movements and fixations. They must divide their attention at signalized intersections among the traffic light, oncoming vehicles (to look for a gap in traffic), and the crosswalk as they approach the intersection. Closer to the intersection, the angle between these increases, resulting in less time to look at the crosswalk for pedestrians. Lack of understanding of pedestrians’ right of way at intersections also plays a role in these accidents. A survey of nearly 800 drivers (Abdulsattar and McCoy, 1999b) found that drivers were less likely to be aware of the pedestrian’s right of way when turning left than when turning right. 16.4 Driver and Pedestrian Behavior It is tempting to assign fault to drivers who run into pedestrians because the driver is seldom hurt in such collisions and the pedestrian nearly always is. However, accident data show that both parties are about equally at fault. Errors made by adult pedestrians typically involve vehicles turning or merging, with attentional conflict and multiple threat. Child pedestrian accidents tend to involve failure to stop or to search for vehicles
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before entering the road. The various types of pedestrian actions are reflected in the accident classifications outlined earlier. In more than 2000 accidents examined by Zegeer (1983), pedestrians were engaged in hazardous actions in 49.2% and drivers in 41.5%. A study by Hunter and associates (1995) found that the pedestrian ran into the road 15% of the time and failed to yield 12% of the time, while the driver failed to yield on 15% of occasions. The driver’s vision was blocked in about 10% of cases. Older pedestrians were more likely than others to be hit in parking lots. Pedestrians over 64 were overinvolved in backing accidents. Pedestrians under 10 were more likely than others to run into or be playing in the street, teenagers were more likely to disobey a signal or walk in the wrong direction, and those over 65 were more likely to jaywalk or fail to yield to a vehicle. The pedestrian alone was culpable in 43.2% of the accidents and the driver alone in 34.8%. Backing vehicles were involved in nearly 7% of the fatal accidents. About one third of the accidents were intersection related and 10% involved turning vehicles, while midblock accidents
TABLE 16.1 Pedestrian Walking and Running Speedsa at Various Ages Age 17–24 months 2 yrs: Walking Running 3 yrs: Walking Running 4 yrs: Walking Running 6 yrs: Walking Running 8 yrs: Walking Running 10 yrs: Walking Running 14 yrs: Walking Running 18 yrs: Walking Running 20 yrs: Walking
15th percentile 50th percentile 85th percentile 2.24
3.34
4.10
2.5 5.2
2.8 5.6
3.4 7.1
2.6 5.5
3.5 8.9
4.3 10.1
3.2 8.0
4.1 10.4
5.1 12.2
4.2 11.1
4.8 12.5
6.2 14.9
4.3 10.7
5.1 13.7
6.4 16.4
4.6 12.8
5.4 14.8
6.3 17.6
— —
5.2 13.7
— —
5.2 14.7
4.7
5.5
Comments Small sample
— —Not reported — —Not reported — — 6.5
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Jogging 9.2 11.6 13.9 40 yrs: Walking 4.3 5.2 6.1 Jogging 7.9 9.5 11.3 60+ yrs: Walking 3.8 4.1 4.6 Jogging 6.7 8.1 8.9 a Feet per second. Source: Eubanks, J.J. and Hill, P.L., 1998, Pedestrian Accident Reconstruction and Litigation (2nd ed.). (Tucson, AZ: Lawyers & Judges Publishing Co.).
constituted about 25% of all fatalities in this study. Road crashes involving a disabled vehicle or someone walking along the road were very frequent (44% each) in rural areas. 16.5 Walking Speed An important consideration in pedestrian safety and intersection design is the walking speed of pedes¬ trians. Eubanks and Hill (1998) studied the walking and running speeds of pedestrians of varying age. Their book, Pedestrian Accident Reconstruction and Litigation, provides a great deal of information about walking and running speeds for pedestrians of all ages; see Table 16.1 for a sample of their findings. Average walking speeds increase gradually until about the age of 10 and then remain fairly steady until age 60+. However, many pedestrians, by definition, will be somewhat slower than this average speed. Running speeds rise rapidly with age from about 2.8 to 5.4 m/s among children aged 2 to 10. Speeds are slightly faster for males. This information is useful in accident investigation—for example, to estimate how long a child running across the street was exposed to traffic or whether a driver might have had the opportunity to stop prior to a dart-out collision. Eubanks and Hill also report the 15thand 85th-
TABLE 16.2 50th Percentile In-Line Skating Speedsa for Skaters of Various Ages Age
Males
Females
<20 17.1 16.2 20–39 11.9 11.5 40–59 12.5 11.3 a Feet per second; 1 ft/s=0.305 m/s. Source: Eubanks, J.J. and Hill, P.L., 1998, Pedestrian Accident Reconstruction and Litigation (2nd ed.). (Tucson, AZ: Lawyers & Judges Publishing Co.).
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TABLE 16.3 Average Walking Speeda as Function of Various Adult Pedestrian Conditions Condition
Speed
Holding child by the hand 2.41 Pushing stroller 4.31 Carrying baby 3.47 Pushing bicycle 5.58 Walking with BAC 0.10–0.18 4.32 a Feet per second; 1 ft/s=0.305 m/s. Source: Eubanks, J.J. and Hill, P.L., 1998, Pedestrian Accident Reconstruction and Litigation (2nd ed.) (Tucson, AZ: Lawyers & Judges Publishing Co.).
percentile walking and running speeds of children. The large range of speeds makes it difficult to establish a “typical” speed for pedestrians. Eubanks and Hill (1998) also provide data on speeds of joggers, in-line skaters (see Table 16.2), and those holding the hand of a child, carrying a baby, etc. (see Table 16.3). They provide considerable detail in a total of 28 tables related to speed of pedestrian movement. As expected, walking speed is faster the closer (in time) a vehicle is to the pedestrian (see Table 16.4). The various studies on walking speed show a large range of speeds that depend on a variety of factors. The duration of pedestrian walk signals at intersections is generally based on the assumption that the walking speed of pedestrians is 1.2 m/s. However, as indicated, many pedestrians walk more slowly than this. The mean speed is considered to be about 1.13 m/s and 35% of pedestrians walk more slowly than the 1.2 m/s design standard (Hauer, 1988). Bowman and Vecellio (1994) report average pedestrian walking speeds of close to 1.0 m/s. A study in Sweden (Dahlstedt, undated) found that pedestrians aged 70 or older considered “fast” to be less than this design standard. The 85th percentile for a comfortable speed was 0.67 m/s. Some jurisdictions recommend a lower-design walking speed where large numbers of
TABLE 16.4 Walking Speeda as Function of Vehicle Approach Time to Impact Vehicle time to impact
Speed
>8 sec 4.0 >6 sec 4.1 >4 sec 4.7 >2 sec 6.5 a Feet per second (1 ft/s=0.305 m/s). Source: Eubanks, J.J. and Hill, P.L., 1998, Pedestrian Accident Reconstruction and Litigation (2nd ed.). (Tucson, AZ: Lawyers & Judges Publishing Co.).
slower pedestrians use the crosswalk; however, it seems reasonable to assume that any crosswalk will occasionally be used by slow walkers.
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Walking speeds and start-up times of 7123 pedestrians, more than half of whom were over the age of 65, were observed by Knoblauch et al. (1996) at a variety of urban intersections under a number of conditions. Older pedestrians were significantly slower than those under 65 and walked more slowly when it was snowing or when the street was covered by snow than under other weather conditions. The mean and 15th-percentile walking speeds were 1.46 and 1.21 m/s, respectively, for young (under 65) pedestrians, and 1.20 and 0.94 m/s, respectively, for older pedestrians. Mean start-up time, from the start of the WALK signal to the moment at which the pedestrian stepped off the curb and started to cross, was longer for older pedestrians (2.48 s) than for younger ones (1.93 s). 16.6 Perception-Response Time One of the human factors often cited by those investigating traffic accidents is perception-response time (PRT), that is, how quickly a driver or pedestrian can respond to an emergency situation and how much distance was between the driver and the pedestrian when the latter was first seen. This plays a role in many traffic accident litigation cases. The components of PRT are search, detection, recognition, decision, and action. PRT slows with fatigue, alcohol, distraction, darkness, and age (older drivers are slower by 15 to 25%). Unexpected situations can slow PRT by 30% or more (Olson and Farber, 2003). Responses are also slower in a more complex driving situation. A reasonable PRT for an alert driver in most situations would be of the order of 1.5 s, but it can be somewhat longer than this, depending on the situation (e.g., darkness) and the age and condition of the person involved in the accident (Olson and Farber, 2003). Although PRT among pedestrians has not been well documented, it seems reasonable to suggest that they would be quicker to respond in an emergency than would drivers because the latter are preoccupied with the driving task, which typically requires greater attention than does crossing the street. Each accident must be examined on its own merits, taking into account the various factors that might have influenced PRT. 16.7 Alcohol Use Driving under the influence of alcohol is a contributing factor in a high proportion of traffic accidents. The “impaired driver” has received a great deal of attention over the years; however, less well known is the influence of alcohol impairment on pedestrians involved in crashes. It is much higher than most people realize. For example, of the pedestrians killed in the U.S. in 1998, 31% were intoxicated, as defined by the maximum blood alcohol content (BAC) allowed for drivers, while the intoxication rate for drivers involved was 12% (BAC 0.10 or higher). Alcohol involvement was greater in accidents in which the pedestrian was walking along the road and was struck from behind. Alcohol influences perception and behavior in a number of ways. It not only slows responses of drivers and pedestrians but also impairs vision (e.g., reduced visual scanning of the environment, reduced night vision), slows decision making, and impairs judgment. In particular, impaired road users have difficulty dividing attention and in making
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decisions, have problems in complex driving situations, and are more easily distracted (Moskowitz, 2002). Thus, drivers and pedestrians who are impaired may not notice each other. They also have difficulty recognizing their degree of impairment when under the influence of alcohol. With these limitations it is easy to see how drivers and pedestrians can make errors that lead to collisions. The effects of alcohol are to reduce the likelihood of detection except when a vehicle is traveling slowly (32 km/h) or the pedestrian is wearing reflectorized marking. Pedestrians with black or gray clothing can almost never be detected within the critical stopping distance by drivers traveling at 97 km/ h or greater (Olson and Farber, 2003). It should be noted that in some jurisdictions it is illegal for a drunk pedestrian to be on a roadway. Therefore, an accident is often the responsibility of the impaired pedestrian, rather than (or in addition to) the driver. However, drivers are also expected to exercise precaution when observing an obviously intoxicated person. This assumes that drivers are capable of making a judgment about degree or impairment of pedestrians. 16.8 Child Pedestrians The behavior of child pedestrians is different from that of adults. Children’s conception of safety is poorly formulated, and their mental representation of relevant behaviors, such as crossing the street, is not well developed. Road accident rate is a function of the age of young pedestrians. It is greatest for those in the 3- to 8-year range. Children aged 5 to 7 are most over-represented, even though they are less exposed to traffic than older children. Boys have more accidents than girls, in part because they also spend more time on the streets. As indicated earlier, street crossing involves observation, perception, judgment, and decision. The road is scanned, traffic is perceived, and judgments are made about the distance and movement of vehicles. On the basis of this information, a decision is made about whether to cross the road, and where to cross. Young children have difficulties with one or more of these subtasks. Children’s perception of driver behavior and cause and effect is not well developed (Sandels, 1968). Drivers are much less likely than young pedestrians to take evasive action in a potential conflict situation. In an observational study, it was found that almost all child pedestrians took action if the vehicle was closer than 20 m, and the majority did so even when the vehicle was 40 m away (Howarth, 1985). Drivers took action when a pedestrian stepped onto the road only if the vehicle was closer than 20 m. The reasons for the relatively high accident rate among young pedestrians are many. Sandels (1968) has examined the behaviors and cognitions of children and suggests that the necessary degree of maturity for safe behavior is reached between the ages of 9 and 12. Several factors contribute to child pedestrian accidents: • They have difficulty distributing their attention and are easily preoccupied or distracted in hazardous traffic situations. • They have difficulty in correctly perceiving the direction of sound and the speed of vehicles.
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• Many believe the safest way to cross the street is to run and that it is safe to cross against the red light. • They have a poor understanding of the use of traffic control devices and crosswalks. Perception of oncoming traffic requires a field of view that may not be available to a small child, who cannot see over parked cars. Young children have limited ability to process information in peripheral vision (i.e., to see “out of the corner of the eye”) and thus need more time to react once objects in the periphery are seen. Planned search is often poor because young children have problems dividing their attention and are attracted by the most salient objects in their environment (e.g., an animal, another child). Systematic search begins about the age of 6. Children under age 6 have difficulty localizing sound, so they may hear a car coming but not know where to look for it. Finding relevant information in a complex environment is difficult for most children, partly due to limitations in speed of eye movements, attention, and memory, rather than visual acuity. A crucial judgment in traffic is whether a vehicle is moving, how fast, and at what distance. Children are generally unreliable in judgments of distance of cars. They often make the error of assuming a greater distance for smaller vehicles; thus, when they encounter small cars, smaller gaps are accepted in crossing the street. Size constancy— the ability to judge accurately the size of objects independent of their distance from the observer—develops with age, as the child learns to interpret different environmental cues to distance. Young children have poor size constancy, so they could easily overestimate the distance of vehicles. A factor in avoiding danger on the road is the speed with which a pedestrian can recognize and react to the situation. Visual reaction time decreases with age in children, by a factor of about three between the ages of 4 and 17 (Reiss, 1977). Auditory reaction times are also slower for younger children and their attention span is shorter than in adults. They have difficulty attending to more than one thing at a time. For this reason, they often run onto the road into the path of moving vehicles in pursuit of objects such as balls. A large proportion of child pedestrian accidents are the result of unsafe or illegal actions on the part of the child. The ability of children between the ages of 5 and 14 to judge the velocity of oncoming cars (as slow, medium, or fast) was studied by Salvatore (1974). Vehicles that could be heard by the subjects were more likely to be classified as fast; inaudible vehicles were judged to be slow. Judgment of vehicle speed was slightly more accurate at near (76 m) than at far (153 m) distances. Many young children are unable to make appropriate use of the information in the traffic environment to judge safe gaps in traffic. In a study of vehicle gap perception in New Zealand, Connelly and colleagues (1998) had children in three age groups (5 and 6; 8 and 9; and 11 and 12) indicate when it was safe to cross a road as vehicles approached an intersection from the right (equivalent to left in Europe and North America). The threshold for distance gaps ranged from 10 to 146 m. Vehicle speeds appeared to be ignored in these estimates because the children set similar distance thresholds at all vehicle speeds. The 8- and 9-year-olds selected the least safe gaps, and most children were safest at the lowest vehicle speeds. The mean times of arrival dropped from 2.34 s with vehicles going up to 50 km/h to 0.47 s for those speeds over 65 km/h. About three fourths of the judgments made were considered safe. When
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asked what information they used in making judgments, 63% indicated distance, 19% indicated speed, and the remainder said both or were unable to express a decision. Zeedyk and associates (2002) observed the actions of children aged 5 and 6 years in a realistic road-crossing situation. Performance by the children was “extremely poor,” with 60% failing to stop before entering the road and fewer than 42% looking for oncoming traffic. When children did look initially, it was often in an inappropriate direction. When crossing between parked cars, only 29% looked before reaching the curb. 16.9 Elderly Pedestrians Pedestrians over the age of 70 are more likely to be involved in a severe accident than are younger ones. This is due in part to greater vulnerability of older people because of physical fragility, more easily broken bones, longer recovery times, etc. An examination of age differences indicated that pedestrians over 64 accounted for 45% of the fatalities but only 15% of the western European population (Choueiri et al., 1993). In the U.S., the older group constituted 22.4% of the pedestrian fatalities and 12.3% of the total population. Problems leading to accidents among older pedestrians include (McKnight, 1988): • Gap judgment—misjudging vehicle speeds and the distances of and intervals between approaching vehicles • Attention—stepping off the sidewalk when distracted • Visual search—watching the traffic signal instead of the traffic • Expectation—misinterpreting vehicle movement • Assuming that drivers will yield • Haste—impatiently crossing after waiting • Crossing midblock between parked cars • Slow walking speed Older pedestrians often have difficulty in assessing the speed of approaching vehicles, thus misjudging when it is safe to cross the road. Even though the vast majority of their accidents occur during the daytime, they frequently report failure to see, or to see in time to take evasive action, the vehicle that struck them. Sheppard and Pattinson (1988) found that about two thirds of the older pedestrians they surveyed saw the vehicle that struck them only when it was within 9 m of them. In addition, many
TABLE 16.5 Mean Walking Speedsa for Disabled Pedestrians and Users of Various Assistive Devices Disability/assistive device Cane/crutch Walker Wheelchair Immobilized knee Below-knee amputee Above-knee amputee
Speed 2.62 2.07 3.55 3.50 2.46 1.97
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Hip arthritis 2.24 to 3.66 Rheumatoid arthritis (knee) 2.46 a Feet per second; 1 ft/s=0.305 m/s. Source: Perry, J., 1992, Gait Analysis (New York: McGraw Hill).
indicated that the vehicle that struck them was doing something unusual before the collision. Frequent reports related to this were: vehicle reversed into me (30%), expected driver to stop or alter course (20%), thought it was not moving (11%), and vehicle came from behind a corner, parked car, etc. (10%). It is possible that reduction in peripheral visual information processing was a contributing factor. Concerning their ability to judge speeds of approaching cars, about 30% said that they could do this “not well at all.” 16.10 Handicapped Pedestrians We tend to think of a handicapped individual as a person in a wheelchair; however, a variety of other handicaps are relevant to understanding pedestrian behavior. Vision and hearing deficits can pose difficulties in traffic. The “handicapped” pedestrian includes those with physical problems, such as restricted mobility or perception, as well as those whose mobility is temporarily reduced because they are encumbered by carrying luggage, packages, children, etc. Handicaps are not only physical in nature, but also mental. Pedestrians with low intelligence, illiteracy, dyslexia, attention deficit, and other such problems often have difficulties understanding traffic control devices. Perry (1992) reported lower speeds for physically impaired pedestrians, as would be expected (see Table 16.5). None of these reaches the average walking speed assumed for design of pedestrian walk-signal timing. 16.11 Nighttime Conditions When light reaches a surface, some of it is absorbed, and some is reflected. Reflectivity refers to the extent to which an object or environment reflects the light falling on it. Nothing in the natural world reflects all the light that it receives. The more distant an object is from a light source, the less light will fall on it. In order to understand pedestrian visibility, especially at night, the concepts of contrast and reflectivity need to be appreciated. Contrast is the difference in brightness between a target and the background against which it is viewed. Positive contrast occurs when an object is brighter than its background, and negative contrast is the opposite. Print on a white page is an example of the latter. There must be a certain contrast ratio before an object is visible. The greater the contrast is, the more likely the object is to be detected. Dark-clad pedestrians at night are more difficult to detect, except when seen against a bright surround. White clothing is highly reflective, but still only about 60 to 70% so. The reflectivity of the roadway background ranges from 2 to 10%, and that of blue denim is about 3% (Olson and Sivak, 1984). Research on the reflectivity of pedestrian clothing suggests that about 60% of it has a reflectivity value of 10% or less (Olson, 2002b). The reflectivity of pavement is typically about 6%; that of wet pavement is about half that of dry pavement,
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especially at distances of less than 121 m. The combination of wet pavement and glare makes it very difficult to see pedestrians at night. Olson and Farber (2003) studied the typical contrast of different parts of an adult pedestrian with clothing of 6% reflectance seen with vehicle low-beam headlights at night and determined that the contrast is greatest at the waist and knees, less at the head, and least at the feet. Even though the feet would be receiving the greatest amount of illumination from low beams, the contrast with the pavement would be relatively less than the contrast of other parts of the body seen against darker pavement (darker because it is further away and receiving less light from the headlights). The upper body would be better illuminated by high beams and would be seen against the darker background of the distant pavement. If the pedestrian were wearing a light-colored top, contrast would be that much better. However, whether the pedestrian would be seen in time to stop depends on the pedestrian’s position and the vehicle’s speed. A bright roadway (e.g., illuminated by a street light, as might be the case in an urban area) behind a dark-clad pedestrian will make him more visible, but the same pedestrian could be nearly invisible in a dark environment until vehicle headlights shine on him at close range (Janoff, 2002). Factors influencing nighttime visibility are: target distance, size, contrast with background, time spent looking for the target, glare, and driver age. The evidence on roadway lighting indicates that accidents reduce when street lights are installed (Janoff, 2002). Glare from headlights of oncoming vehicles obviously makes it more difficult to see pedestrians on the street or the highway. With headlights on low beam, pedestrians will not be visible as far away as with high beam. However, with high beam, less light is cast on the bottom part of a nearby pedestrian and those wearing light pants and dark top may be less visible than expected under high beam. Rain at night reduces pedestrian visibility further. Wet pavement at night greatly increases the amount of glare in oncoming drivers’ eyes from reflections of headlights and street lights off the pavement. The detrimental effects of oncoming headlight glare are described by Olson and Farber (2003). A driver’s visibility distance to detect a 12% reflective target on the right side of the road is unaffected until the headlights are about 300 m away. As the vehicle comes closer, this distance reduces from approximately 90 to 64 m just before the vehicle is passed. With a target on the left, visibility distance begins to reduce at a distance of about 600 m and decreases fairly quickly from 50 to less than 30 m as the distance between the vehicles decreases from 300 to 30 m. It is evident that glare from headlights can make a pedestrian on the road essentially invisible in a collision until the last second or two before impact. Olson (2002b) measured pedestrian visibility under different nighttime viewing conditions. Details of his findings are seen in Table 16.6. It can be seen that the probability of detecting a pedestrian in time at night is much less when the pedestrian is on the driver’s left than when on the right, and less when wearing a dark top. When the pedestrian was unexpected (i.e., drivers were not alerted to the possibility of a pedestrian), probability of hitting the pedestrian increased dramatically under most conditions. It should be noted that the data reported here are for young drivers in a situation in which they expected a pedestrian. Older drivers and those in a typical driving situation would detect the pedestrians at a somewhat closer distance, and all drivers must be closer when the pedestrian is unexpected, as on the highway, for example.
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TABLE 16.6 Percentage of Trials in Which Drivers Would NOT Have Been Able to Stop in Time to Avoid Hitting Pedestrian as Function of Clothing/ Position on Road Speed (km/h)
Dark/ right
Dark/left
White top/right
40 56 73 89 105
White top/left
<1 5 <1 12 70 <1 45 96 3 81 100 15 95 100 40 As above for an unexpected pedestrian 40 25 40 15 56 57 >90 30 73 85 >90 45 89 >90 >90 65 105 >90 >90 90 Source: Olson, P.L. and Farber, E., 2003, Forensic Aspects of Driver Perception and Response (2nd ed.). (Tucson, AZ: Lawyers & Judges Publishing Co.).
<1 4 10 30 65 15 30 50 70 >90
Visual acuity at night is reduced, for example, for those with average vision, from 20/20 in daylight to 20/25 or 20/30 at night; it is typically 20/40 or worse for 70-yearolds. Another factor is that most drivers overdrive their headlights at night. Fog and smoke also reduce night visibility because they reduce contrast of the roadway scene. Glare of another sort (from the sky) can reduce visibility at dusk and dawn because the bright sky viewed just after sunset or before sunrise causes light adaptation, making the eyes less sensitive to objects on the road ahead. Similarly, sun glare just before sunset or after sunrise when an individual is driving toward the sun is a major cause of reduced visibility. It can be seen that pedestrian visibility at night is greatly reduced for several reasons, including dark clothing, headlight condition (beam used, aim), glare, reduced visual information for the driver, and pedestrian and/or driver impairment from alcohol. When a nighttime pedestrian accident is investigated, it is essential to consider all of these factors, as well as driver and pedestrian age. 16.12 Weather Conditions The presence of ice patches, snow, and slush on roads and sidewalks often leads to walking difficulties for pedestrians. The most obvious problems are poor footing, increased chance of slipping, and slower walking speeds. These conditions not only make walking difficult and dangerous, but also distract pedestrians’ attention from vehicles on the roadway. The presence of snow makes it difficult to detect curbs, potholes, and debris
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on the road, thus increasing the chances of a fall. One of the main fears among the elderly is falling, which is clearly justified when walking outside in winter conditions. Additional problems encountered by older people include greater susceptibility to glare from snow and ice, poor contrast due to glare and light conditions, and more hours of darkness. Blowing snow can also distract pedestrians’ attention from traffic or make it difficult to detect vehicles or judge vehicle speed. The observational study by Knoblauch et al. (1996) found that walking speed reduced when snow was present, thus increasing the length of time that the pedestrian is exposed to traffic when crossing the road. 16.13 Roadway Design Roadway design features such as road width, number of lanes, intersection complexity, and refuge islands have an impact upon pedestrian behavior and safety. A search of the literature on pedestrian safety (Zegeer, 1983) revealed several treatments to increase safety. Use of one-way streets will lessen the complexity of crossing for pedestrians because they need to look in only one direction for traffic. Also, drivers can devote more attention to pedestrian traffic because vehicle traffic is moving in only one direction. Left turns are easier here for drivers and safer for pedestrians. A study of 1297 intersections in 15 U.S. cities indicated fewer pedestrian accidents at intersections of one-way streets than at those involving two-way streets. Stemley (1998) indicates the advantages of one-way streets to be: • They are safer as a result of fewer conflict points at intersections (fewer turning movements). • More gaps are available for pedestrians because they need only look in one direction for gaps. • Pedestrians cannot be caught between opposing lines of traffic when crossing. • Drivers and pedestrians are more likely to see each other. • Pedestrians are less likely to become frustrated waiting to cross and to engage in dangerous behavior. • Drivers making turns can monitor pedestrian movements more easily because they do not need to watch for a gap in oncoming traffic. Oxley et al. (1997) found that older pedestrians experience difficulties when crossing two-way streets, as compared with one-way streets, because they tend to cross with closemoving traffic in the near-side lane and with oncoming traffic in the far-side lane. They do not compensate appropriately for their slower walking speeds. Greatest difficulties on two-way streets were experienced by pedestrians 70 years of age and over. These pedestrians waited at the curb longer, delayed their departures longer, and looked at the ground more while crossing than did others. They often crossed with smaller safety margins than did others. A collection of road modification techniques referred to as “traffic calming” has come into use in recent decades, especially in Europe, to slow traffic and increase pedestrian safety. For a detailed review, see O’Brien and Brindle (1999).
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16.14 Pedestrian Traffic Control Devices Pedestrian laws and traffic control devices are poorly understood, according to a large survey conducted by Tidwell and Doyle (1995). For example, 83% of drivers did not know the difference between an ADVANCE PEDESTRIAN CROSSING sign and a PEDESTRIAN CROSSING symbol sign (which includes the crosswalk lines). This study also found that pedestrians are ignorant about many of the basic rules of the road. About half thought that jogging on the road is legal and 80% thought that wearing white clothing at night provided adequate visibility to drivers. According to a questionnaire survey of more than 4700 people by Tidwell and Doyle (1995), just under half indicated that the flashing DON’T WALK signal means to return to the curb, and a similar proportion thought that a WALK signal meant there were no turning conflicts. They also found that about half of the people in a large survey felt that the WALK signal guarantees their safety. Pedestrians often become impatient and start across the street before the WALK signal activates or start across after the DON’T WALK signal has come on. The proportion of pedestrians violating signals has been reported by Virkler (1998) to be about 16% for those entering the crosswalk late and 10% for those starting early. It may be assumed that the use of pavement markings for uncontrolled crosswalks would lead to greater pedestrian safety. However, a large U.S. study (Herms, 1972), based on 5 years of data at 400 intersections (each with one painted and one unpainted crosswalk), found that pedestrian accident rates were about double at marked, as opposed to unmarked, crosswalks. A more recent study of marked and unmarked crosswalks gathered data at 1000 marked and 1000 unmarked pedestrian crosswalks in 30 U.S. cities (Zegeer et al., 2001). Information collected included pedestrian volume, traffic volume, accident history, speed limit, number of lanes, and pavement marking patterns. Crossings with traffic calming measures and school crossings were not included, nor were those with traffic signals or stop signs. Crash rate was lower with raised medians or raised crossing islands with both types of crosswalks, but painted medians did not benefit pedestrians. The factors having no effect on pedestrian crash rate were area (residential, central business district, midblock), traffic operations (one- vs. two-way traffic) and pavement marking pattern. On two-way roads, no differences were found between marked and unmarked crossings. Similarly, on multilane roads with an ADT of 12,000 or less, the presence of markings made no difference in crash rate. However, higher crash rates were found at marked crossings on multilane roads with no raised medians and an ADT of more than 12,000. Even with raised medians, locations with more than 15,000 vehicles per day had higher crash rates with marked crosswalks. Use of marked crosswalks may induce more pedestrians to cross there instead of at a signalized crossing. Marked crossings at multilane sites are especially prone to multiple-threat type collisions—when one driver stops for the pedestrian and another driver approaching in the same direction does not stop and hits the pedestrian. In these cases, usually pedestrian and driver fail to see each other in time. In the Zegeer et al. study, this type of crash constituted 17.6% of all pedestrian collisions in marked crosswalks, but none of these crashes occurred in unmarked crosswalks. The former may lead to a false sense of security and reduced vigilance by pedestrians. Drivers failed to yield to pedestrians in a
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high proportion of accidents (41.5% of the time at marked and 31.7% at unmarked crosswalks). Dart-out collisions were much more likely at unmarked crossings. Pedestrians failed to yield 5.8% of the time in marked crossings and 34.2% in unmarked crossings. Pedestrians over 65 were over-represented in nearly all situations. Whether drivers slow at crosswalks may depend on the action of pedestrians. Knoblauch and Raymond (2000) examined this issue by staging pedestrian activity at six uncontrolled crosswalks before and after the installation of markings. Approaching vehicles slowed slightly when a pedestrian was not present and when the pedestrian was not looking at the driver, but not when the pedestrian did look at the driver. The interpretation was that the driver assumed the pedestrian was not paying attention when not looking and thus thought greater care was needed. However, none of the vehicles actually stopped in the presence of the pedestrian. 16.15 Work Zones Pedestrian movement in work zones can lead to safety problems. In 2000 in the U.S., 1026 fatalities occurred in work zones, including maintenance and utilities areas. Pedestrians frequently need to be guided through the work zone, must walk over rough surfaces, and be alert to the movement of workers and machines. Ideally, pedestrian traffic should be physically separated from the work area. Vertical curbs, barriers, or chain-link fences can be used to accomplish this. Construction and maintenance workers are particularly vulnerable to roadway traffic, especially in high-speed areas. Although those concerned with traffic movement attempt to maintain roadway speeds close to the speed limit, it is often necessary to slow traffic down; however, many drivers fail to slow or to slow in time to avoid a collision. Each year many workers are injured or killed by roadway traffic. For example, about 30 workers are killed each year in the U.S. by vehicles. Safety benefits can be derived from the use of highly visible clothing. Major work zones require a detailed plan with traffic safety as a high priority. This includes safety to workers and pedestrians as well as motorists. 16.16 In-Line Skates, Skateboards, and Scooters The number of certain nonstandard “pedestrians” has increased greatly over the past decade. Use of inline skates, skateboards, and nonmotorized scooters has become a very popular recreational activity. A large proportion of in-line skating accidents are due partly to inexperience. How in-line skating should be accommodated by the transportation system, including infrastructure design and regulatory and operational principles, is not entirely clear. Skaters, skateboarders, and scooter users appear to be somewhere between pedestrians and bicyclists. They may be considered “assisted pedestrians.” One issue is whether they should be allowed to operate on the road, sidewalk, specific facilities such as bicycle paths, or some combination of these. The number of injuries associated with the use of in-line skates and skateboards has increased substantially. Because the manipulation and control of skates and skateboards
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is different from that of bicycles and may require considerable practice for some users, especially young children, a number of hazards are associated with their use. The Centers for Disease Control estimates annual in-line skating injuries in the U.S., based on emergency room visits, to be more than 100,000. It is estimated that there are about 29 million skaters in the U.S., thus yielding an injury rate per skater of 0.356%, up from 0.266% in 1993. The most common injuries are to the wrist (24.2%). Primary causes are falls due to spontaneous loss of control (41%) and hitting a stationary object (40%). Key causes of injury are skating out of control (67%), hazardous road condition (53%), and fatigue (37%). Only a small proportion of those receiving such an injury wore a wrist guard at the time of the fall. The likelihood of sustaining a wrist injury when not wearing a wrist guard was determined to be 10.4 times greater than when wearing one. Similar numbers for other parts of the body, with and without relevant gear, are: elbows, 9.5 times, and knees, 2.2 times (Schieber et al., 1996). Experienced skaters commonly reach speeds of up to 27 km/h. A study by Mulder and Hutten (2002) examined in-line skating injuries (excluding traffic injuries) in several European countries and reported that about 65,000 people were treated in emergency departments in 1996. The most common accident mechanism was falling (53 to 96%, depending on the country). The most common injuries by far were to the wrist. The hazards associated with in-line skating include difficulty controlling movement and stopping; the need for considerable minimal lateral operating space, which can endanger others such as pedestrians; and excessive speed. Also, surface conditions (e.g., steep grades, pebbles, speed, potholes, sidewalk grates, bumps, railroad tracks) can impede safe operation. Downgrades play a role in safe skating, with beginners able to handle grades up to 3%; intermediates, up to 5%; and experienced skaters, up to 10%. The maximum distance of a downgrade is recommended to be 100 m. As estimated by the U.S. Consumer Product Safety Commission, in the U.S. in 2000, 50,000 emergency room visits required treatment of skateboarders, an increase from 24,000 in 1994; in 2001, 84,000 scooter riders required treatment. The vast majority of skateboarding injuries occur to those under the age of 15; about 30% of scooter injuries happen to those under 8. The most common injuries are to the head and face. It is recommended that those under 8 use scooters only under direct adult supervision and that scooters not be ridden in streets, at night, and or on surfaces with water, sand, gravel, or dirt present. Although scooter deaths are rare, the majority (about 80%) involve a motor vehicle and the rest involve falls from the scooter. Young children have difficulty in judging their own skill and strength as well as pedestrian and vehicle traffic activity. In addition, the relatively high center of gravity of young children makes balance and control more difficult. Those using skateboards, in-line skates, and scooters are strongly advised to use protective equipment, including helmets, to avoid traveling on rough or wet surfaces, and not to ride at night. 16.17 Conclusion This brief review of accidents among pedestrians shows that these road users are very vulnerable to injury and death. Older pedestrians are more vulnerable than younger ones,
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due to their slower response and decision times, slower walking speeds, and increased physical frailty. Child pedestrians are also highly vulnerable in the traffic environment, due in part to their risky behavior and their difficulty in dealing safely with vehicle traffic. A recent safety problem has arisen with the increasing use of skateboards and inline skates. Many who use them are young and inexperienced and more likely than adult road users to take risks in traffic. Although it is tempting for the accident investigator to think, “Oh, the poor pedestrian,” when considering pedestrian accidents, it should be kept in mind that pedestrians and drivers are about equally at fault in such collisions. The former often fail to attend properly to the movement of vehicles (assuming that they have the right of way when they do not or that drivers will notice them and stop if necessary) and often take chances when crossing the road. This is particularly the case at night when pedestrians are much less visible than in daylight because of less conspicuity due to low contrast and the effects of glare on drivers’ vision. Pedestrians typically believe that they are more visible to drivers than they really are. On the other hand, drivers frequently do not watch for pedestrians or fail to yield to them when turning. In determining whether a driver had sufficient time to take evasive action (typically, braking) in a pedestrian collision, the speed of pedestrian movement and the reasonable perception-response time on the part of the driver must be considered. Reduced attention and distraction of drivers (especially the use of cell phones) contribute to a large proportion of collisions and are particularly a problem at intersections where vehicles are turning while pedestrians cross in the same direction of travel. Obstruction of vision from within the vehicle can be a problem here. Children pose a particular hazard in many traffic situations because their behavior is quite unpredictable and they often pay little attention to traffic. Older pedestrians may be disadvantaged by reduced walking speed and the inability to react quickly in an emergency. In the investigation of pedestrian accidents, it is important to determine the actions of pedestrian as well as driver. How reasonable were the pedestrian’s behavior and the response of the driver? Did one party fail to yield right of way? Was the pedestrian visible in time for the driver to respond (especially at night)? Was the pedestrian or the driver impaired? Often this question is not asked of pedestrians who are struck. Special consideration may be required in assessing the capabilities (e.g., speed of movement, attention, vision) of children and elderly pedestrians. Finally, it is essential to examine each accident on its own merits because no two pedestrian crashes are identical. References Abdulsattar, H.N. and McCoy, P.T., 1999a, Pedestrian blind-zone areas at intersections. Paper presented at 75th Annual Meeting of the Transportation Research Board, Washington, D.C. Abdulsattar, H.N. and McCoy, P.T., 1999b, Pedestrians’ right of way at signalized intersections. Paper presented at 75th Annual Meeting of the Transportation Research Board., Washington, D.C. Bowman, B.L. and Vecellio, R.L., 1994, Pedestrian walking speeds and conflicts at urban median locations. Transp. Res. Rec. , 1438, 67–73.
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Caird, J.K. and Hancock, P., 2002, Left-turn and gap acceptance crashes. In R.E.Dewar and P.L.Olson (Eds.) Human Factors and Traffic Safety . (Tucson, AZ: Lawyers & Judges Publishing Co.), 613–652. Choueiri, E.E., Lamm, R.L., Choueiri, G.M., and Choueiri, B.M., 1993, Pedestrian accidents: a 15year survey from the United States and Europe, ITE J. , 63(7), 36–42. Connelly, M.L., Conaglen, H.M., Parsonson, B.S., and Isler, R.B., 1998, Child pedestrian crossing gap thresholds. Accident Anal. Prev. , 30(4), 443–453. Dahlstedt, S. Walking speeds and walking habits of elderly people, National Swedish Road and Traffic Research Institute, Stockholm, Sweden, undated. Eubanks, J.J. and Hill, P.L., 1998, Pedestrian Accident Reconstruction and Litigation . (2nd ed.) (Tucson, AZ: Lawyers & Judges Publishing Co.). Habib, P.A., 1980, Pedestrian safety: the hazards of left-turning vehicles, ITE J. , 50, 33–37. Hauer, E., 1988, The safety of older people at intersections. In Special Report #281, Transportation in an Aging Society (Washington, D.C., Transportation Research Board), 194–252. Herms, B.F., 1972, Pedestrian crosswalk study: accidents in painted and unpainted crosswalks, Highway Res. Rec. , 406, 1–13. Howarth, I., 1985, Interactions between drivers and pedestrians: some new approaches to pedestrian safety. In L.Evans and R.Schwing (Eds.) Human Behavior and Traffic Safety (New York: Plenum Press), 171–178. Hunter, W.W., Stutts, J.C., Pein, WE., and Cox, C.L., 1995, Pedestrian and bicycle crash types of the early 1990s. Report No. FHWARD95163, (Washington, D.C.: Federal Highway Administration). Janoff, M.S., 2002, Visibility under roadway lighting. In R.E.Dewar and P.L.Olson (Eds.) Human Factors and Traffic Safety . (Tucson, AZ: Lawyers & Judges Publishing Co.), 459–491. Johnson, C.D., 1997, Pedestrian fatalities on interstate highways; characteristics and countermeasures. Transp. Res. Rec. , 1578, 23–30. Knoblauch, R.L., Pietrucha, M.T., and Nitzburg M., 1996, Field studies of pedestrian walking speed and start-up time, Transp. Res. Rec. , 1538, 27–38. Knoblauch, R.L. and Raymond, P.D., 2000, The effect of crosswalk markings on vehicle speeds in Maryland, Virginia and Arizona. (Washington, D.C., Federal Highway Administration). Lord, D., 1996, An analysis of pedestrian conflicts with left-turning traffic, paper presented at 75th Annual Meeting of the Transportation Research Board., Washington, D.C. McKnight, A.J., 1988, Driver and pedestrian training, In Transportation in an Aging Society , Vol. 2, Special Report #218, Transportation Research Board, Washington, D.C.: 101–133. Moskowitz, H. 2002. Alcohol and drugs. In R.E.Dewar and P.L.Olson (Eds.) Human Factors and Traffic Safety . (Tucson, AZ: Lawyers & Judges Publishing Co.), 177–207. Mulder, S. and Hutten, A. (2002). Injuries associated with inline skating in the European region. Accident Anal Prev. , 34, 65–70. National Highway Traffic Safety Administration, 1999, Traffic Safety Facts 1998: Pedestrians . Washington, D.C. O’Brien, A.P. and Brindle, R.E., 1999, Traffic calming applications. In J.Pline (Ed.) Traffic Engineering Handbook , 5th ed. (Washington, D.C.: Institute of Transportation Engineers), 219–256. Olson, P.L., 2002a, Driver perception-response time. In R.E.Dewar and P.L.Olson (Eds.) Human Factors and Traffic Safety . (Tucson, AZ: Lawyers & Judges Publishing Co.), 43–76. Olson, P.L., 2002b, Visibility with motor vehicle headlamps. In R.E.Dewar and P.L.Olson (Eds.) Human Factors and Traffic Safety . (Tucson, AZ: Lawyers & Judges Publishing Co.), 341–379. Olson, P.L. and Farber, E., 2003, Forensic Aspects of Driver Perception and Response , 2nd ed. (Tucson, AZ: Lawyers & Judges Publishing Co). Olson, P.L. and Sivak, M., 1984, Visibility problems in nighttime driving, In G.A.Peters and B.J.Peters (Eds.), Automotive Engineering and Litigation , (New York: Garland Law Publishing), pp. 383–405.
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Oxley, J., 2000, Age differences in road crossing behavior. Unpublished Ph.D. Thesis, Department of Psychology, Monash University, Melbourne, Australia. Oxley, J., Fildes, B. Ihsen, E, Charlton, J., and Day, R., 1997, Differences in traffic judgments between young and old pedestrians. Accident Anal Prev. , 29, 839–847. Perry, J., 1992, Gait Analysis (New York: McGraw Hill). Preusser, W, Leaf, K., DeBartolo, R., Blomberg, R.D., and Levy, M., 1984, The effect of rightturn-on-red on pedestrian and bicyclist accidents, J. Saf. Res. , 13, 45–55. Preusser, D.F., Wells, J.K., Williams, A.F., and Weinstein, H.B., 2000, Pedestrian crashes in Washington, D.C. and Baltimore. Accident Anal. Prev. , 34, 703–710. Reiss, M., 1977, Knowledge and perceptions of young pedestrians, Paper presented at the 56th Annual Meeting of the Transportation Research Board., Washington, D.C., January. Salvatore, S., 1974, The ability of elementary and secondary school children to sense oncoming vehicle velocity. J. Saf. Res ., 6(3), 118–125. Sandels, S., 1968, Children in Traffic , (London: Paul Elek). Schieber, R.A., Branche-Dorsey, C.M., and Ryan, G.W., 1994, Comparison of in-line skating injuries with roller skating and skateboard injuries. JAMA , 271(23), 1856–1858. Sheppard, D. and Pattinson, M., 1988, Interviews with elderly pedestrians involved in road accidents. Transportation and Road Research Laboratory Research Report #98, (Crowthorne, U.K.). Shieber, R.A., Branche-Dorsey, R.A., Ryan, C.M., Rutherford, G.W., Stevens, J.A., and O’Neil, J., 1996, Risk factors for injuries from in-line skating and the effectiveness of safety gear, New Engl. J. Med. , 335(22), 1630–1635. Shinar, D., 1984, Actual versus estimated nighttime pedestrian visibility, Ergonomics , 27, 863– 871. Snyder, M.B., 1972, Traffic engineering for pedestrian safety: some new data and solutions, Highway Res. Rec. , 406, 21–27. Stemley, J.J., 1998, One-way streets provide superior safety and convenience. ITE J. , 68(8), 47– 50. Stutts, J.C., Hunter, W.H., and Pein, WE., 1996, Pedestrian-vehicle crash types: an update. Transp. Res. Rec. 1538, 68–74. Tidwell, J.E. and Doyle, D., 1995, Driver and pedestrian comprehension of pedestrian law and traffic control devices. Transp. Res. Rec. , 1502, 119–128. van der Molen, H., 1981, Child pedestrian exposure, accidents and behavior. Accident Anal. Prev. , 13, 193–224. Virkler, M.R., 1998, Pedestrian delay effects on signal delay. Transp. Res. Rec. 1638, 88–91. Zeedyk, S.M., Wallace, L., and Spry, L., 2002, Stop, look and think? What children really do when crossing the road. Accident Anal. Prev. , 34, 43–50. Zegeer, C.V., 1983, Feasibility of Roadway Counter-measures for Pedestrian Accident Experience, Pedestrian Impact Injury and Assessment, P-121, (Warrendale, PA: Society of Automotive Engineers), 39–49. Zegeer, C.V., Stewart, J.R., Huang, H., and Langerwey, P. (2001). Safety effects of marked vs. unmarked crosswalks at uncontrolled locations. Transp. Res. Rec. , 1773, 56–68.
Further Information Additional helpful information is available at the following web sites: http://www.walkinginfo.org/insight/features_articles/userguide.htm http://www.walkinginfo.org/rd/devices.htmtfcrosl http://www.walkinginfo.org/rd/for_ped.htm#sidewalk http://www.walkinginfo.org/rd/index.htm
17 Commercial Motor Vehicle Collisions Dennis Wylie D.Wylie Associates 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
Commercial motor vehicles (mostly trucks and busses, in North American terminology) are typically larger, heavier, and more complicated to operate than cars and other personal vehicles. Commercial drivers are subject to the same human errors that car drivers are but typically drive more, and many drive at night and on irregular schedules that sometimes result in fatigue and impaired performance. Commercial motor vehicle operations are held to a higher standard of care because they involve more extensive damage potential than personal vehicles do. Litigations arising from commercial motor vehicle collisions typically involve larger damage claims and a larger set of questions than car crashes, often leading to requirements for detailed forensic study by human factors experts familiar with the specialized aspects of commercial motor vehicle collision analysis. 17.1 Introduction to Human Factors Principles and Relevance to Standard of Care in Commercial Motor Vehicle Operations Human factors/ergonomics is a broad, long-established, internationally recognized scientific discipline and systems design profession. Human factors and ergonomics professionals improve safety, comfort, and productivity by developing better operator selection criteria, licensing systems, training, operating procedures, and equipment designs. They do this by taking into account detailed scientific knowledge of human biomechanical, physiological, psychological, and anthropometrical characteristics. This section introduces some of the human factors principles involved in commercial motor vehicle (CMV) operations and relates them to the standard of care expected of drivers and motor carriers. Each of these principles will be expanded in following sections. Skill and Knowledge Requirements Achieving appropriate standard of care requires that a driver have adequate skill and knowledge to operate the CMV that he intends to drive safely. Minimum skill and knowledge requirements for operating various classes of CMVs have been studied and quantified by human factors specialists, and the capabilities of drivers can be measured to
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determine if they meet required levels. The forensic human factors specialist may be called upon to evaluate a CMV driver’s qualifications. Personnel Selection and Training Standard human factors principles of personnel selection and training apply to the selection and training of drivers by motor carriers. In addition to the intrinsic motivation of motor carriers to achieve safety and efficiency, government regulations specifically assign duties to motor carriers regarding the selection and training of drivers. Government regulations also require specific licensing procedures for CMV operators to ensure that they meet minimum skill and knowledge requirements. A forensic human factors specialist may be asked to evaluate a motor carrier’s personnel selection and training policies, in general, and specifically with regard to a driver involved in a CMV crash. Attention, Perception, Decision Making, and Motor Response (Muscular Reaction) Driver performance in each of these areas is critical to safe operation. Drivers and motor carriers have a duty to ensure that a driver does not operate a CMV if he is impaired by fatigue, illness, or any other factor. Failures in one or more of these functional areas may be proximate causes of a CMV crash. Identifying such causes is often a central issue in forensic human factors analysis of CMV crashes. Fatigue and Circadian Rhythms Many CMV operators work long hours, work through the night, and/or have irregular work-rest schedules. Consequently, fatigue and circadian rhythms are important factors in CMV operations because they can impair attention, perception, decision making, and motor response. Satisfactory standard of care requires that motor carriers and CMV operators understand the causes and effects of fatigue and circadian rhythms, and employ effective countermeasures, chiefly suitable work-rest scheduling (Mackie and Wylie, 1991). Government hours-of-service regulations must be observed. The forensic human factors specialist may be required to analyze the work-rest history of a driver regarding compliance with regulations and for likely effects on the driver’s capabilities in connection with a specific CMV crash. 17.2 Objective and Scope of the Chapter The objective of this chapter is to provide an overview of some important aspects of forensic human factors analysis of commercial motor vehicle collisions. It is intended to be useful to human factors/ ergonomics and safety professionals, defense and plaintiffs’ lawyers, judges, forensic and paralegal professionals, accident investigators, students, government officials, consultants, motor carriers, and commercial drivers. The scope is
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intended to be broad; therefore, the amount of detail is necessarily limited. However, numerous references are cited that provide additional detail. 17.3 Foundations Characteristics of Commercial Motor Vehicles Related to Operator Requirements Various classes of commercial vehicles pose varying skill and knowledge requirements, all generally exceeding requirements for operating ordinary automobiles. The classified licensing system used in the United States (the commercial driver’s license system) is based on knowledge and skills tests suitable to the type of vehicle that the driver operates or will operate. Human factors specialists conducted research to identify vehicle groups that had substantially different skill and knowledge requirements (Mackie et al., 1989). These groups form the basis of the CDL licensing system and are described in 49 CFR §383.91. They are summarized below. Commercial Motor Vehicle Groups Group A vehicles are combination vehicles comprising a large truck towing a large trailer or a truck tractor towing a large semitrailer. A truck tractor is a vehicle that is not directly loaded with cargo; instead, the front of a semitrailer (a trailer with a rear axle but no front axle) is placed on the rear of the truck tractor, which bears half the weight of the semitrailer and provides motive power for the tractor-trailer combination. Group A vehicles have the greatest skill and knowledge requirements, and holders of the Group A license can operate Group B and Group C vehicles as well. Group B vehicles are large, straight trucks and buses. (These are referred to as “straight” vehicles because they do not “bend” in the middle, as Group A combination vehicles do.) A driver with a Group B license may pull a small trailer behind the straight truck or bus and may operate Group C vehicles. Group C commercial motor vehicles are vehicles that do not belong to Groups A or B, but are designed to transport 16 or more passengers or are placarded for hazardous materials. Operational Requirements The three commercial motor vehicle groups were identified because they differ substantially in the skill and knowledge necessary to meet most of the 15 operational requirements that the investigators found to be inherent in commercial motor vehicle operation (Mackie et al., 1989). These operational requirements are: • Determining vehicle and safety system conditions • Basic maneuvering skills including eye-hand-foot coordination and spatial visualization • Coupling procedures • Visual search requirements • Communication requirements
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• Speed control • Space management • Special handling characteristics (e.g., off-tracking, rearward amplification, high center of gravity, surge) • Hazard perception • Night driving requirements • Driving in adverse weather (rain, snow, ice, wind) • Driving in hot weather • Driving in mountainous terrain • Emergency maneuvers and skid control • Cargo-related factors (weight distribution, securement, stability, hazardous materials, passengers) Capabilities and Limitations of Humans as Motor Vehicle Operators Human factors/ergonomics and safety professionals have studied the capabilities and limitations of humans as operators of most kinds of motor vehicles. Human factors considerations play a part in the forensic evaluation of accidents involving any kind of motor vehicle; these include: • Conspicuity • Driver behaviors (e.g., risk taking, car following, gap acceptance, overtaking) • Driver expectation • Fatigue • Impairment • Lighting • Medical condition • Perception-reaction time • Recognition and attention errors • Road characteristics • Signs and signals • Traffic conditions • Viewing sight distances and visibility Because these considerations are the subject of the chapter on traffic collisions, it is recommended that the reader review that chapter. Commercial Driver Licensing The Commercial Driver’s License (CDL) The U.S. standard of licensing requires skill and knowledge testing appropriate to the specific class of commercial vehicle to be operated. The U.S. Department of Transportation (DOT) was directed to develop this modern, uniform, scientifically valid system by the Commercial Motor Vehicle Safety Act of 1986. The system was developed by human factors specialists, with the aid of subject matter experts (federal and state
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regulators, motor carriers, and drivers) (Mackie et al, 1989). The CDL system is defined in the Federal Motor Carrier Safety Regulations at 49 CFR Part 383. The Model Driver’s Manual The Model Driver’s Manual (Wylie and Schultz, 1989) was developed as the knowledge base for CDL testing. The manual reflects, as completely as practical, the full knowledge domain associated with safe operation of commercial motor vehicles. The sections of the manual, like the written knowledge tests, were composed so that they are tailored to the applicant’s particular class of vehicle and, in some cases, the type of cargo to be transported. The major sections of the manual include: • Introduction: brief descriptions of all CDL tests, their purpose, and how the tests that an applicant must take depend on the type of vehicle and type of cargo transported. • Driving safely: a compendium of topics including vehicle inspection, basic control, speed management, space management, night driving, adverse weather driving, mountain driving, emergen-cies, skid control, staying fit to drive, etc. This part of the manual should be read by all applicants. The general knowledge test is based on this material. • Transporting cargo safely: this part of the manual should also be read by all applicants and is covered by the general knowledge test. • Transporting passengers safely: this part should be read by all applicants who will require a passenger endorsement to their CDL. The passenger transport test is based on this material. • Air brakes: this part is to be read by all applicants whose vehicles have air brakes. The air brakes test is based on this material. • Combination vehicles: this part should be read by all applicants who wish to drive a Class A combination vehicle and by those who wish an endorsement to operate with double or triple trailers. The combination vehicles test and the doubles/triples test are based on this material. • Hazardous materials: this part should be read by all applicants who wish a hazardous materials endorsement to their CDL. The hazardous materials test is based on the information in this section. The Model Driver’s Manual defines minimum standard of care for operating commercial motor vehicles in the U.S. It has been adopted, published, and made available to the public by every state. Most states include information concerning state-specific commercial vehicle regulations as well. CDL Knowledge Tests A battery of CDL knowledge tests was developed that reflects the general knowledge required of all commercial drivers and specialized knowledge required of operators of particular classes of vehicles or vehicles hauling particular kinds of cargo. The knowledge tests to be taken by a CDL applicant directly reflect the type of vehicle that he operates or proposes to operate. They include: • General knowledge test of safe driving principles (taken by all applicants)
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• Air brakes test (taken by all applicants with a vehicle having air brakes) • Combination vehicles test (taken by all applicants wishing to drive large combination vehicles) • Tanker test (taken by all applicants who wish an endorsement to their CDL that permits them to drive tank vehicles) • Doubles/triples test (taken by all applicants who wish an endorsement to their CDL permitting them to pull double or triple trailers) • Passenger transport test (taken by all applicants who require an endorsement to their CDL to carry passengers) • Hazardous materials test (taken by all applicants who require a hazardous materials endorsement to their CDL) Two roughly equivalent forms of each of these tests were developed and evaluated. Each meets professional standards for test reliability, content validity, and comprehensiveness in its coverage of the knowledge domain. Details are given by Mackie and colleagues (1989). CDL Skill Tests The CDL licensing system employs three types of driver skill tests: • Vehicle inspection test, to determine whether the driver has an adequate understanding of how to ascertain the condition of key operational and safety systems of the vehicle • Basic control skills test, to determine whether the driver has the fundamental psychomotor and perceptual skills necessary to control and maneuver heavy vehicles • Road test, to determine whether the driver is capable of safely driving the vehicle in a variety of road environments and traffic conditions These tests were designed to be adaptable to different vehicle sizes and configurations. Each meets professional standards for reliability and validity and each measures an important, yet relatively independent, area of required driver skill. Details are given by Mackie and associates (1989). Driver Fatigue and Government Hours-of-Service Regulations Background In the late 1930s, concern about truck driver fatigue led to development of the first hoursof-service regulations of U.S. commercial drivers. These regulations have remained largely unchanged to the present time. For drivers in interstate commerce, they permit no driving after 10 hours of cumulative driving and/or 15 hours of cumulative on-duty time, until an 8-consecutive-hour off-duty break is taken. (A common misconception is that driving is limited to 10 hours in a 24-hour period; in fact, it is limited to 10 hours in an 18-hour period. Therefore, driving up to 16 hours in a 24-hour period is permitted. The 18-hour cycle results in a backward-rotating work-rest schedule.) Furthermore, the hours-of-service regulations permit no driving after 60 hours cumulative on-duty time in any 7-day period, or 70 hours cumulative on duty-time in any
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8-day period (49 CFR §395). An excellent and well-documented review of the history of these regulations and their strengths and weaknesses is given in the Federal Motor Carrier Safety Administration’s “Notice of Proposed Rulemaking for Driver’s Hours of Service” (FMCSA, 2000). Driver Fatigue Remains a Problem Hours-of-service regulations have not eliminated the problem of fatigue. A survey of 511 long-haul tractor-trailer drivers around the U.S. revealed that 57% had been drowsy one or more times at the wheel in the preceding month, and that 28% had dozed or fallen asleep at the wheel one or more times in the preceding month (Abrams et al., 1997). Of those surveyed, 58% said they “sometimes” or “always” get less sleep to keep up with their schedules. The U.S. Department of Transportation held a Truck and Bus Safety Summit that brought together more than 200 people, representing the many organizations involved in motor carrier operations, regulation, research, and safety, to prioritize the safety issues facing the industry. After 2.5 days, the representatives completed their discussions and voted to determine the top issues affecting the safety of motor carriers. The top-priority issue was driver fatigue (U.S. DOT, 1995). Driver fatigue has continued to be a principal concern in highway safety to this day. The Federal Motor Carrier Safety Administration is currently drafting new hours-of-service regulations in light of modern scientific knowledge. Fatigue impairs vigilance, attention, perception, decision making, and muscular reaction—processes that are crucial to safe driving. These objective, measurable fatigue effects are primarily cognitive, or mental, and can occur without any marked degree of prior physical exertion. Driving fatigue is caused by long and/or irregular hours of work and too few hours of sleep or poor-quality sleep. Sleep debt is defined as the difference between one’s sleep requirement (7 to 8 hours daily for most people) and the amount of sleep actually received. In their literature review, Wylie et al. (1996) reported that sleep debt of as little as a few hours can adversely affect vigilance and that commercial drivers, especially those on irregular schedules, can build up such debts in 2 days. The Expert Panel on Driver Fatigue and Sleepiness made statements applicable to this issue: Habitually restricting sleep by 1 or 2 hours a night can lead to chronic sleepiness…. Sleepiness causes auto crashes because it impairs performance and can ultimately lead to the inability to resist falling asleep at the wheel…. Factors recognized as increasing the risk of drowsy driving and related crashes include: Sleep loss Driving patterns, including driving between midnight and 6 a.m.; driving a substantial number of miles each year and/or a substantial number of hours each day;…driving for longer times without taking a break. (NHTSA/NCSDR, 1998)
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In addition, fatigue, loss of alertness, and drowsiness are strongly affected by circadian rhythms (the human body’s “clock”) and other time-of-day effects. Lack of Sleep and Time-of-Day Effects The importance of driver fatigue led the U.S. Department of Transportation and Transport Canada to commission their largest, most comprehensive over-the-road study of driver fatigue and alertness. My associates and I designed, executed, and documented a study involving 80 U.S. and Canadian tractor-trailer drivers in an operational setting of real-life, cargo-hauling trips totaling more than 200,000 miles and 4000 hours of driving. We monitored the drivers and trucks continuously by electronic instrumentation. We found that the drivers obtained less sleep than is required for alertness on the job and that the strongest and most consistent source of variation in driver fatigue and alertness was time of day, due in part to the effects of 24-hour biological rhythms, known as circadian rhythms (Wylie et al., 1996; Mitler et al., 1997). Drowsiness, as judged from video images of drivers’ faces, was markedly greater during night driving than during daytime driving. Peak drowsiness occurred during the 8 hours from late evening until dawn. Circadian rhythms are biological rhythms that repeat approximately every 24 hours. An internal clock, or pacemaker, located in the brain generates circadian rhythms. These rhythms promote sleep during the night and alertness in the day. When sleep periods must be taken in the daytime, circadian rhythms act to reduce quality and quantity of sleep. These rhythms have an adverse influence on the performance of tasks that must be done between midnight and dawn because of the dual effects of depressing performance at night and interfering with sleep in the day. Nighttime drivers are especially susceptible because of the stimulus deprivation associated with driving during those hours. The visual field is restricted mostly to a narrow cone of headlight illumination, traffic is at a minimum, and the likelihood of boredom and monotony, long known to be factors that hinder vigilance (Wylie et al., 1985), is maximized. Accident data also reveal these time-of-day effects. For example, the Notice of Proposed Rulemaking for Driver’s Hours of Service (FMCSA, 2000) shows in Chart 3 the relative risk of truck driver fatigue by time of day, derived by University of Michigan Transportation Research Institute scientists. These relative risk estimates are based on accident data from 1991 to 1996. The shape of the distribution of relative risk over the hours of the day is remarkably similar to the distribution by time of day of the 1,989 video samples judged to show a drowsy truck driver in the Driver Fatigue and Alertness Study (Wylie et al., 1996). The two curves correlate well, r=0.88, reinforcing our conclusions regarding the powerful influence of time of day. The daily variation of drowsiness and fatigue risk is illustrated in Figure 17.1 by a mathematical model indicated by the solid line (Wylie, 2000) and drowsiness data from actual truck drivers indicated by the dotted line (Wylie et al., 1996). It can be seen that time-of-day effects lead to greatly increased incidence of drowsiness by midnight.
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Cumulative Fatigue and Irregular Schedules In 1990, the National Transportation Safety Board completed a study of 182 heavy-truck accidents that were fatal to the driver (NTSB, 1990). The primary purpose in investigating fatal-to-the-driver heavy-truck accidents was to assess the role of alcohol and other drugs in these accidents. The study found, however, that the most frequently cited probable cause was fatigue. The NTSB stated that it believed that the 31% incidence of fatigue in fatal-to-the-truckdriver accidents found in the 1990 study represented a valid estimate of the portion of fatal-to-the-driver heavy truck accidents that are fatigue-related. Therefore, the NTSB initiated another study—of drivers who survived truck crashes— to examine the role of specific factors, such as drivers’ patterns of duty and sleep, in fatigue-related heavy truck accidents. They found that irregular duty and sleep patterns are a significant risk factor. About 67% of the drivers with irregular patterns had fatiguerelated accidents (43 of 64), whereas about 38% of drivers with regular patterns had fatigue-related accidents (9 of 24) (NTSB, 1995). A driver’s duty hours were classified as irregular if the start times of two consecutive duty periods varied by 2 or more hours at least twice during the previous 96 hours (4 days). A driver’s sleep hours were classified as irregular if the start times of two consecutive rest periods varied by 2 or more hours at least twice during the previous 96 hours.
FIGURE 17.1 Daily variation of drowsiness and fatigue risk. Regarding irregular schedules, the Expert Panel on Hours of Service Recommendations appointed by the U.S. Department of Transportation (Transportation Research Institute, 1998) stated what it thought was the primary critical issue of hours-of-service rules for commercial drivers:
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1. 24-Hour Cycle—For most of the history of humankind, the natural light cycle governed activity. Although firelight has long been available, it was not until the advent of lamps and eventually electric lighting that daylight was significantly extended. This change did not occur until very late in the evolution of man, and, from a biological and physiological standpoint, we are very much the same as we were tens of thousands of years ago. Basically, we are on a 24- to 25-hour cycle, and, independent of light cycles, our bodies still appear to respond accordingly. Therefore, whatever hours-of-service regulations are adopted should conform to this cycle that is apparently “normal” from an inherent constitutional standpoint. This biological predisposition cannot be changed by bureaucratic regulation or even economic necessity (Mitler et al., 1988; Wylie et al, 1996; Folkard, 1997) (p. 5). Irregular work-rest schedules cause an accumulation of sleep loss and fatigue as days and nights go by. This point was addressed by the Expert Panel (Transportation Research Institute, 1998): Sleep loss, extended hours of service, and “unnatural” schedules (e.g., night driving) cannot be compensated for by a single night’s rest. Sleep loss is substantial. The FHWA-Transport Canada study that recorded sleep of 80 drivers over a week of driving found average sleep lengths of just under 4 hours to 5.5 hours (Wylie et al., 1996).This is substantially less than the normal length of 7.5 hours to 8 hours (Gallup Organization, 1995), but typical of industries where 12-hour shifts are worked (Smiley and Heslegrave, 1997). Such partial sleep deprivation results in cumulative sleep debt that requires extended time to recover. Recovery time periods must take into consideration the necessity for overcoming cumulative fatigue resulting from such schedules and must include sufficient nighttime sleep. Compared to daytime sleep, nighttime sleep is more efficient, that is, a higher proportion of the time spent in bed is actually spent in sleep (Lavie, 1989). When sleep time occurs during the day, fewer hours of sleep occur (Akerstedt, 1995) (p. 12). Adherence to the current U.S. hours-of-service regulations does not prevent cumulative fatigue for drivers with irregular schedules. The Expert Panel addressed the current policy: Overall, the current policy, Policy Option A, fails on every criterion identified by the Panel as important for a reasonable hours-of-service policy. The 18-hour cycle ignores real physiological factors and violates everything that is known about the powerful effects of circadian rhythms (Mackie and Miller, 1978; Mitler et al, 1988; Home and Reyner, 1995; Gillberg et al., 1995; Wylie et al., 1996; Folkard, 1997). Furthermore, allowing only 8 hours off-duty for sleep, with no additional time for other activities, translates into continuous sleep deprivation that accumulates
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over time (Wylie et al., 1996; Mitler et al., 1997; Smiley and Heslegrave, 1997). The combination of sleep loss and driving during circadian troughs is synergistic, exacerbating the effects of both (Lavie, 1986; Mitler et al., 1988; Rosekind et al., 1997). Furthermore, over a 24-hour cycle, as much as 16 hours on-duty time is allowed, all of which may be spent driving. Such a schedule inevitably results in fatigue and impaired performance (p. 19). Fatigue Can Be Equivalent to Alcohol Intoxication Williamson and Feyer (2000) compared the relative effects of fatigue and alcohol on performance. Performance of 39 transport industry people on more than a half-dozen tests related to safe driving (e.g., reaction time, vigilance) was measured on two occasions. On one occasion, the performance tests were given periodically over many hours as the people consumed given quantities of alcohol. Breath analyzer measurements were used to confirm their blood-alcohol concentration (BAC). On another occasion, the same people were given the same performance tests repeatedly during a long period of being awake starting at about 6:00 a.m. and lasting well past midnight. The test results were then analyzed to find out how many hours of wakefulness were equivalent to various BAC levels. These researchers found that “at a BAC of 0.10%, equivalence occurred after between 17.74 and 19.65 hours of wakefulness which falls in the late evening to early hours of the morning, corresponding in this study to between 2328 [11:28 p.m.] and 0123 [1:23 a.m.]” (Williamson and Feyer, p. 653). This level of BAC is more than twice the 0.04% U.S. federal limit for commercial drivers (49 CFR §382.201). The legal limit was set because the impairment of alcohol intoxication at levels higher than 0.04% BAC is associated with unacceptable probability of injury and death (Transportation Research Board, 1987). 17.4 Human Factors Forensic Analysis of CMV Collisions The goals of the human factors forensic expert are to gain an understanding of the collision from a technical human factors point of view and then to explain it in terms understandable to attorneys, judge, and jury. Pursuing this goal usually requires study of the actions and inactions of all involved motorists, pedestrians, etc., as well as the physical setting of the accident. It can be expected, however, that major emphasis will be placed on the particulars of the CMV driver’s performance. This will involve forensic analysis of the driving environment and the driver’s apparent actions in the proximate time period leading up to and including the accident, as related by witnesses, indicated by analyses of physical evidence, and inferred from reconstructions based on engineering and physics. It is likely that analyses and reconstructions by experts from other fields will be considered, in addition to any performed by the human factors expert. It is the latter, however, who must characterize the driver’s performance with regard to numerous specific human factors elements of driving. If the expert concludes that CMV driver error was a cause of the accident, an important question will then be whether driver fatigue might have been responsible.
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There is no breath analyzer or blood test that can reveal the presence of a critical level of fatigue in an accident-involved driver. However, a forensic driver-fatigue expert can often conclude to a reasonable degree of scientific certainty whether fatigue was a cause of an accident by conducting a human factors analysis of the driver’s work-rest history leading up to the accident. Ideally, a commercial driver’s work-rest history would be adequately documented in the driver’s record of duty status required by the Federal Motor Carrier Safety Regulations (49 CFR §395.8), corroborated by regular work hours and personal routine. Unfortunately, this is not always the case. The driver’s work hours may be very irregular; his log may be days in arrears or may be missing altogether. Even if present, the log may be inaccurate or falsified, so it must be tested against other sources. The forensic driver-fatigue expert examines many records and documents, uses specific tools and techniques to reconstruct the driver’s probable work-rest history, and describes the implications of that history in terms of causal factors of fatigue. If the expert judges that the CMV driver’s actions or inactions were a cause of the accident, the expert may also be requested to analyze whether the motor carrier exercised proper standard of care in performing its duties of selecting, qualifying, training, motivating, disciplining, dispatching, and monitoring drivers in the interest of safety. These forensic human factors analyses often permit the expert to identify any specific deficiencies of CMV driver performance and to conclude to a reasonable degree of scientific certainty whether fatigue was or was not a cause of the accident. The expert may also opine as to the motor carrier’s standard of care. These findings and expert opinions must then be organized and communicated effectively. Driver-error analysis, work-rest history analysis, motor carrier standard of care, and effective communication of opinions will be considered in turn in the following subsections. Analysis of Driver Errors Proximate to the Accident Analysis of driver errors proximate to the accident requires study and assimilation of many different sources of information. Some of the sources that may be available include the police accident report; police accident reconstruction; statements taken by police from witnesses at the scene of the accident; photographs of the scene taken by the police, insurance adjusters, and others; accident reconstruction experts’ reports; and deposition transcripts. The depositions of the CMV driver, CMV passengers, people in other vehicles, and any other witnesses must be studied carefully. Similarly, answers to interrogatories and responses to requests for document production should be examined carefully for their relevance to the human factors aspects of the case. The expert should also review the complaint and other pleadings in the case to gain a better understanding of who is suing whom and what is being alleged. This is likely to give the expert a better understanding of the case, which helps him to be a more effective expert witness. If the expert enters the legal process late in its course, much of this information will already be available, and he will be faced with an intensive reading assignment. If the expert is retained earlier in the matter, the workload will be more spread out, and the expert can consult with and advise his attorney client with respect to important human factors questions that might be posed by plaintiffs’ and defense attorneys.
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In most cases, the expert should visit the accident site to view it directly; to record salient human factors features through photographic, video, or other means; and to take appropriate measurements as needed, such as luminance levels and sound pressure levels. It is difficult to provide a formula or recipe for how all this information should be put together to form an expert opinion. One or more human errors can contribute to an accident in many ways. Some categories of human performance and error have been mentioned in this chapter, and the reader can review additional details regarding traffic collisions in the chapter on traffic collisions. Ultimately, however, proper synthesis requires the education, training, experience, and inquiring mind of a qualified human factors forensic expert. Analysis of Commercial Driver Work-Rest History When there is the question of driver fatigue, an analysis of the driver’s work-rest history is necessary. In the U.S., the Code of Federal Regulations (49 CFR §395) requires drivers engaging in interstate commerce to follow specific rules in making the prescribed driver’s daily records of duty status, commonly called “logs.” (A driver need not cross state lines to be involved in interstate commerce; if the driver transports cargo that has crossed state lines, he is engaged in interstate commerce.) Most U.S. states have similar requirements. The principal reason for these logging requirements is to assist drivers and motor carriers in complying with federal and state hours of service regulations and to permit law-enforcement officials to verify compliance. By reviewing drivers’ logs, the forensic expert can evaluate compliance with the U.S. 10-hour driving limit, 15-hour on-duty limit, and the 70/80 hour cumulative on-duty rules (or corresponding state or other jurisdictional hours-of-service regulations). It is very desirable to have at least 8 days of consecutive logs ending on the day of the accident. It is desirable to have logs for prior weeks as well because these can help to evaluate work-rest patterns and, in some cases, to evaluate place names and travel times between geographic locations that have been visited repeatedly. (Deciphering handwritten place names is no trivial matter in evaluating logbooks; a driver is often asked at deposition to clarify the place names in logbooks, which is very helpful in analyzing the logged data.) The expert should analyze available logbooks to determine compliance with applicable hours-of-service rules and to gain an understanding of the work-rest cycles recorded by the driver during the days leading up to the accident. The expert must be thoroughly familiar with the applicable logging rules and the hours-of-service rules (e.g., for U.S. interstate transportation, 49 CFR §395 “Hours of Service of Drivers,” plus the U.S. DOT “Interpretations” published in the Federal Register on April 4, 1997, plus the subsequent DOT interpretations). The expert must be diligent in doing the required arithmetic; it is sometimes helpful to use logbook audit software (for example, that available from J.J. Keller and Associates) to double-check this work. Analysis of logbooks is usually not sufficient, however. The driver’s logs may be missing important data and may be inaccurate with respect to the places and/or the times of day of changes in duty status, by reason of simple human error, inattention to detail, or willful falsification intended to conceal violations of hours of service rules. (Many drivers have an economic incentive to drive beyond the limits because they get paid by the mile; motor carriers obviously have a similar economic incentive, and drivers and
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motor carriers are often under pressure from shippers and receivers, particularly with the prevalence of current “just-in-time delivery” inventory practices (U.S. DOT, 1995).) Therefore, the forensic expert must aim to reconstruct the driver’s trip itinerary and work-rest schedule to evaluate fatigue and compliance with the hours of service regulations. The reconstructed itinerary should take into account the data in the driver’s logbooks, as well as supporting documents. The U.S. DOT defines in its interpretations that “supporting documents” are the records of the motor carrier maintained in the ordinary course of business and used by the motor carrier to verify the information recorded on the driver’s record of duty status in accordance with 49 CFR 395.8(k)(1), which also requires that they be retained for a period of 6 months after their receipt. Examples are: Bills of lading Carrier pros Freight bills Dispatch records Driver call-in records Gate record receipts Weight/scale tickets Fuel receipts Fuel billing statements Toll receipts International registration plan receipts International fuel tax agreement receipts Trip permits Port-of-entry receipts Cash advance receipts Delivery receipts Lumper receipts Interchange and inspection reports Lessor settlement sheets Over/short and damage reports Agricultural inspection reports CVSA reports Accident reports Telephone billing statements Credit card receipts Driver fax reports On-board computer reports Border-crossing reports Custom declarations Traffic citations Overweight/oversize reports and citations Other documents directly related to the motor carrier’s operation that are retained by the motor carrier in connection with the operation of its transportation business A good approach to assimilating the various available bits of information regarding geographic locations at particular times is to use trip-planning software, such as
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Microsoft Streets and Trips or PC Miler. A first-estimate itinerary can be obtained by entering the geographic place names into the application program in assumed chronological order, assigning durations for periods logged as “not driving,” and assigning assumed average speeds for various types of roads, according to the capabilities of the particular software. (If the software will not account for variations in speed limit by state, the analysis may be done in segments, wherein each segment comprises a state or states with identical speed limits.) The software then calculates an itinerary, and that itinerary is compared to the driver’s logs and the supporting data. The calculated itinerary may be found to be a good fit to the driver’s logbook or it may be very different. In the latter case, the expert must identify likely reasons for discrepancies between the logs and the calculated itinerary; make adjustments to the assumed times, geographic locations, and average speeds; and calculate a new itinerary. In what is typically an iterative process, the expert (hopefully) converges on a calculated itinerary that reasonably explains the most credible bits of data available concerning the work-rest schedule of the driver. The “best fit” itinerary can then be analyzed with respect to hours-of-service compliance and likely fatigue effects. It can also be used to judge probable speed limit violations. (The U.S. DOT, in an interpretation of 49 CFR §392.6, stated that average speed greater than 5 mph below the speed limit over a many-hour period is considered incapable of being made in compliance with the speed limit and hours of service limitation.) The fatigue evaluation must take into account the time of day of the accident, the duration of the preceding period of driving and of wakefulness, the duration and time of day of the last principal sleep, and so on, backward in time, taking account of the duration, time of day, and regularity/ irregularity of principal rest and on-duty periods. As in the case of evaluating driver errors, it is difficult to provide a formula or recipe for how all this information should be put together to form an expert opinion. Ultimately, proper synthesis requires the education, training, experience, and inquiring mind of a human factors forensic expert. Analysis of Motor Carrier Standard of Care U.S. motor carriers are held responsible by the Federal Motor Carrier Safety Regulations for selecting, qualifying, training, motivating, disciplining, dispatching, and monitoring drivers in the interest of safety. Motor carriers must ensure that a driver is qualified to drive a commercial motor vehicle, has sufficient hours of service available, and is not ill or fatigued. The regulations state that whenever a duty is prescribed for or a prohibition imposed upon the driver, it is the duty of the motor carrier to require observance of such duty or prohibition (49 CFR §390.11). “Motor carrier” is defined by U.S. federal regulations as a for-hire motor carrier or a private motor carrier. This term is broadly defined to include a motor carrier’s agents, officers, and representatives as well as employees responsible for hiring, supervising, training, assigning, or dispatching drivers, and employees concerned with the installation, inspection, and maintenance of motor vehicle equipment and/or accessories (49 CFR §390.5). Motor carriers must perform initial qualification of drivers and follow-up qualification. Initial qualification starts with a written application for employment that
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identifies the motor carrier and the applicant; describes the applicant’s experience operating motor vehicles; lists motor vehicle accidents in the last 3 years; lists convictions for violations of motor vehicle laws in the last 3 years; contains statements regarding denial, revocation, or suspension of driver’s licenses; and lists previous employers during the last 3 years. The motor carrier must then check into the applicant’s driving record and employment record. Responses to these inquiries from state driverlicensing agencies and previous employers are to be kept in the driver’s qualification file. The motor carrier is required to administer a road test to drivers that will operate double/triple trailers or tank vehicles to determine if they can safely operate the motor vehicle. For other commercial vehicles, the regulations now permit, but do not require, the motor carrier to accept the commercial driver’s license as evidence of minimum skill. A certificate of road test issued by another motor carrier during the preceding 3 years is also acceptable. If a road test is given, a record of the road test form must be included in the driver’s qualification file. The applicant must have a currently valid DOT medical examiner’s certificate of physical examination, which must be carried by the driver while operating a commercial motor vehicle, with a copy kept in the driver qualification file. Follow-up qualification of a driver by the motor carrier includes assuring that the medical examiner’s certificate is renewed at least every 2 years. At least every 12 months, the motor carrier must check the driver’s driving record by requesting information from each state in which the driver held a license during the year. The motor carrier must evaluate the driving record, judge the driver’s suitability, and keep a written record of the review in the driver’s qualification file. The motor carrier must also require that each driver submit a list annually of all violations of traffic safety laws for which he was convicted. The motor carrier must evaluate this record with respect to the suitability of the driver, and the list must be kept in the driver’s qualification file. Motor carriers know (or should know) that in a legal action, they are likely to be asked to produce numerous documents and answer many questions of interest to human factors forensic analysts for plaintiff and defense. For example, with reference to the driver, the following documents and items may be produced: • Driver’s Record of Duty Status logs (49 CFR §395.8) for 1 month preceding the accident • Records of driver daily report-for-duty times, release-from-duty times, and total on-duty time for the 7 days preceding the accident in question, if driver was exempt from logbook requirements of 49 CFR §395.8 because of the 100 air-mile radius exemption per 49 CFR §395.1(e) • Records of disciplinary action • The truck driver’s qualification file (49 CFR §391.51), including • Employee’s application • List of truck driver’s previous employers for 10 years preceding the date of the application • Reasons for leaving these employments • Medical examiner’s certificate • A note showing when and who reviewed the driver’s record with him for each year of employment (49 CFR § 391.25)
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• A list of certificates showing all violations of motor vehicle laws and ordinances (49 CFR § 391.27) • Responses from state agencies and employers to employer’s inquiries about the truck driver’s employment and driving records (49 CFR §391.23) • Certificate of road test (49 CFR §391.31(e)) • Records of drug and alcohol tests • An accident register listing all DOT recordable preventable accidents (Note: the employer is required to keep the driver’s file in its principal place of business as long as the driver is employed and for 3 years thereafter.) • Copy of all commercial driver’s licenses of the truck driver • All writings giving notification to the employer of the truck driver’s convictions or suspensions for violating a state or local law relating to motor vehicle traffic control (49 CFR §383.31) • All records of the driver’s alcohol tests with confirmed reading of 0.02% or greater, confirmed positive controlled substance test results, documentation and refusal to take alcohol and/or drug tests, instrument calibration documentation, driver evaluation by a substance abuse professional, and calendar year summaries for the last 5 years • All records of alcohol tests with less than 0.02% blood-alcohol reading and negative drug tests • All copies of alcohol test forms, controlled substance standard custody forms, documents related to the refusal of any driver to submit to testing, documents supplied by the driver to dispute test results, and signed acknowledgments of required training documents • Copies of educational materials explaining drug and alcohol testing regulations submitted to drivers • Copies of the employer’s policies and procedures relating to alcohol and drug testing • Copies of the driver’s signed receipt for the preceding materials • Copies of all company manuals governing commercial motor vehicle safety, maintenance, fleet safety programs, and driver’s standards (in lieu of presenting a copy, the responding party may present a list and date of publication of any and all manuals on hand) With regard to the defendant motor carrier’s policies and programs, the following documents and items may be requested: • Defendant motor carrier’s safety program, including studies and tests to determine the safety of the single, double, or triple trailer configurations used by the defendant motor carrier; actions taken to assure that drivers are not violating the federal regulations relating to the maximum hours of work by drivers and that accurate logs are submitted by the drivers and accepted by the defendant motor carrier for filing; as well as the continued testing of drivers for competency and substance abuse • Driver standards • Dispatcher standards • Driver compensation and incentives • Driver disciplinary policy
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The motor carrier may be asked the following: • State the policy with respect to the retention and destruction of drivers’ logs and trip receipts and explain any differences between that policy and the manner in which the defendant driver’s logs and trip expenses for the trip in question were treated. • What steps, if any, the company has taken to assure the accuracy of the logs submitted by its drivers as required by the Federal Motor Carrier Safety Regulations, 40 CFR §390.11 and 390.13. • State the policy with respect to testing drivers for substance abuse and explain any difference between that policy and the manner in which the defendant driver was treated. • Was postaccident testing for alcohol and controlled substances conducted in accordance with 49 CFR §382.303? If not, why not? • State the policy with respect to the operational speeds for the company’s commercial motor vehicles and explain exactly how compliance is enforced. • State the policy with respect to the use of CB radios by the company’s drivers and explain any difference between that policy and manner in which the defendant driver was treated. • State the policy with respect to the use of radar detectors by the company’s drivers and explain any differences between that policy and the manner in which the defendant driver was treated. The answers to these questions and the documents produced may permit the forensic expert to evaluate motor carrier standard of care. Organization and Communication of Findings and Expert Opinions The human factors forensic expert must express his or her findings and expert opinions plainly and in a well-substantiated manner. The expert should use theories and techniques that are tested, peer reviewed, published, and generally accepted within the human factors community. It is also important to identify the known or potential rate of error in the methods used. Various cases will involve varying degrees of challenge to the expert, based upon Daubert and other factors that give the trial judge a gatekeeper role in evaluating expert testimony (see the chapter on general testimony issues). Often, the expert’s client attorney may request his findings and opinions in the form of a letter report. The format of letter reports can vary considerably, but the contents likely would include: • Salutation/introduction • Materials reviewed (often included as an attachment if the list is long) • Short accident summary • Summary of the human factors analysis of proximate driver errors • Summary of the work—rest history analysis (if applicable) • Findings regarding motor carrier standard of care (if applicable) • Explicit statement of expert opinions • Complementary close • Reference list • Figures and tables
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• Attachments such as maps and listings of “best fit” trip itineraries Sometimes, the expert’s client attorney may only want a simple outline or perhaps just an oral report. Regardless, the expert must be prepared to give clear, well-founded summaries of findings and opinions tailored for the average technical level of the intended audience: attorneys, judge, and jury. Charts and other graphical methods can be helpful. For example, in explaining an accident in which a commercial driver failed to detect a yellow traffic signal light immediately, decided it was too late to stop, and broadsided another motorist, a chart like that shown in Figure 17.2 might be helpful to explain the split-second timing involved and the alternative outcomes, based on whether the driver attempts to stop or not. A complex chart like this example should not be expected to stand on its own; the expert should use it as a visual aid for explanation of the underlying concepts. Such charts can be prepared in Excel and other widely used programs. Similarly, it might help to explain an irregular work-rest schedule to use a spreadsheet chart similar to that shown in Figure 17.3. 17.5 Examples Example 1 At 12:20 a.m., a commercial driver on cruise control drove his tractor-trailer at high speed into a well-marked and illuminated mile-long approach to a construction zone on an interstate highway, at the end of which a car was stopped by a flagman. The truck driver reacted only in the last fraction of a second before impact, resulting in fatal injuries to the driver of the car. The highway was straight, level, and dry, and the sky was clear, with good visibility. The human factors forensic expert retained by the plaintiff examined the driver’s logs and found that the driver had had a very irregular work and rest schedule in the 4 days prior to the accident, which he judged led to cumulative fatigue. The cumulative fatigue was made sharply worse during the day of the trip leading to the accident by a longdelayed start, the relentless pace of the trip once it was underway, and circadian rhythms and other time-of-day effects occurring at the late hour of the crash. The truck driver had risen at 5 a.m. on the day of the accident, but had had to wait for his truck to be serviced, and did not leave on his trip until between 2:30 and 3:00 p.m. By the time he got to the crash site, he had been up for 19 hours 20 minutes. The human factors expert reconstructed the driver’s itinerary, revealing that he kept up a relentless pace during approximately 10 hours of driving, averaging about 5 mph above the speed limits in the states through which he passed, which must have involved much higher speeds at some points. By his own testimony at deposition, the truck driver only stopped for a few minutes two or three times during the 10-hour trip. The last time he stopped, he said it was to go to bed for 8 hours because he was tired, but he traveled on because he did not see a parking spot. However, he admitted that there was another truck stop between that place and the accident site, at which he did not stop because he preferred another place farther on.
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FIGURE 17.2 Charts and other graphical methods can help the expert to explain technical points in court.
FIGURE 17.3 Example of a spreadsheet chart. The plaintiff’s human factors forensic expert opined that the truck driver’s failure to slow down and stop at the construction zone was due to fatigue, drowsiness, and a lack of alertness resulting from an irregular work-rest schedule, the long (19+ hours) period
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between starting his day and crashing, the relentless pace of his high-speed driving for almost 10 hours with no significant breaks, and driving past midnight, when time-of-day effects approach maximum likelihood of causing drowsiness. The case was settled out of court. Example 2 At 6:30 p.m., a tractor-trailer driver on a secondary road approached an intersection with a divided highway. The highway had a wide median; traffic on the secondary road was controlled by two stop signs requiring that drivers stop at the first set of lanes and then stop again in the median, prior to crossing the lanes going in the other direction. The truck driver failed to stop at the first stop sign and crossed into the path of an oncoming car, which collided with the truck, resulting in fatal injuries to a passenger in the car. The plaintiff alleged that the crash was the result of extreme driver fatigue and sought punitive damages. The plaintiff’s expert pointed to a payroll timesheet filled out by the driver as indicating excessive and illegal hours of work, leading to fatigue. The defendants retained a human factors forensic expert, who studied the driver’s work-rest history and his driving performance proximate to the accident. The work-rest history analysis revealed that in the two work weeks preceding the week of the accident, the truck driver had a regular duty schedule, with two nights and one day off at the end of each week. The expert concluded that no cumulative fatigue would be expected. During the week of the accident, the truck driver continued the pattern seen in the prior two weeks, which consisted of a medium-length drive to another city on the first day of the work week, followed by daytime local deliveries in that area and sleeping in the same motel each night. The accident occurred on the second day of local, short-haul deliveries, so the expert judged that cumulative fatigue was improbable. Similarly, acute fatigue was judged to be improbable. The driver’s task composition that day had a favorable mixture of activities, driving for a total of 4.75 hours and spending 7.75 hours making deliveries and taking breaks. The total elapsed time was well short of the 15-hour limit and well within the range of normal performance. Circadian rhythms would not be expected to be a factor at 6:30 p.m., and at the time of the accident, the driver had been driving less than 15 minutes since his last delivery, which was of about 30 minutes’ duration. Therefore, the expert judged that the energizing effects of the physical activities associated with the delivery likely carried over during this brief period of driving, making loss of alertness at the time of the accident even less likely. The defense expert used Microsoft Streets and Trips software to calculate an itinerary based on the places to which the driver had made deliveries and found that the calculated itinerary agreed well with the driver’s DOT logs. The payroll timesheet that the motor carrier required the driver to fill out showed time added to the beginning and/or end of the work days recorded in the DOT logs. Because the DOT logs accounted for all the travel that the driver accomplished, the forensic expert concluded that the driver was recording hours on the company payroll timesheet that he did not actually work. This fictitious work earned the driver more money but obviously did not result in driver fatigue. The truck driver testified at his deposition that, at the time of the accident, he was trying to find an on-ramp to the interstate highway in that area. In investigating driver
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performance, the defense expert visited the accident site and retraced the route of the truck driver. He found that the secondary road approaching the divided highway passed through a forested area. Very near the intersection, a driver emerged from the trees and the view opened up, revealing the interstate highway some distance beyond the intersecting divided highway. An off-ramp and an overpass were visible sharply to the left and there were glimpses of the interstate moderately to the left; another overpass and on-ramp signs were straight ahead across the intersection. The expert judged that the complexity of this visual scene and its obvious relevance to the driver’s goal of getting onto the interstate stimulated substantial visual scanning. To interpret most visual cues properly, humans must use their sharp central vision by fixing the gaze upon each visual feature, sequentially. The more cues available, the longer this takes and the more likely it is that one will be missed. The driver testified at deposition that he did see the second stop sign and planned to stop there; unfortunately, he did not detect the first stop sign. The expert explained that driver behavior is influenced by expectations built up from driving experience and that this driver probably expected to see only one stop sign at the intersection. Having detected the expected stop sign (which he now knows was the second of two stop signs), he may have resumed his visual search for an on-ramp to the interstate highway. There was no question that the truck driver committed a fatal error. Extensive analyses of traffic accident data indicate that 45 to 56% of crashes involve “recognition failure.” The defense expert opined that the recognition failure in this case was more likely than not caused by distraction associated with looking for the interstate highway on-ramp. In his opinion, to a reasonable degree of scientific certainty, truck driver fatigue was not a cause of this accident. The case was settled before it got to court.
Primary factor
17.6 Checklist of Main Factors to Consider Considerations
Preceding driver errors Vehicle safety inspection Cargo securement Vehicle operating practices Proximate driver errors Attention Perception Detection Decision making Motor response Cumulative driver Driver’s logs fatigue Supporting documents Itinerary reconstruction Irregularity of rest periods Duration of rest periods Place of sleep (sleeper berth/truck moving, sleeper berth/parked, motel, home, etc.) Irregularity of work periods Duration of work periods Circadian rhythms and other time-of-day effects Sleep debt Duration and frequency of recovery periods (days/nights off)
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Compliance with hours-of-service regulations Sleep disorders Circadian rhythms Daylight/dark Time elapsed since awakening from last principal sleep period Time and duration of naps since awakening from last principal sleep period Time and duration of breaks since awakening from last principal sleep period Time, duration, and effort of cargo loading/unloading since awakening from last principal sleep period Duration of proximate driving period Average speed Monotony
Defining Terms Bus—North American term for a vehicle designed primarily to transport passengers. CDL—Commercial driver’s license. A U.S. driver’s license associated with specific classes of commercial motor vehicles and granted after successfully completing specific tests of knowledge and skill. CFR—U.S. Code of Federal Regulations. Circadian rhythms—Biological rhythms that repeat approximately every 24 hours. An internal clock, or pacemaker, that is located in the brain generates circadian rhythms. These rhythms promote sleeping during the night and alertness in the day. CMV—Commercial motor vehicle—a precisely defined class of vehicle subject to specific government rules and regulations. Cumulative fatigue—A state of fatigue caused by accumulated sleep debt over a period of several days. A work-rest schedule that results in daily sleep debt will cause an increasing state of cumulative fatigue as days go by, requiring a recovery period of days and nights off duty to restore performance. Fatigue—Driver fatigue has been defined in many ways. Wylie and colleagues (1996) defined it as a state of the driver manifested by increased lapses of attention; increased information-processing and decision-making time; increased reaction time to critical events; more variable and less effective control responses; decreased motivation to sustain performance; decreased psycho-physiological arousal (e.g., body temperature, brain waves, heart action); increased subjective feelings of drowsiness or tiredness; decreased vigilance (e.g., watchfulness); and decreased alertness (e.g., readiness to meet danger). Motor carrier—An entity that provides transportation of property or passengers and is responsible for dispatching drivers of commercial motor vehicles for that purpose, regardless of whether the drivers are employees of the motor carrier or independent contractors. An owner-operator is a motor carrier as well as a driver. Motor carriers are subject to government regulation.
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Placard, hazardous materials—A precisely defined type of sign required on commercial motor vehicles to indicate the presence and nature of hazardous materials carried as cargo. Proximate driver fatigue—The state of fatigue proximate to a motor vehicle collision. Proximate fatigue is a combination of cumulative fatigue reflecting work-rest history in previous days and the factors influencing driver fatigue within 24 hours of the accident. Recovery period—A “weekend” or other extended off-duty period that may restore performance after a “work week” resulting in cumulative fatigue. Straight truck—North American term for a heavy cargo-bearing vehicle that is not articulated (i.e., that does not “bend” in the middle). Tractor-trailer—North American term for a heavy vehicle comprising a truck tractor, a semitrailer, and possibly one or more full trailers. Truck tractor—North American term for a heavy vehicle that bears the weight of the front part of a semitrailer and provides motive power for the articulated tractor-trailer combination. Vigilance—Sustained attention for low-probability events under monotonous conditions. There has been a strong interest in vigilance research since the studies of performance decrements of ships’ lookouts and airborne radar operators during World War II. Vigilance is required for the safe operation of motor vehicles, as well as many other critical tasks. References Abrams, C, Shultz, T, and Wylie, C.D., 1997. Commercial motor vehicle driver fatigue, alertness, and countermeasures survey. Decision Research, Santa Barbara, CA. Akerstedt, T. and Home, J., 1995. Work hours, sleepiness and accidents. J. Sleep Res. , 4(suppl. 2), 1–83. FMCSA (Federal Motor Carrier Safety Administration), 2000. Hours of service of drivers; driver rest and sleep for safe operations. Fed. Regist , 65(85), 22540–25611. Folkard, S., 1997. Black times: temporal determinants of transport safety. Accident Anal. Prev. , 29(4), 417–430. Gallup Organization, 1995. Sleep in America. The Gallup Organization, Princeton, NJ. Gillberg, M., Kecklund, G., and Akerstedt, T., 1995. Sleepiness and performance of professional drivers in a truck simulator—comparisons between day and night driving. J. Sleep Res. , 5, 12– 15. Home, J.A. and Reyner, L.A., 1995. Sleep-related vehicle accidents. Br. J. , 310, 565–567. Lavie, P., 1986. Ultrashort sleep—waking schedule, III. “Gates” and “forbidden zones” for sleep. Electro-encephalogr. Clin. Neurophysiol. , 63, 414–425. Lavie, P., 1989. To nap, perchance to sleep—ultradian aspects of napping. In Dinges, D. and Broughton, R. (Eds.) Sleep and Alertness: Chronobiological, Behavioral and Medical Aspects of Napping . Raven: New York. Mackie, R.R. and Miller, J.C., 1978. Effects of hours of service, regularity of schedules, and cargo loading on truck and bus driver fatigue. Technical Report No. 1765. Human Factors Research, Inc., Santa Barbara, CA. Mackie, R.R. and Wylie, C.D., 1991. Countermeasures to loss of alertness in motor vehicle drivers: a taxonomy and evaluation. Proc. Hum. Factors Soc. 35th Annu. Meeting , 2, 1149–1153.
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Mackie, R.R., Wylie, C.D., Shultz, T, Engel, R., Townsend, M., Lammlein, S.E., and Johnson, S., 1989. Development of a recommended testing program for commercial motor vehicle operators: the CDL system. Essex Corporation, Santa Barbara, CA. Mitler, M.M., Miller, J.C., Lipsitz, J.J., Walsh, J.K., and Wylie, C.D., 1997. The sleep of long-haul truck drivers. New Engl. J. Med. , 337, 755–761. Mitler, M.M., Carskadon, M.A., Czeiler, C.A., Dement, W.C., Dinges, D.F., and Graeber, R.C., 1988. Catastrophes, sleep, and public policy: consensus report. Sleep , 11(1), 100–109. National Highway Traffic Safety Administration/National Center on Sleep Disorders Research Expert Panel on Driver Fatigue and Sleepiness, 1998. Drowsy driving and automobile crashes. Report No. DOT HS 808 707. (Washington, D.C.). NTSB (National Transportation Safety Board), 1990. Fatigue, alcohol, other drugs, and medical factors in fatal-to-the-driver heavy truck crashes. Safety Study NTSB/SS-90/01. Washington, D.C. NTSB (National Transportation Safety Board), 1995. Factors that affect fatigue in heavy truck accidents. Volume 1: analysis. Safety Study NTSB/SS-95/01. Washington, D.C. Rosekind, M.R., Neri, D.F., and Dinges, D.F., 1997. From laboratory to flightdeck: promoting operational alertness. Fatigue and Duty Time Limitations—an International Review . (London: The Royal Aeronautical Society), 7.1–7.14. Smiley, A. and Heslegrave, R., 1997. A 36-hour recovery period for truck drivers: synopsis of current scientific knowledge. Report No. TP 13035E. Transport Canada, Montreal. Transportation Research Board, 1987. Zero alcohol and other options: limits for truck and bus drivers. Washington, D.C. Transportation Research Institute, 1998. Potential hours-of-service regulations for commercial drivers: report of the Expert Panel on Review of the Federal Highway Administration Candidate Options for Hours of Service Regulations. University of Michigan, Ann Arbor. U.S. DOT, 1995. 1995. Truck and bus safety summit: report of proceedings. U.S. Department of Transportation, Washington, D.C. Williamson, A.M. and Feyer, A.-M., 2000. Moderate sleep deprivation produces impairments in cognitive and motor performance equivalent to legally prescribed levels of alcohol intoxication. Occup. Environ. Med. , 57, 649–655. Wylie, C.D., 2000. Hours of service, driver fatigue, and crash risk: an operations research model based on human factors data. Technical report prepared for Federal Motor Carrier Safety Administration. D. Wylie Associates, Santa Barbara, CA. Wylie, C.D. and Shultz, T, 1989. Model Driver’s Manual for Commercial Vehicle Driver Licensing . Alexandria, VA: Essex Corporation. Wylie, C.D., Mackie, R.R., and Smith, M.J., 1985. Comparative effects of 19 stressors on task performance: major results of the operator survey. Proc. Hum. Factors Soc. 29th Annu. Meeting , 1, 457–466. Wylie, C.D., Shultz, T, Miller, J.C., Mitler, M.M., and Mackie, R.R., 1996. Commercial motor vehicle driver fatigue and alertness study: project report. Federal Highway Administration Office of Motor Carrier Safety Report No. FHWA-MC-97–002. NTIS Accession No. MIC 10000009. Essex Corporation, Santa Barbara, CA.
18 Human Factors Issues in Motorcycle Collisions Peter A.Hancock University of Central Florida Tal Oron-Gilad University of Central Florida David R.Thom Collision and Injury Dynamics, Inc. 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
18.1 Introduction In the mind of the general public, riding a motorcycle involves certain inherent dangers. Riding differs from driving in some of its basic characteristics. For example, the motorcycle rider sits “outside” in the real world, not “cocooned” inside an enclosed space as with virtually all other road vehicles. In addition, motorcycles with a constant or increasing velocity (i.e., those not slowing down) will remain upright with no immediate control inputs from the rider. However, for some phases of operation, active balance is required. This contrasts with virtually all other road vehicles, which remain fundamentally stable, independent of the driver’s control actions. These nuances of motorcycle operation are poorly understood by most of the traveling public, who rarely ride powered vehicles with less than four wheels. Because of the large differences between motorcycles and regular enclosed vehicles, the rider faces a spectrum of environmental and collision hazards generally not encountered by most car drivers. At the same time, the motorcycle rider involved in collisions is usually less culpable than the other drivers involved. In consequence, there is a circular reinforcement in which unfamiliarity is aligned with the perception of danger that subsequently discourages ridership. Our knowledge of the relative fatality rates confirms that the perception of danger in ridership is not without substance. Many societal stereotypes and associations are made with motorcycle riding through a general cultural perspective. As with all such stereotypes, each is true and false to a greater or lesser degree. This confluence of circumstances has meant that the study of motorcycle riders and their specific issues has been greatly underserved, even within the transportation research community, which itself is poorly supported as an effort to battle society’s death and injury (Hancock and de Ridder, 2003; Evans, 1991; TRB, 1990). In this chapter, we seek to redress this
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imbalance somewhat by our focus on specific motorcycle issues and problems. This approach is selective because a full elaboration of all related issues would require a text of its own. Also, we have approached the respective problems primarily from a human factors perspective, which is one that, as well as stating problems, enjoins us to suggest solutions. 18.2 Organization of the Chapter In the first section of this chapter we seek to describe the scope of the problem of motorcycle-related crashes and examine some informative data on high fatality raterelated factors such as age, licensing, helmet usage, and alcohol consumption. In the second section, we examine motorcycle riders’ attitudes toward other road users and their contingent risk assessment. Because riding is different from driving, a spectrum of different demands is imposed on the motorcyclists. The motorcycle rider’s understandings of other vehicle drivers’ perceptual and attentional limitations are also important in establishing what riders anticipate to be more or less hazardous travel environments. The third section discusses the role of other drivers in violating the motorcyclist’s right of way and tries to elucidate the intrinsic human structural and functional limitations that lead to such driver errors. This exposition includes examining issues such as the conspicuity of the motorcycle, failure to estimate time to collision due to the physical appearance of the motorcycle, and failures related to the sustained performance nature of the driving task. The fourth section is concerned with human factors approaches to collision mitigation. These include a brief examination of means for implementing intelligent transportation systems (ITSs) for motorcyclists. The concluding section presents a summary of our observations, including a general checklist and reference listing of further works as well as a call for a systematic program of privately and federally funded research to serve this most at-risk community of road users. 18.3 Scope and Scale of the Problem In 1999, motorcycles made up less than 2% of all registered vehicles in the United States and accounted for only 0.4% of all vehicle miles traveled (NHTSA, Traffic Safety Facts, 2000). However, per vehicle mile traveled, motorcyclists were approximately 18 times as likely as passenger car occupants to die in a traffic crash and 3 times as likely to be injured. Similarly in Australia, motorcycles represent less than 1% of the traffic stream yet, per 100 million km traveled, motorcyclists were approximately 20 times as likely as passenger car occupants to be involved in a severe or fatal crash (Federal Office of Road Safety, 1997). Motorcycle fatalities in the U.S. have increased more than 50% over the past 5 years, as shown in Figure 18.1, and the percentage of motorcycle deaths in 2002 increased to 7.6% of all motor vehicle fatalities.
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FIGURE 18.1 Motorcyclists killed by year in the U.S. (From Fatality Analysis Reporting System, wwwfars.nhtsa.dot.gov, 2002.)
FIGURE 18.2 Percentages of motorcyclists killed in 2002 in the U.S. by type of event. (From Fatality Analysis Reporting System, wwwfars.nhtsa.dot.gov, 2002.) The distribution of motorcycle-collision typology is shown in Figure 18.2. Collisions between motorcycles and other motor vehicles account for approximately 50% of all fatal motorcycle crashes. Collisions with fixed objects account for another 28% and the rest of the fatalities are attributed to collisions with nonfixed objects or other factors (e.g., loss of stability). The initial point of impact in fatal crashes involving motorcycles and other motor vehicles was predominantly the front, which accounted for approximately 38% of the total number of fatal crashes (NHTSA, FARS, 2003). This collision configuration occurs, for example, when a left-turning vehicle violates the right of way of the
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motorcycle. These collisions are usually followed by the ejection of the rider from the motorcycle, leading to severe injury or death (see Peek-Asa and Kraus, 1996). Age and Gender Traditionally, casualty statistics showed that young motorcyclists (under 30 years of age) were more likely than older motorcyclists to be killed or seriously injured (Rutter and Quine, 1996). The high fatality rate among young motorcyclists has been frequently attributed to inexperience. However, Rutter and Quine (1996) found that it was the pattern of behavior associated with youthful individuals, such as risk-taking, that resulted in the high collision rate, not the level of experience per se. Because neither experience nor risk-taking behavior necessarily correlates with age, the factors can be separated. However, it must be remembered that risk taking and inexperience often do accompany youth; this argues for early training, especially focused on risk assessment, to improve rider safety. U.S. data available from the most recent 4-year period (NHTSA, FARS, 1999–2002) shows an interesting trend in motorcycle fatalities. Such fatalities increased radically for riders who were over 40 and the largest rate of increase in fatalities was among those over 50 (26% in 1 year). Fatality rate remained relatively high among young riders (under 30) but is now even higher among older riders (over 45), as shown in Figure 18.3. This trend should not be ignored and, indeed, older users’ limitations have become of great concern in the recent years for all vehicles (see Hakamies-Blomqvist, 1996). Such trends clearly indicate that more research is especially needed on older motorcycle riders. In general, as we grow older a whole spectrum of cognitive abilities declines (see Fozard et al, 1994; Birren and Schaie, 2001), as do muscle strength, coordination of force and grip, and general freedom of neck and limb movements (see Groeger, 2000). Although this is a general tendency, it need not necessarily be true about any single individual, especially one who is fit and active. However, it is clear that younger individuals can tolerate crashes of any specific severity more successfully than their older peers (Evans, 1988; 1991). These changes in fatality rates maybe reflective of the change in rider demographics because, with the price of some motorcycles, only those with significant disposable income can afford the larger machines. Interestingly, the definition of older users varies according to the vehicle used. Older drivers are categorized as beyond 65 years of age, but for motorcycle riders this threshold is at 40 years of age (see, for example, NHTSA, FARS, 2003). This may well reflect the traditional perception of the user population. With respect to gender differences, the collision statistics continue to confirm that motorcycle riding remains a predominantly male activity: 90% of motorcyclists killed in 2002 were male. Of the females who died in motorcycle crashes, 66% were passengers, while 99% of the males who died in motorcycle crashes were the controlling rider (NHTSA, FARS, 2003). Currently, the riding population is largely undefined due to lack of research in this area. However, evidently there are large demographic differences among the states contingent on demands, wealth, and weather. The denominator for all current motorcycle crash statistics is largely unknown. In 2000, the Motorcycle Safety Foundation and the National Highway Traffic Safety Administration (NHTSA) cosponsored the National Agenda for Motorcycle Safety (NAMS) (available at
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www.ahainc.com/nams). This document consists of a national committee of experts’ prioritized needs for motorcycle safety for the coming decade; one of its top recommendations was to study the population at risk as part of an extensive crash study (similar to the one conducted by Hurt and his colleagues in 1981 (Hurt et al., 1981).
FIGURE 18.3 Number of motorcyclists killed, by age group, by year in the U.S. (From Fatality Analysis Reporting System, wwwfars.nhtsa.dot.gov, 2002.) Alcohol Involvement Alcohol involvement remains a significant factor in single-vehicle motorcycle fatal crashes (Williams and Hoffman, 1979a); 41% of the motorcyclists who died in singlevehicle crashes in 2000 in the U.S. were intoxicated (NHTSA, FARS, 2003). In 2000 in the U.S., the percentage of alcohol involvement in fatal crashes for motorcyclists was approximately 50% higher than for drivers of passenger vehicles, as shown in Figure 18.4 (NHTSA, 2003). Motorcycle riders had the highest intoxication rates, with blood-alcohol concentration (BAC) of 0.10 g/dl or greater. Also, motorcycle riders killed at night were nearly four times as likely to be intoxicated as those killed during the day (43% vs. 12%, respectively) (NHTSA, FARS, 2003). Some calls to decrease the legal BAC level for motorcyclists to a level more consistent with riding coordination and balance requirements have recently been made (Sun et al., 1998). However, legislation might not be as effective in reducing crash severity and fatalities because of a generally low compliance rate. In an effort to explore these questions, NHTSA enlisted a group of researchers in the fields of alcohol and motorcycle safety. This group analyzed numerous ways of exploring the relationship among motor-
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FIGURE 18.4 Proportion of alcoholintoxicated (BAC=0.10+) motorcycle drivers and other drivers involved in fatal accidents in the U.S. (From NHTSA, Alcohol involvement in fatal crashes, 1998, 2001.) cycle riding, BAC, and impairment. These include field surveys, riding experiments, and simulator studies (Becker et al., 2003; NHTSA, 2004). Motorcycle Size and Rider Licensing Internationally, graduated motorcycle licenses restrict a novice or learner or a young rider to a relatively small motorcycle, typically 250 cc. In New Zealand, for example, Langley and colleagues (2000) found that even though about a third of novice riders and restricted license holders did not comply with this engine-size restriction, evidence did not indicate that these individuals were more likely to be involved in injurious or fatal crashes. Other graduated license systems found in the U.S. do not limit the size of the motorcycle, only the conditions and times of use. One problem with specifying limitations using engine displacement is that it does not necessarily reflect the actual performance of the motorcycle. It is possible that measures such as the ratio between power and weight could serve as better predictors of the involvement in high-risk crashes (Langley et al., 2000). However, the assumption that the ratio of power to weight is crash related has not yet been established. Current FARS data show larger motorcycles are increasingly involved in fatal crashes; however, the lack of exposure data limits any conclusion from being drawn. When studied in detail by Hurt and colleagues, larger-displacement motorcycles were actually under-represented in crash data (Hurt et al., 1981). Epidemiologically, it has been established that nearly one out of seven motorcycle riders involved in a fatal crash in 2000 in the U.S. was operating with an invalid license at the time of the collision
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(NHTSA, FARS, 2000). In 2002, 24% of all fatally injured motorcycle riders did not have valid licenses. Furthermore, in 2002 nearly 50% of the young motorcycle riders (15to 20-year-olds) in the U.S. involved in fatal crashes were unlicensed or driving with an invalid license (NHTSA, TSF, 2002). Thus, licensing per se is not likely to have a significant impact on crash reduction if the rule is not enforced. Helmet Usage and Passive Safety Head injury is the leading cause of death in motorcycle crashes (Branas and Knudsen, 2001; Hurt et al., 1981). European as well as American reports attribute great significance in reducing damage to the compulsory use of a helmet, which, in spite of the increase in the number of motorcycles, helps in preventing a parallel increase in fatalities and severe injuries—in particular, incidence of brain and head injuries (Gopalakrishna et al., 1998; Sarkar et al., 1995). Helmets are estimated to be 29% effective in preventing fatal injuries to motorcyclists, which means that 29% of the injured riders would have had a fatal injury without wearing the helmet (NHTSA, FARS, 2000). However, the current helmet design does not provide complete protection against injury. A combination of helmet and protective clothing creates a passive safety envelope. European authorities have set a goal to lower the number of fatalities from 45,000 in 1997 to 25,000 in 2010 within the European Community by enhancing such passive safety measures (ETSC, 1997). Helmet usage in the U.S. varies because it is not now compulsory in all U.S. states. In the recent past, several U.S. states have weakened their helmet laws and overall helmet use decreased after the laws were changed (NHTSA, 2001). Some sources claim that this is the cause of an increase in motorcycle fatalities (although not all studies provide conclusive agreement; see Branas and Knudsen, 2001). A major concern is in the increased cost (the financial burden) of fatalities and injuries that are directly related to unhelmeted riders (e.g., Rowland et al., 1996; Lawrence et al., 2002). 18.4 Motorcycle Collisions from the Inside Out The foregoing has framed the issues with which we now deal. We can approach the forensic issues of motorcycle human factors from two directions. The first is from the perspective of the motorcyclist, essentially from the inside out. The second is from the point of view of other road users, or from the outside in. Almost half of all motorcycle fatalities occur without involvement of other road users (FARS, 2002) and therefore understanding both directions is important. Motorcycle Riding Demands and Capacity (Workload) The Motorcycle Task Analysis Report (MSF/NPSRI, 1974) has analyzed the demands involved in riding and driving and has indicated clearly that significant differences exist, with motorcycle riding much more complex than driving a car (see Hancock, 1995). The relative degree of physical and cognitive workload, then, is one of the factors that distinguish motorcyclists from other drivers.
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Under ordinary driving situations, car and truck drivers have considerable spare attentional capacity, which they can allocate to other tasks. Modern engineering changes have caused cars and trucks to have reduced direct links between road geometry and driving performance. This is very much less the case with motorcycles. Motorcycle riders are by definition forced explicitly to adjust their driving speed and their body position to the demands of the driven road and the changes in the environmental context. Figure 18.5 illustrates these attentional workload differences between motorcyclists and car drivers. As shown in Figure 18.5(a), car-driving demands remain relatively constant throughout the drive unless there are unexpected circumstances. With the motorcycle rider, the contextual demands of the drive are highly correlated with riding demands, thus allowing fewer situations in which the intrinsic attentional capacity is not occupied by the riding. Distractions from this primary task of riding can then easily cause problems. Distraction can be caused by external influences such as high-density traffic, monitoring other displays, poor visibility, and adverse weather, or by internal sources of distraction such as personal concerns, anxiety, fatigue, lack of familiarity with the area, and route confusion. The lack of spare capacity of motorcycle riders is a major concern. As well as restricting adding additional displays to the motorcycle, the high level of chronic load means less attention can be paid to unusual or threatening conditions. This is a strong mandate for training so that riders can “get out in front” of the situation and anticipate rather than react to problems. One of the great problems of powered travel is that normal circumstances can rapidly change into
FIGURE 18.5 Attention capacity and driving demands for motorcycle drivers and other vehicle drivers. conditions requiring emergency response. As shown in Figure 18.5(b), driver and rider respond to emergencies by focusing all of their attention on the situation: the so-called “narrowing of attention” effect (see Hancock and Weaver, 2004). Unfortunately, the higher baseline of demand placed on the rider means that he encounters limitations earlier and more frequently than a driver does. One consequence is that forms of advance such
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as technical adaptive aiding will help the rider more than the driver. Many intelligent transportation systems (ITS) implementations should be made on motorcycles; however, as is evident, because of market forces, they are not. Adaptive aiding strategies, techniques, and interfaces for assistive technologies such as collision warning and collision avoidance would benefit most from facing the higher-level challenge that motorcycles impose. The primary mandate of all advanced vehicle technologies is improved safety, and the best method currently to achieve this is to augment the rider’s natural capabilities. Braking is the most commonly used avoidance response. However, in emergency situations, motorcyclists do not apply the front brake fully or at all and rely predominantly, if not solely, on the rear brake (see Hurt et al., 1981, 1984a; Thom et al., 1985; McLean et al., 1979). The failure to use the front brakes in emergency may be due to the difficulty in reaching the front control rapidly (Mortimer, 2002). Among others, Mortimer (2002) has advocated the use of integrated brake systems, in which the front and the rear brakes have a combined control. Studies have shown no greater tendency to lock the wheels and skid in the integrated brake mode than in the more traditional separated configuration. The current controls provided on most motorcycles require actual training and subsequent practice to use and are fundamentally different from the single automobile brake control. Separated vs. integrated control systems is a very important topic in the human factors aspects of motorcycle design. Several brands and models of motorcycles have been offered with interconnected brakes and/or automatic brake systems (ABS). The effect of such equipment has been discussed from the European perspective but, as yet, not in U.S. field studies (Ecker et al., 2001). Risks of Motorcycling The illusion of control is one behavioral bias likely to be relevant to the cause of many unexplained single-motorcycle crashes. The illusion of control leads to perceptions that “the more control I have, the less likely I am to suffer an adverse event.” The more familiar we are with some activity, the more routine it gets. The more routine it gets, the more confident we become. When one’s degree of competence is correctly assessed, the situation is the best one can expect. However, overconfidence leads to inattention and carelessness. At the same time, the general impression that motorcycle riders are risk takers simply because they choose to ride motorcycles is largely incorrect. Although motorcycles do have a unique appeal, there are many different forms of riding. Individual rider motivations must be considered to understand the spectrum of motorcycle activity. General risk statements about the whole of the motorcycle-riding population are simply inappropriate. Two fundamental motives for riding a motorcycle apply to all forms of transportation. The first is the extrinsic motive of getting from origin to destination. The second is an intrinsic motivation in respect to the form of transport. Although many individuals engage in driving a car for the purpose of pleasure, motorcycle riding is probably more engaged with intrinsic motivation than any other major form of ground transportation. Any statement about risk and motorcycle riding must take these two fundamental motives into consideration. Many motorcycle riders are motivated by the intrinsic appeal, while others are drawn to motorcycling simply because it is one of the most efficient forms of
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urban travel. Therefore, any statement about risk must be considered in light of previous rider choices and even circumstances that change daily, such as the weather. When riding the motorcycle is the motivation, risk taking is related to the envelope of the performance of the specific motorcycle (e.g., fast motorcycles can be ridden slowly). Those primarily motivated by riding a higher-performance machine may be interested in pushing the performance of themselves and the machine to their respective limits. Unfortunately, some individuals adopt this approach in everyday riding situations; for example, 50% of single-motorcycle crashes occur while the rider is negotiating a curve (NHTSA, 2002). This type of riding represents a danger to the rider and to surrounding road users as well. The vast majority of individual riders fall into the combined category in which the goal is explicit travel needs combined with the pleasure of motorcycle use. Often this is a communal activity in which the pleasure of the travel is enhanced by the presence of other individuals with similarly equipped machines. In such cases, the motivation toward risk taking and control of risk-taking behavior is a complex social property. Comparison of capabilities of different machines and different riders may well establish status within the group and create pressure to “push the envelope.” It is also important to note that risktaking behavior varies with age, gender, and experience. It may well be that excessive risk taking is unacceptable in groups of older riders, but may be the primary rationale for younger riders to get together. Unfortunately, little research has been conducted in this area and the issue remains unresolved. 18.5 Motorcycle Collisions from the Outside In To examine motorcycling from a driver’s perspective, consider a scenario in which a collision is imminent. The driver at the intersection is an older individual who has never ridden a motorcycle and never had a close friend or immediate family member who has. He is driving an early-model station wagon but with no obvious obstructions to vision. This driver is at an intersection waiting to turn left across traffic. He has not been waiting an inordinate interval and is not pressed for time. The motorcyclist is riding a newly acquired motorcycle without a fairing. It has active daytime running lights. The rider is experienced, having owned several previous motorcycles. Neither individual has ever had a major accident. It is noon and the intersection is in a suburban area but adjacent to a mini-mall and a gas station. The car driver waits for another car to pass and pulls directly across the pathway of the oncoming motorcyclist. Despite a last second attempt at avoidance, the motorcyclist strikes the front right side of the automobile and is pitched across the hood and onto the pavement beyond. The rider is wearing a helmet and protective clothing and escapes without significant injury. The motorcycle and the side of the car are severely damaged. The car driver sits in shock and later reports to the investigating officer that he never saw the motorcycle at any time (Hurt et al., 1981). This modal account could be modified to fit any number of actual incidents and consequently fosters the hope that common patterns of evidence can be derived from multiple accidents with similar antecedents. Unfortunately, as we penetrate deeper into this scenario, we begin to encounter the idiosyncratic—that is, individually unique—
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characteristics that begin to separate this event from others. The rider is actually in the process of bringing a brand-new vehicle home; this is only the second time that he has ridden it in traffic. The older driver is one of a very few individuals who have had lens replacement using dual-focus implants. The intersection had been resurfaced 2 weeks ago and painting of road markings has left multiple marks upon the surface. The driver had his grandchild’s puppy in the back of the vehicle and was returning from a visit to the veterinarian surgeon. All of a sudden, an apparently bland and generic account of a “typical” left-turn collision is clothed in the detail, which is only evident in real life. For scientists and researchers, it is overwhelmingly tempting to focus on the issues with which they are familiar and on the aspects of accidents that seem amenable to mitigation by established and familiar methods and techniques. In analyzing this accident, and indeed all accident configurations, the focus must be directed first to the human component—always considered in conjunction with the vehicle and the environmental circumstances. It is standard practice to elevate the configuration of collisions to primary consideration (e.g., rear-end, side-impact). However, when we reorient our approach to consider the human as the center of concern, we cannot forget that each individual is different. It is our hope and expectation that some common capabilities shared between all drivers and riders offer some answers to accident avoidance. However, we propose here that it may well be in the differences between individuals that at least part of the answer lies. Although we are used to seeing research on accident “black spots” and now accident “black times” (Folkard, 1997), and even “accident-prone” individuals, we have still not given enough recognition that the unique aspects of some people might involve them in a specific accident event at a specific time and place. The Left-Turn Problem A person-centered accident science is a long way off (Hancock, 2004). Therefore, on the path from the present to the future, consider a predominant motorcycle collision configuration. Left-turning vehicles have always been a problem for motorcyclists. The principal issue in this situation is the failure of the left-turning driver to see the approaching motorcycle and/or to judge adequately the time available to clear the intersection (Hancock et al., 1986; Hurt et al., 1984b; Williams and Hoffmann, 1979b; Wulf et al., 1989b). Such collisions frequently involve motorcycles because they have a small frontal surface area and therefore possess smaller stimulus strength than passenger cars or trucks. An additional aspect is the difficulty in determining the approaching speed of motorcycles. Failure to observe and recognize an oncoming motorcyclist can be divided into two general forms that can be characterized as structural and functional fallacies. In the year 2002 in the U.S., 35% of the motorcycle riders (459 fatalities) died in collisions when another vehicle violated their right of way by turning left while the motorcyclist was traveling straight, passing, or overtaking (NHTSA, 2003). Although alcohol intoxication has been implicated in many motorcycle fatalities (Preusser et al., 1995), for the ran-traffic-control and left-turn-oncoming-crash types of accidents, BAC had little involvement. The majority of collisions occurred between 12 p.m. and 8 p.m. in urban
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settings, mainly on dry pavement and when no adverse weather condition existed (Caird and Hancock, 2002; NHTSA, FARS, 2000). The influence of factors that cause drivers to interact with one another as a result of vehicle size is less clear. However, it is possible that motorcycles are perceived as less threatening because of their size and that this can cause smaller time-to-collision distances. Also, smaller cars and motorcycles are more likely to be hidden temporarily by trucks or large vehicles, which prevent greater sight distances from the driver of the car. Hurt et al. (1981) investigated personal or family motorcycle familiarity and found that individuals who have had riding experience are less liable to cause an accident with a motorcycle when they are the automobile driver than those unfamiliar with motorcycles. In postcollision interviews, the driver of the offending automobile most often claims not to have seen the motorcyclist prior to the collision. Although this might be due to postcrash shock and denial of responsibility, or at present unidentified other factors, it is possible that the collision may have been avoided had the driver been able to detect the motorcyclist earlier. In order to derive systematic and ultimately beneficial collision countermeasures, an understanding of the limitations of the information processing is an important foundation. Failure to observe and recognize oncoming motorcyclists can be divided into two general categories: structural and functional limits, described briefly next. “Structural limits” refers to the physical constituency of the sensory systems used to assimilate information. Here we consider only the limits to the visual systems, but the same principles apply to all other sensory modes. In the visual system, failure to detect a signal might be due to the masking that occurs from line-of-sight obstructions. A largescale study of motorcycle crashes by Hurt and his colleagues (1981) indicated that more than 30% of all accidents in which line-of-site information was available involved some form of physical obstruction between the automobile and the approaching motorcycle. A second form of structural limit is the simple failure to look at the direction of the motorcycle (Hancock et al., 1990). Given the normal range of the functional visual field, where peripheral vision is particularly sensitive to motion cues, such failures would seem unlikely; however, in stressful situations, an effective narrowing of the attentional field can occur (Hancock and Dirkin, 1983). Structural failure can also result from the intrinsic restriction or physical damage to the perceiver’s visual system. From the data available on collisions, the role of the foveal blind spot and scotomic failures cannot be immediately distinguished. However, results concerning the age of the offending drivers, where the groups of individuals 65+ are over-represented, argue for more thorough investigation of the structural limits to the visual system and more thorough testing for visual impairment (e.g., macular degradation). Motorcyclists present the smallest frontal surface area of any powered vehicle; thus, they probably represent the population at greatest risk from such intrinsic structural limitations. Functional limits also act to reduce the detection of the motorcyclist. Driving is a sustained attention task and is therefore fatiguing by its very nature. In the context of comprehension of the psychophysics of vigilance, two main factors influence detection efficiency: the physical characteristics of the signal and the temporal and spatial uncertainty associated with its appearance. Mackie and O’Hanlon (1977), among others, indicated that driving is the most common task that requires sustained attention. In vigilance studies, the primary factor influencing detection efficiency is the physical
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characteristics of the signal to be observed. Principal among these primary factors is signal conspicuity. Another critical factor in sustained attention is the event rate. In general, the lower the signal-to-noise ratio is, the poorer is the detection efficiency (Davies and Parasuraman, 1982); also, as the total number of events per unit time increases, the efficiency of the detection declines (Warm et al., 1976). Motorcycles in the U.S. are approximately 2% of the registered vehicles, but they represent only 0.4% of the traffic density (FARS, 2000). This low probability of appearance is compounded by the fact that, in traffic-congested urban areas, the high traffic volume ensures a high overall event rate. In natural driving conditions, the appearances of other vehicles are not simply neutral background events, so they require the attentional capacity from the driver. These observations suggest that the motorcycle rider is at particularly high risk. With respect to the driver, the number of locations from which a motorcyclist can appear is limited. In approximately 40% of collisions, the motorcycle comes from almost directly in front of the driver. This may suggest that the spatial location is of limited importance, but the temporal uncertainty of appearance becomes of particular concern. Temporal uncertainty is directly related to critical event rate, which is the relative frequency of motorcycles compared to other road users. As the occurrence of motorcycles in traffic becomes more infrequent, the response time to their appearance increases (Warm and Jerison, 1984). It is therefore appropriate that motorcycle safety organizations such as the National Association of State Motorcycle Safety Administrators (SMSA) are trying to promote motorcycle awareness via bumper stickers (see Figure 18.6). Peek-Asa and Kraus (1996) studied the specific injury outcomes of approaching-turn collisions. They differentiate between collisions in which the turning vehicle strikes the approaching vehicle and those in which the approaching vehicle strikes the turning vehicle. They also distinguish between two groups of cases: when the motorcycle is the left-turning vehicle and when the car is the left-turning vehicle, thus creating a 2×2 matrix, as shown in Figure 18.7. In approaching-turn collisions, the car was much more frequently the left-turning vehicle. When the car was turning left, the motorcycle was the striking vehicle in more than 70% of the left-turn collisions. When the motorcycle struck the car, the rider of the motorcycle was much more likely to lose control during collision avoidance. When the left-turning car struck the motorcycle, the motorcycle rider was less likely to be ejected than in any other crash configuration. Approaching-turn collisions in which the car was turning left caused more injuries than those in which the motorcycle was turning left. The average injury severity score (ISS) of a collision was 16.34 compared to 11.26 when the motorcycle turned left. Injuries were also more severe when the motorcycle struck the car (ISS 16.7) than when the motorcycle was struck by the car (ISS 14.5). Riders in approaching-turn collisions frequently suffer lower-extremity and abdominal injuries and have head, chest, and facial injuries less frequently. The average ISS, percent of fatally injured, average days in the hospital, and average number of injuries are greater for riders in left-turn collisions than for riders in other crash types (except head-on collisions). Excessive speed is more often documented in these types of crashes. This is a critical concern and may be incorrectly reported. Drivers of the violating vehicle often state that they never saw the motorcycle prior to the collision (Hurt et al., 1981).
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FIGURE 18.6 Increasing other drivers’ awareness of motorcycles.
FIGURE 18.7 The left-turn matrix. (Percentages taken from Peek-Asa, C.
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and Kraus, J.F., Accident Anal Prev., 28(5), 561–569, 1996.) “Time to contact” is a phrase that describes conditions in which a person estimates when a moving object will collide with another object in space. These objects may be animate or inanimate. Time-to-contact studies describe situations in which vehicles collide with each other as well as those in which vehicles collide with stationary objects. This area has been the subject of intense research in an effort to understand collision events (see Caird and Hancock, 1994; Carel, 1961; Cavallo and Laurent, 1988; Ellingstad and Heimstra, 1969; Gibson and Crooks, 1938; Groeger and Cavallo, 1991; Hoffmann and Mortimer, 1994; Kaiser and Mowafy, 1993; Knowles and Carel, 1958; Lee, 1976; Manser and Hancock, 1996; McLeod and Ross, 1983; Schiff and Arnone, 1995; Schiff and Detwiler, 1979; Schiff and Oldak, 1990; Schiff et al., 1992; Tresilian, 1991, 1999). A review of this phenomenon is available (Hancock and Manser, 1997) and the specific relationship between this capability and motorcycle-vehicle collisions has been addressed by Hancock and colleagues (1991a). Conspicuity and Perceiving Unfamiliar Vehicles Conspicuity can be defined as the degree to which an object is distinguishable against its background—that is, its visual prominence due to its physical characteristics. Wulf and colleagues (1989a) have listed numerous studies that have manipulated the characteristics of the motorcycle and its rider in attempts to enhance Conspicuity. Running headlights during daytime or wearing fluorescent garments have been shown to increase the detection rate of motorcyclists (Bothwell, 1971). During nighttime, additional running lights in varying patterns, as well as illuminated leg shields, have been found to make motorcycles somewhat more conspicuous. However, the validity of most methods used is rather questionable. There has been little compelling evidence that these measures actually increase detectability in real traffic situations (see also Wulf et al., 1989b). In their landmark study, Hurt and colleagues (1981) found that motorcycles with daytime running lights (DRLs) were under-represented in their crash sample. In a number of countries in Europe and also in several states in the U.S., DRLs for motorcycles are compulsory. In addition, several countries have mandated DRLs for all vehicles. Although the conspicuousness of the motorcycle maybe improved by using DRLs, it is possible that this improvement decreases if other vehicles use DRLs. Little research to support both claims has been conducted and the two most expanded studies in this area are now 10 years old (Elvik, 1993; Hansen, 1994). Bothwell (1971) has approached Conspicuity as a biological problem of survival. Motorcycles are “extensions” of the human body, and as they proliferate, they must evolve rapidly in order to be successful. Living creatures use two survival mechanisms in regard to detectability. The cryptic (hiding) creatures merge and camouflage themselves. These animals have evolved complex concealment methods to save themselves from their predators. Often these methods are based upon using color; the animals are camouflaged in order to blend in with their surroundings. This is exactly the opposite of what motorcycles need.
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The aposematic (warning) creatures have characteristics that indicate to potential predators that they are not for eating, or are dangerous or unpleasant; they use color and appearance as a warning that they are poisonous or harmful. Clearly, it is the latter group that motorcyclists need to emulate. A motor vehicle can be regarded as an aposematic creature—one to be avoided at all costs by other road users. Studies of car color for maximum detectability show that certain colors on average show up better against any background than others. Flame-orange is such a color and therefore should be used more often. As traffic density and speed increase, less time is available for identification, so color usage (or nonusage) becomes a more serious problem. The eye is limited in its capacity to sense color in motion. Tone contrast or brightness contrast between a vehicle and its background is the primary identification factor—particularly so in peripheral vision; thus, identification of an overtaking car and registering crossing vehicles at T-junctions are uses of this function. For example, in the fog, black, half-tone grays, and similar colors with tone value lower than the road will effectively “vanish,” so tone values lighter than the road are of greatest benefit. As someone has trenchantly noted, “A gray moving car becomes a half-tone gray metal coffin.” Two-tone colors may also simulate camouflage effects. A stimulus might impinge upon an individual’s senses but might not be recognized as relevant to the situation. Such failure related to stimulus identification can result in misidentification of a motorcycle or incorrect judgment of its speed. Although incorrect judgment of speed can occur for cars and for motorcycles, some evidence suggests that judgments of car speed are more accurate than judgments of motorcycle speed (Stroud et al., 1980; Wulf et al., 1989a). Furthermore, the gap sizes accepted for motorcycles have been found to be smaller for motorcycles than for automobiles or trucks (Hancock et al., 1991b). A number of studies have shown that illuminated highlights increase motorcycle conspicuity so that drivers are more likely to notice them, but there is little evidence that crash incidence has declined (Vredebburgh and Cohen, 1995; Cercarelli et al., 1992; Sparks et al., 1993, Williams and Hoffman, 1979b; Wulf et al., 1989a). Other suggestions to increase motorcycle and rider conspicuity include increasing the frontal surface of the motorcycle, bright clothing, and added elements to the motorcycle (William and Hoffman, 1979b; Hurt et al., 1981). Why are motorcycles overinvolved with other vehicles when the central issue is motion in depth? The total front surface area, that is, the physical size of the respective appearing vehicle, is substantially different for cars and motorcycles. At a common distance, the area they occlude may be similar (Eberts and MacMillan, 1985). The fundamental difference lies in the shape of the respective vehicles. According to strict ecological theory, the “time to contact” or, more precisely, the “time to passage” (Manser and Hancock, 1996) of the two vehicles should be coincident; from this basic perceptual capacity, we should see no differences in the collision rate if front surface area is exactly the same. However, we do not see this equivalence and motorcycles are far more likely to be turned across (see Hancock et al., 199la). Why is this? During daytime, the individual perceiving the motion in depth can see the morphology, or shape, of the oncoming vehicle. This shape is essentially square or rectangular for almost all passenger vehicles and this unitary dimensionality often connects to a manmade object. Indeed, as one goes about the world, it is evident that
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nature abhors straight lines, but human designers revel in them. Because of this characteristic, most vehicles are quickly recognized as human creations. In contrast, the motorcycle and its rider are represented as a fractal shape and, as such, are more likely to be perceptually “camouflaged” against a predominantly fractal background. The color manipulations used to promote conspicuity are a variant of this confluence. By presenting fluorescent orange and yellow that do not naturally occur, one seeks to elevate the salience of the object above its background. However, as Gilbert and Sullivan opine, “when everyone is somebody, then no one’s anybody”; efforts to improve conspicuity can backfire, such as when workers dressed in fluorescent orange garments stand against a fluorescent orange vehicle. Consequently, the fractal argument can be reversed in environments that exclude nature and emphasize manmade objects. The notion of conspicuity and the degree to which a vehicle resembles the background against which it is perceived have much face validity. Obviously, conspicuity is a complex issue, especially in time-varying dynamic environments such as those involved in driving. Well-meaning interventions might well be counterproductive and issues such as modular running lights should be implemented with caution. Some psychological manipulations of the physical characteristics of front profiles can increase perceived size but, again, increasing conspicuity for any other particular vehicle decreases the proportional conspicuity of all other objects in the perceived field of view. 18.6 Human Factors Approaches to Crash Mitigation Ground transport systems were historically developed almost entirely to accommodate trucks and passenger vehicles. In the past years, the needs of other vulnerable road users (pedestrians and cyclists) have been formally recognized and are gradually being incorporated into road and transport systems. This oversight is now changing. For example, the AASHTO Strategic Highway Safety Plan’s current phase 3 specifically addresses numerous operator-related factors. These include distracted and fatigued drivers as well as motorcycles specifically. The earlier phases of this project are available from the AASHTO web site (AASHTO, 2003). Historically, there has been virtually no recognition of motorcyclists as road users with special needs. Instead, motorcycle riders tend to have been subsumed under broader categories of motorists. Authorities have failed to recognize motorcycles as a separate and distinct class of road users. Part of the reason for this failure lies in the low exposure rate of motorcycles compared to other road users. Other reasons for under-representation of motorcycles in future transport system planning and, especially, advanced ITSs are perhaps partly related to technical difficulties in providing motorcyclists with additional information. Consequently, the impact of the implementation of ITSs on the future of motorcycle riding and motorcycle safety is a cause for great concern. The widespread application and development of ITSs gives little, if no, current acknowledgment to motorcycle riders. It appears that many transportation management centers (TMCs) have relatively little reference to motorcyclists. True, they are served as part of the general traveling public, but there has been essentially no plan for their unique user needs or capabilities. For
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example, if motorcycle access to the freeway system is not regulated, the traffic controller has little reason to view motorcycles as entities to be actively “managed.” This might be a seen as a potential advantage for motorcycle riders. In several large freeway ramp-regulated conurbations, motorcyclists have preferential access to highoccupancy vehicle (HOV) “diamond ramps” that provide immediate entry to the freeway system. Like drivers of carpools, buses, and emergency and law enforcement vehicles, motorcycle riders can enter the freeway system without waiting for ramp-metered access. In some jurisdictions, they can use HOV lanes. Consequently, in many current organizational structures, motorcycles are relatively “invisible” to the system. This has benefits as well as drawbacks. If motorcycles are a source of little concern, it is small wonder that vehicles like large trucks occupy a primary focus in TMC operations—especially because they are so visible and influential in the traffic stream. In some jurisdictions, motorcycles are able to “split traffic” and thus are less liable to be of concern in stalled traffic flow. This efficient traffic congestion benefit of motorcycles is illegal in many states, even though it has never been established as a safety problem (Hurt et al., 1981). Unfortunately, motorcycles do affect TMCs in the most critical condition of all—road traffic accidents—especially because motorcycles are often vulnerable to the unexpected maneuvers of other drivers. Thus, when it comes to collisions, motorcycles suddenly enlarge to become of equal concern to the TMC in coordinating emergency response and managing traffic flow around the incident. However, given the problems of access in congested traffic incidents, it may well be that motorcycles hold a unique potential as first responders to collision events. Already such unique capabilities are evident in the response of police officers on motorcycles, who frequently reach crash scenes first and can then take charge of on-scene coordination via ITS communication links. This role is especially important in urban areas that suffer from unique restrictions such as extended tunnels (e.g., Boston) or prolonged bridges (e.g., San Diego, San Francisco). This observation is particularly true for other parts of the world such as Europe, Japan, and some Latin American countries whose traffic problems and constraints on physical access exceed even those in the U.S. Because many motorcycle accidents involve only the single vehicle, one critical question concerns how modern machine-mounted technologies can help the injured or disabled rider. For example, if the motorcycle recorded a sudden stop or a horizontal position, or if information showed that the rider left the saddle in a non-normal manner, an emergency beacon could be activated. Activation of this emergency beacon could be tracked in central facilities such as the TMC (of the immediate future) or perhaps direct a GPS-specified link to emergency services. The warning beacon could also activate emergency systems onboard the motorcycle to attract the attention of individuals in the area. This form of communication is absolutely vital to the motorcyclist given the nature of many single-vehicle, run-off-the-road incidents. First indicated by Hancock (1995), this possible development was discussed in NAMS (2000). Although the majority of accidents occur in urban areas, the current majority of fatal accidents occur in rural areas. This may be in part due to the additional time taken for response in rural environments, which cuts directly into the “golden hour” of survival follow an accident. With emergency transponder beacons directly attached to GPS locator systems, the response time of emergency services in finding and rendering aid to injured
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motorcyclists should significantly improve the motorcyclists’ chances of survival. However, we do not need to think of motorcycles solely as the victim in accident conditions. Frequently, a motorcycle officer is the first to an accident scene, especially when such accidents result in severe congestion. Using the motorcycle’s unique capabilities in navigating very crowded roadways, the officer then becomes the point coordinator for response. With the digital capabilities envisaged in this system, the response coordination role is significantly enhanced, as is the ability to render immediate aid. 18.7 Summary and Conclusions Motorcycle collisions and the over-representation of riders in fatal collisions represent a significant problem in modern transportation. Like market-driven industries, however, governmental agencies seek to place their safety improvement resources in areas that have the greatest return for investment. Under this strategy, the motorcycle-riding segment of the traveling public is neglected purely because of numbers. In consequence, few specific technologies are developed for motorcycle use. Our solution to this conundrum is technology transfer from all ITS innovations and the dissemination of understanding that all collisions are human-centered events (Hancock, 2004). The general perception of motorcycles as dangerous vehicles remains contentious. It is clear from archival data that in motorcycle-vehicle collisions, the principal responsibility in more than 50% of the cases lies with other road users failing to recognize, adapt to, and avoid motorcyclists. After a collision has occurred, there is a further perception that injury from motorcycles is more severe than that from other vehicles involved in similar collision conditions. Here, again, an epidemiological fallacy raises its head. The flaw lies in the use of the term “similar conditions.” Unfortunately, collisions are highly nonlinear events; thus, we never get similar conditions sufficient to make generalizations about equivalent risk. It is the case that motorcycles are sufficiently qualitatively different from other powered road users that trying to compare crash events across automobiles and motorcycles is fundamentally misleading. Regardless of the denominator, the relative lack of occupant protection in motorcycles means more injuries and deaths. Consequently, the perceived risks of motorcycle riding are founded upon eclectic views of different segments of society. Such views of risk, for example, differ radically as to whether someone consistently rides a motorcycle or not. They also differ as to whether an individual has ever ridden a motorcycle or not. Individuals who have had riding experience are less liable to be involved in a collision with a motorcycle when they are the automobile driver. In essence, they become “tuned” to the potential of motorcycle appearance and behave accordingly. This is reflected in bumper stickers such as “look twice save a life—start seeing motorcycles.” Our efforts can be well directed at riders so that they also can understand sources of risk. Accurate perceptions of the potential risks imposed by offending vehicle drivers (e.g., the left-turning driver) are a vital component of the rider’s defense. How to tune such perceptions might be as important in safety as high-level movement skills. Some have argued that skill-based models of rider behavior cannot account for collision likelihood and risk taking. We claim that skilled behavior is valuable in collision
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avoidance and should be encouraged. Thus, high-level training, especially in avoidance maneuvers, is a valuable endeavor. However, it is clear that much more work is needed on this issue. Although some have examined the efficacy of rider-training programs, the use of skills in highly unusual situations and in imminent collision avoidance is certainly a topic that needs to be a strong research focus (Hancock and de Ridder, 2003). This is especially true in light of contemporary efforts to develop artificial, technology-based collision-avoidance systems (see Hancock, 1993). The future of our road transportation systems is uncertain. In North America, it has been evident since the final decades of the 20th century that we cannot simply “build” ourselves out of the problem. In virtually every major global conurbation, we have simply run out of space to do so. The offering of the technology community was to use advanced computational systems, located on the vehicle and in remote management centers, to use the existing space much more efficiently. The promise of ITSs is in part real because there are opportunities to make much better use of existing roadways. Also, an important effort has been made to explore alternative transportation options (such as light rail and personal rapid transit [PRT]), although these encounter significant political opposition from those entrenched in the current automobile industry. In all this, the motorcyclist has largely been passed over. Few have bothered to comment on how motorcycles occupy much less space and could therefore be a much more efficient transport medium in congested spaces. Motorcycles are only evident when they emerge, problematically, in crash statistics and on the road, where such collisions cause significant disruptions to traffic flow and upset the careful computer models of transit time. Initially, ITSs promised to improve safety significantly by reducing vehicle-collision frequency. That promise has yet to be fulfilled, although it is still in its early days in terms of implementation. Eventually, all countries relying on such powered transportation will run out of space altogether. At some point, ever-larger vehicles cannot be packed onto finite freeway space. On the present trajectory, an “auto-freeze” or a state of global gridlock will be reached. It is here that motorcycles may come to the fore. If we can improve perception and reality of their safety, motorcycles can represent a viable personal rapid transit alternative. To accomplish this farsighted aim, we need to invest now in motorcycle ITS systems and in thorough understanding of motorcycle-collision events. Part of this endeavor must come from the forensic and legal community. 18.8 Checklist • Riders • Age, licensing, helmet usage, and alcohol consumption • Brakes and brake control (separated vs. integrated control systems) • Collision mitigation • Distraction • Intelligent transportation systems • Riding demands and workload • Rider’s attitude and risk taking • Training issues
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• Other vehicle drivers • Blind spot and scotomic failures • Conspicuity of the motorcycle • Failure to estimate time to collision • Functional limitations that lead to driver errors • Intersection • Right-of-way violations • Structural limitations that lead to driver errors • Sustained attention and event rate • The left turn • Time to contact
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Ouellet, J.V. (1990). Appropriate and inappropriate strategies for injury reduction in motorcycle. Society of Automotive Engineers Congress, SAE Paper 900747. Peek-Asa, C. and Kraus, J.F. (1996). Injuries sustained by motorcycle riders in the approaching turn crash configuration. Accident Anal. Prev. , 28(5), 561–569. Preusser, D.F., Williams, A.F., and Ulmer, R.G. (1995). Analysis of fatal motorcycle crashes: crash typing. Accident Anal Prev. , 27(6), 845–851. Rowland, J., Rivara, E., Salzberg, P., Soderberg, R., Maier, R., and Koepsell, T. (1996). Motorcycle helmet use and injury outcome and hospitalization costs from crashes in Washington State. Am. J. Public Health , 86, 41–45. Rutter, D. and Quine, L. (1996). Age and experience in motorcycling safety. Accident Anal. Prev. , 28, 15–21. Sarkar, S., Peek-Asa, C., and Kraus, J.F. (1995). Fatal injuries in motorcycle riders according to helmet use. J. Trauma , 38(2), 242–245 Schiff, W. and Arnone, W. (1995). Perceiving and driving: where parallel roads meet. In P.A.Hancock, J.M.Flach, J.K.Caird, and K.J.Vicente (Eds.), Local Applications to the Ecology of Human-Machine Systems . Hillsdale, NJ: Erlbaum, 1–36. Schiff, W. and Detwiler, M. (1979). Information used in judging impending collisions. Perception , 8, 647–658. Schiff, W. and Oldak, R. (1990). Accuracy of judging time to arrival: effects of modularity, trajectory and sex. J. Exp. Psychol: Hum. Percept. Performance , 16, 303–316. Schiff, W, Oldak, R., and Shah, V. (1992). Aging persons’ estimates of vehicular motion. Psychol. Aging , 7, 518–525. Sparks, G.A., Neudorf, R.D., Smith, A.E., Wapman, K.R., and Zador, P.L. (1993). The effect of daytime running lights on crashes between two vehicles in Saskatchewan: a study of a government fleet. Accident Analysis and Prevention , 25, 619–625. Stroud, P.G., Kirkby, C., and Fulton, E.J. (1980). Motorcycle conspicuity. Proc. Intl. Motorcycle Conf. , Motorcycle Safety Foundation, IV, 1705–1722. Sun, S.W, Kahn D.M., and Swan, K.G. (1998). Lowering the legal blood alcohol level for motorcyclists, Accident Anal Prev. , 30(1), 133–136. Thom, D.R., Arao, H.G., and Hancock, P.A. (1985). Hand position and motorcycle front brake response time. Proc. Hum. Factors Soc. , 29, 278–281. TRB (Transportation Research Board). (1990). Safety research for a changing highway environment. Special report #229, National Research Council, Washington, D.C. Tresilian, J.R. (1999). An analysis of recent empirical challenges to an account of time-to-collision perception. Percept. Psychophys. , 61, 515–528. Tresilian, J. (1991). Empirical and theoretical issues in the perception of time to contact. J. Exp. Psychol.: Hum. Percept. Performance , 17, 865–876. Vredebburgh, A.G. and Cohen, H.H. (1995). Enhanced motorcycle visibility through use of motorcycle conspicuity enhancement system. Proc. Hum. Factors Ergonomics Soc. , 39, 1048– 1052. Warm, J.S. and Jerison, H.J. (1984). The psychophysics of vigilance. In J.S.Warm (Ed.), Sustained Attention in Human Performance (15–60). Chichester: Wiley. Warm, J.S., Wait, R.G., and Loeb, M. (1976). Head restraint enhances visual monitoring performance. Percept. Psychophys. , 20, 299–304. Williams, M.J. and Hoffmann, E.R. (1979a). Alcohol use and motorcycle accidents. Accident Anal. Prev. , 11(3), 199–207. Williams, M.J. and Hoffmann, E.R. (1979b). Motorcycle conspicuity and traffic accidents. Accident Anal. Prev. , 11(3), 209–224. Winsum. V.W. (1996). From adaptive control to adaptive driver behaviour. The Traffic Research Centre VSC, Groningen.
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Wulf, G., Hancock, P.A., and Rahimi, M. (1989a). Motorcycle conspicuity: an evaluation and synthesis of influential factors. J. Safety Res. , 20, 153–176. Wulf, G., Hancock, P.A., and Rahimi, M. (1989b). Some causes of automobile—motorcycle collisions. Proc. Hum. Factors Soc. , 33, 910–914.
IV Physical and Cognitive Factors
19 Perceptual-Cognitive and Biomechanical Factors in Pedestrian Falls H.Harvey Cohen Error Analysis, Inc. Cindy A.LaRue Error Analysis, Inc. 0–415–28870–3/05/$0.00+$ 1.50 © 2005 by CRC Press
19.1 Introduction: Human Factors Principles and Relevance to Standard of Care Walking seems like such a simple, natural task that the body performs nearly without thinking. However, this is far from the truth. Breaking down biomechanical processes has shown that walking is actually a series of imbalances. Studies of perceptual and cognitive issues show pedestrians gather information about the walking environment using the processes of the human information model. These processes interact and determine how the individual gets from one point to another in a given environment. In general, pedestrians believe that walking surfaces are flat and uniform, unless they notice a particular discrepancy. Any unnoticed or unexpected variation in the pedestrian’s path can easily lead to a fall and potential injury. Oftentimes, the injury is severe enough to warrant filing a lawsuit to try to recover damages from a party deemed responsible for the dangerous condition. In this case, a human factors/ ergonomic (HF/E) professional can be used to render an opinion as to whether a situation is unsafe and, if so, if it led to the incident in question. When determining the cause of a pedestrian fall, the HF/E professional looks at many human factors issues, including perception, reaction, expectation, visual cues, distractions, attention, motor skills, abilities, limitations, and decision-making. The expert formulates his opinion based on the facts of the case and any applicable law or standard and then must support this theory in a court of law. At issue generally is whether the party responsible for the premises on which the fall occurred met the standard of care. In most cases, this requires the owner/manager of the property to use a level of care of a prudent adult in order to prevent an unreasonable risk of harm. It is up to the HF/E forensic professional to determine if this standard was met.
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19.2 Objective and Scope The objective of this chapter is to discuss the perceptual-cognitive and biomechanical factors involved in pedestrian falls. This chapter also describes the role of forensic HF/E professionals and how they use their scientific background in order to formulate expert opinion. 19.3 Discussion of Principal Issues A discussion of pedestrian falls must begin with an understanding of how people walk and what they notice about the environment in which they are walking. In order to discuss the principal issues involved in pedestrian fall incidents, it is important first to discuss the biomechanical processes involved in human locomotion. Biomechanics of Walking Walking across a flat surface would seem to be one of the least complicated activities performed by a human being on a daily basis. It is generally an almost mindless task requiring little, if any extraneous thought. Obstacles such as steps, curbs, doorways, or ramps receive a rudimentary glance and, although they do register in the brain, require little formal adjustment by the body. On closer examination of walking, the biomechanical and physical parameters of human locomotion present a very different picture. From a biomechanical viewpoint, walking can be seen as a complicated process consisting of a series of continuous losses and recoveries of balance. Center of Gravity On level ground, walking can be considered as the forward translation of the body’s center of mass. The center of mass, also called the center of gravity (COG), is a theoretical point that acts as if the entire mass of an object were concentrated at that point. The location of the COG in relation to the base of the object determines the object’s stability. On a human body, the feet are the supports that create the base area under the body. The size of the base area depends on how far apart the feet are located; the larger the base area is, the more stable the person is. When one is walking, the body is constantly adjusting in order to keep the COG over the base area, thus ensuring stability. If the COG leaves the base area, the body shifts, attempting to re-establish equilibrium. If equilibrium cannot be re-established, a fall results. When upright, the COG of the human adult body is located within the body at the level of the second sacral vertebra, about 2 in. (5 cm) behind the imaginary line joining the hip joints, in the midline of the body. For a male, this is about 55% of the distance from the feet to the top of the head, at about belt level. For women, it is just above belt level, about 57% of the distance from feet to head. The exact COG location varies
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according to body type and age and moves up, down, or sideways in the course of movement and position changes. The accumulation of fat and loss of soft tissue tone are the most common reasons for the altering of the COG; tissue accumulating above the waist raises the COG, while accumulations below the belt lower it.
FIGURE 19.1 Gait cycle. The Gait Cycle The normal walking cycle comprises two phases: stance phase, when the foot is in contact with the ground, and swing phase, when the foot is moving forward through the air. The stance phase makes up approximately 60% of the walking cycle. This phase is divided into three distinct parts: heel-strike; foot flat (support); and push-off. The swing phase, which begins with the push-off and ends with the heelstrike, makes up the remaining 40% of the gait cycle. Figure 19.1 illustrates the up-down displacement of the COG during walking. As shown, each individual step begins with the trailing foot supporting all the weight. Momentum and a push from the supporting foot cause the trunk of the body to move forward. This brings the COG past the forward edge of the supporting leg. Because the COG is now outside the base area, stability is decreasing. Additionally, gravity is now acting on the body, pulling it forward and down. The free leg swings forward and is placed on the ground. The two legs now supply a much wider base area, thereby putting the COG back inside the base of support. This restores stability to the body and saves it from a forward fall. The legs alternate in their function, each in turn pushing the COG out of the support base and then swinging forward to restore it (Rasch and Burke, 1978). Between the two steps, at heel-strike, at the moment at which the weight is transferred from one foot to the other, the support base is bounded by the toes on the posterior foot and the edge of the heel on the anterior foot. This is the point of greatest instability, even though the feet are at maximum separation, creating a very large support base. The instability is due to the extremely small contact area between the supports and the floor (the toes of the back foot and the edge of the heel of the leading foot) and also the angle that they create with the floor. The majority of slip and fall incidents occur at this point.
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Forces of Movement In order for there to be motion of the body, an external force or forces must act through the body’s COG. For a person standing upright, the only forces acting on the body are weight pushing down on the ground and the force of the ground pushing up on the body (Newton’s third law of motion). This upward force is called the ground reaction force (GRF). Because the body does not move up and down, the sum of the two forces acting on the body must be equal to zero. Because the forces act in opposite directions, they must be equal and opposite. If the forces acting through the COG were unequal, then motion would result. The weight of the body does not change, so the only way to achieve motion in the vertical plane is to vary the GRF. This results in an external force on the body that is greater than zero, causing motion. Although the GRF is the force that causes movement, it can only oppose a force applied to it. To change the GRF, the direction of application or its magnitude must change. If the GRF points straight up, opposing the weight of the body, it must be greater than the weight to cause upward motion. If the GRF is less than the weight and still points straight up, the body will move down. Directional motion, away from the vertical, results when the GRF is applied at an angle. In order to move forward, backward, or sideways, the body must be able to create a force for the GRF to oppose. To move forward, it must push back against the ground and create the opposing GRF that will push the body forward. If the foot does not slip, Newton’s third law of motion would predict that the foot will experience a force equal and opposite to the force it is applying, resulting in forward motion (Watkins, 1983). In order for the foot not to slip at push-off and heel-strike, something must hold it against the ground as the force is applied. The frictional force creates a fixed point against which the body can push. Without the frictional force between the foot and the floor, the foot would slide over the floor and not be able to create a force (push) against the ground. Without a force against the ground, there would be no opposing GRF and no directional movement would be possible. It would still be possible to have movement in the vertical plane (i.e., a jump), but unless an external force were applied to the body while it was in the air, the COG would remain over the same spot on the floor. During the gait cycle, lack of frictional force causes the pedestrian to slip and, potentially, fall. At push-off, momentum and gravity are pulling the body forward as the COG moves in front of the support base. The trailing leg pushes off to begin the swing phase in an attempt to restore the support base under the COG. If the frictional force is insufficient to allow the foot to push off, the rear foot slips backward. However, the COG continues forward, usually resulting in a forward fall or stumble. At the other end of the gait cycle is heel-strike. The instability at this point is due to the very small contact area between the edge of the heel and the floor and the strike angle. At this point, the COG has already been restored to its position over the support base, and insufficient frictional force at heel-strike results in a split-like slip and fall, or a backward fall as the body tries to compensate for the slide. Combining all these factors, walking is accomplished by alternate pushes from the legs backward against the ground. Assuming that frictional force is sufficient to hold the foot firmly against the ground, these pushes create the GRF, which pushes back against the legs, causing forward motion. For any translational motion, the body must be able to create a force for the GRF to oppose; this oppositional force creates the motion. The
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vertical forces (GRFs) are greatest just after heel-strike, when the body weight is loaded onto the leading foot, and again at push-off of the trailing foot. Between these two maxima is a force minimum, when the COG is at its highest point in the cycle and is directly over the supporting foot. The magnitude of the forces exerted by the foot depends primarily on body weight, step speed, and the speed of direction of movement of the COG. Energy of Walking The body tries to minimize energy expenditure of all its tasks, and human locomotion is no exception. For walking, this means minimizing the displacement of the COG. Rasch and Burke (1978) describe the body as having adapted five separate but coordinated mechanisms to flatten the curves in the vertical and horizontal planes, therefore minimizint the expenditure of energy: • Pelvic rotation. During walking, a theoretical line connecting the right and left hip bones swings counterclockwise and clockwise around its center point as the right and left feet are planted. This ability to rotate through the pelvis greatly reduces the vertical displacement of the COG. • Pelvic tilt. During normal walking, the pelvis tilts forward and down approximately 5° on the side of the non-weight-bearing leg. This tilt minimizes the amount of vertical displacement of the COG during the swing phase of the gait cycle. • Knee flexion. The knee of the support leg is bent (flexed) approximately 15° at the time at which the COG passes over it. This flexion prevents the COG from the need to rise. If the knee were locked, the COG would rise substantially during the stance phase. • Foot and knee mechanisms. At heel-strike, the foot is flexed up and the knee joint is fully extended. At this time, the COG is at its lowest point. As the body weight passes onto the forefoot and the heel is raised, the knee flexes so that the COG does not need to rise excessively. • Lateral displacement of the pelvis and shoulder. The hips and shoulders move up and down in the vertical plane; in other words, they do not remain level throughout the gait. The movement of the shoulders opposes the movement of the hips, which causes the COG to oscillate slightly from right to left. These five mechanisms maximize the efficiency of the body during walking and minimize the movement of the COG. This results in the least possible energy expenditure by the body. This conservation is demonstrated when one compares the ease with which one walks to the effort required to run a similar distance. Age has an effect on the energy of locomotion. At about age 65, walking appears to become more restrained. Studies in older adults show significant reduction in walking speed, a proportionately longer stance phase, and a shorter swing phase. This effectively shortens the stride length, which decreases the angle at heel-strike and decreases the potential for the foot to slip. In addition, older people of both sexes do not lift their feet as high during the swing phase, which reduces the amplitude of the oscillations of nearly all body parts, thereby maximizing energy conservation (Rasch and Burke, 1978). It does increase the likelihood of a trip, however, because even small displacements have the
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potential to interrupt the swing phase. In fact, the majority of locomotion falls among the elderly are initiated by a trip. To conclude this section, it should be pointed out that walking is a much more complicated activity than previously imagined and is controlled by numerous physiological functions less obvious than simply moving the legs. Although many assume that walking is primarily a voluntary activity, in actuality most of the stability regulators are designed into the body in joints and muscles. Even in cases of age, infirmity, or abnormal physiology, the body works to minimize extraneous motion and thereby conserve energy. Throughout the gait cycle, the moments of least stability present the greatest potential for mishap. At heel-strike and push-off, the forces acting against the ground are at their maxima, and almost all slip-and-fall incidents occur at these two points. Insufficient frictional forces between the foot and the ground cause falls at both of these points of the walking cycle. If the foot is unable to plant at heel-strike or push-off, no opposing GRF can be present to brake the motion of the body (in heel-strike) or to push the body forward (in push-off). Information-Processing Model In order to discuss the role of perception and cognition in walking and pedestrian falls fully, the manner in which humans process the information they encounter when walking must also be covered. The steps taken by humans to process information about their relationship to the walking environment have been an active area of human factors research. As humans walk, they are constantly processing information regarding their perception of the walking environment and their interaction with it. Figure 19.2 presents a model of the information-processing system that depicts the major components of human information processing (Sanders and McCormick, 1996). These components are sensory processing, perception, memory, decision-making, attention, and response execution. Sensory Processing The first step for humans to process information is for the body to receive a stimulus. Of primary importance to pedestrians are the visual sense of the eyes, the tactile sense of the feet, and the kinesthetic senses of the body and limb position. Limitations on each sensory system can influence the quality and quantity of information that maybe registered initially and, potentially, all processes that follow. Detection of certain stimuli by a pedestrian may prevent a fall incident from occuring. Perception There are different levels of perception, with simple detection the most basic type. Detection is simply determining the presence of a target. Beyond simply detecting the presence of an object, perception involves identification and recognition of the object, which require the person to identify the class in which an item belongs. Perception of an
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object depends on the individual’s prior experiences, memory, and associations that have been learned over time.
FIGURE 19.2 Information-processing model. Perception is one very important component of the study of fall incidents. Upon an initial visual scan of the area to be traversed, a pedestrian must be able to perceive a potentially hazardous condition in order to avoid contacting it. If a condition exists that makes it difficult to detect a hazard, the possibility of the pedestrian coming into contact with the hazard is greater. These conditions can include obstructions, confusing patterns, and other lack of sensory cues (predominantly visual) delineating the hazard. The typical pedestrian can see objects ahead and, to a lesser extent, to the sides. The cone of optimum viewing extends about 8 to 10 ft in front of the pedestrian. Objects that are off to the side or closer than 8 ft must be detected by peripheral vision. This usually requires the objects to have high color or pattern contrast, movement, or lighting in order to increase the chance of detection. Memory Memory comprises three components: sensory storage, working memory, and long-term memory. Sensory storage is the temporary storage mechanism for a stimulus. The sensory system associated with the visual system is known as iconic storage. The iconic storage holds an image for a short time, allowing further processing of the image. In order for it to be retained, the information must be encoded and transferred into working memory. In order to transfer the information from sensory storage to working memory, a person must direct his attention to the process. Information is transferred to long-term memory by supplying meaning to the information and relating it to information already stored in
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long-term memory (semantically coding). To recall this information, it must be analyzed, compared, and related to past knowledge. The more organized the information is, the easier it is to transfer to long-term memory and the easier it is to retrieve. Decision-Making The key component in the information-processing model is the decision-making, which is a complex process in which individuals evaluate alternatives and select a course of action. The process involves seeking information relevant to the pressing decision, estimating probabilities of various outcomes, and attaching values to the expected outcomes. The decision-making process is limited by biases as well as the human capacity to process and evaluate information in order to arrive at an optimum decision. For example, once a pedestrian perceives (or remembers) a condition that he considers hazardous, he then has the option of deciding to select an alternate route or continuing the path while cautiously traversing the hazardous condition. The concept of uncertainty affects the decision-making process. As the number of choices increases, the required decision time and potential for error increase. In general, expectedness is a combination of certainty and experience. Therefore, if a pedestrian is uncertain about a particular walking area, has not perceived a hazard, and has no experience walking in that area, any hazard would be unexpected. Experience with a particular walking surface has three advantages: • It is easier to perceive certain important signs of impending hazard. • A greater number of possible evasive actions are stored in memory. • Understanding of probabilities and outcomes is better. Attention At the very top of the model is the pool of attention resources. Because the other processes (perception, decision-making, working memory, and response execution) draw from this pool, if some of these processes require more from it, less is available for the other processes, whose performance will deteriorate. Practice and learning will decrease the demand for the limited supply of resources from the pool. The four categories of attention are: • Selective: monitoring several sources of information to perform a single task • Focused: maintaining attention on one channel of information and ignoring the other sources • Divided: performing two or more separate tasks simultaneously and attention must be paid to both • Sustained: maintaining attention over prolonged periods of time in order to detect an infrequently occurring signal In order to avoid a fall, adequate and appropriate attention must be paid by the pedestrian to the walking path. If his attention is significantly diverted to other factors in the environment, the pedestrian may not perceive or remember the hazard and a fall may occur.
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Response Execution After receiving and processing information, people use it to make responses, which can be in the form of motor responses executed by a person to achieve a goal. The motor responses can be influenced by internal and external information and can range from nearly automatic reflexes to which little to no conscious thought is given to voluntary responses in which all steps are consciously executed. In the model, the actual motor response, as influenced by internal and external information, is compared to some desired goal or set point. An error is considered any difference between the goal and the actual response. If sensory information is available during or after the motor response, it is referred to as feedback and can potentially be used to modify subsequent behavior. The Forensic Process in Pedestrian Fall Incidents The HF/E practitioner analyzes situations involved in litigation and offers opinions that may support or refute the legal theories pursued. Legal proceedings are an adversarial process in which lawyers represent opposing parties; in civil cases, they typically represent the plaintiff (injured party) or defendant (the alleged injuring party). The role of the forensic HF/E expert is to offer opinions in his field beyond the knowledge of the ordinary people comprising a jury. The process typically follows the process outlined in Figure 19.3: consultation with client, review of information, inspection of premises, research, formation of opinion, and expression of opinion (Cohen and LaRue, 2000). Consultation with Client The initial step in the forensic consulting process is discussion with the potential client, who usually is an attorney or insurance company representative. In this conversation, the client provides a description of the case and the issues involved. The forensic professional can confirm that the issues in the case are ones that fall within his area of expertise. The client will want to confirm that the expert has appropriate experience and is qualified to offer opinions with respect to the issues in the case. An agreement on fees is generally signed at this stage.
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FIGURE 19.3 Chart of forensic steps. Review of Information Similar to any other scientific endeavor, the first true step is to review the existing information, which in the legal community is referred to as discovery. It is important for the forensic HF/E professional to review all pertinent discovery in order to understand the relevant background facts of the case. In a typical lawsuit, a variety of information is available regarding the plaintiff in the form of incident reports, statements, and medical records, as well as written and oral answers to legal questions in the form of interrogatories and depositions, respectively. Other important sources of information are witnesses to the incident, if any. Inspection of Site After reviewing the facts of the case, the HF/E professional will conduct an inspection of the location where the incident took place. Unless the site has been dramatically altered or destroyed, an inspection is necessary to gather as much firsthand data as possible. At this inspection, photographs and/or video documenting the scene should be undertaken. It is also important to measure dimensions and conduct testing appropriate to the type of incident. If a fall incident involves a stairway, then measurements regarding the width,
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stair geometry (tread depths, riser heights, and nosings), and handrails must be gathered. Coefficient of friction (COF) tests are used to measure the slipperiness of a surface for slip cases. Other tests at the site can include illumination testing and slope measurements (Cohen and LaRue, 2002). Research and Formulation of Opinion It is generally beneficial to conduct research prior to developing a forensic HF/E opinion on a case. Research for pedestrian falls can include scientific literature, building codes, industry standards, profes-sional design guidelines, or even comparing how similar facilities have handled the design, construction, or maintenance issues at question. The forensic HF/E professional integrates all the information gathered from the discovery, inspection, and research with his knowledge and experience to form an opinion. The expert’s opinions are strengthened when he can provide a sound authority as the basis for the opinion. The types of bases generally used and the strength of each are discussed below. Expression of Opinion The field of forensic HF/E requires the practitioner to analyze situations involved in litigation and offer opinions regarding the HF/E principles involved. After the expert has formulated his opinions based on relevant case information, inspections, and research, an opinion may be rendered by several methods: reports, deposition, and testimony. An oral or written report is generally prepared for the client. The initial verbal report to the client should outline strengths and weaknesses of the case. It is important that both sides of the case are presented so that the client is aware of weaknesses to the case arguments. At this point, the client can decide if he is interested in pursuing the case further and the HF/E professional can determine if he wishes to be named as an expert in the case. A written report generally contains the results of the site inspection along with the opinions of the HF/E expert. A deposition is a formal question-and-answer period, with the same weight as courtroom testimony, in which the opposing attorney has the opportunity to question the designated expert witness under oath. The topics covered at the deposition usually focus on the expert’s qualifications (education and experience), his opinions regarding the case, and the bases for the opinions. The entire proceedings are typed by a court reporter and put into booklet form where they become part of the case discovery. If a case does not settle earlier in the legal process, it culminates with a trial before a judge and usually a jury (in the U.S.). At the trial, the expert witness will be sworn in and questioned by the retaining attorney (direct examination) and the attorney for the opposing side (cross-examination). The cross-examination is usually an attempt by the opposing attorney to impeach unfavorable testimony. Such questioning may be followed by redirect and recross, during which the attorneys are permitted to ask any desired clarifications to prior questions.
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Basis for Human Factors Opinions The forensic HF/E professional will integrate the information gathered from the discovery material, inspection of the site, and applicable research with his knowledge and experience to formulate an opinion regarding causation of the fall and subsequent injuries. The expert’s opinion is strengthened when he can provide a sound authority as the basis of the opinion. These opinions may be based upon a variety of authorities, some providing stronger support than others. These bases are illustrated in a hierarchical manner in Figure 19.4, according to their strength and relative ease with which they can be supported (Cohen and LaRue, 1997). Codes and Laws Codes and laws are legal requirements governing a particular jurisdiction. This basis is used when the expert opines that the situation does not meet the provisions of an applicable code or law. When a clear violation exists, an expert may also need to provide an opinion that the violation has causal bearing on the incident. Examples of relevant codes or laws are the International Building Code (IBC) and the federal Americans with Disabilities Act (ADA). Voluntary Consensus Standards Voluntary consensus standards are a group of standards that have been developed by committees associated with standards-setting bodies through an industry consensus process. These standards are not legally binding, but are usually well known throughout the industry; they usually describe design and safety features for the respective industry.
FIGURE 19.4 Basis hierarchy.
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Examples of these organizations are the American National Standards Institute (ANSI), the American Society for Testing and Materials (ASTM), and the International Standards Organization (ISO). Industry Custom and Practice The way of doing business over the years within a particular industry is considered the industry custom and practice. The custom and practice is typically based on experience and is generally informal; it may not even be documented. In some cases, however, the practices may be formalized as written company policies and procedures. Often, these practices may have evolved from some type of job analysis. These practices can be useful in forming an opinion, especially when evidence is available to support the practice and/or research. Professional Guidelines Most design-related professions have handbooks that offer criteria regarding appropriate and safe design. A citation from an authoritative handbook such as this may be appropriate. Examples commonly used by HF/E professionals include the Illuminating Engineering Society (IES) Lighting Handbook (Kaufman and Haynes, 1987), Woodson’s Human Factors Design Handbook (Woodson et al, 1992), and The Measure of Man and Woman by Henry Dreyfuss Associates (1993). The major disadvantage of citing such an authority as the only opinion basis is that the source may not be widely known, especially by the party deemed responsible, such as the building manager or owner. Scientific Literature Due to backgrounds as research scientists, many HF/E professionals feel most comfortable when citing scientific literature as the basis of their opinions. The primary drawback with using this type of literature as the sole basis of an opinion is that it is typically of very limited circulation. Consequently, citing HF/E scientific literature as an opinion basis may represent information readily available only to HF/ E professionals. Empirical Study Sometimes the specific issue is not significantly addressed by any documented authority and can only be addressed through original empirical research. In addition to the usual areas of possible impeachment of research studies (issues dealing with the appropriateness of experimental design, sample size, bias, confounding, and statistical power), this approach may not always be practical due to time and budget constraints. When feasible, however, research performed to answer specific issues not elsewhere addressed can be helpful in establishing a firm basis for forensic HF/E opinions.
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Professional Judgment Sometimes, when no other foundational source is available, it becomes necessary for a forensic HF/E professional to base an opinion solely on his professional judgment. This opinion is more powerful when it is based on information extrapolated from previously encountered situations. Generally, the more similar the situations are to the current case, the more credible is the expert’s opinion. An expert’s opinion based solely on his judgment is only as powerful as his experience, credibility, and credentials. Such professional opinion is subject to attack, which may include impeachment of the expert’s credentials, experience, and testimony in similar cases. Consequently, a legitimate and sometimes necessary basis for expert opinion, professional judgment alone is the most difficult to support. 19.4 Pedestrian Fall Incidents and Case Examples When walking, pedestrians generally expect the walking surface to remain uniform. If a hazard exists in the walking surface, it must be perceived or recognized as a hazard by the pedestrian in order to decrease the likelihood of a fall incident. If the hazard is seen and recognized, the next stage is decision-making. The decision whether to avoid the hazardous condition, and, if so, how, is influenced by the pedestrian’s attitudes, behavior, and willingness to take risks. If the pedestrian decides to avoid the hazard, his success rate depends on his ability to do so. This ability is based on factors including anthropometry, biomechanics, and motor skills, along with other human characteristics and skills such as experience, training, and reaction time. Even with the best of intentions, after these steps are followed, random factors or chance can play a role in the process. HF/E principles assert that designs must take into account all sizes, shapes, limitations, and capabilities of the user population. Through learning, experience, and culture, pedestrians have certain expectations regarding walking surfaces, which are generally reinforced daily throughout their lives. When these expectancies are violated, the possibility for error and injury occurs. Many of the conditions that lead to falls are induced by design or situation. The chances of falls occurring due to these situations usually could have been reduced through relatively simple design, construction, or maintenance changes. Pedestrian falls commonly result from uncertainty in the presence of danger. In other words, these incidents occur when a pedestrian unexpectedly encounters a hazard in the walkway. Generally, the fall is initiated when the condition violates a pedestrian’s normal expectations or sufficient sensory cues (usually visual and/or tactile) are not available. The subsequent fall occurs when the pedestrian loses his balance irretrievably and adjustment of posture fails to enable him to remain on his feet. Simply put, designs and conditions that violate a pedestrian’s normal expectation or for which sensory cues are not sufficient to indicate a hazard tend to result in fall incidents. These situations can be categorized into four basic conditions of the walking surface:
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• Unexpected change in traction of the walking surface • Unexpected change in level of the walking surface • Unexpected impediment in an otherwise level walking surface • Unexpected variation in stair geometry Each of these conditions presents a unique set of hazards and means for prevention. In the following sections, these four conditions are discussed with litigated cases provided as examples. Unexpected Change in Traction of Walking Surface Leading to a Slip When a pedestrian falls due to the loss of traction, he has slipped. These slips are the result of insufficient friction between footwear and the walking surface. A typical slip is shown in Figure 19.5. Slips generally
FIGURE 19.5 Slip diagram. occur at the points of greatest instability in the gait cycle: heel-strike and push-off. At these points, the entire body weight is concentrated on very small support bases: the heels and toes. When the heel touches the ground (heel-strike), the ground pushes back against the heel with GRF. This serves as a brake to the body’s forward momentum. If friction between the ground and the heel is insufficient, the GRF cannot push back against the heel and the foot slides forward. Typical slips include falling down into the split position as the front foot slides forward or falling backward onto the buttocks as the body overcompensates for the forward motion. During push-off, the toes push against the ground and the GRF pushes back against the toes. If traction is insufficient, the foot slides backward. A typical fall at this point in the walking process would result in a fall down into the splits or down onto one knee. It is generally the unexpectedness of the slippery condition that actually precipitates the person’s loss of balance and slip. If a pedestrian realizes that a walking surface is slippery (such as wet or icy), he can adjust his gait in order to traverse the slippery walking surface safely. Once the slippery condition is identified, the pedestrian can direct full attention to the task of walking across the slippery surface, carefully watching and placing each foot. He can take small, deliberate steps, maintain the center of gravity over the feet, and hold out the arms or use a provided handrail or other type of support for balance. By making these adjustments, it is possible to successfully maintain balance, or, if a slip does occur, the pedestrian is prepared for the possibility of the event so that he can relax, roll with the fall, and thus likely avoid serious injury.
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The remedies for these conditions that lead to slips usually are quite simple. Premises should be designed with uniform, highly tractive flooring surfaces throughout. These premises should be maintained so that pedestrians do not need to be looking constantly for situations such as changes in flooring material, wet floors, or foreign substance such as water or other spills. Wet mopping of the floors should be done when pedestrians are not likely to be in the area; however, in any case, warning signs and cones should be placed in the vicinity to warn individuals of the change in traction. Case Study: Unexpected Change in Traction of Walking Surface Leading to a Slip In one such case, a pedestrian was walking down a carpeted hallway in an office building. As she rounded a corner, the flooring abruptly changed from low-pile commercial carpet into ceramic tile that had just been damp mopped (Figure 19.6). The pedestrian slipped and fell, breaking her right hip. Testimony from the plaintiff indicated that the change in traction between the carpeted and ceramic tile portions of the hallway was completely unexpected to her. The condition was made even more dangerous because the tile was wet from damp mopping. The smooth, nonporous texture of ceramic tile created a film of water on its surface. It was the opinion of the HF/E expert witness that the owners and management of the premises did not maintain a reasonable safety standard of care because they did not provide warning signs or safety cones that should have been used to alert a pedestrian to the presence of a slippery condition. Warning signs or safety cones would have helped the pedestrian perceive that the tile was wet so that she could have adjusted her gait to traverse the damp flooring successfully or avoid it altogether.
FIGURE 19.6 Photograph of change in walking surface traction.
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HF/E principles dictate the following steps should have been taken in this order: 1. Eliminate the hazard. 2. Guard against access to the hazard. 3. Warn about the hazard (least preferable). Based on these principles, the HF/E expert’s primary opinion was to eliminate the unexpected change in traction by installing uniform flooring, preferably continuing the low-pile carpet throughout the hallway. Second, guarding against the slipping hazard could be accomplished by installing carpet runners with rubber-gripped backing on the ceramic tile portion of the floor or temporarily barricading it. In addition, a cleaning policy instructing the janitorial staff to wet mop only during the very late evening or early morning hours would ensure that the floor was not mopped when personnel were likely to be present. Finally, pedestrians could avoid unexpectedly encountering the wet tile if they were warned of potential slipping dangers with “Wet Floor” signs and safety cones delineating the entire area recently wet mopped. Case Study: Identifiable Change in Surface Traction of the Walking Surface In such a case, the plaintiff walked down a grocery store aisle and stepped on a grate that had been removed from the refrigerator case. The employee was crouching down, working in the dairy case with the shelving grate next to her. This grate was white, while the flooring was composed of darker tan vinyl tiles. In general, prudent pedestrians scan their walking pathway for possible impediments as they traverse the path. Once they start walking, people normally cast their gaze outward and downward approximately 8 to 10 ft in a forward direction. The grate clearly became noticeable at a distance greater than 15 ft (cone of vision). An inspection of the site indicated that the plaintiff, walking at a normal speed, would have had well over 8 sec to view the grate on the floor. Not only did the grate contrast in color with the tile, but it was also quite large (30.5 in. by 23.5 in.). In addition, the employee was crouched over adjacent to the grate, thus providing another visual cue more within the normal line of sight. The HF/E opinion indicated some anomalies in the reported dynamics of the fall. The plaintiff claimed a slip and then a fall forward; most typically, slips result in rearward falls. Second, she stated that both feet slipped on the grating, but this would be physically impossible. Finally, the grate sat 0.75 in. off the ground. Normal foot clearance does not generally exceed 3/8 in. (Cohen, 2000); therefore, the plaintiff would have had to lift her foot higher than what is typical in order to step on the grate. Most people would simply have kicked the grate forward midstride rather than unknowingly step on it.
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FIGURE 19.7 Misstep diagram. Unexpected Change in Level of Walking Surface Leading to a Misstep Given no other visual cues, a pedestrian expects a level walking surface to remain level. Pedestrian missteps occur when some form of change in level of the walking surface catches the pedestrian unaware. Examples of this type of error-prone condition include the presence of a single riser down or an unexpected change in walking surface to a lower elevation. Typically, the pedestrian fully expects the walkway to remain perfectly level and then, without warning, the elevation of the walkway drops. A typical misstep is shown in Figure 19.7. Such missteps also occur when a pedestrian puts his foot down wrongly (steps down into a hole or on an angle), misses the step, or miscalculates a stride, often due to the misperception of depth when the walking surface drops unexpectedly. As the figure shows, the resulting fall from this type of misstep is usually forward, and can include a stumble of several steps prior to contacting the ground, wall, or other element in the environment. These single steps or other changes in elevation downward usually do not have visual or depth cues to draw the person’s attention to the elevation change. Typically, the flooring material pattern (e.g., carpeting, concrete, tile, or brick) remains the same and the pedestrian cannot distinguish the presence of the downward step. The remedy here is quite simple: eliminate changes in elevation whenever possible. Single risers should be eliminated if they are structurally unnecessary. If deemed necessary or already present and difficult or costly to eliminate, these level changes need to be made conspicuous to pedestrians. The conspicuity can be maximized by enhancing the contrast visibility of the step edge with the surroundings. This can be achieved by providing direct lighting or strip lighting on the step edges (lighting contrast), changing the color of the steps through the use of a different material or painting the step edge (color contrast), or providing abrasive strips or metal nosing strips to provide tactile (touch) cues. The area surrounding the drop in walking surface can also be altered to enhance, rather than detract from, the available depth cues indicative of an approaching change in elevation. For example, placing furniture or a plant near the bottom of the single riser can cue a person that the elevation is changing. Similarly, a handrail can provide support to a pedestrian and can also serve as a visual cue, more within a pedestrian’s normal line of sight, to a change in elevation.
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Case Study: Unexpected Change in Elevation of Walking Surface Leading to a Misstep Such a case involved an elderly man who had been walking through a parking lot of an auto body shop and died from complications due to misstepping and stumbling forward when the walking surface unexpectedly dropped in level. The gentleman was walking on an asphalt parking lot when he unexpectedly stepped down onto an unpaved portion of the lot (Figure 19.8). He misstepped at the spot where the asphalt dropped in level between 1 and 4 in. He stumbled forward several feet and contacted a chain link fence with his head, causing fatal injuries.
FIGURE 19.8 Photograph of change in walking surface level. At this location, the parking lot was only partially paved, requiring drivers to park their cars straddling an irregular differential of between 1.5 and 4 in. in height (it has since been raised level with the ground). It was the opinion of the HF/E expert that the change in level and material was outside the decedent’s normal line of sight and focus of attention; therefore, the change was difficult to perceive, especially with a car parked directly next to his. Color and other environmental contrasts were not compelling enough to attract the attention of pedestrians. Additionally, people do not normally expect parking lots to have unmarked changes in surface elevations, especially at locations where persons normally would be expected to enter and exit their vehicles. Case Study: Foreseeable Change in Elevation of Walking Surface On some occasions, a HF/E expert will find that the change in a walking surface can be noticed in sufficient time to avoid a loss of balance and fall. One such case involved a plaintiff who was jogging in the early morning hours near a road under construction. Signs and barricades indicated that the road was closed to all traffic. Construction
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equipment was parked on the site. The plaintiff saw the signs indicating that the road was closed, but instead of continuing on a designated alternative route away from the construction, he decided to jog past the signs and alternative path onto the construction site. As he was running on the site, he stepped down into a 6-foot-deep trench and suffered severe injuries. The view of the hole was unobstructed, well within the plaintiff’s normal line of sight, and could be clearly seen at a sufficient approach distance. The primary area of concern for the HF/E expert was whether or not the construction workers took adequate measures to secure the area. The expert opined that deleting the hole was unnecessary and unfeasible because it was in a clearly marked construction zone. However, the barricades were enough of an impediment that a reasonable person would have altered his behavior and taken the designated alternative route. The jogger took deliberate steps to defeat the barricade and ignore the signs. This behavior implied that the jogger understood the risks and decided to venture onto the job site despite the risks. Once on a construction site, the presence of holes and variations in the walking surface should have been expected. Unexpected Impediment on Walking Surface Leading to a Trip When a pedestrian unexpectedly encounters an impediment in the walking surface, typically a trip occurs. The pedestrian generally falls forward after the leading foot contacts the obstacle or obstruction. A typical tripping incident is shown in Figure 19.9. Trips and the resultant stumbles most often occur during the
FIGURE 19.9 Trip diagram. swing phase of the stride when the forward motion of the foot is halted unexpectedly. This can be a brief impediment (when the foot quickly manages to come free), which usually causes a slight, recoverable stumble, or a longer impediment, when the toe or heel actually becomes caught and a more serious fall results. In both cases, as the figure indicates, the fall and resulting stumble are almost always forward and can result in injuries to the hands, elbows, shoulders, head, or knees. The trips usually occur over impediments that are unmarked and provide no visual cue to alert the pedestrian to their presence. If the impediments were marked or expected, the pedestrian would perceive the existence of the impediment and take appropriate steps to avoid or safely traverse the condition. Examples of situations leading to trip incidents include: unmarked or deceptively painted wheel stops, speed bumps, and ramp edges;
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potholes in streets; uplifts on sidewalks from tree root intrusion or other causes; or items dropped or placed in areas where they would otherwise not be expected. Research in HF/E and pedestrian safety, such as Cohen (2000), has indicated that uplifts as little as 3/8 in. are sufficient to present undetected and unexpected impediments to persons walking in a normal fashion. From 3/8 to 0.5 in. appears to be the tripping threshold for most pedestrians—subtle enough not to be perceived easily by a pedestrian scanning the walking surface, yet sufficient enough to catch a striding toe or heel. Once again, the remedy is proper design, construction, and maintenance; the design and construction should ensure no unmarked impediments are created and regular inspections and maintenance should ensure tripping hazards do not develop over time. When an impediment is discovered, the best fix would be to eliminate the hazard entirely. When this is not feasible or otherwise desirable, such as in the case of speed bumps and wheel stops, the potential tripping surface should be clearly and unambiguously painted, preferably in bright hazard yellow, to maximize its conspicuity to pedestrians. Indoor tripping hazards, if not possible to eliminate, need to be identified with a change in surface material, lighting, or other indication of the upcoming impediment. Case Study: Unexpected Impediment on Walking Surface Leading to a Trip An unexpected change in elevation involving an unmarked ramp created a hazard in an outdoor produce market. In this case, an elderly man tripped over the ramp edge, stumbled forward several feet, and hit his head on a steel door jam, rendering him a quadriplegic. The HF/E expert witness opined that the ramp edge was unexpectedly close to an infrequently used entrance and was therefore unexpected because it was never within the plaintiff’s field of view. The area was inadequately illuminated and there were no visual cues to indicate the presence of the ramp. There was no color contrast, lighting contrast, or textural change between the ramp and the flooring material. Furthermore, if the ramp edge had been feathered or at least barrier protected by a railing as called for in the building codes, the plaintiff’s injuries would have been prevented. Case Study: Visible Impediment on Walking Surface In some cases, a defect alone does not necessarily indicate the cause of a fall incident. In this case example, a shopper claimed she tripped over a slightly detached section of a retail store end cap display (Figure 19.10). The display was the type commonly used in the retail trades at the end of an aisle. Upon inspection of the store and location of the incident, the HF/E expert determined that the only way for a person’s striding foot to come in contact with the kick plate while making a left turn into a cross-aisle was to walk too close to the end cap and display. By walking this close, the end cap would have presented a fixed obstruction whether or not the kick plate was detached. Furthermore, if the kick plate were detached more than 1 in. (25 mm) as claimed, it should have offered less resistance to the striding foot, thereby preventing altogether or mitigating the plaintiff’s injuries. Also, a kick plate detached by this much would have been readily noticeable, contrasting in color with the tiled floor below.
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FIGURE 19.10 Falls Due to Irregular Stair Geometry Extensive research over a long period of time has been done in order to determine the best configuration for the design and construction of stairs (see Templer, 1992). Pedestrians develop a specific gait when traversing stairs, based on the expectation that they are uniform in dimension. Typically, pedestrians on stairs do not look at where they are stepping except at the very beginning and end of the flight (Templer et al., 1985). Excessive variations in riser or tread dimensions not only go visually undetected in the initial scan by stairway users, but also disrupt their gait as well. These unexpected variations in geometry disrupt the rhythmic activity of successive foot placements, resulting typically in a loss of balance and, possibly, a fall. For these reasons, the building codes generally allow only up to 3/8-in. (0.95-cm) variation in successive riser heights and tread depths. Case Study: Unexpected Change in Stair Geometry Even seemingly slight variations in stair geometry can lead to serious injuries. In one such case, a spectator was walking down a set of stairs at the auto racetrack when he suddenly misstepped and fell forward. A site inspection revealed that the stairway was composed of 17 prefabricated metal risers with two site-made wooden steps transitioning the metal steps to the ground (Figure 19.11). Each of the risers measured a uniform 7.5 in. (19.05 cm), except for the wooden steps. The riser at the transition from metal to wood measured 6.25 to 6.5 in. (15.8 to 16.5 cm), depending on where the measurement
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was taken. This was a 1.25- to 1.5-in. (3.2- to 3.8-cm) differential from the previous 17 risers. The HF/E expert determined that this excessive variation of about 1 in. (2.54 cm) caused the pedestrian to misperceive the height between steps, disrupting his gait and thus causing him to fall. In addition to this variation violating the building code requirement for uniformity of riser heights, the wooden steps were poorly maintained and without any nonskid material applied.
FIGURE 19.11 Photograph of nonuniform stair geometry. No case study to date could be identified in which an unexpected change in stair geometry could be defended. However, if a pedestrian decides to descend or ascend a stairway that looks like it is very old and in obvious need of repair, he should expect some irregularity in stair dimensions and be prepared by holding the handrail, watching every step closely, and carefully placing each foot. By perceiving and expecting uneven conditions to exist, a pedestrian could safely traverse even a stairway with gross dimensional variations. In conclusion, the forensic HF/E professional can explain a pedestrian fall in terms of the perceptual, cognitive, and biomechanical abilities and limitations of humans. This scientific information, in conjunction with an analysis of the physical evidence and available testimony, is invaluable in determining for the trier of fact the causes of and means for prevention of pedestrian falls.
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19.5 Checklist of Main Factors to Consider in Pedestrian Fall Incidents Primary Factor Considerations Pedestrian expectation
Experience with location Memory of hazard Conspicuity of hazard Warning signs and other sensory cues Pedestrian physical condition Age Eyesight Corrective lenses Mobility or other impairment Pregnancy Weight Pedestrian behavior Talking or other task distractions Visual distractions Alcohol or drug impairment Reasonable conduct
Primary Factor Illumination
Indoor level walking surfaces
Outdoor surfaces
Stairs
Single stair
Considerations Adequate lighting/reflectance Shadows Glare Provide contrast for change in level Conformance to applicable building codes Unmarked rises in elevation (single step up) Unmarked drop in elevation (single step down) Physical obstacles Condition of floor surface Coefficient of friction Appropriate and secured carpeting Adequate illumination Appropriate drainage Slip resistance Weather conditions Unmarked rise in elevation (single step, wheel stop, curb) Unmarked drop in elevation (single step down, pothole) Physical obstacle Uniform stair geometry (treads, risers, nosings) Conformance to applicable building codes Proper handrail dimensions Slip-resistant treads Adequate illumination Discernible step edges Possible removal
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Handrails
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Conspicuity Contrast in color/pattern/material Contrast in lighting (lighting strips) Slip-resistant surface Conformance to applicable building codes Proper ramp geometry Appropriate landings Adequate edge protection Adequate illumination Proper handrail dimensions Coefficient of friction Unexpected change in traction Conspicuous slippery condition Warnings of slippery condition Graspability Firmly attached Height Adequate number Proper extension beyond stairs or ramp Provide appropriate visual cue for change in level Documented maintenance policies and procedures Inspection schedule Documented inspections Matting in appropriate areas Cones and/or barricades used at appropriate times Appropriate floor-finishing products
Defining Terms Coefficient of friction—The degree of traction between the shoe heel/sole and walking surface material; an indicator for slipperiness of the walking surface. It is often abbreviated as COF. Misstep—Loss of balance due to unexpected change in downward level of a walking surface or presence of a hole/dip. Nosing—The front and usually rounded edge of a stair tread; it frequently projects over the riser below it. Riser—The upright (vertical) face of a step. Riser height—The height of one step measured from the top of a step at the nosing to the top of an adjoining step at the nosing. Slip—Loss of balance due to unexpected change in surface traction. Slip resistant—The ability to provide adequate force to resist the tendency of the shoe or foot to slide along a walking surface. Slip resistance is related to a combination of factors including the walkway surface, the footwear heel/sole, and the presence of any foreign material between them.
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Stairway—A system of two or more risers. Tread—The horizontal surface of a step. Tread depth—The length (from back to front) of a tread as measured from the furthermost extension of adjacent treads. Trip—Loss of balance due to an unexpected change in upward level of a walking surface or presence of an impediment. References Cohen, H.H., 2000, A field study of stair descent, Ergonomics in Design , 8(2), 11–15. Cohen, H.H. and LaRue, C.A., 1997, Advice from an expert witness, Ergonomics in Design , 5(4), 19–24. Cohen, H.H. and LaRue, C.A., 2000, Forensic human factors/ergonomics. Chapter in International Encyclopedia of Ergonomics and Human Factors (London: Taylor & Francis). Cohen, H.H. and LaRue, C.A., 2002, Establishing standards of reasonable care through forensic human factors, Ergonomics in Design , 10(2), 15–18. Henry Dreyfuss Associates, 1993, The Measure of Man and Woman: Human Factors in Design (New York: Whitney Library of Design). Kaufman, J.E. and Haynes, H. (Eds.), 1987, IES Lighting Handbook: Application Volume (New York: Illuminating Engineering Society of North America). Rasch, P.J. and Burke, R.K., 1978, Kinesiology and Applied Anatomy: the Science of Human Movement (6th ed.) (New York: Lea and Febiger). Sanders, M.S. and McCormick, E.J., 1996, Human Factors in Engineering and Design (7th ed.) (New York: McGraw-Hill, Inc.). Templer, J., 1992, The Staircase: Studies of Hazards, Falls, and Safer Design (Cambridge, MA: Massachusetts Institute of Technology Press). Templer, J., Archea, J., and Cohen, H.H., 1985, Study of factors associated with risks of stairway falls, J. Saf. Res. , 16, 183–196. Watkins, J., 1983, An Introduction to Mechanics of Human Movement (New York: MTP Press). Woodson, W.E., Tillman, B., and Tillman, P.L., 1992, Human Factors Design Handbook (2nd ed.) (New York: McGraw-Hill, Inc.).
Further Information Amblard, B., Berthoz, A., and Clarac, F., Eds., 1988, Posture and gait, Proceedings of the 9th International Symposium on Postural and Gait Research (New York: Elsevier Science Publishers, B.V.). Carlson, S., 1972, How Man Moves: Kinesiological Studies and Methods (New York: William Heinemann Ltd.). Cohen, H.H., 1998, Performance based analysis of 60 stairway fall accidents, Proc. Pacific Rim Conf. Building Officials , 9–19. (Maui, HI: International Conference of Building Code Officials) (update in press). Ducroquet, R., Ducroquet, J., and Ducroquet, P., 1968, Walking and Limping: a Study of Normal and Pathological Walking (Philadelphia: J.B. Lippincott Co.). Hyde, A.S., Bakken, G.M., Abele, J.R., Cohen, H.H., and LaRue, C.A., 2002, Falls and Related Injuries: Slips, Trips, Missteps and Their Consequences (Tucson, AZ: Lawyers and Judges Publishing Company, Inc.). Inman, V.T., Ralston, H.J., and Todd, F., 1981, Human Walking (New York: Williams & Wilkins).
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International Conference of Building Officials, 1997, Uniform Building Code (Whittier, CA: Author). Keeton, W.P. (Ed.), 1984, Prosser and Keeton on the Law of Torts (5th ed.) (St. Paul, MN: West Publishing Co.). McConnill, M.A. and Basmajian, J.V., 1977, Muscles and Movement—a Basis for Human Kinesiology (New York: Robert E. Krieger Publishing Co., Inc.). Schafer, R.C., 1955, Clinical Biomechanics: Musculoskeletal Actions and Reactions (2nd ed.) (New York: Williams & Wilkins). Steindler, A., 1955, Kinesiology of the Human Body under Normal and Pathological Conditions (New York: Charles C. Thomas Publisher). United States Equal Employment Opportunity Commission and the United States Department of Justice, 1992, Americans with Disabilities Act Handbook 59–0 (Washington, D.C.: Authors). Wickens, C.D., 1992, Engineering Psychology and Human Performance (2nd ed.) (New York: HarperCollins Publishers). Zohar, D., 1978, Why do we bump into things while walking? Hum. Factors , 20(6), 671–679.
20 Measurement in Pedestrian Falls Daniel A.Johnson Daniel A.Johnson, Inc.
0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
20.1 Introduction Just as measurement is the basis of all science, accurate and precise measurement is crucial in the evaluation of environmental factors to determine if they have contributed to a pedestrian’s fall. This chapter considers different methods of measuring these factors. Falls cause a tremendous number of injuries and are the leading cause of accidental death for older citizens. The financial effects are phenomenal. In the United States, in 1990, falls cost more than $50 billion. The number of fall injuries was second only to those suffered in automobile collisions (Pauls, 1991). Falls not only have a devastating effect on the injured person and that person’s family, but also can result in expensive lawsuits. Because of this, forensic ergonomists are often asked to investigate the circumstances surrounding a fall. To do this adequately requires taking accurate measurements and comparing them with relevant legal codes and standards that have a basis in ergonomic research. I am unaware of any source that actually describes how to take measurements of these environmental factors accurately. The one exception involves slips, for which considerable effort has been expended in the design and evaluation of equipment to measure the slip resistance between the shoe and a walking surface. A number of books and standards have been promulgated with regard to this equipment (e.g., English, 1996; Bakken, 2002). Various organizations have published standards, texts, and legal codes that recommend or require that the built environment be designed and maintained so that it provides some minimum level of safety for pedestrians. Often these standards and codes call out for stairways and level and sloped walkways to meet certain specific requirements such as the vertical rise of a stair being no greater than 178 mm (7 in.). Other standards call for qualitative values, such as the one requiring walkways to be “slip resistant,” without defining what that means. However, none of the standards or codes describes the method by which the specified dimensions are to be measured. With the exception of slip resistance, how to measure most environmental factors that can cause a fall has not been treated in depth in the ergonomic literature. A goal of this chapter is to examine the issue of measurement as it is related to pedestrian falls and to suggest some optimal methods of performing these measurements.
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20.2 Importance of Accurate Measurements From a forensic point of view—from a liability point of view—it is important to achieve a high level of accuracy in measuring environmental factors that might relate to a fall. A fall can result when a walkway does not meet some minimum safety standard. Alternatively, a fall may occur because the person was, in some way, predisposed to falling, was inattentive, or was behaving in a manner that increased the likelihood of falling. In the first situation, the Court is more likely to conclude that the fall probably would not have occurred if the walkway had met the standards. In this case, those in charge of that walkway may be held liable for the consequences. In the other situations, in which the walkway did meet standards and the fall occurred, perhaps, because of some behavioral or physiological reason associated with the person who fell, those in charge of that walkway would probably not be held liable. In either case, accurate measurements can assist the Court in determining responsibility for the fall. In yet another set of instances, when falls occur but there are no codes or standards by which a court can judge liability, the forensic ergonomist may be asked to give an opinion as to whether the plaintiff was or was not behaving in an expected or predictable manner. In addition, the forensic ergonomist may be asked if the environmental condition faced by the pedestrian was inappropriate or unexpected. Regardless of the cause of the fall, the ergonomist will need to take accurate measurements of the site where the fall occurred. 20.3 Types of Falls Three basic types of fall are addressed here: trip and falls, slip and falls, and falls on stairs. About 30% of the cases on which I have been consulted have involved slips, 30% have been falls on stairs, 20% have been due to trips, and 7% have been falls on ramps. The remainder includes falls from heights; falls into holes or openings; and falls from equipment, such as ladders and scaffolds. These latter categories, although of concern to the practicing forensic ergonomist, are not addressed here. 20.4 Phases of the Walk Cycle I consider the walk cycle on a flat surface to consist of four phases: the stance phase, toeoff phase, swing phase, and heel-strike phase. On stairs, toe-strike may replace heel-strike in descent as well as ascent. 20.5 Causes of Falls Unintentional falls are nearly always preceded by a misstep, defined here as an unintentional departure from pedestrian gait appropriate for the walkway surface. A misstep can be due to a number of factors such as being jostled by others, a physiological
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condition, perceptual inadequacy (e.g., floor covering materials that camouflaged tread nosings), and inattention. Missteps can also result from poor design or inadequate lighting. 20.6 Trip Hazards The most common method by which an object on the ground will trip a person occurs when the foot in the swing phase is stopped short in its forward movement. The swing phase of the walking cycle is initiated on toe-off when the toes are pointing in a downward direction (Jahss, 1982). As the foot travels, forward movement of the knee and dorsiflection cause the toes and foot to start to point forward. At heel-strike, the toes point in a slightly upward direction. However, approximately midway during the swing phase, the toes describe an arc that comes close to touching the surface of the ground. During this phase, an unexpected object rising above the surface can stop the foot’s movement. If this happens, the momentum of the body will carry its center of gravity forward of the ball of the foot in the stance phase, and a stumble or a fall will result (Bakken, 2002). Height of Trip Hazards A vertical rise of as little as 13 mm (0.5 in.) can stop a foot in flight because the toe may come this close to the surface during swing phase (Cohen, 2000). The U.S. Housing and Urban Development (HUD) rules for routes that are expected to be used by those with difficulty walking have specific requirements: 4.5.2 Changes in Level. Changes in level up to 1/4 in. (6 mm) may be vertical and without edge treatment. Changes in level between 1/4 and 1/2 in. (6 and 13 mm) shall be beveled with a slope no greater than 1:2. Changes in level greater than 1/2 in. (13 mm) shall be accomplished by means of a ramp (CFR 24 1995). Similar requirements for safe walkway surfaces have been put forth in two additional documents. American National Standards Institute (ANSI) document ANSI A117.1 (Accessible and Usable Buildings and Facilities) addresses walkways where people with some mobility impairment might be expected. Virtually the same requirements were published in a document published by the American Society for Testing and Materials (ASTM), entitled ASTM F 1637, Standard Practice for Safe Walking Surfaces. This document, however, was not written for a special group of individuals (i.e., handicapped people) but for all people. In fact, it states that its provisions may not be adequate for those with handicaps. Furthermore, as Bakken reports, the International Building Code (IBC), and its predecessor, the Uniform Building Code (UBC), have adopted the entire text of ANSI A117.1 and have stipulated that those requirements are applicable to all individuals. In order to comply with the IBC and UBC, a walkway must also comply with ANSI A117.1. For an excellent review of building codes and standards, and how they relate to pedestrian falls, see Bakken (2002).
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Thus, it is important not only to measure the height of a suspected trip hazard accurately, but also, if it is over about 6 mm (0.25 in.) and less than about 13 mm (0.5 in.), to measure the beveled edge in order to determine if the slope exceeds 1:2, or 26º. Typical Way of Measuring Trip Hazards In the field, it is not always easy to take accurate and precise measurements of small potential trip hazards using such standard tools as rulers or tape measures. One practical factor that makes it difficult to read a ruler accurately (“ruler” includes tape measures, unless otherwise specified) is that of placing one’s eye close enough to and parallel with the surface to overcome parallax distortion. No accurate measurement of the possible trip hazard can be made if the hazard and the ruler are not in the same plane, parallel to the eye, and at the same distance from the eye. Another practical problem occurs when a fall occurred on a broken and unevenly elevated sidewalk. In this instance, the lifted section, where the plaintiff tripped, might be close enough to 13 mm (0.5 in.) so that it is unclear whether grounds for a lawsuit exist. For example, the height may be about 13 mm (0.5 in.) but the top portion is beveled. The issue, then, is how to take accurate measurements of the rise height and the bevel. Doing so using only a ruler and straightedge is unlikely. Probably even more difficult to measure, using only a ruler, are small but potentially dangerous obstructions on the nosings of some stairways. Cohen looked at whether a raised nail used to fasten a slip-resistant strip to a nosing (the foremost edge of where the stair tread can be) could catch a heel in flight (Cohen, 2000). He found that the heels of six male volunteers cleared the intermediate nosing by an average of 18 mm (0.72 in.) with a range of 5 to 58 mm (0.2 to 2.3 in.). A raised portion on the nosing that protruded more than about 5 mm (0.2 in.) could be considered a trip hazard. Optimal Way of Measuring Trip Hazards A preferable method makes use of a carpenter’s profiling tool—a device with a row of about 180 small stiff wires, each with a diameter of about 0.8 mm (0.3 in.) and a density of about 12 per cm (30 per in.). The typical device is 15 cm (6 in.) long. In-house lab tests show that the tool can provide measurements of vertical risers that are as small as 1 mm (0.04 in.) and as large as 38 mm (1.5 in.). When the wires are pushed down onto a surface such as the sharp rise in a sidewalk, they hold the shape. The profile of the surface can then be traced onto paper and scanned into a computer (see Figure 20.1 through Figure 20.4). A graphics program such as Adobe Illustrator® can then be used to measure the heights and angles of the surfaces (Adobe Systems). In the instance depicted in Figure 20.4, the overall rise was 14 mm (0.54 in.) and the bevel was steeper than 26° for the first 10 mm (0.4 in.), thereby exceeding the limts allowed by HUD. The conclusion from this analysis is that the surface presented a trip hazard.
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Profile Tool Accuracy and Reliability A small metal box, which sat flush on a desktop surface, was used to simulate a vertical rise in a walkway. The height of this box was measured at 32.1 mm (1.26 in.) using a caliper. This provided an external check on the accuracy of the profile tool. The fact that it was considerably larger than 13 mm (0.5 in.) was immaterial because the variation in measurements was of interest, not the absolute height. Measurements were performed by arranging the profile tool so that about half of it was over the top of the box and the other half was over the surface of the desk. The sliding pin elements were pushed down until they were in contact with one of the surfaces. The profile was traced onto paper with pencil. The tool was then reset so that all of the pin elements were again parallel, and another measurement was taken. Ten separate profiles were taken, scanned into a computer, and imported into Adobe Illustrator®. Each profile was examined at magnification of up to 800%. Straight lines were scribed through the center of the pencil marks. The “measuring tool” in the Adobe Illustrator® application was used to determine the vertical distance between the upper and lower levels (the top of the box and the desk). At this magnification, the measuring tool reads out to an accuracy of ±41×10− 3 mm (1.6×10− 3 in.). The mean (sd) of the 10 measures indicated that the height of the box above the surface was 32.0 mm (0.14). That is, its height was found to be 1.26 in. (6×10− 3 in.). The CI95 was 32.0 mm ±0.1 (1.26 in. ±0.01), which was consistent with the caliper-measured height of 32.1 mm (1.26 in.). With this potential level of accuracy, the profile tool should allow an investigator to decide if a rise was significantly (p<0.05) above or below the 13mm (0.5-in.) level when the measured height of the rise was 13 mm ±0.1 (0.5 in. ±0.01).
FIGURE 20.1
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FIGURE 20.2
FIGURE 20.3
FIGURE 20.4 For comparison, a metric ruler, with its smallest gradation of 1 mm, would allow an investigator to interpolate to the nearest millimeter plus or minus 0.5 mm. Thus, the
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profile tool allows a fivefold increase in accuracy over the metric ruler, assuming that the ruler could be read without any distortion due to parallax. For the ruler with the inch/foot scale, the smallest gradation is typically 1/16 in. (0.0625 in.). This allows an investigator, under ideal conditions, to read to the nearest gradation plus or minus a half gradation (±0.031 in.). Thus, use of such a ruler allows one to decide if a rise was significantly (p<0.05) above or below the 0.5-in. level only if the measurements were less than 0.47 in. or more than 0.53 in. The profile tool allows a several-fold increase in accuracy over this in that a decision could be made if measurements were less than 0.49 in. or more than 0.51 in. In summary, the profile tool provides forensic ergonomists the means to measure small potential trip hazards accurately. In addition, it allows for a permanent graphic representation of the profile and slope of the possible trip hazard—something that cannot be obtained with the ruler. It is also useful in determining if the beveled edge of a rise meets the applicable standard found in such documents as 24 CFR. 20.7 Ramps A number of safety issues have been identified in the design of ramps. These include the steepness of the ramp, the slip resistance of its surface, and the presence of handrails. Steepness According to published standards, the consensus apparently is that a ramp is a walkway surface that has a slope steeper than 1:20 (1 unit vertical to 20 units horizontal, or tan− 1 [1/20]=2.9°). In addition, codes and standards mandate or recommend that ramps not exceed a certain steepness (e.g., ASTM F 1637–95; IBC, 2000; Life Safety Code, 2000). For example, if a ramp is needed for access by a frail or handicapped person to enter or leave hotels and apartments, it should not be steeper than 1:12 (4.8°). Other ramps should not be steeper than 1:8 (7.1°). If the change in level is greater than 7.1°, then stairs should be used. (The Life Safety Code, adopted by the National Fire Protection Association, has been approved by the American National Standards Institute (ANSI) and is now considered a national standard in the U.S. The IBC 2000 is an alternate building code that is recognized by a number of states in the U.S.) Based on tests of the elderly and disabled people using short ramps, Templer (1992, vol. 2, p. 45) states that “(r)amps as steep as 1:8 (7.1°) are acceptable for ascending or descending heights of no more than 3 inches (8 cm).” Ramps of greater heights should be less steep because of problems related to physical strength and stamina. Therefore, a ramp that is steeper than about 7° would not be in accordance with these recommendations and standards.
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FIGURE 20.5 People who are frail, handicapped, or confined to wheel chairs often experience safety problems in attempting to ascend or descend sloped surfaces. However, a ramp may also cause the nonhandicapped person problems. If the slope is unexpected and too steep, it can cause a misstep. For example, consider the side slope of a curb cut that has been installed to help those with wheelchairs to move between the sidewalk and the street. Curb cuts, as well as a curb ramps (ramps that extend from a sidewalk down into a street or parking lot), may have side slopes that can cause a person to lose balance or slip. For instance, if someone walking on a sidewalk parallel to a curb encounters the side slope of a curb cut that is not seen, one could lose balance and fall forward just as if one had stepped into a hole (see Figure 20.5). Alternatively, if the surface were wet and did not have a high enough level of slip resistance, stepping onto the side slope could cause the foot to slip forward, resulting in a fall. Steepness and slip resistance of sloped surfaces are important factors in falls and fall prevention. Typical Way of Measuring Slope Steepness Level and Ruler Method In this technique (which is not advocated), a level is placed at some point on the slope (e.g., the top) and extended out over the slope. At some point, for example at the end of the level, a ruler is extended down from the end to the surface. The slope can then be ascertained trigonometrically. This method yields the average slope of the ramp between the two points. However, Perkins (1977) reports that a fall can occur if the foot slips more than about 10 to 15 cm (4 to 6 in.). If a ramp has an uneven surface or a variable slope, then portions
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of that ramp will be steeper than the average. Under these conditions, the “level-and-ruler method” would not detect the steepest section of the ramp. This method would be useful only if it demonstrated that the average slope was so steep as to have contributed to the fall. If this method found that the steepness was less than what is considered acceptable, it does not rule out the possibility that some undetected portion of the ramp was steep enough to have contributed to a fall.
FIGURE 20.6 Optimal Ways of Measuring Slope Steepness Inclinometer Method An alternative and preferable method makes use of an inclinometer, or angle finder, which reads out to the nearest degree the slope of a surface. Inclinometers are about 9 cm (3.5 in.) in length (see Figure 20.6). This instrument has an advantage over the “leveland-ruler method” in that it can easily and quickly measure the slope of several small areas in the vicinity of a fall. Furthermore, the reading can be photographically recorded, assuming that the camera can be focused for a close-up photograph. This might be difficult at night because the face of the inclinometer has specular characteristics, and photographs taken with flash may turn out to be unreadable due to reflection. Photographs from different angles should be taken at night if a film camera is used. If a digital camera is used, the image on the camera’s liquid crystal display screen should be checked for readability before leaving the scene of the fall. Inclinometers are relatively hardy but care should be taken to ensure their accuracy. I suggest that two or three be purchased at the same time and tested against each other.
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This can be done by holding one upside down and against the other and then rotating them so that one is on top, and then the other. The readings in all orientations should be complementary. No calibration is necessary or possible. Electronic Level The electronic level (SmartTool) is one of the most useful and versatile tools that I have found. It is more precise than the inclinometer and it reliably reads out angles to an accuracy of 0.1°. One convenience of this device over the inclinometer is that the measurement can be retained in the display so that it can be viewed in a more convenient position (e.g., where there is more light). Also, like the inclinometer, the electronic level reading can be photographed. The required calibration is relatively simple to perform. 20.8 Slip and Falls Slip and falls can occur on flat or sloped surfaces, as well as on stairs. Numerous mechanical devices have been developed to measure the friction between walking surfaces and the shoe. The field is large and much effort has been put into developing and attempting to validate various instruments that measure this friction. For a recent summary of these devices, see Bakken (2000). I will only discuss the advantages and disadvantages of three such instruments with which I am most familiar. Coefficient of Friction (COF) By definition, the COF between two surfaces is the ratio of the force required to move one surface over the other to the total force pressing the two surfaces together: COF=horizontal force/vertical force A COF of 0.5 exists if it were to take 5 units of horizontal force to slide an object weighing 10 units across a level floor (5/10=0.5). If it took only 4 units of force to cause the weight to slide, then the COF between the surfaces would be 0.4. When tested with a flat sole of a shoe on ice, a COF of less than 0.20 can be measured. Dry, clean asphalt, on the other hand, may exhibit a COF=0.8 or more with the same shoe material. COF readings on flat surfaces generally lie between 0 and 1.0. A reading below 0 is not possible, but readings above 1.0 occasionally occur when one or both surfaces are quite rough. Dynamic vs. Static Coefficient of Friction (COF) Static coefficient of friction (SCOF) is at least equal to, and usually higher than, the dynamic COF. That is, more friction must be overcome in starting an object to slide over a surface than in keeping it sliding. High-speed photography has shown that during heelstrike, the foot often comes to a stop before starting to slide (Perkins, 1977). Thus, some believe that the SCOF is more important in determining whether a slip and fall will occur than the dynamic because, if the slide does not start in the first place, the dynamic COF between the shoe and the surface is moot.
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However, the dynamic COF may be important in determining if a fall will occur after the foot starts slipping. Whether a person recovers balance or falls depends on how far and how quickly the foot has slipped before any counteracting muscular control is exerted. How far the foot slips in that short period between the start of the slip and the point at which a fall becomes irreversible (10 to 15 cm or 4 to 6 in.) depends at least in part upon the dynamic COF (Perkins, 1977). Other factors, such as step length, speed, and reaction time, are also important (Gronqvist et al., 200 1a, b). One problem with testing the dynamic COF is that friction decreases with velocity so that the faster an object slides across a surface the lower the friction between the two surfaces is. The convention in the field of pedestrian falls in the U.S. is to consider the static COF as the important variable when judging whether a surface provides adequate friction. Slip-Resistant Walking Surfaces In the early 1940s, Sydney James and Underwriters’ Laboratories concluded that a COF of 0.5 was the minimum in deciding whether a floor polish could bear the UL seal. In 1953, the Federal Trade Commission recommended the standard of 0.5. For 40 years or more, a walking surface with a COF of less than 0.5 has not been considered slip resistant. This issue has been reexamined periodically and the 0.5 minimum has been verified (Ekkebus and Killey, 1973; Sacher, 1993). Typical Ways of Measuring Slip Resistance Horizontal Pull Slipmeter The horizontal pull slipmeter (HPS), designed by Charles Irvine, is a portable device used to measure static COF in the field. It is equipped with leather “shoes”—three small circular flat slider pads—that are pulled until they slide across a surface. A Chatillon gauge registers and holds the horizontal force that was applied at the moment the device started to slide. The HPS has a battery-powered motor that exerts the horizontal force to pull the shoe across the surface (see Figure 20.7). The motor gives a more
FIGURE 20.7
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FIGURE 20.8 constant pull than a person could exert with the fingers, thereby reducing variance in readings caused by differences in pull strength or speed. The device is to be used on a dry surface; pulls in four different directions are required to meet the standard written for its use (ASTM F 609–96). Materials other than leather can also be attached to the slider pads and tested. American Slip Meter A more portable pull meter, similar in design and operation to the HPS except that it does not use a motor and weighs considerably less than the HPS, is the American Slip Meter (ASM) (see Figure 20.8). It also has three slider pads that can be easily replaced with different materials. One set of three is leather and one set is Neolite®. Comparison of the HPS and ASM I tested the two pull meters on the same surfaces in a dry and dust-free condition. The ASM and HPS provide virtually identical readings on the various surfaces tested. Motor-Pull vs. Finger-Pull If the ASM is pulled quickly so that it starts to slip within 1 second of pull onset, slightly lower but statistically significant readings are obtained than with the HPS. A slower pull of the ASM gives equivalent results to that of the HPS. Because of its portability, I prefer the ASM. However, I do not use either of them on wet surfaces, where most slips occur. Optimal Way of Measuring Slip Resistance Variable Incident Tribometer The variable incident tribometer (VIT) was designed to test the static COF of dry surfaces (ASTM F 1679–00). It also measures the slip resistance between a shoe and a surface, and any lubricant between the two. A COF is defined as the friction between two surfaces. If a lubricant is between the surfaces,
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FIGURE 20.9 English (1996) maintains that slip resistance can be measured but the COF cannot. According to this researcher, the designer and producer of the VIT, the VIT gives readings consistent with the judgments of people walking on surfaces of varying degrees of slip resistance (English, 1996). The VIT, shown in Figure 20.9, is portable and can be used on level surfaces as well as on ramps and stairs. It is powered by compressed gas (CO2). The pull meters (the ASM, HPS, and others) rely on gravity, as humans do (i.e., body weight and machine weight produce the “vertical” force). Pull meters and humans also rely on a horizontal force: the forward momentum for the human and the force from the motor or finger pull for the device. Because of this, pull meters read out lower COFs when they are pulled down an incline and higher COFs when pulled upward. In this regard, they give readings more consistent with the experience of people walking on inclines. The VIT, on the other hand, produces readings independent of slope because the force is supplied by compressed gas. Although a person is more likely to slip on a sloped walking surface than on one that is level, the VIT will provide the same reading on both. Thus, once readings are obtained on a sloped surface using the VIT, the effect of the slope needs to be calculated. After the angle of the slope is measured, the required COF for that surface can be computed to determine whether there was adequate slip resistance between the foot and the surface (Templer, 1992, Table 3.6). For example, consider a walking surface such as ceramic tile that could be considered slip resistant in that it provides a COF of 0.5 when level. However, placing that tile on a slope makes it less slip resistant. To provide the slip resistance equivalent to 0.5 when it
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is sloped, for example, 10°, the surface must provide a required COF (RCOF) of 0.74 when level: RCOF—tan (tan−1 0.5+10°) (20.1) = tan (26.56°+10°) (20.1) = 0.74 Of the equipment with which I am familiar, the VIT is currently the instrument of choice because it gives results on lubricated surfaces, which are the surfaces where slips most often occur. The HPS and ASM devices, as well as other pull meters, reportedly give spuriously high readings on wet surfaces. When a lubricant is placed on a surface and a pull meter is used to test the slip resistance, adhesion (or stiction as it has been called when referring to surfaces having lubricants) gives high readings. The stiction is apparently a function of residence time—the longer the device is in contact with the surface, the greater the adhesion is. With the VIT, there is no appreciable residence time and therefore no stiction. Brungraber, Mk II The Brungraber, Mk II, referred to as the portable inclinable articulated strut tribometer, or PIAST, also measures slip resistance of dry and wet surfaces. It is described in detail in English (1996). Because I have not used one, I cannot comment upon its ease of use or accuracy. However, in a comparison of the two instruments in measuring slip resistance of wet structural steel, the two devices ranked the seven different samples in virtually identical order. Furthermore, the PIAST and the VIT had a high correspondence with the way in which five steelworkers ranked the slipperiness of the same wet steel surfaces (English, 1996, pp. 112–129). 20.9 Variables to Consider in Measuring Slip Resistance Cleaning the Surfaces For forensic purposes, it is probably preferable to test the surface in the condition as found except for removing loose material such as dust and gravel. This should be done with a soft paintbrush so as not to disturb the condition of the floor. Adding a Lubricant When a floor is to be tested in dry as well as wet conditions, the dry testing should be done first. This will keep the slider pads dry until the wet conditions are started. If water was the lubricant reportedly on the floor at the time of the fall, then distilled water should be applied to the surface when testing. Of course, the forensic ergonomist may consider using some other lubricant in order to simulate the condition of the floor at the time of the fall.
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20.10 Falls on Stairs When people fall and injure themselves while walking on stairs, they are much more likely to be descending rather than ascending the stairway. Nearly every stair-fall incident that a forensic ergonomist is asked to evaluate will involve a fall down a stairway. This does not mean that people do not trip when ascending stairs, but rather that injuries in falling up stairs are seldom serious enough to warrant lawsuits. Typically, the person descending stairs will fall due to a misstep as the foot is placed on the next lower tread. Some potential causes for these missteps include perceptual inadequacy (insufficient lighting of a floor covering that camouflaged tread nosings) and inattention (talking to another person or carrying a large bulky item that prevents the person from seeing the stair nosings). Missteps can also occur because of excessive variation between the stairs or because the stairs are too steep or have treads that are too small. Other possible reasons include a sharp edge or nail protruding from the nosing that can catch the sole or heel of the foot, or a nosing that is not adequately slip resistant so that the forward foot slides off or pivots over the nosing as weight is applied. Once a misstep has occurred, a person may stop the fall only by grabbing for and holding onto a handrail. Perceptual Inadequacy—Lighting and Visibility of Stair Nosings The nosing is the most critical location on a step that a person must see and recognize in order to place the foot accurately. If the nosing is difficult to see, the foot may be placed too far forward so that it rotates or slips over the nosing. When this occurs, a fall forward becomes likely. If lighting is a potential problem, the forensic ergonomist should measure the light on the nosings of several steps in the vicinity where the misstep most likely occurred. Several steps should be measured because people who fall cannot always remember with accuracy the exact location of where a foot was when the misstep took place. The measurements should be taken under the same conditions that existed at the time of the fall. The minimum standards in many building codes have, until recently, required only that 1 foot candle (fc) (10.7 lux [1x]) need fall on the steps. However, a new code now requires that 10 fc (107 1x) of light fall on every tread of an interior stairway (IBC, 2002), although for exterior stairs, this code still allows 1 fc (10.7 1x) of illumination. A factor that should be considered is location of the light source. Occasionally, a stairway will be illuminated by a single luminaire placed at the top of a stairway such that those descending tend to cast a shadow onto the lower steps. Standards and codes usually do not address this condition. The forensic ergonomist should measure the incident light falling on the nosings in question with and without a person in the plaintiff’s position when the misstep occurred. This can be helpful in determining if luminaire placement did or did not contribute to the fall. Another factor to consider is the amount of light reflected from the stair tread. Standards and codes only address the amount of light falling onto the surface but not the more important factor: the amount of light available to the stair user. Darker carpets are often used in commercial buildings, perhaps because they do not show dirt readily. However, this can make the nosings more difficult to see, especially under low-light
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conditions. Dark carpeting reflects as little as 6 or 8% of the incident light, while a lighter colored carpeting can reflect 10 times that amount. Although light reflectance should be measured with a light meter, I have also found that calibrated color chips, such as those produced by Munsell, not only indicate the percentage of reflectance under various light conditions (fluorescence vs. sunlight vs. incandescence) but also provide the hue of the carpet, something most light meters do not indicate (Munsell). The calibrated color chips are also useful because photographic prints cannot be relied upon to represent surface colors accurately. In fact, the color of a carpet, say, in photographs taken on the same day by the same camera, may appear quite different depending upon such things as angle of view or light source. Color chips can be helpful later on when the forensic ergonomist wishes to describe the actual color. Although photographs may not provide exact information on such things as color, they are very important in other ways, as described next. Perceptual Inadequacy—Camouflaged Tread Nosings A misstep wherein the person does not place the foot at the correct spot on a tread can be attributed to camouflaged nosings. The “camouflage effect” is here defined as one in which the nosings of the treads are not easily distinguishable due to color or patterns of the surrounding treads or landing. There is probably no better way to demonstrate this than through photographs taken from the plaintiff’s eye position. An example of a camouflaged nose treading is seen in Figure 20.10 and Figure 20.11. In this case, the woman was descending the stairs under a relatively low lighting condition. The carpet as well as the handrail ended one step prior to the bottom landing, thus providing confusing visual cues. (The truncated handrail also violated the local building code.) All of the other treads were covered with a light carpet except for the bottom tread, which was of polished wood, the same as the landing. When she arrived at the next-to-the-bottom step, thinking she was stepping off onto a landing, she took a normal-length pace. The heel of her forward foot landed on the nosing of the bottom step and she fell, causing a severe and permanent injury to her foot (Johnson, 1998). Perceptual Inadequacy—Inattention Taking an adequate history is very important but outside the scope of this chapter. However, it must be said that an in-depth discussion of the fall with the plaintiff or a witness can yield very important clues as to how the fall occurred. Without knowing how the fall occurred, it is not possible to determine the cause. The history could ascertain if the person had been behaving in a manner that may have contributed to the fall. For example, the person may have been distracted, turned and was talking to another person, or, for some other reason, was not attending to the task of walking on the stairs. Other behaviors that could contribute to a fall would include recent drinking of alcohol, not wearing prescriptive lenses needed to perform the task safely, reading, etc.
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FIGURE 20.10 Stairway Design—Measuring Rises and Runs The rise height and the run length—the dimension of the tread in the direction of travel— are very important factors related to stair safety. Risers that are too high, runs that are too short, and variations in each increase the chance of a fall (Templer, 1975). Accurate measurement of these factors is required. Typical Way of Measuring Stair Treads Straightedge Ruler Method The typical and obvious way to measure the rise of a step is to place a straightedge out over the upper tread and then, with a ruler, to measure the vertical distance from the bottom of the straightedge to the next lower tread. This is usually recorded as the riser height. The run is then measured from the point below the adjacent nosing to the next nosing. Unfortunately, this obvious and common method simply does not guarantee that risers and runs have been accurately measured. Standards say that the rise should be measured vertically between the leading edges of adjacent treads, not from the leading edge of one tread to the back of the tread on the next step (e.g., IBC, 2002). Runs are to be measured horizontally between the vertical planes
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of the foremost projection of adjacent treads and at right angle to the tread’s leading edge (see Figure 20.12). Rise Measurement It is clear that riser height is the height of one nosing above another, not the height of one nosing above the rear of an adjacent lower step. The two measurements will be different when the tread is sloped, as
FIGURE 20.11
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FIGURE 20.12 many are through design and wear. External treads are often built to have a “wash,” or slope, from the back to the front that keeps water from pooling on the step. This means that, in these cases, the actual rise will be greater than a measurement taken at the back of the tread would indicate. However, I have found that the tread may also slope even on interior treads. Whether this slope is a result of design or wear is immaterial as far as the user is concerned. Nonetheless, even a minor slope can result in a difference in riser height as experienced by the user. Consider the situation in which the run length is 279 mm (11 in.) and the slope is 1° down toward the nosing. (A slope of several degrees is not unusual.) The height of the riser above the back of the tread, where it is conventionally measured, would be 4.9 mm (0.2 in.) less than at the front, where it is experienced by the user: (tan 1°)(279 mm)=4.9 mm (0.2 in.). To correct for this if one uses the straightedge ruler method, the slope of the tread must be measured. Any deviation off level needs to be calculated to determine actual riser height. Run Measurement Measuring the run using the straightedge ruler method is a little more complicated. I define “run” as the usable portion of the tread. When descending, a person must be able to place the ball of the foot and the heel comfortably on the run. If there is an overhanging nosing, then the portion behind the overhang is not usable in descent because the back of the foot cannot occupy the area of the tread directly behind the nosing. This portion of the tread, therefore, cannot be considered part of the run (see Figure 20.12). Nosing Profile The run is the distance from the front of the nosing back to the point below the furthermost projection of the adjacent nosing; nosings that have a rounded profile will have a reduced effective run length. The portion of the nosing that is rounded more than about 20° does not provide a surface that will support a foot as weight is applied. Such a steep surface will allow the foot to slip off the edge of the nosing. Thus, the effective run will
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be the distance from the forward-most projection of the nosing that is sloped at 20° to a like point, in the same plane, on the next step. Current code now calls for the radius of curvature at the leading edge of the tread not to exceed 12.7 mm (0.5 in.; IBC, 2002, 1003.3.3.3.2). Compared to a nosing with no curvature, a rounded nosing with this curvature has the effective run length reduced by 8.4 mm (0.33 in.), assuming that the portion of the nosing sloped greater than 20° is unusable. If the radius of curvature were 25.4 mm (1.0 in.), the effective run length would be reduced by 16.8 mm (0.66 in.). Taking these measurements is difficult, if not impossible, using simply a straightedge and ruler. Optimal Way of Measuring Stair Treads Nose-to-Nose Method An alternate way of measuring risers and runs, one suggested by Pauls (1998) and actually simpler and more elegant than the straightedge ruler method, makes use of an electronic level such as the SmartTool®. Riser height and run length are trigonometrically related to the distance and angle between two adjacent nosings. If the angle were 35.3° and the distance were 32 cm (12.5 in.), the rise and run can be calculated (see Figure 20.13): Rise=(320 mm) (sin 35.3°)=185 mm (7.3 in.) Run=(320 mm) (cos 35.3°)=261 mm (10.3 in.) This method overcomes any need to measure the slope of the tread in order to obtain an accurate measure of riser height. The issue of the run dimension, which is difficult to measure due to an overhanging nosing, is also overcome. Comparison of the Two Methods on Wooden Steps The straightedge ruler method was compared to the nose-to-nose method on a set of wooden steps that were in relatively good repair. Initially, the differences between the runs and risers calculated using the two methods were quite large. In order to isolate the source of the error, I measured the slope of each step; this, though not obvious, turned out to be significant. Not only did the front portions of the treads have a greater slope than the back, but the slopes on the various treads were also different. This unrecognized effect of slope was the source of the error between the two methods. When the effect of each slope was calculated and factored into the straightedge ruler approach, the results of the two methods were virtually identical.
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FIGURE 20.13 The two methods differed about 1 mm between the average run dimension for each of six different steps and less than 0.5 mm for the riser dimensions for each of the same steps. Because the nosing-nosing distance was measured with a metric ruler having the smallest gradation of 1 mm, the differences of 1 mm and 0.5 mm appear to be within the limit of the measuring device. The nose-to-nose method was much quicker and simpler than the straightedge ruler method. Repeatability of the Nose-to-Nose Method (Wooden Stairs) Standards in the U.S. call for the maximum variation in riser heights or run lengths to be less than 9.5 mm (0.375 in.) within a flight of stairs. That is, within a stairway, the largest riser or run, minus the smallest, is not to exceed this amount. I conducted a series of five repeated-measures tests, using the nose-to-nose method, on a wooden stairway. Although the means were significantly different between the steps, the average standard deviations (SD) for riser heights and run lengths for each step were small. The average SD for the risers was 0.73 mm (0.03 in.); for runs, it was 0.76 mm (0.03 in.). To make a decision with a confidence level of 95% of whether the variation was less or more than the allowable amount of 9.5 mm (0.375 in.), the maximum variation (in a single set of measurements) would need to be less than 8 mm (0.31 in.) or more than 11 mm (0.43 in.) (i.e., 9.5 mm ± [1.96] [0.76]). If the measured variation were within this range, then additional measurements of the particular risers or runs in question should be considered.
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Rises and Runs on Carpeted Stairs It is more difficult to take accurate measurements of the risers and runs on carpeted stairs. One reason is that the underlying structure that supports the foot is not readily accessible. Another is that of carpet compressibility. When a ruler is pushed down onto a carpet by hand, the force exerted is likely to be much less than that produced by a pedestrian’s foot; the foot will compress the carpet to a greater depth. This is a problem when trying to measure the rise height using the straightedge ruler method because a ruler from the upper nosing to the tread below would normally be pushed down on the nap of the lower tread. Pushing down with a greater force by hand would increase the apparent rise height, but the measured distance would still be less than that experienced by a pedestrian’s foot. Rise height measured in this manner would inevitably vary from step to step—for no other reason than that the force applied by hand onto the ruler would likely be different from step to step. The run length, as typically measured using the straightedge ruler method, is also more difficult to measure on carpeted than on uncarpeted stairs. The typical standard (e.g., IBC, 2002) states that the distance from the most forward edge of the nosing on one step to the most forward edge on the adjacent step should be measured. It is not the outer nap or the carpet that is of importance to pedestrian stair safety but the underlying supporting structure. If, for example, the nap protrudes further on one nosing than on another, it could erroneously be concluded the stairs are not consistent in structure when, in actuality, the nosings of the supporting structure may protrude the identical distance on all of the steps. Pin-to-Pin Method A method that overcomes some of these problems makes use of relatively large, 5 to 6 cm (2 to 2.5 in.) long, straight pins that are inserted vertically through the carpet at the nosing. This can be done without damaging the carpet. The protruding edge of the step is located by inserting the pin several times, moving progressively backward or forward through the carpet until the pin just grazes the foremost edge of the nosing. The pin is left in place and another inserted similarly on an adjacent step. The pins should be placed at equal distances from the left or right wall. The forensic ergonomist would then measure the straight-line distance between the pins with a ruler. The pins not only act as “flags” indicating the location of the nosing, but also can act as convenient indices for reading the distance from the ruler. For example, by placing the “0 mm” point at one of the points, the other pin will provide the interpin distance. I found that it is possible to read the ruler reliably to the nearest millimeter. This distance should be equivalent to the distance between the foremost edges of the two underlying nosings. Then, the angle between the nosings should be measured at the same locations at which the pins were inserted, using the electronic level in the manner described here. The rise height and run lengths of the carpeted stairs can then be calculated as before. To ascertain method repeatability, five measurements were made on four interior carpeted steps. The carpet was about 5 years old; its thickness in the unused area was
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about 2 cm (0.8 in.) and about 1.5 cm (0.6 in.) in the used area. The underlying structure was wood, and the steps sloped downward from front to back at an average angle of 2.6°, with a range of 1.8 to 3.3°. The average rise was about 200 mm (8 in.) and the average run was about 280 mm (11 in.). The electronic level gave angular measurements that were highly repeatable, yielding an average standard deviation of 0.09°. The measurements of the pin-to-pin dimension had an average standard deviation of 2.4 mm (0.1 in.). Under these test conditions, the riser height could be determined with a CI.95 of ±3 mm (0.1 in.) and the run length could be determined with a CI.95 of ±3.7 mm (0.15 in.). For a single set of measurements on the steps, one could decide whether the variation in risers was more or less than the allowable 9.5 mm (0.375 in.) if the measured variation were less than 6.5 mm (0.2 in.) or more than 12.5 mm (0.49 in.) For a single set of measurements, one could determine if the runs had more or less than the allowable variation if the maximum variation as measured was less than 5.8 mm (0.23 in.) or more than 13.2 mm (0.52 in.). This method yields precise information about the underlying structural design of a stairway (Johnson, 2005). Profile Measurement I can think of no alternative way of measuring the profile of a nosing other than by using the profile tool. Placing the tool on the horizontal section of the tread and pushing the pins down until they no longer strike any portion of the curvature of the nosing provides a
FIGURE 20.14 shape of the nosing that can then be recorded for later analysis. Scanning the shape, which will probably resemble a quarter circle, and analyzing it with a computer graphics
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program provides the forensic ergonomist with the information needed to decide if the nosing met code requirements. 20.11 Handrails Once a misstep has occurred on a ramp or a stairway, the person can avert a fall, or at least reduce the severity of injury resulting from that fall, by grabbing and holding onto a handrail. However, in order to be useful, the handrail must be of an appropriate height. Furthermore, the handrail must be graspable so that a person can exert adequate force when falling forward or backward. A misstep on a stairway or a ramp could result in a person’s falling backward, hitting the buttocks, back, and head on the surface of the ramp or stairs. To reduce the impact, the person must be able to exert considerable force onto the handrail. To do this, the hand must be curved over the top of the handrail. Alternatively, a misstep could cause the person to fall forward where, especially on stairs, serious and even fatal injuries can occur. To avert this, the person must be able to exert considerable force with the hand curled around and under the handrail. In order to arrest the fall, the person must be able to pull against the rail, exerting vertical and horizontal forces to the handrail (Maki et al., 1984; Maki, 1985). In each of these fall scenarios, the height of the handrail and its shape are important. Height is important because a handrail that is too low will be out of reach, especially for a person who is falling forward (see Figure 20.14). Also, the handrail must be graspable when the hand is curled over the top as well as when it is curled underneath. The design must be such that a person can exert considerable force to the rail—forward, backward, up, and down. Height of Handrail Maki and others conducted research into the maximum forces that could be exerted in various directions by men and women, young and old, on stairs with varying slopes. They found the optimal height of the handrail midline, as measured above the nosing, to be 91 cm (35.8 in.) (Maki et al., 1984). Up until that time, many codes required that handrail heights be between 76 and 86 cm (30 and 34 in.). When ergonomic research showed that these requirements were inadequate, the codes were subsequently changed. The typical code in North America now requires handrails to be between 86 and 97 cm (34 and 38 in.); they are allowed to be even higher in the U.K. (90 to 100 cm, or 35.4 to 40 in.). Standards usually call for the height of handrails to be a given distance from the top of the handrail to the surface of the ramp directly below it. On stairs, the handrail height is measured from the nosing to the top of the rail. Optimal Way of Measuring Handrail Height A ruler (or tape measure) is the most practical and easiest tool for measuring the height of a handrail above a surface.
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Optimal Way of Measuring Handrail Shape In order for a handrail to be grasped adequately, the shape must not be too small, too large, or too sharp. Current codes in the U.S. call for circular cross-sectional diameters to be between 32 and 51 mm (1.25 and 2.0 in.; e.g., IBC, 2002, 1003.3.3.3.11.3). If the handrail is not circular, then code calls for it to provide equal “graspability” by requiring a perimeter dimension of at least 102 mm (4 in.) and not greater than 159 mm (6.25 in.) with a maximum cross-section dimension of 57 mm (2.25 in.). Edges are required to have a minimum radius of 3.2 mm (0.125 in.) (IBC, 2002, 1003.3.3.11.3). An accurate means of measuring the cross-sectional diameter of a handrail, or an edge of a rail, is by use of a caliper (see Figure 20.15). Such a device can give readings to ±0.1 mm (4×10− 3 in.). The perimeter of a handrail may be quite difficult to measure if the shape is irregular or complex. For instance, if there were several small indentations, then the usable perimeter for a human hand would probably not entail these small indentations. Instead, the usable perimeter would entail the general perimeter of the grasping surface. If so, then this usable perimeter could probably best be measured using a cloth tape, one that conforms only to the major protuberances of the handrail and not to small indentations. Codes often call for the handrail to have edges that are not sharp; any edge should have a minimum radius of 3.2 mm (0.125 in.; IBC, 2002, 1003.3.3.11.3). The profile tool, with pins that are about 1 mm (0.04 in.) in diameter, can be used to measure the sharpness of edges on the handrail. However, if an edge appears to be about 4 mm (0.16 in.) or less in thickness, a caliper should be used for a more accurate determination of sharpness. The profile tool can also be used to measure the depth of indentations. Frequently, the forensic ergonomist will see a handrail that apparently was designed so
FIGURE 20.15
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FIGURE 20.16 that a person could hold onto it using just the fingertips for what has been called a pinch grip (see Figure 20.16). However, to avert a fall, considerable force needs to be applied to the handrail and a pinch grip is not adequate for this purpose. The profile tool is helpful in measuring and recording the shape of the handrail, which can be analyzed later. 20.12 Other Factors in Pedestrian Fall Cases Sunlight and Shadows Whether a walking surface was bathed in sunlight or cloaked in shadow can be important in ascertaining the visibility of a hazard. If in sunlight, the object should be easier to detect visually than if in shadow. If it is a trip hazard, such as a raised concrete edge, it may cast its own shadow and would be easier to detect than if it did not cast a shadow. To evaluate these environmental factors, the forensic ergonomist occasionally needs to ascertain the position of the sun (and occasionally the moon) and relate it to the direction in which a person was walking at the time of the fall.
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Location of Sun A computer program that allows the investigator to determine the azimuth and altitude of the sun at any given time, on any day, at any location on Earth is called Voyager® (2000). This information can then be considered along with the location and height of the raised edge, and with the direction in which the person was facing when the fall occurred, to judge whether a shadow was cast by the trip hazard. To perform these calculations and determine how sunlight affected visibility of, say, a trip hazard, a magnetic compass is important in establishing the direction in which the pedestrian was walking. Assume a pedestrian was southbound on a sidewalk and a raised edge ran perpendicular to the sidewalk, that is, east to west. At around noon in the Northern Hemisphere, the raised edge south of the sidewalk break could cast a shadow, making it more visible. The length of the shadow would be greater in the winter because the sun, at noon, would be lower on the horizon. However, in early morning or late afternoon, the sun would be to the pedestrian’s left or right, and thus the raised edge would cast little or no shadow. The Voyager computer program also allows one to determine the phase of the moon, as well as when it rose and set. This could be helpful in determining whether moonlight was available. Magnetic Compass General compass directions should be recorded in most investigations involving pedestrian falls. A compass can be useful even inside buildings; for example, compass headings can reduce ambiguity in describing doorway locations. In the external environment, a compass may be the only method by which one can describe the location and orientation of various landmarks. However, compass readings are based on magnetic north whereas astronomical programs report the azimuth of the sun and moon in relation to true north. The difference between the two may be quite large. For example, in the Puget Sound area of Washington state (U.S.), magnetic north is about 21° east of true north. For accuracy, the forensic ergonomist should know the magnetic correction for the area where sightings are taken. This correction can be gained from an up-to-date navigational chart; it needs to be up to date because magnetic corrections change over time. Photographic Approaches Important forensic issues related to photographs and videotape go beyond the scope of this chapter. It is possible to take a photograph or videotape of a scene and, because of the great sensitivity to light of digital cameras and high-speed film, make the scene appear different than it did. In fact, no photograph or videotape shows what a person sees, for a variety of reasons. The person sees only a small portion of the scene in focus at any one moment, whereas the entire photograph is typically in focus. In a dark environment, the light sensitivity of the eye increases as adaptation occurs, but this does not occur with a camera. Glare, which is the result of light scattering in the ocular media, cannot be photographed. Although a photograph can be observed for seconds or minutes during which important details become obvious, the pedestrian does not have this luxury.
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Even so, the camera is an invaluable asset for the forensic ergonomist. A panoramic view of the scene can be reviewed days or months later for information that may not have been observed or noted at the time of the site visit. The camera can be useful in recording data from instruments, such as the slope of a ramp as displayed on an inclinometer or the electronic level. If a person tripped over a single-step riser which, for example, had been painted over afterward to alert subsequent pedestrians, a photograph of the changed scene can be made to look as it did at the time of the fall. In Figure 20.17 and Figure 20.18, the riser had been painted with a yellow stripe after the plaintiff tripped over it. To show what it probably looked like at the time of the fall, the photograph was scanned into a computer and imported into Adobe Photoshop® (Adobe Systems). The stripe was digitally removed and replaced, using the clone tool, with sections of the unpainted concrete. Occasionally, a hazard has not been altered after a fall. In these cases, a photograph can be digitally enhanced to show what it could have looked like if the hazard had been highlighted, as is recommended in several safety standards. Of course, in any report or testimony, it is absolutely necessary to show and describe the scene as it appeared before and after any digital manipulation.
FIGURE 20.17 Videotape recordings can be helpful whenever time and motion are potentially important variables. Consider the instance in which a person rounds a corner, encounters oil on the floor, and slips and falls. The defense in such a case might show a photograph of the scene, as it would have looked when it first became visible to the plaintiff, and conclude that the plaintiff was not paying attention. However, videotape of the re-enacted event might show that the person did not have adequate preview time. Such a tape might show, as it did in one case, that the person had less than 2 seconds to see the oil, determine what it was, decide on which avoidance action to take (step to the side, step over it, stop), and then start and complete that action successfully. In such an incident, the videotape, plus expert testimony on perception and response times to unexpected hazards, could be useful in demonstrating that the hazard probably could not have been avoided.
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On the other hand, the videotape could show that there was more than adequate preview time and that the hazard could easily have been noticed and avoided if the person had been exercising appropriate vigilance for the situation.
FIGURE 20.18 The videotape can also be useful in measuring walking speeds. For instance, if a plaintiff was walking at, in the plaintiff’s phrase, “a normal speed,” it is difficult to know exactly what that means. By having the plaintiff walk several times over a measured route, with the instructions to walk at the same approximate speed as on the day of the fall, a fairly reliable estimate of the speed—at least in simulation—can be gained from the videotape. This can be done in reviewing the videotape and measuring with a stopwatch the time it took to walk that route. This could be done more accurately by counting seconds and frames (which pass at 30 per second). Of course, if the plaintiff cannot walk with the same speed as before the injury, this approach would not be useful. Photographs and videotapes are very useful tools when investigating pedestrian falls. I have found that proficiency in using them can be helpful not only in recording and analyzing visual data, but also in presenting that information to the court. 20.13 Checklist Following are some of the things that a forensic ergonomist should consider when evaluating a pedestrian fall: • Trip hazards • Height of trip hazard above surrounding area • Vertical profile of trip hazard • If outside a building: • Orientation of profile with regard to the sun • Compass direction of pedestrian’s path
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• Compass direction of profile • Magnetic correction for area • Day and time of fall (standard vs. daylight savings) • Sky conditions (clear vs. overcast) • Location of shadow-producing objects (trees, buildings) • Distance and vertical angle of object • Highlighting of hazard, or absence of highlighting • Illumination levels at time of fall • Preview time • Smoothness/unevenness of previous walkway • Ramp fall • Slope of ramp • If curb cut or curb ramp, slope of side slopes • Length of ramp • Slip resistance of surface • Handrail location, height, graspability • Stairway design • Height of risers • Run lengths • Variation between risers and runs • Width of stairs • Illumination on treads and reflectance • Glare/shadow from luminaire • Distinctiveness of nosings • Camouflage effect on nosings • Handrail location, height, graspability • Photographic approaches • Panoramic view of fall site • View of fall site from several different directions • Videotape when motion and time are important factors
20.14 Standards across Various Countries Following are a few standards used in different countries. These were obtained from members of the Human Factors and Ergonomics Society who reside in these countries, who graciously took the time to respond to the survey. Members from some countries, such as Pakistan and Singapore, could locate no standards related to pedestrian walkway safety. In other countries, including Japan, Canada, the U.K., and the U.S., the standards are quite complex. Therefore, the summary table does not attempt to give a complete or detailed review of the standards in these countries. It is also of interest to note that some of the standards appear to accommodate to the stature of the population. For example, the
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Japanese have stairway standards that accommodate to the size of students in primary and secondary schools.
SUMMARY TABLE Building Standards and Guidelines for Several Countries Country
Canada
China
Do codes Yes Yes address stairs? Allowable 20 cm (7.9 in) 15 cm riser height (5.9 in)
Minimum rise height Maximum run length Minimum run length
12.5 cm (5 in) Not specified 35.5 cm (14 Not in) specified 21 cm (8.3 in) Not Private specified 23 cm (9 in) Public
Japan
Japan
Yes, for Yes, for solid buildings walkways 18 cm (7 in) Small house: 23 cm (9 in) House >200 sq.m: 20 cm (7.9 in) Prim, school: 16 cm (6.3 in) High school, etc.: 18 cm (7 in) Other facilities: 22 cm (8.7 in) 15 cm (6 in) Not specified
UK
US
Yes
Yes
House: 22 cm (8.7 in) Assembly bldgs.: 18 cm (7 in) All others: 19 cm (7.5 in)
17.8 cm (7 in) Public 19.6 cm (7.75 in) Domestic
10 cm (4 in)
10.2 cm (4 in) 30 cm (11.8 Not specified 35 cm (13.8 in) Not in) specified 26 cm (10.2 Small house: House: 22 cm (8.7 27.9 cm (11 in) 15 cm (6 in) in) in) Public House >200 Assembly: 28 cm 25.4 cm (10 in) Domestic sq.m: 24 cm (11 in) All others: 25 cm (9.5 in) Prim, school: (9.8 in) 26 cm (10.2 in) High school, etc.: 26 cm (10.2 in) Other facilities: 21 cm (8.3 in) Handrail 86.5–96.5 cm Not ~80 cm Not specified 90–100 cm (35.4– 86.4–96.5 height (34–38 in) specified (~31.5 in) 40 in) cm (34–38 in) Not specified Not specified 3–5 cm (1.2–2 in) 3.2–5.7 cm Handrail 3–5 cm (1.2–2 Not specified (1.25–2.25 diameter in) in) Handrail 4 cm (1.6 in) Not 3 cm (1.2 in) Not specified Not specified 3.3 cm (1.5 from wall specified in) Minimum 10 lux Not Not specified Not specified 100 lux 11 lux
Handbook of Human factors in litigation lighting on specified stairs External, 20 lux e.g., for bridge For subway 100 lux Landing Same as stair Not 120 cm (47 width width up to specified in) (If ht. 110 cm (43 in) stairs>3m) Maximum ramp slope Trip hazard standards? Trip hazard height Slipresistant surface? Slip resistant criteria:
1:6 (9.5°) or less No
10% (4.5°) No
598
(suggested) 11 lux
120 cm (47 in) Not specified (If ht. stairs>3m)
Same as stair width up to 121.9 cm (48 in) <12% (5.4°) Not specified 1:12 (4.8°) or less 1:8 (7.1°) or less No No Yes Yes
Not Specified Not Not specified Not specified 5 cm (2 in) & 15 specified cm (6 in) max. threshold ht. Yes Yes Yes Yes Yes
Not Specified Not Not specified Not specified <25 high potential specified for slip etc. Roughness measured
How is it to Not Specified Not specified be measured? Standard Section 9.8 of title(s) the National Building Code of Canada, 1995 Edition: Stairs, Ramps, Handrails and Guards.
Not specified Not specified TRL Pendulum, RAPRA Technology Ltd. Building In the Road Solid Regulations Crosswalk Act: (1998) Approved Crosswalk Facility Document K, The bridges and Standard, Stationary Office crossway chapt 2–7 subways for ISBN 0–11– 753394 pedestrians British Standards House and Buildings Act BS5395–1:2000 Stairs, ladders and (Amended 2001), Articles walkways: Part 1. Code of practice 23–27 for stairs
Contributors to the Standards Survey Canada Vanessa Hawes, B.Sc. & Jason Kumagai Human Factors Consultant Humansystems Inc.
1.3 cm (0.5 in) Yes
COF>0.5 Not codified, but generally accepted Not specified IBC 2003, IRC 2003 Life Safety Code 2003 24 CFR
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111 Farquhar Street Guelph, ON, N1H 3N4 http://www.humansys.com/ China Alan Chan, Ph.D. City University of Hong Kong Dept. of Manuf. Eng. & Eng. Mgmt, Tat Chee Avenue, Kowloon Hong Kong, 85227888439
[email protected] Japan Yoko Shintani Hokkaido Development Engineering Center #11, South-1, East-2, Chuo-ku Sapporo, Hokkaido, Japan 060–0051 e-mail
[email protected] http://www.decnet.or.jp/ Yoshio T. Ikeda Dept. of Management and Information Systems College of Management and Information Science Aichi Institute of Technology Toyota-City, Aichi, Japan 470–0392 Pakistan Aized Hasan Mir #24, St. 85, G/6/4, Islamabad Fed 44000, Pakistan, (92) 51–273731 e-mail:
[email protected] Singapore Professor Martin Helander, Ph.D. Nanyang Tech. University, School of Mech. and Prod. Engin. 639746, Singapore e-mail:
[email protected] Lee, Hock Siang Singapore Government e-mail:
[email protected] United Kingdom Mike Roys MSc(Arch) BSc MIHS Principal consultant—Safety, Health and Environment BRE Environment BRE, Garston, Watford WD25 9XX
599
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E-mail:
[email protected] http://www.bre.co.uk/ References Adobe Systems, http://www.adobe.com/. American Slip Meter, Inc. (Englewood, FL: American Slip Meter, Inc). ANSI A1 17.1–1992, 1992, Accessible and Usable Buildings and Facilities. (Falls Church, VA: Council of American Building Officials). ASTM F 609–96, 1996, Standard Test Method for Using a Horizontal Pull Slipmeter (HPS). (West Conshohocken, PA: ASTM). ASTM F 1637–95, 1996, Standard Practice for Safe Walking Surfaces. (West Conshohocken, PA: ASTM). ASTM F 1679–00, 2000, Standard Test Method for using a Variable Incident Tribometer (VIT). (West Conshohocken, PA: ASTM). Bakken, G.M., 2002, Human factors and legal aspects of fall injuries. In Hyde, A.S., Bakken, G.M., Abele, J.R., Cohen, H.H., and LaRue, C.A. (Eds.). Falls and Related Injuries: Slips, Trips, Missteps and Their Consequences (Tucson: Lawyers and Judges Publishing), 229–393. CFR, 1995, Code of Federal Regulations, Housing and Urban Development, Title 24, Part 40, Appendix A, 4.5.2. (Washington, D.C.: US Government Printing Office). Cohen, H., 2000, A field study of stair descent. Ergonomics Design , Spring, 11–15. Ekkebus, C.F. and Killey, W, 1973, Measurement of safe walkway surfaces, J. Soap/Cosmetics/Chemical Specialities , December. English, W., 1996, Pedestrian Slip Resistance: How to Measure It and How to Improve It (Alva, FL: William English). Gronqvist, R., Chang, W., Courtney, T., Leamon, T., Redfern, M., and Strandberg, L., 2001a, Measurement of slipperiness: fundamental concepts and definitions. Ergonomics , 44(13), 1102–1117. Gronqvist, R., Abeysekera, J., Card, G., Hsiang, S., Leamon, T., Newman, D., and Gielo-Perczak, K., 2001b, Human-centered approaches in slipperiness measurement. Ergonomics , 44(13), 1167–1199. International Building Code, 2002, (Falls Church, VA: International Code Council). Jahss, M., 1982, Disorders of the Foot (Philadelphia: W.B. Saunders Company), 44–46. Johnson, D., 1998, New stairway…old problems. Ergonomics Design , October, 7–10. Johnson, D., 2005, Increased precision reveals common error in stair measurements, Ergonomics in Design , Spring. Life Safety Code Handbook, 2000, (Quincy, MA: National Fire Protection Association). Maki, B.E., Bartlett, S.A., and Fernie, G.R. 1984, Influence of stairway handrail height on the ability to generate stabilizing forces and moments. Hum. Factors , 26(6), 705–714. Maki, B.E., 1985, Influence of handrail shape, size and surface texture on the ability of young and elderly users to generate stabilizing forces and moments. Contract No. 0SR84–00197, National Research Council, Ontario, Canada. Munsell charts for judging reflectance factor for illuminating engineers, television engineers, architects, designers and decorators. (Baltimore: Macbeth Division, Kollmorgen Corp.). Pauls, J., 1991, The cost of injuries in the United States and the role of building safety, Building Standards , 24, 18–22.
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Pauls, J., 1998, Techniques for evaluating three key environmental factors in stairway-related falls, Proc. Human Factors Ergonomics Soc. , 1630. Perkins, P., 1977, Measurement of slip between the shoe and ground during walking. In Anderson, C. and Senn, J. (Eds.) Walkway Surfaces: Measurement of Slip Resistance , ASTM Special Technical Publication 649, (Philadelphia: ASTM), 71–87. Sacher, A., 1993, Slip resistance and the James Machine 0.5 static coefficient of friction—sine qua non, ASTM Standardization News , August. SmartTool, Builder’s Angle Finder. (Oklahoma City: Macklanburg-Duncan). Templer, J., 1975, Stair shape and human movement, (Ann Arbor: U.M.I. Dissertation Information Service). Templer, J., 1992, The Staircase: Studies of Hazards, Falls and Safer Design , (Cambridge, MA: MIT Press). Uniform Building Code, (Whittier, CA: International Conference of Building Officials). Voyager III Dynamic Sky Simulator, Version 2.0, 2000. (San Ramon, CA: Carina Software).
21 Balcony Falls Magdalen Galley Ergonmics Consultant 0–415–28870–3/05/$0.00+$ 1.50 © 2005 by CRC Press
21.1 Introduction to Human Factors Principles and Relevance to Standard of Care Human beings slip, trip, and fall in many different circumstances and for many different reasons. For most children and able-bodied adults, the majority of these falls are not serious most of the time. However, for older or disabled adults, or when falls involve significant changes in level, the consequences of falling can be serious and even fatal. Balustrades are therefore provided to prevent people from falling from elevated structures such as balconies and stair landings. It would thus seem to be self-evident that these must be designed so as to protect all sizes of persons, from small children to tall men, including those who may be inebriated or under the influence of drugs. They must also protect the elderly and infirm, who may fall or suffer some sort of fainting fit and lose consciousness. Of the many disciplines that make up ergonomics, those most relevant to the design of balcony balustrades are anthropometry and biomechanics. Only by understanding the dimensions of people and how they move, especially in rotation about their center of gravity, can the size and design of environments, architectural features, and products generally have any relevance. It is self-evident that small children can pass through smaller gaps than can large adults; thus, the regulations controlling gaps in stair and balcony rails reflect this. Conversely, because an adult can accidentally fall or be pushed over a much higher barrier than can a small child, the regulation heights of a balcony balustrade, when they exist, are set accordingly. In order to offer this protection they should therefore take account of the height of tall men and the behavior and relatively small size of small children to prevent the former from overbalancing over the top and the latter from climbing over or falling through gaps in the balustrade. To stop adults inadvertently falling over them, balustrades need to be as high as or higher than the center of gravity of a tall man (99th centile) and to take account of human behavior, including the consumption of excessive amounts of alcohol. Although many ergonomists would readily accept this argument, it is not a universal concept, and in the author’s experience the design and construction of balustrades around the world have often failed to meet this expectation. Even in what we might consider to be the “civilized” world of London, at least one example exists in which ergonomics
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principles and standards of care fell far short of what the reasonable person might expect, although it took a court case and an appeal to prove this. In many more cases in hotels around the world, people visit for exotic holidays and suffer serious injuries instead. 21.2 Objective and Scope of the Chapter This chapter will look at examples of balcony falls involving adults and relate these to building regulations, standards and codes of practice, and how these have been seen to govern the standard of care offered to users of buildings (particularly public). Although falls from domestic balconies do occur, most accidents that involve litigation occur in public buildings or hotels where the victim is not familiar with the surroundings generally, and the balcony or balustrade specifically. Victims are usually, but not always, tall (95th centile or over) and have often consumed at least a moderate amount of alcohol prior to the fall; some accidents happen late at night. Typical injuries are fractured skulls and spines with a number of victims left as para- or quadraplegics from spinal injuries. Falls in which victims were attempting to climb between balconies or otherwise behaving in a reckless fashion will not be considered. Children’s falls as a result of climbing over or falling through balustrades will also be excluded from detailed examination because the causes of these falls are behavioral rather than biomechanical. Important cases will be highlighted and legislation, standards, and codes of practice cited. 21.3 Discussion of Principal Issues Issues Relating to the Balcony In the cases in which the author has been involved, the principal, overarching question has been “Were the height, construction, and design of the balustrade on the balcony at the time of the accident sufficient to provide a reasonable level of safety to users of the balcony?” This can be divided into a number of subquestions, as follows: 1. Where is the approximate position of the center of gravity of the fall victim? 2. How does this relate to the presumed height of the balustrade on the balcony at the time of the accident? 3. How does the minimum height of balustrades in the relevant building regulations in the victim’s home country (U.K., U.S., Europe, etc.) relate to the center of gravity of adult persons generally and the fall victim in particular? 4. How does the minimum height of balustrades in the local building regulations, if any exist, relate to the center of gravity of adult persons generally and the fall victim in particular? In order to address these questions, we need to look at the way in which the human body rotates and falls as well as at body size and human behavior.
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Research on Moments of Inertia and Centers of Gravity Introduction Moments of inertia and centers of gravity of the human body are fundamental parameters that enter into all computation involving body rotation. (Santschi et al., 1963). The center of gravity of a human body is located at the point of intersection of three orthogonal planes (at right angles to each other), as shown in Figure 21.1. The z-axis is formed by the intersection of the sagittal or median plane (front to back) and the frontal or coronal plane (side to side); the y-axis is formed by the intersection of the frontal (coronal) and transverse (horizontal) planes; and the x-axis is formed by the intersection of the sagittal (median) and transverse (horizontal) planes. Thus, the z-axis operates in an up-and-down direction, the y-axis acts in a side-to-side direction, and the x-axis acts in a front-to-back direction.
FIGURE 21.1 The location of the center of gravity of the human body.
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Basically, two methods of approach have been used in determining the location of the center of gravity of the human body: the direct (or whole body) approach in which the body under consideration is considered as a whole, and the indirect (or segmental) approach in which various parts or segments of a body are considered separately and the results used to compute values for the whole body. Since the 19th century, much research has been undertaken using these techniques to determine man’s center of gravity. The following section details the findings of this research. The Center of Gravity of the Human Body One initial source for research methods and data is the NASA Anthropometric Source Book (1978), which cites numerous earlier studies into the determination of the center of gravity or mass of the human body. Many of these earlier studies, most of them American, have only looked at adult males. There are two basic approaches to measure the mass distribution of the human body: living humans and cadavers. However, many different variations of these have been used. The NASA source book says that “the center of mass of the whole body in every position is approximately at the site of the pelvis” and that “in general, the center of mass in living adult males and females in the standing position is 55% of stature as measured from the floor.”
TABLE 21.1 Estimates of Center of Gravity for Various Statures Method of estimation
5th percentile male (1640 mm)
50th percentile male (1760 mm)
95th percentile male (1880 mm)
54% of stature 885.6 950.4 1015.2 55% of stature 902 968 1034 Santschi et al. 852.6 972.6 1092.6 Ignazi et al. (range) 964.9 (869) 964.9 964.9(1011) Source: Data from Pheasant, S., 1996, Body space. Anthropometry, Ergonomics and the Design of Work (2nd ed.) (London: Taylor & Francis).
This latter statement is supported by Page (1974) in a research study: “…the frequently made statement that the vertical position of the center of gravity is 55% of the full height of the young adult male is supported by this study.” Page continues: “Thus, we can conclude that the weight of a subject does not influence the position of his center of gravity as much as his height does.” Watkins (1999) states that the center of gravity is about 54% of stature. Swearingen (1962) looked at the effect of varying the body posture on the location of the center of gravity. After looking at a total of 67 different positions, they concluded: …in spite of the wide variation of body sizes and mass distributions there is surprisingly little variation in the location of the body e.g. [center of gravity] when measured from a reference point on the pelvis. In a given body position the e.g. of at least 90% of the adult male population falls within a sphere 2 inches in diameter.
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Other researchers, notably Santschi and colleagues (1963) and Ignazi et al. (1972), give the center of gravity as a mean (average) value plus a standard deviation (an indication of the spread of the values) and, in the case of Ignazi and associates, the range itself (869 mm min. to 1011 mm max. above the floor). However, the precise location for an individual can only be obtained by measuring it directly because a simple calculation shows that, although this method may well hold good for those of average stature, it is a poor predictor for the very short and the very tall. Table 21.1 indicates this; to compound this situation, there is quite a spread of heights across male populations, as indicated in Table 21.2. It can be seen that if the tallest population—namely, Dutch students aged 18 to 30—is considered, then the center of gravity (based on estimates of 54 and 55% of stature) is located at around 1040 to 1060 mm above the ground for 95th centile males and 1065 to 1085 mm for 99th centile males. If we then add 25 mm as a footwear allowance, this rises to a maximum of around 1110 mm for 99th centile males. The height of a balustrade that is needed to prevent such a tall individual from overbalancing is therefore around 1100 mm, and certainly no lower. Alternatively, an individual’s center of gravity may be fairly accurately estimated by comparing him with subjects of a similar stature included in the various experiments. Nevertheless, the fact remains that it is self-evident that, to obtain an estimate of the center of gravity of an individual, his stature must be accounted for in some way. As well as calculating the position of the center of gravity of the human body on the zaxis, this must also be located on the x- and y-axes. For the position on the x-axis, Santschi et al. (1963) quote a mean value of 88.9 mm measured from the back plane, and Ignazi et al. (1972) quote 88.3 mm (range 76 to 97 mm). For the y-axis, Santschi et al. quote 122 mm from the iliac crests and Ignazi et al. quote 150 mm (range 134 to 177 mm). Again, reference to the data from individual subjects would enable a more accurate estimate for an individual because body depth and thickness at the pelvis will obviously affect the precise location. As a final method of estimation, the center of gravity of an individual can be measured directly; however, this is a complex and expensive process requiring specialist equipment.
TABLE 21.2 Male Stature Variation Population Dutch students 18–30 Dutch adults 18–66 Loughborough University (U.K.) students U.S. 18–39 U.S. 25–50 U.S. 18–25 U.S. 18–64 German 25–50 U.S. 18–64, high income German 18–64
95th percentile value (mm)
99th percentile value (mm)
1927 1913 1903
1973 1963 1948
1879 1879 1878 1877 1877 1877 1865
1929 1929 1927 1925 1922 1921 1910
Balcony falls European 18–64 U.S. 25–50, low income French 25–50 U.S. 18–64, low income U.S. 18–39, low income U.S. adults 18–64 U.S. 18–25, low income Italian (North and Central) 18–83 French 18–64 British adults 18–64 Italian (south) 18–83 Chinese urban 18–45 Japanese 18–55 Source: data from Peoplesize, 2002.
607
1861 1858 1856 1852 1852 1851 1851 1847 1846 1845 1804 1792 1781
1913 1909 1904 1900 1900 1908 1896 1897 1894 1899 1848 1834 1820
Research on Balustrades and Guard Rails Height of Handrails, Balustrades, and Guard Rails Unlike the handrails found on stairs, guard rails and balustrades on landings and balconies are needed for very different purposes. A handrail is usually too low to prevent people from falling over the edge and should not be perceived as providing protection unless it is positioned at a higher level—a solution that would limit its effectiveness as a handrail. A balustrade or guard rail is one of several ways of preventing people from falling over the edge of a landing, platform, balcony, ramp, stair, and so on. The choice of an effective height for a guardrail was studied by Fattall et al. (1976), who concluded that it should be set approximately equal to the height of the center of gravity of the 95th centile adult male, thus giving a value of 1092 mm (43 in.) for the U.S. This is similar to the requirements for the current U.K. Building Regulations, which quotes a minimum height of 1100 mm and seems to be the basis for U.S. regulations as well. Injury Severity and Fall Height Falls from relatively low heights are frequently serious, and it is not unusual for falls from 1.2 m (4 ft) to be fatal. On this basis, Snyder (1977) and Chaffin et al. (1978) recommended the use of physical barriers when fall distances exceed 1.2 m. The consequences of a fall over an edge are dependent not only on the height of the fall but also on the surface that is hit. A fall of 0.6 m onto rocks is likely to be more serious than a fall onto a padded carpet. Nevertheless, any fall is risky. Analysis of fall accidents (Snyder, 1977) has shown that people who fell less than 6 m (20 ft) landed on their heads 76% of the time. However, people who fell more than 6 m landed on their feet 63% of the time. Therefore, in relatively short falls, the head is more likely to be injured than in the higher falls. Thus, lower balustrades at lower heights are not justified.
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Recommendations for Guard Rails and Balustrades Studies in the U.S. (Fattall et al., 1976) used anthropometric dummies to simulate various postures of humans as they lean against or walk into a balustrade at brisk speed; the conclusion was that the height needed to be equal to the center of gravity of the 95th percentile adult male. This gave a height of 1070 mm (42 in.) for the subject in a straight posture on a level surface. For safety, a more cautious recommendation might have been to use the 99th centile value of 1090 (43 ft) to take account of the dynamics of the increasing stature of the population and to protect people who are more than 1.85 m (73 in.) tall (Templar, 1992). As the width of the top of the balustrade increases, the risk of overbalancing apparently decreases, so Fattall and colleagues suggested a relaxation of the 1070-mm rule when the horizontal width of the balustrade is greater than 152 mm and the adjoining interior floor surface is level. They recommended that, under these circumstances, the minimum height of the balustrade should not be less than 1220 mm minus the minimum width of the top surface of the balustrade. Thus, if the width of the top surface of the balustrade is 250 mm, the required height might be 970 mm. However, they concluded that the balustrade should not be set less than 760 mm high in any instance. A final effective factor that should be considered is that people may choose to sit on a balustrade, particularly if it is in the form of a wall with a flat top. A loss of balance from the wall may obviously lead to a fall. This type of design is not unusual in many locations. The solution is to make the wall impossible to sit on (Templar, 1992). Contributing Factors In addition to the duties owed by those who design, build, and maintain balconies—as well as those who provide balconies as part of a service provision—users have a corresponding duty to act responsibly and to exercise ordinary care for their own safety. It is not unusual for a claimant’s compensation in a balcony fall case to be reduced because he or she failed to act in a responsible fashion, for example, by being excessively inebriated. However, to the author’s knowledge, no compensation has been denied because a balustrade was so evidently dangerous because of its inadequate height that nobody with any sense should have ventured onto the balcony. The main important factor in the cases in which the author has been involved is the consumption of alcohol and, sometimes, legal or illegal drugs. The view frequently taken by the owners of the buildings in which the falls occur is that consumption of excessive quantities of alcohol by the victim absolves the owners of responsibility because the fall victim did not have proper regard for his safety. Although this is undoubtedly true, it is still reasonable to expect a balustrade to provide a degree of protection, even for the falling drunk. Many of these accidents occur when the victims are on holiday, so it is arguable that the hotel owners should assume that many of the residents will be a little “worse for drink” on many occasions. Whether one approves of this behavior is not relevant because even drunks have the right to a safe environment and are questionably more in need of it than the sober. In support of this view, U.S. Judge Heydenfeldt opined in 1855, “If the defendants were at fault in leaving an uncovered hole in the sidewalk of a public street, the intoxication of the plaintiff cannot excuse such gross negligence. A
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drunken man is as much entitled to a safe street, as a sober one, and much more in need of it.” Another factor that contributes to fall accidents is age and infirmity. As people age, their balance and coordination deteriorate and they fall more frequently. The consequences of falling also become more severe with age because bones are more fragile, fracture more readily, and take longer to heal. Protecting older and infirm people from falling is therefore particularly important. Legislation, Standards, and Codes of Practice The preceding research has shown that the center of gravity of a tall (99th centile) male is estimated at between 1065 and 1085 mm above the ground when he is barefoot. The addition of shoes (usually taken as 25 mm for men) will raise the upper limit to around 1110 mm. If tall males are to be prevented from inadvertently falling over barriers, the balustrade needs to be at least as high as and preferably higher than this figure. Thus, the common regulation height of 1100 mm is a minimum height for a balustrade. Regulations change over time, but they are not retrospective; thus, those relevant at the time of construction of the property must be used when putting together a case. However, if any renovation of the balcony has occurred, then the expectation is that the balustrade will be upgraded to meet the standards and regulations applicable at the time of the upgrade. References to some historic regulations are therefore included when information is available. Also, because in some jurisdictions building regulations are not mandatory, it is frequently necessary to demonstrate that a noncompliant balustrade is dangerous and was a contributory factor in the fall. Noncompliance alone is seldom sufficient to carry the case. In cases in which no regulations exist, the case must be built from first principles. The U.K. • Building Regulations 2000. Part K: protection from falling, collision, and impact, cited in the current U.K. regulations, requires a minimum height of 1100 mm for the balustrade of a balcony. It also requires gaps to be sufficiently small to prevent the passage of a 100-mm-diameter sphere, so that small children cannot fall through. • British Standard BS 6180:1999 Barriers in and about Buildings—Code of Practice. This code gives the minimum barrier heights as 1100 mm for external domestic balconies and balconies in all other settings, except those in front of fixed seating within 530 mm of the barrier, such as in the balcony of a theatre. • Statutory Instrument 1992 No 3288 The Package Travel Package Holidays and Package Tours Regulations 1992. This statutory instrument is based on a European directive designed to protect holiday makers from financial loss in the event of problems with a package holiday or tour company, but has the added clause that makes the package tour operator liable to the consumer for any damage to him by the failure to perform the contract or the improper performance of the contract. This includes the provision of accommodation. There are exceptions, but this does offer great help to the injured person when seeking redress because he or she is then in
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dispute with the tour operator in the U.K. or home country in Europe, rather than a hotel in some remote holiday destination. The U.S. The situation is rather complex in the U.S. A number of building codes can be adopted and enforced by any jurisdiction and no single code regulates the entire country. Under the Tenth Amendment to the Constitution, states and their localities retain the authority to adopt and enforce laws that regulate the design and construction and use of buildings; consequently, no two states have chosen to regulate the built environment in exactly the same way. For example, 43 states adopt codes and standards for state-owned construction and 25 states have chosen to adopt and enforce such regulations for all construction on a statewide basis; 49 states enforce only energy conservation requirements for buildings statewide, and 36 states regulate factory-built structures at the state level. The remainder of the states leaves such structures to be covered by local laws, if at all. In total, more than 40,000 political jurisdictions in this nation adopt or enforce the modern building codes and standards that provide for the public’s safety. Ninety percent of all Americans live and work in jurisdictions in which their health and life safety are protected by buildings constructed or renovated based upon model building codes and standards. Diverse sets of codes and standards, covering such areas as structural, electrical, mechanical, plumbing, energy conservation, accessibility, and life safety, are developed for states and localities to adopt by not-for-profit private sector associations using voluntary labor from the building, fire services, trade union, and construction communities. Such codes and standards lack cohesiveness and technical uniformity. In the past, multiple private-sector groups produced diverse and often conflicting codes, leaving the states to blend the best provisions from these documents into a patchwork of construction codes. In the 1990s, the nation’s model-building and fire codewriting bodies came together to write and publish (for state and local adoption) a uniform, cohesive, single set of codes and standards covering all of the preceding technical areas (see Figure 21.2). However, this is proving difficult, and as things stand at the time of writing, control is still piecemeal, as indicated in Figure 21.2. The Standard Building Code belongs to the Southern Building Code Congress International (SBCCI), the National Building Code belongs to Building Officials and Code Administrators International (BOCA), the Uniform Building Code belongs to the International Conference of Building Officials (ICBO), and the International Code belongs to the International Code Council (ICC). The ICC is a combination of SBCCI, BOCA, and ICBO and, at the time of writing, it is revising the international existing building code to form a comprehensive building code that encourages the use and reuse of existing buildings. The required height for a balustrade would therefore depend on which of the codes is enforced, but is reported to be typically 1070 mm, somewhat lower than the U.K. requirement.
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FIGURE 21.2 Map of building code influence as of January 2001. European The Package Tours Directive 90/314/EEC gives similar protection to European travelers to that provided by the U.K. regulations. See Subsection “The U.K.”. Other • The Barbados National Building Code, 1993. The Barbados National Building Code, 1993, section 3.5.10, stipulates the requirements for stair guards and balustrades. However, it is not mandatory in Barbados. For changes of level of 3 m or more, the section requires the guard rail or balustrade to be 1 m high and to have no openings wider than 150 mm and no horizontal rails or ledges that could provide a toe hold. • Greater London Council Code of Practice on Means of Escape in Case of Fire 1974. The GLC Code of Practice 1974 had a lower requirement for the minimum height and specified 1050 mm. This minimum height is some 50 mm (just under 2 in.) lower than the national building regulations applicable at the same time. • British Standard Codes of Practice CP3:1971 and CP499:1972. The two British Standard Codes of Practice had a minimum height requirement of 1070 mm
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(approximately 3 ft 6 in.). This is some 30 mm (just over 1 in.) lower than the building regulations applicable at the same time.
21.4 Examples Ward v Ritz Hotel (London) Limited This was a widely reported and cited case in which the plaintiff (claimant) was severely injured when, as a result of a faint, he fell backward over a low balustrade on the balcony of the defendants’ hotel restaurant. The author was the expert ergonomics witness (and the only ergonomist in the case) for the plaintiff. The defense made use of the services of an architect as an expert witness. The case hinged around whether or not the Ritz Hotel had exercised a reasonable duty of care to Mr. Ward as a visitor to the hotel. The case was taken under the Occupiers’ Liability Act, 1957, and also drew on the importance and legal status of standards and regulations relevant at the time. When the hotel had been constructed in about 1905, the balustrade had been about 1003 mm above the floor. In about 1976, the floor of the balcony had been resurfaced, raising the floor level by about 100 mm and resulting in the balustrade being less than 915 mm above floor level. In 1976, the British Standards Institution’s recommended standard for the height of any balustrade was 1067 mm. (It has since been raised to 1100 mm.) The Occupiers’ Liability Act, 1957 “requires an occupier to take such care as in all the circumstances of the case is reasonable to see that the visitor will be reasonably safe in using the premises for the purpose for which he is invited or permitted by the occupier to be there.” The plaintiff took action under this act, claiming that the defendants, the Ritz Hotel, were in breach of their common duty of care. Originally the Judge (MacPherson J) dismissed the claim on the grounds that the plaintiff had failed to prove a want of reasonable care on the part of the defendants despite the fact that they had effectively lowered the height of a balustrade (by raising the floor level) so that it was between 890 and 920 mm high, with an average height of 910 mm. This was between 147 and 177 mm lower than the standards for 1976 and between 210 and 180 mm lower than the standard minimum height for balustrades in this type of location at the time of the accident. In his judgment, the judge stated that although on the facts the plaintiff’s fall would not have occurred if the balustrade had been of a height required by the British standard, failure to observe a British standard did not necessarily constitute a breach of the defendants’ duty of care to the plaintiff as a lawful visitor. As a consequence of this judgment, Mr. Ward appealed and his appeal was upheld (with one of the three appeal judges dissenting). These judges concluded that the judge had given too little weight to the British standard. Such standards represent the consensus of professional opinion and practical experience as to sensible safety precautions. Although they were not legally binding, they were guides that provided strong evidence of competence at the date they were issued. During the case, the plaintiff did not merely rely on the authority of the British standard but called the author as an expert witness to explain the background and justification of the standard and thus demonstrate to the court that a height of 1067 mm
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was a reasonable minimum height to provide protection. Because this was a personal injury case, it was also necessary to demonstrate that the low balustrade was a risk to Mr. Ward, even though he was below average height at 1691 mm or 5 ft 6 in. (28th-centile adult British male), and not just to tall men. Mr. Ward’s estimated center of gravity was taken to be 930 mm and, thus, the balustrade over which Mr. Ward fell was, even at its highest point, some 30 mm lower than his center of gravity. It was also quite narrow. If he had placed his feet on the 100mm-high sloping plinth at the base of the balustrade, this would have improved the situation with regard to keeping his center of gravity over his feet (in the x-axis), but would have worsened the amount by which his center of gravity (in the z-axis) was above the top of the balustrade. In allowing the appeal, Lord Justice McCowan stated that if MacPherson J “thought Miss Page [the author] only considered this balustrade to be a danger to a very tall man he misunderstood her evidence. That evidence was, in my judgment, clearly to the effect that the balustrade was unsafe for the plaintiff.” Lord Justice Nourse added, “If he [MacPherson J] had appreciated that it was certainty that it [Mr. Ward’s center of gravity] was some five inches above that level, he would very likely have accepted Miss Page’s evidence that no upwards movement was necessary.” MacPherson J concluded by saying that with regard to the status of British standards, he agreed with Judge Newey, QC, when he stated that: British Standards Codes of Practice are not legal documents binding upon engineers or upon anyone else, but they reflect the knowledge and expertise of the profession at the date when they were issued. They are guides to the engineer and in my view they also provide strong evidence as to the standard of the competent engineer at the date when they were issued. This judgment set an important precedent in British law by setting the status of British standards. Despite the height of the fall, Mr. Ward did not suffer serious long-term physical injury, but the consequences of his head injury meant that he never returned to his former occupation as a senior accountant. Fall from Balcony of a Hotel in Barbados The amount of eyewitness information available on the exact details of this accident is limited because the victim had very little recollection and the other eyewitnesses had only limited information. The victim was approximately 1956 mm in height and weighed approximately 15 stone (95.5 kg). He was 24 years old at the time of the accident and the balustrade was 740 mm high. One witness reported that “a tall figure in white flew out over the balcony backwards with some considerable force.” Another stated that he “saw a tall figure wearing a white shirt falling out over the balcony at a considerable pace.” A third eyewitness, who shared a room with the victim, reported that the last time he saw the victim before the fall he was
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silhouetted on the balcony with his back to the rail and then he was aware of the victim falling over the rail. After the accident, the victim’s roommate reported that when he first looked over the balcony to the grass below and saw the victim, he was sprawled face down with his head nearest the wall and about 2 ft from a stone step. A waitress and the hotel manager also reported that he was face down, but the manager added that his knees were drawn up. When the paramedics arrived with the ambulance, they also reported the victim to be lying face down. The balcony floor appeared to be covered in tiles or paving bricks with a somewhat uneven surface. The balustrade was of an open, fairly rough, framed timber construction that the police estimated to be approximately 3 ft high (914 mm). The victim’s father measured it to be 29 in. or 29.5 in. (737 to 749 mm). It is also apparent that the gaps in the balustrade were large, of the order of 6 in. wide by 9 in. high (150 by 230 mm). The police estimated that the vertical drop to the ground from the balcony was about 10 ft (3.05 m); however, on the basis of the photographs, the author estimated that this was rather too low and a more likely figure was between 4 and 4.5 m from the top of the balustrade to the ground. No other information was available regarding the dimensions of the balcony or balustrade (see Figure 21.3). From the evidence of witnesses, it seemed reasonable to conclude that the victim fell backward over the balustrade and ended up on the ground below, face down and with his head toward the wall of the building. His head appeared to have been about 1.3 m from the wall. The author concluded that had he been pushed forcibly over the balustrade, as seemed to be suggested by some witnesses, it would have been more likely for him to have landed on his back with his feet toward the wall. The position in which he was found seemed to be much more consistent with an overbalancing and rolling backward and then to lie face down with his head toward the wall. The reason for this conclusion was that, when overbalancing in a rearward direction, a person has very little time and limited ability to stop and then reverse the rotation. The only way to do this is to “jackknife” the body to move the center of gravity effectively forward, but this is counterintuitive. The tendency is to throw the arms out, which actually increases the rotation. Once the center of gravity is external to the midline of the top of the balustrade, a fall is inevitable. The lower the pivot point is, the more difficult it is to regain equilibrium.
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FIGURE 21.3 The balcony viewed from the ground to show the balustrade and the drop. Because the victim was approximately 1956 mm in height and the balustrade was 740 mm, if he pivoted over this balustrade and rotated backward, his head would be expected to hit the ground at some point equivalent to the proportion of his body that was above the balustrade—i.e., 1956–740=1216 mm. At this point, he could have crumpled into a heap or the rotation could have continued. If the body roll continued, one possibility is that he would be found face down with his head at around this distance from the midline of the balustrade. The available evidence seems to indicate that this is how he was found. In this case, the defense employed another ergonomist to consider its case. However, in reviewing his report, this author concluded that: As far as I am able to see Mr. X and I do not differ in our opinions on any significant matters of fact or interpretation with regard to the ergonomics aspects of the accident to Mr. Y. Our main divergence of opinion is in
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relation to whether or not a person who is intoxicated still has the right to be protected from falling off a balcony by the design of the balustrade. Mr. X seems to imply, although does not specifically state, that there was a degree of contributory negligence on the part of Mr. Y, whereas I share the view of Judge Heydenfeldt in the U.S. who, in 1855 opined, If the defendants were at fault in leaving an uncovered hole in the sidewalk of a public street, the intoxication of the plaintiff cannot excuse such gross negligence. A drunken man is as much entitled to a safe street, as a sober one, and much more in need of it. Whether or not Mr. Y did contribute to his own misfortune by drinking alcohol is not, I believe, a matter for me or Mr. X to comment on, although intoxication of any degree would have adversely affected Mr. Y’s reactions once he found himself falling. The author therefore concluded that the most likely scenario was that the victim did overbalance backward, for whatever reason, and fell to the ground below, sustaining compression fractures to his neck. His resultant disability was serious, with paralysis of all four limbs. The case eventually settled out of court. Fall from Balcony of a Hotel in Ibiza The victim in this case was again a tall man of approximately 6 ft 3 in. (1905 mm) unshod, and he gave his weight at the time of the accident at about 14.5 stone (92.3 kg). He was 24 years old at the time of the accident, and witnesses report that he had consumed a very moderate amount of alcohol during the evening of the accident. At some point during the night, it is assumed that he went out onto the balcony and for some reason fell over the balustrade. The author was provided with details of the balustrade present at the time of the investigation, but all of the evidence from the witnesses and photographs indicated that this was not what was present at the time of the accident. However, there was no reliable way of knowing the exact height of the balustrade at the time, and the only indication available was the statement of a witness that it did not come up to her waist (she stated her height to be 5 ft 1 in. [approximately 1550 mm] and her waist height to be approximately 37 in. [940 mm]); on this basis, she estimated that the balustrade was between 33 and 34 in. (840 to 864 mm) in height. The balustrade was measured sometime after the accident as 37 1/8 in. (943 mm), but was lower by between 1/4 in. (5.35 mm) and 1/8 in. (3.18 mm) locally, giving a range of heights between 937 and 943 mm. This is approximately level with the witness’s reported waist height. The balcony was reported as being in a poor state of repair and poorly lit. Although indication was strongly to the contrary, in the absence of firm evidence, the author was obliged to assume that the balustrade at the time of the accident was at approximately the same height and of a similar design to that present and measured some time later. For the purposes of the remainder of the investigation, it was assumed that the average height of the balustrade was 940 mm. On the basis of his height, the victim’s estimated center of gravity was taken to be between 1023.6 and 1077.0 mm (40.3 and 42.4 in.) and situated approximately 192 mm
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(7.5 in.) in from the front of his abdomen. This was between 83.6 and 137 mm (3.3 and 5.4 in.) higher than the top of the balustrade, which was taken as 940 mm. If, in addition, the victim was leaning slightly forward—for example, to get a better view—or somehow tripped so that his upper body was in a forward position, it would be very likely that his center of gravity, which was only approximately 192 mm (7.5 in.) in from the front of the abdomen, could easily have been positioned exterior to the center line of the top of the balustrade. In this position, it would have been a very easy matter accidentally to overbalance forward. An alternative possibility is that he tripped while moving about on the poorly lit balcony and fell forward. In such circumstances, it is quite foreseeable that his center of gravity would have been above the height of the top of the balustrade, which would therefore not prevent him from falling over it. As a result of the fall, the victim suffered a fractured spine but, fortunately, the spinal cord was not severed and his residual disability was relatively limited. Again, the case settled out of court. Fall from Balcony of a Hotel in Crete The victim in this case was again a tall man of approximately 6 ft 1 in. (1854 mm) unshod and he gave his weight at the time of the accident at between 11 and 12 stone (70 to 76 kg). He was 20 years old at the time of the accident; no one witnessed the event and he had no recollection of the accident other than that he fell over the balustrade some 26 ft (8 m) to the ground below. His cervical spine was fractured, causing quadriplegia. By the time a site visit was arranged, the balustrade of the balcony of the apartment from which the victim fell had been altered by the addition of infilling and additional rails installed on top of the original balustrade wall. The estimated height of the balustrade at the time of the fall was 797 mm (31 3/8 in.) and its estimated thickness was 135 mm (5 5/16 in.). The balcony was quite narrow, with a depth immediately in front of access doors of only 724 mm (28.5 in.); also, a high threshold strip between the room and the balcony may have presented a tripping hazard. On the basis of his stature, the victim’s center of gravity was calculated to be between 1036 mm (40.8 in.) and 1047 mm (41.2 in.) above the ground and situated approximately 150 mm (6 ft) in from the front of his abdomen. Thus, his center of gravity was likely to lie between 239 and 250 mm (9.4 and 9.8 in.) higher than the top of the balcony balustrade, which was taken as 797 mm. It was not possible to know how the victim came to overbalance, but he might have tripped when going out from the room onto the narrow balcony or simply overbalanced and the balustrade was too low to provide a safe barrier to his fall. The victim had severe residual disability with paralysis of all four limbs, and the case settled out of court. 21.5 Summary and Conclusions In most cases in which the author has been involved, the victims of balcony falls have been tall men, who are clearly most at risk of overbalancing. Frequently in the supplied statements, these men or their companions had noted that the balustrade seemed low
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compared with what they were used to, but none felt so unsafe that he avoided the balcony or took extra care. Whether this lack of awareness of the risk was due to impaired individual judgment or to a more general failure by people to make proper risk assessment is not known. However, the fact that in most cases the victims were on vacation or were at a celebratory function may have had an effect on their assessment of their safety. It would appear that people expect to be safe in hotels and similar locations and that the owners and operators will have exercised a reasonable degree of care to protect the safety of visitors. Alcohol also seems to be involved and, in several cases, there has also been a suggestion of “horseplay” among young men (although this latter fact has never played a major part in any cases in which the author has been involved). It is undoubtedly true that both of these factors could be seen as contributory negligence; however, if the balustrade was of a safe height, i.e., 1100 mm, then young men could drink and behave as they do with a much reduced risk of falling over the edge. Most of the falls investigated by the author have occurred at night, but whether this is due to personal factors such tiredness or inebriation, or to environmental factors such as poor lighting or tripping hazards that cannot be seen in the dark, is unknown. However, the latter factors can be addressed and would seem to be worthy of attention. Balcony falls always involve a number of factors, some of which can be easily controlled and some that cannot. The design of the balcony and the balustrade can undoubtedly be improved to make them safer and offset the behavioral factors that are so difficult to change. 21.6 Checklist of Main Factors to Consider Primary factor Considerations Balustrade characteristics Height Design and thickness of top/guard rail Gap sizes Design, including whether toe holds are present Presence of a plinth at the base Materials of construction State of repair Security and strength Apparent safety
Primary factor Balcony characteristics
Environmental conditions
Considerations Depth Length Surface finish Lighting Access from room Presence of a threshold or other tripping hazard Presence and type of furniture Rain causing slipping hazard Sun causing deep shadows Glare/reflections Heat/cold
Balcony falls User physical characteristics
User psychological and social characteristics User expectations and experience
Medical condition
Impairment
Fatigue
Recognition and attention errors
Involvement of others Behaviors
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Height Weight Center of gravity Age Gender General experience Familiarity with balconies in general Specific familiarity with this balcony Activity at the time, e.g., vacation Vision Hearing Balance/vertigo Disability Alcohol Medication/illegal drugs Stress Anger/emotion Time of day Shift-work/“jet lag” Circadian rhythm Lack of sleep Sleep disorders/poor rest due to unfamiliar surroundings Awareness of hazard Activity on balcony Presence of other people Inattention Recognition and judgment errors Benign or malign involvement Distraction Risk taking Reckless behavior Climbing/sitting on balustrade Leaning out over balustrade Impaired judgment Building regulations Building standards Codes of practice Duty-of-care laws Regulations and laws on service provision
Defining Terms Balustrade—The whole infilling from handrail down to floor level at the edge of the balcony. Barrier—Any element of a building or structure, permanent or temporary, intended to prevent persons from falling and to retain, stop, or guide persons or vehicles.
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Center of gravity—The point through which the line of action of the weight of an object or body acts, irrespective of the position of the object or body. Frontal or coronal plane—The vertical plane perpendicular to the sagittal or median plane. Body parts in front of the plane are anterior (e.g., the face) and those behind are posterior. Guard rail—A protective railing designed to prevent people or objects from falling into open wells, stairwells, or similar spaces. Handrail—A rail forming the top of a balustrade usually designed to offer support, especially when climbing stairs. Sometimes the term is used instead of guard rail. Sagittal or median plane—The vertical plane that divides the body down the middle into more or less symmetrical left and right portions. Sometimes sagittal is used to describe any plane parallel to the median plane. Standard deviation—An index of the degree of variability in the population concerned. Top rail—Structural rail that may also act as a handrail. Transverse or horizontal plane—Any horizontal plane perpendicular to the sagittal or median plane and the frontal or coronal plane. References Board of Governors of the Hospital for Sick Children v. McLaughlin and Harvey plc. 19 Con. L.R.25. British Standards Institution: BS 6180:1999 Barriers in and about building—code of practice. Chaffin, D.B., Miodoski, R., Stobbe, T., Boydstun, L, and Armstrong, T., 1978, An ergonomic basis for recommendations pertaining to specific sections of OSHA Standard 29CFR Part 1910, subpart D—walking and working surfaces. OSHA Department of Labor, Washington, D.C. Fattall, S.G., Catteneo, L.E., Turner, G.E., and Robinson, S.N., 1976, A model performance standard for guard rails. Center for Building Technology, Washington, D.C. Ignazi, G., Coblentz, A., Pineau, H., and Prudent, J., 1972, Position du centre de gravite chez l’homme: determinations, signification fonctionelle et evolutive. Anthropol. Appl. , 43, 72, Paris. NASA, 1978, Anthropometric Source Book. Vol. 1. Anthropometry for Designers . NASA reference publication 1024. Page, R.L., 1974, The position and dependence on weight and height of the center of gravity of the young adult male. Ergonomics , 5, 603–612. Pheasant, S., 1996, Bodyspace. Anthropometry, Ergonomics and the Design of Work (2nd ed.) (London: Taylor & Francis). Santschi, W.R., Dubois, J., and Omoto, C., 1963, Moments of inertia and centers of gravity of the living human body. Technical Documentary Report No. AMRL-TDR-63–36. Snyder, R.G., 1977, Occupational Falls . Ann Arbor: Highway Safety Research Institute, University of Michigan. Solomon Heydenfeldt , Robinson v. Pioche , 5 cal. 460, 461 (1855). Swearingen, J.J., 1962, Determination of centers of gravity of man. Report No. 62–14, Civil Aeromedical Research Institute, Federal Aviation Agency. Templar, J., 1992, The Staircase: Studies of Hazards, Falls and Safer Design (Cambridge MA: MIT Press). United Kingdom Parliament Statutory Instrument, 1992, No. 3288, The Package Travel, Package Holidays and Package Tours Regulations 1992.
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United Kingdom Parliament Statutory Instrument, 2000, No. 2531, The Building Regulations 2000. Ward v the Ritz Hotel ( London ) (1992). PIQR P315 C.A. Watkins, J., 1999, Structure and Function of the Musculoskeletal System (Champaign, IL: Human Kinetics).
Further Information Chandler, R.F., Clauser, C.E., McConville, J.P., Reynolds, H.M., and Young, J.W., 1975, Investigation of inertial properties of the human body. Final Report AMRL-TR-74–137, Aerospace Medical Research Laboratory. Dempster, W.T., 1955, Space requirements of the seated operator. Wrights Air Development Center, Ohio. Dubois, J. and Santschi, W.R., 1962, The determination of the moment of inertia of the living human organism. In: Int. Congr. Hum. Factors Electronics , CA. Hay, J.G., 1973, The center of gravity of the human body. Kinesiology , III 20–44. International Code Council, 2003, International Existing Building Code, Final Draft, August 2001. Falls Church, VA. http://www.iccsafe.org/. Lohman, T.G., Roche, A.F., and Martorell, R., Eds., 1988, Anthropometric Standardization Manual (Human Kinetics Books: Champaign, IL). McConville, J.T. and Clauser, C.E., 1976, Anthropometric assessment of the mass distribution characteristics of the living human body. 6th Congr. Int. Ergonomics Assoc. , Maryland.
22 Preplacement Strength and Capacity Assessment for Manual Materials Handling Jobs Patrick G.Dempsey Liberty Mutual Research Institute for safety 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
22.1 Introduction There has long been an interest in matching the physical demands of workers with the demands imposed by manual tasks. Some of the early efforts were directed at selecting workers capable of producing high output, such as the studies Frederick Taylor performed to optimize how much pig iron could be loaded on train cars by workers (Taylor, 1911). As ergonomics became more prominent, the approach of designing jobs to fit the capacities of a high percentage of workers was more often advocated. Ergonomics has contributed a great deal to the knowledge of the parameters of tasks and workplaces that are sources of physical demands of manual materials handling (MMH) tasks. Similarly, considerable research has been conducted in the area of how human strengths contribute to MMH ability. The preferred approach to minimizing injury risk is to design tasks and workplaces so that the demands are within the capabilities of a high percentage of the working population. Although designing work to accommodate the capabilities and limitations of workers is the preferred approach, considerable interest remains in selecting workers with sufficient capabilities to perform physically demanding jobs. In some cases, economic and technical limitations prohibit reducing job demands to the level at which a high percentage of the working population can successfully perform the job safely. Thus, worker selection provides an alternate means of increasing the compatibility between job demands and worker capacity. In some cases worker selection is incorrectly assumed to be capable of preventing all future injuries. The decision to select workers for a job has many implications, including technical and legal considerations. These considerations have considerable overlap, and the importance of using scientifically sound methods has been reinforced through legislation in the U.S. A common theme that will emerge is that preplacement tests need to be related to the demands of the specific job for which the test is used. The intricacies of the different aspects of deciding to use the approach of selection for materials handling jobs will be discussed in more detail in the following sections.
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22.2 Objective and Scope The process of matching workers to jobs through selection procedures is extremely complex, and the assessment of whether a screening test was conducted without violating the laws or regulations discussed in this chapter is a complex process that also must incorporate interpretations subsequent to the initial enactments. For example, the Equal Employment Opportunity Commission (EEOC) publishes enforcement guidance for the Americans with Disabilities Act (ADA) based on court decisions. Thus, the process of assessing the appropriateness of a particular application of selection must include a consideration of the laws and regulations, as well as subsequent interpretive guidance that results from court decisions. Because of these complexities, Johns and colleagues (1994) recommended that decisions regarding a test should be made by a multidisciplinary team that includes legal counsel (Johns et al., 1994). Many basic principles apply to all selection procedures. The goal of this chapter is to discuss the most important concepts, as well as provide examples of proper and improper application of preplacement strength testing for placing workers in manual materials handling jobs. 22.3 Discussion of Principal Issues The Uniform Guidelines on Employee Selection Procedures (1978) (29 Code of Federal Regulations, Chapter XIV, Part 1607) were designed to provide a “framework for assessing the proper use of tests and other selection procedures.” These guidelines apply to all selection procedures, as opposed to the ADA, which applies specifically to individuals with disabilities. An important standard provided by these guidelines is related to validity studies of the selection tests. Types of validity include criterion-related, content, and construct validity. Acceptable means of establishing validity include determining that a test is predictive of or significantly correlated with elements of job performance (criterion-related validity), that the content of the test is representative of important aspects of performance on the job (content validity), or that the protocol measures the degree to which candidates have identifiable characteristics that have been determined to be important for successful job performance (construct validity). If a validity study cannot be conducted, selection procedures should be “as job related as possible.” The Uniform Guidelines on Employee Selection also encompass technical standards for validity studies. One aspect of these standards is that the validity study should include a review of the job, including a job analysis to determine measures of work behavior or performance relevant to the job. From an ergonomics perspective, it is critical to assess job demands as well as worker capacity in order to assess the match (or mismatch) between demands and capacity. Ergonomics techniques, in particular task-analytic techniques, are very useful for defining job demands and determining potential mismatches with the relevant human capabilities. Task analysis, a robust ergonomics technique for job analysis, begins with a task description. This description is a written set of components (or elements) of the job. The level of detail often depends upon the job but, in the case of materials handling
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demands, may include components such as “lift a 22-kg box from floor to knuckle once every 4 to 5 minutes.” Because the ADA requires a written job description, it is beneficial to have detailed task descriptions so that such descriptions can be easily generated. Once the task description is completed, the actual analysis occurs. This is when potential mismatches between demands and capabilities are determined. Often, a specific ergonomics approach is used depending upon the nature of the task (see Wilson and Corlett, 1995, for a wide range of methodologies for different types of tasks). As part of the examination of the relationship between a screening test and job demands, a considerable body of literature deals with lifting and lowering tasks. Job demands for these types of tasks are often defined by task parameters including frequency and lifting range (starting and ending vertical locations of materials handled). When the appropriateness of a preplacement test is assessed from an ergonomics standpoint, one of the first considerations is whether the test mimics the kinematics of the actual tests. Isometric strength tests involve exerting force against a stationary measurement device. Isokinetic tests involve exerting force against a measurement device moving at a constant velocity. There has been isokinetic testing of individual joints and whole-body strength. Free dynamic tests (also called isoinertial tests in the literature) do not restrict movement; an example is the psychophysical approach, in which the subject selects a load to lift that he believes is the maximum he can lift without becoming unduly fatigued or exhausted. The closer the test is to mimicking the kinetic and kinematic properties of the actual job tasks, the higher is the expected correlation between the test and the underlying capability. For example, Dempsey and colleagues (1998) found that the highest correlation between different types of tests to predict low-frequency, floor-toknuckle lifts and the maximum acceptable weights chosen was for a dynamic test of lifting power. Correlations for the isometric and isokinetic tests were statistically significant, but the magnitudes were lower. For an overview of additional literature in this area and examples of specific tests that have been developed, see Gallagher et al. (1998). When it comes to assessing the demands of pushing and pulling tasks, considerably less literature and guidance are available (Bos et al., 2002). In any case, it is important that the test measures the capacity relevant to the actual task. The guidelines also discuss requirements for statistical relationships between procedure scores and criterion measures. Generally, a correlation or relationship must be statistically significant at the α= 0.05 level. However, there is no suggestion of how strong the relationship needs to be, which is not necessarily captured by a p-value. The Americans with Disabilities Act went into law in 1990 to prevent discrimination against “qualified individuals with disabilities.” Title I and Title V of the ADA prohibit employment discrimination against “qualified individuals with disabilities.” The specific regulation of the ADA (Public Law 101–336) is contained in 29 Code of Federal Regulations Part 1630—Regulations to Implement the Equal Employment Provisions of the Americans with Disabilities Act. This law has specific implications for performing selection tests, and its principles are consistent, albeit more explicit in a few areas, with the Uniform Guidelines on Employee Selection Procedures discussed earlier. The basic premise of the ADA is that employers cannot discriminate against a “qualified individual with a disability.” A qualified individual with a disability is an individual who can perform the essential functions of the job in question with or without
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a reasonable accommodation. A reasonable accommodation cannot impose an undue hardship on the employer. It should be noted that applicants engaging in illegal drug use are not covered by the ADA. The preceding paragraph is fairly short; however, interpreting the ADA context of the terms is very intricate. First, disability refers to an individual who has a substantial physical or mental impairment that limits a major life activity (e.g., hearing, walking, performing manual tasks), has a record of such an impairment, or is regarded as having such an impairment. Disabilities under the ADA are not acute injuries such as sprains or broken bones. In 1999, Supreme Court rulings indicated that determining whether someone is disabled must consider whether a major life activity is substantially limited when using a mitigating measure. If a person is not substantially limited for any activity while using a mitigating measure, then he or she is not considered disabled (EEOC, 1999). These rulings also stressed the importance of conducting the disability assessment on a case-by-case basis. Essential functions must be known in order to assess whether an individual is capable of performing the functions, with or without a reasonable accommodation. A reasonable accommodation involves changing the work environment or the way tasks are carried out so that a qualified individual with a disability can successfully perform the job. According to the Code of Federal Regulations, a reasonable accommodation may include: (A) making existing facilities used by employees readily accessible to and usable by individuals with disabilities; and (B) job restructuring, part-time or modified work schedules, reassignment to a vacant position, acquisition or modification of equipment or devices, appropriate adjustment or modifications of examinations, training materials or policies, the provision of qualified readers or interpreters, and other similar accommodations for individuals with disabilities. Determining what a reasonable accommodation would be can involve the individual with a disability. The individual can identify limitations and suggest potential accommodations. In many cases, fairly simple, inexpensive solutions are available, often through in-house capabilities. For example, some industrial facilities have machine shops that can produce hardware for ergonomics improvements. The author has observed tables and jigs for positioning products to eliminate the need for bending, all the way up to a custom-designed hydraulic device that could raise, lower, and rotate in two axes heavy parts so that different operations could be performed with minimal postural deviations. Such approaches should be examined for reasonable accommodations as well. A related concept is that of undue hardship. If an accommodation causes undue hardship to the employer, then the accommodation would not be considered reasonable. Factors that would be considered include the economic burden as well as adverse impact of the accommodation on the operation of the facility. These determinations also require a case-by-case analysis. No specific definitions or monetary values are specified to make this decision. With respect to preplacement testing for physically strenuous jobs, the scope of the concepts mentioned is reduced somewhat. During an interview, an employer cannot ask
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job applicants about the existence, nature, or severity of a disability, but they can be asked about their ability to perform specific job functions. If a preplacement test is given, it must be given to all applicants, after a conditional job offer is made. If a preplacement test is given to assess materials handling capacity, this would imply that materials handling has already been determined to be an essential function. For example, lifting and lowering would be essential functions of a warehouse order-picker job because the job exists to perform these tasks (e.g., load boxes onto pallets or conveyors). As was mentioned earlier, it is important that the tasks comprising the preplacement exam are based upon a job analysis. For example, the test should mimic the types of lift performed, lift range, etc. Lifting boxes from floor level is not representative of lifting boxes from a table because the former requires certain trunk postures and capabilities. Matching the test to the job will maximize the relevance of the assessment. One difficult assessment is whether a worker poses a “direct threat” to his safety or the safety of others if he were to perform the job duties. For example, a worker with chronic, recurrent back pain is likely to have future episodes. For this reasons, Johns and colleagues (1994) suggested delineating the potential direct threat for material handlers. They suggested that a likely direct threat would be an applicant with three or more documented low-back pain episodes over the previous 5 years involving lost work days or medical treatment. One problematic aspect of this determination is that it is almost impossible to definitively assess the risk of direct threat of low-back disorders that the individual would face. See Johns et al. (1994) for an in-depth discussion of the many facets associated with chronic, recurrent low-back pain in this context. 22.4 Examples Dempsey (1999) developed an example in which a hypothetical Company X rents temporary outdoor tents, including delivery and setup. There was a low-back disorder problem among the crews that provided the delivery and setup service. Strength Testers Inc. approached the company with a proposal to provide preplacement strength-testing services. The tests would be administered at a local clinic and involve strength testing using a patented strength-testing device developed by Strength Testers Inc. The company indicated that they would use proprietary statistical models to determine which employee candidates would be least likely to get injured in the future. When the program was evaluated, a primary issue was that validation of the relationship of the tests to the actual job demands had not been conducted. Strength Testers Inc. produced additional testimonials from previous users but little other information. Based upon the low relation to actual job requirements and limited information on the ability of the test protocol to predict injury among its workers, Company X decided to decline and seek additional providers for bids. Had this company chosen to utilize this preplacement approach, several potential issues were possible. The lack of validation or relationship with actual job demands could be challenged with the Uniform Guidelines on Employee Selection Procedures and possibly the ADA. Although it would be clear that the materials handling tasks were essential functions of the job, the question as to whether the test was related to the job could be questioned.
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A second example is a job that requires a forklift driver to change a battery on occasion. The battery weighs 32 kg and the operator must lift the battery, carry it a short distance, set it down, and then install a new battery. The remainder of the job involves operating the forklift and paperwork. For this job, no preplacement testing for the battery task would be allowed. A reasonable accommodation would be for another worker to perform the task or to use a mechanical assist. For a wider range of examples going beyond materials handling, the interested reader is referred to Blanck (1995). Additional real cases and recent court rulings can be found on the World Wide Web by accessing the EEOC web site (http://www.eeoc.gov/). 22.5 Checklist The checklist in Table 22.1 summarizes the main issues discussed here. No checklist will cover every issue for all situations; however, the checklist provides a good starting point to assess a preplacement strength test.
TABLE 22.1 Summary of Primary Factors to Consider When Assessing Preplacement Strength Testing Primary factor
Consideration
Test validity
Criterion-related, content, or construct validity needs to be demonstrated Validity study should include review of job Statistical significance of relationship Essential functions Reasonable accommodations need to be examined Essential functions should be reflected in written job description Consider the amount of time spent in determination Function is essential if position exists to perform that task Function may be essential due to limited number of persons available to perform function Medical and Must be given to all employees Must be postconditional offer Drug tests are not preplacement considered medical exams Medical exams do not need to be job related and exams consistent with business necessity, but any criteria used to exclude applicants for a job must be Pre-employment inquiries about disabilities are prohibited Reasonable Reasonable accommodation is a modification or adjustment that enables a accommodation qualified applicant or employee with a disability to participate in the application process or to perform essential job functions A reasonable accommodation cannot cause undue hardship A reasonable accommodation can include transferring an employee to a vacant position for which he is qualified
References Blanck, P.D., 1995, Implementing the Americans with Disabilities Act: a case report on Sears, Roebuck, and Co. Spine , 20(19), 2161–2167. Bos, J., Kuijer, P.P.F.M., and Frings-Dresen, M.H.W., 2002, Definition and assessment of specific occupational demands concerning lifting, pushing, and pulling based on a systematic literature search. Occup. Environ. Med. , 59, 800–806.
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Dempsey, P.G., 1999, How to choose a strength-testing program. Ergonomics Design , 7, 18–23. Dempsey, P.G., Ayoub, M.M., and Westfall, P.H., 1998, Evaluation of the ability of power to predict low frequency lifting capacity. Ergonomics , 41, 1222–1241. EEOC (Equal Employment Opportunity Commission), 1999, Instructions for field offices: analyzing ADA charges after Supreme Court decisions addressing “disability” and “qualified.” http://%20www.eeoc.gov/policy/docs/field-ada.html. Equal Employment Opportunity Commission, 1991, The Americans with Disabilities Act: Questions and Answers (Washington, D.C.: Author). Equal Employment Opportunity Commission, 1992, A Technical Assistance Manual on the Employment Provisions (Title 1) of the Americans with Disabilities Act (Washington, D.C.: Author). Gallagher, S., Moore, J.S., and Stobbe, T.J., 1998, Physical Strength Assessment in Ergonomics (Fairfax, VA: Amercian Industrial Hygiene Association). Johns, R.E., Bloswick, D.S., Elegante, J.M., and Colledge, A.L., 1994, Chronic, recurrent low back pain: a methodology for analyzing fitness for duty and managing risk under the Americans with Disabilities Act. J. Occup. Med. , 36, 537–547. Taylor, F.W., 1911, The Principles of Scientific Management (New York: Harper and Bros.). Wilson, J.R. and Corlett, E.N. (Eds.), 1995, Evaluation of Human Work (2nd ed.) (London: Taylor & Francis).
23 Identifying the Real Issues in Work-Related Upper Limb Disorders Celine McKeown Link Ergonomics 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
23.1 Introduction The basic aim of ergonomics, or human factors as it is referred to in some countries, is to provide the worker with an optimum, safe environment. Although ergonomics can be applied to any aspect of human life, it tends to be viewed in the work context. It allows a scientific foundation for a user-centered approach to design and offers significant benefits to any organization. In very simple terms, ergonomics enables us to develop an effective match between the person, the task, and the environment. Because this ergonomics approach is so positive and practical, it is shocking that it is neglected in so many facilities. People are frequently required to interact with equipment, machinery, tools, and systems without any thought as to the “fit” between the individual and his or her surroundings. As a consequence of such short-sightedness, people are exposed to working conditions that can cause them harm. One of the more commonly recognized signs that the individual might be working in an unsuitable environment is the development of an upper limb disorder (ULD), alternatively known in some countries as cumulative trauma disorder (CTD). This chapter is dedicated to the discussion of ULDs. It will consider the possible work-related causes of the conditions and early warning signs that should alert an employer to an individual’s difficulties. It will also review the employer’s expected state of knowledge and how the potential for harm can be identified long before an individual starts to experience difficulties. Although significant overlap in the application of sound ergonomics principles occurs within all types of environments, this chapter will refer separately to office-based organizations and industrial/factory-type environments because each of these facilities has its own unique issues to address. 23.2 Disorders and Symptoms The term upper limb disorder (ULD), or cumulative trauma disorder (CTD), is an umbrella term covering a wide range of conditions that affect the upper limbs at any point
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from the fingertips along the length of the arm to the shoulder and into the neck. Each condition is confined to an individual area of the limb and produces its own specific symptoms. The medical professional will diagnose the exact condition on the basis of the location and type of symptoms and signs. A number of the conditions falling under the heading of ULDs are regularly identified among individuals in today’s workplaces. These include: tenosynovitis, Dupuytren’s contracture, carpal tunnel syndrome, vibration white finger, epicondylitis, tendinitis, “frozen” shoulder, and a number of other conditions such as cervical spondylosis, ganglion, and osteoarthritis. Tenosynovitis Of all ULDs, tenosynovitis has been identified (Pheasant, 1996) as the most important in the U.K. In the past, it was probably used more inaccurately than any other term in the U.K. when conditions of the upper limbs were described. It was once used as an umbrella term in its own right to record that an individual had suffered a condition affecting the upper limbs. However, it is confined to a specific area of the upper limbs and displays quite specific symptoms. It is experienced by the individual when there is inflammation in the lining of the synovial sheath of the tendons, most commonly in the hand and wrist. Tendons and their sheaths can be seen in Figure 23.1.
FIGURE 23.1 Tendons and their sheaths in the hand. (From PutzAnderson, V., 1992, Cumulative Trauma Disorders: A Manual of
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Musculoskeletal Diseases of the Upper Limbs, London: Taylor & Francis.) Tendons are cords or narrow bands of connective tissue that attach muscle to bone. Under normal circumstances, the tendons move unhindered within the sheath, which is lubricated. The sheath offers protection to the tendon as it passes under ligaments or around corners, such as when the wrist is bent. Those who have developed tenosynovitis may experience symptoms such as aching in the wrist, swelling or even the sensation of swelling without any visible signs, a weakness of grip, and sometimes a creaking or crackling sound in the wrist on movement. This creaking or crackling is known as crepitus and sounds similar to someone walking over dry snow. If the movement of the tendon inside the sheath is impaired, the condition is referred to as stenosing tenosynovitis. If the abductor pollicis longus and extensor pollicis brevis tendons, which form the outer boundary of the “anatomical snuff box” on the back of the hand at the base of the thumb, are involved, the condition is called De Quervain’s disease. This is likely to be found in situations in which the worker is involved in forceful grasping when the wrist is bent, particularly when holding a large object that causes the thumb to be moved outward and away from the hand. If the tendons of the finger flexors are affected, the diagnosis will be trigger finger. This usually occurs when the tendon sheath becomes so swollen that the tendon cannot move within the sheath. Trying to move the finger results in a jerky movement. Activities that require repetition, forceful gripping, and irregular hand/wrist postures have been associated with the development of tenosynovitis. Dupuytren’s Contracture The palmar fascia is a fan of fibrous tissue on the palm of the hand. Sometimes it can shorten and thicken, which causes gradual bending of the fingers. More commonly, the little and ring fingers are affected by the condition and can only be straightened by surgical intervention. Although this condition has been shown to be congenital in some individuals, it has also been identified as resulting from a laceration type of injury, heavy manual work (NIOSH, 1997), or repeated trauma as might occur in an activity in which an assembly operator repeatedly knocks components into position with the palm of the hand. Carpal Tunnel Syndrome The median nerve, which can be seen in Figure 23.2, is responsible for sensation in the thumb; the main body of the palm; and the index, middle, and part of the ring fingers. It travels from the forearm, along with the tendons and blood vessels, into the hand through the carpal tunnel in the wrist area and passes under the carpal ligament. The condition known as carpal tunnel syndrome is caused by compression of the median nerve. This can occur as a result of irritation and swelling within the confines of the carpal tunnel, such as might be found with tenosynovitis. In addition to work-related causes such as forceful gripping, deviation of the wrists, and vibration, carpal tunnel syndrome has also
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been associated with pregnancy, menopause, diabetes, rheumatoid arthritis, and local trauma such as a fracture. Sufferers of carpal tunnel syndrome usually experience numbness and tingling, more often in the areas of the hand served by the median nerve. Symptoms are commonly more severe at night, often causing the sufferer to wake up. Sufferers may experience a loss of sensation in their hands, which results in their feeling particularly clumsy when trying to pick up small objects. Vibration White Finger This condition is associated with the use of vibrating equipment and results from an impairment of the blood circulation in the fingers. This is accompanied by transient blanching of the fingers and sensations of numbness, tingling, and feelings of cold. As the condition progresses, the affected area increases in size and the attacks increase in frequency. Once the blood flow is restored to the fingers, they become red and painful, and usually throb. Prior to the change in color to red, the fingers may take on a bluish color. This blue/purple color may become a permanent feature if the fingers have been affected over an extended period of time. In severe cases, dexterity can be impaired and in some extreme but rare cases, gangrene can occur. Vibration white finger should not be confused with Raynaud’s phenomenon, which is a constitutional disorder displaying similar symptoms, usually bilaterally. Exposure to cold conditions usually provokes the appearance of symptoms with this condition.
FIGURE 23.2 Cross-section of the wrist showing the median nerve. (From Putz-Anderson, V., 1992, Cumulative
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Trauma Disorders: A Manual of Musculoskeletal Diseases of the Upper Limbs, London: Taylor & Francis.) Epicondylitis Epicondylitis is commonly referred to as tennis elbow or golfer’s elbow, depending on whether it is lateral or medial epicondylitis. In lateral epicondylitis, the area around the epicondyle, i.e., the bony prominence on the outside of the elbow, becomes inflamed. The epicondyle is the point of origin for the muscles responsible for extending the wrist and fingers (i.e., moving the hand upward at the wrist). If the muscles are overused, such as with forceful throwing movements, the epicondyle can become swollen and tender and the pain can radiate into the forearm. Medial epicondylitis is very similar to lateral epicondylitis but is not quite as common. It results from irritation on the inside of the elbow at the point of origin of the flexor muscles, which bend the hand downward at the wrist. Repetitive wrist flexion and supination/pronation are linked to the development of this condition (Pheasant, 1991). Supination involves the rotation of the forearm to bring the palm of the hand into the face-up position. Pronation involves the rotation of the forearm to bring the palm of the hand into the face-down position. Tendinitis Tendinitis is considered to be the second most common disorder in the working population (Hagberg, 2000). It is described as inflammation of the tendon and can affect any tendon in the body. It can occur when the muscle/tendon unit is repeatedly tensed. With continued use, some of the fibers making up the tendon can start to fray. As a consequence, the tendon becomes thickened, bumpy, and irregular. Humeral tendinitis, also known as rotator cuff tendinitis, affects the tendons of the muscles responsible for rotating the arm at the shoulder and abduction of the arm, i.e., moving the arm away from the body. Forceful or repetitive work has been associated with the development of tendinitis (Violante et al., 2000), as has working with the arms raised (Health and Safety Executive, 2002). “Frozen” Shoulder Any individual suffering from a frozen shoulder will experience the gradual development of stiffness and pain in the shoulder, culminating in severe restriction in all shoulder movements. Pain is particularly evident at night. This condition results from an inflammation or degeneration of shoulder joint tissue and has been associated with working with the arms raised (Putz-Anderson, 1992). Cervical Spondylosis Cervical Spondylosis is a common condition that affects the neck and spine. It results from inflammation of the synovial joints of the neck and is considered to be related to
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age. There is some debate at present about its possible relationship to repetitive head movement and/or irregular head and neck posture. Ganglion A ganglion is a fluid-filled cyst usually found on the back of the hand or wrist. The fluid is synovial fluid arising from a joint or tendon sheath. A ganglion is usually about the size of a small grape and normally is not painful. Although some would suggest that a ganglion is not work related, it is generally considered that a high incidence in one workplace is a sign that the operators are exposed to inappropriate working conditions. Osteoarthritis The more accurate term for osteoarthritis is osteoarthrosis; it is caused by wear and tear affecting the articular cartilages of the synovial joints. This is accompanied by associated changes in surrounding bone and can affect any articulating joint. Sufferers can experience stiffness, aching on movement, and restriction of movement; the pain can radiate from the neck into the arms. Sufferers will also hear a crunching sound on movement (i.e., crepitus). It is believed that localized osteoarthritis can occur when a particular joint has been subjected to long-term stress (McKeown and Twiss, 2001)—for example, the elbow joints of slaughterhouse workers involved in pulling the skin off animals. 23.3 Causes of Upper Limb Disorders (ULDs) Many people have little or no knowledge about what causes ULDs. Part of the problem relates to the terminology used to describe the conditions. Until about 1990, the U.K. relied on the term repetitive strain injury (RSI) to identify that an individual was suffering from a condition affecting the upper limbs. However, this created the impression that only repetitive work caused the condition and offered only a partial explanation for development of the condition. Using the word “injury” to describe the condition also suggested that the individual had developed a long-term injury, although some workers experience only transient discomfort. Other countries have developed their own terms. In Japan the term occupational cerviobrachial disorder (OCD) is used. As previously indicated, the term cumulative trauma disorder (CTD) is used in the U.S. Some countries use the names of specific conditions to denote the whole range of disorders that an individual might experience. It is hardly surprising that when there is no agreement about the most suitable and most accurate term to use, those responsible for managing and introducing change to the workplace have no real understanding of the issues of importance. In addition, the ambiguity that surrounds the terminology used offers legal professionals the opportunity to argue in court that if there is no agreement on what to call the conditions or how to define them, then they cannot be recognized and managed successfully. This chapter is based on the belief that ULDs are a real problem in today’s workplace and, in most cases, could be avoided by simple planning and adequate consideration of
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the human element. That is not to say that ULDs are only caused by work-related elements. It is accepted that factors outside the workplace are likely to contribute to the development of ULDs and aggravate them once they have developed. Therefore, when a worker starts to complain of symptoms such as discomfort or pain, an assumption should not be made that work alone is responsible. When investigating complaints, a complete review of factors prevalent at work and home should be considered. The likely causes of ULDs can be divided up into the main causative factors and other contributory factors. Often these act together, resulting in the individual developing symptoms of a ULD. The main causative factors are considered to be repetition, force, poor posture, and static muscle work. More often than not, a combination of these factors acts to the detriment of the worker. However, it is generally accepted that exposure to one element alone will be sufficient to trigger the onset of symptoms (Health and Safety Executive, 2002). It is important that no assumption should ever be made that exposure to any one of these elements will guarantee that an individual will develop a ULD. Whether he or she does or not usually depends on other contributory factors such as exposure time, availability of breaks, and variety in the work, etc., all of which will be discussed in this chapter. Repetition Repetition is considered to be problematic because it results in a worker using the same muscle groups repeatedly in an identical fashion for extended periods of time. Repetition can involve the execution of the same single movement repeatedly and without interruption or it can involve a series of movements completed rapidly within a short cycle time. Muscles that are required to work rapidly develop less tension than muscles allowed to work slowly; as a consequence, they must work harder to complete an operation carried out at speed. Few people have an appreciation of what constitutes a repetitive and a highly repetitive task. Putz-Anderson (1992) has provided a guide for classifying tasks on the basis of the cycle time or the percentage of the cycle spent performing the same fundamental series of tasks. He stated that jobs can be considered highly repetitive if the cycle time is less than 30 seconds or if more than 50% of the cycle time involves performing the same kind of fundamental cycle. An example of a situation in which the same fundamental cycle is repeated can be seen when operators pack bottles of wine into cases. It might take one operator 42 seconds to fill one case, which might suggest that the packing task was not highly repetitive. However, as he or she placed six bottles in each case, he or she actually handled bottles at a rate of one bottle every 7 seconds; this would allow the task to be classified as highly repetitive. Any operator who performs an operation identified as highly repetitive should be considered at risk. The speed of operation and thus the degree of repetition are often influenced by other factors, apart from simply the rate at which an assembly line or conveyor belt moves. Piece-rate systems of pay or productivity targets are aimed at increasing production rates. Operators who receive such systems of pay are encouraged to work at a faster rate so that they can earn more money, often working through breaks to increase their take-home pay. It is not uncommon to find in a factory-type environment that the fastest workers report the most symptoms. This outcome is also evident in offices where keyboard users
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involved in data entry tasks are paid by the number of key depressions they make per hour. Data-entry operators can often increase their typing speed from under 10,000 depressions per hour to anything between 16,000 and 25,000 per hour depending on the incentives. It is generally accepted that keying at a rate in excess of 10,000 depressions per hour should be viewed as placing the keyboard operator in a higher-risk category. The degree of repetition can also be influenced by the working practices adopted by the operator rather than those imposed on him or her by managers or the process. Some workers are given a target to meet by the end of the day, but are not given guidance on how they should achieve that target. In some assembly-type situations in which an operator is required to assemble a unit comprising several parts, the operator will choose to work on a number of units simultaneously, fitting the first component to all of the base units, then adding the second component to each individual unit, and so on. As a consequence, he or she turns a potentially varied task into a series of highly repetitive subtasks. In other situations, operators will choose to work as quickly as possible at the start of the shift so that they can work at a more leisurely pace toward the end. For particular groups of operators, once they finish a set task, they can leave work. Therefore, the sooner they finish, the sooner they can go home. A prime example of such a group would be refuse collectors, who can go home once they have finished their round. It is not uncommon to observe them running as they complete the round and throwing bags of refuse toward the wagon rather than carrying them to the wagon for compacting. A number of these operators may have second jobs to get to, so they want to finish quickly. More often than not, all of these operators will have no appreciation that developing such a system of work could have quite detrimental effects. These examples clearly demonstrate the need to communicate with the workforce and ensure that its members appreciate the need to adopt appropriate working practices. One of the fundamental failures in the workplace is the assumption made by those in positions of authority that their workers know what will cause them harm. This is rarely the case. It is common to find that in a personal injury case the defense will particularize the claimant’s contributory negligence as including working in a manner contrary to safe working practices. No reputable expert involved in this case would accept this as a valid argument if the individual had not been advised about the need to avoid inappropriate working practices and exactly what constituted an inappropriate working practice. Despite the fact that some evidence clearly shows a link between repetition and the onset of disorders such as tenosynovitis, performing a repetitive operation does not guarantee that an injury will occur. It is possible to control the effects of the repetitive task through appropriate rest-break schedules and/or job rotation. For rest breaks to be effective in any program of risk reduction, they should be offered at regular intervals on a consistent basis from day to day. It is not uncommon within workplaces for managers to change break times to suit the targets for that day or for managers to assume that “idle” time is sufficient between production cycles and therefore eliminates the need for additional rest breaks. No one should ever assume that workers have sufficient rest breaks throughout their shift unless this is reviewed specifically. For instance, in an office setting, it is not uncommon for the official midmorning and midafternoon breaks to be eliminated on the basis that it is believed the workers have plenty of opportunities to leave their workstations to complete a series of varied tasks and
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to get drinks from the dispensers whenever they want one. The reality of the situation is often very different. Most office workers have access to a vast array of online reference materials and databases and can e-mail colleagues working within the same site rather than walk to their work areas and speak to them. Therefore, they have no reason to leave their desks. Added to this, many office workers work within teams and each team member will usually take it in turn to collect drinks for the rest of the team, perhaps on an hourly basis. If a worker was part of an eight-person team, he or she might not have a reason to leave his or her desk for up to 6 or 7 hours. This cannot be viewed as acceptable if the user performs a continuous screen-based operation. On the other hand, the claimant can sometimes offer a very inaccurate view of break taking. He or she may claim that they had no rest breaks and had no reason to leave their desk because their work involved solely computer-based operations. Closer scrutiny of the actual system of work might reveal that although there were no official midmorning and midafternoon breaks, the individual could, and did, collect drinks whenever he or she wanted and, because he or she was a smoker, would leave the work area, and sometimes the building, at regular intervals for a cigarette. In addition, it often transpires that this computer user might have had to leave the workstation frequently to collect printed documents from a shared printer at a distance from the desk or to use a remote fax machine. Claimants often develop a perception that they do not leave their workstations at all if they do not have official midmorning or midafternoon breaks. The important aspect about break taking is not actually how long the workers are allowed for breaks, but how frequently they take them. The aim should be to have short, frequent breaks to avoid the onset of fatigue rather than longer, infrequent breaks during which the individual recovers from the effects of fatigue. This has quite serious implications for negotiations involving union and safety representatives at sites where their focus is on how long the workforce is given for breaks as opposed to how frequently they can take a break. Also, it is not uncommon for union representatives to negotiate a deal in which the workforce works through lunch or without an afternoon break so that its members can leave early at the end of the day. Although they have negotiated with the best interests of the worker in mind, they do them a disservice in that they install a pattern of work more likely to result in the workers developing a ULD because they are exposed to the undesirable features of their work for longer periods without interruption. Job rotation is also considered to be an effective means of reducing the risk of a repetitive operation. Those responsible for creating systems of work should develop an understanding of how job rotation needs to be used if it is going to be effective. Its aim is to remove the individual from a potentially harmful task at regular intervals, and move him or her to an alternative task that does not contain the same harmful elements. Difficulties arise when the manager in a particular work area does not understand what it is about a specific operation that has the potential to cause harm and simply moves the worker from one job to another, often transferring him or her to an operation in which the aggravating factor remains unchanged. This is a common mistake in factory environments in which a number of operators work on a production line. Job rotation usually involves the worker moving one place to the left or right at set time intervals, following the natural sequence of the line. However, on many production lines, the tasks performed at the second, third, and, possibly, fourth positions along the line are often identical. For instance, the workers may be simply
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dropping the toppings onto a pizza as it passes on a conveyor and each workstation along the line is responsible for a different ingredient. If the operator moves from a workstation where he or she sprinkles cheese on the pizza to the next workstation, where he or she sprinkles peppers on the pizza, he or she is not going to experience much in the way of a qualitative change in activities. The only way to ensure that jobs included in a job-rotation program will be effective is to carry out a task analysis of each of the operations; this offers a complete breakdown of the subelements of the tasks. Any defense argument suggesting that job rotation was used as a means of combating risk will most likely be tested by the assigned expert in the case to determine whether the rotation was likely to have been effective. The use of rotation will not be considered an adequate response unless it is shown to have been effective. Force It has been established that applying undesirable forces for extended periods of time or repeatedly is likely to contribute to the development of ULDs (Kuorinka and Forcier, 1995). The force levels necessary to complete any operation do not always remain at a constant level. The level required is influenced by a number of factors, such as the characteristics of the material being manipulated. In workplaces where fabrics are stitched together, some operators will find it more difficult to work with leather and vinyl materials than with cottons or linens. A machinist will find that he or she must pull leather with greater force to make the two pieces being stitched line up because leather has less “give” than other types of material. One of the ways of making materials such as leathers, vinyls, and rubber easier to work with during machining or assembly operations is to warm them under heat lamps before use, thereby making them more pliable. This is particularly important in winter. The level of force required to complete an operation is also influenced by the type of tool in use. If the handle has not been designed to be held easily in the hand, the operator must grip it more firmly to maintain the grip and to guide and operate the tool. In assembly-type operations, it is not uncommon for operators to work with offspecification parts. In environments where just-in-time deliveries are used, the company does not have the option of sending the parts back to the supplier and waiting for new parts to arrive. Its workforce must use the components available at the time, irrespective of their condition. Off-specification parts cause the operator to use more force when fitting them together and can encourage use of the hand like a mallet to knock the parts into place. The weight of objects being handled also influences the forces required during the operation. This applies to situations in which the individual is manually handling objects or handling a heavy tool while completing an operation. Clearly, reducing the load weight reduces the forces required to complete the operation. However, there are a number of other guidelines for reducing the levels of force associated with any operation: • Equipment should be included in a regular maintenance programs to ensure that it functions correctly. This will ensure that the operator does not need to overcome any shortfalls in the functioning of the equipment. • Operators should be trained not only in how to complete a task but also in how much force to employ when completing that task.
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• Scissors, knives, and other cutting tools should be kept sharp to reduce the effort required to use them. • The forces required to operate controls and triggers should be kept to a level at which the least resistance is offered to operation while still avoiding accidental activation. • Other means of applying forces, such as with the use of tools, should replace the need for manual effort. • Tool handles should be of a length that makes it easier for the operator to apply forces. For instance, a long-handled spanner will offer greater leverage than a short-handled spanner. Posture Awkward posture is considered a significant contributor in the development of ULDs (Kroemer and Grandjean, 1997). If the individual can work with the upper limbs in positions considered to be neutral, he or she is less likely to encounter difficulties. Figure 23.3 shows a series of hand and wrist postures including the neutral position of the hand. Particular hand and wrist positions have been associated with specific disorders. Postures that involve moving the hand from side to side (i.e., ulnar and radial deviation) or bending up or down at the wrist (i.e., extension and flexion) repetitively or for extended periods of time are considered likely to result in operator discomfort.
FIGURE 23.3 Hand and wrist postures including the neutral position of the hand. (From Putz-Anderson, V.,
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1992, Cumulative Trauma Disorders: A Manual of Musculoskeletal Diseases of the Upper Limbs, London: Taylor & Francis.)
FIGURE 23.4 Diagram illustrating distinct work areas. (Adapted from Pheasant, S., 1996, Bodyspace, Anthropometry, Ergonomics and the Design of Work, 2nd ed., London: Taylor & Francis.) Repeated extension of the wrist has been associated with tennis elbow, repeated radial and ulnar deviation have been associated with the development of tenosynovitis, and repeated flexion and/or extension of the wrist, when combined with gripping, has been associated with carpal tunnel syndrome (Pheasant, 1991). Irregular upper limb postures are usually the result of poor workstation design. As a general starting point, the workstation should be designed and used so that the operator is able to work with his or her upper arm hanging naturally by the side of the body and a 90° angle at the elbow so that the forearm is parallel with the floor. This ensures that a straight line is maintained through the wrist area. To achieve this working posture, the workstation should be designed so that the operator can work at, or slightly below, elbow height. (The exact setting will vary depending on the type of task performed). Working outside this level can result in the need to adjust the arm position to accommodate the working height presented. It is common to find in cases involving ULDs that the individual was required to work at a high work surface for extended periods. This would have caused the individual to work with his or her shoulders and arms raised. In addition to ensuring that the operator can work at the appropriate height, care must be taken when setting reaching distances. The aim should be to allow the operator to grip an object, or reach toward a work area, without significantly changing posture or using excessive energy. For simplicity, reaching distance is usually divided into two distinct zones (see Figure 23.4). The zone of convenient reach, or secondary work area, is the area within the sweep of the outstretched arm. This represents the maximum distance that the operator can reach when his or her arms are extended forward, sideways, and upward. Although an individual can reach such areas relatively easily, working in the extremes of
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this area repeatedly or for extended periods of time will be fatiguing for the limbs. On that basis, only occasional work in this area is usually considered acceptable. Work performed for sustained periods or work that requires repetitive reaching should fall within the area identified as the normal work area or primary work area. This is the area that can be easily swept by the forearm when the upper arm hangs by the side of the body and there is a 90° angle at the elbow. Deciding on acceptable reaching distance is not a hit-or-miss affair because designers have access to anthropometric data applicable to their user population. These data provide guidance on body dimensions such as stature, limb length, and elbow height. Using such data will ensure that the majority of the workforce can work within a comfortable range and adopt a series of appropriate upper limb postures. On the same note, anthropometric data can be used in a personal injury case to show whether the demands placed on the worker in terms of reaching distances or working heights were acceptable or not. The posture of the upper limbs will also be influenced by the work being completed. It is often the case that the operator must alter his or her working position to come within range of the object being addressed. For instance, when locating and tightening a screw at the rear of a piece of equipment, the operators must often reach over the top of the equipment to reach the screw. This will cause them to raise their arms and then bend their wrists downward at the wrist. If the operators are unable to work with their hands in a neutral, or slightly extended, position, the degree of force required to complete the operation will be increased.
FIGURE 23.5 Change in grip strength following change in wrist posture. (From Putz-Anderson, V., 1992, Cumulative Trauma Disorders: A Manual of Musculoskeletal Diseases of
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the Upper Limbs, London: Taylor & Francis.) As Figure 23.5 shows, as the hand is moved into more extreme positions, grip strength is reduced, which will have an impact on the ease with which the task can be completed. Adopting such irregular postures repeatedly is likely to result in discomfort, particularly in the preceding example in which it is combined with both a pinch grip, as the screw is held between the tips of the fingers and the thumb, and force as the screw is located and tightened. If consideration had been given to this operation at the planning stage, the need for some means of rotating the piece of equipment so that the operator had direct access to the area being addressed would have been evident. This would have enabled him to work in more appropriate postures. Sometimes, when combined with the height of the work surface, the dimensions of the tool or equipment used or the product assembled present a level too high for the operator. In this situation, the work surface should be reduced in height so that the working height, i.e., the point at which the hands work, is set at a more acceptable level. Static Muscle Work Static muscle work, in which the muscles are tensed, is required to hold the limb in a fixed position for extended, uninterrupted periods of time. Many people assume that the non-movement of a limb during the course of an operation means that it is involved in little or no work; as a consequence, it is frequently overlooked during the assessment of potentially hazardous tasks. However, static muscle work is actually more tiring than dynamic muscle work in which the muscles contract and relax rhythmically when moving the limbs. As an indicator of how demanding static muscle work can be, the muscles involved in static muscle work need more than 12 times the length of the task duration to recover from the resulting fatigue. Other Contributory Factors Although repetition, force, posture, and static muscle work are considered the main causes of ULDs, a number of other contributors exist, including: • Vibration. It has now been well established that working with vibrating equipment and tools increases the likelihood that an individual will develop a ULD (Health and Safety Executive, 1994; Kuorinka and Forcier, 1995; Bovenzi, 2000). However, the extent to which vibration has an impact on the individual will be influenced by the vibration magnitude and exposure time. In addition, the degree of force needed to hold and operate a tool has a bearing on the effects of vibration. A poorly designed tool must be gripped more firmly, thus allowing more vibration energy to be transferred to the hand. The area of exposure, such as the whole hand or part of it, will have an impact on the outcome when vibrating tools are used. Environmental conditions, particularly colder conditions, have been recognized as increasing an individual’s susceptibility to developing a disorder. Then, of course, individual issues may make an individual more susceptible, such as whether he or she is a smoker.
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• Temperature. Working in lower temperatures and handling cold products or tools have been identified as increasing the risk of ULDs. As a consequence, operators should be protected from the effects of colder conditions as far as possible. If gloves are provided, care should be taken that they are suitable for the operator and the task performed; otherwise, they may make it more difficult for the operator to grip, manipulate, and move objects. If operators cannot be protected adequately from the effects of the cold while working, they should be given frequent breaks so that they can move to warmer areas of the site. • Organizational factors. As previously indicated, rest breaks and rotation can play a large part in increasing or decreasing the likelihood of an individual developing a ULD. Job enlargement is a means of offering the operator a greater variety of work, thereby reducing the need to repeat only a few movements within a short timescale. Job enrichment offers greater responsibility and, consequently, operators experience higher levels of satisfaction which itself has been associated with a lower level of reporting difficulties (Moon and Sauter, 1996). Simply making an individual responsible for his own quality control will offer a degree of job enrichment. Overtime can also determine, to an extent, whether the individual is more likely to experience difficulties. Although most people accept that overtime extends the length of time that an individual is exposed to unsuitable working conditions, they often overlook the corollary of this that overtime reduces the length of time available to an operator for rest and recovery. Any operator known to be suffering from a ULD should not be permitted or expected to work overtime. • Training and supervision. Typically, workers are simply trained how to complete their task. They are not always trained how to complete it safely and efficiently. For example, it is not always the case that a keyboard operator will be shown the appropriate postures to adopt when sitting at a computer workstation and assembly operators will not be advised about the need to put a tool down at intervals when it is not in use so that the hand can rest. As a consequence, operators can work in ways that inadvertently increase their risk of injury. In addition to effective training, operators need to be monitored and encouraged to maintain good working habits through appropriate supervision. Unfortunately, in many situations supervision simply amounts to ensuring that the targets are met for the day. • Peaks in workload. It is generally accepted that the individual will work most effectively if the demands placed on him by the system remain constant from day to day. This is due to the fact that the body develops a level of task fitness or stamina to meet the everyday requirements of work. If the workload increases suddenly, such as due to seasonal demands, and the operator does not have an opportunity to adjust to the changing demands, he or she may become overloaded. It has been shown that operators who are required to respond to peaks and troughs in activity may have an increased susceptibility to developing a ULD (Kuorinka and Forcier, 1995). • Sudden change. As indicated earlier, the body develops a level of task fitness that matches the daily demands of the work. Demands may take the form of the effort required, the sequence of tasks, the postures adopted, or the pace of work. If the demands change suddenly without an accompanying acclimatization period in which the operator can adjust to the changes, the result is a mismatch between the individual’s task fitness and the demands of the work. Even if a workplace is changed
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as a result of improvements, the workers need to be given time to adjust to the changes. This is also the case for people returning from absences following illness, injury, or holiday. During their absence, the body will not retain the same level of fitness and, consequently, they will require a gradual reintroduction into the work routine if they are to avoid becoming overloaded. This has particular significance in situations in which an organization has a seasonal shutdown such as two weeks in the summer or for Christmas. It also has particular significance in personal injury cases in which the worker is signed off work for the first time following the development of symptoms and, upon his or her return, expected to pick up where he or she left off. Frequently, no allowance is made for the fact that the worker has suffered an injury or that he or she may have been absent from work for weeks or even months. In some cases, the returning employee is also faced with a backlog that has built up during his or her absence. It is not surprising that a second absence prompted by a reappearance of symptoms often follows. Nonwork Factors Although work-related factors are considered to play a large part in the development of ULDs, the potential contribution of other “personal” factors cannot be overlooked. Certain medical conditions, activities, and hobbies are considered to predispose an individual to developing a disorder. People who have suffered a traumatic injury to the upper limb have been identified as being more susceptible to developing a ULD, as have those suffering from conditions such as diabetes and those who are pregnant or going through menopause. Hobbies such as racquet sports, computer games, and knitting, which could be considered hand-intensive activities, have been associated with the development of ULDs. Playing certain musical instruments has also been associated with the development of area-specific disorders. For instance, playing the piano is recognized as having similar effects to using a computer keyboard repetitively. Violinists often complain of neck pain associated with gripping their instrument under the chin and brass instrument players can experience shoulder pain from supporting the weight of the instrument and holding it away from their body. However, as was the case with workrelated factors, people engaged in these activities for extended uninterrupted periods of time are considered more likely to develop problems. As a comparison, when the time spent on hobbies is matched against the time spent at work, the percentage of time spent at work within a 24-hour cycle is likely to be far greater than that spent on a hobby. It is important that this issue be kept in mind when weighing the likely contribution of leisure pursuits. It has been suggested that the female workforce has a higher incidence rate of ULDs than the male workforce, thereby implying that females are more susceptible to developing these conditions. The question should be asked whether females represent the majority of employees performing mundane, highly repetitive operations within factorytype environments; thereby explaining their presence in the statistics in large numbers.
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23.4 Designing the Workplace Most of the problems encountered in the workplace are a result of a lack of understanding of basic human requirements. Although those responsible for developing workstation designs and equipment layouts are trained to develop a system that works, they are not necessarily trained to design a system compatible with the human operator. In addition, the managers and supervisors responsible for running a facility once it has been established do not necessarily have an understanding that the decisions they make regarding production rates, rest break schedules, opportunities for rotation, etc. have a significant impact on the workers and the likelihood that they will develop an injury as a result of their work. Today, so much advisory material is available for employers and their representatives that there is no excuse for poor decision making in terms of the physical layout of the working environment or how it is managed. There is an appreciation that many workplaces have the potential to cause harm to the workforce, yet many individuals fail to investigate what might be highly undesirable in their workplace. Throughout the European Community, assessing and reducing risk in any and every working environment are required. Despite this requirement, in many workplaces the true extent of the problems is yet to be uncovered. As a consequence, the operators continue to be exposed to working conditions that are likely to promote the development of ULDs. In the U.K., if an individual takes a claim out against his or her employer for developing a work-related injury, investigations will be made regarding the assessment procedures adopted by the company concerned and whether it applied the available knowledge at the time to its workplace as a means of identifying and reducing risk. The Health and Safety Executive in the U.K., the body responsible for overseeing the health and safety of people at work, has published much in the way of advisory information since about 1990. In addition to publishing documents at low cost, this organization also provides many free leaflets offering the latest information as well as checklists for the identification of work-related factors with the potential to cause harm. Many well-respected authors now produce ergonomics books aimed at facility managers, designers, engineers, occupational health departments, etc., and these publications provide workplace design advice and guidance. It can no longer be considered the case that advice can only be found in inaccessible, impractical academic textbooks. Designers and planners should understand that applying sound ergonomics principles to the workplace as a means of combating ULD problems does not mean that significant financial investment must be made. In many situations, very simple changes to the workplace, such as providing an assembly-line operator with a platform on which to stand or a VDU user with a more suitable mouse, may have a dramatic impact on the levels of well-being of the workforce. In the U.K., an employer is expected to introduce what are referred to as “reasonably practicable” measures to reduce risk. “When determining whether a proposed change is considered reasonably practicable and whether it should be implemented, the employer must weigh the sacrifices that need to be made to improve the workplace against the level of risk identified. The sacrifices included in the equation are time, trouble, and cost. If the degree of sacrifice is considered to equal the level of risk, the employer should introduce the proposed changes.
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Employers in many countries now recognize that ergonomics is a practical, usable tool that can be used in the day-to-day running of their workplaces. However, some individuals still feel that ergonomics is simply “common sense” and therefore specialist input is not needed. Only those who do not understand the real aims and actual benefits of ergonomics hold such beliefs. 23.5 Scientific Basis for Ergonomics Expertise Ergonomics comes from the Greek words “ergon” meaning work and “nomos” meaning law. The term “ergonomics” was actually applied by Murrell in 1949. After the Second World War, the U.S. started to use the term “human factors.” The subject of ergonomics calls upon a number of separate disciplines such as anatomy, which considers the physical structure of people; biomechanics, which evaluates the relationship between posture and strength; physiology, which is concerned with the functioning of organisms; psychology, which studies human behavior; and engineering. Ergonomics is defined as the scientific study of human work. The term “work” is used in a very broad sense and does not mean that ergonomics is concerned only with people once they enter the workplace. Ergonomics applies to all people and their needs, whatever their environment may be, so it can be applied equally well in a home environment, such as when setting the heights of kitchen work surfaces, or in terms of consumer goods, such as clothing, bicycles, and seats. On that basis, the scope of ergonomics can be considered to be very wide. If ergonomics is viewed in a working context, it can be described as aiming to ensure that human needs for safe and efficient working are met, the interaction between the body and its physical surroundings is optimized, and the task is fitted to the person. Fitting the task to the person, rather than the person to the task, is considered to be the most superior approach to the design of the workplace. It is based on designing tasks to suit the characteristics of the worker, whereas the latter approach is based on increasing productivity and efficiency by selecting workers with certain aptitudes. Ergonomics is not a gimmicky discipline that only gets used as a sales ploy. Many benefits can be gained from applying it in any workplace: • It provides a scientific foundation for a user-centered approach to design. • It is known to be cost effective in that ergonomics interventions result in performance improvements and decreased operating costs. • It enables key areas within a single facility to be identified irrespective of the particular system in place and it can be applied consistently across many different systems. • It takes a holistic view of the workplace and considers the interdependent nature of workplace elements. • It applies knowledge from different areas of science to the analysis of problems and design specifications. • It enables one to develop an effective match between not only the person and the task but also the product and the user—an effective match being one that optimizes working efficiency, health and safety, comfort, and ease of use.
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Given the aims of ergonomics as a discipline, what part does the ergonomist play? Ergonomists are able to describe the person at all levels appropriate to any system. They can apply scientific information concerning people to the design of objects, systems, and environments. They ensure that all aspects of an environment are considered in a systematic way. Ergonomists tend to divide into two categories: researchers and consultants. The consultants rely on the researcher to identify the characteristics of people and contribute to the drafting of standards and guidelines. The consultants take this information and guidance and apply it in a “real” setting where they use the accumulated knowledge about people and their needs to investigate the interface between the person, job, and environment, as well as to specify systems. When evaluating the person-workplace interface, the consultant identifies sub-units and their boundaries, highlights points of interaction, analyzes points of interaction, and applies knowledge that results in the specification of systems. When specifying systems, the consultant aims to fit the task to the person and does so at the biomechanical, physiological, behavioral, linguistic, and cognitive levels. Although ergonomists can offer very valuable advice in terms of developing or improving the workplace, in many situations, in-house personnel will be given the responsibility for identifying problematic features related to the tasks, tools, or environment. As a means to assist these individuals carry out an adequate and accurate assessment of the potential for harm in their workplace, they should call upon available data-collection tools. Task analysis is a basic starting point that provides the assessor with an indication of the subcomponents of each task, how they are performed, in what order, at what speed, and over which areas of the workplace. It enables the assessor to identify mismatches in workplace layout or workstation design and inefficiencies in work routine. Specific checklists for the identification of causes of ULDs are becoming increasingly common. The Institute for Occupational Ergonomics at Nottingham University in the U.K. has developed the RULA, i.e., rapid upper limb assessment, which provides a systematic means for investigating the extent of ULDs in a workplace. This assessment is particularly useful because it contains a series of diagrams illustrating potentially hazardous upper limb postures and movements; the assessor only needs to match the postures and movements in evidence with the diagrams to determine whether there are any concerns. This system eliminates any reliance on the assessor to interpret complex questions relating to very precise hand/wrist/ arm postures. The Robens Institute based in the University of Surrey in the U.K. has also provided a checklist entitled the QEC, i.e., the quick exposure checklist for work-related musculoskeletal disorders. This checklist is intended to be used as a “before and after” checklist and requires the assessor and the worker to provide details relating to the operations performed. Ultimately, a score is calculated for the operations performed prior to any changes. Once changes have been made to the operation with the aim of improving the situation and reducing the risk of injury, the checklist is completed for a second time. The second score is compared with the first; if the changes have led to improvements, the score will have been reduced. A number of other data-collection methods can be used when there is a desire to collect information directly from the workers about how they feel about their working environment and whether they are experiencing any difficulties. Ratings scales can be
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developed that can measure levels of satisfaction and dissatisfaction in relation to specific aspects of the workplace. Care should be taken when developing such scales that the choice of ratings for each question is equally spread in meaning, starting from a neutral position at the center and working to the extremes. Body parts discomfort surveys are a simple and effective means of identifying whether an individual is experiencing discomfort while working and where he experiences that discomfort. The worker is provided with a basic diagram of the body, with a front and rear view, and asked to shade the areas where he or she feels discomfort. These forms can be used effectively throughout the course of a working day at predetermined intervals to plot the development of discomfort as the day progresses or as the demands of the work change. Irrespective of the methods used to collect information relating to the functioning of any environment, it is imperative for the employer to ensure that the individual given responsibility for investigating problems in the workplace actually has the knowledge and understanding needed to perform an adequate assessment of the situation. If an individual has not developed an appropriate knowledge base, how can he or she assess the environment and identify areas with the potential for harm? Accurate data collection is also fundamental to the management of a personal injury claim. Only by compiling accurate information can a precise profile of the operation performed by the claimant be developed. Unfortunately, it is very common for the claimant’s case to contain many inaccuracies and serious omissions. This happens for a number of reasons. When developing a case, the solicitor acting on behalf of the claimant will rely on the claimant’s statement, probably given in the solicitor’s office, to specify formally what the individual was employed to do and how the injury came about. It is likely that the solicitor will never have seen a facility such as the one described by the claimant. Therefore, he or she is not in a position to query possible exaggerations by the claimant nor to identify the lack of detail relating to the task. Added to this, many claimants who have suffered an injury will have done so as a result of performing a mundane, repetitive, possibly physically demanding task. It must be kept in mind that • Individuals who have self-selected to fulfill such a role may not necessarily have the intellect to be able to describe task demands in any great detail. • The worker may not have a vocabulary developed fully enough to express the nature of his or her work adequately. • The claimant’s first language may not be that of the country in which he or she is pursuing a claim. • The individual has probably been at a very low level within the company for a long time, carrying out the bidding of superiors without question and never facing “professionals” in a formal setting to state his or her case. All of this is bound to have an impact on the contents and quality of the statement prepared by the legal team. This is also likely to have an impact on the conclusions reached and opinions offered by the medical professionals involved in personal injury claims. As was the case with the legal team, in order to reach their conclusions, the medical professionals will rely on the appointment with the claimant in their consulting rooms and the contents of the documents provided by the solicitors. In most cases, the medical experts will never have
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visited the type of workplace described by the claimant and therefore have no comparison base from which to work when reaching their conclusions. The medical consultants may come to their conclusions based on the contents of the claimant’s statement, which may not be an accurate account of the work; on the other hand, given their lack of experience of observing real working environments, they may find it hard to accept that the workplace could be as adverse as the claimant described. At this point, the ergonomics expert becomes a valuable element in the case. He or she is the only individual who is able to define the true nature of the operations. Although the claimant’s statement may be used as a basis for understanding the operations performed, the ergonomist carries out an objective assessment of the operations, the environment, and working practices. Based on the information made available, the ergonomist is able to offer an opinion as to whether the activity should have been identified as likely to cause harm. 23.6 Working with VDUs Although ergonomics can be applied equally well in any work setting, offices do have their own specific considerations, which warrant separate discussion. The main sources of ULDs in the office are poor workstation design, layout, and use and unreasonable task demands. In the first instance, many office managers do not appreciate the need to provide appropriate workstation furniture and to train their workforce how to use it. The desk should be chosen with the task demands in mind. It should be of a sufficient size to allow users to work with their screen directly in front of them, at about fingertip distance away when they are in the seated position, and with their keyboard in alignment in front of the screen. The aim should be to allow the user to adopt an upright, forward-facing position. Frequently, screen size outstrips the surface area of the desk and, as a consequence, it must be pushed to one side of the desk, thus causing the user to work in a twisted position. One of the biggest mistakes made in an office is to assume that the provision of expensive adjustable chairs will rid the office of problems. It is pointless providing appropriate seating if the individuals do not know how to operate them. Therefore, training should always accompany the provision of new chairs. The user should learn to adjust the height of the seat first so that the elbow is level with the home row of the keyboard. This ensures that he or she has a straight line running from the elbow, through the wrist, and into the hand. By working with the wrists in a neutral position, the user is less likely to encounter discomfort in his or her hands and wrists. The backrest of the chair should be altered so that the lumbar support is lined up with the small of the back. There is a lot of confusion around the need for armrests on chairs. Some users believe that they will develop a ULD if their chair lacks armrests. This is not the case. More often than not, armrests introduce problems that were previously unknown. It is common for them to come in contact with the leading edge of the work surface as the user tries to sit close to the desk. As a consequence, the user must sit farther away from the desk than he or she might wish. This causes the user to lean forward at the waist, which is stressful for the lower back, or to reach forward toward the keyboard and mouse, thus increasing the workload for the arms.
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Some users think that they can get around this problem by lowering their chairs to get the armrests under the surface of the desk. (Some users also mistakenly do this to get their feet on the floor). However, the consequence of this action is that the desk surface in effect increases in height as the user’s sitting level drops. This results in the keyboard and mouse being at a higher level in relation to the user than should be the case. The user therefore must raise his or her shoulders and arms to perform work; the static muscle work involved in maintaining this position for long periods of time can have detrimental effects on the user. Screens are usually located in one of two positions: directly on the desk surface or on top of the hard drive. Unfortunately, unless the user happens to be the “perfect” size to suit the positioning of the screen, he or she will need to adopt a head position dictated by the location of the screen. Ideally, the screen should be set at a height at which the user can view the screen easily without needing to raise or lower his or her head excessively. This is usually accomplished if the user can sit upright and look downward by between 15 and 30° below the horizontal line of sight. Laptop screens present the user with unique problems. They are presented at a low level when compared with a standard computer screen. This causes the user to look downward at a more extreme angle as he or she views the display. Working in this manner for extended uninterrupted periods has been known to result in neck discomfort. The correct positioning of the keyboard and mouse a\re often overlooked because these pieces of equipment are viewed as rather superficial concerns. However, their positioning dictates the positioning of the upper limbs, so the aim should be to move them to a point where the user can adopt and maintain comfortable working postures. The keyboard should be positioned so that it is close enough to the leading edge of the desk to prevent over-reaching, but should leave a small gap in front so that the user can rest the hands and wrists on the desk surface between bouts of keying. The mouse should be kept close, again to avoid unnecessary over-reaching. It is common to see a user position the mouse at such a distance that he or she must fully extend the arm to grip and operate it. Mouse mats should always be used in conjunction with a mouse. Using the keyboard on a laptop computer can also be problematic—usually because locating the screen at an appropriate distance results in the keyboard being pushed away from the user, which causes him to reach. The mouse on a laptop is often in an awkward position on one side of the laptop or, alternatively, it relies on the user operating it with the tip of one finger. As a consequence, the user adopts a highly irregular wrist posture to operate the mouse or focuses the load on a single digit of the hand as he or she works. It is a straightforward process to make the use of a laptop more acceptable for the user. A number of options are available. With the first option, the user can attach the laptop to a docking station, which allows him to run the laptop but use a standard screen and keyboard. This is a relatively expensive option and this facility is not considered to be particularly mobile, which is, of course, the intention behind a laptop computer. The second option involves the provision of a “Y” cable plugged into the back of the laptop; a standard keyboard is plugged into one end of the Y cable and a standard mouse is plugged into the other end. The laptop can be raised off the work surface onto a platform or simply by using reams of copier paper. The user is then presented with the screen at an appropriate height and has the flexibility to position the keyboard and mouse wherever he or she wishes.
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Although the general principles of VDU use will apply in the majority of work settings, in some “atypical” situations more specialist consideration is required. Examples of this are in trading rooms or CCTV rooms where users will observe multiple-screen displays simultaneously, with some wall mounted and others embedded in the desk surface and the users may need to operate several keyboards in rapid succession. Some compromises must be made in these situations and the arrangement of the equipment should be based on priority positioning for most frequently used items. Finally, it is important that office managers keep in mind that, even in the perfectly designed office environment, users still require regular breaks away from their work. Computer-based operations have evolved in such a way that users have little reason to leave their workstations. E-mail facilities mean that messages can be passed around an office, online fax facilities eliminate the need to visit a remote fax machine, and online reference materials remove opportunities for users to walk to another work area to collect a file or look up some information. As a consequence, a system of work has developed in which users spend long periods of time sitting in a fixed position with little or no variety in their work. If they are not provided with regular breaks, they are likely to experience difficulties. In the U.K., the current advice is to allow users a 5- to 10-minute break every hour after continuous screen-based activities. This does not mean that the user requires a rest break at these intervals; he or she can simply be given another task to perform that will give him or her a break from the computer-based work. However, if such opportunities do not exist, the employer is expected to offer rest breaks. 23.7 Working within Industry Office and industrial/factory-type environments share many similar problems. The only real difference is that the inappropriate working practices, postures, and workstations operate on a much more subtle level within an office. Within industry, the inadequacies in the workplace tend to be magnified, making them more obvious. As was the case with offices, poor upper limb posture is usually the result of badly designed and badly laid out equipment and workstations. Reference to any ergonomics textbook and anthropometric data should eliminate the need for such poor design. There does tend to be a greater focus on timescales, deadlines, and targets within industry, which drives the operator to work at rapid rates, increasing the repetitiveness of the operation. The more specific problems faced by workers within industry involve the use of machinery and tools. The same lack of consideration is usually given to the design of these items as is the case with workstations. The control panels on machinery and equipment often cause operators to work at high levels and with their arms raised. The handles and triggers on tools are especially problematic. Although the handle is the means by which an operator holds, controls, operates, and guides a tool, it is often the most poorly designed aspect of any equipment used. The handles are often too small or too large to hold easily, which forces the operator to hold the handle more firmly to secure the grip. Often, tools such as pliers have handles that are so short they press into the palm, causing, over time, the development of problems affecting the hand. The materials used to cover handles are often incompatible with a secure grip due to being
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smooth and flat. In this situation, if the hand gets hot and sweaty it will start to slip, causing the operator to grip the handle more firmly. Many tools have stainless steel covers that remain cold throughout the shift, causing a degree of heat exchange each time the operator grips the tool. The orientation of use of a tool is often ignored and, as a consequence, the operator may use a tool in a location that causes extreme deviation of the wrists. Vibration is a well-recognized source of problems and, although many options are available to reduce the extent of the vibration, few employers have the desire or the awareness to search for these. If the effort involved in using a tool, and thus the likelihood that it will promote the development of a ULD, is to be kept to a minimum, the tool and its handle should be designed and selected carefully. The handle should be of a diameter compatible with the hand size of the user—bearing in mind that a male or female may be the user. The diameter of the handle should not necessarily change in size to suit the size of the tool head; the size of the hand does not change even though the demands of the task might change, so the handle size should remain constant. The length of the handle should be sufficient to avoid impact injuries to the palm of the hand. The handle should be covered in a soft, compliant material that makes it easy to hold even if the operator’s hands are sweating. The weight of the tool should be kept to the lowest level possible but should not be so low that it undermines the usefulness of the tool or allows increased vibration transmission. The handle should be angled for operations in which the operator might normally need to bend the wrists to complete the operation. Cold blowback from air tools should be directed away from the operator or the operator should be provided with gauntlets to protect him or her from the effects of the cold air. Torque responses, which can cause rapid and violent twisting of the operator’s wrists, should be monitored and controlled. The tool should be put down at times when it is not in use so that the operator’s hand can rest. Provisions should be made to facilitate this practice, such as providing line-side holsters, waist-fitted holsters, or other supporting surfaces. 23.8 Checklist of Contributory Factors The following checklist provides a brief outline of the factors that should be considered during the investigation and consideration of any personal injury claim involving a ULD. Primary considerations Task demands
Workstation design
Influential factors Repetition Force Speed of operation Duration of activity System/self-paced Static/dynamic muscle work Work area layout Working heights Reaching distances Work surface layout
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Railings/guarding Clearance
Primary considerations Equipment/tool design
Posture
Organizational issues
Environmental issues
Vibration
Personal factors
Product characteristics
Influential factors Postures required to operate controls Effort required to control and operate Torque response Handle design Areas of application Frequency of operation Duration of activity Opportunities to release grip Forearm raised above horizontal Rotation of forearm Upper arm raised sideways or forward away from body side Upper arm raised upward at shoulder Arm moved across body midline Hand bent up/down at wrist Hand bent side to side at wrist Extreme flexion/extension of fingers Pinch grip Rest breaks Job rotation Job enlargement Autonomy Overtime Payment system Training Supervision Acclimatization periods Seasonal demands Working in cold environments Handling cold products/tools Cold blowback from tools/equipment Heat-induced fatigue Personal protective equipment Lighting levels Vibration Source Frequency of operation Exposure time Design of tool and tool handle Weight of tool Environmental conditions (e.g., cold) Inexperienced Medical history Pre-existing condition Bad habits/poor working practices Hobbies/leisure pursuits Personality Degree of manipulation
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Pliability Temperature Quality control Packaging
References Bovenzi, M., 2000, Health disorders caused by occupational exposure to vibration. In Violante, F., Armstrong, T., and Kilbom, A. (Eds.), 2000, Occupational Ergonomics, Work Related Musculoskeletal Disorders of the Upper Limb and Back (London: Taylor & Francis), 89–104. Hagberg, M., 2000, Epidemiology of neck and upper limb disorders and work-place factors. In Violante, F., Armstrong, T., and Kilbom, A. (Eds.), 2000, Occupational Ergonomics, Work Related Musculoskeletal Disorders of the Upper Limb and Back (London: Taylor & Francis). Health and Safety Executive, 1994, Hand-Arm Vibration (U.K.: Health and Safety Executive). Health and Safety Executive, 2002, Upper Limb Disorders in the Workplace (2nd ed.) (HSG60rev) (U.K.: Health and Safety Executive). Kroemer, K.H.E. and Grandjean, E., 1997, Fitting the Task to the Human: a Textbook of Occupational Ergonomics (London: Taylor & Francis). Kuorinka, I. and Forcier, L., 1995, Work Related Musculoskeletal Disorders (WMSDs): a Reference Book for Prevention (London: Taylor & Francis). McKeown, C. and Twiss, M., 2001, Workplace Ergonomics: a Practical Guide (Leicestershire, U.K.: IOSH Services Limited). Moon, S.D. and Sauter, S.L. (Eds.), 1996, Beyond Biomechanics, Psychosocial Aspects of Musculoskeletal Disorders in Office Work (London: Taylor & Francis). NIOSH, 1997, Musculoskeletal disorders and workplace factors (Washington, D.C.: NIOSH) Publication No. 9, 7 (141). Pheasant, S., 1991, Ergonomics: Work and Health (London: Macmillan). Pheasant, S., 1996, Bodyspace, Anthropometry, Ergonomics and the Design of Work (2nd ed.) (London: Taylor & Francis). Putz-Anderson, V., 1992, Cumulative Trauma Disorders: a Manual of Musculoskeletal Diseases of the Upper Limbs (London: Taylor & Francis). Violante, F., Isolani, L., and Raffi, G.B., 2000, Case definition for upper limb disorders. In Violante, F., Armstrong, T, and Kilbom, A. (Eds.), 2000, Occupational Ergonomics, Work Related Musculoskeletal Disorders of the Upper Limb and Back (London: Taylor & Francis).
Further Information Arksey, H., 1998, RSI and the Experts: the Construction of Medical Knowledge (London: UCL Press). Fahy, F. and Walker, J. (Eds.), 1998, Fundamentals of Noise and Vibration (London: E & FN Spon). Feyer, A.M. and Williamson, A. (Eds.), 1998, Occupational Injury: Risk, Prevention and Intervention (London: Taylor & Francis). Freivalds, A., 2002, Biomechanics of the Upper Limbs: Mechanics, Modelling and Muskoskeletal Injuries (London: Taylor & Francis). Gross, C.M., 1996, The Right Fit: the Power of Ergonomics as a Competitive Strategy (New York: Productivity Press). Helander, M., 1995, A Guide to the Ergonomics of Manufacturing (London: Taylor & Francis).
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Hutson, M.A., 1999, Work-Related Upper Limb Disorders: Recognition & Management (Oxford, U.K.: Butterworth-Heinemann). Kroemer, K.H.E. and Kroemer, A.E., 2001, Office Ergonomics (London: Taylor & Francis). Kroemer, K.H.E., Kroemer, H.B., and Kroemer-Elbert, K.E., 1994, Ergonomics: How to Design for Ease and Efficiency (Englewood Cliffs, NJ: Prentice Hall). Kumar, S. (Ed.), 1999, Biomechanics in Ergonomics (London: Taylor & Francis). Kumar, S. (Ed.), 1997, Perspectives in Rehabilitation Ergonomics (London: Taylor & Francis). Mohan, D. and Tiwari, G. (Eds.), 2000, Injury Prevention and Control (London: Taylor & Francis). Morris, A. and Dyer, H., 1998, Human Aspects of Library Automation (2nd ed.) (Hampshire, U.K.: Gower). Rice, V.J.B. (Ed.), 1998, Ergonomics in Health Care and Rehabilitation (Stoneham, MA: Butterworth-Heinemann). Rutter, B.G. and Dainoff, M.J., 1996, The Ergonomic Office: Standards, Specifications, Design Guidelines (Missouri: Metaphase). Watkins, J., 1999, Structure and Function of the Musculoskeletal System (Champaign, IL: Human Kinetics). Whiting, W.C. and Zernicke, R.F., 1998, Biomechanics of Musculoskeletal Injury (Champaign, IL: Human Kinetics). Wilkinson, C., 2001, Fundamentals of Health at Work: the Social Dimensions (London: Taylor & Francis). Wilson, J.R. and Corlett, E.N. (Eds.), 1995, Evaluation of Human Work: a Practical Ergonomics Methodology (2nd ed.) (London: Taylor & Francis).
24 Exercise Injuries: Human Factors in Fitness Facilities Max Hely Safety Science Associates Pty., Ltd. 0–415–28870–3/05/$0.00+$ 1.50 © 2005 by CRC Press
24.1 Introduction Attaining physical fitness through exercise is well understood to provide long-term health and performance benefits. Considerable attention has been paid to improving the effectiveness of fitness services; however, the safety of exercise participants while they are engaged in the pursuit of fitness has been less well catered for. This shortcoming has resulted in costly personal injury litigation. Although the adverse effect on human safety of a deficient interface between human capabilities and task demands is well known in the occupational ergonomics domain, the primary emphasis in the sports and fitness domain appears to be on performance and/or long-term health outcomes rather than on the immediate safety of the participant. This chapter will take a human factors/ergonomics perspective to consider the similarities and differences between exercise and work settings, particularly with respect to the safety of the humans involved. From that viewpoint, deficiencies evident in the provision of various fitness services that resulted in injury and litigation are analyzed. Consideration is then given to the implications of these analyses for development of a safe practice model directed to ensuring an improved standard of care in the delivery of fitness services. A safe practice model can be used to: • Establish an appropriate, comprehensive safety standard for the delivery of exercise services • Consequent upon establishing this standard, minimize the potential for injury to participants during the delivery of exercise services • Reduce the opportunity for personal injury litigation • Provide protection or defense against allegations of negligence to defendants • Assist plaintiffs in identifying and particularizing the items of negligence with respect to an expected standard of care for their safety
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24.2 Objectives and Scope The objectives of this chapter are threefold: • To alert safety and fitness professionals to the critical distinction between the long-term benefits of exercise participation (often referred to as health and well being) and the immediate safety of exercise participants during their pursuit of those long-term goals • To analyze representative exercise-related personal injury cases qualitatively from a human factors/ ergonomics perspective in order to identify common deficiencies in the standard of care and, from these, develop a safe practice model for the delivery of exercise services • To provide a safe practice model, or standard, and a checklist derived from its components as guidance for fitness professionals to address the ongoing safety of their clients during their pursuit of health and well-being via exercise participation The scope of the chapter primarily encompasses issues pertaining to the administration or management of exercise service delivery rather than the structural or physical safety of equipment and facilities per se. It is these administration/management issues that appear to be the major source of participant safety concerns and the least well accommodated by current practice. 24.3 The Fitness Industry—an Overview Throughout the latter part of the 20th century, the sport, fitness, recreation, and leisure industries were among the fastest-growing industry sectors in terms of employment (DEET, 1991). Indications of increased community demand for these services and facilities are consistent with the trends in Australia, Europe, and North America toward greater promotion of, and participation in, active lifestyles and fitness pursuits. Such public health promotions and programs have long been directed toward influencing community members to increase their involvement in physical activity and exercise. As with the rapid expansion of any potentially profitable industry, the early phases were characterized by ardent attempts to encompass the full scope of market potential, with emphasis placed on expanding the range of services offered. In addition to a proliferation of publicly available fitness facilities and services, there was also early recognition of the potential to reach the community in its workplaces through corporate fitness facilities and programs. By the mid-1990s, even national occupational health and safety (OHS) bodies were providing advice on the establishment of corporate health promotion programs, which included, among many other health-related initiatives, physical fitness programs (e.g., NOHSC, 1995). With the accumulated wealth of decades of scientific research in exercise science and a growing industry determined to apply this knowledge commercially, better standards of care than ever were—or should have been—available to the users of fitness-related products and services. Historically, however, the foundations of the fitness industry were laid in what was, by today’s standards, a relatively dark past wherein its activities were largely informed by
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the principle of “no pain, no gain”—loosely translated as “you’re not making progress unless it hurts!” Recognition of the adverse effects of that mentality on exercise adherence (to say nothing of injury risk) among a largely sedentary and unfit community (Rejeski and Kenney, 1988; Dishman, 1988), together with a number of crises of consumer confidence (primarily arising from unscrupulous or incautious financial arrangements), eventually led the fitness industry (as it came to be known) to embrace professionalism in all its respects. Among other things, this led to the advent of professional accreditation and training courses for fitness instructors. These continue to develop in sophistication and scope through the auspices of representative and advisory bodies such as the American College of Sports Medicine, Fitness Australia, and the Fitness Industry Association (U.K.). Unfortunately, however, as will be seen in the following sections, careless, outdated, and potentially injurious practices are still quite evident in many quarters. In light of the preceding discussion, an important distinction should be clarified between two kinds of physical activity outcome and the procedures intended to produce them. On the one hand, engagement in exercise is widely promoted, particularly by fitness industry advocates, as a path to health and well being. Although health and wellbeing are recognized as important objectives of many fitness activities, they are frequently perceived as rather general and diffuse outcomes usually assumed to be gained simply by participation in exercise and other fitness-related activity. It is not being claimed here that health and well-being, as with most other concomitants of fitness activities, cannot be reasonably clearly defined and their characteristics quantified. However, this does not occur in many fitness settings and, anecdotally, these outcomes are often perceived to be the inevitable, if somewhat vague, consequences of long-term participation in fitness pursuits. On the other hand, the term safety has quite different implications relating to acute as well as chronic outcomes and calls for special attention to the stresses placed on the musculoskeletal system as a result of the immediate conditions, regardless of the kind of activity involved. Indeed, as will become clear in the course of this chapter, the pursuit of health and well-being through fitness activities may well place (and in many instances has placed) exercise participants at risk of acute physical injury as a result of unsafe conditions and/or practices. Therefore, unless the fitness service provider also has the immediate safety of the participants while they are engaged in pursuing longer term health, fitness, and well-being as an explicit objective, the former can be (and often has been) neglected in pursuit of the latter. 24.4 Legal Context for Exercise Service Delivery It is a truism to state that all physical activity, whether occupational or recreational, entails risk. Occupational experience has been that greater levels of physical activity (e.g., high levels of manual work) are associated with greater injury risk (Kelsey and Golden, 1987), whether that activity is examined at the individual level, in terms of increased frequency, duration, or magnitude of the loading, or at the population level, in terms of participation rates and overall exposure. The nature of musculoskeletal injury
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associated with increasing physical demands in occupational tasks has been well documented (Bernard, 1997; Waters et al., 1993). One of the most common justifications for engaging in fitness-related physical activity is to improve musculoskeletal health. Yet, in light of the preceding occupational experience, there would seem to be no a priori reason to assume that more involvement—whether in terms of the amount of such activity undertaken by individuals or the overall number of people involved—will not lead to an increased potential for injury, as does increased exposure to physically demanding occupational activities. Although the ultimate purpose of fitness equipment and activities may differ from industrial equipment and tasks, the types and extent of musculoskeletal injury risk associated with each are probably quite similar, if not identical. The injury-prevention obligations imposed upon employers and persons in control of workplaces by OHS legislation are well known among ergonomists. Although the specific requirements may vary from place to place, they usually include, in general terms, the requirements to provide: • Safe equipment • Safe physical environment • Safe activities • Effective supervision • Adequate information (including instructions, training, and warnings) However, many (including many OHS professionals) do not view the fitness venue in the same light as they would a workplace. That the fitness industry has not suffered greater involvement in personal injury litigation to date—at least when compared to workplaces—may well be more a reflection of the community’s lack of expectations about the standards of care in exercise venues than of universally high professional standards. Notwithstanding this, the many recent and quite public lawsuits suggest that this situation may be changing, at least in relation to outdoor recreation and leisure pursuits. Anecdotally, the general community and the fitness industry appear to have relatively little appreciation that exercise service providers owe the same duty of care with respect to consumers’ immediate physical safety as they do with respect to their financial dealings and, indeed, as do employers or providers of any other products and services. In fact, the apparently low injury rate in the fitness industry may well reflect a low reporting rate, rather than a low incidence of injury (Sedgwick et al., 1988, 1994). Not only may individuals have little understanding of the level of care they should expect, but they may also be averse to taking legal action against providers in an industry in which participation is widely (if somewhat inaccurately) seen to be entirely at one’s own risk. From that perspective, pain and injury may be thought to be natural concomitants of the fitness process (harking back to those “dark ages”) or reflections of one’s own errors or limitations rather than due to inadequate or inappropriate systems of service delivery. Moreover, as for many musculoskeletal injuries in industry, exercise injuries only rarely result in emergency department attendance or hospital admission and therefore escape the attention of injury surveillance systems. 1 However, recent high-profile public liability cases have led to a realization that, like others in sport and recreation, fitness centers and providers of exercise and related
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services are not insulated from the legal processes to which any member of the community has recourse should he or she be injured allegedly as a result of the actions or inactions of others. A survey of more than 400 sport- and recreation-related lawsuits in North America (Dougherty et al., 1994) found that: • 24% related to faulty or inadequate supervision • 40% related to inappropriate selection or conduct of activities • 36% related to unsafe environmental conditions In other words, approximately two thirds of cases were related to deficient management of programs, while only approximately one third related to unsafe physical conditions. Reasonably consistent with these findings were the results of a 20-year survey of weighttraining injuries in the United States (Jones et al., 2000), which reveal the most common causes of injuries to have been: • Unsafe behavior (63%) • Lack of supervision (30%) • Inattention (10%) • Equipment malfunction (37%) Because more than one cause was assigned to some injuries, these totals combine to more than 100%. However, it is notable that the “unsafe behavior” classification (63%) included any incident not due to physical environment or equipment malfunction (37%) and included “lack of supervision” and “inattention,” as well as inadvertent errors and equipment misuse (Jones, 2002). Therefore, this appears to suggest that, again, almost two thirds of the injuries were related to deficiencies in the administration or management of exercise activities and facilities. 1
For example, Victorian Injury Surveillance and Applied Research System (VISAR), Monash University Accident Research Center. Summary data published in Hazard, e.g., Cassell, E. and Clapperton, A. (2002) Preventing injury in sport and active recreation. Hazard, 51, 1–25.
In OHS, provision of sound management and supervisory practices is widely accepted as essential in environments in which demanding, potentially injurious physical work is performed. Given the physical demand inherent in most fitness activities, sound administration and management practices might also be expected to be of the highest priority in any exercise facility. Yet, again from U.S. experience (Herbert and Herbert, 1988), the absence of adequate program management and supervision in fitness settings has resulted in a variety of negligence claims, which included but were not limited to: • Failure to evaluate participants’ capabilities and identify limitations that may contraindicate certain exercises or activities • Failure to monitor exercise tests properly • Failure to instruct on the appropriate use of exercise equipment or on the correct performance of exercises • Failure to prescribe exercise intensity appropriately in accordance with metabolic, muscular, or cardiovascular demand • Failure to provide advice on appropriate modifications or restrictions on an individual basis
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How might a human factors/ergonomics perspective contribute to evaluation of the conditions leading to such injuries and the development of effective preventative measures? To address this, it is instructive first to consider the similarities and differences between the occupational setting (with which many ergonomists are more familiar) and the fitness setting. 24.5 The Exercise-Ergonomics Dichotomy The conventional objective of ergonomics with respect to physical activity is to reduce the demands imposed by the task to a level that does not induce excessive physical stress. The closer the task’s physical demands approach what are understood to be the upper threshold of some human capacity, the higher is the risk of error or injury. This is reflected, for example, in the quite familiar approach taken in the domain of industrial manual handling risk management (Mital et al., 1993). The logical and familiar outcome of this perspective is to aim for the design of tasks that reduce demands to a level that leaves a significant margin of safety. In ergonomics terms, participants in exercise activities are analogous in many respects to workers in industrial settings—i.e., there is a system of work (or activity) with attendant mental and physical demands; there are individual limits beyond which safe performance is compromised; and the design of the human-task system should ensure that demands do not exceed human limits, thereby ensuring safe, efficient, and effective human performance. However, in contrast to occupational tasks, the defining characteristic of fitness activities is the emphasis on increasing a person’s physical capacity. This is also in quite marked distinction to the design approach taken with most other products or services in which the emphasis is often on increasing the efficiency or reducing the utility demands of the product or service and thereby reducing the demands on the human. The ergonomist confronting fitness-related phenomena may find that the emphasis on increasing, rather than decreasing, the demands on the human is unusual in several respects. As noted earlier, the familiar ergonomics criteria are aimed at producing a situation in which “normal” human capacities or capabilities are not exceeded. This approach seems, prima facie, oddly inappropriate or even inapplicable in an exercise context. The aim of most exercise activities is to expose the person to demanding physical stimuli with a view to inducing a level of physical stress that is at, or very near to, the human organism’s tolerance threshold. The objective of doing so is to encourage physiological adaptation so that, in the near future, the participant can further exceed his or her present capacity. 2 Although beyond the scope 2
This is, of course, not an unfamiliar concept in rehabilitation. However, the emphasis there is on a return from “injured” to “normal” rather than, in fitness pursuits, on engaging in a dedicated effort to attain “supranormal” capacities.
of this chapter, another unusual and often-ignored feature of the fitness setting (compared with the industrial environments that ergonomists usually examine) is that, from the clients’ perspectives, they are involved in it in addition to their normal occupation, rather
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than as part of that occupation. The clear implications here for physical stress, cumulative loading, and workload titration are not usually considered in occupational ergonomics. A further important, though subtle, distinction between occupational and fitness settings relates to the differences in emphasis placed on the qualifications of personnel as opposed to the conditions (including procedures and processes) where the work or activity occurs. Although many specific, indeed quite prescriptive, conditions, including behavioral guidelines, facility standards, etc., have been developed for fitness facilities and services (ACSM, 1992, 2000; AFAC, 1987), fitness industry accreditation bodies tend to place much greater emphasis on the education and qualifications of the fitness instructors as the primary factor determining the effectiveness, appropriateness, and safety of the services delivered. By contrast, the dictates of OHS legislation (as well as the principles underpinning human factors/ ergonomics approaches to dealing with injury risk) emphasize the standard of the conditions that must be established in the work environment to ensure the safety of the workers, regardless of the qualifications of those responsible for implementing the standards. 24.6 Standards of Care: Evaluation of Case Studies This section briefly summarizes personal injury incidents (Table 24.1) that occurred in corporate as well as commercial fitness facilities and led to costly personal injury litigation. This small and relatively recent sample was drawn from a large number of sport-, recreation-, and fitness-related personal injury occurrences investigated by the author. They are presented here as exemplars of some of the major issues emerging as important in fitness-related personal injury. Notably, and consistent with the findings in the North American studies referred to earlier, relatively few cases in the author’s experience arose from unsafe equipment per se. The majority arose from deficient management of the process of providing the exercise services to novices or relatively inexperienced exercise participants. Moreover, the majority of the exercise venues were controlled by accredited fitness professionals—a disturbing fact that raises the issue of supervision that is dealt with in a subsequent section.
TABLE 24.1 Sample of Exercise-Related Personal Injury Occurrences Injury Lower back
Injury occurrence
Sustained during the use of exercise apparatus (reverse leg press) to perform an unsafe version of an exercise Shoulder Sustained during the incorrect use of a pulleybased exercise apparatus
Contributory factors Excessive rate of progression over a short period of time; no or inadequate evaluation, instructions, advice, or supervision by fitness instructor; inadequate evaluation of equipment and exercise suitability No supervision of novice exercise participant; incorrect recall of exercise performance by novice due to excessive number of exercises prescribed by fitness instructor; inadequate attention by supervisor to individual’s limitations;
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Foot, ankle
Neck
Sustained while using stationary exercise cycle without properly affixing restraints Sustained while performing abdominal exercises with incorrect, unsafe technique
663
inadequate prior supervision Absence of instructions, warnings, or supervision by fitness instructor; deficient information and warning design
No evaluation of participant’s capacity to perform exercise; inadequate instruction in exercise performance; inattention by fitness instructor to adverse feedback from participant; failure of fitness instructor to prescribe modifications of technique and intensity to suit individual’s capacity; inadequate supervision Neck, Sustained while attempting No determination of safe starting loads; no advice, shoulder machine-based pulling instructions, or warnings in relation to exercise performance exercise with excessive and risks; inadequate supervision load and poor technique
Space constraints do not permit a detailed narrative of each exercise participant’s interaction with the respective fitness center. However, in order to illustrate some of the relevant standard-of-care issues further, an abbreviated summary of the characteristics of three of these cases, including the interaction between the participant and the fitness facility and the conditions to which he or she was exposed, is presented in point form. Factors directly relevant to causation of the participant’s injury will be emphasized, although in some cases, the deficiencies that led to the injury were only part of a more widely deficient system. A somewhat more detailed description of the history and evaluation is given for Case Study A in order to illustrate the range of standard-of-care considerations better. The remaining cases will be treated more briefly and will illustrate similar or related considerations. Case Study 1: Mr. A and the Alpha Gym 3 Mr. A, who had very limited experience in resistance training, suffered a lower back injury while using a “reverse leg press machine” during his sixth workout at the Alpha Gym. This apparatus required him to lie on his back on a padded platform close to the floor and place his feet flat against the underside of a load carriage which slid vertically above him along two slide poles. The exercise required alternate flexion and extension of the hips and knees to raise and lower the load carriage vertically above his supine trunk. Mr. A described quickly lowering the load carriage by rapidly flexing his knees and hips. He also described lifting up his pelvis from the padded platform and rotating it posteriorly in order to bring his knees as close to his chest as he could. At the lowest point in the carriage’s range of motion, he would then rapidly push up again to repeat the exercise. On the occasion of his injury, Mr. A had just lowered the weight carriage of the machine down to its lowest point and had begun to push it away from his body when he experienced sudden, severe lower back pain. By Mr. A’s descriptions, he performed this exercise in a “ballistic” manner, with the maximum loading on his musculoskeletal system occurring during the brief impulse of force required at the bottom of the carriage’s range of movement in order to overcome its downward momentum and reverse its direction of movement. Significantly, this also
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occurred at the point at which his hips were maximally flexed, his pelvis was maximally rotated, and his lower back was forced into extreme flexion. In other words, the greatest force exerted during the exercise—i.e., the force required to rapidly stop the carriage’s downward momentum and subsequently propel it away from his body—occurred in the position at which his lower back was most vulnerable to injury (Adams and Dolan, 1995; Adams et al., 2002). The following points summarize the pertinent characteristics of Mr. A’s interaction with the fitness instructor, the fitness center, and his exercise program and provide an evaluation of some of the critical issues: • No assessment of his initial health or general or specific fitness status was conducted prior to prescribing his resistance exercise program and his undertaking it. • He was provided with a resistance training program by an accredited fitness instructor, but without any instruction or demonstration of exercise performance methods or advice on adjusting critical training parameters (including training frequency, duration, rest breaks, load magnitude, exercise selection, rate of progression, etc.). • Although the front desk was usually staffed, a supervisor was rarely in attendance in the weight training area during his workouts, and neither Mr. A’s individual exercise performances nor overall workouts were personally supervised—initially or at any subsequent time. Generic instructional guidelines, which might have offset the risk to Mr. A (for example, in this case, lowering weights slowly, avoiding ballistic movements or rapid changes of direction, stabilizing the pelvis, and 3
The cases related in this chapter are real. However, the names of the fitness facilities are entirely fictional. They were selected from the first three letters of the Greek alphabet in order to correspond with the plaintiffs’ designations, i.e., A, B, and C. No resemblance to the name of any actual facility is intended or implied.
maintaining normal lumbar curvature [among many others]), have long been widely appreciated and accepted as essential components of safe resistance exercise technique (Baechle et al., 1994; Yessis, 1992). It is also quite evident that, in order for unsafe exercise behaviors, postures, or techniques to be detected and immediate remedial action taken, the workout area needs to be supervised by the fitness professional at all times during use. In addition, specific exercises such as the reverse leg press (among others), which involve relatively heavier loads, higher forces, or other characteristics that present a greater risk of injury (especially if the exercise is performed incorrectly), demand a greater level of instruction and supervision than other less potentially dangerous exercises. • As a novice, Mr. A was subjected to a potentially excessive rate of progression over a relatively short period of time. After receiving his initial program from the accredited fitness instructor, he commenced using the reverse leg press machine with an additional load of 60 lb (27 kg), building up to an additional 120 lb (55 kg) over the course of six workouts. This represented a 100% increase over five workouts. Although considerable individual variation is present in adaptation, this borders on an excessively rapid increase in intensity (Kraemer et al., 2002). This may have been expected to put him at an increased risk, especially if no supervision was provided, if the load was increased at the expense of proper and safe technique, or if appropriate load magnitude and/or technique were not used in the first place.
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• The training area had no signs or written instructions on the use of the exercise apparatus or any other written information regarding exercise performance or related matters. Subsequent to an appropriate induction, the maintenance of correct and safe exercise technique can be facilitated by providing well-designed, prominently displayed signs incorporating diagrams and written instructions. However, these could not be regarded as a substitute for direct instruction and supervision. • Mr. A believed that he had warmed up prior to starting the exercise in question. From his descriptions, his warm-up was largely limited to “a few bends and twists.” It is therefore also quite likely that his musculoskeletal system was inadequately prepared for intense exercise. Most novice exercise participants require a cogent explanation of the warm-up process in order to emphasize its importance, motivate its adoption, and ensure its efficacy. Failure to warm up adequately, especially for exercises involving constrained postures and relatively high loads (relative to the individual’s capacity), is widely regarded to hold significant injury potential. Scientific opinion on the precise mechanics of the warm-up process varies. However, conservative and long-standing minimum recommendations for warming up include the performance of approximately 5 to 10 minutes of low-intensity rhythmic exercise (e.g., jogging, cycling) to increase circulation and body temperature (and thereby increase soft tissue elasticity and/or contractility) followed by stretching and/or other preparatory exercises specific to the activity or exercise to follow (Egger and Champion, 1983/1998; ACSM, 1980/2000). • Mr. A unsafely performed an exercise resulting in his lumbar spine being placed in extreme flexion while subject to a high-magnitude, rapidly applied load. The more extreme postural deficiencies permitted, if not overtly encouraged, by the design of the reverse leg press exercise may have been overcome by the use of a seated leg press machine, if available. This alternative allows safer performance of the leg press exercise by facilitating pelvic stabilization on the upright seat and a greater inclination of the back rest toward the line of action (dependent on the construction of the particular machine), thus reducing the potential for extreme pelvic rotation. Many other exercises also involve the use of dumbbells and barbells and effectively use the same or similar muscle groups and motion patterns as those targeted by the reverse leg press exercise. Case Study 2: Ms. B and the Beta Center Prior to taking out membership at the Beta Center, Ms. B informed the fitness instructor of her overt anxiety about using weights and equipment and of a previous “whiplash” injury sustained some years ago. She was assured that she would be given personal supervision. No other information was provided to her about risks inherent in the performance of exercise or the use of exercise equipment, nor was she given advice about frequency of attendance. After joining, she was provided with an exercise program comprising approximately 25 to 30 separate exercises, some involving floor activities and about 10 or 15 using various pieces of equipment. On her third visit to the center (separated from the previous two workouts by some 3 months), Ms. B found only the center manager present, although she had made an appointment for personal supervision. No fitness instructor was available to supervise her. The manager told Ms. B that she was busy, but instructed her
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to commence her workout and that she would “keep an eye on [her]”. Shortly after, the manager left the exercise area. Ms. B could not recall precisely what to do next, but believed one of the exercises that she had previously performed under the guidance of the supervising fitness instructor involved the use of a wall-mounted pulley device. Ms. B also did not recall that she should adjust the weight affixed to the pulley. While attempting to use that apparatus with an excessively heavy load and with improper technique and posture, Ms. B lost control of the tensioned cable and suffered a sudden rapid imposition of force at her shoulder joint, resulting in musculoskeletal injury. In using the pulley, she had attempted to exert force from a disadvantageous position. With her arm partly extended, she found it suddenly and forcefully pulled backward into horizontal extension and external rotation. Overcoming that sudden demand safely would have required considerably more strength and movement control than Ms. B was likely to possess, given her negligible experience with resistance training. The pertinent characteristics of, and some of the critical issues involved in, Ms. B’s interaction with her fitness center and exercise program include the following: • Inadequate attention was paid to Ms. B’s individual limitations and concerns in relation to the exercise environment. • Despite Ms. B’s emphasizing her anxiety regarding exercise and making an appointment for a supervised workout, no fitness instructor was available to supervise her third workout in 3 months. • No counseling or advice was provided to Ms. B regarding her attendance frequency. This factor had an impact not only upon her physiological adaptation to exercise, but also on the cognitive processes inherent in familiarization with the exercise facility and equipment and the correct recall of the performance details of her program and its specific exercises. • For a novice exercise participant, 25 to 30 exercises represent a potentially excessive number. To the uninitiated, many fitness exercises, particularly those involving the use of equipment, are quite unlike other normal daily activities and are therefore unfamiliar in terms of the postures to be adopted, the kinds and magnitude of the exertions to be made, and the methods of execution. Exercise participants, especially if inexperienced, can lapse into poor technique after initial instruction. This can obviously include exhibiting poor recall of specific instructions and information. Although it is not uncommon for beginners’ routines to comprise some 10 to 15 separate exercises, accurate recall of the details of even that number of exercises, let alone those of 25 to 30 exercises, constitutes a significant mental workload for a novice participant. That Ms. B would fail to recall how to perform one of such a number of exercises properly and safely when unsupervised was quite foreseeable. Case Study 3: Ms. C and the Gamma Studio On Ms. C’s first attendance at the Gamma Studio—her first attendance at any fitness facility—she participated in an exercise class in which all participants rode stationary exercise cycles. Before the class, Ms. C had placed her feet into toe pieces on the pedals in what she thought was the correct manner. She had never used such a cycle and was not aware that she also had to secure her feet onto the pedals by tightening the straps.
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In what was an entirely unfamiliar environment to Ms. C, many stimuli were competing for her attention; she had received no prior information on any aspects of the class to assist her in orienting her attention to potentially critical aspects such as use of the foot restraints. During the course of the class, while pedaling rapidly, one of Ms. C’s unsecured feet slipped from its pedal, jammed against the frame of the cycle, and was severely injured. As for the previous cases, the following points summarize the pertinent characteristics of Ms. C’s interaction with the fitness studio, instructor, and equipment and provide an evaluation of some additional critical issues: • Although Ms. C identified herself to the instructor as new to the class, no attention was paid by the instructor to ensure that Ms. C had properly and securely affixed her foot restraints prior to beginning the workout. • Prior to the start of the workout, no instructions were given to Ms. C or to the class as a whole regarding any safety issues, including the use of foot restraints. • The stationary cycle used by Ms. C featured a small (11 cm by 2 cm), faded, worn, and thus partly illegible warning label on which was printed 4-mm-high uppercase text. This label was affixed sideways on the cycle’s crossbar (rather than oriented correctly for a user when seated on the cycle) at a distance of a little over a meter below Ms. C’s eye height. The label’s content was a quite strongly worded warning related to the overt injury risk if the user were to remove his feet from the pedal while using the cycle—the manufacturers’ clear acknowledgment of an inherent risk, yet one apparently not considered by the fitness center or its instructors. The necessity to design instructional and warning signs and labels according to sound human factors principles has long been recognized and an abundance of guidance material on this issue is available (for example, see Edworthy and Adams, 1996; Laughery et al., 1994; Wogalter et al., 1999). Similar considerations in relation to the provision, presence, and/or effectiveness of instructions, signs, and warnings could also be raised in relation to the previous case studies. Emergent Themes for a Standard of Practice Consideration of the characteristics of each of the preceding cases suffices to identify a number of common themes underlying negligent professional practice; thus, some useful direction in terms of principles and design recommendations 4 can be provided that can reduce the risk of these types of injury occurrences. As already noted, the most salient difference between exercise and occupational settings is that, unlike workers, exercise participants intentionally expose themselves to levels of musculoskeletal stress that they plan to be sufficiently intensive, when combined with adequate rest and nutrition, to induce an adaptive response. In light of the injury occurrences briefly related previously, it seems that, from a human factors/ ergonomics perspective, several essential conditions should attend such exercise performance. These include the following: • The actions and postures adopted during the exercise performance should facilitate the intended physical stress but not inadvertently result in excessive stress being imposed on some component of the musculoskeletal system less able or unprepared to tolerate that stress.
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• The selected intensity of the exposure to physical loading should not be excessive for the current physical condition of the participant. • The rate at which a participant increases his exposure to the exercise stimulus (whether in terms of intensity, frequency, or duration) over time should be sufficiently conservative to accommodate the potentially (given that many other factors may variously contribute) nonlinear and variable rate of physiological adaptation. These conditions necessitate, in turn, some prerequisites, including: • The exercise participant should be provided with sufficient information and instruction to understand the inherent risks and expected safety behavior as well as acquire the necessary skill for each exercise. In relation to safety behavior and skill, one can frequently observe an exercise participant 4
The term “design” is used here in its widest sense, including the design of systems, processes, procedures, and information as well as physical design.
—often someone with considerable experience—using equipment or performing ostensibly simple exercises improperly or unsafely to varying degrees. The rate and degree to which one acquires expertise in any unfamiliar skill depend on, among other things, appropriate early instruction and ongoing monitoring. Moreover, although many exercises and their associated equipment do not appear overly complex or difficult to use, the difficulties faced by novices usually do not pertain to the complexity of the movements or apparatus per se but, rather, to the control of their own bodies and limbs when exerting themselves in unaccustomed ways. • The exercise participant should be provided with adequate supervision to detect inadvertent, unsafe lapses or deviations in performance. Notably, effective supervision requires more than the mere presence of a fitness instructor (Nygaard and Boone, 1985)—a fact that apparently has escaped many of those subject to litigation. The quantitative dimension of supervision (i.e., supervisor/participant ratio), although a necessary consideration, is not sufficient for participants’ safety if the qualitative dimension is deficient. Quality supervision demands, in addition to minimum fitness industry qualifications, a proactive approach by supervisors to actively attend to all aspects of the setting under supervision. This includes attempting to detect and/or anticipate potential problems and taking effective action to avoid them. Supervisory quality can further be seen to include general supervision—i.e., an overview of the whole group and activity environment—and specific supervision, which relates to the direct interaction of the supervisor with one or more individual participants (Dougherty et al., 1994). Clearly, an accredited fitness instructor’s presence and qualifications per se do not ensure that appropriate standards of practice in relation to participants’ safety are implemented any more than, for example, the possession of OHS qualifications by a staff member in an industrial setting ensures the provision of a safe work environment, or the presence of a medical doctor ensures that good medical practice is adopted. Therefore, industry- and activity-specific standards and codes of practice must exist. It is these that a trained
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professional must interpret and implement and to which he or she should refer when ensuring that practices are in compliance with the required safety standards. 24.7 Proposed Safe Practice Model for Provision of Fitness Services General facility-related safety issues, such as those pertaining to plant, equipment, access, surfaces, and hygiene, are already well accommodated under the various occupational safety and building regulations, standards, and codes. These apply equally to fitness facilities as to any other place of employment or business. These regulations and guidelines, however, are largely silent in relation to participant safety during the provision of fitness services. Consideration of the circumstances and characteristics of each of the preceding cases, and the resultant identification of desirable standards in which the service providers in those cases appeared to be deficient, have been used here to propose, in qualitative terms, a safe practice model for exercise and fitness service delivery. The model aims to: • address the identified shortcomings in practice • overcome the necessity for a laboriously prescriptive approach to providing exercise safety • provide a template consistent with exercise science best practice The model described in Table 24.2 proposes a number of considerations that should apply to the prescription and administration of exercise to ensure the safety of the participants rather than effectiveness in achieving fitness goals. However, all are entirely consistent with the numerous sources of guidance to the fitness industry regarding program effectiveness. The components of the safe practice model in Table 24.2 were extracted from activity analyses including, but not limited to, case studies described in this chapter. These analyses identified the demands placed upon relatively novice participants when performing unaccustomed actions in what, for them,
TABLE 24.2 Safe Practice Model for Exercise Service Delivery Standard item Determination of the health status of the participant for physical activity in general
Considerations
This should include a general medical screening questionnaire to exclude any contraindications to physical activity, and specific reference to any possible contraindications to exercises, activities, and equipment immediately available to the participant in that facility. Determination of the entering status The participant’s current capacity (“fitness”) to perform each of the participant into the program, prescribed exercise should be assessed under the supervision i.e., the participant’s current level of of the fitness professional. This applies initially as well as for specific fitness for the proposed major changes or addition of exercises to the participant’s program of exercises program. Physiological and biomechanical It is reasonable to expect that a general understanding of exercise physiology and biomechanics should inform the evaluation of the prescribed
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exercises and equipment, in relation process of prescribing exercises that require participants to to the normal range of human perform a variety of actions or adopt a variety of postures capabilities and limitations as well under load. as to those specific to the individual participant Accurate and appropriate The initial instructions for any exercise should include instructions given for the demonstrations by the fitness supervisor of correct technique performance of the prescribed and common technique faults, especially those relating to exercises and their integration into postural deviations, stability, and uncontrolled ballistic the overall exercise program movements of the body. Instructions should include explanation of the inherent risks of any exercise and the measures to be taken to minimize the risks. Advice should also be given about progression, overload, and recovery, as well as about precautions when exercising in the presence of other people or near other equipment and fixtures. In addition to specific instructions for each exercise and piece of equipment, the participant should be shown how to prepare properly and sufficiently in order to reduce the risk of injury. The novice client should, initially, be personally supervised. Adequate supervision of the exercise program provided initially This supervision should continue until he or she can and at regular intervals to ensure the demonstrate acquisition of safe and proper techniques for the acquisition and maintenance of safe exercise. Regular routine checks should be made to ensure the novice maintains safe and correct technique and posture. and correct techniques, postures, and general exercise behavior The exercise area and those The workout area should be supervised by the fitness professional at all times during use in order that unsafe performing within always under equipment, conditions, behavior, or techniques can be detected qualified supervision while and immediate remedial action taken. participants are exercising
were largely unfamiliar environments and activity systems. The results of these analyses pointed to quite evident mismatches between novice individuals’ capabilities and the perceptual, attentional, cognitive, and movement demands of those situations and environments. Elimination or reduction of the extent of mismatch could have been achieved by designing program administration procedures that were sensitive to the potential for these human-system mismatches. The proposed safe practice model provides, in qualitative terms, guidance for the safe as well as effective delivery and administration of exercise programs. It does not prescribe specific actions necessary to effect each component because these are embodied in the numerous and extensive resources and guidelines widely available to fitness professionals since the late 1970s and that have long formed the basis of professional fitness instructor training (Egger and Champion, 1983; ACSM, 1975/2000, 1992; AFAC, 1987). The model does, however, offer a framework for the translation of that knowledge into a practice regime that aims to ensure the safety of participants while they are undertaking exercise in fitness facilities. In this respect, it represents a domain-specific application of the more general risk management approach with which OHS/ergonomics professionals are familiar (Bamber, 1990; WorkCover NSW, 2001) and should be seen as a major risk control component in the safety management system of fitness service providers. In other words, many of the injury risks identified as arising from deficiencies in the delivery of
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exercise programs, such as those emerging from an analysis of the personal injury cases summarized earlier, could be controlled by adoption of this model. A checklist of items derived from the safe practice model framework in Table 24.2 has been included with this chapter (see Appendix). Notably, it is quite common for corporate as well as commercial fitness facilities to comply with the first step of this model by requiring potential users to complete a preexercise medical screening questionnaire. Unfortunately, however, this is often the only one of the model’s elements that is routinely and rigorously pursued. Moreover, it is the one element which emphasizes the responsibility of the participant for risk reduction. The other elements, most or all of which are too often given scant attention, emphasize the fitness provider’s responsibility for the participant’s safety. Human Factors/Ergonomics Contribution to Fitness-Related Litigation The impetus for the development of the safe practice model was recognition of the significant potential for personal injuries and resultant litigation arising as a consequence of identifiable deficiencies in the delivery of exercise services by fitness industry providers. When an adverse incident occurs during any human performance—whether a frank injury or, just as importantly, a near-miss—an investigation is indicated in order to determine the source of the problem. In some cases, the cause can be isolated as being of primarily engineering concern. For example, an inadequately specified support pin on a squat rack or a welded bracket on a bench press support, if subject to impact loading over a long period of time, may undergo sufficient metal fatigue to eventually fail. Information about the maximum likely loads and frequency of use, together with an appreciation of expected fatigue-related decrements in the users’ movement control leading to dropping of weights and resultant impact loading on the supports, is useful in specifying appropriate components for such equipment. Provision of this information is certainly within the realm of human factors data. However, the failure of the support and the injury, or near-injury, that occurs is not related to a mismatch between human capabilities and task demands. By contrast, the major proportion of exercise-related injuries discussed in this chapter that have resulted in litigation appears to have arisen from activity demands that exceeded the normal physical and/or cognitive capacities of the novice or inexperienced exercise participant, leading to musculoskeletal overload and/or movement-related errors. When injuries occur as a consequence of some deficient aspect of a product or service, the provider is potentially subject to a claim of negligence and may be held liable (i.e., legally responsible) for the injury. The question then arises as to whether an appropriate standard of care has been applied in the specific circumstances. With respect to fitness testing and prescription and related health and medical services, the standard of care has been defined as an expression of the “ways and means by which services should be delivered to clients so as to give reasonable assurance that the desired outcomes will be achieved in a safe manner” (ACSM, 2000; p. 264). Legal determinations in the U.S. have proposed that an appropriate standard of care be defined as “that level or quality of service ordinarily provided by other normally competent practitioners of good standing in that field” (Paxton v County of Alameda, 1953) or more
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simply, in Australia, by the “reasonable (person)” test (Wyong Shire Council v Shirt, 1980). Because safe performance of activities, including those that involve the operation of equipment or products, requires compatibility between the demands of the activity and the capabilities of the user (or performer), human factors knowledge is central. Thus, this knowledge may be sought to determine whether demands exceeded capabilities (thus leading to a high probability of injury) as well as whether safer alternative measures were known, feasible, and available (thus indicating preventability). The standard of care expected in any industry therefore might be expressed as the quality-of-service provision that can successfully withstand a “reasonableness” test. One such set of test criteria for reasonable risk (cf. Wade, 1965) includes the following: • Utility. Is the activity useful and does it meet the participant’s specific objectives? • Risk. What is the risk (probability and potential severity) of an injury occurring with this activity? • Risk transparency. Are the presence and degree of risk obvious to the service provider as well as to the participant? • Alternatives. Are safer alternatives that meet the same objective available? Applying the preceding questions to the fitness industry and the standard of care expected in the delivery of exercise services offers clear implications for informed consent, screening (not only of the participants but also of the exercises and equipment), development of strict performance protocols (for service delivery as well as exercise performance), and safe physical and informational design. To assist in answering forensic questions about causation, probability, foreseeability, and preventability, a human factors/ergonomic evaluation must address the central question of whether the imposed demands of the activity or exercise system exceeded the limited capacities of the human in the system. Some diversity exists in the approaches taken to conceptualizing and examining human—system interactions (cf. Vicente, 1995). However, the information-processing approach (Proctor and Van Zandt, 1994) has long provided a coherent and comprehensible framework for systematically exploring human limitations in acquiring external information as well as processing and responding to external demands. Table 24.3 illustrates an abbreviated example of adopting a human factors/ergonomics approach using a simplified information-processing model comprising perceptual, cognitive, and movement-related factors (Proctor and Van Zandt, 1994). This has enabled the identification of system design implications arising from a consideration of the interaction between human limitations and the demands of the exercise setting. Such a human factors/ergonomics approach to system or incident analysis can thus be applied to identifying deviations from an established standard of care such as that delineated in the safe practice model and thereby assist in answering the forensic questions raised earlier. 24.8 Conclusion The usual purpose of practice standards, codes, or guidelines is to provide practical advice in meeting clearly specified objectives within a particular context. Progressive
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management practices and recent legislation 5 have adopted the proactive risk management approach—i.e., proactively identifying and assessing risks and implementing and monitoring controls—with a view to ensuring the safety of people in virtually all environments. There is little reason for the fitness industry to be regarded as exceptional in this respect. The incorporation of a safe practice model such as that suggested in this chapter into existing fitness industry standards can effectively address many safety deficiencies in the delivery of exercise services. Although most, if not all, of the components of the proposed model could be seamlessly incorporated into the extant practices of many fitness service providers, its use should, like risk management practice, be subject to evaluation and modification through monitoring of its implementation and effects. In its favor, in recent times the fitness industry has not been averse to initiatives aimed at increasing the professionalism with which it delivers its products and services. Moreover, an increasing number of exercise and sports science, or human movement science, graduates are well qualified to guide the industry toward comprehensive and systematic professional approaches rather than depend upon the piecemeal application of acquired (and often questionable) wisdom so prevalent in the fairly recent past. Compared to most other occupations and industries, in which the mechanisms for promoting and providing for human safety have been developing over very many decades, the fitness industry is a fledgling. Therefore, at this stage, only ongoing development of practice standards will yield a mature approach that will provide its consumers with the physical, as well as financial, protection to which they are legally and ethically entitled. 5
See, for example, in Australia, the New South Wales OHS Act 2000 and OHS Regulation 2001.
TABLE 24.3 Example of a Human Factors/Ergonomics Approach to Identifying Exercise-Related System Design Considerations Based on Human Limitations Human factors
Example considerations applied to fitness settings
Perceptual and attentional factors Detection of relevant Presence, location, color, and other visual attributes of instructional, information behavioral, and warning signs; active supervisory assistance; detection of Attentional demands exercise performance errors Simplicity/complexity of design and layout of exercise area; presence of visual clutter; use of information or guidance tools (including instructors/supervisors) to assist user to narrow attentional focus to relevant aspects of equipment/activity Cognitive factors Comprehension and Content and method of exercise instruction delivery; instructional language retention of and style; complexity of exercise sequence relative to participant’s experience information and skill level; number of exercises prescribed; retention aids (e.g., program records) Decision-making; Availability of cues for program or exercise execution or equipment use; problem solving supervisory assistance
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Availability of relevant, proximate information about specific risks; evaluation of attitudes; supervision of behavior; provision of viable and valid alternatives
Movement factors Anthropometric factors
Postural and motion demands of activity; equipment design and adjustment range; likely activity envelope based on normal or expected anthropometric distributions Biomechanical and Specific physiological capacity to perform activity; individual physiological factors contraindications; activity/exercise-specific testing to determine entering status and initial load magnitude/exercise intensity Biomechanical demands of activity; activity/equipment evaluation to determine specific demands imposed relative to objectives; determination of loading imposed due to alternative uses; information about preparatory and adaptive processes Movement control Skill/coordination demands of exercise; complexity of motion patterns relative to participant’s skill level Exercise movement speed and/or accuracy demands; size, shape, and location of supports for weighted equipment; exercise movement trajectory Clearance demands; movement envelopes around exercise/activity stations and floor class participants; delineated walkways; unimpeded access to equipment Movement variability demands; fatigue-related decrement in accuracy; placement of loads after exercise
Acknowledgment The author gratefully acknowledges the assistance and input provided by A.W. (Tony) Sedgwick, who reviewed an early draft of this chapter. Defining Terms Ergonomics/human factors—The science and practice of improving human safety, security, and performance by designing systems, equipment, products, and environments that make the best use of human capabilities without exceeding human limitations (adapted from AS1837–1976). Exercise—Physical exertion of sufficient intensity, duration, and frequency to achieve or maintain physical fitness or other health or athletic (skill) objectives (adapted from Nieman, 1995). Fitness (physical)—In general, a dynamic state enabling one to carry out daily tasks, engage in active leisure time pursuits, and meet unforeseen emergencies without undue fatigue (adapted from Nieman, 1995). More specifically, a state of being well adapted or suited to responding to specific demands and/or with the capacity to perform required work or exercise (adapted from Anshel et al., 1991; Thompson, 1995). Health—The ability of an individual to mobilize his or her physical and psychological resources to his or her preservation and advantage; more than merely freedom from disease; synonymous with well-being (adapted from Kent, 1994; Thompson, 1995). Human factors—See ergonomics. Physical activity—Any form of muscular movement (Nieman, 1995).
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Safe practice model—A generic framework for guiding fitness professionals in the safe delivery and management of exercise programs and related services to their clients in fitness facilities; an approach consistent with health and performance enhancement but with a focus on acute safety considerations. Safety—In principle, the condition of being free from, or not exposed to, danger, hazard, or injury risk; in practice, impossible to achieve in absolute terms and therefore understood to be a condition of relative protection from exposure to danger; the antonym of “danger” (adapted from Hammer, 1989; Thompson, 1995). Standard of care—An expression of the ways and means by which services should be delivered to clients so as to give reasonable assurance that the desired outcomes will be achieved in a safe manner (ACSM, 2000). Well-being—See health. References Adams, M., Bogduk, N., Burton, K., and Dolan, P. (2002) The Biomechanics of Back Pain . Churchill Livingstone, London. Adams, M. and Dolan, P. (1995) Recent advances in lumbar spinal mechanics and their clinical significance. Clin. Biomech. , 10(1), 3–19. ACSM (American College of Sports Medicine) (1975; 1980) ACSM’s Guidelines for Exercise Testing and Prescription . Lea & Febiger, Philadelphia. ACSM (American College of Sports Medicine) (2000) ACSM’s Guidelines for Exercise Testing and Prescription . Lippincott Williams & Wilkins, Philadelphia. ACSM (American College of Sports Medicine) (1992) ACSM’s Health/Fitness Facility Standards and Guidelines . Human Kinetics, Champaign, IL. Anshel, M.H., Freedson, P., Hamill, J., Haywood, K., Horvat, M. and Plowman, S. (1991) Dictionary of the Sport and Exercise Sciences . Human Kinetics, Champaign, IL. AFAC (Australian Fitness Accreditation Council) (1987) Standards and Guidelines for the Planning and Conduct of Fitness Programs . AFAC, Parkside, SA. Australian Standard AS 1837–1976. Ergonomics in factory and office work. Standards Australia, Homebush, New S. Wales. Baechle, T.R., Earle, R.W., and Allerheiligen, W.B. (1994) Strength training and spotting techniques. In Baechle, T.R. (Ed.) Essentials of Strength Training and Conditioning—National Strength & Conditioning Association . Human Kinetics, Champaign, IL. Bamber, L. (1990) Principles of the management of risk. In Ridley, J.R. (Ed.) Safety at Work . 3rd ed. Butterworth-Heinemann, London. Bernard, B.P. (1997) Musculoskeletal disorders (MSDs) and workplace factors: a critical review of epidemiologic evidence for work-related musculoskeletal disorders of the neck, upper extremity, and low back. U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Cincinnati, OH. DEET (Department of Employment, Education and Training) (1991) Australia’s Workforce in the Year 2000 . AGPS, Canberra. Dishman, R.K. (1988) Exercise Adherence: Its Impact on Public Health . Human Kinetics, Champaign, IL. Dougherty, N.J., Auxter, D., Goldberger, A.S., and Heinzmann, G.S. (1994) Sport, Physical Activity and the Law . Human Kinetics, Champaign, IL. Edworthy, J. and Adams, A. (1996) Warning Design: a Research Perspective . Taylor & Francis, London.
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Egger, G. and Champion, N. (Eds.) (1983; 1998) The Fitness Leader’s Handbook . Kangaroo Press, Sydney, New South Wales. Hammer, W. (1989) Occupational Safety Management and Engineering . 4th ed., Prentice Hall, Englewood Cliffs, NJ. Herbert, W.G. and Herbert, D.L. (1988) Legal considerations. In Blair, S.N. et al. (Eds.) American College of Sports Medicine Resource Manual for Guidelines for Exercise Testing and Prescription . Lea and Febiger, Philadelphia. Jones, C.S. (2002) Personal communication. Jones, C.S., Christensen, C., and Young, M. (2000) Weight training injury trends: a 20-year survey. Physician Sportsmed . (Online), 28(7), July. Kelsey, J.L. and Golden, A.L. (1987) Occupational and workplace factors associated with low back pain. In Deyo, R.A. (Ed.) Spine: State of the Art Reviews—Occupational Back Pain , 2(1), 7–16. Kent, M. (1994) The Oxford Dictionary of Sports Science and Medicine . Oxford University Press, Oxford. Kraemer, W.J. et al. (2002) ACSM position stand: progression models in resistance training for healthy adults. Med. Sci. Sports Exercise , 34(2), 364–380. Laughery, K.R., Wogalter, M.S., and Young, S.L. (1994) Human Factors Perspectives on Warnings . Human Factors & Ergonomics Society, CA. Mital, A., Nicholson, A.S., and Ayoub, M.M. (1993) A Guide to Manual Materials Handling . Taylor & Francis, London. NOHSC (National Occupational Health and Safety Commission) (1995) Health Promotion in the Workplace Programs: a “How to” Manual for Workplaces . AGPS, Canberra. Nieman, D.C. (1995) Fitness & Sports Medicine: a Health-Related Approach . 3rd ed., Mayfield Publishing Co., Mountain View, CA. Nygaard, G. and Boone, T.H. (1985) Coaches’ Guide to Sport Law. Human Kinetics, Champaign, IL. Paxton v County of Alameda (1953) 119 C.A. 2d 393, 398, 259 P. 2d 934 (USA). Proctor, R.W. and Van Zandt, T. (1994) Human Factors in Simple and Complex Systems . Allyn & Bacon, Boston. Rejeski, W.J. and Kenney, E.A. (1988) Fitness Motivation: Preventing Participant Dropout . Human Kinetics, Champaign, IL. Sedgwick, A.W., Davies, M.J., and Smith, D.S. (1988) Musculo-skeletal status of men and women who entered a fitness programme. Med. J. Austr. , 148, 385–391. Sedgwick, A.W., Davies, M.J., and Smith, D.S. (1994) Changes over four years in musculo-skeletal status in men and women. Med. J. Austr. , 161, 482–486. Thompson, D. (Ed.) (1995) The Concise Oxford Dictionary of Current English . Clarendon Press, Oxford. Vicente, K. (1995) A few implications of an ecological approach to human factors. In Flach, J., Hancock, P., Caird, J., and Vicente, K. (Eds.) Global Perspectives on the Ecology of HumanMachine Systems . Lawrence Erlbaum Associates, Hove, U.K. Wade, D. (1965) Strict liability of manufacturers. Southwestern Law J., 19, 5. Cited in Proctor, R.W. and Van Zandt, T. (1994) Human Factors in Simple and Complex Systems . Allyn & Bacon, Boston. Waters, T.R., Putz-Anderson, V., Garg, A., and Fine, L.J. (1993) Revised NIOSH equation for the design and evaluation of manual lifting tasks. Ergonomics , 36(7), 749–776. Wogalter, M.S., DeJoy, D.M., and Laughery, K.R. (1999) Warnings and Risk Communication . Taylor & Francis, London. WorkCover NSW (2001) Risk management at work. NSWGPS; Catalog No. 425. Wyong Shire Council v Shirt (1980) High Court of Australia, 146 CLR 40. Yessis, M. (1992) Kinesiology of Exercise . McGraw-Hill, New York.
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Further Information American College of Sports Medicine (2000) ACSM’s Guidelines for Exercise Testing and Prescription . Lippincott Williams & Wilkins, Philadelphia. American College of Sports Medicine (1997) ACSM’s Health/Fitness Facility Standards and Guidelines . 2nd ed. Human Kinetics, Champaign, IL. Baechle, T.R. (Ed.) (1994) Essentials of Strength Training and Conditioning—National Strength & Conditioning Association . Human Kinetics, Champaign, IL. Blair, S.N. et al. (1998) American College of Sports Medicine Resource Manual for Guidelines for Exercise Testing and Prescription . 4th ed. Lippincott Williams & Wilkins, Philadelphia. Dishman, R.K. (1988) Exercise Adherence: Its Impact on Public Health . Human Kinetics, Champaign, IL. Dougherty, N.J., Auxter, D., Goldberger, A.S., and Heinzmann, G.S. (1994) Sport, Physical Activity and the Law . Human Kinetics, Champaign, IL. Egger, G. and Champion, N. (1998) The Fitness Leader’s Handbook . Kangaroo Press, New South Wales. Fleck, S.J. and Kraemer, W.J. (1997) Designing Resistance Training Programs . Human Kinetics, Champaign, IL. Healey, D. (1989) Sport and the Law . New South Wales University Press, New South Wales. Heyward, V.H. (1991) Advanced Fitness Assessment & Exercise Prescription . 2nd ed. Human Kinetics, Champaign, IL. Kelly, G.M. (1989) Sport and the Law: an Australian Perspective . The Law Book Company Ltd., Sydney. Kraemer, W.J. et al. (2002) ACSM position stand: progression models in resistance training for healthy adults. Med. Sci. Sports Exercise , 34(2), 364–380. Nygaard, G. and Boone, T.H. (1985) Coaches’ Guide to Sport Law . Human Kinetics, Champaign, IL. Patton, R.W., Grantham, WE, Gerson, R.F., and Gettman, L.R. (1989) Developing and Managing Health/ Fitness Facilities . Human Kinetics, Champaign, IL. Pollock, M.L. (1998) ACSM position stand: recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in adults. Med. Sci. Sports Exercise , 30(6), 975–991. Rejeski, W.J. and Kenney, E.A. (1988) Fitness Motivation: Preventing Participant Dropout . Human Kinetics, Champaign, IL. Rushall, B.S. and Pyke, F.S. (1990) Training for Sports and Fitness . The Macmillan Co., Melbourne, Australia. Sarre, R. (1987) Leisure Time and the Law . CCH, Sydney, Australia.
Appendix: Safe Practice Model Checklist for Exercise Service Delivery The following checklist is intended to help the exercise professional to identify any major deficiencies in his practice with respect to the safety of his clients while undertaking exercise. Its focus is acute safety. It is not intended as guidance in relation to testing procedures, exercise prescription, program design, and progression for maximizing or optimizing performance. It may not be comprehensive with respect to all potential hazards; the exercise professional should therefore use discretion in identifying and controlling any additional injury risks.
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Health status and preparation for physical activity • Provide pre-exercise screening • Obtain medical clearance if indicated • Provide full disclosure and obtain informed consent regarding exercise risks and contraindications Entering status of the participant • Determine participant’s objectives • Develop exercise program specific to goals • Determine participant’s current capacities in relation to proposed exercise demands • Determine training parameters (including initial loads) for each exercise • Reassess training parameters for any major program change or addition Exercise, environment, and equipment evaluation and/or selection • Determine structural safety of equipment • Assess biomechanical adequacy of equipment design with respect to intended and imposed loads, postures, and methods of use • Determine biomechanical/physiological suitability of selected exercises and equipment with respect to individual’s goals, capacities, limitations, and characteristics • Assess safety of selected exercises with respect to postural and movement demands • Identify potential for incorrect or unsafe equipment use due to design, construction, or location • Identify potential for incorrect or unsafe performance of exercise • Identify potential for errors or accidents during exercise performance arising from: • Layout of exercise area • Positioning of equipment • Activity envelope of each exercise station • Any other proximity or clearance considerations • Any support surface or access considerations Instructions • Develop and provide accurate and concise instructional and demonstration protocols for each exercise • Provide instructions and demonstrations to participant for each exercise • Instructions and information should incorporate: • Warm-up/preparation process and methods • Correct technique performance • Common technique faults • Inherent risks specific to the exercise and/or equipment • Any other recommendations, cautions, or contraindications specific to the exercise or equipment
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• Advise participant about overload, recovery, progression, and attendance frequency • Alert participant to general exercise area safety issues (see list under “identify potential for errors or accidents during exercise performance…) • Develop, when relevant, concise visual aids or reinforcements (signs, labels, warnings, posters) • Avoid excessive visual clutter; visual aids should supplement or reinforce, not substitute for, direct instruction and supervision Supervision—individual • Provide specific supervision to participant when novel exercise or activity is undertaken or novel program demands are imposed • Ensure participant has acquired safe and correct exercise technique before withdrawing specific supervision • Provide frequent review of exercise behavior soon after initial acquisition • Periodically review exercise behavior of each participant in facility Supervision—general • Maintain constant supervision of exercise area(s) when participants are present • Develop and implement regular, comprehensive inspection and maintenance schedules for all exercise facilities and equipment • Carry out frequent spot checks of equipment during direct supervision of area(s) Note: The items in this checklist address many of the main acute injury risks arising from the delivery and management of exercise programs in fitness facilities. However, it should not be presumed to be fully comprehensive or final. Each fitness professional should monitor and evaluate the use of such a checklist in light of local conditions and make additions or alterations on the basis of evidence.
V Product Liability and Warnings
25 Preventing “Accidental” Injury: Accountability for Safer Products by Anticipating Product Risks and User Behaviors Stuart M.Statler Safety Strategies 0–415–28870–3/05/$0.00+$ 1.50 © 2005 by CRC Press
25.1 Introduction When a consumer product is implicated as the possible cause of serious injury or death, inquiry often focuses on what company officials knew about the risk and when they knew it. How soon after learning about the possibility of danger, or its foreseeability, did they do something to correct the problem? What measures were in place to avert needless injuries? To what extent were human factors considerations weighed, early on, to identify and anticipate the risk? How conscientious was the company in addressing a hazard, once it was brought to its attention? Bottom line, what is the responsibility of a manufacturer—or seller, importer, or distributor, for that matter—to detect product hazards early in the process, before the death or injury statistics begin to accumulate? How much danger is too much for a consuming public to endure, or for a legal system to countenance? For many years, product makers and sellers—and, sometimes, entire industries—have come to know about certain risks. Often, they learn a great deal about a product’s risks and dangers through product testing, behavior analysis, warranty follow-up, consumer complaints, litigation, insurer reports, competitor actions, newspaper clippings, and a multitude of other sources. Yet still, today, highly flammable fabrics find their way to store shelves. Sofas and chairs too-readily ignite. Lightweight extension and step ladders buckle and topple. Chain saws kick back. Gas water heaters explode when exposed to flammable vapors. ATVs roll, flip, and topple over on hills and turns or suddenly veer out of control. Automatic garage doors come crashing down on unsuspecting toddlers. Improperly guarded power saws sever the hands and fingers of users. The blades of lawn and garden tractors, when operating in reverse, mow down unseen toddlers. Fires from TVs, electric heaters, and clothes dryers ravage homes. Faulty extension cords and disposable lighters that are not child resistant ignite havoc. Fireworks misfire. Pilot lights from gas water heaters and ranges torch combustible vapors from household cleansers
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and adhesives. Tap water scalds sear infants as well as the aged and infirm. Poorly insulated or ungrounded electric pressure washers, hair dryers, and curling irons electrocute users. Dangling cords from blinds and shades strangle children, while faulty bunk beds, playpens, and cribs collapse upon or entrap and suffocate them. Toxic emissions from kerosene heaters and wood stoves asphyxiate whole families. The litany goes on and on, as does the needless toll of tragedy. All these hazards, and so many more, are well known to the companies that make and sell these products. 25.2 Determining Whether a Risk Is Reasonable or Unreasonable In weighing product risks, it is never enough to cite injury statistics—whether the figure is large or small—and attempt to determine, on that basis alone, whether the risk is reasonable or unreasonable. The fact that tens of thousands or even hundreds of thousands of injuries yearly are reported from falls on stairs, or from various recreational sports (e.g., football, baseball, rollerblading), does not make those activities or the products associated with them unreasonably dangerous. Neither by traditional common law principles nor under the Consumer Product Safety Act do sheer numbers of injuries ever, by themselves, render a product an unreasonable risk. By the same token, the absence of sizeable injury figures does not mean that a product is safe or that it does not constitute an unreasonable risk. For example, many thousands of dangerous products have been recalled over the years, voluntarily by the manufacturer or compelled by government officials, because of the presence of one or more design or production flaws or the absence of needed safeguards or warnings that render a product unreasonably dangerous. Such products may have very few or no actual incidences of serious injury or death reported from their use, but their flawed design causes them to have the recognized potential for leading precisely to those results. Consider, for the moment, the instance of a design flaw affecting an entire line of products. During my tenure as Commissioner of the U.S. Consumer Product Safety Commission (CPSC) in the early 1980s, vertical convection heaters first made their way into the American market. They were instantly popular. However, before the first death was reported and with very few reported injuries associated with the product, CPSC engineering and human factors staff identified a series of design flaws capable of causing severe burns from improper guarding and fires from overturning. As a result, the entire line of units, from a dozen or more producers, was voluntarily recalled and replaced with units incorporating safer designs, which largely eliminated the acknowledged dangers. Over many years, product liability cases in state and federal courts have attested to both of those truisms: mere injury statistics (i.e., frequency of injury) do not mean that a product is an unreasonable risk and their absence does not render a product reasonably safe. The legislative history of the Consumer Product Safety Act reflects the notion that frequency of injury alone, without any other consideration, may be an excellent early alert to an emerging problem, but it does not provide the basis for any conclusion about the reasonableness of the risk from any consumer product. In fact, the driving theme of the National Commission on Product Safety’s seminal 1970 Final Report (which established the basis and need for the Consumer Product Safety Act and an independent, regulatory panel to administer it) is that, as a nation, we
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should not need to await a body count of injuries and deaths from any particular consumer product before corrective action is warranted. As that report forcefully points out: Manufacturers have it within their power to design, build, and market products in ways which will reduce if not eliminate most unreasonable and unnecessary hazards. Manufacturers are best able to take the longest strides to safety in the least time. The capacity of individual manufacturers to devise safety programs, without undue extra cost, has been demonstrated repeatedly in the course of our short history…[at 3]. Forthright action is expected on the part of the manufacturer in the first instance, and by the government as a last resort, to avert what may otherwise be a foreseeable and preventable risk to safety. Apart from the presence or absence of figures pointing to the frequency of injury and regardless of how large or small those figures may be, several other factors must be taken into account in determining whether a particular product constitutes a reasonable or unreasonable risk. Many of those factors have been suggested or identified over the years in judicial proceedings and learned treatises, as well as by the provisions of the Consumer Product Safety Act and its underlying legislative history. Any listing of those critical considerations would include: • A first principle, as indicated earlier, of whether the design of the product can reasonably be made safer. Does the product incorporate a design that directly causes it to be capable of producing needless risks to safety or otherwise fails to incorporate features that might avert or significantly reduce known risks when the product is used in an anticipated or foreseeable manner? To the extent that certain ways in which the product is routinely or even occasionally used—even if unintended—create dangers, what redesign efforts are undertaken to design or guard against just that? It is never sufficient for the supplier simply to accompany the product or its sale with educational literature or even on-product cautions or warnings, when reasonable design alternatives are apparent. They are reasonable if they are technically practical and cost effective in anticipating user behaviors and thereby significantly lessening the risk. • The severity of the risk(s) brought about by the product’s usage. For example, are the consequences of using the product likely to result in deaths, disfigurations, brain or spinal injury, paralysis, blindness, loss of limb, or other permanent or severe damage? As in the case of the often-cited skateboard or hula hoop statistics for which the frequency figures are large, are the great bulk of reported incidents likely to be minor abrasions, bruises, or cuts? • The vulnerability of the population affected. Are an appreciable number of the injury incidents occurring to infants, toddlers, or children generally, who do not have or are not likely to have the mental development to understand or appreciate the risk or the physical ability to deal with it? Are they occurring to a largely elder population, or impaired or physically handicapped population, which for similar reasons is unaware of the risk or otherwise incapable of dealing with it?
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• The functionality or utility of the product. How much is the product needed? Is it used exclusively or primarily for essential or functional purposes, or for recreational purposes? • The availability of substitute, similar-use products. Can or do other similar products on the market serve the same purposes? • The availability of alternative designs for the same product. What design options are available or technologically feasible and at what added cost, if any, to redress known or anticipated product risks? • The transparency or latency of the risk. How well does the consuming public understand or appreciate dangers from the hazard or risk (the likelihood of it occurring)? How open or obvious is it, or how hidden? Are users likely to grasp the dangers from ordinary or anticipated usage, and how likely are they to take actions to assuage or mitigate the perceived risk? • Comparative safety considerations, when available. How does the product’s safety record compare with other similar products…with other types of products capable of performing similar functions…with other models of the same product, or competitive brands, incorporating alternative, safer designs aimed at redressing known or foreseeable risks? • Cost/benefit considerations of adapting design modifications to redress known or foreseeable hazards. How cost effective would it be to adopt or implement practical and technologically available design solutions to the problem at hand? • Economic considerations, such as the approximate number of such products in use, profit factors, market share, etc. • Alternative means of achieving the safety objective, while minimizing adverse effects on competition or disruption of the product’s production. • Responsible manufacturing and marketing practices. This is demonstrated in assessing known or foreseeable risks, having a viable product safety program in place for dealing with them, and incorporating policies to mitigate or eliminate preventable risk. A more extensive discussion follows. These factors are not meant to be exhaustive. The listing is simply intended to show that the determination of whether the risk from a consumer product is reasonable or unreasonable must necessarily take into account an array of complex factors. The remainder of this discussion addresses many of these considerations in the context of what constitutes responsible manufacturing and marketing practice on the part of producers and sellers of consumer products, in the context of known, foreseeable, and wide-scale risks of serious injury and death. 25.3 Responsible Manufacturing and Marketing Practices What follows derives from my threefold involvement in product safety: regulating consumer product safety, providing counsel to companies in matters affecting the safety of consumer products, and assisting in the area of product litigation. That background affords a long-term familiarity with the kinds of policies and procedures that, in the aggregate, comprise responsible manufacturing practices. Those practices constitute,
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essentially, a sine qua non for any viable product safety program, including the design and sale of most consumer products. The criteria set forth next, honed by my product safety involvement over the past quarter of a century, reflect the well-considered efforts of the Consumer Product Safety Commission, early in its tenure, to develop a “system standard” for companies manufacturing safer products. Toward that end, the agency published and widely circulated a Handbook and Standard for Manufacturing Safer Consumer Products (June, 1975; rev. May, 1977), which embodied considerable input from affected companies and industries. The CPSC clearly recognized that persons and organizations needed guidance concerning the reasons underlying the criteria set forth in the system standard, as well as suggestions for its implementation. By its terms, the handbook was “intended to help industry establish product safety systems as an integral part of manufacturing, thereby serving the interests of industry and the public.” Without going into meticulous detail, key components of such a product safety program are discussed in the following subsections. Overall Policy From an overall policy standpoint, a firm commitment by the manufacturer is essential— at the highest executive level and throughout the organization—to the primacy of safety at all stages of product design, testing, production, distribution, and marketing. Preferably, such a policy should be clearly and concisely set forth in writing and consistently emphasized by corporate executives and managers alike. It should be a regular focus of employee training sessions. Under all circumstances, the preeminence of product design in ensuring consumer safety must be at the forefront of a manufacturer’s overall safety policy. This is particularly true when a consumer product is known to have a potential for causing or being associated with death or serious personal injury, or when especially vulnerable populations like infants, young children, the aged, or the infirm may be most affected. First and foremost, if such a product can be made materially safer by incorporating safer design features that are technologically feasible and cost effective, then that should become the focus and target of the conscientious manufacturer. The responsibility of a distributor or retailer of any such product is no less, from a policy standpoint. Any marketer or seller bears a responsibility to come to know and understand a product’s potential for serious injury and to make it clear to suppliers that a safer design is the starting point for a safer product. Equally critical, the seller needs to emphasize regularly that alleviating or eliminating the risk of death or serious personal injury through safer design must be a priority for any manufacturer supplying that product. A reasonably safe product is one that reflects state-of-the-art design intended to address not only foreseeable product use but also anticipated error or misuse, with proper consideration given to feasibility and cost factors associated with improving the product’s safety design.
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Management and Organization of the Product Safety Function Management and organization of the product safety function within a manufacturer of consumer goods needs to be clearly assigned to a person or persons possessing high-level executive responsibility and authority, as well as sufficient resources, to assure that safety concerns are accorded the highest priority within the company. Safety concerns must not be compromised by possible conflicts of interest arising from any other duties— marketing, legal, or otherwise—that such individuals may assume. Lines of communication with respect to possible safety concerns must be open and encouraged throughout the organization to accommodate sharing of critical safety information and prompt corrective response, as needed. Moreover, in addressing issues of safety, the input of design and safety engineers is vital at every stage. Their involvement needs to be routine and ongoing. They need to be kept abreast of any emerging safety concerns. If a known and serious product risk— particularly one that can be lethal—is to be adequately addressed, thorough disclosure throughout the organization should be the norm, and safety engineering and product redesign must be actively encouraged. Otherwise, profit considerations can have the effect of obscuring or impeding doing what is most needed in the interest of safety. Product Usage Considerations In ensuring against unreasonable risks, product usage considerations must always be kept foremost in mind. Early and ongoing evaluation of potential hazards or risks is essential, ideally, with pre-established criteria appropriate to the product and the gravity of any possible risk. Particular emphasis should be given to: manner and conditions of use and foreseeable misuse or abuse, whatever contingencies may reasonably arise, use or exposure by especially vulnerable populations (infants, children, the aged, and physically impaired), and redesign to accommodate predictable use patterns. Every reasonable consideration must be given to how the product is actually used, as opposed to how the manufacturer would like it to be used. Once that is ascertained, every avenue should be explored to come up with improved or alternative design factors to anticipate those uses, including likely errors of usage, to enhance the safe operation of that product. Having done what it reasonably can to design out acknowledged risks, a company should then strive to enhance safety further through proper guarding and protective systems, warnings, and accompanying educational and informational materials. Identifying Product Risks Thoroughly identifying and understanding product risks are an essential first measure for any responsible product manufacturer. Over the years, very few really “new” products have been marketed. Of approxi-mately 15,000 product categories that fall within the CPSC’s jurisdiction, all or most of them have a rather comprehensive and welldocumented safety profile. That profile is replete with discussions and analyses, injury and death statistics, and briefing materials and journal articles from such diverse sources as the CPSC and its predecessor agencies, and state and local officials (coroners, medical
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examiners, attorneys general, etc.), as well as from industry associations and individual companies. In addition, a conscientious search would turn up studies, assessments, reporting, or commentary by academics, engineers, human factors specialists, epidemiologists, doctors, health and medical professionals, standards organizations and committees, product-testing organizations, think tanks, foundations, journalists, public interest and consumer groups, law enforcement officials, attorneys handling cases involving the product or one similar to it, and other such sources. For any particular product— especially one tied to the occurrence of death or serious injury—a comprehensive information base and history concerning the product and/or its risks are waiting to be retrieved and analyzed. Any company that undertakes to make or market such a product can benefit from affirmatively reaching out to all or most of these critical information sources. Doing so provides a thoroughgoing and straight-forward assessment of the relevant risk factors. It also provides leads as to how best to deal with those risks through designing reasonable safety into the product and then accompanying that with effective guarding and protective systems, product warnings, user training, educational and informational literature, and whatever else may be appropriate to the particular circumstances to lessen the likelihood of harm. Failure to do so leaves a company in the dark as to the risk implications of its product line. It also compromises consumer safety and needlessly endangers countless lives of those who have assumed that a responsible producer or seller would fully understand those product risks and exercise due care to protect against them. Ensure Compliance with Federal and State Safety Regulations A concerted effort must be made to identify and ensure compliance with all federal and state safety regulations that apply to the product or risk, and with any voluntary industry standards, codes, or guidelines that may also apply. Especially when serious risk of death or injury pertains, compliance with all such safety criteria, backed by outside, independent testing and certification, constitutes minimal response for a responsible manufacturer to undertake. Clearly, however, compliance with minimum standards, in those few areas in which criteria are spelled out concerning safety, is not the be-all and end-all of a supplier’s responsibility. It barely scratches the surface. This is especially so when voluntary industry standards are the only ones applicable. Why? Too often they tend to be “sweetheart” standards, agreed to by industry representatives routinely watching out largely for the economic interest of the company or the industry at large. Such standards frequently represent the lowest common denominator of safety. Because they are minimal, these standards do not assure safety. Typically, they do not address all identified, serious hazards in the actual or foreseeable use of the product. This fact is recognized by the Consumer Product Safety Act, as well as numerous Congressional studies and traditional common law principles. Consequently, beyond complying with industry-set standards, a manufacturer needs to actively explore the feasibility of alternative, safer designs; upgraded efforts at improving guards; protective systems and fail-safe devices; and more meaningful product warnings.
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Documentation Thorough, diligent documentation and record-keeping are vital to any viable product safety program. This means having in place an effective policy for requiring that records be kept in sufficient detail and format to allow for the timely detection of safety problems. Changes in design, warnings and cautions, production, marketing, and product distribution need to be recorded and retained, particularly when safety is at all at issue. Special attention should be accorded to the results of product inspections, tests, and calibrations; the monitoring of warranty data and product returns, as well as consumer complaints or expressions of concern that may be safety related; and company actions taken to redress any safety concern or deficiency. Also, responsible manufacturers must meticulously keep track of where units are within the production and distribution chain in order to facilitate prompt repair or recall of a product line if such action should ever become necessary. Data Sharing With respect to safety, data sharing should be unimpeded to everyone within the organization who is in the best position, early on, to identify or correct an emerging or perceived product risk—especially those in safety and design engineering, and risk evaluation. Any possible future litigation concerns that the legal staff may have must be deemed secondary to establishing optimal circumstances, through the full and open sharing of incident and investigation reports, to detect, identify, and correct preliminarily an emerging risk to consumer safety from any of the company’s products. Quality Control Rigorous quality control (QC) procedures are a vital component of an effective and responsible product safety program. QC efforts undertaken throughout the manufacturing process help to ensure that product flaws and risks to safety are detected early and corrected immediately, before personal injury to consumers or property damage may occur. This includes ongoing inspection and testing of products and new product lines while using objective and uniform guidelines or standards that can engender reproducible results. Proper use of reliable statistical methods and sampling procedures is essential. Equally so is written documentation throughout, particularly concerning how nonconforming materials and results are treated. Also, proper devices and equipment for inspecting, testing, and measuring need to be calibrated and maintained regularly to ensure the integrity of the QC program. Guidelines for Corrective Action and Recall Corrective action or recall guidelines, including a crisis management plan, are an integral facet of an effective product safety program. Product manufacturers need to have a ready procedure in place internally to successfully implement their commitment to the primacy of safety in making available to consumers products that have a potential to do serious harm to person or property. This includes:
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• Timely means for assessing risk by a high-level management team sensitive to the impact of harm to consumers from product hazards. • Determination to act with dispatch and not sit back to await a body count sometime well into the future. • Company posture aimed at preventing a recurrence of any injury or damage that may already have been reported. • Commitment to remove any hazardous units or product line promptly from consumer homes and distribution channels, or otherwise repair or correct the problem. An important step in any such plan is acknowledgment of and compliance with the hazard-reporting responsibility set forth in Section 15(b) of the Consumer Product Safety Act. The provision covers “Every manufacturer of a consumer product distributed in commerce, and every distributor and retailer,” and requires the reporting to the CPSC of “information which reasonably supports the conclusion that such product…contains a defect which could create a substantial product hazard [emphasis added].” This discussion of critical elements of an effective product safety program and attendant responsible practices is hardly complete. It is meant, however, to provide a helpful backdrop for assessing the actions, and the inaction, of product makers and sellers alike in dealing with known and foreseeable risks. 25.4 Case Study: Riding Mower Backover Incidents What Was Known about the Risk? Almost from its inception in 1973, the U.S. Consumer Product Safety Commission (CPSC) has been involved with the dangers associated with power rotary mowers and riding mowers. A federal regulatory panel, the CPSC has exclusive jurisdiction over thousands of consumer products used in and around the home and in recreation. Lawn and garden mowers constitute one of these products. The Commission is the only federal agency with authority to ensure against unreasonable risks related to these kinds of mowers. More than 25 years ago, the mower industry knew—because the Commission presented them with the evidence back in the mid-70s—that upwards of 70% of all mower injuries involved contact with the mower blade. Producers and sellers were told by the Commission, specifically with respect to riding mowers, that as many as one in eight incidents involved backing over a bystander. They were also told that the tragedy in these backover incidents was compounded because the bystander was usually a young child. The historical record is replete with warnings to individual suppliers, and to the rest of the mower industry, about this hazard, as well as proposals for redressing the danger and mitigating the severity of resulting injuries. To cite just a few instances: • Even before the inception of the CPSC, as far back as 1965, riding mower manufacturers were presented with hard information, in the form of a professional paper presented to the American Society of Agricultural Engineers (ASAE) by Joseph
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Silbereis, that 13.2% of the safety incidents attributable to riding mowers were associated with the machine backing over a bystander. • Just 2 years later, in 1967, a second ASAE report discussed at some length six specific riding mower backover incidents to children under 5 years of age. This report included a clear-cut recommendation for a rapid-stop, automatic blade/brake clutch, which would assure blade stoppage within 3 seconds, together with a panic stop switch to reduce appreciably the severity of any injury that did occur. • In June 1969, writing in the Journal of the Iowa Medical Society, L.W.Knapp cited backover as a critical incident category associated with riding mowers. He pointed up how extensive and severe the resulting injuries often proved to be as a result of blade contact with a child. • The next year, in March 1970, working jointly, the industry’s professional trade association, the Outdoor Power Equipment Institute (OPEI), and the University of Iowa’s Institute of Agricultural Medicine issued a research report demonstrating a rear-bumper device. The device instantaneously halted the riding mower engine and blade upon contact with a bystander when the vehicle was operated in reverse. • A third ASAE paper in late 1970 by W.H. McConnell again noted the unusual severity of injury from backover incidents and further reported that such incidents amounted to 11% of all injuries tied to riding mowers. • In March 1973, the CPSC’s summary analysis of riding mower incidents lists no fewer than 11 documented reports of serious injury from April 1966 to October 1971—all occurring while the mower was being operated in reverse. • As early as 1974, Consumers Union, a product-testing organization and publisher of the much-heralded Consumer Reports, urged upon the newly created CPSC a proposed preliminary standard for all mowers. The recommendation included the concept that riding mowers incorporate an interlock to allow blade rotation only when the mower was moving forward. The interlock would assure blade stoppage within 2 seconds if the unit was shifted into reverse. • A comprehensive CPSC Hazard Analysis in 1981 urged a specific requirement for riding mowers to avert backover injuries. Whenever the mower was operating in reverse, the report recommended that the blade be stopped and that an alarm sound to signal the backing maneuver and warn anyone nearby. • When the industry undertook on its own, under the auspices of the Outdoor Power Equipment Institute, a rewrite of the B71.1 standard for riding mowers, the resulting effort was tellingly disapproved by the governing Standards and Review Committee of the American National Standards Institute (ANSI). The review panel cited, as a deficiency, the conspicuous failure of the proposed standard to include a requirement that the mower blade be stopped during the vehicle’s reverse travel. • As most of the mower industry continued to ignore this known and especially egregious hazard, the CPSC reiterated its concerns in 1988 in another exhaustive report, entitled Hazard Analysis—Ride-On Mowers. The analysis was based on 475 sample incidents culled from the CPSCs projected 19,100 yearly injuries associated with riding mowers, for the period of 1983 through 1986. With an estimated 9.3 million riding mowers then in use, the survey pointed to 200 backover blade-contact incidents per year, nearly all occurring to young children. Factoring in an estimated 10-year useful life for these units, about 1 in 5000 would be involved in the maiming of a child
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through blade contact during backing-up procedures. The study also showed that almost 20% of the death incidents associated with riding mowers were related to runover/backover of bystanders. This was the second most common cause of fatalities overall from these vehicles. Many of these deaths were occurring in the most vulnerable of populations—namely, very young children—who could neither understand nor appreciate the risk. • Warning about the preventable trauma to children from riding mowers, the American Academy of Pediatrics (AAP) in 1990 identified the manufacturers as most culpable for these tragedies. It noted that “the most common means of injury to children were runover or backover by another driver.” In an accompanying policy statement, the AAP urged the producers to “develop a more safely designed product.” It added that, from the standpoint of child safety, “although most rideon mowers now have a ‘deadman’ switch that shuts off the engine when the blades are engaged and the operator leaves the mower seat, this is not enough to provide maximum safety.” • Yet another CPSC analysis in 1993, Ride-On Mower Hazard Analysis, covering the years 1987 through 1990, reported on 644 sample incidents occurring over that period. It confirmed, anew, an estimated 200 serious backover blade-contact injuries occurring each year, mostly to young children. Each required emergency room medical attention. Again, in view of the roughly 10 million units then in use and a useful life thought to be about 10 years, the study corroborated the earlier projection that, in the course of their useful life, out of every 5000 riding mowers produced, at least one was likely to be involved in the maiming of a child as a result of blade contact when the vehicle was operating in reverse. Throughout the 1970s and 1980s and beyond, there was considerable awareness and knowledge on the part of the entire riding mower industry with respect to this risk. Despite that, most of the affected companies made a conscious decision not to correct an all-too-predictable and foreseeable pattern, namely, young children maimed by riding mowers whose blades were engaged while the vehicle was operating in reverse gear. More than a decade earlier, the National Commission of Product Safety, between 1968 and 1970, had conducted numerous hearings in major cities across the U.S. From the evidence adduced at these sessions, the president-appointed expert panel issued a formal report to the President and the Congress, and ultimately to the public, identifying critical safety concerns. The Commission specifically designated lawnmowers, referencing riding lawnmowers, as one of 20 of the most unreasonable product risks to consumers. Although the primary focus of the National Commission was the walk-behind lawnmower, that panel identified problems associated with riding mowers as well, based upon the extensive evidence garnered through public hearings and from the mower industry, as well as from medical professionals, product safety engineers, and health officials across the country. Moreover, the 1970 NCPS Final Report referenced the special vulnerability of innocent bystanders in general and children in particular. Furthermore, the NCPS report documented the inadequacy of the mower industry’s response to hazard concerns and the failure of the voluntary standards process in this regard. Almost 35 years ago, the industry’s effort in dealing with safety concerns was deemed essentially de minimis. The mower industry tended, as the report identified, to focus on the lowest common denominator in terms of establishing a level of responsibility for mower producers to agree to meaningful voluntary safety standards.
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The report noted that resulting industry standards were deficient and the very manner through which they were approved and promulgated tended systematically to exclude any significant public or consumer interest from the fact-gathering and decisional processes. In the 1970s, as riding mowers began to take on more popularity with American families, recognition of the problem of backing up as a foreseeable risk to bystanders, particularly to young children, increased. The industry met on numerous occasions, through its ANSI B71.1 Committee, and explicitly designated a subcommittee to discuss the issue. Contemporaneously, the CPSC began a concerted regulatory investigation of lawnmower risks and commenced a formal standards proceeding. The proceeding focused upon the walk-behind mower, but it ultimately came to target the risk of death or severe injury from riding mowers, also. The CPSC undertaking identified the need for a blade/brake stoppage for rotary mowers in general and that, too, came to be a focus for riding mowers. Through its hazard analysis and investigation of riding mower incidents, the Commission discerned unacceptably high frequency and severity of reported injuries to children. In particular, very young children were identified as the most common victims of runover/backover incidents. The Commission analysis also determined that many of these incidents involved the most serious and horrific types of injuries. Specifically, the CPSC identified amputations to toes, feet, hands, and other body parts, as well as mutilations and crushing injuries to these very young victims. Furthermore, according to the Commission study, which was shared with mowerindustry representatives, the gruesome nature of the injuries often led to extended hospitalizations, repeated surgeries, and prolonged medical attention and care after release from the hospital, as well as deep and lasting psychological scars to victims and their families. Routinely, the incidents occurred when, suddenly and without warning, these youngsters, unseen by the vehicle’s operator, came in contact with the fast-moving blades of the riding mower operating in reverse. The CPSC’s analysis was meant to energize the mower industry to incorporate, through safety engineering and design, a means of promptly disengaging the cutting blade when mowing was not taking place and when the vehicle was placed in reverse gear. Risk Factors and Industry Response During the mid-1980s, although safety concerns over riding mowers gained a more prominent place within the Commission’s priority safety efforts, this was not the case for most of the mower industry. However, a few producers of riding mowers, to their credit, began responding to CPSC urgings to expedite remedial action. In short order, they demonstrated that an effective design to address the risk was technologically possible and feasible from a cost standpoint. Previously, in the 1976 to 1977 period, IHC had produced a Model 1450 Cub Cadet for test purposes. It incorporated a no-mow-in-reverse (NMIR) system that disengaged the rotating blade upon any shift of the transmission into reverse. Then, in 1981, MTD undertook production of a rear-discharge riding mower with an NMIR feature that stopped the engine altogether whenever an operator shifted the transmission into reverse with the blades engaged. Within just 2 years, the entire Cub Cadet line of riding mowers—all 11 models produced—was equipped with NMIR safety devices, as
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highlighted in the company’s advertising brochure. Four incorporated an engine cutoff in reverse gear, while the remaining seven models shut down the power takeoff whenever the mower was shifted into reverse. Since that time and to this day, all MTD riding mowers, without exception, have incorporated no-mow-in-reverse safety devices. Thus, an alternative, safer design was technologically and economically feasible. However, by and large, the rest of the industry ignored the human and product risk factors or failed to assign them sufficient importance. Collectively, those factors cried out for attention. As to the critical factors for assessing the reasonableness of any risk, reference already has been made to the unusually severe patterns of injury in mower backovers to an especially vulnerable population of very young children. Moreover, the nature of the backover hazard has always been latent, rather than obvious or apparent. In the aggregate, those several factors understandably caused the Commission to accord greater import to mower backovers in terms of assessing the risk. That is, the fact that the hazard was largely unknown to, or not grasped and appreciated by, most operators became yet another important consideration weighing on the unreasonableness of the risk. Too many losses of hands, arms, feet, and legs were occurring to young children and many of the incidents involved a scenario in which the operator and the child had no sense of appreciation of the danger and the child was completely unaware of being at risk. Typically, the operator is also unaware of the presence of nearby children to the rear of the mower or unaware of the true nature of the risk to unseen children. The CPSC pointed this out in its 1979 report, Hazard Analysis—Power Lawn Mower Baseline Study. Even if the operator knows to look to the rear before proceeding in reverse, because of the confining configuration of the seat, typically, the operator’s ability to turn neck and body fully is restricted. As a result, his view is limited, particularly with regard to anything directly behind the seat. With young children directly to the rear, because of their small physical stature, the operator’s visibility is even more restricted. Moreover, having once looked back, for his own safety the operator probably should not keep doing so because he needs to concentrate on the vehicle controls from that point on while backing up. At any given moment thereafter, a child may suddenly and unexpectedly run or dart onto the mower’s rearward path. Certainly from the mid-1970s forward, the mower industry was on notice and acutely aware of this risk. Manufacturers were in the best position to do something about it. However, most essentially chose to finesse the danger from any design standpoint, preferring, instead, to insert insipid cautions in vehicle owner’s manuals and accompanying videos, on the vehicle, or both. Because that approach had not worked previously to eliminate or significantly reduce the risk, in the absence of mower redesign, there was no logical reason to believe that it would work then—and it did not. The incidents continued, largely unabated. Looking back, the principal focus of the CPSC’s early attention with respect to riding mowers was the problem of a blade/brake disengagement involving the operator directly. However, over time, the Commission persistently tried to get the industry to pay heed to the problem involving backover blade contact incidents, precisely because of the exposure of young children and the underlying latent or hidden nature of the hazard. Nevertheless, most companies made a conscious choice not to address this hazard as a design issue or a priority safety concern.
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The federal government or, more specifically, the CPSC did not ever require backover protection for lawn and garden mowers. However, to put that in perspective, from an earlier experience, the CPSC was well aware of the mower industry’s prior strenuous opposition to any federal safety standards. In relatively few instances (most relating to products intended for infants or small children) did the CPSC promulgate a federal consumer product safety standard to cover particular product risks or hazards. To this date, no mandatory federal safety standards are applicable to riding mowers. When the federal government has not entered the field, it becomes all the more incumbent upon responsible producers to take the lead in reducing or eliminating known product risks. This is especially true when acknowledged, life-threatening risks persist, such as with backover incidents involving riding mowers. Responsible manufacturing practices require that firms deal with recognized human behaviors by designing safety into the product when it is economically and technologically feasible to do so. With lawn and garden mowers, nothing could be more evident. The backover risk to young children was well known and appreciated by safety professionals and within the riding mower industry. Also, a means of minimizing the effect of that risk was well known and technologically feasible and cost effective. Companies knew or should have known this, yet they settled for far less. Most chose to follow a voluntary industry standard, the ANSI standard for ride-on mowers, which was conspicuously silent on the subject of backover protection. It was a consensus standard, signed, sealed, and delivered by their peers within the industry who sat on the B-71.1 Committee, with little or no outside input from safety professionals or the consuming public. As far back as 1970, the NCPS completed its comprehensive 2-year study, at the direction of the U.S. Congress, to recommend to the Congress and the President a broadbased statutory scheme to provide for better protection of Americans against unreasonable risk of injury from consumer products. After studying in detail the operations of industry standards committees, with the B.71.1 mower efforts directly in its scope, the fact-finding NCPS concluded in its Final Report: Industry activities to develop safety standards can provide an important forum for marshaling the technical competence necessary for this work, but the voluntary nature inherently inhibits the development of optimal standards. The consensus principle, which is at the heart of all voluntary standards making, is not effective for elevating safety standards. It permits the least responsible segment of an industry to retard progress in reducing hazards [at 2]. At a later point in its report, the panel found that Unfortunately, these [industry] standards are chronically inadequate, both in scope and permissible levels of risk. They do not usually address themselves to all significant foreseeable hazards. They give insufficient consideration to human factors such as predictable risk-taking, juvenile behavior, illiteracy, or inexperience. The levels of allowed exposure…are frequently too high [at 54].
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Not unexpectedly, the industry standard for riding mowers in effect over the past two decades represents, more or less, a low point for safety for a product that, by its very nature, engendered the highest degree of risk to life, namely, severe injury or death from backover. As an industry-promulgated standard, it was developed, as is typically the case, by companies involved in producing the product, with minimal public or consumer presence. These firms agree to be bound by however much (or little) to which their peers are willing to agree. As such, these standards are widely viewed to be minimum safety standards and, sometimes, as here, a bare minimum. Just as most of the mower producers failed to incorporate safety against backovers into their product design, so, too, did they fail to warn prospective buyers or users adequately about the hazard. Clearly, under these circumstances, no warning, however explicit, is a satisfactory alternative to producing a safe design in the first place. However, at no point (in the owner’s manual accompanying the vehicle or on the vehicle) did they provide clear and concise information about the specific hazard. Nowhere did they inform operators about the nature, frequency, severity, or latent characteristic of the hazard to young children from the vehicle moving in reverse gear with the blades engaged. Nowhere did they let the operator know that as many as 200 children were maimed or killed each year from backover blade contact injuries. Instead, failing to design out the hazard as they could, the industry endorsed two warnings to appear on the vehicle’s frame. They did this knowing that, over a period of 30+ years, such cautionary language has proven to be entirely ineffective in averting these tragedies. The language found on these riding mowers states the following: “Do not mow when children and others are around” and “Look down and behind while backing.” The warnings were imprecise, insipid, nonspecific, and therefore flawed. Application of Risk and Responsibility Principles The riding mower industry effectively chose to overlook the hazard and risk consequences of common user behaviors associated with a product known to be capable of causing death and serious injury. In the broader context of responsible manufacturing practices, this was a calculation made without consideration for how it might adversely affect those to whom mowers were marketed and sold. Such inaction is at odds with a viable safety program and inconsistent with any semblance of responsible manufacturing practice. Most companies ignored proven, safer product designs. Inexplicably, they ignored the critical need for a prompt means of stopping the engine or automatically disengaging the blade when the vehicle was placed in reverse, even though a cost-effective means to accomplish precisely that was known and available. They ignored the need for guarding to prevent aggravated injury. They also ignored their responsibility to warn users of the danger of backover satisfactorily by placing more meaningful warnings on the vehicle and in the owner’s manual. This kind of inaction is indicative of a safety program gone awry. In the aggregate, such conduct—in the context of a product known from the outset to be fraught with danger—contravenes all known principles of responsible manufacturing and marketing practice. As a result, safety was seriously compromised in theory and in fact. Unsuspecting youngsters, usually under 5 years old, to this day continue to be disabled
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and disfigured for the rest of their lives due to the wholly foreseeable chain of events set in motion by a systemic disregard for safety at all levels. From at least the early 1970s, backover injuries from riding mowers were widely known to present a severe risk to children. Yet, most companies chose not to pay heed to all the background information, data, and analysis provided to them by the CPSC and many other sources. Responsible manufacturers, armed with this knowledge, should have provided an adequate means for protecting those most imperiled, while minimizing the extent of injury when the blades of these riding mowers continued to whirl after the vehicle was put in reverse. In terms of the severity of injuries resulting from vehicle backovers, the companies knew that they were not dealing with minor abrasions, bruises, and band-aids. Nevertheless, most ignored the extensive record compiled by the CPSC of numerous, recurring amputations of hands, arms, legs, feet, and toes, and even deaths from unprotected riding mower backovers. The industry also knew that a highly vulnerable population—very young children, typically under the age of 5—were most commonly the victims of these incidents. The companies had access to the persistent injury and death reports compiled by the CPSC annually, at least since 1980, which identified young children as frequent victims. The mower industry knew that the design of its riding mowers was somehow tied to the prominence of these incidents. Yet, most companies conspicuously failed in their prime responsibility as product manufacturers and sellers to analyze the facts and circumstances associated with these backovers and respond, in an affirmative way, to materially improve the design safety of their mowers. As to the availability of alternative designs, the companies knew that technologically feasible and cost-effective design options were readily available for successfully addressing vehicle backovers. Indeed, such design factors were being incorporated or offered as options by a number of their competitors. Did the industry ever examine the comparative safety of riding mowers operating in reverse that incorporated a means of automatically disengaging the blade compared to those without such a means? If so, it could only have concluded that the former were materially safer. If the companies ever examined the costs vs. benefits of designing in such backover protection, the equation could only have corroborated the cost effectiveness of a readily available technology that was certain to reduce such incidents significantly and materially cut back on their severity. The industry acted in disregard of the safety of its customers and innocent family members—usually young children. These children were repeatedly victimized by (1) such evident lack of a reasonably safe design, (2) the absence of some kind of fail-safe means to prevent injury or to lessen the severity of the resultant injuries, and (3) the absence of sufficient on-vehicle warnings and other proper safety warnings and instructions to highlight and help to avert these tragedies. 25.5 Conclusion As suggested by the examples cited at the outset of this discussion, in so many instances, companies and the industries of which they are a part come to know about the likely risks
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to the public from their products. Like the mower industry, too often they do not live up to their responsibility to be conscientious in addressing those risks early on, from a design perspective. Across the board, many accidents can be averted and many injuries prevented. It really does not matter whether the frame of reference is household goods, toys, products used in recreation or at school, autos, tires, pharmaceuticals, medical devices, or the like. Untold lives can be saved, to the extent that manufacturers and sellers adjust their policies and mindsets to make safety a priority in order to better anticipate the way in which their products are actually used, and to insist upon incorporating that awareness into the product’s design. 25.6 Checklist Main factors to consider: • Risk considerations: • Whether product design reasonably can be made safer • Severity and frequency of risk • Vulnerability of population most affected • Functionality and utility of product • Availability of substitutes • Latency of the risk • Comparative safety considerations • Cost-benefit analysis • Profit and market share • Alternative means of achieving safety objective • Responsible manufacturing and marketing practices: • Priority accorded to product safety • Management and organization of product safety function • Conditions of use and foreseeable product misuse or abuse • Researching and identifying product risks • Ensuring compliance with laws and regulations • Analysis of safety-related claims and warranty data • Documentation of changes in designs and warnings • Record retention • Transparency in sharing safety information • Rigorous quality control • Recall guidelines • Crisis management plan
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References Adler, R.S. (1989). From “model agency” to basket case: can the Consumer Product Safety Commission be redeemed? Administrative Law Rev. , Winter, Washington, D.C. Felcher, E.M. (2001). It’s No Accident—How Corporations Sell Dangerous Baby Products . Monroe, ME: Common Courage Press. Herzog, F., Hoes, C., and Bass, L. (1986). System safety engineering approach, in Product Liability: Design and Manufacturing Defects . Shepard’s/McGraw-Hill: Colorado Springs. National Commission on Product Safety (June, 1970). Final Report . Washington, D.C.: U.S. Government Printing Office (Library of Congress Card No. 76–606753). Office of the General Counsel, U.S. Consumer Product Safety Commission, Ed. (October 2000). Compilation of Statutes Administered by the CPSC. Washington, D.C.: CPSC. Statler, S.M. (1984). Reporting guidelines under Section 15, Consumer Product Safety Act. J. Prod. Liability , June, New Haven. U.S. Consumer Product Safety Commission (June 1975, rev. May 1977). Handbook and Standard for Manufacturing Safer Products . Washington, D.C.: CPSC.
26 Human Factors Issues to Be Considered by Product Liability Experts Alison G.Vredenburgh Vredenburgh & Associates, Inc. Ilene B.Zackowitz Vredenburgh & Associates, Inc. 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
26.1 Introduction to Human Factors Principles and Relevance to Standard of Care New technologies have provided a multitude of products intended to improve quality of life, simplify tedious tasks, and provide entertainment or recreational enjoyment. Although these products are intended to be—and often are—helpful, their design may also result in injuries to users. Such injuries are sometimes due to misuse of the products; users may fail to follow the instructions and warnings or put the product to some unforeseeable use. Other times, the problem lies with the product. When a product is designed in such a way that it can cause injury or death when used in its intended manner (or in a foreseeable misuse), the manufacturer may be held strictly liable for damages caused by hazards associated with the product. As part of, or in anticipation of, consumer product liability litigation, human factors consultants are frequently asked to investigate accidents. Attorneys often seek forensic human factors consultants when an injury was caused by a consumer product. These consultants study the product, determining which, if any, product features may have contributed to the accident and injury. Manufacturers and distributors of products are legally responsible for managing and communicating hazard information. The scope of and compliance with this responsibility can become a matter of dispute. In this regard, a human factors consultant provides expertise concerning specific design, labeling, and instruction characteristics of the product, as well as the interaction between the user and the product. Specifically, how, if at all, did the product contribute to the incident? Based on legal precedent (Pease v. Sinclair Refining, 1939), manufacturers have what is called a “duty to warn” if their product is associated with known hazards. 1 If a product is designed with known hazards and if the manufacturer fails to warn of these hazards, the manufacturer may be held responsible for accidents and injuries that result. Human factors experts evaluate the reasonableness of manufacturer and user conduct,
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determining whether the manufacturer had (and fulfilled) a duty to warn and whether user behavior was appropriate for—or a foreseeable misuse of—the particular product. That is, one key consideration in product liability cases concerns whether the user’s conduct was “reasonable.” In addition, such “reasonableness of conduct” concerns extend to decisions and actions of the product’s manufacturer. The human factors consultant may offer expertise concerning both of these important considerations. This chapter will address several questions of importance to practitioners hoping to gain a deeper understanding of product liability human factors issues. For instance, • What steps must a manufacturer consider when developing a product? • Can we (or, when can we) expect consumers to read and adhere to product labels and instructions? • How can human factors consultants contribute to products cases?
26.2 Objective and Scope of the Chapter In this chapter, we will discuss some product liability issues that human factors experts should consider when investigating accidents that occur when someone is injured while using a consumer product. The objective is to demonstrate how a human factors consultant would evaluate a product liability case. This discussion will include an analysis of product design, effectiveness of warnings and instructions, and the human conduct contribution to these incidents. To demonstrate the evaluation of product liability cases, three case studies will be discussed. One case will describe design issues pertaining to the interaction between a motorcycle fuel valve and fuel gauge. A second case involves the use of barriers on a hot/cold compress. A final example will illustrate how warnings come into play by discussing a case involving latex glove hypersensitivity. Although only these cases are discussed, the analytical approach presented in this chapter can be applied by human factors experts to other products cases. 26.3 Discussion of Principal Issues With all the modern conveniences available today, it is not surprising that the interface between consumers and new products continues to grow. Manufacturers attempt to develop the next “must-have” product and get it to market prior to their competitors. However, manufacturers must be accountable to consumers by ensuring that the products they sell are safe. When consumers purchase a product, they, too, have responsibilities. They must understand the purpose and intended use of the product, read warnings and instructions, and use the product in an intended or foreseeable manner. If the manufacturers or the consumers neglect their responsibility, injury may result. 1
Although this chapter includes discussions of litigation, this information is not offered as legal advice.
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Product liability cases often include a human factors expert to explain hazard communication issues. Typically, attorneys seek a “warnings” expert; however, warnings are only one part of the equation. Human factors experts should also evaluate hazard management and communication by the manufacturer. What did the manufacturer do to determine the hazards of its product? What design changes (if any) were performed (or considered) by the manufacturer to control the hazards? What is the current technology (standard of care) for similar products? Is a safe design readily available on similar products? Were barriers developed? How were the hazards communicated to the users? Finally, experts should evaluate the “human” component of the equation: consumers have expectations, attitudes, and beliefs that have an impact on their behavior. Who Is Qualified to Be a Human Factors Product Liability Expert? Experts are qualified by their knowledge, skill, experience, training, or education (Federal Rule 702). Graduate degrees or specific types of experience are not explicitly required. Experts working on cases involving products need to examine the design of the product as well as accompanying instructions and warnings. Accordingly, they should have completed education and conducted research in the development and testing of warnings. They should also have experience evaluating equipment for user interface and hazard identification and have knowledge concerning how to communicate hazard information effectively to the expected user population. Human factors products experts usually have education in psychology, human factors, and communication. Warnings experts make assumptions based on information from engineers, medical literature, and other subject matter experts. Although engineers often are designated as warnings experts, they typically lack the expertise in communications and human behavior. With Which Standards Should Products Experts Be Familiar? Experts should be knowledgeable about several important standards. ANSI Z535.4 provides basic guidelines for formatting a product warning. ANSI Z535.3 discusses the development and testing of safety symbols. If the case involves a chemical product, ANSI Z129.1 applies. Numerous American Society of Testing Materials (ASTM) standards are relevant to various types of products, which can be accessed through their web site. Underwriters Laboratories (UL) develops standards and certifies products for electrical safety (Collins, 1999). Workplace injuries involving chemical products implicate OSHA regulations such as the Hazard Communication Standard (1985), which specifies training requirements and describes a requirement for a downstream flow of hazard information. Cases involving prescription drugs will require knowledge of federal regulations (21 CFR §201.57), which specify requirements for the content and format of labeling for human prescription drugs. Federal regulations (21 CFR §369.10) also specify the requirements for conspicuousness of warning statements and recommended warnings for certain types of drugs (21 CFR §369.20). Medical devices also are federally regulated. The FDAs Labeling Regulatory Requirements for Medical Devices (1989), published by the Center for Devices and Radiological Health, specifies many labeling requirements.
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Topics include false and misleading labeling, the prominence of labeling information, and the content of advertisements. Which Types of Data Should Be Considered by a Human Factors Products Expert? Several sources of information can be considered in evaluating products. From his client (the attorney), the expert should receive all discovery materials concerning liability, including the following: • The complaint • Statements • Depositions • Accident reports • Product materials (packaging, operator’s manual, warnings, package inserts) • Reports and depositions of other expert witnesses If retained before the discovery cutoff, experts should ask their client attorney to request all product testing records and all procedures and testing involved in development of the warnings and labeling. Experts should be familiar with standards and government regulations related to the subject product. Relevant product safety records may also be available through the U.S. Consumer Product Safety Commission (CPSC). Requests can be made to the CPSC for incidents of injuries caused by or related to a specific product or type of product through the Freedom of Information Act. The plaintiff’s deposition will provide experts with information concerning the plaintiff’s past safety behaviors. It should also describe how the plaintiff used the product on the day of the incident, his or her expectations about the product (based on prior use of this or similar products), and whether the plaintiff read or complied with instructions or warnings (if available). Testimony by percipient (fact) witnesses may also help inform experts about the plaintiff’s reasonableness of conduct. 26.4 Hazard Control Hierarchy When manufacturers become aware of (or should be aware of) hazards associated with use of their products, several fundamental hazard control strategies can be employed to limit the risk. The first and most effective approach is to design out the hazards so that they are eliminated or effectively removed from the product or system. When a design remedy is not feasible, a second hazard control strategy is to guard or place a barrier to separate the hazard from product users. If the hazards are not eliminated through design or guarding, then a third strategy is to develop an effective system of communication that informs product users about the nature and likely consequences of the hazard and tells them specific ways to avoid injury. Removing a hazard through design changes may be achieved at the outset of product development when a potential hazard is anticipated. A product can be redesigned to eliminate a hazard after it has been identified. When a hazard is well known and
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anticipated, designing out the possibility of an incident is most effective. For example, choking is a well-known hazard among babies; therefore, manufacturers attempt to avoid making toys and equipment for babies that have small parts that can fit in the mouth and become lodged in the throat. However, this is not always avoided in the manufacturing process. Toys with small parts are still made and often recalled after they have gone to market because of the potential for injury or death. A product may have hazards associated with its proper use that cannot be eliminated through design changes. This is typical with tools such as power saws. Because the intended purpose of a saw is to cut wood or other materials with a sharp blade, it is not possible to design out the cutting hazard. Therefore, manufacturers typically move to the second tier of the hazard control hierarchy and address the hazard with barriers or guards. Typically, these consist of a physical barrier separating the user from the danger. On saws, a plastic blade guard typically is included in the product design to separate the user from the blade. Although manufacturers design products with guards, the user must follow through in order for the barrier to be effective. Sometimes users remove guards because they are perceived as bulky or awkward. When this happens, the consumer is assuming the risk by choosing to expose himself to the hazard. If manufacturers are going to market and sell a product with a hazard that has not been eliminated through design or physical guarding, they need to go to the third and final tier of the hazard control hierarchy: an effective communication system. This goal can be accomplished through the use of a well-designed system of instructions and warnings. Manufacturers have a duty to warn of a hazard when the product is dangerous, the hazard is or should be known to the manufacturer, the danger is not one that is obvious to the user, and the danger is not one arising because the product is put to some unforeseeable use (Madden, 1999). The Restatement of the Law Third, Torts: Products Liability §2(c) states: A product is defective because of inadequate instructions or warnings when the foreseeable risks of harm posed by the product would have been reduced or avoided by the provision of reasonable instructions or warnings by the seller…and the omission of the instructions or warnings renders the product not reasonably safe. The manufacturer has primary responsibility for ensuring that critical safety-related information reaches end users, who are most at risk of injury. The manufacturer is clearly in a position of superior knowledge with respect to its products and the hazards associated with their use. For chemical products, there must be a downstream communication of hazard information, beginning with the source (manufacturers). It is the manufacturer’s obligation to determine the hazards of each product, generate material safety data sheets (MSDS), and pass on information to those in an inferior position. It is the responsibility of downstream suppliers and distributors to pass on the MSDS and warnings in their labeling (29 CFR §1910.1200). Intermediate suppliers do not have an obligation to evaluate independently the hazards of the products that they are using. According to OSHA Hazard Communication Guidelines for Compliance (OSHA 3111, 2000, p. 3),
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“You can rely on the information received from your suppliers. You have no independent duty to analyze the chemical or evaluate the hazards of it.” The Human Side: Behavioral Expectations of Product Users When evaluating a products case, human factors experts often address the reasonableness of conduct of the product user. Was his or her use (or misuse) of the product foreseeable? What attitudes and beliefs did the user bring to the situation? What are the expectations of the typical user of this type of product? This section will briefly review some of the research concerning human behavior and warnings. In failure-to-warn cases, plaintiffs must demonstrate that if the seller had provided adequate warnings, they would have altered their behavior so as to avoid injury (Madden, 1999). Many factors outside the design of a product or warning affect people’s motivation to perform self-protective behaviors. These influences are the result of situational factors such as motivation, attitudes, social influences, and the cost of compliance. People evaluate the extent to which they expect their self-protective measures to produce a desired result. These nonwarning factors can have as great an impact on compliance as the product and warning design and should be considered when evaluating product liability cases. This section explores the effects of how people-related variables have an impact on self-protective behavior. Even the best-designed warning is unlikely to override the beliefs and expectations that people have concerning a product (DeJoy, 1991). People evaluate how susceptible they believe themselves to be to sustaining injury from a given product. This perception can be reduced with benign experience or familiarity. Furthermore, people tend to be overly optimistic that injury will not happen to them. Weinstein (1987) calls this “optimism bias.” An injury to a co-worker may serve as a “cue to action”; such events provide an incentive for self-protective behavior (DeJoy, 1991). When human factors consultants speak of the “cost of compliance,” they are referring to any type of impediment to performing a behavior specified in a warning or instruction. These costs include increased task time, discomfort, or perceived impact on attractiveness (i.e., not looking cool) while wearing personal protective equipment (Dingus et al., 199 1a). A reduction in such costs can greatly increase warning compliance; however, increasing the cost even a seemingly minor amount can greatly reduce compliance (Dingus et al., 1991a). Of particular concern is the possibility that a product user may perceive a benefit in unsafe behavior (Clark and Lehto, 1999). People may ignore warnings and intentionally perform unsafe acts to save small amounts of time or to avoid minor inconveniences. Therefore, one way that manufacturers can push the cost-benefit tradeoff in the direction of warning compliance is by increasing the costs associated with noncompliance. Warnings research indicates that people do not tend to weigh the likelihood of injury in their judgments of product safety; rather, it is the severity of injury that motivates people to comply with instructional warnings (Young et al., 1990). Therefore, warning messages need to contain explicit information about the likely consequences as well as their severity. People are limited in their ability to think quantitatively about risk; their risk perceptions are often based on availability and representativeness heuristics. These
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perceptions are often inaccurate and biased when risk involves low-probability events (Slovic et al., 1980). Studies of risk perception and warning compliance have consistently reached several important findings. Women read and comply with warnings more than men (LaRue and Cohen, 1987; Vredenburgh and Cohen, 1995). Risk has been found to be less acceptable when the likely results are catastrophic (Slovic, 1978). If a product is substantially different from the types of products typically used by the present user (e.g., x-ray machine), the likelihood of injury will become more important to risk perception and, subsequently, the user will tend to act cautiously (Young et al., 1992). In evaluating the human component of an incident, experts need to determine if changes to the warning system would have made a difference. If the warnings were inadequate but unrelated to the incident, then changes would have had no effect. Defense experts will often cite warnings research indicating that warnings do not change behavior. Although even excellent warnings will probably not always be effective (100% compliance), a substantial amount of evidence indicates that, in many circumstances, warnings are very effective in informing product users and eliciting self-protective behavior (Wogalter et al., 1989; Dingus et al., 1991b; Chy-Dejoras, 1992; Vredenburgh and Cohen, 1993). The expert needs to consider the design of the warnings and instructions, the type of task or product, and the demographics of the population of product users (Laughery, 1999). Experts should be familiar with warnings research, including the effects of cost of compliance, social factors, and risk perception. 26.5 Examples Illustrating Product Liability Human Factors Cases This section will describe hypothetical cases in order to demonstrate forensic product liability analyses. Each example primarily corresponds to one of the three levels of the hazard control hierarchy: design issues, guards and barriers, and warnings. These examples illustrate typical product liability cases and how they are evaluated in a forensic investigation. In each case, various human factors issues will be discussed in terms of how they would be addressed by plaintiff and defense experts. Case 1: Product Design A 30-year-old woman was riding down a busy freeway on her new motorcycle. As she was riding, she felt the bike begin to sputter and decelerate. She looked at her fuel gauge, which indicated she had almost a quarter of a tank remaining, so she believed that she was not running out of gas. Thinking that the bike was experiencing a mechanical failure, she attempted to pull over to the left shoulder of the freeway. Her speed continued to plummet until she was virtually stopped in the number 1 lane of the freeway. Surrounding traffic had to swerve out of the way to avoid colliding with her. Ultimately, she changed lanes in front of a car traveling at freeway speed. The driver of that car did not have sufficient time to perceive and react to the motorcycle. He struck and killed her. What are the human factors issues involved in this accident? The first part of an analysis evaluates the equipment design and determines the task demands of the operator. Carbureted motorcycles traditionally have used a fuel reserve system; when the bike is
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low on fuel, it begins to sputter. At this point, the operator must turn the fuel valve to “reserve” to tap the bottom of the fuel tank. The placement of the reserve valve requires the operator to reach under the left side of the tank to feel for the fuel valve and rotate it to its reserve setting. If the valve is not actuated in time (5 to 10 seconds), the bike will lose power and may require restarting. Although the fuel gauge looks similar to automobile gauges, with a red section on the last one eighth of the tank, the motorcycle will require the operator to turn the valve to “reserve” when the gauge reads between one fourth and one eighth of a tank (see Figure 26.1). A human factors expert should consider whether the design increases the probability of error and whether it is possible to modify the design to remove or reduce the hazard. For instance, once fuel gauges
FIGURE 26.1 Relationship between fuel gauge and reserve tank. were added to motorcycles, there was no longer an engineering requirement to have a reserve system (in combination with the gauge). A human factors expert examining the operator’s task demands would evaluate mechanics of switching to the reserve tank. The requirement of motorcycle operators to feel for the fuel valve, which is located under the fuel tank, may be problematic for novice users, who may take longer than the allotted 5 to 10 seconds to rotate the valve or who may turn it in the wrong direction, effectively turning the fuel off. The feedback to the operator as to when to switch to the reserve tank adds a second human factors issue for evaluation by the expert. The correlation between the fuel gauge and fuel valve is counterintuitive because the gauge reads that the motorcycle has plenty of fuel but needs to switch to reserve. The human factors expert may consider behavioral expectations of users and their beliefs that similar gauges will behave in a similar manner across motor vehicle types (transfer of training). An automobile automatically goes to reserve after it reaches “E” on the fuel gauge. In this case, a human factors analysis may find that the design of the reserve fuel system in conjunction with a counterintuitive fuel gauge is a hazard best removed through design modifications (making the fuel reserve passive, operating like cars and some other models of motorcycles). Assuming impossibility of design modification or that modifications would take some time, the second level of analysis would be to place a barrier between the hazard and the
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operator. This seems impractical for this situation. The final level of analysis concerns warnings and instructions. Several manufacturers have a warning light indicating when to switch to the reserve tank. A few manufacturers have detailed instructions and warnings in the owner’s manual explaining when to switch to reserve. A human factors expert will want to evaluate the warnings to determine whether they effectively communicate the nature of the hazard, the symptoms for which to look (important in this case because the cues to the operator are subtle), and how to avoid the hazard. Now assume that the fuel system was designed with a red warning light on the instrument panel to indicate when the rider needs to switch to reserve. Assume the rider did not attend a training course. Also assume that our novice rider did not read her owner’s manual, which explains the significance of the red light. In this situation, the rider would have a visual cue indicating precisely when to switch the valve to the reserve setting. This greatly reduces the ambiguity of the situation and improves the likelihood that a novice rider will switch to the reserve setting in the 5- to 10-second time frame. The red light is a much clearer indicator of when to switch to reserve as opposed to the subtle loss of power and sputtering of the engine that can be easily misdiagnosed as engine problems. In this set of circumstances, the human factors expert may find that an effective warning system (warning light and written warnings and instructions) was in place and that the rider’s conduct was not reasonable. The expert may find that the motorcycle rider was a novice user who did not get formal training and did not read her manual; she did not understand the significance of the red indicator light and, as a result, was responsible for the outcome.
FIGURE 26.2 Diagram of the hot/cold compress. Case 2: Guarding against the Hazard Sometimes it is impossible to eliminate a hazard through design changes because the hazard is a necessary element of the manufactured product. When that is the case, the
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best option is for manufacturers to incorporate a barrier into the design of the product to separate the user from the hazard and prevent possible injury. Although a physical barrier will not eliminate the hazard associated with the product, it will reduce the likelihood of injury if its use does not interfere with the intended function of the product. However, if the barrier is viewed as cumbersome or perceived as reducing the function of the product, users may attempt to remove it. Therefore, the barrier must be incorporated in such a way that it does not reduce the effectiveness of the product for its intended purpose. Consider the case of a 65-year-old man who had just heated a hot/cold compress in his microwave oven. The plastic membrane surrounding the gel material ruptured, causing the gel to eject rapidly and burn his face, neck, and chest. He had heated the compress for 1 minute on high power, tested it, and then decided to heat it for an additional 30 seconds. As he removed the compress from the oven, he had it at about chest-high level when the product failure occurred, causing second-degree burns to his upper body. This compress had been used about 20 times before it ruptured. Prior to this incident, the product had not leaked gel. The product comprised a cloth square subdivided into three parallel pouches. Inside each pouch was gel encased in a plastic membrane. On one side of the compress was an overlapping flap of 0.25 in., where the gel bags could be removed and replaced (see Figure 26.2). The instructions specified heating on high for 60 seconds and encouraged multiple reheatings of 30-second intervals if greater heat was desired. The instructions also said to squeeze the compress after heating. Nowhere was the possibility of overheating the product or rupturing the membrane indicated. Inspecting the product, the expert removed the ruptured gel bag from the cloth case. The failure of the plastic membrane appeared as a straight tear that ran across the 3-in. dimension of the bag. The alignment of the tear in the gel bag was consistent with the bottom hem of the overlapping enclosure flaps. One of the other gel bags also showed initial signs of failure; it had an abraded line consistent with the location of the hem. The repeated heating and/or freezing of the bag caused it to fail when it came into contact with the enclosure hem. This area had several layers of fabric and was most restrictive. In this case, the plaintiff used the compress after reading the instructions provided with the product and following the directions. Because the materials provided with the product did not indicate the possibility of the compress rupturing, the user was unaware of the risk. He had used the product numerous times in the past with no incident, so he did not anticipate a danger associated with heating it in his microwave. The expert’s course of action here would include an evaluation of the conduct of the plaintiff and the manufacturer to determine whether the product was designed and used safely. Clearly, the manufacturer faced difficulties in designing out all possibility that the gel bag would rupture. To be effective, it had to contain gel in a container that could be heated in a microwave oven and frozen. However, it was probably possible to redesign the cloth covering to provide a barrier if the gel escaped from the plastic interior membrane. The overlap in the flaps could be increased and Velcro added to hold the flap openings shut so that the cloth bag could provide a barrier between the hot gel and the user. In addition, an instruction should have been included with the package materials providing a limit on the amount of time the compress should be heated. Now assume that the hazard associated with this product could not be effectively designed out or eliminated by a barrier. If the manufacturer had communicated hazard
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information through instructions and warnings, the likelihood of injury would have been significantly reduced. This is especially true when the hazard information is provided on the product and not solely on the packaging or inserts included with the product that will likely be discarded or lost. If a warning regarding overheating had been provided directly on the compress, it would not have been reasonable for the user to ignore that information. Case 3: Warning about the Hazard At times, the nature of a product and its associated hazards are not possible to eliminate through design changes and difficult and/or ineffective to provide a barrier against. This is the case with latex gloves, a seemingly innocuous product that can be fatal to some users. Latex contains a protein to which some people are hypersensitive. The protein cannot be completely removed from latex, so all latex gloves contain the allergenic protein. With repeated exposure, users can develop a systemic hypersensitivity (Type I response), which may be fatal, as is the case in this example. A 28-year-old nurse died after suffering from anaphylaxis due to her latex hypersensitivity. She typically used up to 10 different pairs of gloves a day to protect herself from disease and illness caused by exposure to blood and other bodily fluids. In fact, her hospital had a requirement, known as Universal Precautions, that its staff use gloves when interacting with patients. In the past, she had noticed a rash on her hands and itchiness, but she disregarded it because she thought she was sensitive to the soap at the hospital. One day she suffered a severe anaphylactic reaction evidenced by respiratory shutdown and was rushed to the emergency room, where she later died. At the time of this incident, the boxes of gloves had a content statement indicating that the gloves contained latex. This information is virtually meaningless as a hazard communication system. It does not indicate what the hazard is, how it may exhibit itself, or how to avoid the hazard. It does not indicate the potentially serious consequences. A plaintiff’s expert would likely begin by reading depositions of the nurse’s coworkers, latex glove industry employees, and FDA documents. He would find that, although the hazard is not obvious to the users, it was known to the glove manufacturers and the FDA by 1991. A warning would serve the important function of alerting healthcare workers to this hazard. In addition, it would indicate the symptoms associated with the allergy so that affected users would recognize the symptoms in themselves. It would also tell users what to do to avoid the hazard, i.e., avoid gloves that contained latex. As a population, healthcare workers are likely to read and comply with warnings when they are provided. They tend to be an educated group and they are aware of the generic risks of exposure to many hazards in the healthcare setting—from dangerous equipment to disease exposure. Because attending to product information and warnings is an important part of their jobs in most cases, a complete warning with all necessary information components would likely be effective in this population. A human factors expert hired by the defense in such a case may discuss the OSHA hazard communication requirements and find fault with the nurse’s hospital for failing to train her properly. The defense expert may also discuss the requirement for nurses to complete continuing education units and to be knowledgeable about latex
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hypersensitivity to protect their latex-sensitive patients. This expert may also point out that the content statement was the only “warning” required by the FDA. 26.6 Checklist of Main Factors to Consider The following is a checklist of product liability factors to consider when performing a human factors forensic analysis of a product-related accident. The checklist indicates the primary factors to consider for analyses involving consumer products. The points listed under “Considerations” are issues that may potentially apply to a case. The checklist is meant as a guideline and is not exhaustive of all factors that may be relevant in any case. Primary factor Considerations Accident investigations Environmental or situational factors Individual differences Hazard control hierarchy Designing out a hazard Guarding Hazard communication/warnings Designing out a hazard Feasibility Engineering requirements Available technology Guarding Feasibility Can hazard be designed out? Hazard communication Is it possible to design out or guard? Does warning clearly communicate hazard information? Has warning been tested on user population? Warnings ANSI Z535 Signal word Consequences/severity How to avoid injury
Defining Terms Behavioral expectations—Expectations of product users that affect warning compliance. Design—Feasibility of eliminating the hazard from the product. Guards—Barriers that separate consumers from hazards. Foreseeable misuse—Consumers’ misuse of a product that should be foreseeable to product manufacturers. Hazard control hierarchy—Hazard-control strategies that product manufacturers can employ to limit risk. Reasonableness of Conduct—Behaviors consistent with societal norms for a given population. Warnings—Effective communication of known hazards associated with the use of a product.
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References ANSI (1998). Z535.3, Criteria for Safety Symbols; Z535.4, Product Safety Signs and Labels. ANSI (1994). Z129.1, Hazardous Industrial Chemicals—Precautionary Labeling. Chy-Dejoras, E.A. (1992). Effects of an aversive vicarious experience and modeling on perceived risk and self-protective behavior. Proc. Hum. Factors Soc. 36th Annu. Meeting . Santa Monica, CA: Human Factors Society, 603–607. Clark, D.R. and Lehto, M.R. (1999). Reliability, maintenance and safety of robots. In S.Nof (Ed.), Handbook of Industrial Robotics , 2nd ed., chap. 36. New York: John Wiley & Sons, 717–754. Collins, B.L. (1999). Standards and government regulations in the USA. In M.S.Wogalter, D.M.DeJoy, and K.R. Laughery (Eds.), Warnings and Risk Communication . London: Taylor & Francis. DeJoy, D.M. (1991). A revised model of the warnings process derived from value-expectancy theory. In Proc. Hum. Factors Soc. 35th Annu. Meeting . Santa Monica CA: Human Factors Society, 1043–1047. Dingus, T.A., Hathaway, J.A., and Hunn, B.P. (1991a). A most critical warning variable: two demonstrations of the powerful effects of cost on warning compliance. In Proc. Hum. Factors Soc. 35th Annu. Meeting . Santa Monica, CA: Human Factors Society, 1034–1038. Dingus, T.A., Hunn, B.P., and Wreggit, S.S. (1991b). Two reasons for providing protective equipment as part of hazardous consumer product packaging. In Proc. Hum. Factors Soc. 35th Annu. Meeting . Santa Monica, CA: Human Factors Society, 1039–1042. FDA (1995). (Code of Federal Regulations 21 CFR §201.57) Specific requirements on content and format of labeling for human prescription drugs. FDA (1995). (Code of Federal Regulations 21 CFR §369.20 Subpart B), Warning and caution statements for drugs. FDA (1989). (88–4165) Regulatory Requirements for Medical Devices: a Workshop Manual . 4th ed. LaRue, C. and Cohen, H.H. (1987). Factors affecting consumers’ perceptions of product warnings: an examination of the differences between male and female consumers. In Proc. Hum. Factors Soc. 31st Annu. Meeting . Santa Monica, CA: Human Factors Society, 610–614. Laughery, K.R. (1999). The expert witness, Chapter 15 in Warnings and Risk Communication , Wogalter, M.S., DeJoy, D.M., and Laughery, K.R. (Eds.) London: Taylor and Francis. Madden, M.S. (1999). The law relating to warnings. In Wogalter, M.S., DeJoy, D.M., and Laughery, K.R. (Eds.), Warnings and Risk Communication . London: Taylor & Francis. OSHA (29 CFR §1910.1200) OSHA hazard communication standard. OSHA Publication 3111 (2000). OSHA hazard communication guidelines for compliance. The Restatement of the Law Third, Torts: Products Liability (1998) Product liability §2(c). St. Paul, MN: American Law Institute Publishers. Slovic, P. (1978). The psychology of protective behavior. Journal of Safety Research , 10, 58–68. Slovic, P., Fischoff, B., and Lichtenstein, S. (1980). Facts and fears: understanding perceived risk. In Schwing, R. and Albers, Jr., W.A. (Eds.), Societal Risk Assessment: How Safe is Safe Enough . New York: Plenum. Vredenburgh, A.G. and Cohen, H.H. (1993). Compliance with warnings in high-risk recreational activities: Skiing and scuba. In Proceedings of the 37th Annual Meeting of the Human Factors and Ergonomics Society . Santa Monica, CA: Human Factors and Ergonomics Society (2), 945– 949. Vredenburgh, A.G. and Cohen, H.H. (1995). High-risk recreational activities: skiing and scuba— what predicts compliance with warnings. Int. J. Ind. Ergonomics , 15, 123–128. Weinstein, N.D. (1987). Unrealistic optimism about illness susceptibility: conclusions from a community-wide sample. J. Behav. Med. , 10, 481–500.
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Wogalter, M.S., Allison, S.T., and McKenna, N.A. (1989). Effects of cost and social influence on warning compliance. Hum. Factors , 31, 133–140. Young, S.L., Brelsford, J.W., and Wogalter, M.S. (1990). Judgments of hazard, risk and anger: Do they differ? Proceedings of the Human Factors Society 34th Annual Meeting , Santa Monica, CA: Human Factors Society, 503–507. Young, S.L., Wogalter, M.S., and Brelsford, J.W. (1992). Relative contribution of likelihood and severity of injury to risk perceptions. In Proceedings of the Human Factors Society 36th Annual Meeting , Santa Monica, CA: Human Factors Society, 1014–1018.
Further Information Wogalter, M.S., DeJoy, D.M., and Laughery, K.R. (Eds.) (1999). Warnings and Risk Communication . London: Taylor & Francis. Miller, J.M. and Lehto, M.R. (Eds.) (2001). Warnings & Safety Instructions , 4th ed. Michigan: Fuller Technical Publications.
27 Products Liability Law: What Engineering Experts Need to Know Dick Moll University of Winconsin Patricia A.Robinson Coronado Consulting Services, LLC Henry M.Hobscheid Products Liability Consultant and Legal Editor 0–415–28870–3/05/$0.00+$ 1.50 © 2005 by CRC Press
27.1 Introduction Forensic and human factors engineers become involved in products liability litigation in several ways. Some are accident reconstruction experts who regularly testify about the causes of accidents and the potential defects in the products involved. Others work as consulting engineers who occasionally serve as expert witnesses in cases involving allegations of product defects. Still others work for manufacturing companies and may find themselves called to testify in cases involving company products. Regardless of the different avenues that bring engineers to products liability litigation, they all share one thing in common: they were trained as engineers, not lawyers. Just as attorneys share a common vocabulary and conceptual point of view, so do engineers. For engineers to be effective witnesses in products liability cases, they must understand the basics of products liability. This chapter provides a “primer” on products liability law and highlights some recent developments, with the goal of helping forensic and human factors engineers better understand the context of their testimonies and present their engineering expertise to best effect. A word of caution: although understanding products liability law is important, so too is understanding good engineering practice. Product safety depends in large part on the traditional elements of sound management, design, and manufacturing practices. Attention to such things as evaluating alternative design and material options, monitoring suppliers of raw material and fabrication to ensure technical competence, and incorporating new technologies and methods to improve product safety is crucial to developing safe products. A product designed and manufactured to be optimally safe automatically reduces liability exposure and lessens the chance of an engineer’s needing to testify in a products liability case.
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Another word of caution: no uniform law of products liability exists among the state and federal courts. Products liability laws vary, sometimes significantly, from state to state and court to court. A good attorney will help the engineer to understand the law of the jurisdiction applicable to his case. Section 27.4 illustrates a considerable difference in two tests used by courts to determine a product’s defective design. 27.2 What Is Products Liability and When Is a Product Defective? Products liability is a term that encompasses claims for personal injury, property damage, or other loss arising out of the use of a product. A manufacturer, seller, or other entity in a product’s chain of distribution might be liable if the product has a defect that renders it unreasonably dangerous to a user, a consumer, or even a bystander (Black’s Law Dictionary, 1991, p. 840). In bringing an action under products liability law, the plaintiff must prove four elements (Kimble and Lesher, 1979; this is a general rule and variations do exist—for instance, Maryland uses a six-factor formula, while New Jersey applies three elements [Phipps v. General Motors Corp., 1976; Myrlak v. Port Authority of N.Y. & N.J., 1999]): 1. There must be a defect in the product. 2. The defect must have been present when the product left the control of the defendant. 3. There must be injury or damage. 4. There must be a causal relationship between the defect and the injury or damage. In practice, the causal relationship between an alleged defect and the injury or damage is one of the more important elements and should be well understood. Products liability litigation is civil litigation. Although some written statutes govern conduct, such as the Uniform Commercial Code, much of products liability law is based on common law principles or case law. The common law system established law based on the customs of the people—in other words, how things were generally done. Case law follows the same idea, only the law is based on the decisions of the courts. As the written laws are applied to particular situations in court, judges and juries decide each case. Over time, a body of these decisions develops, and each new case is judged in light of those that have gone before. Thus, over time the law evolves. This is not a tidy process—a court in one state may decide a case one way; within the same time frame, a court in a different state may reach the opposite decision in a case involving similar facts. Courts are well aware that the decision made will influence future decisions. Occasionally, a court will issue an opinion with the clear intent of establishing a rule for the future, dramatically departing from past decisions deemed incorrect, or otherwise “settling” the law. It is not unusual for high-level courts to reverse their own rulings. Nevertheless, as more and more cases are decided, trends solidify and the law becomes more established. 27.3 Legal Theories Used in Products Liability Litigation Most products liability actions are brought under one of three legal theories:
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1. Breach of warranty 2. Negligence 3. Strict liability in tort Currently, most cases now are brought under negligence or strict liability in tort, although breach of warranty is still used. Breach of Warranty Warranty is covered under contract law. Contract law principles are described in the Uniform Commercial Code, particularly Article 2, Sales, and its section on implied and express warranties. Contract actions seek to protect the parties’ legal interests in having promises performed. Essentially, breach of warranty actions rest on the claim that the defendant promised the plaintiff that the product would perform in a certain way, but that promise was not fulfilled. The focus in breach of warranty actions is therefore on the nature of the (express or implied) “promise” between the defendant and plaintiff. The plaintiff must show that a contract existed between defendant and plaintiff and that the terms of this contract were violated by the product’s failure to perform as warranted. By way of illustration, the court decision in Sullivan v. Young Brothers & Co., Inc. (1996) involved a claim based on a breach of an implied warranty of merchantability. The U.S. First Circuit Court of Appeals ruled that a lobster boat’s builder was not liable for such a breach because the vessel was fit for its ordinary purpose and thus merchantable. A defective fiberglass tube, which the builder installed in the vessel’s exhaust system, cracked and caused the boat to sink. Another manufacturer produced the tube. The tube’s defect did not make the entire boat unfit; thus, there was no breach on the builder’s part (Sullivan v. Young Bros. & Co., Inc., 1996). In contrast, an implied warranty of fitness for a particular purpose would arise only if a product manufacturer or seller knew of the specific or special purpose for which the product was used. Unlike implied warranties, which are imposed by law and are not explicitly stated in a contract, an express warranty will actually be part of the oral or written contract. In the lobster boat case, a specification sheet provided by the tube maker created an express warranty (see Sullivan v. Young Brothers & Co., Inc., 1996; see also CCH Products Liability Reports at paragraph 595 [discussion of express warranty], paragraph 660 [fitness for particular purpose], and paragraph 700 [merchantability]). Negligence By contrast, negligence and strict liability in tort focus on protecting the legal interest in freedom from injury, property damage, or commercial loss. Both causes of action are covered under tort law. Torts are civil wrongs not based on contract, for which the court will provide a remedy in the form of an action for damages (Prosser, 1979). The presence or absence of a contractual relationship between the defendant and plaintiff is irrelevant; the cause of action centers on whether the product is defective. In negligence actions, the plaintiff must show that the product causing the harm was defective as a result of the defendant’s negligent conduct. Negligence is defined as “the failure to use such care as a reasonable prudent and careful person would use under similar circumstances” or “…[c]onduct which falls below the standard established by law
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for the protection of others against unreasonable risk of harm”(Black’s Law Dictionary, 1991, p. 716). In other words, the defendant acted unreasonably, resulting in a defective product. The Sullivan case mentioned earlier involved a negligent design claim in addition to the warranty claim. The lobster boat builder was not negligent in using the fiberglass tubing because the use was customary in the builder’s industry (see Sullivan v. Young Brothers & Co., Inc., 1996; see also CCH Products Liability Reports at paragraph 1090 through paragraph 1150 [discussion of negligence concepts]). Strict Liability in Tort In contrast to negligence, actions based on strict liability in tort focus primarily on the alleged defectiveness of the product. The defendant’s exercise of reasonable care—or lack of it—is not important. A manufacturer who acts reasonably may still produce a defective product and the manufacturer’s due care does not protect it against liability for harm caused by the defective product. Section 1 of The Restatement of the Law Third, Torts: Products Liability makes this very clear: “One engaged in the business of selling or otherwise distributing products who sells or distributes a defective product is subject to liability for harm to persons or property caused by the defect”(The Restatement of the Law Third, Torts: Products Liability, 1998, p. 5). As the name implies, this is a very strict standard, centering entirely on the product—not the relationship between defendant and plaintiff or the manufacturer’s exercise of reasonable care. Turning again to the Sullivan case, the U.S. Court of Appeals held that, despite exercising all possible care, the lobster boat builder was strictly liable for the vessel’s sinking under a state products liability statute (see Sullivan v. Young Brothers & Co., Inc., 1996’, see also CCH Products Liability Reports at paragraph 1520 through paragraph 1900 [discussion of strict liability concepts]). The Restatement Third represents a distillation and simplification by the American Law Institute (ALI) of products liability law as it has developed over 30 years in the U.S. Although it provides an authoritative representation of the current state of products liability, it has no official status in the absence of judicial adoption by a state’s highest court. Some state supreme courts, such as Iowa’s, have adopted certain sections as a statement of applicable products liability law (Wright v. Brooke Group, Ltd., 2002); other states, such as Wisconsin and Missouri, have rejected certain sections (Green v. Smith & Nephew AHP, Inc., 2001; Rodriguez v. Suzuki Motor Corp., 1999). Despite the new Restatements publication in 1998, most states still follow Section 402A of the Restatement of the Law, Torts, Second, the fountainhead of strict liability law. Forty-five states have adopted this section, published by the ALI in 1965, or some variant form of strict liability reflecting its influence: §402A. Special Liability of Seller of Product for Physical Harm to User or Consumer (1) One who sells any product in a defective condition unreasonably dangerous to the user or consumer or to his property is subject to liability for physical harm thereby caused to the ultimate user or consumer, or to his property, if (a) the seller is engaged in the business of selling such a product, and (b) it is expected to and does reach the user or consumer without substantial change in the condition in which it is sold.
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(2) The rule stated in Subsection (1) applies although (a) the seller has exercised all possible care in the preparation and sale of his product, and (b) the user and consumer has not bought the product from or entered into any contractual relation with the seller. Five states have never adopted strict liability as the basis for products liability claims: Delaware, Massachusetts, Michigan, North Carolina, and Virginia. These states rely on negligence and implied warranty theories; however, these states’ courts have used strict liability concepts, particularly Massachusetts and Michigan. Arguably, these two states apply “strict liability” but officially refuse to use the term. No state has ever completely repudiated Section 402A once it has adopted it, although some states might have altered its effects through case law or statutes (Restatement of the Law Torts, Second, 1965; for a further discussion of §402A, see CCH Products Liability Reports, paragraph 1520; a detailed chart on the acceptance of strict liability appears at paragraph 1570). 27.4 Types of Product Defects The Restatement of the Law Third distinguishes among three types of product defects: 1. Manufacturing defects 2. Design defects 3. Defects in instructions and warnings Section 2 of The Restatement of the Law Third establishes different standards of liability for these categories of defect. (Note that the standards of liability described for each of these categories are applicable to most products; however, special categories such as prescription drugs and used products may have different standards applied to them.) Manufacturing Defects A product “contains a manufacturing defect when the product departs from its intended design even though all possible care was exercised in the preparation and marketing of the product” (Restatement of the Law Third, § 2(b), 1998, p. 14). Removing the issue of negligence—and therefore fault—from the equation and imposing strict liability on manufacturers for manufacturing defects is intended to promote product safety because then manufacturers have an incentive to produce safe products. Furthermore, the price of defective products would need to be increased (to reflect the expected costs of defects); thus, imposing strict liability may discourage consumers from purchasing defective products by making them more expensive (Restatement of the Law Third, § 2, comment a, 1998, p. 15). The Texas Supreme Court case of Torrington Co. v. Stutzman (2001) provides a good example of a manufacturing defect. The estates of two Marines killed in a Navy helicopter crash proved that the aircraft’s tail rotor bearing was defectively manufactured. The bearing became contaminated during the manufacturing process, causing the part to fail. The defect arose not from the bearing’s design but from the manner in which it was produced (Torrington Co. v. Stutzman, 2001).
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Cases involving manufacturing defects are substantially outnumbered by cases involving design and instructions and warnings defects. Design Defects Determining whether a product is defective in design can be helped by a risk-benefit analysis, also known as the risk-utility test. Section 2(b) of Restatement of the Law Third states that a product is defective in design when …the foreseeable risks of harm posed by the product could have been reduced or avoided by the adoption of a reasonable alternative design by the seller or other distributor, or a predecessor in the commercial chain of distribution, and the omission of the alternative design renders the product not reasonably safe (Restatement of the Law Third, § 2(b), p. 14). Note that this does not require the manufacturer or distributor to make a product absolutely safe, but only reasonably so. Dangerous products can still be useful products, and completely removing the dangerous elements can also diminish the product’s function to such a degree that it is no longer useful. The goal is to establish optimum levels of safety, not necessarily maximum levels of safety (Restatement of the Law Third, § 2, comment a, p. 16). Note also that the risks of harm must be foreseeable. To expect manufacturers to make design decisions based on unforeseeable risks would be patently unfair and unreasonable. In evaluating manufacturing defects, the standard against which the product is measured is in a sense absolute: the product’s intended design. However, for evaluating design defects, no absolute standard exists; instead, the manufacturer is held to the standard of reasonableness. In Clay v. Ford Motor Co. (2000), the U.S. Sixth Circuit Court of Appeals applied the risk-benefit test to a sport utility vehicle involved in a rollover accident. The federal court held that the vehicle’s design presented a foreseeable risk of harm regarding instability that outweighed its benefit, especially so in the presence of five alternative designs that could have eased the rollover potential (Clay v. Ford Motor Co., 2000). Some states apply a consumer expectations test derived from the earlier Restatement of the Law Second, Torts, Section 402A, in addition to or rather than the risk-utility test (see Clay v. Ford Motor Co., 2000, applying both tests as alternative bases upon which to find the SUV defectively designed). Under that test, a product is defectively designed if it does not meet the expectations of the reasonable consumer. However, Comment g of Restatement of the Law Third § 2(b) rejects this test and relegates consumer expectations regarding a product to one of many factors applicable to the risk-utility test (Restatement of the Law Third, § 2(b), comment g, p. 27). Beware: an expert must determine which test applies under a particular state’s case law or statutes before evaluating a design defect claim. An example of a state court rejecting the risk-utility test in favor of the consumer expectations test appears in the Wisconsin Supreme Court’s opinion in Green v. Smith & Nephew AHP, Inc. (2001). A latex glove manufacturer was liable under the consumer expectations test for causing a healthcare technician’s allergic reaction. The state court
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criticized Restatement of the Law Third § 2(b)’s test as blurring the line between strict liability and negligence theories and as levying a heavier burden of proof on plaintiffs than that of the consumer expectations test. It also stated that the negligence concept of foreseeability had no bearing on strict liability (Green v. Smith & Nephew AHP, Inc., 2001. Wisconsin is not alone in rejecting Section 2(b)’s test. See CCH Products Liability Reports, paragraph 1730, which fully discusses the risk-utility test; for further details on the consumer expectations test, see paragraph 1725). Defects in Instructions and Warnings Like design defects, defective instructions and warnings have no absolute standard against which they can be judged. Again, as defined in The Restatement of the Law Third, the standard is one of reasonableness: [A product] is defective because of inadequate instructions or warnings when the foreseeable risks of harm posed by the product could have been reduced or avoided by the provision of reasonable instructions or warnings by the seller or other distributor, or a predecessor in the commercial chain of distribution, and the omission of the instructions or warnings renders the product not reasonably safe (Restatement of the Law Third, § 2(c), p. 14). Note also that, as with design defects, the risk of harm must be foreseeable. In the Massachusetts Supreme Judicial Court case of Vassallo v. Baxter Healthcare Corp. (1998), a group of breast implant manufacturers were held not liable, based on a failure to warn, for a woman’s injuries. Although there was no duty to warn or instruct about hazards not reasonably foreseeable at the time of sale, there could have been a postsale duty to warn. The Massachusetts standard followed Section §2(c) and Comment m (Vassallo v. Baxter Healthcare Corp., 1998; see also CCH Products Liability Reports at paragraph 1800 through paragraph 1840 [discussion of warning defects]). The commentators in The Restatement of the Law Third note that in many cases it is even more difficult to evaluate the adequacy of warnings and instructions because of the wide variety of expected users. They note that “no easy guideline exists for courts to adopt in assessing the adequacy of product warnings and instructions. In making their assessments, courts must focus on various factors, such as content and comprehensibility, intensity of expression, and the characteristics of expected user groups” (The Restatement of the Law Third, § 2(c), Comment i, p. 29). Different standards may be applied when the product is intended for use by children or specialized professional groups, such as licensed electricians. Although adequacy can be difficult to determine, a California Court of Appeal tried to specify some determinative factors: Whether a warning is adequate depends on several factors, among them “the normal expectations of the consumer as to how a product will perform, degrees of simplicity or complication in its operation or use, the nature and magnitude of the danger to which the user is exposed, the
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likelihood of injury, and the feasibility and beneficial effect of including a warning” (Schwoerer v. Union Oil Co., 1993, quoting Jackson v. Deft, Inc., 1990). Restatement of the Law Third makes clear, however, that a good warning is no substitute for a bad design. Whenever possible, hazards should be eliminated by a change in design. Warnings can address those residual hazards that cannot reasonably be designed out. Note that hazards considered “open and obvious” need not ordinarily be warned about. For example, it is not necessary to warn that charcoal briquettes become hot when ignited—after all, they are used for cooking. Hazards that cannot be eliminated and might not be obvious to users should be warned against—such as the fact that burning charcoal produces deadly carbon monoxide gas as a product of combustion. 27.5 What Does It Mean for the Engineer? Forensic or human factors engineers who may be deposed or called to testify in court in a products liability case can be more effective witnesses if they have a better understanding of the preceding principles of product liability law. Counsel may discuss testimony with a witness ahead of time, explaining what he or she will ask on direct examination and helping to identify those questions likely to be asked on cross-examination, but the engineer should also make sure that he or she • knows the government and industry standards applicable to the product • understands how the three legal theories described in this chapter might apply to the case • can address the issue of causation • can explain engineering decisions in plain English Knows Government and Industry Standards In an action brought under negligence or strict liability in tort, one of the issues that may arise is whether the product met applicable standards. Standards may be mandatory or voluntary. In general, most government-issued standards are mandatory and have the force of law. Failing to comply with legal requirements in the design, manufacture, or marketing of a product (including failing to provide mandatory warnings) is prima facie evidence of manufacturer negligence and a defective product. Industry standards, often developed by industry associations in concert with standards organizations such as the American National Standards Institute (ANSI), are typically voluntary; compliance is not mandatory, but manufacturers do comply because the standards represent “best practices” in a particular industry. Adhering to applicable standards does not guarantee that a product will be found free of defect; however, failing to do so puts the seller in a difficult position. Even voluntary standards are generally considered a minimum standard that manufacturers are expected to meet. A departure from a voluntary standard may be appropriate in some situations, but the seller must be prepared to defend that choice as resulting in a better product.
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Clearly, engineers who are called to testify about product safety issues must be familiar with the standards that apply to the particular product. An expert not only must be familiar with government and industry standards but also must demonstrate that the standards in fact apply to the product being contested. For example, an agricultural engineering expert correctly relied upon guidelines of the American Society of Agricultural Engineers (ASAE) and general engineering principles to establish a hay baler maker’s standard of care. However, he failed to apply the guidelines and principles to the baler’s design. Thus, the expert’s testimony was inadmissible to prove that the baler was negligently designed and, as a consequence, had injured a farmer. The expert’s failure to apply the ASAE standards properly was fatal to the farmer’s claim (Masters v. Hesston Corp., 2002). Understands the Legal Theories As discussed earlier, products liability actions may be brought under three theories: breach of warranty, negligence, and strict liability in tort. A particular action can be based on one, two, or all of these theories. Engineers who testify in products liability cases should consider how each of these theories might apply to the product in question. For example, a case involving a glass baking dish that broke when placed in a 350° oven might involve all three theories: 1. Breach of warranty might be used to allege that the seller provided an express or implied warranty that the dish would be suitable to use in an oven at typical baking temperatures. 2. Negligence might be used to allege that the manufacturer failed to exercise reasonable care in formulating and/or heat-treating the glass to withstand reasonable temperatures. 3. Strict liability in tort might be used to allege that the product was inherently defective, as evidenced by the fact that it broke when used in a foreseeable manner. The testifying engineer who spends some time thinking about these issues and discussing them with counsel will be a more effective witness. Can Address the Issue of Causation As noted earlier, to prove a products liability claim, regardless of the legal theory under which it is brought, the plaintiff must prove all four elements: 1. The product had a defect. 2. The defect was present when the product left the defendant’s control. 3. The plaintiff suffered injury or damage. 4. The injury or damage was caused by the defect. Forensic and human factors engineers are likely to be more comfortable addressing whether or not a product was defective in some way than addressing causation; however, proving (or disproving) causation is critical to the outcome of a products liability case. Establishing causation may or may not be complicated. The injury has already happened, accounts of victim and witnesses may conflict or be internally inconsistent, and it is never
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possible to recreate exactly the conditions that existed when the injury took place— particularly the state of mind of the injured party. In many cases, more than one factor can be identified as having contributed to the injury or damage. The central question then becomes which factor is the proximate, or legal, cause of the injury or damage. In Clay v. Ford Motor Co. 2000, discussed earlier, a mechanical engineer stated in his expert testimony that the sport utility vehicle had stability problems, citing specific design factors contributing to the SUV’s rollover propensity. This testimony was crucial to the plaintiffs’ proof that the SUV was defectively designed, resulting in a multimillion dollar jury award (Clay v. Ford Motor Co., 2000). Engineers are trained as scientists and thus dislike dealing with matters not easily managed using the familiar tools of the scientist: experimentation, measurement, and statistical analysis. Questions of causation are often not amenable to these methods. The engineer must be prepared to state an opinion about proximate cause, even though the answer cannot be scientifically proven as fact. Although experimentation or other quantitative analysis may contribute to that opinion, ultimately, the engineer must be willing to make a judgment based, in part, on experience because that is the role of the expert. Can Explain Engineering Decisions in Plain English The design, manufacture, and marketing of products involve many decisions, some of which are based on engineering principles. Testifying engineers may be asked to explain why a certain design decision was made or how materials were chosen for fabrication or formulas developed for products. Other engineers may be asked to describe (or critique) the hazard analysis procedure used in product development or the decisions made to design out, guard, or warn against identified hazards. In actions based on negligence and strict liability in tort, the alleged negligence or product may be judged against a “reasonableness” standard: did the manufacturer act reasonably? Was the product reasonably safe? Did the product meet the expectations of a reasonable consumer? Engineers are familiar and comfortable with using technical language. A statement such as “Perceived hazardousness correlated highly with the degree of precaution reported by subjects when using products” (Chy-Dejoras, 1994) would be familiar territory for human factors engineers. Most juries and judges, however, would find such a statement obscure and confusing at best—and it is juries and judges who must decide if the seller’s decisions were “reasonable.” The preceding example of a statement translates rather easily into plain English: “People tended to be more careful using products that they thought were more dangerous.” As a further example, one of the authors of this chapter testified in a case involving an improperly installed surge arrestor that exploded when it became overloaded. During trial testimony, the surge arrestor was described to the jury as similar in function to a household fuse (with the exception that an overloaded household fuse usually fails in a safe manner). Explaining technical language in familiar terms can help the jury understand expert testimony better—as long as the analogy is accurate. Juries may base their decisions not only on the facts of the case, but also on their perceptions of a witness’s attitude. An engineer who uses overly technical language may be seen as arrogant or pompous —or worse, as trying to hide something damaging behind
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a smoke screen of technical terms. Engineers should strive to couch their testimony in plain English whenever possible, without “dumbing down” the information to the point of inaccuracy or condescending to the jury or judge. Doing so makes the engineer a better witness and gives the jury and judge better access to important information, therefore resulting in better decisions. 27.6 Conclusion Forensic and human factors engineers are often called to testify in products liability cases. Products liability law is complex and evolving. Although no one expects engineers to become lawyers, the engineer who becomes familiar with the preceding basic concepts of products liability law and how they may apply in a particular case will be a more effective expert witness. Coupling engineering expertise with an understanding of the legal context, familiarity with applicable standards, and skill in presentation will enhance the testimony of forensic and human factors engineers. References Black’s Law Dictionary, Abridged 6th ed., West Publishing Co., St. Paul, MN, 1991. CCH Products Liability Reports , CCH Inc., Riverwoods, IL, 1962-. Chy-Dejoras, E.A. Effects of an aversive vicarious experience and modelling on perceived risk and self-protective behavior, in Human Factors Perspectives on Warnings (K.R.Laughery, Sr., M.S.Wogalter, and S.L.Young, (Eds.), Human Factors and Ergonomics Society, 1994, 11. Clay v. Ford Motor Co. (CA-6 2000) 215 F.3d 663 (applying Ohio law). Green v. Smith & Nephew AHP, Inc. 629 N.W.2d 727 (Wis. 2001). Kimble, W. and R.V.Lesher, Products Liability , West Publishing Co., St. Paul, MN, 1979, p. 1. Masters v. Hesston Corp. 291 F.3d 985 (CA-7 2002) (applying Illinois law). Myrlak v. Port Authority of N.Y. & N.J. 723 A.2d 45 (N.J. 1999). Phipps v. General Motors Corp. 363 A.2d 955 (Md. 1976). Prosser, W.L., Handbook of the Law of Torts , West Publishing Co., St. Paul, MN, 1979, p. 2. Restatement of the Law Third, Torts: Products Liability , American Law Institute Publishers, St. Paul, MN, 1998. Restatement of the Law, Torts, Second , American Law Institute Publishers, St. Paul, MN, 1965. Rodriguez v. Suzuki Motor Corp. 996 S.W.2d 47 (Mo. 1999). Schwoerer v. Union Oil Co. 17 Cal.Rptr.2d 227 (Cal.App. 1993), quoting Jackson v. Deft, Inc. 273 Cal.Rptr. 214 (Cal.App. 1990). Sullivan v. Young Bros. & Co., Inc. 91 F.3d 242 (CA-1 1996) (applying Maine law). Torrington Co. v. Stutzman 46 S.W.3d 829 (Tex. 2001). Vassallo v. Baxter Healthcare Corp. 696 N.E.2d 909 (Mass. 1998). Wright v. Brooke Group, Ltd. 652 N.W.2d 159 (Iowa 2002).
28 Human-Centric Approach to Forensic Analysis for System Liability Gary M.Bakken Analtica Systems International, Inc. 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
28.1 Introduction to Human Factors/Ergonomics Principles and Relevance to Standard of Care When considering the human factors/ergonomics issues associated with system liability, whether from a design or forensics perspective, it is essential to understand fully the involved system space components’ dynamics—that is, the component interactions and interfaces. However, in order to do so, one must know and understand the essential system components: those that assist in as well as those that detract from the system’s performance. Not all system components affecting system performance are designed, intended, or desired. System, in this context, is used in the most generic sense, stemming from the assumption that all existence comprises a system. That system, THE system, and all systems comprising THE system, from a human-centric perspective (HCP), comprise human, technological, and environmental components and, most importantly, the components’ interactions and interfaces. A forensic function is to investigate and determine the system component interactions and interfaces of concern and the nature and severity of the effect on the system components. This human-centric perspective can be represented by the simple system model: a system is the combination of human, technological, and environmental components relevant to system performance; the interactions among the various human, technological, and environmental components; and the interfaces that facilitate or hinder the various interactions. Reviewing the contextual definitions for the terms system, human, technology, and environment will assist in gaining a better understanding of the humancentric approach to design and forensics analysis. (Refer to “Defining Terms”) Of course, the human-centric system model is only a simplistic representation that is helpful in reminding us of the three main system components and the various interaction combinations and interfaces facilitating those interactions. Moreover, in any given system, multiple interfaces will potentially take place among multiple humans, multiple technological components, and multiple environmental considerations or constraints. There may be subsystems and confusion or conflict in the manner in which specific
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system attributes are defined. One person may define a particular system attribute as a subsystem, while another may define it as a system component. To bend a cliché: “One person’s system is another person’s system component.” From a human-centric perspective, none of this potential conflict is particularly important as long as the primary goal of the system is to optimize the objective or outcome of the system for the human component. Therefore, from a human factors/ergonomics perspective, it is essential that the fundamental relationship between the human component and other system components be defined so that the human component possesses the highest priority for accommodation within the system. To this end, the human-centric approach (HCA) can be used to identify and bound system characteristics for consideration when developing and implementing socially and ecologically responsible engineering solutions for the design of systems for enterprises, organizations, facilities, products, work, procedures, etc. To maximize the accommodation for and the usability of a system by the probable or predictable human population, specific consideration must be given to identifying and developing measurable human performance criteria to ensure overall system success. Moreover, the human-centric approach recognizes that the system component over which the greatest control can be exerted is the system technology. Thus, a well-designed technological system component will embody characteristics that provide the optimum technology-human interaction for the widest possible range of expected or predictable human population throughout the life span of the technology, with appropriate controls against injury or property damage for all possible modes of use and misuse. Simply stated, it is better to design technology in a manner that prevents hazard exposure than to rely on the human component to avoid hazard exposure through behavior, whether or not the human is apprised of the system hazards. Realistically, however, this chapter will focus on the more practical concept of the interface among the human, environmental, and technological components over which we have, or should have, control. For the purpose of this chapter, a “system” will be considered to be inclusive of the components and the mutual interfaces among the human, environmental, and technological components of a given system. 28.2 Objective and Scope of the Chapter The overall objective of the human-centric approach is to provide a set of guidelines to those who conceptualize, design, build or construct, implement, maintain, repair, use, or evaluate (forensics) a system so that the system ultimately presents itself to the human interface population with the maximum level of durability and functionality possible, with elevated emphasis on efficiency, safety, and satisfaction. The system should perform in the most efficient manner possible to maximize the preservation of natural resources, minimize the physical and mental effort required by the human interface population, and perform its designed functions in the most efficient manner possible. The system must, at a minimum, conform to all applicable laws, codes, and standards propounded for the safety of the probable human interface population. In addition, a reasonable effort must be made by those responsible for system design and manufacture
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to ensure the safety of the probable human interface population and the environment with respect to identified or foreseeable hazardous conditions resulting from the exposure of the human to the system—even if these hazardous conditions are not identified within published laws, codes, or standards. That is, under human-centric approach principles, the duty is placed upon the designers, developers, and manufacturers of a system to reasonably ensure that all reasonably identifiable or reasonably foreseeable hazards have been eliminated from the system, including those that may have been created by conformance with applicable laws, codes, and standards, or have been adequately controlled so that, under foreseeable conditions of use and misuse, the human interface population and the environment are safeguarded from hazard exposure. Refer to Appendix A for more on system safety. The system should provide the human interface population with an appropriate level of gratification to instill a heightened desire by the affected population to continue utilizing it. Implementing and adhering to human-centric approach principles, from system conceptualization through system recycle, will significantly reduce the liability exposure of all parties who might affect or be affected by the technological components of the system, including the end users. 28.3 Discussion of Principal Issues As technology takes on an ever-increasing role in human existence, the result is a proportional increase in the absolute necessity for technology to be controlled or bounded within definable human and environmental constraints. For example, a century ago, there was no concern for the consequence of catastrophic failure in a nuclear reactor’s containment system. Recent history has taught us, however, that the failures at Chernobyl and Three Mile Island subjected, or potentially subjected, humans and the environment to extremely severe hazards created through advanced technology implemented seemingly for the good of humankind. Furthermore, the need for sound human-centric design principles is reserved not only for extremely complex systems such as nuclear power plants, spacecraft, and aircraft, but also for every developed, manufactured, or constructed system or product that is conceived and implemented. Of course, it makes sense to commit the greatest effort to the systems that have the greatest potential for inflicting injury or property damage, but it is absolutely essential that the same techniques of the human-centric approach be utilized at the appropriate level for even the simplest of systems. To obtain the full potential of the human-centric approach concept, it is essential to be knowledgeable about the capabilities and deficiencies of the human component of the system. Despite the obvious complexity and remarkable capabilities of the human species, we are very limited in our tolerance to hazardous conditions. We cease to exist if we are deprived of oxygen for more than about 3 minutes. We cease to exist if we are exposed to very minor changes in ambient temperature when compared to the wide range of temperatures for which we have awareness. Our skin is relatively fragile and our musculoskeletal structure is relatively weak. We succumb to disease relatively easily. However, our ability to understand and predict our environment and our ability to develop and implement technology has provided us with an advantage that supplements
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our natural frailties quite nicely. It is precisely this ability to develop and implement technology that can ultimately give rise to the betterment of humankind when the technology is appropriately interfaced with the human and environmental components of the system. In contrast, technology that is improperly interfaced can give rise to unexpected and, oftentimes, disastrous results. For example, the prevalent cause for “accidental” death in the United States is motor vehicle “accidents.” If it were not for motor vehicles (technology), approximately 50,000 deaths annually could be avoided. Placing the human component at the highest priority level throughout all phases of a system’s life, from concept to recycle, will increase the probability that hazards associated with the system will be effectively eliminated through design procedures or will be adequately controlled through engineering procedures. The remainder of this section briefly describes the rationale for implementing the human-centric approach to minimize liability exposure. Human Capabilities Where and how do we begin to implement the human-centric approach? Quite simply, we begin at the beginning: with the capabilities of the human component, which at times can be the strongest system component but at other times can be the weakest. Furthermore, like any other system, human beings (yes, we are systems) have definable capabilities including, but not limited to, physical, physiological, psychological, and biomechanical capabilities. The dimensions of our bodies, our anthropometries, define in great part our physical ability to perform a task. If an automobile brake pedal is located next to the steering column so that a person with big feet cannot immediately access the pedal because the steering column prevents ready access, the driver may not be able to stop the vehicle to prevent injury or property damage in sufficient time, thus resulting in a situation that may ultimately lead to a liability exposure on the part of the designers, manufacturers, owners, and/or maintainers of the system. Examples of useful references for designers involved in interfacing the human component with the technological component are listed in Further Information. Additionally, our bodies have inherent range-of-motion limits, kinematics, that further limit us. For example, a workstation that requires a seated operator to view a control immediately to the rear of the seating position is poorly designed because the operator cannot rotate his neck the necessary 180° to view the control. If the poorly placed control is critical to the completion of a task that can endanger the user or other humans, or is a warning device for an impending critical condition, the user’s inability to monitor the control conveniently can create dangerous conditions with the consequential liability implications. Again, examples of useful references for designers involved in interfacing the human component with the technological component are listed in the Suggested Bibliography. Our physiological capabilities include our sensory systems. Our senses provide us with data that we transform into information regarding the condition of the environment and the status of the technology with which we interact. Our eyes provide visual data, but only if the visual stimuli are within the visual field of the person seeking the information and only if the visual stimuli possess the appropriate
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levels of persistence, contrast, and conspicuity to provide meaningful data to the viewer of the stimuli. Furthermore, the data are only useful if they are meaningful to the user. Under natural, prehistoric conditions when visual stimuli provided feedback almost exclusively regarding the condition of the environment, all that was necessary to ensure survival was to identify the natural hazards and avoid them: basically, steer clear of the larger predators, do not fall off a cliff…that sort of thing. However, with the introduction of human-designed (vs. natural) technology into the human-environment system, the need for more defined, more refined visual stimuli has increased dramatically. Moreover, as technology continues to take on a more commanding role in our existence, the need for improved visual stimuli to permit us to exist with and use the technology increases. For example, when motor vehicles were capable of traveling at only 15 mph, there was little need for traffic controls. Consider the consequences of driving today without a traffic signal at each intersection providing the system users with continuous visual stimulus regarding the probable or at least the expected condition of the intersection. Consider also the liability implications if the traffic control system malfunctions and provides an “all-ways-green” condition at a relatively busy high-speed intersection. Similarly, our ears provide us with auditory input regarding the condition of the environment and the status of the technology with which we interface. In the case of sound stimuli, and in contrast to visual stimuli, it is not necessary for the sound’s originating source to be situated specifically at a required location to be useful. That is, in general, a claxon behind a user will provide the same auditory stimulus to the user as a similar claxon placed in front of him. Furthermore, sound stimuli can be very useful in supplementing visual warnings by eliminating the need for a user to monitor a control or a potentially hazardous condition constantly. Consider, for example, a vehicle operator driving toward an uncontrolled railroad crossing at grade when a train is approaching that will arrive at the crossing at the same time as the driver’s vehicle. Furthermore, consider that, for whatever reason, the driver fails to observe the approaching train even though no obstacles impede his view. That is, the visual stimulus is present, but it is outside the driver’s field of view. Fortunately, when the locomotive reaches the whistle post, the engineer activates the whistle that provides the driver with the necessary auditory stimulus with sufficient perception and reaction time to respond and avoid a collision. Our skin provides us with tactile stimuli. Although less informative than the relatively richer visual and auditory sensory inputs, tactile input can play an important role in hazard identification and injury prevention. For example, it is possible to judge the relative slip resistance of a shower stall floor simply by “feeling” the surface roughness of the floor with one’s feet. A relatively rough surface signals a relatively slip-resistant surface with a generally reduced propensity for persons to slip, fall, and incur injury. Our sense of smell provides us with olfactory stimuli. This capability can be particularly valuable in situations in which a dangerous condition does not present with visual, auditory, or tactile stimuli. Consider, for example, awakening in the night to an overwhelming odor of rotten eggs, which is associated with the odor ant added to the otherwise odorless, colorless, tasteless, neutral-smelling natural gas used to cook our meals. Clearly, in this hypothetical situation, through the sense of smell alone an almost certainly fatal mishap will have been avoided.
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Our ability to receive stimuli through the sense of taste can similarly provide valuable information in situations in which visual, auditory, tactile, and olfactory stimuli are lacking or otherwise masked or concealed. Our ability to maintain a controlled posture continuously, which without constant neuromuscular intervention would almost certainly result in collapse of the body, is an example of our vestibular sensory capability. Upright, bipedal ambulation is nothing short of a miracle, but the human “sense of balance” makes it possible for this complex task to be one of the first highly complex skills we master. Our ability to control the movement of our bodies is demonstrative of the human proprioceptive sensory capability. Consider, for example, eating with a fork while blindfolded. For a person who has some experience with using a fork to place food in his mouth, the occurrence of poking himself in the eye with the fork while trying to reach the mouth would have a very low probability. Thus, the inherent sense of body part position, acceleration, deceleration, velocity, and proximity to other body parts is embodied within the human proprioceptive sensory capability. As humans, our physiological capabilities include other systems, including, for example, metabolism, which is a chemical process necessary for the maintenance of life. The body uses metabolism to break down (metabolize) certain substances to produce energy for vital processes; other substances necessary for life are synthesized through the processes of metabolism. Trauma or disease that alters the body’s metabolic capability can result in mild to severe consequences affecting our performance and thus our risk for injury and even death. The neurological system is essentially the body’s communication network or information highway. All of the sensory inputs traverse the neurological system, and virtually every process within the body is controlled through bidirectional information transfer within the body’s neurological system. Relatively minor damage or injury to the nervous system or the effects of aging can have significant consequence regarding our performance and thus our risk of injury, including paralysis and death. The body’s hormonal system produces substances called hormones in one tissue mass that are then conveyed by the bloodstream to another tissue mass to cause physiological activity, such as growth or metabolism. Hormonal imbalance resulting from trauma or disease can have wide-ranging consequences, most of which are undesirable, again affecting our performance and thus risk of injury. The human digestive system processes the foods and liquids we ingest, initiating the transfer of nutrients and other substances into the body and disposing of the unused or unusable materials. Clearly, ingesting substances that are poisonous or toxic, thereby introducing them into the digestive system, can have devastating results, again affecting our performance and thus risk of injury. The human cardiovascular system circulates the nutrients and other substances necessary to sustain life through the complex system of arteries, capillaries, and veins. Damage or injury to the cardiovascular system can have immediate, life-threatening results if remedial measures are not quickly implemented. Poor circulation resulting from injury, lack of activity, or other factors can affect our performance and thus risk of injury. The cardiopulmonary system is responsible for intake of the gases necessary to sustain life and for exhausting the gas when the useful components have been removed within the lungs. Similar to damage or injury to the cardiovascular system, disease or injury to
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the cardiopulmonary system can be life threatening as well as affect our performance, resulting in increased risk of injury. The body’s immune system is the body’s chemical watchdog. It is designed to defend us against bacteria, microbes, viruses, toxins, and parasites that would otherwise invade and ultimately destroy our bodies. If the skin is cut or punctured, bacteria and viruses enter the body through the break in the skin. The immune system responds immediately to eliminate the unwanted visitors while the skin heals and the wound is closed. In some cases, the immune system is unable to deal with the foreign entities successfully and the wound becomes infected. Thus, injury can again affect our performance and the risk of further injury. During the normal process of breathing, we inhale thousands of germs (bacteria and viruses) that are floating in the air. The immune system most often removes these dangers, except in instances when a germ gets past the immune system and we catch a cold, get the flu, or worse. When we eat, we ingest hundreds of germs; again, most of these are handled by the immune system. The effects of such illnesses can result in reduced performance and increased risk of injury. When the immune system malfunctions, problems generally arise. For example, some people have allergies, which are an over-reaction by the immune system to certain stimuli. Some people have diabetes, which is caused by the immune system’s inappropriate attack of cells in the pancreas. Some people have rheumatoid arthritis, which is caused by the immune system acting inappropriately in the joints. In many different diseases, the cause is actually an immune system error. The effects of such conditions can result in reduced performance and increased risk of injury. In addition to our physical and physiological capabilities, we as humans also have psychological capabilities, such as information processing and decision making. Information processing is utilized in conjunction with decision making to control the body’s response to just about every stimulus received through the sensory functions, as well as many of the other functions. When one considers these psychological capabilities during system design, it is absolutely essential to ensure that the information provided to the human through the technology-human interface is appropriate in quantity in order to avoid information overload or deficiency. It also needs to be properly formatted, adequately persistent, timely, sufficiently compelling to elicit the expected or necessary response, consistent, and unambiguous. In the early days of computer programming, a descriptive phrase was coined to remind us of the importance of providing accurate information for processing. This phrase is “garbage in-garbage out,” or “gi-go,” and it is still applicable. The same principle applies to the human information-processing and decision-making functions. If the information presented for processing is less than precise, it is highly probable that the response to the information precipitated by the decision-making process will be less than optimum as well. Consider, for example, the implications of a traffic control system that displays a red light to signify stopping at the intersection for northbound and southbound vehicles and a green light to proceed, but displays a red light to signify consent to proceed for eastbound and westbound vehicles, and a green light to stop. Obviously, such a system could be easily implemented, but the implications of doing so are rather obvious as well. Furthermore, as indicated earlier, when we begin to define the human-centric approach, the information presented for processing must accommodate or make suitable
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compromises for the intrinsic potential for conflict or increased complexity arising from the wide diversity of human-defining characteristics including, but not limited to, culture, ethnicity, anthropometries, religious and social beliefs, and environmental and climatic exposures as well as the full range of educational levels and intelligence levels of the probable targeted human user population. Cognitive task analysis, a unified perspective on design, provides a specific way of approaching the psychological characteristics of the human, technological, and environmental components’ interaction. Thus, it provides a way of thinking about the liability issues associated with the cognitive aspects of the system. Hollnagel (2003) enumerates a set of principles that laid the foundation for this way of thinking: 1. Designed systems and their components have consequences. 2. The consequences are manifested through the interactions created by the design conception and planning, intangible component effects on the human, as well as the traditional physical interaction. 3. Realization of the system and its components is as much a function of planning and organization as it is the physical components. 4. The focus is on consequences resulting from how the system component is used—how the use changes the way we think about and work with them at individual and organizational levels. The forensic objective is to use this tool to identify and analyze the cognitive task aspects to determine the causal relationship between the cognitive tasks and the event and the consequent losses, if any. Our bodies also have biomechanical capabilities. When we exert forces with our bodies, or when forces are exerted against our bodies, we are utilizing our biomechanical functions. Pushing, pulling, lifting, twisting, turning, and typing are examples of biomechanical functions. A fair amount of study has gone into human biomechanical capabilities; this has provided a significant amount of information regarding human strength and endurance limitations. It is always important to match the strength and endurance requirements of the task to the strength and endurance limits of the predictable user population. For example, if pulling a brake lever requires more upper-body strength than the predictable fifth percentile female operator can produce, the design is defective with clear implications for liability on the part of the system designers. Conversely, if the keys on a console keyboard are so small that the predictable 95th percentile male cannot strike a single key without striking one or more adjacent keys, the design is equally defective and may also give rise to liability implications. Using the human-centric approach, it is always necessary to design the technological component to accommodate the widest possible range of biomechanical criteria identifiable for the predictable human interface population. Human Categories Similar to our capabilities, with respect to almost any conceivable situation, we can be categorized with respect to our direct or indirect interface with system technology. For example, in any given situation, we and the rest of the population predictably affected by the given technology may fit into one or more of the following categories:
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Operator (user) Customer Acquirer Manufacturer Developer Designer Scientist Tester Installer Maintainer Executive Project manager Government Society Organization (public and private) General public Co-workers Of course, this list is not all inclusive but is offered as an example of the variety of human categories that may be affected by any given technological component. Each conceivably affected category must be identified and the implications of the expected and unexpected effects of every predictable technological interface must be analyzed to ensure that each and every detrimental effect has been eliminated or reasonably controlled. The level of effort must be matched to the level of potential harm to the human components. For example, the procedure for ensuring the efficacy of a nuclear power plant will clearly be different from that necessary to ensure the efficacy of a yo-yo. Human Facets Although all humans are very similar, we are also very different from one another. Some humans are stronger and some are smarter. Some humans are more predisposed to disease. Gender, body type, age, intelligence, and other characteristics define our abilities to cope and interface with the technological component of the system. We all have inherent, natural physical, physiological, psychological, and biomechanical differences that must be accommodated by the technological component. A desirable rule of thumb for designers is to accommodate as much of the predictable user population as possible without compromising the functionality or safety of the technology. Consider, for example, the curb ramps installed in sidewalks at intersections. When designed according to appropriate standards, they provide ready access for sidewalk users in wheelchairs but do not decrease the safety of ambulatory sidewalk users. Some people seem to be able to figure out how to use technology while others do not have as much luck. Certain human characteristics define our ability to interface with technology: • Knowledge has a great deal to do with our ability to use technology. When an individual is trying to turn on the computer or use it to control a complex manufacturing process, a person who knows what a personal computer is and what its function is will have a
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significant advantage over a person who has never seen a computer, with the implication that improper computer inputs would give rise to a dangerous condition. Conversely, the most knowledgeable computer user quite likely would not possess the knowledge to survive in the Australian Outback using the simple technology developed by people who have lived there for many generations. • Age is also a determinant when understanding a person’s ability to interface with technology. Older eyes do not see as well as younger eyes and older ears do not hear as well as younger ones. Older muscles are not as strong as younger muscles and older bones are more brittle than younger bones. Our proprioceptive and vestibular capabilities diminish with age. Furthermore, as we age, our ability simply to cope with technology generally diminishes as well. We generally become less patient and are more easily confused as we grow older. The curiosity we had as children and young adults is replaced by cynicism or routine. We tend to consider technology to be overly complicated and we often long for the “good old days” when things were simpler. As the world’s population ages and as a greater percentage of the population becomes less willing and/or less able to interface with technology, it becomes more important for its providers to accommodate this natural penchant for rejecting technology with advanced age. • Disease and injury can also interfere with a person’s ability to interface with technology. Toward the end of the last century, the U.S. Government recognized that disabled persons were being discriminated against by many forms of technology and, as a result, passed the Americans with Disabilities Act (ADA) in an effort to ensure that technology intended for the use of the general population would be suitably designed for persons with atypical physical and mental capabilities. Similar consideration must be made when designing technology for persons who are ill or injured and who do not have the same physical or mental capabilities as the rest of the user population, whether the condition is temporary or permanent. • Another capability determinant is the environment. Of course, technology must be designed to withstand the intended environment in which it is to be utilized. However, some human characteristics related to environment directly affect our ability to interface with technology. As an example, consider a military rifle developed for desert warfare that serves its intended purpose reasonably well. Furthermore, assume that the same firearm is well suited for the extreme climate variation offered by service north of the Arctic Circle. Although the inherently well-designed technology leaves no cause for dismay regarding reliability, rate of fire, or accuracy, because the trigger guard has been designed for a nongloved hand, the soldiers who are forced to use such a weapon while wearing severe weather clothing including heavy gloves may not be able to use the firearm effectively, if at all. Alarming liability consequences are associated with a military firearm designed in a way that does not permit its user to operate it when it is absolutely imperative to do so. Thus, it remains essential to design technology in such a way that it withstands the environment. However, it is equally important to design technology to facilitate human variations related to the environment.
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Technology Technology itself plays a role in the way in which humans interface with it. A person who does not know what a cell phone is will likely have a very different reaction to the sound of a ringing cell phone than the person who owns the phone. Technology sometimes comprises relatively simple objects. A good example of this concept is an ordinary axe used for chopping wood. A relatively large percentage of persons who observe an axe in use would be able to determine its rudimentary uses and would be able to learn to use it quite readily. Furthermore, even a relatively neophyte axe user would have little difficulty determining that the axe edge impacting the wood is sharp and could cause injury. Quite often technology that is embodied by simple objects is relatively straightforward in nature and incorporates relatively simple principles to utilize. However, if the axe handle is designed so that its diameter or thickness is too great for the majority of users, its functionality can be severely limited and its safety will likely be compromised as well. Conversely, if the handle is too small in breadth, similar functionality limitations can arise along with similar safety compromises. Thus, the solution is to design the object so that it maintains its functionality and safety throughout the full spectrum of human capabilities for the intended user population. Machines and equipment are groups of objects assembled to create technology. Consequently, in general, machines and equipment are more complicated than simple objects of technology. A chainsaw is an example of a machine that is clearly more complicated than an axe, although both have the same general purpose: cutting wood. The function of an axe may be relatively straightforward to a person who has never seen an axe; however, a chainsaw would be much more difficult to figure out for a person not exposed to power equipment. The increased complexity of the chainsaw over the simple axe also gives rise to increased complexity in determining the hazards associated with the use of a chainsaw. Furthermore, even persons who are skilled in the use of certain machines or equipment may not be able to determine the function of or to use other machines or equipment effectively. For example, a person skilled in using a chainsaw for the purpose of felling trees may not be able to step up to an engine lathe and cut a thread on a steel shaft. Much worse, the person who has learned all the hazards associated with chainsaw use and developed skills to avoid chainsaw hazard encounters may not be able to ascertain all the hazards associated with using an engine lathe. Thus, if the engine lathe is not designed with sufficient inherent hazard controls to protect a user who is not well informed, the liability issues could be relatively grave. In addition, when a machine or a piece of equipment is designed, it is essential to design it in a manner to ensure that it is functional and durable as well as that it accommodates the human characteristics of the intended user interface population. For example, the machine or equipment must be designed so that its manner of control is intuitively clear to the operator. A lathe with a lever that, when pushed toward the work piece, moves the tool away from the work piece and that moves the tool toward the work piece when the lever is pulled away from the work piece is counterintuitive in design. Moreover, aside from the obvious need for intuitive control characteristics, machines and equipment must be designed to accommodate the user’s human limitations. A control that
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requires more force to activate than can be applied by the fifth percentile female operator not only is useless but also may be dangerous. Processes are the actions, changes, or functions that effectuate the desired, or sometimes undesired, outcome of a system. In many situations, the processes required by the system may be inalterable. For example, the process utilized to convert iron into steel is relatively fixed, requiring the combination of a variety of materials at high temperatures to make the conversion. To be successful, the process must be regulated appropriately to ensure that the proper mixture of materials is exposed to the appropriate temperature profile for the appropriate time. Relatively small variations in one or more of these components can give rise to varying degrees of undesirable results. In general, technology must be designed to ensure that the process can be completely controlled by the human interface if that is the role of the human in the system; or the technology must be designed with adequate inherent control as necessary to supplement the human component; or the technology must be designed to supplant completely the need for human intervention to effectuate the desired outcome. Consider, for example, the evolution of manned flight from the early days of the biplane to the space shuttle. When the Wright brothers first took off, it was completely up to the pilot to control the entire process of flight from liftoff to touchdown. As aircraft became more sophisticated, they became more complicated, requiring technology supplements to ensure the success of the flight process. For example, some military aircraft cannot remain in stable flight without continuous modifications to the flight process controlled by onboard computers directly causing trim adjustments beyond the human capability of the pilot. Finally, when the space shuttle was designed, it was determined that the process of landing the craft was too complicated for humans to control. A sophisticated system of hardware and software was designed and implemented to permit the shuttle to land in a “dead stick” mode, meaning that pilot intervention is not needed. Clearly, as reliance on technology for task accomplishment increases, potential liability for technology designers and implementers increases as well. Procedures are the steps taken to cause a process to come to fruition. If we consider the procedures necessary for the process of cooking an omelet, we would most probably find them in a recipe book. If we consider the procedures for landing the space shuttle, we would find them hidden in the thousands of lines of computer code used to control the servomechanisms that effectuate the landing. Using the former example, a good way to differentiate between processes and procedures is to assume that the process is the menu item and the recipe and instructions for preparing the menu item are the procedures. Thus, in the case of the latter example, the menu item is a safe shuttle landing and the recipe consists of the millions of logical statements and calculations within the code that effectuate the landing. Techniques are modifications to procedures generally intended to improve the outcome of the procedures. For example, assume a lumberjack with an axe is standing in a forest. In other words, this is a system with a human component (the lumberjack), a technological component (the axe), and an environmental component (the forest). The process to be accomplished by the system is the felling of a tree. The procedures to be implemented involve the repetitive swinging of the axe, causing the sharpened blade of the axe to strike the trunk of the tree. This all sounds relatively simple and straightforward. However, techniques known to lumberjacks make these procedures
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much more efficient than when the same procedures are undertaken by persons unskilled in using an axe, even if the unskilled persons are bigger and stronger and have more stamina. Furthermore, and more importantly, the experienced lumberjack has skill in controlling the fall trajectory of a felled tree, which provides the lumberjack with a significant advantage over the amateur with respect to personal safety and exposure to the danger of being crushed by the tree. Thus, system optimization can be obtained by implementing techniques that modify procedures to effectuate the process. It follows then that, if the system designers are cognizant of techniques necessary or available for optimum safe system operation, these techniques must be made known to the predictable user interface population in a manner that can be readily comprehended and successfully implemented by the users. Environment We cannot overlook the environment when considering the human-centric approach. Quite simply, the natural environmental component existed for billions of years before the human and the technological components came into play. Therefore, it seems a bit egotistical for the human component to elevate itself to the most critical level within the human-technological-environmental system when implementing the human-centric approach. How often do we prove our fragility when we fail to control the natural environment? Earthquakes, tornadoes, hurricanes, volcanoes, ice ages, tidal waves, and droughts are constant reminders of the insignificance of humans and the insignificance of our meager technology in the human-technological-environmental system. However, we are driven with an intrinsic self-preser-vation penchant coupled with a fair measure of special (not exceptional, but pertaining to the species) arrogance that essentially demands we place ourselves at the top of the priority list. Nevertheless, the environmental components, manufactured as well as natural, must be addressed in the design of the system to obtain system optimization. For example, an earthquake is an extension of the natural environment that can have devastating consequences on the manufactured environment if the manufactured components of that environment are not designed to withstand the forces applied to them by the earthquake. The climate in which the human and technological components are to function must be considered in system design. If the temperature is too high or too low, sensitive computer-controlled equipment may malfunction or fail. Depending upon the criticality of the process, the malfunction or failure may give rise to consequences ranging from benign to catastrophic, with the associated liability implications. If the humidity is too high, a steel component may rust, causing a structural failure over time. Conversely, if the humidity is too low, other system components may dry out with similar structural compromise. Either condition may give rise to unwanted liability on the part of the designer or manufacturer. Wind can wreak havoc on technology inadequately designed for use in severe wind conditions. Conversely, it would be nonsensical to design and construct a windmill farm to generate electrical energy using the wind in an area where there is little, if any, wind.
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Precipitation is another environmental phenomenon that can give rise to technology malfunction. Consider, for example, the consequences of continuous build-up of ice on overhead power lines that finally causes them to fail. Cloud cover can also cause technology to fail. If a solar energy generation facility is constructed in a location where the sun is usually concealed by clouds, little can be gained from the installation. The Earth is also part of the environmental component. Any system that includes an interaction with the Earth must have a compatible interface. The type of soil and the soil condition are critical in agricultural systems. Constructing a skyscraper on a foundation of natural rock (called bedrock) will help ensure that the building will not incur structural damage from the natural phenomenon of settling when compared to a similar structure built on a less stable base. An active volcano is not a good place to construct a residence. Vegetation can also cause system failure because root systems can actually deform concrete foundations not sufficiently robust to withstand the onslaught. All forms of water, including salt water, fresh water, moisture, ice, and steam, are parts of the environment that can cause damage to technology. The damage can come in the form of rust or corrosion caused by chemical activity between metallic components and the water, or the damage can come from undesirable electrical current flowing through spurious circuits created by the presence of water or moisture. The environmental gases we breathe are generally harmless to humans if they are relatively unpolluted. However, they can sometimes cause damage to technology that can in turn compromise human safety. A component subject to rapid oxidation if exposed to ambient oxygen levels in the air must be sealed in a manner to prevent failure of the seal under reasonably foreseeable conditions. Natural environmental components such as rocks, leaves, and dust particles must be considered in system design and implementation to ensure that all reasonably predictable encounters with these objects will not cause undesirable system degradation or failure. The air filter on the diesel engine of an earthmover that becomes easily clogged with dust is an example of a poorly designed technological component if it was foreseeable that the equipment would be used under particularly dusty environmental conditions. Human activities also affect the environmental component. Humans are almost continuously engaged in activities during waking hours. Some activities are quite strenuous, such as manual labor or participation in sporting events, while others, like reading or typing, are much more sedate. Technology should be designed to accommodate typical or predictable human activities wherever possible. Consider, for example, the transatlantic air commuter who wants to read the latest mystery novel during an overnight flight. If the overhead reading light is not adjustable to provide adequate illumination of the pages, the passenger’s satisfaction level will be reduced. Although this design defect may not be a candidate for a tremendous amount of liability exposure, it is certainly easy to offer one that is. For example, the gymnasium floor in a high school must be designed to provide adequate slip resistance for all participants in all reasonably predictable sporting activities under all reasonably foreseeable conditions. Failure to provide adequate slip resistance is certain to lead to liability issues sooner or later. Even the presence of other humans must be taken into account when considering the environment. In many ways, humans can be very hazardous to other humans, even
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without intending to be. If a stairway is designed to accommodate 400 persons per hour based on the average projected stairway usage over an 8-hour period, it may not be capable of safely handling the pedestrian traffic at lunch time or quitting time. This phenomenon of pedestrians grouping into “platoons” is readily foreseeable and must be accounted for in the design of ingress and egress features, especially when emergency conditions are possible. Another similar situation straight from the headlines involves thousands of screaming rock fans trapping and crushing the helpless leaders of the pack against the improperly designed doors to a stadium shortly before the concert begins. Environmental lighting, whether artificial or natural, is a critical component in many systems. Because humans rely so heavily on visual information for survival, it is often critical to provide the right amount of light—not too much and not too little—in order to ensure system success. Automobile headlights that do not adequately illuminate the roadway are hazardous as may be those that are too bright or aimed in a manner that “blinds” oncoming vehicle operators. In either case, the liability issues will ultimately be related to improper illumination. As previously mentioned, unpleasant odors can be warnings of otherwise undetectable hazardous conditions. However, pleasant odors may not necessarily be indicative of safe conditions. Odor ants deliberately introduced into the environment with pleasing intentions, such as perfume and air fresheners, can trigger allergic reactions in some people and cause migraine headaches in others. It is also unwise, for example, to construct a restaurant downwind from a sewage treatment plant. As a rule of thumb, the controlled introduction of odorants for hazard warning into the human-technologyenvironment system should be sufficiently unpleasant to compel the desired reactive behavior but benign enough to ensure that the exposed persons are not injured or rendered ill. Conversely, the introduction of odorants to improve the olfactory experience should be controlled sufficiently to prevent allergic reaction or other conditions triggered by the odorant in predisposed persons. Toxins are generally poisonous substances, many of which produce unhealthy or injurious conditions in the human component of a system. Any system that uses or produces toxic substances must be designed to protect the human and environmental system components reasonably from exposure if such exposure is hazardous. Such design consideration must be given for all reasonable phases of the toxic substance’s reasonably foreseeable life, whether the toxic substance is a component or a byproduct of the process. 28.4 Examples With a little imagination, one can readily discover one or multiple hazards associated with just about anything that has ever been manufactured or constructed. For example: A victim alleges a broken neck as the result of having been struck on the head by a 5-oz box of facial tissue pushed off the top shelf of a display rack by an employee in an adjacent aisle. Sound impossible? Not so. At the time the individual was struck, the injured party was recovering from a previous injury involving the fusion of cervical vertebrae and the
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placement of alignment hardware to supplement the fusion. The individual’s autonomic response to the impact of the box of facial tissue was sufficiently violent to cause the structural failure of the implanted alignment hardware, which, in turn, gave rise to the failure of the fused vertebrae. A concrete saw operator falls into the saw’s unguarded rotating saw blade, which is still under motive power, incurring severe injuries that ultimately give rise to his death 2 days after the incident. Immediately prior to the incident, the operator was attempting to forcibly displace (push and/or pull) a feature in the workplace to facilitate the sawing procedure. Prior to doing so, the operator had neglected to turn off the saw or otherwise disengage the rotating blade. When he lost his footing, the operator fell backward into the high-speed rotating blade. Of course, this entire chapter could be devoted to listing such incidents. However, the point is that by emphasizing the human-centric approach, along with good design and engineering practices and system safety engineering concepts, a significant improvement can be made to the safety of any system. The benefit of increased system safety is reduced liability exposure for those responsible for introducing the technology into the human-environment-technology system interface. Furthermore, it is imperative that the forensic analysis of a potentially errant or defective system be appropriately bounded. That is, the focus of analysis must be sufficiently broad to encompass the relevant system reasonably while concurrently narrow enough to prevent dilution of the key liability issues. Rarely is it the case that the errant or defective system comprises a single human component, a single environmental component, and a single technological component. Consider the first example in this section. From a forensic perspective, it is relatively straightforward to assert that insufficiently retained or insufficiently contained merchandise, whether it is a box of facial tissues or a lawnmower, will fall if it is displaced from an overhead storage feature. The simple laws of physics will confirm this assertion rather quickly. Moreover, with a little knowledge of the relationship between kinetic energy and work, along with an understanding of the body’s biomechanical response to dynamic loading, it is possible to predict probable injury severity from such an impact. Given this information, it is possible to opine accurately that improperly stocked merchandise can cause injury to unsuspecting customers as a result of being struck by the merchandise if it is displaced and falls while the customer is in its fall trajectory. From physics we know that a direct proportion exists between the mass of a falling object and the kinetic energy attained through falling. Specifically, we know that the greater the mass is, the greater is the kinetic energy of the object. From the work-energy relationship we know that the greater the energy is, the greater is the force applied to the impacted target (the human component in this case). The foregoing is a relatively simple analysis of a falling merchandise incident. Many times it will be possible to establish that the merchandise could or should have been more adequately retained or contained, or perhaps should have been stored elsewhere.
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However, if the analysis ends there, it may not be complete because, for example, who gets hurt when struck by a 5-oz box of facial tissues? In this example, predisposing conditions greatly affect the liability of the retailer responsible for permitting the merchandise to become displaced. Through discovery in previous litigated matters with this defendant, it has become readily evident that the retailer has a computerized system that includes records for all falling merchandise claims made since the late 1980s. The sophistication of the data analysis capabilities of this retailer rivals that of the U.S. government and discovery reveals that literally thousands of falling merchandise claims have been made against the defendant, with many claims for very severe injuries, including multiple fatalities. Through discovery analysis, it has become clearly evident that this retailer has made its employees (human components of the retailer’s overall system) aware of the dangerous condition created by their stocking techniques for many years, but has not substantively changed its stocking and merchandising techniques (here are technological and environmental system component implications) to control or eliminate the hazard, even with the voluminous data quantifying the magnitude of this dangerous condition that are available to it. The point of this is that if the simple system of human-package of facial tissues-shelfand-stocking procedure becomes the primary focus for liability assessment, the liability for the retailer becomes questionable, and perhaps nonexistent, in the mind of the Court. After all, who really gets hurt when a 5-oz box of facial tissues falls 3 ft to the victim’s head? However, when the more applicable system of humans, technology, and environment is analyzed, the liability of the defendant becomes much more defined, more credible to the Court, and, ultimately, gives rise to a more significant assessment of liability for the errant retailer. Thus, in this example: • When the Court realizes that the retailer has had a computerized system that has provided it with access for many years to information regarding the severity of its falling merchandise hazard but has essentially adopted a policy of “paying off” victims rather than eliminating or controlling the blatantly obvious dangerous condition, the liability of this retailer in the “facial tissue matter” becomes significantly more credible. • When the Court hears that the merchandising system implemented by the retailer follows the philosophy established by its founder that stacking merchandise to the ceiling creates an increased desire in the customer to purchase the merchandise, the liability of this retailer in the “facial tissue matter” becomes significantly more credible. • When the Court hears that the retailer has systematically been less than forthcoming with its admissions about its notice of the hazard and its accuracy in the discovery process, the liability of this retailer in the “facial tissue matter” becomes significantly more credible. • When the Court hears that the retailer’s primary system for controlling the hazard of falling merchandise essentially involves its employees (the human component of the hazard control system) kicking the shelving (the environmental-technological system components) to see if merchandise (the technological system component) falls, the
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liability of this retailer in the “facial tissue matter” becomes significantly more credible. • When the Court hears that the retailer purposefully stocks the merchandise according to a system calculated to control the visual and cognitive focus of the customer (human system component) away from the potentially dangerous conditions on upper shelving units, the liability of this retailer in the “facial tissue matter” becomes significantly more credible. Consider also the second example. If the simple system of operator (human component), concrete saw (technological component), and workplace (environmental component) is considered without expanding the focus to include other not so obvious but highly relevant system components, relatively high liability exposure exists for the designer and manufacturer of the seemingly defectively designed concrete saw. However, by expanding the focus to include other system components, it was possible to establish that the liability was, in fact, not with the manufacturer but with the operator, who misused the product in a manner that was beyond the scope of reasonable predictability by the designer-manufacturer, as well as with the employer for failure to control the hazardous condition through supervisory methods and training. For example, it was possible to demonstrate to the Court that the proximate cause of the fatal injury was not product related, but rather related to multiple system failures outside the control of the saw’s manufacturer. This was accomplished by expanding the aforementioned simple system to include: • The lack of training by the operator’s employer (a procedural and/or technique system failure on the part of the employer) • The deliberate displacement of the blade guard by the operator (a failure of the human system component to follow reasonable procedures and a failure of the employer’s safety and supervisory systems) • The observation that the concrete surface being sawed (the environmental component of the system) was wet, which lowered the slip resistance of the working surface (another environmental system component) • The recognition that the task (technology-human interface of the system) undertaken by the operator at the time of injury significantly contributed to the failure of the operator to maintain a stable posture (another failure of the employer’s safety and supervision systems) Therefore, when the focus of investigation is broadened to include other relevant system components beyond the somewhat obvious, a much more credible case can be made. 28.5 Checklist The following is an illustration of various factors and topical considerations for those factors when applying the human-centric approach. Clearly, the factors and considerations can be further decomposed (a few examples have been included). Building this model will assist designers and others in ensuring that the essentials of human-centric approach are incorporated into their product and premises designs. Furthermore, continued development of the model, in breadth and depth, will reduce the time spent
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thinking of the issues, thereby providing more time to think about the issues. The obvious benefits for human-centric design are improved system safety, performance, and satisfaction. The benefits for the forensics professional are similar: more time can be spent thinking about the issues and their causal role in an incident vs. identifying the issues. Human-Centric Modeling Human categories Operator (user) Customer Acquirer Manufacturer Developer Designer Scientist Tester Installer Maintainer Executive Project manager Government Society Organization (public and private) General public Co-worker Human Facets Physical Anthropometries Upper Torso Head Neck Arms Chest Abdomen Lower torso Pelvic Legs Upper leg Lower leg Calf Muscles Ligaments Tendons Bones Tibia Fibula
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Ankle Foot Kinematics Physiological Sensory Visual Eye Cornea Aqueous humor Pupil Lens Vitreous humor Retina Optic nerve Brain Auditory Tactile Olfactory Taste Vestibular Proprioceptive Temperature Electrical Systems Metabolic Neurological Hormonal Digestive Cardiovascular Cardiopulmonary Immunological Neuromuscular Musculoskeletal Psychological Sensory data storage and analysis Memory Short term Long term Information processing Decision making Risk identification and assessment Biomechanical Pushing Pulling Lifting Twisting
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Turning Typing Pinching Grasping Impact Pressure Performance Measures Effects Aging Illness Injury Technology Knowledge Objects Machines Equipment Processes Procedures Techniques Organizational cultures Environment Climatic Temperature Humidity Wind Precipitation Cloud cover Earth Soil Soil condition Rock Volcano Vegetation Water Salt Fresh Moisture Ice Steam Air Quality Flow Barometric pressure Objects Humans Activities
747
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Toxins Light Odor Sound Defining Terms Danger—The relative exposure to a hazard; the opposite of safety. A hazard may be present but there may be little or no danger because of other circumstances, such as the absence of humans to be exposed to the danger. Thus, although the hazard exists, because its existence does not result in damage or injury, there is no danger. If a confined space contains poisonous gas, there is little danger to nearby workers if the containment system for the deadly gas is designed sufficiently to prevent their exposure to the hazard. Environment—The totality of surrounding things, conditions, or influences that have an effect on the system components’ performance and, thus, the system performance. These environmental characteristics can include, but are not limited to, social, cultural, organizational, and economic forces and influences; natural and artificial objects; other humans; other technologies, other living organisms; sensory inputs; weather; ambient temperature; ambient lighting conditions; the atmosphere; the Earth; the solar system; the galaxies; and the universe, which have an effect on the accomplishment of the desired or probable objective or outcome of the system. Pragmatically, some practical boundary must be placed on the number and types of environmental characteristics included in the list. That boundary, whether for design or forensic purposes, is determined by assessing which groups of environmental characteristics have the most significant effect on the system and, in particular, on the human component. Significance can be established by any number of measures, such as money or the potential for inflicting injury. The system always includes at least one environmental characteristic. Hazard—A condition or set of conditions that will cause personal injury and/or property damage as a result of system use or misuse. When a hazard is present, the possibility exists that injury or property damage will be the outcome, whether or not it is the desired outcome, of system operation. A confined space filled with poisonous gas is a hazardous condition. Human—The individual or the group of individuals affected by the system or having an effect on the system. One of those individuals is often referred to as the “user” or “operator,” but that is not the only relevant person in a system. For example, it takes more than a pilot to fly a plane, particularly a complex aircraft. Other, and sometimes more important, individuals, depending on one’s perspective, include the people who
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decided to have the plane built, designers, people who managed the design process, manufacturer management team, people performing the manufacturing, people responsible for maintaining and inspecting the plane and its myriad systems, person responsible for in-flight systems management, ground crew, air traffic control personnel, passengers…the list goes on. The same is true for any system. Theoretically, the human race could be listed. Pragmatically, some practical boundary must be placed on the number and types of persons included in the list. That boundary, whether for design or forensic purposes, is determined by assessing which groups of persons have the most significant effect on the system and which are most significantly affected by the system. Significance can be established by any number of measures, such as money or injury nature and severity. The system always includes at least one human being who is affected by the system. Every system is conceived, designed, developed, implemented, and/or maintained by a human for the purpose of meeting a human need, whether or not the value of that need is agreed upon. Interaction—Refers to the reciprocal action, effect, or influence one or more components have on one or more other components. Interface—Refers to the boundary or connection between components; a point or means of interaction between two or more system components. Interfaces may be tangible or intangible and may exist as the result of neglect or design. Either tangible or intangible interfaces may have a beneficial, detrimental, or insignificant effect on the component or system performance. Risk—The probability (sometimes quantitative and sometimes qualitative) of loss or injury as a result of ongoing system operation. The risk associated with continued system operation in which the o-rings used for containment of deadly gases in a confined space are degraded is relatively high if humans are nearby. The more humans present and the greater their proximity to released gases upon o-ring failure is, the greater is the risk. Safety—In its purest form, safety is the absolute freedom from exposure to hazardous conditions. In practical terms, it is more appropriate to define safety as a reasonable level of protection from hazardous conditions. System—The combination of the human, technological, and environmental components; the component interactions; and the component interfaces that generally creates a means by which the desired or probable system objective or outcome can be accomplished. A practical example of a simple human-centric perspective system would be a person brushing his teeth. Of course, the person manipulating the toothbrush (the “user”) is a human component. Other important human elements would include the toothbrush designer, manufacturer, advertiser, and seller; the dentist or oral hygienist who may have recommended the toothbrush; the dentist who examines the teeth; and so on. The toothbrush (an object) is
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certainly a technological component. Other important technologies include the design process; the manufacturing process, including quality control and testing; knowledge of when and how to use the toothbrush as well as transmittal of that knowledge to the user; the dentist; and the oral hygienist. Warnings regarding toothbrush use and misuse may be important. Knowledge of what to look for regarding misuse of the toothbrush would be important. Characteristics such as the bathroom, toothpaste, artificial lighting, and all surrounding features, whether natural or artificial, represent portions of the environmental component. Technology—The individual or multiple system components including concepts, knowledge, equipment, machines, processes, procedures, methods, and/or manipulated objects that are generally utilized by the human components or have an effect on the human components. Important: technology is not restricted to tangible objects. Theoretically, as with the human component, quite an extensive list of technological components could be compiled. Pragmatically, some practical boundary must be placed on the number and types of technologies included in the list. That boundary, whether for design or forensic purposes, is determined by assessing which groups of technologies have the most significant effect on the system and, in particular, on the human component. Significance can be established by any number of measures, such as money or the potential for inflicting injury. The system always includes at least one technology.
Reference Hollnagel, E. (Ed). (2003). Handbook of Cognitive Task Design . Mahwah, NJ: Lawrence Erlbaum Associates. Further Information Chapman, W., A.T.Bahill, and A.W.Wymore. (1992). Engineering Modeling and Design . Boca Raton, FL: CRC Press. Dresser, D. (2001). AnthroCalc Software . Tucson, AZ: Lawyers & Judges Publishing. Konz, S. and S.Johnson. (2004). Work Design—Occupational Ergonomics . Scottsdale, AZ: Holcomb Hathaway. Sage, A. and W.Rouse. (1999). Handbook of Systems Engineering and Management . New York: John Wiley & Sons. Salvendy, G. (1997). Handbook of Human Factors and Ergonomics , 2nd ed. New York: John Wiley & Sons. Sanders, M. and E.McCormick. (1993). Human Factors in Engineering and Design . New York: McGraw-Hill, Inc. Schraagen, J.M., S.F.Chipman, and V.L.Shalin (Eds.). (2000). Cognitive Task Analysis . Mahwah, NJ: Lawrence Erlbaum Associates. Stephans, R.A. and W.W.Talso (Eds.). (1993). System safety society, in System Safety Analysis Handbook , Albuquerque, NM.
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Tilley, A. (1993). The Measure of Man and Woman . New York: The Whitney Library of Design. Wickens, C., J.Lee, Y.Liu, and S.Becker. (2004). An Introduction to Human Factors Engineering , 2nd ed. Upper Saddle River, NJ: Pearson Prentice Hall. Woodson, W., B.Tillman, and P.Tillman. (1992). Human Factors Design Handbook , 2nd ed. New York: McGraw-Hill, Inc. Wymore, A. (1993). Model-Based Systems Engineering . Boca Raton, FL: CRC Press.
Appendix A: System Safety Engineering System safety engineering is the branch of engineering devoted to ensuring that systems are designed, constructed, marketed, installed, operated, maintained and repaired, and recycled with optimum safe-guarding against injury and/or property damage. A fundamental precept within system safety engineering practice is the recognition that the elimination or reasonable control of hazardous conditions will reduce the probability of personal injury or property damage arising from system use or misuse. Specifically, the elimination or reasonable control of hazardous conditions will eliminate the danger of system operation and reduce or eliminate the risk associated with ongoing system operation. Reviewing the contextual definitions for the terms danger-, hazard, risk, and safety, in addition to the terms system, human, technology, environment, interaction, and interface will assist in gaining a better understanding of the role of systems safety in the humancentric approach to design and forensics analysis. (Refer to the definitions section.) The classical (and still reliable) methodology used for hazard analysis consists of the following steps: 1. The hazard must be identified. Some hazards are relatively obvious, but others may be subtle to the point that they may be overlooked. A variety of techniques for hazard identification are explained in detail in other works, including but not limited to those listed in the suggested bibliography; these are beyond the scope of this chapter. The level of sophistication and effort to identify hazards should be commensurate with the level of complexity and sophistication of the system. A human-occupied spacecraft requires a great deal more scrutiny for hazards than does a lawnmower, although each is capable of inflicting potentially fatal injuries upon the user. 2. Each hazard must be evaluated regarding its relative severity level. For example, the expected severity of exposure to the hazard of falling off an improperly designed subway platform just as the train enters the station is significantly greater than the hazard of smashing one’s thumb with a hammer. It is therefore helpful to categorize the levels of hazard severity and the probability of hazard exposure to determine the required emphasis to be placed on hazard elimination or control in any given system. It is useful to classify as the first parameter the relative severity of a hazard, which is usually related to the expected or predictable consequence of hazard exposure. Here, we define four categories, which describe increasingly more dire consequences as the category numbers increase in value. Higher severity generates an increase in the need for hazard control or elimination to reduce the danger of system operation. Category I—Negligible: hazards will not result in injury or occupational illness. Category II—Marginal: hazards may cause minor injury or minor occupational illness.
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Category III—Critical: hazards may cause severe injury or severe occupational illness. Category IV—Catastrophic: hazards may cause death. The second parameter to classify is the qualitative probability of occurrence, which has six categories: Qualitative Level Description probability Impossible Extremely improbable Remote
1 2 3
Occasional
4
Reasonably probable Frequent
5 6
Physically impossible to occur Probability of occurrence cannot be distinguished from zero; so improbable that it can be assumed that injury will never be experienced So improbable that it can be assumed that this will not be experienced by a specific individual, but for a group of individuals, it is unlikely to occur but possible Unlikely to occur for one specific individual but may occur several times for a group of persons Will occur several times for each individual and will occur frequently for a group of individuals Likely to occur frequently for an individual and continuously for a group of individuals
With these parameters, we can create a matrix that qualitatively defines the relative urgency for design or engineering intervention to eliminate or control system hazards.
TABLE A1 Hazard Severity Index
Notes: The values in the “combinations permitted” and the “combinations not permitted” cells are calculated by multiplying the category value (1, 2, 3, or 4) by the qualitative probability of exposure value (1, 2, 3, 4, 5, or 6). Thus, a hazard severity index of 9 or greater would not be permissible. A hazard severity level lower than 9, although permissible, might expose those responsible for reducing system liability issues to undesirable liability consequences, with progressively more costly consequences as the index number approaches 9. The third element of hazard analysis is the process of eliminating or adequately controlling hazards to prevent or significantly reduce the probability of injury or property damage resulting from hazard exposure. The best way to prevent injury or property damage is, through design, completely
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to eliminate the hazard from the system. An example of hazard elimination is the reduction of operating voltage for an electrical system. If the operating voltage can be reduced to a level below that fatal to human beings, the hazard of electrocution will have been effectively eliminated. The next best method for preventing injury or property damage is to control the hazard in a manner that reliably ensures that hazard exposure is highly improbable. For example, if the operating voltage cannot be lowered beneath lethal levels, then a durable guard that is reliably interlocked can be implemented to ensure hazard control. With this hazard control system, the human component of the system is safeguarded from hazard exposure by the guard. If the guard is removed, the interlock feature disables the system and removes the electrical hazard. The next best method for preventing injury or property damage after controlling the hazard is through administrative controls. For example, if the operating voltage cannot be lowered beneath lethal levels or a durable, reliably interlocked guard cannot be installed, then procedures can be devised to minimize the risk of exposure to the lethal hazard. With this hazard control system, the human component’s ability to comply with the procedures is the system safeguard. The least reliable method for preventing injury or property damage involves warning the human system component of the hazard’s existence and instructing the human component in hazard avoidance behavior modifications. Hazard control should only be relegated to warning when there is absolutely no alternative because warnings rely upon the user to remain 100% hazard vigilant 100% of the time, which is an unrealistic expectation.
29 Product Liability for the Human Factors Practitioner Ron Wardell University of Calgary 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
29.1 Introduction Product liability cases in the media often raise questions about the logic and justice behind the decision, as well as about the role of human factors practitioners in liability prevention. What we first need to understand is that legal decisions are based on specific theories in law in force in the particular jurisdiction and at the particular time. These are not theories in the scientific sense of empirically tested frameworks of cause and effect, but rather statements of what considerations are deemed relevant and admissible to the legal argument based on philosophical, social, and political positions. The theory in force varies with the place and the time. The product liability case is initiated on the grounds of one or more of the theories acceptable to the court. We will first introduce the range of theories that exist, then comment on international variations, and lastly suggest how the human factors practitioner can contribute to product liability prevention. This presentation is intended to provide a simplified layperson’s introduction to the topic and does not replace the expert advice of a qualified professional in the jurisdiction in question. 29.2 Theories The three primary theories for product liability are negligence, strict liability, and no-fault compensation; two lesser theories are implied warranty, and express warranty and misrepresentation (Epstein, 1980; OECD, 1995; Kolb and Ross, 1980; Wilson and Corlett, 1995; Wilson, 1984). All of these also require the demonstration of harm to the plaintiff, for which the product is the proximate cause. Negligence As the name suggests, the theory of negligence admits the question of whether the defendant was negligent in some way that resulted in an unreasonably great risk of
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causing harm. The defendant may be deemed negligent if he or she failed to exercise ordinary or reasonable care. The terms “ordinary” and “reasonable” have particular meanings in law that recognize that the plaintiff need not do everything possible at whatever cost, but rather is expected to do what is commonly done and what can be done at reasonable effort. What is considered ordinary and reasonable is a judgment of the court in each individual case. One of the common expectations for reasonable care is to use new developments that reduce risk; this places an onus on the designer and manufacturer to stay abreast of developments in their product technology. A related issue is the state-of-the-art defense that, in some jurisdictions, does not hold defendants liable for hazards that were unknown with the best available information at the time at which the product was produced. Strict Liability In contrast to the negligence theory, strict liability is concerned about the quality of the product rather than the action of producer. Harm can occur if a product is inherently dangerous. Strict liability addresses the fact that, if harm has been done, someone needs to pay for the damages. The costs of the harm are shifted to those who are capable of paying, namely, those who stand to profit from the commercial existence of the product. This extends the potential defendants to include the whole chain of designer, manufacturer, distributor, wholesaler, and retailer according to who has the deepest pockets. In line with the notion that those who profit from a product should be strictly liable for harms that may arise, the conduct of the defendant is not at issue and they may be deemed liable regardless of having exercised reasonable care. Similarly, a disclaimer that attempts to limit the exposure of the defendant may not prevent a claim. No-Fault Compensation The no-fault compensation system does not need to prove fault on the part of the supplier or manufacturer or on the part of the perpetrator of an incident. Instead, the question is only whether the victim suffered personal injury. If this is proven, then compensation is provided from Social Security or other insurance funds. This system is argued to reduce legal costs and time delays. Implied Warranty The theory of implied warranty states that products must be fit for the ordinary purposes for which such goods are used. The warranty is implied by the normal expectations about the nature of the product. This is sometimes referred to as “merchantability.” If the harm occurs when a product is used in the normal manner for such a product, then liability may be concluded. The ergonomic question raised that will be addressed again later is how one establishes the ordinary use of a product. For example, are screwdrivers “ordinarily” used as pry bars and should liability be a possibility if a person is harmed while using a screwdriver as a pry bar—even though this is not the primary intended use of the product? A disclaimer about the appropriate use of the product may or may not be a sufficient defense.
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Express Warranty and Misrepresentation An implied warranty arises simply from the ordinary expectations for a product; an express warranty is an explicit statement by the defendant about the safety of the product. If the harm can be shown to be a failure by the product to satisfy this explicit statement, then liability under the express warranty theory could be established. This is the one theory for which it is not necessary to prove that the product was defective; it is only necessary to prove that the express claim was not met. 29.3 Product Defect Under all theories except express warranty, it is necessary to prove that the product was defective. The occurrence of an injury is necessary but not sufficient. The product defect can be a flaw in the manufacturing process, as when a particular product does not meet the manufacturer’s design standard, or a flaw in the design itself. The judgment that a product was defective, however, is a complicated matter. It is not sufficient to show that the product was dangerous because many products, such as knives, are necessarily and inherently dangerous. Rather, the product must be shown to be “unreasonably dangerous” because all products present some risk. Whether the danger in a product is unreasonable is a balance of risk against usefulness and cost. Some of the factors that might be argued to evaluate this balance include: • Is the product useful and desirable because of its characteristics so that its risk is accepted by the user? For example, a knife is useful and desirable because of its ability to cut and the risk of being cut is known to the user. An unnecessarily sharp edge on another product might pose an unacceptable risk. • Are other, safer products available for the same use? For example, a safety razor is available and safer than a straight razor for the purpose of shaving. • What is the likelihood of injury and its probable seriousness? For example, suffering a nick while shaving is fairly likely but not very serious, so this risk may be acceptable. • Is the danger obvious and/or what is the extent of warnings of the danger? (We will comment on warnings later.) • What is the common knowledge and normal public expectation about such products? A danger that is not obvious, not warned, and not commonly known may be deemed unreasonable. • Can injury be avoided by care in use? This point raises the question of whether the plaintiff and defendant are considered to share responsibility for the injury if it can be shown that the user is partially to blame. Rules for this vary from contributory negligence to comparative liability, ranging from no liability if the user is responsible beyond a certain threshold percentage of fault to a reduction in compensation proportional to the distribution in fault. • Is it possible to eliminate the danger without seriously impairing the usefulness or incurring excessive expense? The factors considered in the judgment of a product defect depend on the jurisdiction and present state of the law. For example, an alternative list is given in Ryan (1983). Some points require careful consideration; for example, at one time, according to the Campo
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doctrine, the potential for liability may actually increase if, in designing to reduce a hazard (e.g., by guarding machinery), the danger becomes less evident (e.g., by the worker perceiving the machine to be safer than it actually might be). 29.4 International Trends The applications of product liability theories at a given place and time are continuously evolving. They depend not only on the prevailing social and political will, but also on interactions with other conditions such as the social welfare system and the rules for the practice of law. The Organization for Economic Co-operation and Development surveyed 20 countries to explore issues in product liability and international diversity (OECD, 1995). They concluded that no country has adopted one of the three primary theories “in [its] pure form”; rather, they use hybrid systems with varying degrees of emphasis and technical refinements. In addition to the relative emphasis on different doctrines of liability, different countries also vary in other respects that affect the practice of product liability law. Because these are less directly important to the practice of human factors, without elaboration, they include: • Joint and several liability: rules for cases with multiple defendants • Statutes of repose: rules for limitations on the delay in initiating an action • Damages: rules for types of compensation and limits on compensation, including noneconomic damages such as pain and suffering, hedonic compensation, and punitive damages • Judge vs. jury trials • Attorney compensation, particularly contingency fees • Distribution of legal costs for defendants and plaintiffs • Attorney advertising • Option of class-action suits • Nonlitigation alternatives and their national or cultural acceptance As examples, the U.S. largely follows strict liability, with variations among the states. This, combined with contingency fees for attorneys, jury trials, pretrial discovery procedures, and noneconomic damages, produces a litigious environment that has dampened innovation (OECD, 1995). Other evidence indicates that some companies have responded by improving and redesigning product lines. By contrast, Canada is more oriented to negligence theory and New Zealand has adopted a no-fault system. Another complication in the international situation arises when the damage occurs in a country other than that of the source producer. Because a suit is executed in the place where the injury occurred, it can be difficult to lay claim or to enforce a judgment against a foreign defendant. The claim may only be effective against the local distributor.
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29.5 Implications for the Designer and Human Factors Practitioner The actions and expectations of the user are important to safety and to liability judgments. The human factors practitioner, therefore, has essential expertise and roles in making products safer and in contributing to liability prevention. He also has a reactive role in providing expertise to the plaintiff or defendant in a liability case. Proactive Practices Some of the practices that can be proactive in reducing liability exposure follow. A similar set of guidelines is given by Cushman and Rosenberg (1991). • Be aware of the current rules for product liability for your venue. If negligence receives emphasis, then your conduct may be in question. You need then to act in ways that make the product safer and to be able to demonstrate that you took reasonable care. If strict liability is operative, then be aware of the potential constraints on innovation and be prepared to argue for product improvement. Although safe design practices may not be a defense if a suit occurs under strict liability, a product that is inherently safer should reduce the likelihood that an incident would occur that would lead to a suit. • Document your work so that you can mount a defense of exercising reasonable care on your part and of objectively describing a reasonable user. Records should be kept of test information, safety analyses, regulations and standards used, safety and consumer information on similar products or previous models, design of manuals and warnings, and the process for design decisions and trade-offs. • Know the user because part of the judgment of product defect is a comparison of the product to ordinary knowledge and expectations. All of the aspects of human factors and ergonomics are potentially relevant aspects of knowledge of the user. The human factors areas of perception, cognition and motivation, and their interaction are all important. The accident sequence model (Ramsey, 1978, as cited by Sanders and McCormick, 1987; Cushman and Rosenberg, 1991) shows how unsafe behavior can result from failures in the perception of a hazard, the cognition of a hazard, the decision to avoid, and the ability to avoid. Knowing the users’ abilities in these areas is necessary to designing within their limitations and expectations (Drury and Brill, 1983). The ergonomic areas of anthropometry, biomechanics, anatomy, physiology, and physical environment may also be important. For example, a particular body dimension may be important for reach or clearance, as illustrated by the standards for part size on products for children (see ASTM, 2003). Similarly, knowing the potential user’s strength, work capacity, and functional anatomy can be important. This is, of course, standard human factors and ergonomic design practice; the emphasis for liability prevention is on detailed knowledge about the particular potential user. • If your new design departs from normal products of that type, then pay particular care to draw the user’s attention to the differences and to prevent dangerous actions. Go beyond the common stereotypes for controls and displays to the specific expectations for the type of product.
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• Design for foreseeable misuse. This can be done by thinking through slips and mistakes that might arise in the user’s perception, cognition, attention, expectations, and mental set. The various models for human error can be useful, for example, Rasmussen’s classification of human performance and corresponding sources of error (Hoyos and Zimolong, 1988). • Conduct user testing. The testing should (1) compare the designer’s expectation of use against the actual uses, as an indicator of foreseeable misuse; (2) test the safety of intended and unintended uses; and (3) test compliance with applicable standards and regulations. Independent testing has additional value as impartial verification. • Design over the product life (Cushman and Rosenberg, 1991). Failures early in the product’s life are commonly related to part failure and quality control and assurance. Failures in the middle life are often due to environmental stress or unusual uses not considered in design. Failures in the late life result from wear and tear. Analyze the safety hazards of these different types of failures. • Conduct safety analyses such as failure mode and effects and/or preliminary hazard analysis (Cushman and Rosenberg, 1991; Vincoli, 1993). Stobbe and Plummer (1982) provide examples of these methods. • Use the latest information on warnings, labels, and instructions. Although some research indicates that these have little effect, they are legally prudent (Godfrey et al., 1983). Warnings are a regular topic in the proceedings of the annual meetings of the Human Factors and Ergonomics Society. • Use applicable standards. Standards provide a minimum consensus of the state of knowledge; as a minimum, they are not necessarily sufficient or a defense. Reactive Approaches Knee and colleagues (1987) identify two sets of defenses for product liability cases. The first set attempts to negate the plaintiff’s claims. The defense may assert that the manufacturer was not negligent and acted prudently in the design and manufacture of the product with evidence from the records mentioned earlier. The defense may assert that the product was not unreasonably dangerous as demonstrated by compliance with regulations and standards, open and obvious hazards, or other arguments under the balance of risk and benefit that determines whether a product is defective. Taking the issue away from the product, the defense may assert that the product was not the proximate cause of the harm, or that the product at the time of the incident was not in the condition in which it was manufactured, for example, due to modification by others. The other approach to lessen the liability burden is to attribute the situation to the user’s behavior or that of a third party, in whole or in part. The defense asserts that the user assumed the responsibility for the risk and his or her conduct contributed to the outcome. Alternatively, a third party was involved that contributed to the incident by his conduct, for example, by failing to warn or to follow codes of practice or regulations. The role of the human factors specialist can be to report prudent conduct through proactive practices such as those listed earlier and to analyze the case retrospectively. The latter activity looks at what could have contributed to the incident, whereas the proactive practice looks at what might happen. The proactive approach may use methods such as failure mode and effects analysis to analyze potential hazards; the reactive approach
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needs to use methods such as incident investigation. Some of the safety analysis models can be used to investigate possible contributing human factors; for example, the accident sequence model (Ramsey, 1978, as cited by Sanders and McCormick, 1987; Cushman and Rosenberg, 1991) provides a model to look for failures in the perception of a hazard, the cognition of a hazard, the decision to avoid, and the ability to avoid. 29.6 Conclusion Ergonomics and human factors can make products safer, but that is not the same thing as protecting the designer and manufacturer from liability. The five possible theories for product liability (negligence, strict liability, no fault, implied warranty, and express warranty) are applied variously in different countries and jurisdictions. Under the negligence theory, proactive liability prevention is a driving force for practices that not only produce safer products but also demonstrate due care in design and manufacture. The onus is increased on knowledge about the users and their behavior, capabilities, limitations, and expectations. There is a need to use proactive analysis methods that identify potential hazards and for documented resolution of these hazards in the design. In jurisdictions that emphasize strict liability, care is not enough to defend against a claim. Then the hope is that human factors and ergonomics can produce safer products that reduce the chance of an incident. Either way, sound human factors practice is an essential part of liability prevention for the manufacturer and of liability attribution for consumers. References ASTM. (2003). F963–03 Standard Consumer Safety Specification for Toy Safety. ASTM International. Cushman, W.H. and Rosenberg, D.J. (1991). Human Factors in Product Design . Amsterdam: Elsevier. Drury, C.G. and Brill, M. (1983). Human factors in consumer product accident investigation. Hum. Factors , 25, 329–342. Epstein, R.A. (1980). Modern Products Liability Law . Westport, CT: Quorum Books of Greenwood Press. Godfrey, S.S., Allender, L, Laughery, K.R., and Smith, V.L. (1983). Warning messages: will the consumer bother to look? In Proc. Hum. Factors Soc. 27th Annu. Meeting (950–954). Hoyos, C.G. and Zimolong, B. (1988). Occupational Safety and Accident Prevention . Amsterdam: Elsevier. Knee, H.E., Terranova, M., Carter, R.J., and Haas, P.M. (1987). Utilization of a reverse systems engineering approach for the assessment of defendant’s positions in product liability cases. In Proc. Hum. Factors Soc. 31st Annu. Meeting (605–609). Kolb, J. and Ross, S.S. (1980). Product Safety and Liability . New York: McGraw-Hill. OECD. (1995). Product Liability Rules in OECD Countries . Paris, France: Organization for Economic Cooperation and Development. Ryan, J.P. (1983). Human factors design criteria for safe use of consumer products. In Proc. Hum. Factors Soc. 27th Annu. Meeting (811–815).
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Sanders, M.S. and McCormick, E.J. (1987). Human Factors in Engineering and Design (6th ed.). Toronto: McGraw-Hill. Stobbe, T.J. and Plummer, R.W. (1982). Case study: ergonomic and hazard evaluation of a new consumer product. In Proc. Hum. Factors Soc. 26th Annu. Meeting (515–519). Vincoli, J.W. (1993). Basic Guide to System Safety . New York: Van Nostrand Reinhold. Wilson, J.R. (1984). Design and development of safer consumer products in the United Kingdom. Proc. 1984 Int. Conf. Occup. Ergonomics , 67–71. Wilson, J.R. and Corlett, E.N. (1995). Evaluation of Human Work (2nd ed.). London: Taylor & Francis. Wilson, J.R. and Kirk, N.S. (1980). Ergonomics and product liability. Appl. Ergonomics , 11, 130– 136.
30 The Warning Expert Kenneth R.Laughery Rice University Michael S.Wogalter North Carolina State University 0–4150–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
30.1 Introduction In recent years, human factors and ergonomics specialists have increasingly filled the role of a warning expert in civil litigation. Such litigation usually involves personal injury and product liability cases. Questions typically addressed by the warning expert are: • Is a warning needed? • Is an existing warning or warning system adequate? • What would an adequate warning system be? • Would an adequate warning system make a difference (effectiveness)? In this chapter, we will review a few of the rules that govern product liability as it pertains to warnings. We will then address several topics regarding the warning expert, including the expert’s role, the definition of a warning expert, typical activities of the warning expert, and problems or issues associated with being a warning expert. 30.2 Some Rules Related to Warnings In this section, we will comment on some of the rules that govern product liability as it pertains to warnings. For more complete coverage of the law relating to warnings, see Madden (1999). The manufacturer is generally considered to have the greatest expertise regarding risks associated with its products. Conversely, a consumer or user is considered less informed about the risks of product use than the manufacturer or seller. The manufacturer is held to be expert on how the product is used and to be knowledgeable of developments and the state of the art of the industry at the time the product was manufactured. This “should know” standard carries the burden of determining product dangers and providing warnings about foreseeable dangers from foreseeable uses as well as foreseeable misuses. Thus, this standard requires a manufacturer to anticipate how the product will be used
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and misused (uses incidental to those intended). Reciprocal logic dictates that when injury results from unforeseeable uses or misuses, the manufacturer is generally not held responsible. Under common court rules of product liability, product manufacturers have an obligation to provide warnings sufficient to permit a product to be used safely or for an informed decision to be made not to use the product. Over the past several decades, this duty has developed on the basis of a large number of decisions brought in state and federal courts, which in turn have been developed into a collection of rules and doctrines called The Restatement (Second) of Torts and the Restatement (Third) of Torts. The claim that a manufacturer has failed to provide adequate warnings has been increasingly common in product liability litigation. The restatements contain several warnings doctrines. A product can be found defective because of defective warnings or instructions when the foreseeable risks of harm could have been reduced or avoided by the manufacturer or seller providing reasonable instructions or warnings. Omission of necessary warnings and instructions renders the product not reasonably safe (or, similarly, unreasonably dangerous). A warning must be communicated so as to permit ordinary users to use a product safely or to avoid the risk. It is not always the case that the injured party needs to be warned directly. A bystander hit by debris from a lawnmower would typically not be warned directly by the manufacturer. Rather, the warning needed to be directed to the product user who, in turn, should have taken measures to avoid injury to others. Similarly, the doctrine of the learned intermediary has been used in cases such as those involving prescription drugs, in which, under many circumstances, the manufacturer’s obligation traditionally has been to communicate risks to prescribing doctors, who in turn decide how the risks are controlled. Generally, common law courts have ruled that there is no duty to warn of obviously hazardous conditions. The concept of “open and obvious” typically refers to circumstances in which the appearance or function of a product communicates the necessary hazard information. Similarly, hazards that are common knowledge such as knives and darts may not be deemed defective without a warning. An exception to these open-and-obvious and common-knowledge circumstances may be situations in which a warning is needed as a reminder; that is, the purpose of the warning is to direct the product user’s attention to the hazard at the critical point in time. The visual and auditory seat belt signals in automobiles are intended as reminders. Usually, there is no duty to warn members of a trade or profession against dangers generally known to that group. This professional user doctrine follows from the “no duty to warn” doctrine about known or obvious dangers because of training or experience. Presumptive familiarity with the hazards associated with a job depends on whether pertinent product safety information has reached the individual using or exposed to the product. This presumption relates to the manufacturer knowing how the product is used and whether warnings are provided to the end user or those exposed. It is not simply whether or not a warning is given that decides the fate of a product liability claim. A warning that is given must be considered adequate; otherwise, the warning is defective and thus the product is defective. For a warning to be adequate in the legal sense, it must render the product reasonably safe for its intended and foreseeable
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uses and misuses. The adequacy of a warning considers the product’s form and its content. As mentioned earlier, manufacturers are held to the state of the art concerning their products when the product was manufactured. Tort law has said that defective warnings make a product defective. This would indicate the importance of manufacturers considering the state of the art of warnings. Many companies do not make use of current standards, guidelines, and scientific research on warnings. Many use warnings based on industry custom (copycats) without considering the warning literature or subjecting warnings to testing to evaluate their effectiveness. The guiding inquiry is whether the warning design is effective in providing persons in the target audience with informed consent about risks and how to avoid them. Warnings can be evaluated to determine whether they are effective or whether alternatives might be better. Increasingly, the plaintiff and defense sides of product liability cases are using human factors experts in evaluating the warning obligation and the adequacy of warnings given. It would seem imprudent in the current litigation environment for a manufacturer not to evaluate the effectiveness of its warnings, not only for the primary purpose of enhancing safety but also for the purpose of knowing how its product might be judged with respect to future injury claims. The next section considers the role of a human factors expert in warning cases. 30.3 The Warning Expert’s Role The role of the warning expert can be characterized along two dimensions: the formal and informal. The formal role is essentially defined by the law or by the courts. The informal role refers to the activities or tasks actually carried out by the expert. The Formal Role There are three Federal Rules of Evidence to be noted regarding the expert’s role: Rule 702. If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education may testify thereto in the form of an opinion or otherwise. Rule 703. The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence. Rule 403 (the “balancing” rule). Although relevant, evidence may be excluded if its probative value is substantially outweighed by the danger of unfair prejudice; confusion of the issues; misleading the jury; or by considerations of undue delay, waste of time, or needless presentation of cumulative evidence.
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Thus, the expert’s role is to educate the trier of fact (the judge and/or jury) with regard to information that is beyond his “common sense” or personal experience. The expert must be impartial and must not demonstrate an interest in the outcome of the case. Although the expert is employed by one side in a case (plaintiff or defense) and may form attitudes or opinions about the distribution of fault or blame, the role calls for neutrality. The Informal Role Generally, the expert in a case does not simply examine facts and express opinions. Many other types of activities are carried out in working on a case. The informal role may include serving as a consultant, analyst, investigator, researcher, and/or report writer. Often when contacting a warning expert for possible work on a case, an attorney will not have a clear understanding of what the expert has to offer regarding the warnings issues. In such instances, the expert may function as a consultant regarding the nature of such expertise and what he or she can and cannot do. For example, for a given set of circumstances, it may be possible to determine that a warning was needed when none was provided or that a given warning was inadequate. However, it may not be possible to develop an exemplar of an adequate warning given the available information. The inhalation hazard associated with a chemical solvent may not be adequately addressed in a warning, but the development of a complete warning system for such a product might require other information such as ingestion and skin contact hazards. The warning expert is frequently an advisor, analyst, investigator, and/or researcher (data collector). Often the warnings issues in a case are not as simple as whether or not a warning on a product label or a sign is adequate. Rather, the various media through which such information was, could have been, or should have been communicated must be determined and assessed. Furthermore, the knowledge the target audience already had is relevant. This target knowledge is an example of when an expert may collect such data, thus functioning as a kind of researcher. Frequently, experts are asked for or required to submit a written report. In such reports, experts indicate their opinions and the basis of those opinions. Given the adversarial context of litigation, one can expect that such reports will receive extensive examination and critique, including scrutiny by others with similar expertise. 30.4 Defining the Warning Expert What qualifies a person to be a warning expert? Many people give expert testimony on warnings; not all are qualified. In the following subsections, we discuss what constitutes a warning expert and who is not a warning expert. Who Is a Warning Expert? Rule 702 states that a person may qualify as an expert on the basis of knowledge, skill, experience, training, or education. Advanced academic degrees or specific kinds of experience are not necessarily required. An experienced auto mechanic with limited formal education might be accepted as an expert witness on some subject of auto repair.
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A university professor in mechanical engineering may have never designed an internal combustion engine (or any other engine), but he or she may be qualified on the basis of education and knowledge. Ultimately, the issue of whether a person is qualified to testify as an expert is decided by the court. What education, knowledge, experience, etc. should a warning expert have? A degree in warnings obviously is not a criterion because such degrees do not exist. Some answers may be gleaned from noting what a warning is. It is a communication. It has the purpose of attracting attention and providing information about hazards, consequences, and instructions. It is also intended to influence people’s behavior appropriately. Warnings are also displays. From this perspective, developing or evaluating a warning requires information about hazards, consequences, and appropriate forms of behavior as well as knowledge about how such information should be communicated or displayed in order to influence behavior. This set of requirements may seem substantial (and it is), but a closer look reveals a workable definition of the warning expert. First, information about hazards, consequences, and appropriate behaviors is generally not the bailiwick of the warnings person; instead, these are matters about which warning experts make assumptions based on information from engineers, toxicologists, safety professionals, etc. The warnings person does not have expertise in the physiological reactions to breathing the vapors of a chemical solvent or the center of gravity and handling dynamics of an off-road vehicle. Such information is typically gleaned from other experts or technical literature. The relevant expertise for the warning expert is communications, displays, and human behavior. Thus, psychologists, human factors specialists and ergonomists, and people in the field of communications represent the most likely pool of people with such expertise. Whatever the pool is from which a warning expert is drawn, the expert should have certain specifics in his bag of knowledge and methodological tools. The first arena of knowledge is a thorough familiarity with the substantial body of scientific, peer-re viewed research literature that has emerged over the past two decades. For a review, see Wogalter and Laughery (this volume). This literature provides a basis for understanding the issues associated with warnings design and effectiveness. Expertise should also include relevant methodologies such as hazard, fault-tree, and failure-modes analyses; task analysis; display design; and data collection and analysis techniques. Another important knowledge domain is human cognition—that is, how people process information. The earlier work of Lehto and Miller (1986) has been important, in part, for its emphasis on the cognitive perspective. Who Is Not a Warning Expert? The preceding suggestions and criteria regarding warning expertise need to be supplemented with a few observations about who is not a warning expert. Examples would be: A mechanical engineer with expertise in vehicle design, vehicle dynamics, and the hazards associated with uses of vehicles may be an outstanding engineering expert, but that knowledge does not qualify him as an expert on warning about these hazards.
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A toxicologist or physician may have excellent knowledge about illnesses or diseases associated with exposure to chemicals and may qualify as an expert on these topics, but such knowledge does not qualify him to be a warning expert. A person who has produced warnings (perhaps many) in his career, which by most criteria are not very good, is not necessarily a warning expert. These examples, of course, are not intended to be critical of mechanical engineers, toxicologists, or physicians. The intent is to help clarify what a warning expert is, or should be. Experience indicates that people with a wide variety of credentials and experiences have been permitted to give expert testimony about warnings in the courts. The qualifications of many could be seriously questioned. The Court’s Judgment on Warning Expertise Courts (judges) must distinguish between legitimate warning experts and those who do not have such expertise. Such decisions are not simple, particularly when one considers that judges are not expert in the vast array of subject matter, including warnings, addressed by expert witnesses. It is beyond the scope of this chapter to address this decision-making issue. However, it is important for the potential warning expert to be aware that such decisions are made and that information may be sought as a basis for the decision. Some examples of information that may serve as a basis for such decisions include: • Is the content area of the person’s education and knowledge in an area such as psychology, human factors, ergonomics, or communications? • What is the level of knowledge about or familiarity with the technical literature on warnings that the expert possesses? • What is the record in carrying out and publishing research on the topic of warnings? Has the research been funded? By whom? Have the publications appeared in peerreviewed journals, proceedings, and books? • What is the expert’s experience in designing warnings? • Has the expert played a role in relevant national organizations, advising government agencies, consulting with and/or working for industry on relevant projects, serving as an editor or reviewer of scientific literature, etc.? All of these factors or considerations need not be met to qualify as a warning expert. However, to be accepted and to function as an expert in this field, at least some of these credentials must be satisfied. 30.5 Activities and Functions of the Warning Expert As already noted, the warning expert may engage in a variety of activities. Every case is different to some extent, and the expert’s activities will vary from case to case. Figure 30.1 presents a general overview of the expert’s activities. It shows a sequence of
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activities from initial contact to trial. Although the timeline of activities is shown as a linear sequence, in some cases the order may be different and steps may be
FIGURE 30.1 A generalized sequence of activities of a warning expert involved in litigation. repeated. The expert should remain flexible about the expectations of his activities in a case because different jurisdictions have different rules, and attorneys and judges try cases differently. The Initial Contact Usually the expert’s involvement in a case begins when he is contacted by an attorney. This contact normally takes the form of a phone call, a letter, a fax, or an e-mail. Following introductions, the attorney will provide a brief description of the accident or exposure, the injuries or illness, and the issues or aspects of the case about which the
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attorney is seeking expert help. If the expert’s credentials and the issues match, and if agreement is reached on procedures, fees, etc., the expert’s role in the case will begin. Some experts require a formal agreement in the form of a contract, but others proceed on a less formal basis. Such contracts are normally two- to three-page documents that spell out the scope of the work and billing and payment procedures. Some experts require a retainer and others do not. Another consideration that should be sorted out at this point is the time frame, that is, what the client expects from the expert and when. Will a report be required and, if so, by what date? Must a deposition be completed by a certain date? Has a trial date been set? Although not typical, it is not uncommon for an attorney to decide well into the development of a case that a warning expert is needed. For example, a defense attorney may have recently deposed the plaintiff’s warning expert and decided that he also needs to employ such a person. The expert is well advised to take into account the time requirements in deciding whether to get involved. Analysis As indicated earlier, although Figure 30.1 implies a sequence of activities that occur serially, it is not entirely accurate. Actually, analysis may continue right up to the time of courtroom testimony. As new, relevant information becomes available in discovery, the expert may prepare supplemental reports or even be deposed more than once. Sometimes, with the help of the expert, attorneys will prepare an affidavit or a declaration before or after a deposition. Nevertheless, early work on a case focuses on analysis of information and the formulation of opinions. Information The information examined by a warning expert typically comes from two sources: the attorney and the expert. By the time the expert is employed, a great deal of information is often available. Such information may include: • The complaint or petition • Accident reports • Information about the product (if a product was involved) • Information about the job and work environment (if the injury/illness was job related) • Statements and/or depositions of fact witnesses • Reports and/or depositions of other experts • Standards and guidelines Sometimes the warning expert is involved early in a case and has an input to the kinds of information that will be useful in evaluating the warnings issues. The expert may assist the retaining attorney in formulating interrogatories and requests for production asking the opposing side for additional information. Such information may include: • Hazard analyses results (failure mode, fault tree, etc.) that have been done • Procedures and criteria involved in developing the existing warning system • Relevant past safety behaviors of the plaintiff • Safety history of the product or environment
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The warning expert may also raise issues and assist in the formulation of questions for the retaining attorney to ask fact witnesses and other experts during deposition and trial testimony. The expert may also gather information, including the relevant scientific literature. The expert may carry out tests, surveys, and other procedures (e.g., consumer interviews and focus groups) to gather relevant information if necessary. For the warning expert, relevant information might include: • Are the hazards, consequences, and appropriate modes of behavior “open and obvious”? That is, do the appearance and/or function of a product or environment provide the warning information? • What do people already know about the relevant hazards, consequences, and appropriate modes of behavior? • How do people use a product? • Do people notice, understand, and respond to the warning system? Testing with relevant target populations may not be possible or practical in the context of litigation consulting. For example, many cases are on a short fuse, and sometimes resources to conduct warning effectiveness testing are not available. Also, formal testing in the litigation context may not be necessary, in cases in which there is a complete absence of a warning, or when many of the features known to benefit warning effectiveness (see Wogalter and Laughery, this volume) were not employed in the subject warning. Problems can arise during the information-gathering phase. One potential problem occurs when the attorney does not provide relevant information. This omission could occur because the attorney did not realize the information was relevant or because he withheld it, thinking it was harmful to his case. The latter circumstance cannot be tolerated. An example would be a highway accident in which the driver (plaintiff) was drunk and the blood alcohol content analysis was withheld from the expert. On the defense side, an example might be a letter or memorandum from the product manufacturer’s file indicating that the warning system was deliberately downplayed so as not to have a negative impact on sales. Such withholding of information is rare, but it can be embarrassing to the warning expert. It can also change the expert’s opinions. The absence of relevant information is another potential information problem. Information about whether the plaintiff noticed or understood the warnings or what the plaintiff knew or understood about the hazards, consequences, and correct modes of behavior is not available in a death case. Contradictory information is still another problem. Multiple witnesses to an accident often report different and contradictory accounts. These problems, among others, must be taken into account by the expert. Assumptions vs. Opinions The distinction between assumptions and opinions is important. En route to formulating opinions, the warning expert typically makes assumptions about a number of things, for example: • Hazards and consequences associated with the product being used • Hazards and consequences associated with the activity being carried out
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• Warnings that were provided and how they were provided • What relevant people knew about the hazard and consequences • Where, when, and how the accident, injury, and/or illness occurred These points refer to factual matters. The facts, or assumptions, may be associated with varying degrees of confidence, depending on the quality of available information, but they are still assumptions. Assumptions made by the warning expert may also be based on opinions of other experts. The hazards and potential consequences of handling some chemical solvent may be defined by the opinions of an expert toxicologist. To the warning expert, they are assumptions. Formulating Assumptions Two of the major difficulties in formulating assumptions are (1) missing information and (2) contradictory information. What a brain-damaged or deceased person knew about hazards is important to the warning expert, but it is not available. Assumptions regarding this knowledge may be based on testimony of co-workers and family members as well as records of training, experience, and past performance of the person. Information about a product warning system may not be available if the product was destroyed in an accident. Was the label legible? Was the manual available? Contradictory information presents different but often equally difficult problems for the warning expert. Different perspectives and memories of fact witnesses is a problem noted earlier. Simple answers or solutions to these problems do not exist for the warning expert who is trying to decide the appropriate assumptions to make. The following are a few suggestions to use when carrying out the analysis: 1. Be clear about the information needed or the issues about which one needs to make assumptions. 2. Do not hesitate to ask questions or request information. 3. Be prepared to recommend that steps be taken to obtain information not currently available. 4. Be prepared to express opinions based on two or more different sets of assumptions. The last point warrants an additional comment. Often, the plaintiff’s attorney will be happy with one set of assumptions, but the defense attorney will prefer a different set of assumptions. During deposition or trial testimony, the expert may be asked his opinions given the different assumptions (e.g., whether a product manual was available or read). If different assumptions warrant different opinions, give the different opinions. Formulating Opinions There are several categories of issues about which the warning expert typically expresses opinions: • Was a warning needed? • Was the warning adequate? • Would the warning have made a difference?
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The expert can also expect to be asked about the basis of the opinions. It should be recognized that when the term “warning” is used here, it is referring to a warning system, perhaps consisting of several warning components. Is a Warning System Needed? Several considerations are relevant to this question. The first is whether or not a hazard exists. There is no need to warn about nonexistent hazards. Second, is the hazard open and obvious? In the law, it is generally not necessary to warn about a hazard that is open and obvious. Most would agree that a fire is an obvious burn hazard, but the inhalation hazards of solvent vapors are not open and obvious. Many hazards, however, are not so easily classified. For example, how an ignition source could start a fire may not be open or obvious. A third consideration is whether or not people already know about the hazard. If so, a warning may not be needed. A fourth consideration is whether a warning is needed as a reminder. Circumstances such as high task loading may necessitate a reminder warning. Is the Warning System Adequate? This question is central to the warning expert. An important consideration is the definition of adequacy. In the context of litigation, a warning is adequate or inadequate. However, the goodness or badness of a warning system is a continuum: it may be good or very good; it may be bad or very bad. The expert’s task includes deciding where to draw the adequacy cutoff. Some rules of thumb for such a decision follow; they may be helpful, but not always applicable: • The warning system must be considered as a whole. A poor warning in a manual, which may or may not be seen, may not render the warning system inadequate if a good warning is on the product. On the other hand, for many products an adequate onproduct component is necessary for the system to be adequate. The point is that the different components of the system do not necessarily get equal weight in judging adequacy. • Minor violations of criteria or guidelines may not be a basis for inadequacy. Using the signal word “caution” instead of “warning,” when the latter is appropriate to the hazard, is probably not a valid reason alone for declaring a warning inadequate. • An opinion that the warning system probably would not have changed the outcome is not a basis for declaring the system adequate. The issue of whether or not the warning is adequate from a design perspective is not the same question as whether it would have made a difference. Would the Warning System Have Made a Difference? This issue is also central to the work of the warning expert because it goes to the issue of causation. If a warning system was inadequate but had no bearing on the accident, injury, or illness in question, then its inadequacy is irrelevant. The effectiveness issue is often a difficult one for the warning expert. No one would argue that bad warnings will be effective, and most people would agree that good warnings are more likely to be effective
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than bad warnings. Furthermore, even the best warning system is not likely to be effective 100% of the time. The difficulty lies in formulating opinions about how effective the warning system would be or, in other words, in quantifying effectiveness. Categorical judgments may be made, such as “more likely than not,” but they must be made with careful consideration of the best information available. Factors such as the design of the warning system, characteristics of the target audience, circumstances of the task or activities of the people involved, and the empirical scientific literature are relevant to the issue. Sometimes questions arise in a case for which the existing technical literature contains no directly relevant information or data. Examples might be a specific risk perception issue (e.g., what do people know about this hazard or its consequences?) or a specific warnings issue (e.g., is the existing warning understandable to this target audience?). Sometimes, straightforward inferences can be made from the technical literature. In other circumstances, relevant data may be collected through an experiment or a survey. An excellent example of this latter approach was reported by Senders (1994), in which a survey was carried out to determine how people would connect a gas heater. Preliminary Feedback to Attorney At some point, the expert will provide feedback to the attorney regarding preliminary opinions. This feedback may be more interactive than the sequence of steps reflected in Figure 30.1 might suggest. The attorney will want to know what the expert thinks in order to decide whether to continue to employ him in the case. If his opinions are not supportive of the case, the expert’s work will be finished. This, of course, is a potential pitfall for the expert in that a job and a fee are lost. However, the alternative is filled with even greater pitfalls. The feedback should be as frank and as complete as possible. It is also important that the attorney understand the assumptions of the expert that form the basis for his opinions. When questions about the validity of the assumptions or alternatives need to be considered, the attorney needs to know how the expert’s opinions would be influenced by such alternatives. Preparing Reports Reports are essentially intended to provide the opposing attorney with information regarding who the expert is, what he has done, and what his opinions are. Reports are not required in all cases. Cases in federal courts require a report as well as a current curriculum vitae and a list of cases in which the expert has given testimony during the preceding 4 years. Report requirements for cases in state courts vary; commonly, no report is required. Report requirements may vary in specificity. A report may be brief and very general, stating opinions in the broadest terms. Such a report might state only that the warning was inadequate and that, if a good warning had been provided, the accident or injury would have been prevented. In other instances, reports must be specific and complete. If a warning is judged to be inadequate, the specifics of its inadequacies must be spelled out as well as the basis for the opinion. In some circumstances, if an opinion is not provided
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in the report, the expert may not be permitted to express that opinion in trial. Thus, the warning expert must know the report requirements early in his work on a case because such requirements influence the level of analysis carried out before the report is prepared. Typically, the opinions in the report of a warning expert will address the issues posed earlier: was a warning needed? Was the warning system adequate? Would the warning system have made a difference? A final point on reports: they should be prepared with great care. Odds are that they will be scrutinized extensively and every point subjected to questioning and, perhaps, challenged. Deposition Testimony The next step in most cases is a deposition. The procedure usually involves the attorney for the opposing side examining the expert in a question-answer format. There may be more than one questioning attorney, such as when an expert is working for the plaintiff and there are multiple defendants. The expert is under oath, the procedure is recorded, and the testimony is considered part of the formal record of the case. It can be used later during trial and possibly in future testimony in other cases. It is important for the expert to be well prepared and consistent. Contradictions between deposition testimony and trial testimony are likely to be noticed and can discredit the expert. The deposition is adversarial, and the opposing attorney will be attempting to establish such things as: • Questions or shortcomings regarding the expert’s credentials • Flaws in the analyses carried out • Contradictions in or concerns about the opinions • The basis for the opinions (scientific data, theory, and experience) The tone of depositions is generally professional. Attorneys come prepared and they get on with the business at hand. There are exceptions, and bad manners and hostile behaviors sometimes emerge. It is critical that the expert not get caught up in the argumentative or emotional aspects of the situation. The opposite of bad manners and hostility can also occur—overfriendliness. Watch out if the attorney starts a question with “Doctor, you will agree with me won’t you, sir, that…” Also, if you have previously provided deposition and trial testimony, the opposing attorney may have researched your previous work, and questioning may focus on opinions in earlier cases. Such situations are one of the reasons to maintain consistency. Trial Testimony The final step in the activities of an expert is to testify in court. The attorneys representing both sides question the expert. Credentials are established and opinions are expressed. Three aspects of the warning expert’s role in the courtroom are noted here. First, he is in the position of communicating the nature and results of an analysis that includes methodology and data, as well as opinions that may be technical in nature, to an audience of lay people—the jury. Metaphors, visual aids, and demonstrations can be exceptionally helpful and should be developed as part of the warning expert’s communication tools. Charts listing criteria for warnings and examples of good and poor warnings can help the jury to understand the expert’s opinions.
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The second aspect of courtroom testimony is directed to the warning expert more than to other kinds of experts. The jury may have attitudes or information that must be overcome or changed. One point concerns information. By the time the warning expert begins testimony, the jury will usually have heard descriptions of the accident or illness and presentations about the hazards associated with the product. A role of the warnings person is often to provide an analysis in terms of how a product was used and, sometimes, to evaluate what the injured party knew or did not know about the hazards at the time of the accident. In short, the warning expert must help the jury analyze the issues in the proper context, not in terms of what everyone in the courtroom knows now. Another point concerns attitudes. People often have a predisposition to believe that if someone gets hurt, it is because he made a mistake. The warning expert needs to help the jury take a more systems-oriented view of systems involving people. The third aspect of courtroom testimony regarding warnings is that juries do have experience with and knowledge about warnings. Correct or incorrect, complete or incomplete, this knowledge exists. It is appropriate to assume that most juries will have a limited understanding of the display design and communication principles relevant to warnings design, and they will not appreciate how warnings fit into the overall safety scheme. Thus, another role of the warning expert is to expand the jury’s understanding of warnings and their role in safety so that the expert’s opinions can be better appreciated and accepted. 30.6 Issues, Problems, and Temptations Numerous issues, problems, and temptations are associated with expert witness role. A few examples will be discussed in this section. Anyone working as an expert is well advised to keep them in mind in carrying out such work. The adversarial context in which the expert functions is quick to capitalize on errors, usually at some cost to the expert. Ethics Codes of ethics generally define principles applicable to the role of the warning expert in litigation. The code promulgated by the Human Factors and Ergonomics Society is an example. The expert should be familiar with applicable ethics codes and follow them carefully. Boundaries One of the success rules of the expert game is for the expert to know what he knows and to know what he does not know. It is critical that the expert stay within the boundaries of his expertise. The warning expert should limit his analyses and opinions to warnings issues; he should not address matters associated with engineering design, child development, or a host of other potentially “nearby” topics. This rule is not as straightforward as it may seem—for various reasons: • Boundaries are often fuzzy. The psychologist serving as a warning expert may (hopefully) know a great deal about human cognition. When testimony from different
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fact witnesses is contradictory as to the circumstances of some accident event, it may be tempting to offer opinions about that testimony based on knowledge of human memory. A good rule of thumb is for the expert not to do so unless he really is expert on memory and has specifically been asked to evaluate and form opinions about such issues. • Boundaries are also violated because the expert gets questions in a deposition or in trial about peripheral issues such as a design feature of some piece of equipment. Although the warning expert may be tempted to provide an answer, this is a temptation to be avoided. Such questions may represent an effort to maneuver the expert out onto a limb that can then be sawed off from behind. • The boundary rule can be difficult because an expert represents a cost in litigation, and the attorney who hired him may understandably want to keep costs under control. If the expert provides opinions on the other issues, the attorney may not need to hire other experts, thus cutting expenses. Avoid such “favors.” Consistency Given the boundaries of one’s expertise, it is also important to be consistent within those boundaries. An opinion today that differs from an opinion tomorrow is not likely to go unnoticed—at least not for long. This also may seem like an easy rule to follow. For example, if one applies the criteria for warnings design and the factors that influence when warnings will and will not be effective, it would seem relatively easy to be consistent in formulating opinions, but this is not so: • Situations or circumstances are seldom the same or different; rather, they vary as shades of gray. Accidents, injuries or illnesses, products, and people vary in numerous dimensions; this, in turn, makes the analyses- and formulation of opinions complex. • Being consistent can be difficult because, through artful questioning, the opposing attorney may attempt to get the expert to be contradictory. • Consistency can be a challenge because the warning expert may have opportunities to work on the defense side in some cases and the plaintiff side in other cases. The attorneys representing the different sides are looking for different opinions. Warning experts who work only for defendants or for plaintiffs will have less difficulty being consistent, but they will face other challenges regarding integrity and impartiality. It is important to keep in mind that one is a warning expert, not a defense or plaintiff expert. The real solution to the consistency challenge is to be true to the empirical and theoretical science of warnings. Being Current Related to the consistency issue is the challenge of staying current with the empirical and theoretical science in the area of warnings. This is not a minor challenge, given the increase in research activity during the past 20 years. There have also been significant efforts in the development of standards and guidelines for warnings. It is imperative that the warning expert be knowledgeable about the current state of the science. The growth
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and development of knowledge about the design and effectiveness of warnings is probably the one legitimate basis for changing opinions about how warnings should be designed and how they function. The Adversarial Setting The warning expert functions in many aspects of the adversarial setting. Several such points have already been noted. A few general “rules of the game” are: • The expert’s role is to advise or educate the jury. Although the expert is employed by one side, he must be impartial and unbiased. The expert does not win or lose. • The plaintiff attorney’s role is to win the case for the plaintiff. He does win or lose. • The defense attorney’s role is to win the case for the defendant. He does win or lose. • The attorneys in a case will do whatever is necessary within the boundaries of the law and acceptable practice to win. • The attorney for the other side will make every effort to discredit the expert and his testimony. This effort will include getting him to contradict himself, including researching his work in past cases to identify inconsistent opinions. It will also include employing other warning experts whose opinions differ from the expert’s. • The attorney for the other side may attempt to discredit the entire domain of warning expertise (e.g., Hardie, 1994). This effort may include the argument that the issues of warnings design and effectiveness are within the province of the jury; that is, these are issues that jurors (lay people) are capable of evaluating without the help of experts. The effort may also include the argument that no “hard science” is associated with warnings. However, given the extensive research literature on warnings, an expert should be able to deal with scientific merit challenges. The preceding examples of “rules” relevant to the adversarial litigation setting may at first seem excessively critical of attorneys and the system, but that is not the intent. Rather, these are characteristics of many or most of the circumstances associated with the context in which the warning expert functions, and potentially serious pitfalls await one who is not aware of them. Again, the expert’s best defense against the various challenges inherent in the role is to be true to the empirical and theoretical science of warnings. Nothing Is Secret The expert’s credentials, past experiences in other cases, and specific work on a case must be revealed on request when working on a case. This rule varies in different jurisdictions, but generally the expert should assume that everything he does in a case will be revealed to the other side. This information would include anything provided or revealed by the attorney who hired him. It includes all handwritten and typewritten notes, conversations, activities, publications reviewed, etc. related to the case. It can also include work in other past and present cases. Thus, the warning expert needs to be aware that “nothing is secret.”
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30.7 Conclusions The expert witness is in a potentially powerful position with regard to litigation. This influence is due primarily to two aspects of the role. First, the expert is generally interacting with people who know much less about his area of expertise. Thus, except for similar experts who may be employed by the opposite side of a case, no one is qualified to challenge or evaluate the opinions of the expert at a scientific or technical level. The second source of influence stems from the fact that the expert can give opinions. This aspect of the role differs from the fact witness, who provides information but is not permitted to render an opinion. As the body of scientific literature in the field of warnings design and effectiveness has grown and developed (see Wogalter and Laughery, this volume), so apparently has the role of warnings issues in product liability and personal injury litigation. As these issues continue to be addressed in litigation, the need for capable experts in the subject matter will continue. The role of the warning expert can be challenging, but it is also important—and it is important that it be done well. In this chapter, some of the techniques, procedures, and challenges associated with the role of the warning expert have been presented and explored. Most of the topics presented could be addressed in much greater depth than the scope of this chapter permitted. It is increasingly common for each side of a case to have a warning expert and for these experts to disagree. Such circumstances are to be expected and are not a reason to abandon the role of the warning expert in litigation. Engineers, physicians, toxicologists, and economists also disagree and work on both sides of cases. The important point is that the people who serve as warning experts should be qualified and that they should do their best to provide high-quality expertise to the judicial system. References Hardie, W.H. (1994). Critical analysis of on-product warning theory. Prod. Safety Liability Reporter , (February 2), 145–163. Lehto, M.R. and Miller, J.M. (1986). Warnings: Volume I, Fundamentals, Design, and Evaluation Methodologies . Ann Arbor, MI: Fuller Publications. Madden, S.M. (1999). The law relating to warnings. In M.S.Wogalter, D.M.DeJoy, and K.R.Laughery (Eds.), Warnings and Risk Communication . London: Taylor & Francis. Senders, J.W. (1994). Warning assessment from the scientist’s view. Ergonomics in Design , 2, 6– 7. Wogalter, M.S. and Laughery, K.R. (2004). Chapter 31, this volume.
31 Effectiveness of Consumer Product Warnings: Design and Forensic Considerations Michael S.Wogalter North Carolina State University Kenneth R.Laughery Rice University 0–415–28870–3/05/$0.00+$ 1.50 © 2005 by CRC Press
31.1 Introduction Warnings have two main purposes. First, they are a method for communicating important safety or safety-related information to a target audience who can then make better, more informed decisions regarding safety issues. Second, warnings are ultimately intended to reduce or prevent health problems, workplace accidents, personal injury, and property damage. Warnings can be in the form of signs, labels, product inserts and manuals, tags, audio- and videotapes, face-to-face verbal statements, and so forth. Printed warnings are generally text and graphics. Auditory warnings may be verbal or nonverbal. In this chapter, we will describe factors generally applicable to all types of warnings, although examples are geared mostly toward visual warnings associated with products. Although the topic of this chapter is warnings, it should be recognized that warnings are not the best method of controlling hazards and promoting safety. Even the best warnings are not always 100% reliable or effective. The classic safety hierarchy (design, guard, and warn) offers a context for the role of warnings. The best method of hazard control is to eliminate (or remove) the hazard. If the hazard is not present, then the likelihood of injury is greatly reduced. Reformulating paint to eliminate lead or removing a flammable propellant such as propane in pressurized spray cans is an example of a design alternative that would eliminate hazards associated with such products. Hazards cannot always be eliminated. For example, one cannot eliminate all of the hazards associated with the use of chemical solvents. Likewise, one cannot remove all of the mechanical hazards related to power tools. For hazards that cannot be eliminated, the next best hazard control strategy is to guard against contact with the hazard. Guarding can take several forms. The debris shield on the back of a lawnmower is mechanical guarding. The “dead-man” switch on a lawnmower that shuts off the rotor when the handle is released is procedural guarding. Requiring a prescription for certain drugs is expert-referent guarding. Unfortunately, not all hazards can be eliminated or guarded against, so warnings are necessary. As noted earlier, warnings do not always accomplish their intended purpose; thus, an important issue is how to design warning systems that will maximize their effectiveness.
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A starting point for warning designs is guidelines such as those of the American National Standards Institute’s Z535 document (ANSI, 2002). According to these guidelines, written warnings should possess four textual components: • A signal word such as DANGER, WARNING, or CAUTION (with corresponding red, orange, or yellow color) to attract attention to the warning and give an idea of the level of hazard • A hazard statement that briefly describes the nature of the hazard • A description of the possible consequences associated with noncompliance • Instructions for how to avoid the hazard In addition, a pictorial symbol depicting the hazard, consequences, or appropriate or inappropriate behaviors is also recommended. Research has verified the importance of these components for enhancing warning efficacy (Wogalter et al., 1987; Young et al, 1995). Table 31.1 shows a checklist of factors, based on guidelines, standards, and empirical research, that should be considered in designing effective warnings. Although this is not an exhaustive list, it lists a minimum set of factors that a product manufacturer should consider in the communication of warnings. Of course, these are considerations; for example, not all of the textual components in the table are necessary if members of the target audience are aware of the hazard and procedures needed to avoid injury. However, even with this knowledge, the presence of a warning may serve as a reminder by cuing pre-existing safetyrelated knowledge from long-term memory into conscious awareness (e.g., Young and Wogalter, 1990). Warning design and effectiveness therefore comprises many factors and considerations. A conceptual model has been developed for purposes of analyzing and evaluating these various factors and considerations (Wogalter et al., 1999a). The model combines basic components of communication and human information processing theory. It is a useful tool for forensic specialists in analyzing the adequacy of warnings. 31.2 The Communication-Human Information Processing (C-HIP) Model The communication-human information processing (C-HIP) model (Wogalter et al., 1999a) is a framework for showing information flowing from a source to a receiver whereby the latter then processes the information to subsequently produce behavior. The model is displayed in Figure 31.1. The conceptual stages of source, channel, and receiver are taken from communication theory (Lasswell, 1948; Shannon and Weaver, 1949). The receiver stage is broken down further into several human information processing substages prior to carrying out the compliance behavior. These substages are attention switch, maintenance, comprehension, beliefs and attitudes, and motivation. At each stage of the model, information can be processed and flow through to the next stage, or it can produce a bottleneck that blocks or deteriorates/distorts the flow before the process ends in the desired behavioral compliance. Although the process might not go all the way to behavioral compliance, it still might effectively influence earlier processing stages. For example, information can positively influence comprehension about the
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hazard and be consistent with beliefs and attitudes but still not motivate compliance behavior. Such a warning cannot be said to be totally ineffective because it does produce better understanding and lead to more informed decisions. However, it is ineffective in the sense that it does not necessarily produce the desired safe behavior. The C-HIP model can be particularly useful in diagnosing and understanding warning failures and inadequacies. If a source does not issue a warning, no information will be transmitted through a channel stage and thus nothing will be communicated to the receiver. Even if a warning is issued, it will not be effective if the channel or medium of transmission is poorly matched with the message, receiver, or environment. Each of the stages within the receiver can also produce a bottleneck preventing further processing. The receiver might not notice the warning in the first place. Even if the warning is noticed,
TABLE 31.1 Warning Design Guidelines Warning component Signal words
Format
Wording
Pictorials/ symbols
Design guideline • According to ANSI Z535 (2002): • Danger—indicates immediately hazardous situation that will result in death or serious injury if not avoided; use only in extreme situations. Red should be used. • Warning—indicates potentially hazardous situation that may result in death or serious injury if not avoided. Orange should be used. • Caution—indicates potentially hazardous situation that may result in minor or moderate injury. Yellow should be used. • Notice—indicates important nonhazard information. Blue should be used. • Message panel should be high contrast, preferably black print on white background or vice versa. • Text should be left justified. • Consistently position component elements. • Orient messages to read from left to right. • Each statement starts on its own line. • Use white space or bullet points to separate statements or sets of statements. • Place most important warning statements at the top. • Use as little text as necessary to convey the message clearly. • Remove unnecessary connector words, e.g., prepositions, articles. • Use short sentences rather than long, complicated ones. • Give information about the hazard, instructions to avoid hazard, and consequences of failing to comply • Be explicit—tell the reader exactly what to do or not to do. • Use short, familiar words. • Avoid using abbreviations unless they have been tested on user population. • Use active voice rather than passive voice. • Use concrete rather than abstract wording. • Avoid using words or statements that might have multiple interpretations. • Use multiple languages when necessary. • When used alone, symbols should have at least 85% comprehension scores, with no more than 5% critical confusions (opposite or “very” wrong answers)
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• Pictorials not passing a comprehension test should be accompanied by words. Symbols that produce critical confusions should be avoided. • Use bold shapes. Avoid including irrelevant details. • Prohibition (circle slash) should not obscure critical elements of symbol. Font • Warning must be large enough to be seen by the intended audience and across expected viewing distance. • Use mixed-case letters. Avoid using all caps except for signal words or for emphasis. • Use sans serif fonts (Arial, Helvetica, etc.) for signal words and larger text messages. • Use serif fonts (Times, Times New Roman, etc.) for smaller text messages. Other • Locate/position so that presentation is where it will be seen or heard. • Test to assure message will be seen, heard, and positively affect safety. Source: According to ANSI Z535 (2002), Arlington, VA: National Electrical Manufacturers Association.
the individual might not direct attention to the warning. Even if the receiver examines the warning, he or she might not understand it. Even if the warning is understood, it might not be believed, and so on.
FIGURE 31.1 The communicationhuman information processing (C-HIP)
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model. (Adapted from Wogalter et al., 1999a.) Although the processing described here is linear, there are feedback loops from later stages to earlier stages, as illustrated in Figure 31.1. For example, when a warning stimulus becomes habituated over time from repeated exposures, attention is less likely to be allocated to the warning on subsequent occasions. Here, memory (as part of the comprehension stage) affects an earlier stage of processing: attention. Another example is that some people might not believe that a product or situation is hazardous and consequently not look for a warning. A third example would be if a person did not understand the warning and therefore went back to attentional processes and read it again. These feedback or nonlinear effects between the stages of the information processing model provide a means by which later stages influence decisions at earlier stages. In the subsections that follow, each of the stages of the C-HIP model is described together with a brief description of influential factors. Table 31.2 shows a summary of some of the primary considerations associated with successful processing at each stage. Source The source is the originator or initial transmitter of the risk information. The source can be a person or an organization (e.g., company or government). Research shows that, given the same information, differences in the perceived characteristics of the source can influence people’s beliefs about the relevance of the warning (Wogalter et al., 1999b). Information from a reliable, expert source (e.g., the Surgeon General) is given greater credibility (Wogalter et al., 1999b), which in turn may correct erroneous beliefs and attitudes (a stage of processing described later). Channel The channel is the way in which information is transmitted from the source to one or more receivers; the channel has two basic dimensions. The first concerns the media in which the information is embedded. Warnings can be presented on product labels, on posters, in brochures, as part of audio—video presentations, given orally, etc. The second dimension of the channel is the sensory modality used by the receiver to capture the information. This dimension is intimately tied to the medium in which the message is transmitted. Most commonly, warnings are received via the visual (printed text warnings and pictorial
TABLE 31.2 Methods and Influences of Communication-Human Information Processing (C-HIP) Stages C-HIP stage Source Channel
Methods and influences • Determination that hazard is not designed out or guarded • Credible, expert • Visual (signs, labels, tags, inserts, product manuals, video, etc.) • Auditory (simple and complex nonverbal, verbal, live, electronic, chip,
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radio) • Other senses: vibration, smell, pain • Generally, transmission in more than one modality is better Receiver • Message delivered to • Consideration of demographics of target audiences (e.g., older adults, illiterates, cultural and language differences, persons with sensory impairments) Attention switch • High salience/conspicuity/prominence in clutter and noise • Visual: high contrast, large, proximal in time and space, presence of pictorial symbols • Auditory: louder and distinguishable from surroundings • Present when and where needed • Avoids habituation by changing stimulus Attention maintenance • Visual: legible font and symbols, aesthetic formatting, brevity • Auditory: intelligible voice • Enables encoding of message by examining/reading or listening to message Comprehension/memory • Enable informed judgment • Understandable message that provides necessary information to avoid hazard • Relate information to knowledge already in user’s head • Explicitness enables elaborative rehearsal • Enable storage of information • Pictorials beneficial for demographic groups • Subsequently, warning cue reminds user of information • Comprehension testing needed to determine whether warning communicates intended/ needed information Beliefs/attitudes • Affect receiver’s earlier stages • Perceived familiarity reduces perceived hazard; perceived hazard reduces warning processing • Persuasive argument and excellent warning design needed when beliefs are seriously discrepant with truth Motivation • Energizes person to carry out next stage • Low cost (time, effort, money) for compliance • Perceived high cost for noncompliance • Benefited by explicitness and perceived injury severity • Affected by social influence, time stress, mental workload Behavior • Carrying out safe behavior; i.e., does not result in injury
symbols) and auditory (alarm tones, live voice, and voice recordings) modalities. There are exceptions: an odor added to flammable gases such as propane makes use of the olfactory sense, and a pilot’s control stick designed to vibrate when the aircraft begins to stall makes use of the tactile sense.
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Receiver The receiver’s mental activities can be categorized into a sequence of informationprocessing stages. For a warning to communicate information and influence behavior effectively, attention must be switched to it and then maintained long enough for the receiver to extract the necessary information. Next, the warning must be understood and must concur with the receiver’s existing beliefs and attitudes. If it is in disagreement, the warning must be adequately persuasive to evoke an attitude change toward agreement. Finally, the warning must motivate the receiver to perform proper compliance behavior. The next several subsections are organized around the stages of information processing that occur within the receiver. Attention Switch The first stage in the human information processing section of the C-HIP model concerns the switch of attention. An effective warning must initially attract attention. Generally, this must occur in environments that also have other stimuli competing for attention. Because many environments are cluttered, visual warnings must stand out from the background (i.e., be salient or conspicuous) in order to be noticed. This is particularly true when people are not actively seeking hazard and warning information. In many situations, people are focused on the tasks that they are trying to accomplish. Safety considerations, which can be part of one’s background knowledge (stored in long-term memory), would tend to receive less attention under high task focus. One way of making a visual warning more salient is to increase the print size and the print’s contrast against the background (Barlow and Wogalter, 1993). Signal words and pictorials also tend to attract attention. In the U.S., current standards and guidelines such as ANSI Z535 (ANSI, 2002) recommend that warning signs and labels contain a signal word panel that includes one of the terms DANGER, WARNING, or CAUTION along with a specific color (red, orange, and yellow, respectively) and an alert symbol (a triangle surrounding an exclamation point). According to ANSI, these terms are intended to denote decreasing levels of hazard, respectively. DANGER should be used for hazards in which serious injury or death will occur if warning compliance behavior is not followed, such as around high-voltage electrical circuits. WARNING is used when serious injury might occur, such as severe chemical burns or exposure to highly flammable gases. CAUTION is used when less severe personal injuries or damage to property might occur, such as getting hands caught in operating equipment. Research shows that lay persons often fail to differentiate between CAUTION and WARNING, although both are interpreted as connoting lower levels of hazard than DANGER (e.g., Wogalter and Silver, 1995). The term NOTICE, associated with blue color, is intended for messages that are important but do not relate to injuries. Pictorials and symbols used in communicating content information are also useful in capturing attention (Bzostek and Wogalter, 1999; Laughery et al, 1993a). One general symbol is the alert icon (triangle enclosing an exclamation point). The placement of a warning in time and location is an important factor in facilitating attention switch. A warning, even a good one, not readily in view or not available at the
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time needed is less likely to be effective. Even though placement of warnings directly on a hazardous product is preferred (Wogalter et al., 1987), the available surface area on which warnings can be printed is sometimes limited. Methods are available to increase the surface area for print warnings (Barlow and Wogalter, 1991; Wogalter et al., 1999d). A related issue is that repeated and long-term exposure to a warning may result in a loss of attention-capturing ability (Wogalter and Laughery, 1996). This habituation can occur over time, even with well-designed warnings. Altering a warning’s appearance by periodically changing its format or content can show the habituation process. Attention Maintenance Individuals may notice the presence of a warning but not stop to examine it. A warning that is noticed but fails to maintain attention long enough for its content to be encoded is of little value. For adequate processing of warning information to occur, attention must be maintained on the message (Wogalter and Leonard, 1999). With brief warnings, the message information might be acquired very quickly, sometimes as fast as a glance. For longer warnings to maintain attention, they must have qualities that generate interest and do not require much effort. If a warning contains large amounts of text, individuals may decide too much effort is required to read it and thus direct their attention to something else. Some of the same design features that facilitate the switch of attention also help to maintain attention (Barlow and Wogalter, 1991; Wogalter et al., 1993a). For example, large print not only attracts attention but also increases legibility, thus making reading less effortful and more likely. Another factor that can influence attention maintenance is formatting. Visual warnings formatted to be aesthetically pleasing, with plenty of white space and coherent information groupings (Hartley, 1994), are more likely to attract and hold attention while the contents are examined and information is extracted (Vigilante and Wogalter, 1998). In general, bulleted lists are preferred to long paragraphs (Desaulniers, 1987; Wogalter and Post, 1989). Although aesthetically pleasing at a distance, full justification (the straight alignment of the beginning and ending words at both margins) is more difficult to read than “ragged right” (justification only of the left margin). In ragged right, the spacing between letters and words is consistent. Interest is also facilitated by the presence of well-designed pictorial symbols. Furthermore, research indicates that people prefer warnings that have a pictorial symbol to warnings without one (Kalsher et al., 1996; Young et al, 1995). Comprehension A warning that is attended to and examined has little value if the recipient does not understand its message. A warning message should give the receiver an appreciation of hazards and consequences and enable informed judgment. For this reason, warnings should state the message as explicitly as possible (Laughery et al., 1993b). For example, a warning for a solvent product that says “Use outdoors or only in a room where there is air exchange between windows” conveys more meaning than the statement “Use with adequate ventilation.” The latter statement is vague and can be interpreted to mean something very different from what was intended by the product manufacturer. Similarly,
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a statement such as “Hazardous to your health” does not provide an appreciation of potential consequences in a situation in which breathing a toxic vapor may cause lung damage. Whether a warning will be understood depends on characteristics of the warning and the receiver. To maximize comprehension, warnings should be written to take into account the lowest-level abilities in the target population. For warnings targeted to the general U.S. population, one cannot assume that every person who receives the warning can read English or is competent in a particular knowledge domain. For situations in which such factors are a concern, solutions may take several forms: complex messages may be written using simple, high-frequency terms and more detailed explanations; languages other than or in addition to English may be employed; and pictorial symbols may play a more important role. With rising international trade, products increasingly are produced for highly diverse audiences. For such audiences, multiple languages and understandable pictorials can be useful. Pictorial symbols should be tested to determine their understandability. According to ANSI Z535.3, safety symbols or pictorials that are not accompanied by text should surpass a criterion of 85% correct in a comprehension test with no more than 5% critical confusions (opposite or unsafe interpretations). Pictorials not meeting this criterion can be used, but only if they are accompanied by text and the critical confusion level is minimal. The ISO standard for symbols or pictorials has a criterion of 67% with a somewhat different scoring system. Even though the standards do not specify testing text, they should probably be evaluated with representative members of the target audience before being used to verify their suitability in doing the job of warning. Wogalter and colleagues (1999c) provide a methodology for iteratively testing warnings to ensure their comprehension. Testing will not only identify warnings that are difficult to understand, but also identify those whose meaning could to be misinterpreted. Misinterpretation (critical confusion) can be a more serious problem than simply a lack of comprehension. A warning that is not understood might simply be ignored, but a warning whose meaning is misinterpreted could potentially suggest hazardous behaviors. Beliefs and Attitudes If a warning successfully captures and maintains attention and is understood, it still might fail to elicit safety behavior due to discrepant beliefs and attitudes held by the receiver. Beliefs refer to an individual’s knowledge of a topic that is accepted as true. Attitudes are similar to beliefs but have greater emotional involvement. According to the C-HIP model, a warning will be successfully processed at this stage if it concurs with the receiver’s current beliefs and attitudes. The warning message will tend to reinforce what the receiver already knows and, in the process, make those beliefs and attitudes stronger and more resistant to change. If, however, the warning information does not concur with the receiver’s existing beliefs and attitudes, they must be altered by the warning in order for it to be effective. Following is a brief description of how familiarity, hazard perceptions, and perceived severity of injury relate to beliefs and attitudes. In general, when people believe that they are familiar with a product, task, or environment, they are less likely to search for warnings and less likely to attend to or read
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them (e.g., Godfrey et al., 1983; Wogalter et al., 1991), even if they are noticed. Familiarity beliefs are formed from past similar experience in which at least some relevant information has been acquired and stored in memory. Familiarity produces the belief that everything that needs to be known about a product or situation is already known (Wogalter et al., 1991). A person who is familiar with a piece of equipment might assume that a new, similar piece of equipment operates the same way (which may not be true), thus reducing the likelihood that a warning would be read. Hazard perception also influences warning processing at the beliefs and attitudes stage. It is related to familiarity in that familiar products tend to be perceived as less hazardous. Persons who do not perceive a product as hazardous are less likely to notice or read an associated warning (Wogalter et al., 1991, 1993b). Perceived hazard is also closely related to the expected injury’s severity level. In other words, the greater the likelihood of injury, the more one perceives the hazard (Wogalter et al., 1991). Furthermore, even if the warning is read and understood, compliance may be minimal if the level of hazard is believed to be low. If warning information does not conform to or is discrepant with existing beliefs and attitudes, then an effective warning must be sufficiently persuasive to change those beliefs and attitudes. This difficult task is facilitated if the information is presented in a form that will be noticed, read, and understood using the warning design characteristics discussed earlier. The message must be strong and persuasive to override pre-existing knowledge and experience and motivate compliance. Motivation If a warning is noticed, read, and understood, and concurs with a person’s beliefs and attitudes (or brings about a change in discrepant beliefs and attitudes), the process moves to the motivation stage. To be effective at this stage, warnings must motivate the desired behavior. Motivation is affected by the cost of complying with a warning and the cost of noncompliance. The cost of complying with a warning may be in terms of money, time, and/or convenience. When people perceive the cost of compliance to be greater than the benefits, they are less likely to perform the behavior directed by the warning. The requirement to expend even a minimal amount of extra time or effort can reduce motivation to comply with a warning (Wogalter et al, 1987, 1989). One way of reducing the cost of compliance is to make the directed behavior easier to perform. For example, if hand protection is required when using a product, gloves might be enclosed with the product. The costs of noncompliance with a warning can also have a powerful influence on compliance motivation. This effect is particularly true when the possible consequences of the hazards are severe. Possible injuries associated with noncompliance should be explicitly stated in the warning (Laughery et al., 1993b). Explicit injury-outcome statements such as “Can cause liver disease—a condition that almost always leads to death” provide reasons for complying and are preferred to general, nonexplicit statements such as “Can lead to serious illness.” Another factor influencing motivation to comply is social influence. If people observe others not complying with a warning to wear protective equipment, they may not believe
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it is necessary for them to do it (Wogalter et al., 1989). Similarly, observing others complying can have a positive influence. Other factors that influence motivation to comply with a warning are time stress (Wogalter et al., 1998) and mental workload (Wogalter and Usher, 1999). In high-stress and high-workload situations, competing activities absorb some of the cognitive resources available for processing warning information and carrying out the compliance behavior. In conditions such as these, considerable emphasis on safety may be required to overcome the cognitive barriers. Behavior If sufficiently motivated, individuals are likely to carry out the warning-directed behavior. Behavioral compliance research shows that warnings can change behavior (e.g., Laughery et al., 1994; Cox et al., 1997). See Silver and Braun (1999) for a review of published research that has measured compliance with warnings under various conditions. 31.3 Discussion The preceding review of factors influencing warning effectiveness was organized around the C-HIP model. This model breaks the processing of warning information into separate stages that must be completed successfully for compliance behavior to occur. A bottleneck at any given stage can inhibit processing at subsequent stages. The basic C-HIP model can be a valuable tool in developing and evaluating warnings. By identifying potential processing bottlenecks, it can be useful in determining why a warning may or may not be successful in achieving safe outcomes. Its application, particularly in conjunction with empirical data obtained in various types of testing, can identify specific deficiencies in the warning system. For example, suppose a manufacturer finds that a critical warning on its product label is not working to prevent accidents. The first reaction to solving the compliance problem might be to increase the size of the sign so that more people are likely to see it. However, noticing the sign (the attention switch stage) might not be the problem. Potentially, user testing could show that all users report having seen the warning (attention switch stage), read the warning (attention maintenance stage), understood the warning (comprehension and memory stage), and believe the message (the beliefs and attitudes stage). Thus, the problem with the manufacturer’s warning in this case is likely to be at the motivation stage; users are not complying because they believe the cost of complying with the warning (e.g., wearing uncomfortable personal protection equipment) outweighs the perceived likelihood of getting injured by not wearing the equipment. By using the model as an investigative tool, one can determine the specific causes of a warning’s failure and not waste resources trying to fix the wrong aspect of the warning design. For the forensic practitioner, the model has utility in providing assistance in determining the adequacy and potential effectiveness of a warning. To the extent that a warning fails to meet various design criteria, the model can be a basis for judging adequacy. The lack of signal words, color, and pictorials or a poor location can be a basis
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for opining about its adequacy regarding attention. A high reading level, the use of technical terminology, or the omission of critical information maybe a basis for its inadequacy regarding comprehension. The failure to provide explicit consequences information in circumstances in which the outcome of noncompliance may be catastrophic is not consistent with adequacy regarding motivation. Considerations such as these, in conjunction with information obtained in discovery for a particular case, can also be useful in formulating opinions regarding why a warning may not have been successful in a particular instance. For example, the deposition testimony of an injured plaintiff that contains statements such as “I didn’t notice the warning,” “I thought I was supposed to do this (a wrong action),” or “I didn’t realize I could get injured this seriously” may provide a basis for opinions regarding how a different warning may have been effective. On the other hand, the adequacy of the warning may be judged not to be a casual factor in the outcome to the extent that design criteria are met, the content regarding hazards and consequences is explicit and understood, and the person made an informed decision to “take the risk.” References ANSI (2002) Accredited Standards Committee on Safety Signs and Colors. Z535.1–5, Arlington, VA: National Electrical Manufacturers Association. Barlow, T. and Wogalter, M.S. (1991) Increasing the surface area on small product containers to facilitate communication of label information and warnings, in Proc. Interface 91, Santa Monica: Human Factors Society, 88–93. Barlow, T. and Wogalter, M.S. (1993) Alcoholic beverage warnings in magazine and television advertisements, J. Consumer Res. , 20, 147–155. Bzostek, J.A. and Wogalter, M.S. (1999) Measuring visual search time for a product warning label as a function of icon, color, column, and vertical placement, Proc. Hum. Factors Ergonomics Soc. , 43, 888–892. Cox, E.P., III, Wogalter, M.S., Stokes, S.L., and Murff, E.J.T. (1997) Do product warnings increase safe behavior? A meta-analysis, J. Public Policy Marketing , 16, 195–204. Desaulniers, D.R. (1987) Layout, organization, and the effectiveness of consumer product warnings, in Proc. Hum. Factors Soc. 31st Annu. Meeting , Santa Monica: Human Factors Society, 56–60. Godfrey, S.S., Allender, L., Laughery, K.R., and Smith, V.L. (1983) Warning messages: will the consumer bother to look? In Proc. Hum. Factors Soc. 27th Annu. Meeting , Santa Monica: Human Factors Society, 950–954. Hartley, J. (1994) Designing Instructional Text (3rd ed.), London: Kogan Page/East Brunswick, NJ: Nichols. Kalsher, M.J., Wogalter, M.S., and Racicot, B.M. (1996) Pharmaceutical container labels and warnings: preference and perceived readability of alternative designs and pictorials, Int. J. Ind. Ergonomics , 18, 83–90. Lasswell, H.D. (1948) The structure and function of communication in society, in L.Bryson (Ed.), The Communication of Ideas , New York: Wiley. Laughery, K.R., Vaubel, K.P., Young, S.L., Brelsford, J.W., and Rowe, A.L. (1993b) Explicitness of consequence information in warning, Saf. Sci. , 16, 597–613. Laughery, K.R., Young, S.L., Vaubel, K.P., and Brelsford, J.W. (1993a) The noticeability of warnings on alcoholic beverage containers, J. Public Policy Marketing , 12, 38–56.
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Laughery, K.R., Wogalter, M.S., and Young, S.L. (Eds.) (1994) Human Factors Perspectives on Warnings: Selections from Human Factors and Ergonomics Society Annual Meetings 1980– 1993 , Santa Monica: Human Factors and Ergonomics Society. Shannon, C.E. and Weaver, W. (1949) The Mathematical Theory of Communication , Urbana: University of Illinois Press. Silver, N.C. and Braun, C.C. (1999) Behavior, in M.S. Wogalter, D.M. DeJoy, and K.R. Laughery (Eds.), Warnings and Risk Communication , London: Taylor & Francis, 245–262. Vigilante, W.J. and Wogalter, M.S. (1998) Older adults’ perceptions of OTC drug labels: print size, white space, and design type, in S.Kumar (Ed.), Advances in Occupational Ergonomics and Safety , Louisville, KY: IOS Press and Ohmsha. Wogalter, M.S., Allison, S.T., and McKenna, N.A. (1989) The effects of cost and social influence on warning compliance, Hum. Factors , 31, 133–140. Wogalter, M.S., Brelsford, J.W., Desaulniers, D.R., and Laughery, K.R. (1991) Consumer product warnings: the role of hazard perception, J. Saf. Res. , 22, 71–82. Wogalter, M.S., Brems, D.J., and Martin, E.G. (1993b) Risk perception of common consumer products: judgments of accident frequency and precautionary intent, J. Saf. Res. , 24, 97–106. Wogalter, M.S., Conzola, V.C., and Vigilante, W.J. (1999c) Applying usability engineering principles to the design and testing of warning messages, Proc. Hum. Factors Ergonomics Soc. , 43, 921–925. Wogalter, M.S., DeJoy, D.M., and Laughery, K.R. (1999a) Warnings and Risk Communication , London: Taylor & Francis. Wogalter, M.S., Forbes, R.M., and Barlow, T. (1993a) Alternative product label designs: increasing the surface area and print size, in Proc. Interface 93 , Santa Monica: Human Factors Society, 181–186. Wogalter, M.S., Godfrey, S.S., Fontenelle, G.A., Desaulniers, D.R., Rothstein, P.R., and Laughery, K.R. (1987) Effectiveness of warnings, Hum. Factors , 29, 599–612. Wogalter, M.S., Kalsher, M.J., and Rashid. R. (1999b) Effect of signal word and source attribution on judgments of warning credibility and compliance likelihood, Int. J. Ind. Ergonomics , 24, 185–192. Wogalter, M.S. and Laughery, K.R. (1996) WARNING: sign and label effectiveness, Curr. Directions Psychol , 5, 33–37. Wogalter, M.S. and Leonard, S.D. (1999) Attention capture and maintenance, in M.S. Wogalter, D.M. DeJoy, and K.R.Laughery (Eds.), Warnings and Risk Communication , London: Taylor & Francis, 123–148. Wogalter, M.S., Magurno, A.B., Dietrich, D., and Scott, K. (1999d) Enhancing information acquisition for over-the-counter medications by making better use of container surface space, Exp. Aging Res. , 25, 27–48. Wogalter, M.S., Magurno, A.B., Rashid, R., and Klein, K.W. (1998) The influence of time stress and location on behavioral compliance, Saf. Sci. , 29, 143–158. Wogalter, M.S. and Post, M.P. (1989). Printed computer instructions: the effects of screen pictographs and text format on task performance, in Proc. Interface 89 , Santa Monica: Human Factors Society, 133–138. Wogalter, M.S. and Silver, N.C. (1995) Warning signal words: connoted strength and understandability by children, elders, and non-native English speakers, Ergonomics , 38, 2188– 2206. Wogalter, M.S. and Usher, M. (1999) Effects of concurrent cognitive task loading on warning compliance behavior, Proc. Hum. Factors Ergonomics Soc. , 43, 106–110. Young, S.L. and Wogalter, M.S. (1990) Comprehension and memory of instruction manual warnings: conspicuous print and pictorial icons, Hum. Factors , 32, 637–649. Young, S.L., Wogalter, M.S., Laughery, K.R., Magurno, A., and Lovvoll, D. (1995) Relative order and space allocation of message components in hazard warning signs, Proc. Hum. Factors Ergonomics Soc. , 39, 969–973.
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32 Legibility of Warnings in Color Thomy Nilsson University of Prince Edward Island Murray Kaiserman Health Canada 0–415–28870–3/05/$0.00+$ 1.50 © 2005 by CRC Press
32.1 Introduction Warnings and other text are useless if they cannot be read. Restricted to black and white, the legibility of warnings is primarily a matter of letter size and letter contrast against some background. Other geometric characteristics of the letters, including height-towidth ratio, stroke width, and spacing between letters, also affect legibility. Though the effects of subtler font characteristics are not fully understood, the basic requirements are well established (Sanders and McCormick, 1993; Tinker, 1963). However, the resulting recommendations for good legibility refer only to text in black and white. Technology has made color ubiquitous in printed and electronic display media and evidence is ample that color can attract attention, and organize and improve recognition accuracy of information presented in print and pictures (Braun and Silver, 1995; Jarvis, 1992; Liu and Wickens, 1992; MacDonald and Cole, 1988; Quiller, 1989; Serig, 2000; Smallman and Boynton, 1990; Weimer, 1995). However, no standards for the legibility of colored text or the visual effectiveness of colored graphics have been developed. 32.2 Objectives We review a situation in the early 1990s when lack of standards for the legibility of colored print led to a legal dispute about whether health warnings on cigarette packages met government requirements. We explain why standards related to color were thought to be unnecessary and what was wrong with the research indicating that color had no effect on legibility. A method of measuring legibility that has withstood legal challenge is described. Evidence that color does affect legibility is reviewed. We conclude with recommendations for a legibility standard and a standard methodology to ensure the legibility of warnings in color.
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32.3 Issues On January 1,1989, Health and Welfare Canada, as the Canadian Department of Health was then known, implemented the Tobacco Products Control Act and the Tobacco Products Control Regulations, which required manufacturers and importers of tobacco products to print prescribed health warning messages on their products (Canada, 1988, 1989). The messages were required to be “legible” and “in contrasting colors” (Canada, 1989). Unfortunately, these terms were not spelled out and manufacturers were advised that they could use colors that already appeared on the packs. Given the opportunity to choose any color, manufacturers chose colors such as gold or silver, which tended to blend into the background. This led to an outcry within the health community, which contended that the health warning messages were next to invisible and thus “useless” as a means of informing the public. Measuring Legibility At the heart of the controversy is the question of whether the subjective effect of “being legible” can be objectively measured. The sophist dilemma is avoided by focusing on the practical implications of legibility. If a word is legible, the reader can correctly identify that word. Understanding of perception is based on psychophysics—measuring the physical conditions when stimuli are correctly perceived or distinguished. Advancing technology for direct measurements of brain responses continues to verify the insights gained from psychophysical methods. Legibility is not an all-or-none effect. That it exists in degrees is self-evident because some messages are easier to read than others. To measure the degree to which a subjective quality such as legibility is present, the psychophysical approach is to reduce the strength of stimuli along some physical parameter until the quality in question just disappears. This limit is called the parameter threshold for that quality. For example, to test legibility, the duration, brightness, or size of the words could be reduced to obtain a duration, brightness, etc. threshold for legibility. The rationale is that stimuli that are more effective in terms of this quality will withstand a greater strength reduction before the quality disappears. This does not produce absolute measurements, but the resulting relative measurements of various stimuli have been found reliable and consistent with physiological and behavioral data. Applied to legibility, this psychophysical approach is the basis of the recommendations for optimal height-to-width ratio, stroke thickness, etc. of letters. Legibility and Color Time is a physical parameter that is readily controlled and measured in the laboratory. Therefore, it has been used widely to vary the strength of text formats to measure their legibility (Rea and Oullette, 1991). Shorter viewing durations reduce the strength of the retinal stimulation produced by a printed word. Numerous studies varying the time parameter have shown that hue—the characteristic of color that pertains to redness, yellowness, greenness, etc.—has no effect on legibility when words printed in different hues are equated for lightness contrast against their background (Tinker, 1963;
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Knoblauch et al, 1991; Legge and Rubin, 1986). Accordingly, the legibility of colored words on colored backgrounds should be determinable from the light-dark contrast between the letters and background. On this basis, it should not have been a problem to determine legibility of the warnings printed in color on cigarette packages. So what is the problem? The Trouble with Color Asked to devise an objective method of measuring the legibility of warnings printed on cigarette packages, Nilsson and Percival (1989) felt that duration thresholds could be questioned as unrepresentative of how warnings would be read in the marketplace. A customer waiting at a counter or holding a package would not be constrained to read the warning as quickly as possible. Appearances measured during brief glimpses might differ from what is seen during a steady view. A special problem arises when the effectiveness of colored stimuli is assessed at short durations. Color appearance changes during brief presentations (Courtney and Buchsbaum, 1991; Nilsson, 1972) Thus, the colors seen during rapid presentations would not necessarily be the same as the colors seen during normal viewing. It is also known that information about hue is conveyed by small-diameter, slowly conducting parvocellular pathways while information about hue is conveyed by large-diameter, quickly conducting magnocelluar pathways (Yamagishi and Melara, 2001). Because the brain receives information from lightness contrast sooner than from color, the contribution of color information gets left out when decisions are made rapidly, as would be the case when legibility is measured in terms of duration thresholds or reading speed (Dresp and Grossberg, 1999). Measurements of legibility in terms of time were neither physiologically nor situationally valid. An alternative psychophysical method was needed. What other physical parameter of a printed message can be reduced to measure legibility in terms of a parameter threshold? It would be easy to reduce the illumination, i.e., make it dimmer, but colors also change in hue as brightness decreases. Furthermore, dim lighting is hardly representative of the marketplace. Another basic physical parameter, reading distance, was more difficult to vary, but it did not alter color. Reading distance also had market relevance. If a warning could be recognized at a greater distance, it would more likely capture the reader’s attention. Before describing how we measured legibility distance thresholds and what was found, let us consider how reading distance is related to legibility. Legibility and Retinal Image Compared to books and other folios, warnings vary in letter size from medication labels to billboards and are intended to be read at various distances. Obviously, the size needed depends on the distance, but consider why this is so. The image on the back of the eye determines how many receptor pixels are available to convey letter details to the brain. Letters 2.5 mm high viewed at 30 cm have the same image size as letters 25 mm high viewed at 3 m and letters 250 mm (0.25 m) viewed at 30 m. Various sizetimes-distance combinations produce the same-size image because they subtend the same angle with
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respect to the eye. Figure 32.1 illustrates this concept, which is called “visual angle” and enables describing letters in terms of image size regardless of their physical size and distance. A single receptor cell in the retina of the eye has a surface area that is about .002 mm in diameter. The image of a printed detail whose height and width subtended a visual angle of 25″ (seconds) would cover about 1 receptor. (A 12-mm detail viewed at 100 m has a visual angle of 25″.) Although various
FIGURE 32.1 The relationship among an object’s size, viewing distance, visual angle, and size of retinal image. The E at position A has the same size retinal image as the larger E at position B. Both subtend the same visual angle. When the E at position A is moved back to B, it produces a retinal image that is half the height and one fourth the area of that from A when B is twice as far as A. aspects of detail shape, surrounding features, brightness, color, eye condition, and neural information processing also affect how fine a detail can be recognized, a 25″ visual angle is a common limit for resolving details under good viewing conditions (Woodhouse and Barlow, 1982). How many receptors are needed for letter recognition? A rough estimate can be found by considering the 9.5-mm height of a letter on a standard Snellen eye chart, which is just legible for the average person at 20 ft. This corresponds to a visual angle of 5′ 21″, which is about 12 receptors high. Squaring that for the area of the letter’s image gives a total of 144 receptors involved. In ergonomic practice, prescribing the number of receptors for legibility is avoided by basing recommendations on the visual angle that has been found suitable for reading messages in any situation. This perspective is reversed to describe human visual acuity. The Snellen eye chart typically used by optometrists has standardized letters printed in rows of different sizes to produce letters with various visual angles when viewed at a fixed distance of 20 ft (6 m).
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If, at 20 ft, a certain person can only read letters that are three times as large as those that can be read by the average person, he or she is reading what the average person could read at three times 20 ft. Thus, his or her acuity is described as 20/60. The average person can read those larger letters at 60 ft because at that distance the letters have the same visual angle as the smaller letters at 20 ft. The inference is that the person with 20/60 vision needs the larger image to obtain enough letter details for recognition. Measuring Legibility in Terms of Distance Threshold Changing distance at which a warning is read does not affect its color. In terms of information processing, messages recognized at greater distance have smaller retinal images and therefore require fewer neural pathways to convey the information to the brain. Assuming that some minimum amount of information is needed to reach a decision, it is reasonable to conclude that warnings that convey enough information along fewer pathways are more effective. Furthermore, legibility described in terms of distance can be directly related to the 20/20 clinical, and in some instances legal, definitions of human visual acuity. On these bases, we recommended using distance thresholds to measure legibility of the colored warnings on cigarette packages. 32.4 Examples Measuring Legibility of Tobacco Warnings—1991 Preliminary measurements of legibility distance thresholds were done with a manually operated, illuminated display box holding some examples of cigarette packages and also some warnings on over-the-counter pharmaceuticals (Nilsson and Percival, 1989). The results demonstrated that legibility distance thresholds produced consistent measurements representative of subjective impressions of the difficulty of reading these warnings. Based on this report, Health Canada requested a full study of the legibility of the thencurrent warnings printed in various colors on various-colored backgrounds of cigarette packages then on the market. Additionally, it wanted similar measurements of such warnings printed in black and white on comparable packages. Method The warnings on cigarette packages became small enough to be illegible at 8 m. To hold illumination constant at any distance, the light sources moved with the packages. To obtain true color rendering, continuous spectrum, black-body radiation would enable the visual system to maintain color constancy. To facilitate reproducibility, we chose common 100-W, incandescent bulbs with good diffusion for uniform illumination (General Electric “Soft White”). To reduce scattered light and glare, the light was confined by a baffled housing and directed passively toward the packages by lensless projection, which would not alter the color of the light. Two of these projectors illuminated the packages at a 45° angle from both sides, as recommended by the
Legibility of warnings in color
799
American Society for Testing and Materials (ASTM, 1989), at a distance of 0.60 m to obtain uniform illumination over a 13×18 cm area encompassing the cigarette
FIGURE 32.2 Drawing of the track in the UPEI Legibility Laboratory. To measure legibility thresholds using the psychophysical method of limits, the display box moves toward and away from an observer seated at the end. Materials to be tested are mounted inside the box and illuminated by enclosed lamps. packages. This arrangement produced a luminance of 110 cd/m2 on a Leeds Northrup test plate and had a 2700K color temperature and no discernable variation. The assembly was enclosed in a 1.0×1.0×0.6 m box lined with black velvet to keep stray light to minimum. The display box traveled on rubber wheels along a Formica track guided by a linear bearing. Figure 32.2 shows a schematic drawing of the test track. A computer-controlled stepping motor moved the box by means of a dual chain drive. Distance-threshold measurements at slow velocities minimize the effects of the observer response time but produce slow changes that are difficult to see and also lead to boredom. Velocities in the range of 14 to 19 cm/sec were found to be a good compromise, depending on observer experience and stimulus complexity. The observer was seated at one end of the track with head position maintained by a chin rest. The measurement procedure used the psychophysical “method of limits.” This involved alternate trials in which the cigarette package was moved away until the subject no longer could clearly read the warning or moved toward the subject until the message
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was readable. Ten such measurements were made and then a new package was tested. Measurements for all packages were repeated four times in quadratic counterbalanced sequences to minimize order effects. The subject initiated the trials and distance measurements by push-button signals to a computer, which managed the data collection. Three observers with normal acuity and color vision made the measurements. Results Table 32.1 shows the mean distance thresholds for 11 brands with the warning “Smoking during pregnancy can harm the baby” printed in various colors of letters and backgrounds. One package, labeled *Peter Jackson, had its production warning replaced by one in black on white. Seven other packages with different warnings in black on white were also tested. Arranged in descending order of distance, the most legible brands are at the top. Duncan’s multiple means test was used to determine distance ranges that differed significantly. Also shown are the colors of the warnings and the lightness difference of the letters and their background measured in terms of delta L* in the L*u*v* system. Discussion The most legible brand, Sweet Caporal, had a mean distance threshold of 126 cm, which is one third farther than the 91-cm threshold of the least legible brand, Player’s Plain. That difference in threshold
TABLE 32.1 Letter/Background Colors of Warnings on 12 Brands of Cigarette Packagesa Brand
Warning color
Lightness difference
Threshold distance
Mean sd
Duncan’s range
Relative legibility
Black/white 82 127 1.2 1 1.00 Sweet Caporalb B & H Lights Green/silver 62 117 7.6 2 0.86 MacDonald Silver/cream 23 117 4.1 2 0.86 Select *Peter Black/white 60 115 6.9 2 0.83 Jacksonc Matinee Slims Gold/white 32 111 5.8 3 0.77 Medallion Gold/yellow 34 109 8.6 3 0.75 Peter Jackson White/silver 22 108 5.2 3 0.75 Player’s Gold/dark52 104 2.7 4 0.68 Special blue Player’s Gold/white 35 103 7.8 4 0.66 Medium MacDonald Gold/green 10 103 4.4 4 0.66 Export B & H Special Black/gold 25 98 4.9 5 0.60 Player’s Plain Gold/blue 2 91 2.7 6 0.52 a Along with their lightness difference (L*); mean distance threshold (cm) and its standard
Legibility of warnings in color
801
deviation; significantly different distance ranges by Duncan’s test and their “relative legibility” (see text). b The letters in this warning were spaced farther apart than in all the other warnings. c The *Peter Jackson package had its production white/silver warning changed to black/white.
distance seemed modest compared to the subjective difference in their legibility. However, when one considers the area of their retinal images at threshold, the Sweet Caporal was barely half as large, 52%, as the Player’s. An image that could be read with half as many receptors could well be considered twice as effective in legibility. Because area of an object’s retinal image varies inversely with its distance squared, legibility should be measured as the reciprocal of distance threshold squared. Setting the farthest threshold to 1.00, reciprocal ratios of the threshold distances squared were used to produce a scale of relative legibility based on retinal area. This scale is presented in Table 32.1 When the packages were rotated 22.5° so that the illumination was not at the optimal 45° angle, a major flaw with metallic inks and glossy coatings was revealed. Due to glare, three brands—Matinee Slims, Sweet Caporal, and Peter Jackson—had average legibility distances of 27, 22, and 18 cm, respectively. These close distances should be considered estimates because changes in the illumination reduced the glare and facilitated reading. Many persons would have difficulty focusing on words that close. One package with a glossy finish could not be tested because of glare. If the cellophane wrappers had been left on the packages as when they were sold, many warnings would not have been legible at any distance due to glare. Because consumer products usually are not viewed in optimal lighting, these data indicate the importance of measuring legibility in marketplace conditions. Table 32.1 reveals that lightness contrast was not an adequate indicator of legibility. True, the most legible, Sweet Caporal, and the least legible, Player’s Plain, had the highest and lowest lightness contrasts, respectively, when viewed perpendicularly in 45° incident illumination. However, the gold/dark-blue warning on Player’s Special had an above average contrast ratio, but was among the least legible. Legal Resolution The legibility threshold data provided quantitative evidence that many of the warnings printed on cigarette packages were significantly less legible than warnings printed in black on white. These measurements also showed that metallic inks produced specular glare that made some warnings impossible to read in some lighting conditions. The results also showed that with colored warnings, lightness contrast of the letters with their backgrounds would not ensure legibility. The simplest answer was to restrict warnings to black and white. The data withstood challenge. Finally, in January 1991, the thenMinister of Health, the Honorable Perrin Beatty, announced his intent to amend the regulations so as to make the messages more legible. Minister Beatty proposed that the messages were to be in black and white and to occupy the top 25% of the package. Previously, the messages had occupied the bottom 20% of the pack. It was almost 4 years before the revised health warning messages came into effect (December 14,1994) (Canada, 1993). In support of these regulations, Health Canada had undertaken a number of studies that were ground breaking for their time, including
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consumer research about knowledge, attitudes, and behavior with respect to current and proposed health warning messages and measuring legibility of the current messages with respect to distance. The research indicated that the messages then appearing on cigarette packs had, in addition to being illegible, “worn out.” On August 11, 1993, amendments to the Tobacco Products Control Regulations that would require larger health warning messages in black text on a white background, and white text on a black background, were published (3). Because the Supreme Court of Canada had agreed to hear the appeal on the Tobacco Products Control Act, the tobacco industry filed for a stay of these regulations directly to the Supreme Court. On October 4, 1993, the Supreme Court heard the arguments and on March 3, 1994, rendered its decision. The Court dismissed the application for the stay on the grounds that no compelling reason offset the public health gain associated with these messages. In a subsequent ruling of September 21, 1995, regarding the Tobacco Products Control Act, while striking down most of the Act, including the section on health warning messages, the Supreme Court recognized the right of government to require health warning messages but felt that these messages should be attributed to government. Reliability and Validity of Distance Thresholds Initially, we sought to evaluate the warnings under illumination from clear, 100-W light bulbs. These would be easy to specify for future reference. However, when we went to test the warnings at a 22.5° viewing, it was impossible to read any brands with warnings printed in metallic inks due to specular glare. Accordingly, we switched to the “soft white” coated light bulbs as reported earlier; however, the work was not a total loss. The data obtained with clear bulbs at 90° viewing provided a check on the reliability of distance thresholds measurements. They correlated +0.94 with the data in Table 32.1. This shows that the distance thresholds are a reliable measurement method. A contract with the Canadian Space Agency provided opportunity to examine how measurement procedures affected legibility distance thresholds (Clements-Smith et al., 1993). We used the same cigarette packages as in the Health Canada study. In one experiment, 40 untrained observers each made only two measurements for each package: (1) when the warnings were no longer clearly readable as the package moved away and then as the package approached and (2) when the warnings first became clearly readable as the package returned. These thresholds had a grand mean threshold distance of 197 cm and mean standard deviation of 41. This was longer and more variable than the mean 110-cm threshold and 5.2 standard deviation of the three experienced observers in the Health Canada study. Less experienced observers tended to interpret “clearly readable” more as “no longer unreadable” than did practiced observers; the former may be an easier judgment. The two sets of results correlated +0.65. For comparison, the mean correlation of the three experienced observers was +0.64. Interobserver reliability of the distance threshold measurements was much the same for experienced and inexperienced observers when the number of measurements was the same. In another experiment, 40 different untrained observers saw only the package moving away and were asked to respond only when the warning “could no longer be read.” The 297-cm mean threshold distance and 53 standard deviation of these were understandably longer and still more varied than those of the 40 who judged clearly readable and made
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803
two measurements for each package. Nevertheless, the results obtained using these different criteria correlated +0.85. This indicates that distance threshold measurements were robust in terms of the criteria of judgment. An invitation from NATO to evaluate the effectiveness of camouflage provided opportunity to compare distance thresholds with other methods of evaluation. Images of tanks and personnel carriers in mixed terrains (Toet et al., 1998) were rear-projected onto a screen mounted on the test track. The same method of limits as described previously was used to make measurements. Details are available in Nilsson (2001). The results from five UPEI students were compared with search-time results from 60 NATO observers.
TABLE 32.2 Color Characteristics of Letters and Background Papers Used to Make Various Colored Words on Various Colored Backgrounds Letraset colored letters Pantone background papers Color u* v* L* Pantone name u* v* L* Black 0 White −15 Red 101 Yellow 25 Green −44 Blue −30.5
0 3.8 0.3 32.6 16 −37
0 Black on black 0 0 0 89.5 White −3 8 99.7 42.4 #200 Red 97 −1.3 54 78.7 Process yellow 2 25 34 95.5 37.5 #348 Green −38 10.3 48 34.2 #293 Blue −26 −27 40
The two sets of data correlated +0.80. Furthermore, Duncan’s test revealed little overlap in the images that could not be distinguished in effectiveness by distance thresholds and by search times. This indicates that the two methods were sensitive to different image characteristics. In those circumstances that correlation suggests a strong consistency in what the two methods measured in common. This comparison also showed that distance thresholds distinguished the effectiveness of more images than did search times. Given the fewer subjects with presumably less experience, this indicates that distance thresholds were the more sensitive indicator of visual effectiveness. Legibility of the Six Primary Colors Testing cigarette packages provided information only on certain combinations of colored print. Interaction between colors of objects and their backgrounds makes it difficult to predict appearances on the basis of the measurement of isolated colors (McFadden, 1992). The Space Agency contract enabled systematic measurement of how the six primary colors (red, yellow, green, blue, black, and white) in all letter/background colors affected legibility (Clements-Smith, et al, 1993). The method was basically the same as that used for the Health Canada measurements. Benjafield and Muckenheim (1989) present a list from which 20 four- and five-letter, color-neutral words of high familiarity and high imagery were selected. The words were made from colored Letraset™ 36 Pt. Helvetica medium transfer letters applied to clear acetate sheets. These sheets were laid over Pantone™ papers to provide colored
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backgrounds. Table 32.2 provides the color measurements of these materials under the test box illumination. The words were tested in sequences derived from an initially randomized, selection-without-replacement technique that changed the word, letter color, and background color on each set of eight measurements. ABBA counterbalancing was achieved across the six observers who made the measurements. Averaging across words and observers provided a total of 960 measurements of the legibility of each of the 30 color combinations. Table 32.3 shows the results. Duncan’s range test indicated three color combinations (green/white, black/yellow, green/yellow) that were significantly more legible than black on white. Another 13 color combinations did not differ significantly from black/white (from white/green to yellow on red). These results are consistent with a rarely cited report by Preston and colleagues (1932), who also used the distance method to measure legibility. Though Pastoor (1990) found that color had little effect when legibility depended on reading speed, his observers’ ratings of effectiveness had several color combinations that were better than black/white. In our measurements, lightness contrast correlated only +0.52 with relative legibility. This indicates that contrast accounts for only 25% of the differences in legibility of the various color combinations. Adding the contribution of combined chromaticity, calculated as the root mean square average of u* and v*, improved that correlation +0.64. Trial-and-error calculations were able to obtain correlations in excess of +0.85 by accentuating the contribution of the blue opponent pathways together with a small negative effect of chromatic contrast. Clearly, some color combinations were significantly more legible and many color combinations’ legibility did not differ significantly from black-on-white. This knowledge should facilitate designing warn-
TABLE 32.3 Word Color, Mean Distance Thresholds, Statistically Significant Ranges, Light Contrast (δ)L*, Root Mean Square Chromaticity, and Relative Legibility Compared to Most Effective Green/White Color Combination Letter color
Background color
Distance sd threshold (cm)
Duncan’s ranges
L* rms C*
Relative legibility
Green
White
547
11 1
62
34
100
Black
Yellow
541
11 1 2
96
29
98
Green
Yellow
531
11
58
44
94
White
Green
529
12
3 4
42
29
93
Blue
Yellow
525
13
3 4 5
61
45
92
Black
Red
525
12
3 4 5
54
69
92
Blue
White
522
12 6
3 4 5
66
34
91
Black
White
518
12 6 7
4 5 100
6
90
Black
Green
515
12 6 7 8
28
89
2 3
5
48
Legibility of warnings in color
805
Yellow
Blue
512
11 6 7 8
39
35
88
White
Blue
512
11 6 7 8
50
28
88
Yellow
Black
511
11 6 7 8
79
23
87
Blue
Red
510
12 6 7 8
20
77
87
Green
Red
510
12 6 7 8
17
76
87
Blue
Green
509
12 6 7 8
14
34
87
Red
White
509
12 6 7 8
57
72
86
Yellow
Red
505
12
7 8 9
25
72
85
White
Red
504
12
8 9
36
69
85
Red
Yellow
496
12
9
53
77
82
Yellow
Green
495
11
9
31
36
82
Red
Black
495
12
9
42
72
82
Black
Blue
474
12
10 40
37
75
White
Black
473
11
10 90
10
75
Red
Blue
463
11
10
2
77
72
Green
Blue
388
11 11
3
42
50
Green
Black
371
11
38
33
46
Red
Green
353
13
6
76
42
White
Yellow
282
10
14
6
32
26
Blue
Black
276
10
14
34
34
25
Yellow
White
240
10
15 21
24
19
12 13
ings that are legible, can attract attention, and still use various colors to organize information when several aspects need to be conveyed. Measuring Colored Graphics Symbols as well as words are often used in warnings. The Space Agency contract also called for measuring the effectiveness of various colors of symbols on colored
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backgrounds. Ten symbols were selected from a reference book of standard symbols (Dryfuss, 1972). We chose symbols of approximately equal complexity, which were relatively color neutral and not so familiar as to be associated with particular color combinations. The symbols included a person digging and a lighthouse. Because the purpose was not to evaluate the shapes, results were averaged across the symbols in terms of color combination. The measurements were obtained by the same methods as described previously. Additional details are presented in Clements-Smith et al. (1993) and Nilsson and Connolly (1997). Table 32.4 shows the mean distance thresholds, standard deviations, Duncan’s ranges, relative legibility, lightness contrast, and a measure of the combined chromaticity of the two colors as a root-mean-square average of their u* and v* chromaticity characteristics. There were 14 significantly different ranges of distance thresholds for clearly recognizing the symbols. Two combinations—black/red and black/yellow—were significantly more legible than black/white. Seven other color combinations (from white/blue to
TABLE 32.4 Effects of Symbol Color and Background Color on Recognition Distance, Significantly Different Distance Ranges According to Duncan’s Test, Other Color Characteristics of the Display, and Relative Legibility Compared to the Most Easily Recognized Black/Red Symbols Symbol Background Recognition sd color color distance (cm) Black Black White Black Blue Red Green Yellow Black Blue Red White White Green Yellow Yellow Green Yellow White Red
Red Yellow Blue White Yellow Black Yellow Green Green White Yellow Red Green White Red Blue Black Black Black White
442 12 442 11 433 11 427 11 423 13 423 11 422 11 421 12 418 10 418 11 415 12 414 11 414 12 413 12 411 11 408 11 407 10 407 9 403 10 402 11
Duncan’s ranges 1 1 1 2 2 2 2
6 6 6 6 6 6 6 6 6 6
7 7 7 7 7 7 7 7 7
3 3 3 3 3 3 3
8 8 8 8 8 8 8
4 4 4 4 4 4 4 4 4 4
9 9
δL*
5 5 5 5 5 5 5 5 5 5
52 92 61 99 54 52 47 47 50 61 40 47 49 49 40 54 50 92 99 47
rms Relative chromaticity legibility (%) 70 35 27 7 43 70 46 46 38 27 77 69 38 38 77 43 38 35 7 69
100 100 96 93 92 91 91 91 89 89 88 88 88 87 86 85 85 85 83 83
Legibility of warnings in color Blue Red Black Blue Blue Green Green Red Yellow White
Red Blue Blue Black Green Red Blue Green White Yellow
401 12 394 11 10 389 11 10 376 11 11 375 13 11 369 10 11 357 10 354 10 235 9 224 9
8
12 12
807 9 9
14 14 38 38 12 2 12 2 13 7 14 7
74 74 26 26 46 79 48 79 35 35
82 79 77 72 72 70 65 64 28 26
blue/white) were not significantly different in legibility from black/white despite the fact that some of these (green and yellow) had less than half the lightness contrast of black and white. The correlation of relative legibility with lightness contrast was +0.64. Trialand-error calculations applying various weights for lightness contrast, chromaticity, and other color characteristics resulted in a correlation of +0.95, with the following formula: +0.8 L*+rms C* −0.4 mean u* −0.4 mean v* −.05 C*. According to this formula, chromaticity has a greater influence on legibility than lightness contrast, blueness is beneficial, and chromatic contrast is somewhat detrimental. However, better solutions may be possible. Revised Tobacco Warnings—1999 In 1999, Health Canada sought to improve the effectiveness of warnings on cigarette packages further. In particular, it wanted the warnings to be still larger. Whereas the 1991 warnings had 33% of the front of a cigarette package, 40, 50, and 60% were considered. The larger areas would enable larger print and provide room for graphics to reinforce the verbal message. The warnings varied in complexity from “Smoking kills babies” to “This year the equivalent of a small city will die from smoking.” The graphics included illustrations of diseased lungs, children, and bar graphs presented in color and in black and white. Anticipating challenges from the tobacco companies, the UPEI Legibility Laboratory was asked to measure the effects of total warning size and font characteristics on legibility and to measure the effectiveness of various types of added graphics (Nilsson, 1999). Legibility To evaluate legibility of the warnings’ text, we used the method of measuring distance thresholds described earlier. The observers were 14 UPEI students screened for normal acuity and color vision. The sequence of the 26 package designs was arranged so that successive packages varied as to type of design and size of the overall warning. Each observer viewed all packages in a single 2-hour session, which was repeated another day in reverse sequence to obtain within-observer ABBA counterbalancing. The results are presented in Table 32.5, arranged in descending order of legibility. As expected, the larger the font was, the greater the distance threshold was (r=+0.94). This follows directly from the relationship among letter height, legibility distance, and
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visual angle. Consider the black-on-white warning “Die hard smokers die hard deaths,” which was provided in three letter heights of 6,4.8, and 3.7 mm on otherwise similar designs. Their respective legibility thresholds of 360, 292, and 273 cm define visual angles of 5.73, 5.65, and 4.66′. A similar effect occurred with the three sizes of the “Cigarettes cause strokes” warning. The smaller warnings led to slightly less stringent criteria for legibility. Both sets of warnings involved retinal images of letters that were about 13 receptors high. Given that a Snellen chart letter for 20/20 acuity is about 12 receptors high, this result is reasonable considering the “clearly readable” criterion here. The results also revealed effects of other characteristics of the words. For a given font size, black letters on white backgrounds were more effective than white on black. In these samples, the black and the white
TABLE 32.5 Warnings Listed in Descending Order of Distance Threshold along with Other Characteristics and Rated Overall Effectiveness Size (% of front)
Letter height (mm)
Warning Cause strokes Kills babies Die hard Kills babies Children sick Children sick Children see Children see Mouth cancer Cause strokes Children see Children sick Kills babies Children see Mouth
Letter/ background color
Picture Distance color (cm) Mean se
Relative Rating legibility (%) Mean se
60
7
Black/w
Color
387
10.7
100
6.6 0.39
60
7.8
W/gray
Color
385
12.4
99
6.4 0.38
60 50
6 7
Black/w W/gray
Color Color
360 348
7.5 10.8
87 81
6.4 0.41 6.1 0.40
50
6
W/black
B&W
343
9.7
79
5.6 0.44
60
6
W/black
B&W
343
12.2
79
5.4 0.52
60
6
W/black
B&W
342
8.2
78
5.1 0.54
60
6
W/black
B&W
335
13.9
75
5.4 0.43
60
6
W/flesh
Color
334
8.6
75
7.1 0.36
40
5
Black/w
Color
315
10.6
66
6.4 0.43
40
5
W/black
B&W
311
10.1
65
5.1 0.36
40
5
W/black
B&W
305
8.6
62
5.5 0.53
40
5
W/gray
Color
302
7.5
61
5.9 0.37
40
5
W/black
B&W
301
6.5
61
4.9 0.41
50
5
W/flesh
Color
294
10.3
58
7.1 0.29
Legibility of warnings in color cancer Die hard Mouth cancer Children see Current— duM Children see Current— duM Cause strokes Die hard Yearly deaths Yearly deaths Yearly deaths
809
40 40
4.8 5
Black/w W/flesh
Color Color
292 287
10.1 8.9
57 55
5.9 0.45 6.9 0.29
50
4.8
W/black
B&W
282
7.8
53
4.9 0.41
33
4
Black/w
None
282
6.4
53
2.1 0.32
50
4.8
W/black
None
278
7.4
52
4.9 0.36
33
4.2
W/black
None
278
8.1
52
1.9 0.44
50
4
Black/w
Color
277
8.2
51
5.9 0.41
50 60
3.7 4
Black/w Black/w
Color B&W
273 271
9.9 7.8
50 49
6.4 0.30 3.0 0.67
50
3
Black/w
B&W
225
10.9
34
3.4 0.56
40
2.5
Black/w
B&W
223
14.3
33
3.5 0.71
letters had the same stroke width. As Sanders and McCormick (1993) point out, legibility of white letters on black backgrounds can be improved by using slightly narrower stroke widths. The white letters on gray in the “kills babies” warnings were still less legible, which is consistent with the effects of lightness contrast on legibility. Least legible were the white letters on varied flesh-colored backgrounds in the mouth cancer warnings. Based on the results with six primary colors, shown in Table 32.4, black letters on this reddish background might have been more legible. (Research currently in progress is measuring legibility with a greater variety of color combinations.) However, variations in the color background of this warning, ranging from the teeth to dark recesses, would make it difficult to select a single, optimal color for the letters. Effectiveness of the Graphics The Space Agency project had used distance thresholds to measure the effects of various image-enhancement techniques on identifying certain features in complex images (Nilsson et al., 1994) and the effects of various graphic and text designs on identifying the contents of potato bags. However, those tasks involved recognition, which was not the issue with the variety of graphic information in the cigarette warnings. Instead, at the end of the second session, the observers reviewed the packages and rated each for overall effectiveness of its warning. They used a scale in which 0 was “not effective,” 4 to 5 were “moderately effective,” and 9 was “very effective.” In Table 32.6, the results are arranged in descending order of the ratings. All warnings that employed colored graphics were judged more effective than those with black and white graphics. All warnings with graphics were judged more effective
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than the two duMaurier warnings without graphics. Based on mean ratings, black and white graphics were more than twice as effective as
TABLE 32.6 Warnings Listed in Descending Order of Rated Overall Effectiveness along with Other Characteristics and Distance Thresholds Size (% Letter of front) height (mm) Warning Mouth cancer Mouth cancer Mouth cancer Cause strokes Kills babies Cause strokes Die hard Die hard Kills babies Kills babies Cause strokes Die hard Children sick Children sick Children sick Children see Children see Children see Children see Children see Children
Letter/ background color
Picture Distance Relative Rating color legibility (cm) (%) Mean se Mean se
60
6
W/flesh
Color
334
8.6
75
7.1 0.39
50
5
W/flesh
Color
294
10.3
58
7.1 0.38
40
5
W/flesh
Color
287
8.9
55
6.9 0.46
60
7
Black/w
Color
387
10.7
100
6.6 0.40
60
7.8
W/gray
Color
385
12.4
99
6.4 0.44
40
5
Black/w
Color
315
10.6
66
6.4 0.52
60 50 50
6 3.7 7
Black/w Black/w W/gray
Color Color Color
360 273 348
7.5 9.9 10.8
87 50 81
6.4 0.54 6.4 0.43 6,1 0.36
40
5
W/gray
Color
302
7.5
61
5.9 0.43
50
4
Black/w
Color
277
8.2
51
5.9 0.36
40 50
4.8 6
Black/w W/black
Color B&W
292 343
10.1 9.7
57 79
5.9 0.53 5.6 0.37
40
5
W/black
B&W
305
8.6
62
5.5 0.41
60
6
W/black
B&W
343
12.2
79
5.4 0.29
60
6
W/black
B&W
335
13.9
75
5.4 0.45
60
6
W/black
B&W
342
8.2
78
5.1 0.29
40
5
W/black
B&W
311
10.1
65
5.1 0.41
50
4.8
W/black
B&W
278
7.4
52
4.9 0.32
50
4.8
W/black
B&W
282
7.8
53
4.9 0.36
40
5
W/black
B&W
301
6.5
61
4.9 0.44
Legibility of warnings in color see Yearly deaths Yearly deaths Yearly deaths Current— duM Current— duM
811
40
2.5
Black/w
B&W
223
14.3
33
3.5 0.41
50
3
Black/w
B&W
225
10.9
34
3.4 0.30
60
4
Black/w
B&W
271
7.8
49
3.0 0.67
33
4
Black/w
None
282
6.4
53
2.1 0.56
33
4.2
W/black
None
278
8.1
52
1.9 0.71
no graphics; colored graphics were more than three times as effective as none. For overall effectiveness, “Cigarettes cause mouth cancer” with its horrendous illustration of diseased gums, was rated most effective, regardless of the size of its letters and despite the fact that they were the least legible of all letters of the same size. This shows that excellent graphics can overcome poor legibility. However, interaction between legibility and overall effectiveness with graphics is not a simple matter. Interaction between Letters and Graphics The effects of a pictorial background interfering with legibility were noted above for the “mouth cancer” warning. Additional evidence that background pictures interfered somewhat with legibility was provided by the (then) current DuMaurier black-on-white warning. Enclosed in its own box and without accompanying graphics, this warning was not significantly less legible than many warnings using larger letters combined with graphics and was the most legible (though not significantly) of all warnings using its 4mm letter size. In terms of overall effectiveness, interaction between letters and graphics was not simple. Larger letters correlated +0.60 with higher ratings of effectiveness. This was evident in the “mouth cancer,” “causes strokes,” and “kills babies” warnings, but not the “die hard” and “yearly deaths” warnings. Yet, larger warning size, which generally provided larger graphics, correlated only +0.40 with higher ratings of effectiveness. This was evident with the “mouth cancer,” “kills babies,” and “die hard” warnings, but not for the “causes strokes,” “children sick,” and “yearly deaths” warnings. Reliability With a grand mean of 397 cm and a mean standard error of 9.5, the legibility measurements were 97% consistent. That the ratings were somewhat less consistent (92%) is consistent with their less precise scale and fewer measurements. Two identical sets of warnings, “Children see, children do,” in three sizes were distributed across the testing sequence to provide an indication of the reliability of the distance thresholds and ratings. The 7-cm mean difference in their distance thresholds was 2% of their mean distance (see Table 32.6), indicating 98% reliability. Similarly, their ratings were 97% reliable.
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Legal Outcome On June 26, 2000, the Tobacco Products Information Regulations were registered by the government of Canada (Canada, 2000). These regulations require manufacturers to print health warning messages that incorporate pictures or graphics with text on 50% of the package. 32.5 Ensuring Legibility The present data provide some information on the most legible combinations of colors for words and symbols and on which combinations to avoid. Duncan’s range test on these data indicates several different color combinations that are not significantly different in effectiveness. With several comparably effective color combinations, designers can create a variety of visually effective warnings that would suit other color-coding needs. However, with hundreds of letter fonts, millions of color combinations, and innumerable other options for symbols interacting in their effects on legibility, it is evident that it would be impossible to provide specific guidelines to ensure legibility. Legibility Standards There is an alternative to specific guidelines that involves a standardized, simple method of measuring legibility and visual effectiveness in terms of distance along with a “legibility standard.” Copies of a legibility standard would be used for comparison with an uncalibrated warning to determine its relative legibility. Legal requirements for vision are already based on distance. The widely used 20/50 criterion for adequate vision of drivers means that the driver must be able to see at 20 ft what the average person can see at 50. Distance specifications of legibility and effectiveness can therefore be directly related to medical and legal practices. Consider the following. For a person with 20/20 vision, comparing a warning with a legibility distance of 360 cm with a warning that has a legibility distance of 180 cm is like degrading that person’s vision to 20/40. 1 Furthermore, a warning with a legibility distance of 80 cm for people with normal vision would be unrecognizable at any distance by people with 20/60 vision because they could not bring the warning close enough before it was too close to be focused. Because the ability to focus closely deteriorates with age, this limitation should be considered in the design of warnings intended to be readable for elderly people. The distance method is also conceptually simple to implement. In principle, it involves only a tape measure and a means of moving the display or the observer back and forth. Printed warnings require a certain level of even, glare-free illumination from a continuous spectrum source. This can be obtained from ordinary, 100-W light bulbs. No complex electronics or optics are essential. To ensure uniform illumination if the warning is moved, guidelines could be provided for an inexpensive viewing apparatus that would enable manufacturers and design houses to do their evaluation during design development. A legibility standard need only be a certain, agreed-upon warning. For verbal warnings, this could be one of the warnings in black on white currently used on cigarette packages. “Smoking can harm the baby” for example, contains a reasonable mixture of
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letters for a short, simple warning. The most frequent and widely seen warning in the English-speaking world is probably that on the back of school buses, “Do not pass when lights are flashing”; this also seems suitable. A separate standard for the recognition of symbols should also be considered; perhaps the widely used road sign for a school bus stop. The acceptability of any other warning would be determined by comparing its relative legibility to that of a copy of the standard using the same measuring facility for both designs. With the standard’s relative legibility set to 100%, any design, regardless of color, font, etc., whose relative legibility was at least 75% (for example) could be defined as acceptable. The provision of a legibility standard reduces the need for stringent specification of the testing apparatus because variations that might somewhat increase or decrease the legibility distance of the design being tested would similarly affect the measurements of the standard. The distance method, together with a legibility standard, offers a robust means of ensuring visually adequate warnings. Effective Color Combinations In comparison, the most effective color combinations for words (Table 32.3) and those for symbols (Table 32.4) differ. Granted, the colors did not match perfectly but they were similar enough to pass a quick inspection. Their legibility correlated +0.81. The Space Agency project also measured the effectiveness of different two-color combinations of the same six primary hues in line drawings. These results differed somewhat from the words and the symbols. Their correlation with word colors was +0.79 and with symbols was +0.89. Lightness contrast contributed considerably more to the recognizability of line drawing (+0.86) than it did for words (+0.52) and symbols (+0.64). However, some color combinations were always significantly more effective than black and white, which has the highest lightness contrast, of course. Visual effectiveness of any of these colored displays was not well predicted from lightness contrast. The differences may be due to an interaction between relative size of the foreground compared to the background and differences in receptive field size of the different color pathways. In a manner similar to the differences in legibility of black-on-white and white-on-black (Sanders and McCormick, 1993), retinal glare likely contributed to differences in effectiveness of the same colors, depending on which was figure and which was background. These differences occurred somewhat more often for combinations with large lightness differences. Measurements now underway may reveal a systematic relationship. Until then, what can be recommended for producing effective warnings in messages that combine words, symbols, and pictures? We arrived at a solution by averaging the legibility distances of the three sets of measurements. A relative averaging technique was used to equalize the contributions from the three formats despite 1
A reader with 20/20 vision or vision corrected to 20/20 may experience this effect by borrowing a pair of glasses from a person with 20/40 vision. Compare any warning with how it appears with and without those extra glasses; this illustrates the loss of legibility that results when legibility distance is halved.
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TABLE 32.7 Average Legibility Distances, Standard Deviations, Duncan’s Range, and Relative Legibility Averaged across Words, Symbols, and Line Drawings Figure Ground Legible sd Duncan’s Relative Figure Ground Legible sd Duncan’s Relative distance range legibility distance range legibility Black Yellow Black Red Black White Black Green Black Blue White Blue White Green White Red White Black White Yellow Red Black Red White Red Yellow Red Blue Red Green Yellow Blue Yellow Black Yellow Green Yellow Red Yellow White Green Yellow Green White Green Red Green Black Green Blue Blue Yellow Blue White Blue Red Blue Green Blue Black
426 11 421 11 417 11 403 10 370 11 424 11 417 11 403 11 397 10 215 8 406 11 395 11 394 10 379 10 313 10 410 10 409 10 407 11 403 11 209 8 413 10 412 11 375 10 348 10 321 10 414 12 408 11 393 11 367 11 296 10
2.8 3.5 3.8 6.5 10.7 3.2 4.0 6.8 6.7 14.7 5.7 8.3 8.2 9.3 12.7 5.7 5.5 5.3 6.8 14.3 4.7 5.2 10.0 10.0 12.3 4.3 5.7 8.7 10.7 12.7
1.00 Yellow Black 0.98 Red Black 0.96 White Black 0.90 Green Black 0.76 Blue Black 0.99 Black White 0.96 Green White 0.90 Blue White 0.87 Red White 0.26 Yellow White 0.91 Black Red 0.86 Yellow Red 0.86 White Red 0.79 Blue Red 0.54 Green Red 0.93 Black Yellow 0.93 Blue Yellow 0.92 Green Yellow 0.90 Red Yellow 0.24 White Yellow 0.94 White Green 0.94 Yellow Green 0.78 Black Green 0.67 Blue Green 0.57 Red Green 0.95 White Blue 0.92 Yellow Blue 0.85 Red Blue 0.74 Black Blue 0.48 Green Blue
409 10 406 11 397 10 348 10 296 10 417 11 412 11 408 11 395 11 209 8 421 11 403 11 403 11 393 11 375 10 426 11 414 12 413 10 394 10 215 8 417 11 407 11 403 10 367 11 313 10 424 11 410 10 379 10 370 11 321 10
5.5 5.7 6.7 10.0 12.7 3.8 5.2 5.7 8.3 14.3 3.5 6.8 6.8 8.7 10.0 2.8 4.3 4.7 8.2 14.7 4.0 5.3 6.5 10.7 12.7 3.2 5.7 9.3 10.7 12.3
0.93 0.91 0.87 0.67 0.48 0.96 0.94 0.92 0.86 0.24 0.98 0.90 0.90 0.85 0.78 1.00 0.95 0.94 0.86 0.26 0.96 0.92 0.90 0.74 0.54 0.99 0.93 0.79 0.76 0.57
differences in their general distance thresholds. These averages are presented in Table 32.7. To facilitate their use, the results are arranged in descending order for the six basic colors used for the figure (word, symbol, or line) and again for these colors used in the background. Mean values of Duncan’s ranges may be subject to interpretation because averaging produces decimal values. Nevertheless, it seems reasonable to consider combinations whose mean range values differ by 1.0 as differing significantly.
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Other Recommendations Based on the results of the present study and related research, the following nine recommendations would help maximize the legibility and visual effectiveness of health warnings. Based on other data and observations, Kroemer and colleagues (2001) provide some similar recommendations for the use of color in displays. • Use the largest letters possible. Letter size was more important than size of the warning area; of course, bigger letters require more space. • Place the words on a uniform background instead of on top of pictorial details. • The legibility of warnings can be improved by the use of letter/background colors other than black and white. The effects of letter size on optimal color combinations should be determined. • Black letters on white backgrounds are slightly more legible than the reverse. This also tends to happen with light and dark colors. Sanders and McCormick (1993) suggest that the legibility of white letters on black may be optimized by using slightly narrower stroke widths than those for black/white. It seems reasonable that this would also work for light colors, but this remains to be determined systematically. • When other aspects of the warning design lead to a background color that is neither black nor white, a letter color that is neither white nor black may maximize legibility. The present data on the six primary colors for words and symbols and for an average of words, symbols, and lines are presented in Table 32.3, Table 32.4, and Table 32.6, respectively. Further systematic testing of additional color combinations is underway. • Avoid glossy surface coatings and metallic inks. Under certain common lighting conditions, these produce glare that can severely degrade legibility. A flat or matte finish would make the warnings legible under a wider range of lighting conditions. • Use color pictures and/or symbols to improve effectiveness. • Use the biggest pictures possible to improve visual effectiveness. • The number of relevant factors in a warning, such as color, size, interactions between words and pictures, style, and theme of the words and picture, make specifications an unfeasible means of ensuring legibility or visual effectiveness. Instead, a comparative standard for the legibility and effectiveness of health warnings should be established. The acceptability of any warning design could then be specified relative to this standard using distance measurements.
Defining Terms Acuity—A measure of the visual system’s ability to identify stimulus spatial details. “20/20” acuity means that the person in question can identify at 20 ft letters of a size that the average person can identify at 20 ft. “20/200” acuity means the person can identify at 20 ft what an average person can at 200 ft. The height of a letter that defines 20/20 acuity has a visual angle of 5′ 21″. The height of its retinal image would cover about 12 light receptors. Legibility—A characteristic of a warning (or symbol) arising from its physical properties that describes how clearly it can be seen and thereby be potentially understandable independently of its semantic characteristics.
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Legibility distance threshold—When using the “method of limits,” it is the mean of the distances where a receding word first could no longer be seen clearly and the distances where an approaching word first could be seen clearly. Method of limits—A way to determine thresholds by averaging two sets of alternating measurements. For one set, the size, strength, or other quality of a stimulus is decreased until a certain characteristic of the stimulus is no longer perceived. For the other measurement, the size, strength, or other quality of a stimulus is increased until a certain characteristic of the stimulus is perceived. Relative legibility—The ratio of a given warning’s legibility distance threshold squared to the distance threshold squared of a standard warning. The size of a warning’s retinal image is inversely related to the square of its distance. Assuming that a more legible warning requires fewer visual pathways to be clearly seen, the ratio represents the legibility of the given warning compared to the standard warning. Retinal image—Image of a warning (or any object) focused on the back (retina) of the eye. In the center of the retina where detail is best sensed for reading, there are about as many neural pathways to the brain as there are light receptors. A single receptor receives light from a directional cone that is about 25″ in visual angle. Threshold—A measurement of the size, strength, or other physical quality of a stimulus when a certain characteristic of that stimulus is just barely perceptible. Visual angle—The plane angle subtended by a certain dimension of an object (such as its height) with respect to the center of the viewer’s eye. Visual angle defines the size of an object’s retinal image at various height and distance combinations. References ASTM (1989 ) Standard practice for visual evaluation of color differences of opaque materials. Publication D 1729–89. (Philadelphia: American Society for Testing and Materials). Benjafield, J. and Muckenheim, R. (1989) Dates of entry and measures of imagery, concreteness, goodness, and familiarity for 1046 words sampled from the Oxford English Dictionary. Behav. Res. Methods Instruments Computers , 21, 31–52. Braun, C.C. and Silver, N.C. (1995) Interaction of signal word and colour on warnings labels: differences in perceived hazard and behavioural compliance. Ergonomics , 38, 2207–2220. Canada (1988) The Tobacco Products Control Act. Review Statistics Canada , Ch. 20, 1988. Canada (1989) Tobacco Products Control Regulations. Canada Gazette , part II; 123(2); SOR/DORS/89–21 (December 27, 1988), amended by 123 (11): SOR/DORS/89–248 (May 4, 1989). Canada (1993) Tobacco Products Control Regulations, amendment, SOR/DORS/ 93–389. Canada (2000) Tobacco Products Information Regulations, SOR/DORS/2000–272. Clements-Smith, G., Nilsson, T.H., Connolly, G.K., and Ireland. W. (1993) Development of an industrial service utilizing new technology to optimize visual information displays for both human and machine vision. (Report 9F006–2-0021). Canadian Space Agency, Ottawa. Courtney, S.M. and Buchsbaum, G. (1991) Temporal differences between color pathways within the retina as a possible origin of subjective colors. Vision Res. , 31, 1541–1548. Dresp, B. and Grossberg, S. (1999) Spatial facilitation by color and luminance edges: boundary and attentional factors. Vision Res. , 39, 3431–3443. Dreyfuss, H. (1972) Symbol Sourcebook . New York: McGraw-Hill. Jarvis, L.R. (1992) The microcomputer and image analysis in diagnostic pathology. Microscopy Res. Technique , 21, 292–299.
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Knoblauch, K., Arditi, A., and Szlyk, J. (1991) Effects of chromatics and luminance contrast on reading. J. Opt. Soc. Am. A , 8, 428–439. Kroemer, K., Kroemer, H., and Kroemer-Elbert, K. (2001) Ergonomics (2nd ed.). Upper Saddle River, NJ: Prentice-Hall. Legge, G.E. and Rubin, G.S. (1986) Psychophysics of reading IV. Wavelength effects in normal and low vision. J. Opt. Soc. Am. A , 3, 40–51. Liu, Y. and Wickens, C.D. (1992) Use of computer graphics and cluster analysis in aiding relational judgment. Hum. Factors , 34, 165–178. MacDonald, W.A. and Cole, L. (1988) Evaluating the role of color in a flight information cockpit display. Ergonomics , 31, 13–37. McFadden, S. (1992) Discrimination of colours presented against different coloured backgrounds. Colour Res. Application , 17, 339–351. Nilsson, T.H. (1972) The effects of pulse length and pulse duration on hue of monochromatic stimuli. Vision Res. , 12, 523–529. Nilsson, T.H. (1991) Legibility of tobacco health messages with respect to distance. Report to the Tobacco Products Division of Health and Welfare Canada (contract H4078). Nilsson, T.H. (1999) Legibility and Visual Effectiveness of Some Proposed and Current Health Warnings on Cigarette Packages. Report to the Bureau of Tobacco Control, Health Canada, contract H4097. Nilsson, T.H. (2001) Evaluation of target acquisition difficulty using recognition distance to measure required retinal area. Opt. Eng. , 40, 1827–1834. Nilsson, T.H. and Connolly, G.K. (1997) Chromatic contribution to shape perception revealed in a nontemporal task using distance. In Dickinson, C., Murphy, I., and Garden, D. (Eds.), John Dalton’s Colour Vision Legacy . Bristol, PA: Taylor & Francis, 197–206. Nilsson, T.H., Connolly, G.K., and Ireland, W. (1994) Evaluating the effectiveness of image enhancement techniques in terms of visibility distance. Perception , 23, suppl. 12 (abs.). Nilsson, T.H. and Percival, T.Q. (1989) Evaluating the legibility of tobacco health warnings with a method suitable for defining market guidelines. (Report K302507). Health and Welfare Canada, Ottawa, 1989. Pastoor, S. (1990) Legibility and subjective preference for color combinations in text. Human Factor , 32, 157–171. Preston, K., Swankl, H.P., and Tinker, M.A. (1932) The effect of variations in color of print and background on legibility. J. Gen. Psychol , 6, 459–461. Quiller, S. (1989) Color Choices . New York: Watson-Guptil. Rea, M.S. and Oullette, M.J. (1991) Relative visual performance: a basis for application. Lighting Res. Technol. , 23, 135–144. Sanders, M.S. and McCormick, E.J. (1993) Human Factors in Engineering Design . New York: McGraw-Hill. Serig, E.M. (2000) The influence of container shape and color cues on consumer product risk perception and precautionary intent. Proc. Int. Ergonomics Assoc. Hum. Factors Ergonomics Soc. 2000 Congr. , 4, 290–293. Smallman, H.S. and Boyton, R.M. (1990) Segregation of basic colors in an information display. J. Opt. Soc. Am. , A, 7, 1985–1004. Tinker, M.A. (1963) Legibility of Print . Ames, IA: Iowa State University Press. Toet, A., Bijl, P., Kooi, F.L., and Valeton, J.M. (1998) A high-resolution data set for testing search and detection models. (Report TM-98-A020). TNO Human Factors Research Institute, Soesterberg, The Netherlands. Weimer, J. (1995) Research Techniques in Human Engineering . Englewood Cliffs, NJ: PrenticeHall. Woodhouse, J.M. and Barlow, H.B. (1982) Spatial and temporal resolution and analysis. In Barlow, H.B. and Mollon, J.D. (Eds.), The Senses . Cambridge: Cambridge University Press, 133–164.
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Yamagishi, N. and Melara, R.D. (2001) Informational primacy of visual dimensions: specialized roles for luminance and chromaticity in figure-ground perception. Percept. Psychophys. , 63, 824–846.
Further Information Boff, K.R. and Lincoln, J.E. (1988) Engineering Data Compendium: Human Perception and Performance . Wright-Patter son Air Force Base, Ohio. Laughery, K.L., Sr., Wogalter, M.S., and Young, S.L. (Eds.) (1994) Human Factors Perspectives on Warnings . Santa Monica, CA: Human Factors and Ergonomics Society. Rogers, W.A., Lamson, N., and Rousseau, G.K. (2000) Warning research: an integrative approach. Hum. Factors , 42, 102–139. Sanders, M.S. and McCormick, E.J. (1993) Human Factors in Engineering Design . New York: McGraw-Hill. Wogalter, M.S., Young, S.L., and Laughery, K.L., Sr. (Eds.) (2001) Human Factors Perspectives on Warnings , vol. 2. Santa Monica, CA: Human Factors and Ergonomics Society. Wyszeki, G. and Stiles, W.S. (1983) Color Concepts, Methods, and Formulae . New York: Wiley.
33 A Human Factors View of Product Liability and Malpractice Litigation Martin I.Kurke Kurke Associates 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
33.1 Introduction When a human factors practitioner is called upon by an attorney as a potential consultant or a potential expert witness, that practitioner is expected to have certain knowledge and skills pertaining to his field of expertise. However, to be effective, he also must possess a reasonable amount of knowledge and skills pertaining to the environment that he has been invited to enter. The typical human factors/ergonomics professional’s base of knowledge and experience may be in one or more disciplines as diverse as psychology, engineering, medical, or life or computer science, but the number includes less than a handful with formal training in law (Human Factors and Ergonomics Society, 2002). The forensic human factors practitioner must blend his training and experience to the requirements of a legal system that demands compliance with its peculiar system of logic, procedures, and concepts of truth. In this chapter, we will concern ourselves with how such practitioners can support litigators in their support of tort actions such as products liability and other cases involving personal injury and/or property damage, destruction, or wrongful death. We must have a basic understanding of the legal theories and action objectives of the plaintiff’s and the defendant’s attorneys and how a systems approach can help resolve the issues of law and fact brought to trial. The chapter will provide the reader with a brief discussion of the legal theories under which product liability actions are brought with emphasis upon the role of human behavior. It is postulated that all accidents have their roots in human error, whether by participants in the accident or by designers of the product or of the operation, maintenance, or production procedures earlier in the system’s life span. The chapter continues with a discussion of human reliability and how it may be degraded. It proposes a forensic task analysis to assist the human factors/ ergonomics expert in helping the trier of fact determine whether liability should be attributed to a defendant in an action alleging defective products or behaviors associated with their use.
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33.2 Forensic Human Factors Experts Must Understand the Legal Environment The system of jurisprudence followed in American and most British Commonwealth countries is adversarial in nature. It relies upon attorneys acting on behalf of the litigants, who may call upon witnesses to testify on behalf of their client’s cause. The decision supporting the position of one of the adversaries is determined by the trier of fact, who may be a jury or the judge. The judge also presides and settles issues of law that will come up during trial. In this system, two types of witnesses may be called upon to testify at trial. The first kind is one who may testify only as to facts that are in the witness’s possession. Such witnesses are not permitted to express any opinion as to the meaning of those facts; the attorney for each side of the controversy must try to convince the trier of fact to interpret those facts as the attorney would prefer. Under the adversarial system, it is recognized that, at times, the triers of fact may be faced with technical matters for which their life’s experience and education have not prepared them. Under such circumstances, the attorneys for either or both sides may call upon expert witnesses, whose job is to educate the trier of fact and to offer an opinion, interpreting established facts related to their fields of expertise. Because the attorneys for each side will have conflicting objectives, it should not be surprising to find that the attorneys representing each side of the conflict almost unvaryingly will select only expert witnesses who will focus their testimony upon facts most favorable to the client’s position. This may lead to a battle of the experts with conflicting testimonies or, more often, with each witness testifying on limited aspects of the totality of events involved in the issues at trial. As a result, a jury may be faced with expert information from one or more plaintiff’s witnesses who support and interpret one set of facts on behalf of the plaintiff’s position in the conflict. Although the defendant’s attorney will attempt to discount plaintiff’s expert testimony through cross-examination, the defendant may also offer experts to testify to similar, or even different, aspects of the case that their experts will interpret to support the defendant’s case. Of course, that testimony will be challenged by the plaintiff’s attorney’s cross-examination of the defendant’s experts. 33.3 Legal Theories of Negligence and Product Liability Products liability is defined in the legal system by lawsuits in which the plaintiff (the injured party) seeks to recover or recompense (damages) for personal injury or loss of property from the defendant (the seller, manufacturer, or designer) who, it is alleged, is responsible for foreseeable and preventable injury or property damage caused by a defective product. Products liability has also been used when a commercial loss is alleged to have resulted from a product’s breakdown or inadequate performance. Product defects resulting in products liability actions arise from manufacturing or production defects in most cases (Weinstein et al., 1978), although many cases in which human factors/ergonomics experts are involved are based on alleged design defects. Since the time of Hammurabi (ca. 1792–1750 B.C.), artisans and engineers have been made accountable for their negligent errors. Modern tort law involving the liability of
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designers, manufacturers, and sellers for property damage or destruction, as well as for injury or deaths resulting from the delivery of defective products, has evolved from those early legal principles. In a very large measure, products liability lawsuits are actions for alleged engineering malpractice. Indeed, if no more than services are alleged to be defective, the litigation focuses upon negligence, often in the form of malpractice (Portner, 1986). Products liability actions may be brought based on one or more of three legal principles: negligence, strict liability and implied warranty, and express warranty and misrepresentation. Actions based on the first of these principles, negligence, test the conduct of the defendant. Actions based on the second principle test the quality of the product, and actions based upon express warranty and misrepresentation test the performance of the product against explicit representations made by the manufacturer and sellers. In this chapter, we consider the behavior of all the participants in the events that lead to the litigation in a system context. These participants include the designer and the manufacturer of any and all equipment, tools, and products involved in the incident, the proper (and foreseeable improper) use of the device or service, and the environment in which the incident occurred; the user/operator of the device; and the victim (who may or may not be the user). All of the foregoing were explicitly or implicitly designed, created, and/or instructed to perform a function in a safe and systematic way. Our interest is drawn to the system when, sometime during its life cycle, an incident (accident?), malfunction, or other system failure occurs that results in property damage or destruction and/or personal injury or death. Subsequently, a lawsuit is filed in which one party to the incident (the plaintiff) seeks compensation for the harm done, alleging that another party (the defendant) is responsible through misrepresentation, willfulness, or negligence. A great number of product liability action results from allegations of negligence. Black’s Law Dictionary, the standard reference in American jurisprudence, defines negligence as “the omission to do something which a reasonable man, guided by those ordinary considerations which ordinarily regulate human affairs, would do, or the doing of something which a reasonable and prudent man would not do” (Black, 1968). Although what a “reasonable and prudent man” would do is the standard of care in determining whether a party to litigation has been negligent, negligence may be determined in whole or in part upon whether the design of a product, tool, or service delivery has been compliant with standards and specifications for such products or services. In product liability litigation involving negligence, the plaintiff’s attorney must build a case relying on positive answers to four questions (Kurke, 1986): 1. Was the defendant’s product or service instrumental in causing harm? The answer to this question will have been alleged in the initial pleadings and will be supported by plaintiff’s witnesses who can testify to the fact or by experts who can, by virtue of their expertise, opine such is the case. Defendant’s attorney may cross-examine the witness, or provide other witnesses to testify to the contrary. Often the role of a human factors expert in product liability and malpractice litigation is to determine (within the context of his expertise) to what extent, if any, the actions of the participants resulted in the incident of concern to the parties. Conversely, the expert may be asked to testify as to the severity of the harm done by the incident.
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2. Did a defect in the product or service make the harm more likely? The human factors expert who has conducted an investigation of the incident and/or examined the standards and specifications of the product or services involved may identify the existence of human factors-related defects in the design, training and operational procedures, or communication of crucial information that makes the system “accident prone” for a significant portion of the expected user population. Based upon the expert’s training and experience, he should be able render an opinion as to whether a defect in the system increased the likelihood of harm to the victim. 3. Did the defendant have a duty to assure that the plaintiff was not harmed by the product or service? This is a question of law rather than of fact. The human factors expert will not be expected to render an opinion on this question. 4. Given such a duty, was the defendant negligent in providing it? Counsel for either side may ask the expert whether the service or product could have been designed or operated in such a way that the harm done could have been prevented or mitigated, and whether, in the expert’s opinion, some safer design, procedure, or communication should have been incorporated by the defendant during the design or operational phase of the system’s life cycle.
33.4 Human Factors Perspective on Product Liability The adversarial process followed by attorneys has two objectives: the assignment of liability (whose fault its it?) and the assessment of damages (how should the person at fault make restitution?) for the accident; the role of the human factors/ergonomics expert is to help determine the cause and, in some cases, explain how the accident could have been prevented or its effects ameliorated. Although the practitioners of human factors/ergonomics may have had their knowledge and experience base in fields as different as engineering, psychology, biological science, medicine, or a variety of other disciplines, their primary professional focus is on the interaction of humans with their artifacts and the environment in which they interact. Product liability litigation may ensue when this operating system fails and harm or injury occurs to any element of the system. The litigation process and, consequently, the system analysis conducted to investigate the cause may center upon the behavior of persons at some point during the life of the system from its very inception to the actual accident. Assuming that all persons in the life of the system have a legal duty to ensure that its design and operation will cause no harm, it seems inherently reasonable to determine whether some form of human error occurred during or as a result of the design, manufacturing, or operational lifetime of the system. 33.5 Etiology of an Accident Determinations of liability can be viewed in an historical context starting with the creation of the functional and operational requirements for the product. It was at this time that the product’s utility and its users were identified. Design standards and engineering specifications were then identified or developed and adopted to ensure economically
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viability and safe, efficient production, utilization, and maintenance of the product during its system lifetime. Having identified the users of the product, it would be prudent to identify how the product is likely to be misused as well. User and maintenance manuals, warnings, labels, and other information-transfer modalities to ensure safe and efficient use may be required. These information-transfer tools and training may have been designed to eliminate the likelihood of error and, like the product, should be compatible with the foreseen user’s and misuser’s knowledge, skills, and abilities. The accident will have taken place as a result of the confluence of a hazardous situation occurring in an ambient environment; the product’s engineered capabilities and limitations; the relevant knowledge, skills, and abilities of the human participants; and their level of cognitive and emotional functioning. With the testimony of witnesses of fact and expert witnesses, attorneys for the principals on each side of an action will gather evidence to support their version of the truth in determining who should bear responsibility for the accident. 33.6 Accidents and Human Error The event that culminates in an action for product liability is usually referred to by at least one of the parties as an accident resulting in injury to person or property. The term “accident” involves the connotation of misfortune. In legal practice, an accident is defined as “that which ordinary prudence could not have been guarded against…an event happening unexpectedly and without fault” (Black, 1968). In actions alleging negligence and product liability, the plaintiff’s attorney alleges that the defendant was indeed at fault. However, in nonlegal parlance, an accident has been described as an event that “creates disturbances interfering with performance or causes a system to perform abnormally, and may be due to error, mistake or fault” (Senders and Moray, 1991). For the convenience of the reader, the term “accident” will be used in this chapter in the latter sense without prejudice as an event resulting from an error for which fault has yet to be determined. The idea of human error as a source of an accident calls for an assumption that the system in which the accident occurs is to be regarded as an extension of the human operator. It is therefore implied that opportunities for human error exist in the performance of usage, maintenance tasks, and associated procedures. Errors may be categorized as slips, in which a person correctly assesses a need and acts accordingly, but errs in carrying out the correct intention; mistakes, in which a person fails to make a correct judgment about what needs to be done; and violations, in which a person deliberately chooses to act in a proscribed way. Slips and mistakes may result from receipt of erroneous information or from erroneous or negligent processing of correct or erroneous information. If an error categorized as a slip or mistake results in harm, the maker of that error may be called to account in a product, liability, malpractice, or other tort action under civil law. Violations, on the other hand, possess the characteristic of motive and intent and may in some cases also be subject to action under criminal law. In their text on the cause, prediction, and reduction of human error, Senders and Moray (1991) list four levels of inquiry concerning errors to be considered by scientists,
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engineers, and lawyers. The first level of investigation asks, “Why did the error occur?” This question may be asked by psychologists, lawyers, and the courts to assign personal responsibility, to advance the understanding of human behavior, or to develop methods of eliminating error. The second level of inquiry asks, “What error occurred?” This question is asked by applied scientists and reliability analysts for use in designing systems resistant to error, as well as to identify sources of system unreliability. The third level asks, “Which object was involved?” Applied scientists, designers, and reliability analysts want this information to improve design of work environments, to assign equipment responsibility, and to assess system reliability. The fourth level of inquiry inquires, “To whom, where, and when did the error occur?” Lawyers, courts, behavioral scientists, and reliability analysts are interested in answers to this question in order to assign responsibility, to increase understanding of human behavior, and to increase their understanding of effects of stress, fatigue, narcotics, work schedules, etc. 33.7 Human Reliability and Product Liability When we consider an accident as a system malfunction, we are talking about human error and the construct of human reliability, which has been defined as “the obverse of the tendency of a human to make an error” (Moray, 1994). Because products liability and other forms of legal action involving human error call for an assessment of such errors, these assessments of the error’s causes and effects may appropriately be based on seeking understanding of breakdowns of human reliability. Various aspects of prevention of breakdown of human reliability have been adapted as a useful basis for training pilots (Besco, 1990); structuring police selection and training (Hibler and Kurke, 1995); managing organizational stress (Kurke, 1995); and investigating human factors issues in law enforcement agencies (Kurke and Gettys, 1995). Domains of human reliability degradation include factors such as influencing human performance degradation; knowledge and skill levels; social and organizational pressure and attitudes; and equipment, service delivery systems, and procedures. Sources of reliability degradation and, for each source, influencing factors and means of prevention or correction of lowered reliability are listed in each tabulation. Recent (but so far unpublished) thinking by the present author would restructure reliability domains into four domains, most of which have implications for human factors professionals: 1. Personal performance capabilities and limitations. Such factors include health; fatigue; disabilities; inadequate environment; interpersonal conflicts; stress; personal history impediments; and clinical, social, legal, and economic history of the individuals involved. 2. Knowledge and skill level. Influential factors might include education, training, warnings, and the ability to retain acquired knowledge, skills, and abilities. 3. Affinitive needs and pressures. To varying degrees, familial, cultural, work group, and other organizational affiliations may influence experience, value systems, beliefs, and attitudes, and, consequently, the appropriateness of behaviors brought into the accident situation.
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4. Ergonomic considerations. Here the primary concern is whether an unreasonably dangerous condition existed. If so, did the condition result from defective design and performance characteristics of products, service delivery systems, or communications systems involving training, instructions, warnings, and labels? Did design defects lead to dangerous degradation of human reliability as a result of equipment failures? The following checklist of human factors/ergonomic factors that influence human reliability is adopted from Besco (1990) and Kurke and Gettys (1995); it might be consulted in exploring accident causality. Source of human Factors influencing human reliability reliability degradation Equipment failures
Structural, electrical, software, system failure modes; quality control standards and procedures Health deficits Incapacitation, illness, physical condition, nutrition, injury, disease, substance abuse, emotional health Irregular rest or sleep System Sleep cycle, poor facilities, irregular schedule, shift work cycle beyond limits of human Frequency thresholds, response time requirements, workload capabilities Ineffective safety demands Design and location of warnings, signs, labels, and instructions or warnings instructions; personal attitudes; awareness; vigilance levels; level of reinforcement concerning compliance with safety procedures Inadequate or hazardous Light and air quality, air flow, acceleration, vibration, seat comfort, environment temperature, visibility Awkward input alternatives Location, sensitivity, incompatibilities, ergonomic considerations Inadequate feedback Sources and reliability of feedback Prior proficiency Where, when, proficiency-level maintenance Infrequently used skills Required skills, personal acceptance of deficiencies, influence of leaders and peers
Although these ergonomic considerations are of primary significance to the human factors/ergonomic expert, the impact of the other three domains should be considered, if only to determine whether an alternate design of the product involved in the litigation was or should have been considered. Did the designer foresee, or should he have foreseen, that the user or victim of the accident may have had personal characteristics, lacked essential knowledge or skills, or been subject to affiliative stress that acted to create a virtual hazard? If so, should ergonomic considerations have countered the risk thereby created? 33.8 Action Plan for the Consultant: Forensic Task Analysis The human factors/ergonomics professional who has been engaged as a consultant and potential expert witness has the job of determining whether actions of the defendant caused events culminating in personal injury, wrongful death, or damage to or destruction of property. According to Bliss (1979, 1987), the primary function of the human factors/ergonomics expert is to conduct a task analysis that “consists of a highly detailed description of everything a particular man-machine system has to do in performing a certain task or function.” The task analysis describes what the product and its operator (or
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victim) need to do, or have done, in sequence to get the job done. Alternatively, the task analysis could be designed to describe the events that actually led to the occurrence of harm. A wide variety of task analysis methods have been catalogued and described in detail (see Kirwan and Ainsworth, 1992). However, a modified form of task analysis first presented by the author for use as a tool in investigating the role of human error in automobile accident investigation and reconstruction (Kurke, 1997; Kurke and Corbin, 2005) would be equally useful for attorneys and human factors professionals in establishing liability for incidents involving negligence in malpractice and product liability litigation. This “forensic task analysis” is structured to seek answers to the following eight questions: 1. What did the system, consisting of involved parties (victim, operator, service provider, system designer, manufacturer), the product/equipment, and the accident environment and procedures to be followed, intend to do prior to and during the accident? Answers to this question are essential to the determination of negligence and represent a basis for the remaining questions. A complete answer will identify all persons involved in the actual incident and the intent of the designers of the system, the manufacturers, and the system’s users. Design engineers, the specification and standards writer, the user, and maintenance manual writers may have had input into the intent of the system and its user, culminating in the incident. In addition, the intent of the victim at the time of the incident should be known. The analysis may be based on a time line. If so, start at the actual time of the incident and go back to learn the objectives of the designer. Also, determine the intended purpose of the victim and of the operator of the device (who may or may not be the same person) during the series of events leading to the incident. This question addresses the preliminary intent of each element of the system involved in the incident, i.e., involved humans (operator, victim, service provider, system managers, job supervisors, etc.). It addresses the relevant elements of the environment in which the actual incident occurred, the actual device, and the parts thereof. Finally, it addresses the appropriate procedures meant to be followed under situations similar to those in which the incident occurred. Relevant inquiries might include questions to determine the primary and peripheral functions or purpose of each element of the system, and how those functions were expected to be performed. If an operator uses a component in a way that does not coincide with its intended purposes, such usage might be responsible for the system’s ultimate breakdown and, thus, the incident. This investigation might assist in the determination of whether the incident was actually foreseen or whether it should have been foreseen—essential elements in determining negligence. 2. What did each element actually do? Was that foreseen? Here we are concerned with identifying differences between the designer’s intent and what actually happened. Specifically: • What deviations from the intention actually occurred; i.e., what deviations caused and/or contributed to the incident?
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• Was there any equipment failure, abnormality in the environment, or counterproductive behavior on the part of any person? • What, if any, human failure to follow appropriate procedures led to the accident? • Was there a misuse of the product? • Did such misuse make the product unreasonably dangerous? • Was the misuse foreseen by the defendant? • Should it have been? • Did the defendant do anything to reduce the hazard? • Did the plaintiff’s actions increase the risk of injury or harm? • Did such actions constitute contributory negligence? These questions are concerned with specific actions of any element of the system that directly or indirectly caused the system’s ultimate malfunction and the resulting accident. They are important in establishing a match or mismatch between the system’s intended and actual activities. They also help to determine whether each party acted in an unreasonable or imprudent manner. 3. Did the design of the equipment, working environment, procedures, training, and/or other safety information transfer procedures facilitate or inhibit the likelihood of the accident or the severity of its consequences? If so, is the product unreasonably dangerous? This question addresses whether the particular elements somehow could have encouraged or discouraged the incident’s likelihood of occurring. Answers may establish whether: • The design may have been faulty or inconvenient. • The incident environment could have provided distraction or hindrance. • The procedures could have been designed beyond human perceptual or performance capabilities. • Training or instructions could have been inadequate. • The operator, victim, or service provider’s performance may have been influenced by alcohol, drugs, fatigue, age, or chronic ill health, or by transient conditions such as a fit of sneezing or a wasp in close proximity. An additional factor that needs to be considered after determining factors that may have encouraged or discouraged the likelihood of occurrence of the incident is whether the element is or is not controllable. If not, could—or should—it have been anticipated and made so? Here, again, we touch upon the issue of foreseeability. Could—or should—the designer of the system have foreseen the consequence of the design that led to the incident? The question of whether the product is “unreasonably dangerous” is often of critical import in product liability litigation. To a large extent, the human factors/ergonomics expert will be required to offer a subjective opinion on this matter. Wade (1965) cites seven factors that should be considered when offering an opinion concerning unreasonable dangerousness: • Usefulness or desirability of the product • Availability of other and safer products to meet the same needs • Likelihood of injury and its probable seriousness
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• Obviousness of the danger • Common knowledge and normal public expectation of danger (especially for established products) • Ability to avoid injury by care in use of the product (including the effect of instructions and warnings) • Ability to eliminate the danger without seriously impairing the usefulness or making it unduly expensive 4. What information (instructions, training manuals, labels, warnings, signals, signs, or other devices) that could have averted the incident and/or mitigated its consequences was/was not available to the victim, operator, or service provider? Was there compliance with the manuals, labels, or instructions? If not, why? This set of questions focuses on potentially preventive information that may or may not have been available to the operator, victim, or service provider. Was it sufficient to create an awareness of hazards? It would be helpful if the human factors/ergonomics expert could learn (perhaps through the attorney’s discovery process) whether the user complied with available training, warnings, or other safety communications. What communications were remembered and how were they complied with? If disregarded, what reasons were given for noncompliance? Answers to such questions are important in demonstrating the effectiveness of warnings that may have prevented the incident or ameliorated the resultant harm. 5. What did the designer of the product/equipment, accident environment, or procedures do to increase or reduce the likelihood of the accident or the severity of its consequences? This question centers upon the potential liability of the designer of the product, equipment, incident environment or their related procedures. It helps establish what, if anything, the designer did with these elements that encouraged or discouraged the likelihood of occurrence of the incident and the severity of its consequences. The question focuses on whether the designer overlooked any important factors in regard to those elements that may have been in the chain of events leading to the incident. This is related to the foreseeability issues mentioned in earlier questions. The designer may have overestimated or underestimated the severity of the consequences associated with the incident. 6. When and how did the equipment user and/or the incident victim become aware of the imminence of the accident? What, if anything, did each person do to try to prevent or minimize the consequences (personal injury or property damage) of the accident? This question is one that will be answered by the users and/or the injured person during the discovery phase of the action. The human factors/ergonomics expert should review this information carefully and be prepared to advise his client attorney about how design features of the product and/or warnings were likely to have influenced the person’s behavior to the extent that they may have exacerbated or ameliorated any damage or injury sustained during, or as a consequence of, the incident. Such information may be helpful in establishing the assignment of liability or the award of damages. 7. Did the victim, operator, or service operator provide (or lack) any personal characteristics that materially increased or reduced the likelihood of the accident or its
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expected consequences? Should the designer have taken the likelihood of occurrence of such personal characteristics into account when he designed the system? The human factors/ergonomics professional’s concern with these questions may be peripheral to his contribution to resolution of a product liability or other negligence-related action. The questions relate to two human reliability domains often not of central concern to that expert, but possibly of considerable relevance to his testimony. They involve personal performance conditions, which include factors such as physical and mental health states and some of their significant factors: fatigue, ambient environment, interpersonal conflicts, personal stress, and personal history, which may include episodes in their social, cultural, clinical, and legal histories. They also involve knowledge, skills, and abilities of the parties involved in the incident. They relate to human error in a distal and an immediate temporal sense. They are important in establishing the person’s background in terms of how he deals with stressful events similar to those that occurred leading to and during the incident that resulted in harm and the present trial or in relation to products with design characteristics similar to those involved in the current litigation. 8. Did the accident and/or any of its consequences arise from any other deficit in any involved person’s human reliability? This final question explores whether any additional problems arise from the human element in the system. In essence, it explores the compatibility of all human-equipment linkages and their contribution to causes and consequences of or prevention of harm in the instant case. The wise attorney will encourage his consultant to explore the foregoing questions. Each one addresses a particular aspect of certain elements of the system that alone, or in concert, are potentially responsible for the occurrence and the extent of the injury or damage alleged at trial. Answers to these questions may enable the trier of fact to arrive at conclusions as to • Whether the product was unreasonably dangerous • Whether the incident was a foreseeable result of a preventable defect in the product’s design or operating procedures • Who, if anyone, involved in the design or the incident was negligent • Whether such negligence was a proximal cause of the incident
References Besco, R.O., 1990, Making Leaders More Effective with the Professional Performance Analysis Checklist (Lakewood, CA: Professional Performance Improvement, Inc.). Black, H.C., 1968, Black’s Law Dictionary (4th rev. ed.) (St. Paul, MN: West Publishing Co.). Bliss, W.D., 1979, Defective product design—role of human factors. In Am. Jurisprudence: Proof Facts , 2nd series. 18, 117–178 (also Supplement, 1987). Christensen, J.M., 1986, Forensic human factors psychology. In M.I.Kurke and R.G.Meyer (Eds.), Psychology in Product Liability and Personal Injury Litigation (Washington: Hemisphere Publishing Corp.), 33–79.
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Hibler, N.S. and Kurke, M.I., 1995, Ensuring personal reliability through selection and training. In M.I. Kurke and E.M.Scrivner (Eds.), Police Psychology into the 21st Century (Hillsdale, NJ: Lawrence Erlbaum Associates), 57–91. Human Factors and Ergonomics Society, 2002–2003, Directory and Yearbook (Santa Monica, CA: HFES). Kirwan, B. and Ainsworth, L.K. (Eds.), 1992, A Guide to Task Analysis (London: Taylor & Francis). Kurke, M.I., 1986, Multispecialty forensic psychology teams and the consulting forensic psychologist. In M.I.Kurke and R.G.Meyer (Eds.), Psychology in Product Liability and Personal Injury Litigation (Washington: Hemisphere Publishing), 209–224. Kurke, M.I., 1995, Organizational management of stress and human reliability. In M.I.Kurke and E.M. Scrivner (Eds.), Police Psychology into the 21 st Century (Hillsdale, NJ: Lawrence Erlbaum Associates), 375–390. Kurke, M.I., 1997, Human error and psychological make-up in traffic accident investigation and reconstruction. Invited lecture to Institute of Police Technology and Management, 24 April, Jacksonville, FL. Kurke, M.I. and Corbin, A.M., 2005, Human error and traffic crash investigation and reconstruction. In R.W.Rivers (Ed.), Evidence in Traffic Crash Investigation: Identification, Interpretation and Analysis (Springfield, IL: Charles C. Thomas). Kurke, M.I. and Gettys, V.S., 1995, Human factors psychology for law enforcement agencies. In M.I. Kurke and E.M.Scrivner (Eds.), Police Psychology into the 21st Century (Hillsdale, NJ: Lawrence Erlbaum Associates), 467–496. Moray, H., 1994, Error reduction as a systems problem. In M.S. Bogner (Ed.), Human Error in Medicine (Hillsdale, NJ: Lawrence Erlbaum Associates), 67–92. Portner, A.D., 1986, Products liability with personal injury sequella: legal perspectives. In M.I.Kurke and R.G. Meyer (Eds.), Psychology in Product Liability and Personal Injury Litigation (Washington: Hemisphere Publishing Corp.), 19–32. Schaden, R.F. and Heldman, V.C., 1982, Product Design Liability (New York: Practicing Law Institute). Senders, J.W. and Moray, N.P., 1991, Human Error: Cause Prediction and Reduction (Hillsdale, NJ: Lawrence Erlbaum Associates). Wade, D., 1965, Strict liability of manufacturers. Southwestern Law J., 9, 5. Weinstein, A.S., Twerski, A.D., Piehler, H.R., and Donaher, W.A., 1978, Products Liability and the Rea-sonably Safe Product (New York: Wiley).
VI Human Factors Applications
34 The Impact of Shiftwork on Manufacturing and Transportation Workers Donald I.Tepas University of Connecticut 0–415–28870–3/05/$0.00+$ 1.50 © 2005 by CRC Press
34.1 Introduction In the last 50 years, work scheduling practices have changed significantly. The number of workers employed in around-the-clock, 7-days-a-week operations has increased. This expansion in work hour use appears to be a global trend, evident within most industrialized nations. It does not appear to be restricted to a specific industry. To some degree, it is a by-product of • Unfettered introduction of automation • Development of continuous process methods • Use of just-in-time manufacturing practices • Expanding global shipment of goods and materials • Ease of doing business across multiple time zones • Increased public demand for around-the-clock services From a human factors and ergonomics perspective, around-the-clock operations appear to increase the likelihood that workers will be exposed to additional health and safety risks. These are risks associated with long work hours, night-shift work, and irregular hours. On a positive note, however, it is also possible that these same workplace changes can lead to increases in employment, decreases in overtime use, and more flexible lifestyles. In contemporary legal cases, the primary task of the human factors expert is often one of identifying whether the specific work schedule system under question has a significant (positive or negative) health and/or safety impact on the workers in question or the public in general. During this 50-year period in which work schedule practices have been changing, there has also been a significant increase in what science knows about the impact on people of long work hours, night-shift work, and irregular hours. Laboratory, survey, and field study research have all confirmed that some work schedules are often associated with unacceptable occupational safety and health risks. In addition, research has also identified work schedule and workplace changes that employers or workers might use to improve safety, worker well-being, and productivity. Given current practices, work
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schedules now take (literally) thousands of forms. These work schedules interact with a wide range of variables (Tepas and Price, 2001). In some cases, the overall effect of a work schedule is a positive one, but in others it is negative. When negative work schedule implications are suggested, a systematic examination by legal, ergonomic, and health experts is often needed to evaluate the merits of the specific work schedule in question. In most cases, the initial focus of these investigations should be one aimed at precisely defining and describing the actual work schedule in practice. This is not as easy as it sounds because terminology and practices vary from place to place. A terminology and notation system is helpful for this; the “Defining Terms” section of this chapter provides an introduction to work schedule terminology. Within these standard definitions, the term “shift” is defined as the hours of a given day that an individual or group is scheduled to be in the workplace. A schedule whereby one works at the same time of day on every workday is called a “permanent” shift. When the work hours change from time to time following a schedule, it is called “rotating” shiftwork. In addition, if the schedule includes work scheduling for 7 days a week and requires weekend work, it is often referred to as “continuous shiftwork.” In any case, given these broad definitions, all work is performed on a shift, and within these definitions all workers are shiftworkers. Thus, manufacturing as well as transportation workers are shiftworkers. Although all shiftworkers are governed by the same biology and psychology, the laws and regulations governing manufacturing and commercial transportation workers are often quite different. This introduction to work schedule terminology is neither comprehensive nor exact. A more comprehensive statement of common American shiftwork terminology and a notation system for work schedule description can be found in Tepas and colleagues (1997). In any case, it is very important to note that, in practice, shiftwork terminology does vary by legal jurisdiction, culture, and workplace colloquial use. The following discussion is linked to the terminology and definitions presented in the “Defining Terms” section. 34.2 Objectives and Scope The primary focus of this chapter is to review briefly the fundamental human factors and ergonomic principles that may apply to an accident or illness alleged to have been caused by a poor work schedule practice. This chapter is not a review of litigation, law, or regulation. Unfortunately, litigation often appears to center on the issue of employers’ vs. workers’ liability, rather than an assessment of the human factors work schedule practices associated with the event and how they might be improved. The legal literature is complex, diverse, and dated; litigation most often appears to end with an out-of-court settlement. There are major national and international differences in how shiftwork is defined and regulated. In addition, nations appear to differ significantly in the manner and degree to which they manifest their medical and safety concerns with regard to hours of work. These legal differences may have evolved from medical concerns, or vice versa. Although a comprehensive international review of legal and regulatory differences is beyond the scope of this chapter, links to this literature are referenced later. It is proposed
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that the human factors variables, which may be relevant to an event or case, are equally complex and diverse. However, unlike regulations and laws, human factors variables will be reviewed because they appear to transcend regulatory diversity and many cultural differences. 34.3 Discussion of Principal Human Factors Issues Legal and Regulatory Issues For the present, it appears that the major international differences in shiftwork practices are framed, to a significant degree, by legal differences in work hour regulation (Gartner and Popkin, 2000). Few significant changes in work hour regulation have been made in the U.S. since before World War II. Other than commercial transportation worker hours of service (HOS) laws, rules governing the length of work hours, and subsequent rest periods, no federal legislation in the U.S. has ever limited night work or overtime use. For the U.S., it is estimated that less than 4% of the night work force is covered by any night work hour legislation (Steinberg, 1982). Although federal law does provide additional compensation for overtime work, no special compensation is required for night work. Thus, in the U.S., one might argue that federal law encourages night work because paying a premium for this work is not required. On the other hand, in Europe and other locations, significant changes in work hour legislation have been made since World War II. The premiums paid for working the night shift are often quite large by American standards, and they may be mandatory. In some cases, night work is limited or even prohibited. On the one hand, this does not encourage employers to schedule night work, but, on the other hand, it may make night work more attractive to some individual workers. In recent years, European Council (EC) 93/104/EC directives, as well as revised International Labour Organisation (ILO) conventions 171 and 178, have led many employers to review and revise their work schedule practices. A dated, but fairly comprehensive, review of shiftwork international work hour legislation has been published (U.S. Congress, Office of Technology Assessment, 1991c). Three more recent, but less comprehensive, reviews have been presented by Kogi (1998), Patton et al. (2001), and Rajaratnam (2001). Although the long-term impact of the EC directive and ILO conventions on work scheduling practices is difficult to evaluate at the present time, the immediate impression is that EC employers are now paying more attention to the human factors aspects of their work schedule practices. In the U.S., transportation federal HOS regulations are older than general work hour legislation. HOS regulations vary with mode of transportation and a review of U.S. HOS regulations has been published (U.S. Congress, Office of Technology Assessment, 1991b). Similar, but not identical, HOS regulations are found in most industrialized nations. In part, HOS regulations were installed to prevent accidents and protect the public. However, there is reason to suggest that, in most cases, economic and political factors played a much more significant role in shaping these rules. In any case, it is important to note that they predate much of our knowledge about circadian variation and the impact of work scheduling systems.
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Health and Weil-Being Issues Shiftworkers, for the most part, are diurnal animals. That is, they normally tend to be most active and alert during daylight hours and least active and sleepy at night. This circadian behavior is driven by the normal circadian synchrony of a genetically set biological clock, daily environmental changes in the Earth’s physical environment, and the social rhythms of a day-oriented society. When workers are required to work at night and/or have irregular work times, their jobs may require that they perform as if they were nocturnal animals. Research has clearly and repeatedly demonstrated that people are diurnal circadian beings and that the changes required to work the night shift or irregular hours are not easy for workers to make. In addition, long work hours result frequently in increased time-on-task fatigue, may limit recovery, and do interact with the time-of-day changes associated with circadian variation. Work schedule investigators now agree that exposure to the night shift and/or long work hours does place workers at risk for serious health and performance problems. In the U.S., most regulations precede circadian research. As a result, they ignore important time-of-day differences in alertness and their interaction with time-on-task fatigue. In addition, these regulations govern acute exposure to work schedule, but most often ignore the possibility of chronic exposure effects. The fact is that all hours of the day are not the same. The duration of exposure to a work schedule is a significant variable when one considers the impact of work hours on health and performance. A recent publication in a European Foundation BEST Report (Wedderburn, 2000) provides the best current support for the theory that around-the-clock operations, irregular work schedules, and extended work hours can have a negative impact on worker health and well-being. This report provides a comprehensive and fair review of how work schedule variables affect health. Most of the studies reviewed in this report are European, but this is an accurate reflection of the work-scheduling literature on health effects. When this diverse literature is considered, a careful examination of study details is warranted in each case. This research literature should be approached with a bit of caution for several reasons. First, one must recognize that health and social practices vary from culture to culture. The variable interactions present within one society may not be present in another. Second, one must be sensitive to the so-called “healthy worker effect.” When studies lack adequate controls, this effect may make night workers appear to be healthier than day workers. Third, premium pay for bad work schedules may attract less than healthy workers with job tenure to more risky schedules. Finally, many studies use only crosssectional research methods and/or unproven measurement tools, and these flaws may mask important and significant longitudinal effects. In response to these health problem issues, for many years some European physicians have proposed the use of shiftwork predeployment and periodic follow-up physical exams for night-shift workers (see Rutenfranz et al., 1981). Scott and Ladou (1990) discuss a version of this for use in the U.S., and Costa (1998) presents a more contemporary European view of this proposal. Basic to the use of this methodology is the assumption that the physicians making these medical assessments have been properly trained with regard to which symptoms/diseases should be assessed and/or monitored. However, this may not be a reasonable assumption. In the U.S., the operators of commercial transportation equipment are required to take periodic medical examinations,
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but the validity of these examinations as a prescription leading to better worker health and safety is not clear. Another approach to improving work schedule health and well-being is to offer workers training programs on how to cope with their work schedules. A wide variety of variables is available for inclusion in these programs (Rosa et al., 1990; Wedderburn, 1991). A shift hygiene program for workers can be custom tailored to fit a specific job or worker group, and/or it can be a program aimed at shiftworkers in general. These programs are sometimes produced as stand-alone self-help tools for use by individual workers or as group activities. In any case, they are often perceived, by employers and workers, as an attractive employee assistance program and/or as a quick fix for the problems associated with a bad work schedule. Often, the implicit assumption of some of these programs is that the health and well-being of workers will be improved by using the program and thus that no work schedule changes are needed. This may not be true. The ability of any training program to educate workers so that they then change their health and safety status should be evaluated in each case (Tepas, 1993). At least three studies now confirm that the merit of worker shift hygiene training programs is open to question (Popkin, 1994; Smith-Coggins et al., 1997; Rankin and Wedderburn, 2000). Performance and Safety Issues It has long been assumed that performance and safety decrease as time on task increases. This traditional view is backed by years of research that was unaware of or failed to consider the potential impact of circadian variation. A more recent view of performance and safety most often places a great deal of emphasis on time-of-day circadian variation, but sometimes fails to consider the more traditional time-on-task variables. Within this more recent viewpoint, time of day is often seen as more important than time on task. Human alertness and performance are said to co-vary as a circadian rhythm, with both reaching a minimum at night during the early morning hours. For example, a consensus group of established professionals concluded that circadian variation in alertness is the determinant of major workplace accidents (Mitler et al., 1988). At the other extreme, one review of the literature concludes that no controlled studies in the literature clearly show that industrial accident injuries are related to shiftwork (Frank, 2000). A contemporary approach to performance and safety issues recognizes that time on task and time of day are legitimate and interacting concurrent variables that must be considered when evaluating work schedule practices. Rail accident data, for example, show that, in some cases, a reduction in HOS length might increase risk (Mead, 1992). More recent research has revealed a time on task 2- to 4-hour peak in transportation accidents (Folkard, 1997; McFadden et al., 1997) and manufacturing accidents (Macdonald et al., 1997). Similarly, an increase in risk, when time on task exceeds 8 hours, has been demonstrated (Nachreiner et al., 2000). Overall and in context, these studies clearly demonstrate the importance of doing time-on-task (as shown by a microanalysis) and time-of-day (as shown by a macroanalysis) analyses of performance and safety data with reliable and valid data. Clearly, time on task and time of day can have a significant impact on performance and safety.
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Rest and Recovery Issues With regard to workplace exposure to toxic substances and physical agents, industrial hygiene recommendations provide a good model for considering the ergonomic impact of work schedule practices on individuals and events. In an ideal form, these industrial hygiene recommendations are often framed with the assumption that one must regulate or monitor three temporal factors: acute instantaneous exposure levels; exposure during a 7 day, 40 hour workweek; and chronic exposure level over years and months. In some cases, frequent medical and/or physical monitoring is recommended. The usual basic general assumption of the hygiene approach is that exposure rules and recommendations should consider the length of breaks and nonworkday times. Nonworkdays and breaks should be long enough to allow a worker full recovery from workplace exposure. However, many manufacturing workplaces do not regularly monitor all three of these temporal concerns as they apply to the impact of work schedule systems. Transportation HOS regulations usually consider acute exposure time and nonworkday recovery time, but often give little consideration to chronic exposure levels. However, in most cases, a periodic medical examination is required for continued employment. In general, for U.S. manufacturing shiftwork, no medical examination of any type is required by law, and work schedule health impact may or may not be systematically monitored. Work-hour legislation in the U.S. sets no objective exposure limits, but it does provide premium pay for long work hours. Although these regulations may give employers or employees more flexibility in their choice of work hours, it is important to note that most of the existing regulations are quite dated in their origin. They are mainly based upon economic and political factors and are not necessarily in tune with hazards suggested by contemporary applied science. During the last 30 years, a growing body of evidence has confirmed that many of these regulations should be re-examined, revised when appropriate, and expanded to include a broader range of health, performance, and safety concerns. Because revisions have not been made, most work experts conclude that it is possible for an employer to meet the demands of current work-hours legislation and at the same time expose a worker to unhealthy conditions and increased safety risk. Similarly, an individual worker may elect to work an unhealthy and/or risky work schedule because he falsely assumed that his health and safety are fully protected by existing work hour regulations. In either case, the question of employer liability may be raised by a plaintiff in court. Acute and Chronic Exposure Issues The traditional (time-on-task) and circadian (time-of-day) viewpoints place an emphasis on the impact of acute exposure. The industrial hygiene viewpoint adds an emphasis on the impact of chronic exposure. For example, the industrial hygiene approach considers not only if an individual noise exposure is harmful, but also if extended exposure (over months or years) to a workplace noise level will lead to deafness. Studies of industrial workers on permanent night shifts clearly suggest that chronic exposure is a problem. Contemporary data indicate that long-term exposure to permanent night-shift work, long work hours, and/or rotating hours with night work can also have a chronic exposure impact.
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Although the literature clearly suggests that events may be related to acute exposure work schedule variables, it also suggests that chronic exposure is perhaps an even more important concern. Sleep behavior provides an important benchmark for monitoring the chronic impact of work schedules. Night-shift work is associated with a concomitant decrease in the length of sleep. Irregular hours may have a similar impact, especially when the locus of work schedule control is poorly informed. Contrary to colloquial thought, these reductions in sleep length do not normally disappear with exposure. That is, most night-shift workers do not fully adapt to their night work. One must consider the impact of total accumulated sleep loss (TASL), not just the impact of one night of lost sleep (Tepas, 1999). Research also indicates that chronic exposure to night work has a chronic impact on performance (Tepas et al, 1981); health (Wedderburn, 2000); and social variables (Gordon et al, 1981). Workers are not always good judges of their own status with regard to some of these variables. For example, micro-sleeps, which may be undetected by the affected worker (Tepas and Mahan, 1989), are commonly associated with TASL. In addition, good data suggest that sleep deprivation increases the length of sleep inertia (Tassi and Muzet, 2000). Both of these symptoms are of special concern when one considers their implications for transportation system operators. Cautions and Pitfalls In considering the impact of shiftwork on manufacturing and transportation workers, the layperson should be aware of several issues present in the research literature. Each of these issues has the potential to confuse and misdirect the casual reader. They are discussed briefly here because a complete review of these issues is not the focus of this chapter. The reader is encouraged to read the following sections to minimize the potential for confusion. Laboratory and Field Research As a general rule, laboratory research allows an investigator to control a large number of variables and make very precise measurements on a few variables. Often laboratory research uses students, unemployed workers, or animals as subjects. In most cases, laboratory research is dedicated to the study of acute exposure effects. On the other hand, research conducted in the field can control only a few variables and measurements may be less precise. Field research can study experienced and employed individuals, with significant job and shift tenure, in their workplace. Most field research is dedicated to the study of chronic exposure effects. Given these usual differences between laboratory and field research, it is not surprising that the results of work schedule studies in these two domains are not always in agreement (Tepas, 1982). The 2- to 4-hour peak in transportation and manufacturing accident studies, noted earlier, has not been easy to confirm in the laboratory (Tucker et al., 2000). It is often reasonable to argue that in some cases the disagreement between research studies is not surprising. That is, it is mainly related to the fact that one study is looking at the acute impact of a work schedule on inexperienced people or animals, while the other is looking at the chronic impact of a work schedule on experienced workers.
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Circadian Rhythms and Biorhythms The circadian variation of biological, psychological, and social variables is a wellestablished scientific finding based on thousands of studies well done by highly regarded investigators. Clearly, circadian variation is related to many of the problems associated with night-work and irregular-work schedules. However, circadian rhythms should not be confused with the concept of “biorhythms,” which postulates three cycles said to act in a concerted way to determine human behavior. Unlike circadian rhythm findings, the biorhythm concept has a nonfactual origin, and many efforts to validate it using accident data have failed (U.S. Congress, Office of Technology Assessment, 1991a). Biorhythm theory may have entertain-ment value, but it has little predictive value. Circadian variations, on the other hand, are significant, established scientific facts. Sleep Disturbance and Sleep Deprivation Many shiftworkers report reduced sleep length, unusual sleep times, and sleep complaints. One way to label these reports is to call them “sleep disturbances” or “sleep disorders.” These labels suggest that many shiftworkers might be diagnosed as abnormal, sick, and/or in need of treatment. These diagnoses may be more in the realm of a clinicbased observer than they are in the domain of the shiftworkers. Early research examined (only) the sleep of individuals acutely exposed to the night shift and found disturbed sleep. However, subsequent research has repeatedly demonstrated that chronic exposure of manufacturing workers to the night shift mainly and simply reduces sleep length. This reduction in sleep length produces shifts in sleep patterns of the sort that one would expect to see in normal humans who are sleep deprived. Thus, for example, initial claims that commercial truck drivers have a much higher than expected prevalence of sleep apnea have not been supported by a more extensive study using better controls (Pack et al, 2002). Chronic Fatigue Syndrome and Chronic Exposure Although they sound similar, chronic fatigue syndrome (CFS) is not the same as chronic exposure. “Chronic exposure” is a descriptive work scheduling term that simply describes a work schedule variable as it relates to shift tenure. CFS, on the other hand, is a diseasediagnostic classification. The conditions that trigger CFS are a bit elusive, but a standard listing of probable cause does not include the shift worked (U.S. Centers for Disease Control, 2002). It is reasonable to presume that many CFS patients are not employed on the night shift or at irregular hours. Although a night-shift or irregular-hour worker may have CFS, little evidence to date supports the notion that CFS is more prevalent in these workers than it is in any other group of employed workers. Stress and Fatigue The use of “stress” and “fatigue” varies; these broad terms often refer to quite different things. On the other hand, sometimes they appear to be synonymous terms. Use of these two terms is popular with laypeople but can be misleading when assessing the usability of
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a given work schedule (Tepas and Price, 2001). For example, night work is often said to be stressful, yet some workers elect to work the night shift because it is less stressful. Equating long work hours with physical fatigue may be a bit misleading because time on task may increase monotony or boredom. Stress and fatigue are catchall terms for making handy comments, but they are not always helpful when trying to understand the complex and changing variable interactions that most work schedule assessments embrace. Multiple variables determine the usability of a given work schedule and the degree to which workers are placed at risk. A complex and systematic human factors analysis by an expert is needed if one is to obtain a reliable and accurate assessment (Tepas, 1999). Flextime and Employer-Determined Irregular Hours In their initial use, flextime work systems were presented as an attractive alternative work schedule system that allowed workers to decide (usually within a set of rules or limits) when and how long they would work (Tepas, 1985). At its best, this increased flexibility can improve worker job satisfaction and productivity. At its worst, this form of work scheduling can lead to worker-deter mined risky and/or irregular work hours. The introduction of just-in-time and lean-production methods can significantly change the locus of work schedule control for this flexibility. When using these methods, the employer calls for worker scheduling flexibility to match changing production or service schedules. This form of work scheduling is sometimes called employer-determined irregular work hours. At its worst, this form of work scheduling can also lead to risky and/or irregular hours. In either form, a flexible but unfettered irregular or extended work schedule may place a worker at risk (Tepas, 1994). For some cases, the issue of locus of work schedule control can become a factor to be considered in determining liability. 34.4 Case Examples The following cases are briefly presented to provide an introduction to and sample of past legal activity in this area. In each case, details have been changed to maintain anonymity. In some instances, the case is an amalgam of several similar cases. Out-of-court sealed settlements were the norm for most of these cases. Handicap Work Schedule Accommodation After working on a three-shift, rotating-8-hours shift system for about a year, a 45-yearold computer operator became ill with hypertension and was briefly hospitalized. After his hospitalization, he returned to work as a day shiftworker. After 1 month of day work, the employer advised the worker that he was scheduled for permanent night-shift duty. The worker responded by saying that night work would make him sick, as evidenced by his hypertension. He was informed by the employer that the ability to work the night shift was and had always been a condition of employment. After a written medical report from his doctor was provided, the hypertension of the worker was confirmed in a medical exam by a doctor employed by the company. The worker again refused the night shift assignment. The employer told the worker that the company had failed in its efforts to
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place him on another shift, so the worker would be placed on leave. During this leave time, worker hourly pay continued, but health benefit payments ceased and became the responsibility of the worker. The plaintiff then alleged that he had a handicap produced by his rotating hours shift tenure with the company. His counsel argued that a reasonable effort had not been made to accommodate the plaintiff (as required by state law) and worker compensation was due. Prior to working for the employer, the plaintiff had no night shift tenure with any job. In this case, no predeployment physical examination was given to the plaintiff by the employer. There was no evidence that the worker had hypertension prior to employment. The employer had no usability data to support the work schedule practices. No training was offered to any workers at this site on how to cope with shiftwork. The company had no written policy or regulations addressing shift assignment methods. Moonlighting Ambulance Driver Crash A 40-year-old ambulance driver crashed into a car at an intersection, killing a mother and her child, who were the only occupants of the car. The driver was employed 40 hours or more per week by the ambulance company and had a second job as a hospital worker. Both jobs were minimum-wage hourly employment. The ambulance company was aware of the moonlighting by the driver, but the hospital reported that it did not know about the second job. A work schedule reconstruction revealed that the driver had had only two nonwork days in the 30 days prior to the accident. Total daily work time for 15 of these 30 days was 16 hours or longer, including three 24-hour workdays. The immediate family of the deceased was the plaintiff, charging that the privately owned ambulance company was at fault, due to the fatigue of the driver. The ambulance company did maintain a dormitorylike sleeping room for drivers to use when they were working but not answering a call. They had no record of who used it or when it was used. Company records indicated that this driver averaged one call for every 2 hours he was on duty during the 30-day period just prior to the accident. Although driver call activity was recorded, it was not systematically used with rules to minimize driver fatigue or stress. The company had no written policy concerning sleeping room use, break behavior, or moonlighting. Drivers were offered no training in fatigue management, stress management, or defensive driving skills. Performance after Completion of Paid Work Hours The 30-year-old assistant manager of a chain food store struck and killed two pedestrians as she drove to a nearby bank to deposit store revenues. The assistant manager was an hourly employee working on the day shift at a 24-hour store. She was paid to work (only) five 8-hour workdays per week. However, work schedule reconstruction revealed a schedule placing her in the workplace for 14 hours on the day of the accident, but she only reported working an 8-hour workday on her time card. During her unpaid overtime, she allegedly completed a required store inventory and other recordkeeping. Her deposition suggested that this extended workday was a common practice for her. She was driving in her own car, having logged off on her time card, when the accident occurred.
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The mother of one of the pedestrians was the plaintiff, charging that the food store chain was at fault, due to the fatigue of the driver while working long hours for the company. As a condition of initial employment, the assistant manager was required to read the corporate operations manual and pass a test on its contents. This manual included a specific prohibition against any overtime work by hourly employees without specific written home office approval. No overtime approval was ever requested or given with regard to this worker. In the course of her employment, the assistant manager had been given videotape training in defensive driving and stress management. In both cases, she had passed a written test on training content. The validity of the training and the reliability of the testing were not clear. 34.5 Checklist of Main Factors to Consider Table 34.1 presents a checklist of the main factors to consider when investigating the alleged impact of shiftwork on manufacturing and transportation workers. Nine primary factor categories are included in this table, and a number of variables that might be considered are listed within each category. In addition to serving as a guide to human factors forensic investigation, this fairly comprehensive listing demonstrates an important point: the impact of work schedules is multifaceted and interactive. Although individual measures or methods can provide good benchmarks and clues, a systematic examination of a large number of factors by trained human factors specialists is often needed to produce a quality work schedule evaluation. 34.6 Summary and Conclusions Research and case history clearly demonstrate that irregular hours, long workdays, and night-shift work are practices related to the likelihood of injury and illness. In most cases, the likelihood that these practices will lead to injury and illness increases when they are combined with the effects of a wide variety of behavioral, biological, and social variables. In a few cases, this likelihood decreases when they interact with these variables. In every case, a quality legal investigation should recognize that the acute and chronic impact of work schedules is multifaceted and interactive with a wide variety of variables. A simplistic one-dimensional analysis is not appropriate or warranted in most cases. Although Table 34.1 provides a good starting point for a comprehensive legal investigation, it is not evaluative in most respects. This is a checklist that, for the most part, intentionally evades and avoids specific literal assessments. Given the complexity of most work schedule interactions, advance blanket assessments can lead to erroneous legal conclusions. Evaluation of the data that this checklist produces requires the skills of a human factors/ergonomics expert trained in systems analysis and knowledgeable with regard to the contemporary work schedule research literature. This literature is international in origin, has a diverse discipline basis, and in the U.S. is rarely directly linked to existing law or regulation. A qualified human factors expert can provide the
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needed link from multiple-discipline work system knowledge to legal precedent and practice. Although U.S. HOS and labor-hour legislation suggest a link to occupational health and safety factors, it is important to recognize that their origin lies primarily in political and economic factors. These regulations were, for the most part, enacted more than 50 years ago—well before the contemporary work schedules research database was established. One must also recognize that technological developments have significantly changed the nature of work and the workplace in the last 50 years. We now know that it is quite possible to meet the requirements of current work-hour regulations and at the same time place the worker and/or the public at risk. Thus, legal council has at least two major questions to
TABLE 34.1 Checklist of Factors to Consider Primary factor
Considerations
Worker fitness Physical examination results Physical/mental status at the time of the event Prescription medication use Reported use of over-the-counter medication Results of tests for drug and alcohol use Results of behavioral fitness-for-duty testing Selfreports of fitness and health Age of worker Worker Task training Job safety training, schedule, and content Fatigue management plan training and training Stress management plan and training Physical fitness and/or exercise programs Periodic testing for knowledge of safe practices Employee assistance program practices Workplace Federal regulations for hours of work and pay State regulations for hours of work rules and and pay Employer-written regulations Collective bargaining agreements and/or practices employer-set service and pay standards Common intra-industry practices Employer monitoring of actual workplace practice Work Usual exposure to toxic substances Usual noise exposure Average temperature and environment humidity of workplace Workplace light levels Geographic location Toxic substance exposure on day of event Noise exposure on day of event Temperature and humidity on day of event Lighting conditions at time of event Task and skill Job to be performed by worker Tasks required from the worker Worker task ability analysis assessment program Legal credentials/licenses/certificates required Criticality/utility of the tasks performed Skill maintenance systems requirements Acute work Locus of schedule control on day of event Time notified of work schedule for shift schedule event day Work times for previous workday Time of day work started on day of event Time of day of event Time on task at time of event Locus of event Break schedule for day of event Chronic work Usual locus of system control Regularity of work hours Length of usual workday shift system Total hours scheduled for usual work week Time(s) of day worked Continuous or discontinuous operations Schedule for days off Break duration, schedule, and spread Vacation time practices Personal/illness days practices
Primary factor
Considerations
Worker Worker shiftwork history Work shift system tenure Job tenure Tenure with employer behavior Moonlighting behavior Reported sleep and napping Typical work commute time Mode for commuting to work Operator license violations and accidents Worker behavior monitoring by employer Human resource performance appraisal reports Worker
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Second job
845
compensation claims OSHA accident and injury records Fatigue management plan provisions use Physical fitness program use Other unusual but notable behaviors Awareness by either employer of moonlighting Second-job worker fitness Second-job workplace rules and practices Second-job workplace environment Second-job task analysis Second-job acute work shift schedule Second-job chronic work shift system Second-job worker behavior
probe: have the applicable labor hour regulations been violated, and has the worker or the public been exposed to an unacceptable risk? Defining Terms The discussion in this text follows the terminology and definitions presented here. It is very important to remind the reader again that shiftwork practice and terminology do vary with legal jurisdiction, culture, and workplace colloquial use. In reading this text, one should remember that a given term might have a different definition in another context. As noted previously, this section contains an introductory list of common American work schedule terms. These terms, additional definitions, and a notation system are found in Tepas et al. (1997). Acute exposure—Short-term or single exposure to a work schedule variable; for example, one long workday or working one night shift. Afternoon/evening shift—A work shift that in the U.S. mainly falls between the hours of 1500 and 0100. Often called the second shift or the swing shift. Break—A time period within a shift when a worker is not employed at his job; usually less than 1 hour in duration, and often paid. When the break is longer, the worker may not be paid for the break time. Some work schedules include more than one break per shift. Circadian—Oscillations or rhythms in biological, psychological, and social variables with a frequency of about 24 hours. Chronic exposure—Long-term exposure to a work schedule variable; for example, 1 year of exposure to the night shift. Continuous operations—A workplace that operates 7 days a week and around the clock. Some workers are scheduled to work nights and/or weekends. Day shift—A work shift that in the U.S. mainly falls between the hours of 0600 and 1700 hours. Often called the first shift or the morning shift. Discontinuous operations—A workplace that does not employ workers 7 days a week. Usually workers are not employed on weekends. Event—The time when the alleged accident, error, ordeal, or illness occurred. This may be a point in time or a time period of specified or unspecified length. Healthy worker effect—Less-than-healthy workers may terminate their participation in a given work schedule. This effect may falsely suggest that exposure to this schedule is not associated with a safety or health problem. Sometimes called the “survivor effect.” Hours of service (HOS)—Regulations or laws limiting the work hours of those who operate commercial transportation vehicles. These rules vary with mode of transportation and legal entity.
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Irregular hours—Work shift hours that vary in their starting time and/or shift duration in an erratic manner. Locus of schedule control may vary; there currently is no formal criteria or definition of irregularity. Job—The tasks a worker is employed to perform in the workplace when on duty. In some cases this may also include off-duty tasks. Job tenure—How long a worker has been employed on a specific job. Locus of work schedule control—The document, person, or organization with the power to select, maintain, or change the work-hour and/or break schedule of an individual worker. This may, for example, be a labor law, manager, or individual worker. Microsleep—A period of sleep with duration of a fraction of a second or many seconds. Workers may not be aware of the onset and/or occurrence of these periods of sleep. Precipitated by sleep deprivation. Night shift—A work shift that in the U.S. mainly falls between the hours of 2200 and 0700. Often called the third shift or the graveyard shift. Nonworkday—A calendar day within which an individual worker does not work any or most of the time. Sometimes called a day off or time off. Permanent shift—Any shift whereby an individual worker does not usually change the hours of the day on which he works. That is, the worker has fixed hours, working the same hours each workday. Rotating hours—A work schedule that normally requires an individual to work more than one shift. These work hours may change in a predetermined manner, or they may be irregular hours. Second job—Working another job for additional income. Usually this is a part-time job. Also called “moonlighting.” Shift tenure—How long a worker has been employed on a specific work schedule. This may or may not be the same as job tenure. May also be called work shift system tenure. Sleep inertia—A transition period of significant reduced alertness and temporary performance decrement, which occurs immediately after awakening from sleep. Split shift—A work schedule whereby a person works a given number of hours, is released from work, and then returns for additional work on the same day. Usually, this break is 1 hour or longer and the worker is not paid for this time. Task analysis—A systematic way for the description and study of the tasks that a worker employs when he performs his job. There are many ways to do a task analysis. Tenure with employer—How long a worker has been employed in any way, manner, or form by the employer when the event of major interest is reported. Time of day—The clock time of day; for example, the clock time of day at which work begins or ends. Time on task—How long an individual has been working on the job and/or a task during a given shift; may also be called time on duty. Total accumulated sleep loss (TASL)—A state of chronic sleep deprivation. May be the result of reductions in sleep on workdays. Sometimes referred to as sleep debt, cumulative sleep loss, or chronic undersleeping. Work shift usability testing—An ergonomic process for the design, installation, and/or evaluation of a given work schedule system.
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Workware—The array of tools and knowledge that can be used by the human factors expert to describe, compare, review, schedule, design, maintain, and/or diagnose a given work schedule system. References Costa, G., 1998, Guidelines for the medical surveillance of shift workers. Scand. J. Work, Environ. Health , 24, suppl 3, 151–155. Folkard, S., 1997, Black times: temporal determinants of transport safety. Accident Anal Prev. , 29, 417–430. Frank, A.L., 2000, Injuries related to shiftwork. Am. J. Prev. Med. , 18, 33–36. Gartner, J. and Popkin, S., 2000, Influence of law on shift schedule design: USA and Europe. In: S. Hornberger, P.Knauth, G.Costa, and S.Folkard (Eds.), Shiftwork in the 21st Century (Frankfurt am Main: Peter Lang), 381–387. Gordon, G.H., McGill, W.L., and Maltese, J.W., 1981, Home and community life of a sample of shift workers. In: L.C.Johnson, D.I.Tepas, W.P.Colquhoun, and M.J.Colligan (Eds.), Biological Rhythms, Sleep and Shift Work (New York: Spectrum), 357–369. Kogi, K., 1998, International regulations on the organization of shift work. Scand. J. Work, Environ. Health , 24, suppl 3, 7–12. MacDonald, I., Smith, L, Lowe, S.L., and Folkard, S., 1997, Effects on accidents of time into shift and of short breaks between shifts. Int. J. Occup. Environ. Health , 3, S40-S45. McFadden, E., Popkin, S., Tepas, D., and Folkard, S., 1997, Time-of-day and hours-on-duty effects for railroad accidents in the United States. Shiftwork Int. Newsl. , 14(1), 47. Mead, K.M., 1992, Railroad safety: engineer work shift length and schedule variability, GAO/RCED-92–133 (Washington, D.C.: U.S. General Accounting Office). Mitler, M.M., Carskadon, M.S., Czeisler, C.A., Dement, W., Dinges, D.F., and Graeber, R.C., 1988, Catastrophes, sleep, and public policy: consensus report. Sleep , 11, 100–109. Nachreiner, F., Akkermann, S., and Haenecke, K., 2000, Fatal accident risk as a function of hours into work. In: S.Hornberger, P.Knauth, G.Costa, and S.Folkard (Eds.), Shiftwork in the 21st Century (Frankfurt am Main: Peter Lang), 19–24. Pack, A.I., Dinges, D.F., and Maislin, G., 2002, A Study of Prevalence of Sleep Apnea among Commercial Truck Drivers . FMCSA Publication DOT-RT-02–030 (Washington, D.C.: Federal Motor Carrier Safety Administration). Patton, D.V., Landers, D.R., and Agarwal, I.T., 2001, Legal considerations of sleep deprivation among resident physicians. J. Health Law , 34, 377–417. Popkin, S.M., 1994, An evaluation of the impact of an educational program for freight locomotive engineers on irregular work schedules. Proc. 12th Triennial Congr. Int. Ergonomics Assoc. , 5, 33–35. Rajaratnam, S.M.W., 2001, Legal issues in accidents caused by sleepiness. Shiftwork Int. Newsl. , 18(1), 18. Rankin, A.D. and Wedderburn, A.A.I., 2000, Evaluation of a shiftworker’s guide. In: S. Hornberger, P. Knauth, G.Costa, and S.Folkard (Eds.), Shiftwork in the 21st Century (Frankfurt am Main: Peter Lang), 405–410. Rosa, R.R., Bonnet, M.H., Bootzin, R.R., Eastman, C.I., Monk, T., Penn, P.E., Tepas, D.I., and Walsh, J.K., 1990, Intervention factors for promoting adjustment to nightwork and shiftwork. In: A.J. Scott (Ed.), Shiftwork (Philadelphia: Hanley and Belfus), 391–415. Rutenfranz, J., Knauth, P. and Angersbach, D., 1981, Shift work research issues. In: L.C.Johnson, D.I. Tepas, W.P.Colquhoun, and M.J.Colligan (Eds.), The Twenty-Four Hour Workday. DHHS NIOSH 81–127 (Cincinnati: NIOSH), 221–259.
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Scott, A.J. and Ladou, J., 1990, Shiftwork: effects on sleep and health with recommendations for medical surveillance and screening. In: A.J.Scott (Ed.), Shiftwork (Philadelphia: Hanley and Belfus), 273–299. Smith-Coggins, R., Rosekind, M.R., Buccino, K.R., Dinges, D.F., and Moser, R.R, 1997, Rotating shiftwork schedules: can we enhance physician adaptation to night shifts? Acad. Emergency Med. , 4, 951–961. Steinberg, R., 1982, Wages and Hours (New Brunswick, NJ: Rutgers University Press). Tassi, P. and Muzet, A., 2000, Sleep inertia. Sleep Med. Rev. , 4, 341–353. Tepas, D.I., 1982, Work/sleep time schedules and performance. In: W.B. Webb (Ed.), Biological Rhythms, Sleep, and Performance (New York: John Wiley & Sons), 175–204. Tepas, D.I., 1985, Flexitime, compressed workweeks and other alternative work schedules. In: S.Folkard and T.H. Monk (Eds.), Hours of Work (New York: John Wiley & Sons), 147–164. Tepas, D.I., 1993, Educational programs for shiftworkers, their families, and prospective shiftworkers. Ergonomics , 36, 199–209. Tepas, D.I., 1994, Technological innovation and the management of alertness and fatigue in the workplace. Hum. Performance , 7, 165–180. Tepas, D.I.., 1999, Work shift usability testing. In: W.Karwowski and W.S.Marras (Eds.), The Occupational Ergonomics Handbook (Boca Raton, FL: CRC Press), 1741–1758. Tepas, D.I. and Mahan, R.R, 1989, The many meanings of sleep. Work and Stress , 3, 93–102. Tepas, D.I., Paley, M.J., and Popkin, S.M., 1997, Work schedules and sustained performance. In: G. Salvendy (Ed.), Handbook of Human Factors and Ergonomics , 2nd ed. (New York: John Wiley & Sons), 1021–1058. Tepas, D.I. and Price, J.M., 2001, What is stress and what is fatigue? In: P.A.Hancock and P.A.Desmond (Eds.), Stress, Workload, and Fatigue (Mahwah, NJ: Lawrence Erlbaum Associates), 607–622. Tepas, D.I., Walsh, J.K., Moss, P.D., and Armstrong, D., 1981, Polysomnographic correlates of shiftworker performance in the laboratory. In: A.Reinberg, N.Vieux, and P.Andlauer (Eds.), Night and Shift Work: Biological and Social Aspects (Oxford, England: Pergamon Press), 179– 186. Tucker, P., Sytnik, N., MacDonald, I., and Folkard, S., 2000, Temporal determinants of accident risk: the “2–4 hour shift phenomenon.” In: S.Hornberger, P.Knauth, G.Costa, and S.Folkard (Eds.), Shiftwork in the 21st Century (Frankfurt am Main: Peter Lang), 99–105. U.S. Centers for Disease Control, National Center for Infectious Diseases, 2002, Possible causes of chronic fatigue syndrome, http://www.cdc.gov/ncidod/diseases/cfs/causes.htm. U.S. Congress, Office of Technology Assessment, 199 1a, Introduction and overview. Biological Rhythms: Implications for the Worker , OTA-BA-463 (Washington, D.C.: U.S. Government Printing Office), 29–34. U.S. Congress, Office of Technology Assessment, 1991b, Legal and regulatory issues. Biological Rhythms: Implications for the Worker , OTA-BA-463 (Washington, D.C.: U.S. Government Printing Office), 123–140. U.S. Congress, Office of Technology Assessment, 1991c, International regulation of shift work. Biological Rhythms: Implications for the Worker , OTA-BA-463 (Washington, D.C.: U.S. Government Printing Office), 199–216. Wedderburn, A.A., 1991, Guidelines for shiftworkers. BEST European Studies on Time (Dublin: European Foundation for the Improvement of Living and Working Conditions). Wedderburn, A. (Ed.), 2000, Shiftwork and health. BEST European Studies on Time (Dublin: European Foundation for the Improvement of Living and Working Conditions).
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Further Information Hancock, P.A. and Desmond, P.A. (Eds.), 2001, Stress, Workload, and Fatigue (Mahwah, NJ: Lawrence Erlbaum Associates). Rosa, R.R., Bonnet, M.H., Bootzin, R.R., Eastman, C.I., Monk, T, Penn, P.E., Tepas, D.I., and Walsh, J.K., 1990, Intervention factors for promoting adjustment to nightwork and shiftwork. In: A.J.Scott (Ed.), Shiftwork . (Philadelphia: Hanley and Belfus), 391–415. Tepas, D.I., 1999. Work shift usability testing. In: W.Karwowski and W.S.Marras (Eds.), The Occupational Ergonomics Handbook (Boca Raton, FL: CRC Press), 1741–1758. Tepas, D.I., Paley, M.J., and Popkin, S.M., 1997, Work schedules and sustained performance. In: G. Salvendy (Ed.), Handbook of Human Factors and Ergonomics , 2nd ed. (New York: John Wiley & Sons), 1021–1058. U.S. Congress, Office of Technology Assessment, 1991. Biological Rhythms: Implications for the Worker , OTA-BA-463 (Washington, D.C.: U.S. Government Printing Office). Wedderburn, A. (Ed.), 2000, Shiftwork and health. BEST European Studies on Time (Dublin: European Foundation for the Improvement of Living and Working Conditions).
35 Preschoolers, Adolescents, and Seniors: AgeRelated Factors Pertaining to Forensic Human Factors Analyses Ilene B.Zackowitz Vredenburgh & Associates, Inc. Alison G.Vredenburgh Vredenburgh & Associates, Inc. 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
35.1 Introduction to Human Factors Principles and Relevance to Standard of Care Human factors consultants are asked to investigate accidents that involve people of all ages. Inherent age-related capabilities and limitations often make it necessary to look beyond the basic facts of a case. Specific cognitive and physical characteristics can be identified and addressed for the populations of preschoolers, adolescents, and older individuals to gain a thorough understanding of their behavior in accident scenarios. When conducting a human factors analysis, it is important to analyze the aspects of the situation or environment as well as of the individuals involved. Attorneys often seek human factors experts with an understanding of age-related capabilities and limitations to address how these factors may be related to reasonableness of conduct. What is reasonable and expected behavior for an adolescent or older adult may not be so for a preschool-age child. Because of the differences in the physical and cognitive abilities and limitations of different age groups, people may be held to different standards of conduct. When investigating accidents, a thorough analysis of the interaction between the individual and the situation-specific characteristics of the case must be considered as part of the investigation to help arrive at opinions concerning accident causation. 35.2 Objective and Scope of the Chapter In this chapter we will discuss the age-related issues one may consider when investigating accidents that occur among preschoolers, adolescents, and older individuals. The objective is to illustrate how factors beyond the basic facts of a case can be evaluated before a thorough analysis is complete. Research in psychology provides us with insight into developmental issues for many age groups. Combining forensic human factors and
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psychology will provide useful age-related guidelines for consultants to consider when investigating accidents. To demonstrate the evaluation of age-related human factors, six cases that we have investigated as forensic consultants will be discussed. Two cases for preschool-age children will be presented: a pedestrianvs.-vehicle accident and a playground accident. Two cases illustrate adolescent issues: a child in traffic and a fall from a height. Two cases concern older adults: a trip-and-fall accident and a driving accident. Although specific cases are used as examples, this information will be useful to many practitioners in human factors forensic consulting because it can be applied to many different accident scenarios. We frequently use age-related factors as our basis for opinions when investigating accidents because human performance capabilities and limitations are a crucial consideration in behavior. By the time these types of cases reach the court system, they are discussed in terms of “reasonableness of conduct.” What behavior is reasonable for a 5-year-old? What tasks can we expect teenagers to be able to perform consistently? How do physical degradations that come with aging affect the performance of older adults? These are the kinds of questions that this chapter will address in order that practitioners can gain a more thorough understanding of accident participants’ age-related physical and cognitive capabilities and limitations. 35.3 Discussion of Principal Issues Preschoolers Parents often breathe a sigh of relief after their youngster has been safely deposited at school, despite the fact that many accidents occur on school or daycare premises during the day or immediately after children are released. Parents tend to feel secure because it becomes someone else’s job to look after their precious child. Surely a system at the school will ensure that the children are kept safe and out of harm’s way while they are learning and going about their daily activities. With a trend toward both parents working, it is not always possible to monitor children’s safety without outside assistance such as daycare, preschool, and kindergarten. Parents tend to rely on these outside resources for functions that they may have traditionally performed. Although most schools have a barrier system in place, it is not foolproof. As part of the system, kindergarten and first-grade teachers usually know how their students get home. Typically, if they see a young student wandering around campus alone, they will escort him or her to the office so that he or she can call a parent or guardian. Preschool accountability should be one to one, with each student released to a responsible adult. When the system fails, results can be tragic, as we will see in one of the cases to be described in the next section. In order to assure children’s safety, as well as to conduct a complete and thorough accident investigation, it is important to keep in mind that children have abilities and limitations based on their developmental level. Therefore, an understanding of what children can and cannot do at each stage is important for understanding realistic expectations for behavior. Young children’s abilities and limitations, based on their
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developmental level, are not necessarily the same as their age level. Maturity varies due to individual differences, and behavior is governed by biological processes that guide each stage of development. An understanding of what an average child can and cannot do at each stage is important in order to reach realistic conclusions in an accident investigation (Zackowitz and Vredenburgh, 1998). Average 5-year-olds share several physical and cognitive capabilities. They have welldeveloped motor control; they can run, hop, and articulate clearly. They may hesitate to carry out directions but usually complete them (Gesell and Ilg, 1949). Children at this age are able to grasp many simple logical concepts and to process in their heads what they previously had to do with their hands (Elkind, 1978). Children pick up a single sound or sight that interests them and focus their attention on it. They tend to ignore much of what else is happening in the world around them. In addition, they still have difficulty seeing another person’s point of view (Zackowitz and Vredenburgh, 1998). This is of particular importance for accidents in traffic. If a child can see a car, he believes the car can see him as well. We have seen this kind of faulty, but age-appropriate, thinking lead to numerous accidents. Preschoolers and young children have limited cognitive and physical abilities depending on their developmental level. Physically, they often need adult help. Children may take heed before they run across the street to meet the mother who is waiting for them. What they cannot do is make adequate allowances for oncoming cars. Young children need clear and simple directions to perform most activities because of their cognitive limitations. They maybe able to describe basic concepts like time and distance; however, they cannot make absolute or relative judgments at this age (Zackowitz and Vredenburgh, 1998). Furthermore, they have little or no understanding of their mortality or the mortality of others. What seems risky or dangerous to an adult does not seem so to a young child (Turner and Helms, 1995). They do not yet use the type of “if…then” analysis that leads people to understand the consequences of their behavior. Five-year-olds do little monitoring of their own memory and comprehension. They tend to forget things very easily. They understand “me—now—here” better than “you— then—there.” Underdeveloped attending skills prevent children from seeing the whole picture and from being able to explore the totality of their surroundings carefully. Because people make decisions based on prior experiences, young children may make illogical choices because existing knowledge is limited (Vredenburgh and Zackowitz, 2002). Efficient problem-solving requires many skills, including the ability to use trial and error and to notice, evaluate, and correct one’s errors. These skills require considerable brain maturation that typically has not occurred in this age group. Children are usually between the ages of 6 and 8 before they perceive hazards such as traffic or a fall from an elevation as a threat. In addition, a child’s field of vision is one third narrower than an adult’s; therefore, children have less peripheral vision and are less able to view all possible stimuli (Department of the Interior, 1995). Young children are not small adults. Their understanding and knowledge are limited by age, development, and experience in the world. Rules and regulations by which they have to live were created by adults. It is difficult and sometimes impossible for preschoolers to understand the reasons for these rules. These factors should be considered when investigating accidents that involve young children.
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Adolescents The gradual evolution from dependent child into independent adult has widespread physical, psychological, and social consequences. This monumental change brings with it many new risks and dangers that younger children have not yet confronted. Often, the desire for developing one’s unique personality and the demands of parents and greater society on this group are in conflict. Therefore, many adolescents test the limits of society by placing themselves in dangerous situations. Although adolescents typically have the ability to think through the consequences of their behavior, they are often impulsive. Children in this age group perceive a whole new set of pressures and social rules that must be followed for fear that they may be shunned by their peers. Peer pressure drives adolescents’ behavior more so than their own independent thought processes. What pressures affect the behaviors of adolescent children? Are they cognitively advanced enough to think before they act and to consider the consequences of their actions? During early adolescence (from 12 to 14 years of age), children are moving toward independence while living in a world of social pressures. Parents and their teenagers are struggling between the youth’s wanting independence while still needing parental guidance. Although at this age, the child is able to think abstractly and to assume the viewpoints of others (Selman, 1980), he or she does not always think through to the consequences of behavior. Faced with a problem, children at this age consider possible alternatives; however, they do so in a haphazard fashion (Hoffman et al., 1994). They often ignore possible solutions and stick rigidly to others that may be obviously impossible from an adult perspective. This is the age of bending rules and testing limits. Adolescents want to determine their boundaries. Because adolescents live in a microcosm where the events occurring in their lives are all-important, they will often disregard other important information to the detriment of their own safety. They may be focused so intently on one aspect of a situation that they fail to notice others. We will see an example of this in the next section. At times, young adolescents cannot easily explain why they act as they do; they see risky behavior as an appropriate way to cope with situations that they experience (Hoffman et al., 1994). Adolescent boys are more often the victims of accidents because males of this age are more impulsive, active, competitive, and aggressive than females. This makes it more difficult for boys to adapt to school rules and expectations. By midadolescence (age 14 or 15), children know that different people can consider their own, as well as others’, views (Selman, 1980). Also typical at this age is extremely egocentric thinking (not unlike the preschoolers). Although adolescents often perceive that other people are thinking about them, their peers do not place as much attention on their behavior and appearance as the person focuses on himself. However, these false perceptions may affect behavior (Hoffman et al., 1994). Adolescents tend to think in terms of what has been referred to as the “personal fable” (Elkind, 1985)—a term that refers to a young person’s belief that he or she is generally indestructible. Teenagers who engage in dangerous activities such as drinking and driving, drugs, and unsafe sex are demonstrating their belief in the personal fable of indestructibility. Although they believe that negative consequences may happen to others, they feel these outcomes do not apply to them.
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Adolescents place an extremely strong emphasis on their peer group. They feel pressure to act and sometimes to act out in certain ways so that they conform to the culture of the “in-group.” Group identity and superiority lead to competitiveness and risky decision-making. Children in this age group are often led by their peers toward behaviors in which they would not have engaged if they were making the decision independently (Hoffman et al., 1994). Despite the fact that adolescents have much of the cognitive ability to make sound decisions such as abstract thought and “if…then” reasoning, they have many outside pressures that must also be considered. Peer pressure, egocentrism, and personal fables are natural parts of adolescence that can have a great impact on behavior. These types of age-related issues may be considered when analyzing why an adolescent has engaged in risky or rule-breaking behavior and whether this conduct can be expected given the facts of the case coupled with the adolescent’s developmental stage. Seniors Although seniors (over 65 years) comprise about 13% of the population, they account for 26% of fall-related injuries treated in emergency rooms (about 1.8 million annually; Zackowitz and Vredenburgh, 2002). In addition, various studies have demonstrated a positive relationship between a higher rate of vehicular accidents and older age (Klein, 1991). As one ages, the body experiences cognitive and physical changes that must be considered when an expert performs forensic accident investigations. Several factors that have an impact on accidents involving seniors, especially fallrelated accidents, include reduced visual acuity, muscular weakness, arthritis, osteoporosis, abnormal gait, medication side-effects, and cognitive impairment (Zackowitz and Vredenburgh, 2002). The functioning of the systems necessary for safe walking and driving, including perception, cognition, and motor coordination, often diminishes with age. These changes affect all facets of movement initiation (Stelmach and Nahom, 1992). Older people may have more difficulty recovering after they lose their balance. In addition, for people who need to wear bifocals, details in the lower portion of their visual field (on the ground) are more difficult to see. Older people often walk more slowly, with a shorter stride. They have a greater tendency to drag their toes during the swing phase of the stride and thus have less ability to clear obstructions or changes in elevation of a walkway. Senior women tend to fall and become injured more often than men. This is the only age group in which women outnumber men in occurrences of accidents. Because of these physical characteristics, the amount of friction of the floor surface of facilities frequented by an older population should be higher than the minimum acceptable standard of 0.5 static coefficient of friction (Turnbow, 1996). There are other gender-associated limitations in the older population. Women tend to lose their balance more often due to changes in the configuration of their lower extremities. Whereas younger women have a straight or slightly knock-kneed stance, women over 75 manifest some degree of bow-leggedness. They also have a narrow walking and standing base, making their stature less stable. Because of osteoporosis, when women fall, the injuries are typically more severe (Zackowitz and Vredenburgh, 2002).
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As people age and begin to experience failing health, it is typical for them to consume an increased number of prescription and nonprescription medications. The effects of these drugs on the body and, more specifically, the central nervous system cause reactions that may affect the systems necessary for safe locomotion and driving (Cowart and Kandela, 1985). Older people have a higher active blood level of the drugs in their systems for longer periods of time, reducing the body’s ability to inactivate and excrete many medications. In addition, the decrease in the functioning of perception, motor coordination, and cognition seen in older people reduces their capacity to compensate for drug-induced impairment of the central nervous system (Ray et al., 1992). Perception-reaction time—the time that it takes for an individual to respond to a given stimulus—is critically important in many accident scenarios, particularly driving situations. Studies have shown that elderly drivers display a significant increase in reaction time (Olson and Sivak, 1986). This means that as a person’s age increases, so does the time for him or her to respond to stimuli in the environment. Using actual driving situations involving roadway hazards, brake reaction time is longer for adults aged 50 to 84 than for adults aged 18 to 40 (Olson and Sivak, 1986). Furthermore, for every 5 years between the ages of 15 and 75, brake reaction time increases by approximately 2% (Stelmach and Nahom, 1992). The physical environment is a significant factor in many accident scenarios that involve older adults. Problems may include poorly designed walkways, floor surface coverings in ill-repair, uneven walkways, insufficient lighting, and objects left on the ground as tripping hazards. An unexpected change in elevation is one environmental condition that is particularly dangerous to the elderly population. Courts often treat elevation changes of up to three fourths of an inch as a “trivial defect.” For older people, a half-inch or more elevation difference can be problematic because their gait often produces less than a half-inch clearance during the swing phase of a walk. Changes in motor coordination coupled with vision degeneration and muscular weakness create conditions that make accidents more likely among the elderly (Zackowitz and Vredenburgh, 2002). The additional physical variables inherent with the aging process should be considered as they interact with environmental variables. For example, a change in elevation of a floor surface may be more difficult to see for those with reduced visual performance or for those wearing bifocal prescription eyeglasses. Reduced illumination also contributes to accidents because age-related visual deterioration is more pronounced in lower lighting levels (Turnbow, 1996). It is important to remember that there are a lot of individual differences in the rate and degree of changes occurring during the aging process. When accidents among the older population are investigated, it is essential to identify related physiological factors and analyze how they may have interacted with the environment and other facts of the case. After these issues are identified, it becomes possible to identify the causal factors for accidents among the elderly.
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35.4 Examples Illustrating Age-Related Human Factors This section will describe two cases for each of the three age classifications described earlier in order to demonstrate age-related analyses. The cases will be discussed from the plaintiff’s and defendant’s per-spectives. This analysis will follow the case descriptions in order to illustrate how age-related capabilities and limitations can be considered and evaluated in a forensic investigation. Preschoolers Case 1 On a little girl’s sixth birthday, she happened to go on a school field trip with her class. The outing ran a little long and the bus returned to school late. The crossing guard was already gone for the day. The little girl typically walked home from school with her older brother, but on that day the brother was not in their usual meeting spot. The little girl waited for what seemed like a long time and she decided to walk home alone. She was struck by a car as she entered the designated pedestrian crosswalk that she used daily. What is important to include in a human factors investigation is whether the child’s behavior was consistent with that expected of a 5- or 6-year-old child. Was supervision for that age group appropriate? Was an effective barrier system in place at the school? Did the system have contingencies for unexpected events (like a late-returning field trip)? Did the parents have notice that they had to provide alternate transportation on that day? Was the parents’ conduct a causal factor for this incident? In this case, the victim’s behavior was appropriate for her age. This little girl had been described as bright, obedient, and a good listener by her parents and teachers. She followed the rules as they had been taught to her, but she had little or no ability to interpret the rules based on her cognitive ability and knowledge base. Children are between the ages of 6 and 8 years before they can even perceive traffic as a threat or hazard (Department of the Interior, 1995). It would be typical for a child to assume that the car could see her because she could see the car. In addition, her frame of reference was that cars always stopped when she walked across the street in that location; therefore, she did not believe that it would be different on this occasion. The defendant (school district) would most likely ask a human factors expert to evaluate the reasonableness of conduct of the parents. Were the parents aware that the field trip ran late? Did the parents receive notice that they were responsible for providing their children with alternative transportation home at the end of the day? The discovery phase of the investigation provides the forensic investigator with these important facts. What information had been provided to the parents? Did they sign a permission slip? Based on this information, a human factors expert can conclude whether the parents’ conduct was reasonable. The plaintiff will likely ask a human factors expert to evaluate the effectiveness of the safety system of the school. What information was given to the parents on the permission slip? Did the school keep to the schedule? What provisions did the school make for a late
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arrival? How were the children released? What was the overall effectiveness of the barrier system? In this case, the system at the school that was put in place to protect this little girl failed. The school was not prepared for the possibility of a class returning late from a long field trip. When it did occur, there was no plan for getting these youngsters home, whether they typically took a school bus or walked with the assistance of a crossing guard. Adult supervision was inadequate to assure that the children did not wander off. Because of this, the school failed to meet the appropriate standard of care when dealing with preschool-age children. If the parent had signed a permission slip that said that the bus would arrive late and that it was the parent’s responsibility to provide the child alternate transportation, his or her conduct would have been less appropriate and he or she would have shared the responsibility for the breach in supervision. Case 2 In another case, a 3-year-old boy suffered a serious head injury as a result of falling from a slide. He had been shown the proper way to use the slide by his parent on previous occasions. In addition, he had successfully negotiated the slide in the past. Despite these facts, this time the toddler decided to climb up the sloped surface of the slide instead of using the ladder. As he was climbing, he lost his balance and fell, striking his head on the ground below. After the incident, the child’s guardian noted that the sand around the play equipment seemed hard and that there was not very much of it. When the guardian was questioned about this incident, he did not have any details because he did not see the child fall. In this case the child was not using the playground equipment properly. Physically, children need adult help at this age. They need to be directed to age-appropriate equipment and then should be supervised closely while they are playing. It is foreseeable that an unsupervised young preschooler on a playground may misuse the equipment. Because these children have poor memories, instructions they may have received in the past may not be recalled. Because of these limitations, supervision is of utmost importance. A 3-year-old cannot be held accountable for his behavior, but his parent or guardian can be. If the guardian had been paying closer attention to what this little boy was doing, he would have seen that he was engaging in an unsafe behavior that could have been corrected before the fall occurred. In addition to the lack of supervision in this case, other playground issues were relevant. Adequate maintenance may not have prevented the incident, but it may have reduced the severity of the injuries sustained. The guardian noted that the sand around this piece of equipment was very hard. Parks and recreation departments have the responsibility of maintaining their playgrounds in a safe manner. In this case, the conduct of the plaintiff (guardian) and defendant contributed to the injuries. If the child had been properly supervised as he was playing on the equipment, misuse of the equipment could have been corrected before the accident occurred. On the other hand, if city maintenance had met the standard of care, the result may not have been such a serious head injury.
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Adolescents Case 1 A 13-year-old boy was struck by a vehicle as he was crossing a busy street to catch the city transit bus that took him home from school. Students were given 8 minutes after dismissal from their last class to board the city bus at its stop across a main thoroughfare from the school. Bus drivers were known to leave the bus stop with students still in the crosswalk. This young teen did not want to miss the bus because the later bus carried high school students who tended to bully the junior high school students who were easy to identify in their uniforms. The traffic signal changed as he was entering the intersection. He attempted to run to the bus against the traffic light and was hit by a car. There were two systems of school bus service for this school. The first was a designated school bus that was boarded with supervision adjacent to the school. The second system (based on the distance of the student’s home from the campus) was the city bus. This required crossing a busy intersection with time pressure and no supervision. The defendants would ask a human factors expert to evaluate the child’s behavior and determine if it was unreasonable. The plaintiffs would ask an expert to evaluate the two systems of school transportation to determine if both were safe for the teenage user population. This case demonstrates how social pressure can influence an adolescent’s perception of appropriate behavior. Despite the fact that other pressures affected his decision-making process, we can expect that the teen was old enough to know the rules of the road for pedestrians. He knew to wait for the signal and also had prior experience at this location. He was aware that it was a busy intersection with heavy traffic. This child was so concerned and preoccupied about catching the bus that he did not think through the consequences of his actions. Consistent with the behavior of fellow students, he ran across the intersection as the light was changing and was killed as a result. Boys of this age are typically impulsive. Although he was cognitively able to think through the consequences of his behavior, more pressing matters concerned him. His past experiences riding the later bus resulted in bullying by older high school students—a situation that was important for him to avoid. His past experience told him that, even if he was in the intersection approaching the bus stop, the bus would leave him. Therefore, his overriding objective was to get on that bus. Based on what we know about children of this age, his behavior was foreseeable and not unreasonable for his peer group. System deficiencies at the school and in the city transit program should have been designed to protect these students as they left school premises to ride public transportation. The school district instructed students to ride the city transit bus to and from school if they did not reside in an area serviced by school buses. The district treated these two groups of students differently. The school bus riders were provided with adult supervisors during boarding of the school buses. The city transit riders were left on their own to dash across the busy intersection. The school bus students were picked up and dropped off on a quiet residential street bordering the school. The city bus students had to negotiate a busy intersection. In this case, the school district failed to provide safe afterschool pickup for the students who rode the city bus. Coupled with the impulsiveness and
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outside pressures experienced by adolescents of this age, the system was not designed with consideration of the typical age-based behavior of the population using the services. Case 2 A 15-year old was injured when he fell off the roof of a baseball dugout. The victim and his friend were looking for their baseball team at a large park with many different playing fields. They were having trouble locating the team, so they decided to climb to the top of a dugout to get a better view. When they reached the top, they saw a school chair up there with an attached desktop. This desk was located close to the edge of the dugout roof. The friend decided to sit in the chair while the victim sat down on the desktop surface. When the friend stood up from the chair, he left all the weight at the front of the desk. As a result, the desk tipped over and the boy seated on the desktop fell about 15 ft off the dugout roof and landed on the ground with the desk on top of him. He suffered a serious back injury. Several issues would be discussed by a plaintiff’s expert, including the foreseeability of children climbing the dugout roof, warnings, and barriers. A defense expert would discuss the reasonableness of conduct of the boy and his assumption of risk. This case involves the reasonable conduct of an adolescent based on the situational factors available and apparent to him at the time of the incident. The boy had seen other people on the dugout keeping score during games (observational learning). Nothing deterred the youngsters from climbing on top of the dugout; in fact, wood planks were attached to the side of the dugout and were effectively used as a ladder. At the time of the incident, the dugout was under construction and the guardrail had been removed. It was foreseeable that people would climb up on the roof and sit on the desk (which should have been removed). No warnings were present regarding construction and denying access to the roof. Once the children climbed to the roof, there was even a place for them to sit—an indication that they were allowed to be up there. They made observations about their environment and acted on the information they were given. If some sort of notice had told people not to be on the dugout roof, such as a warning sign, the evidence would have more strongly supported the defense. If it were difficult to access the roof of the dugout, and the boys had to engage in risky behavior to climb up there, the arguments given by the defense would be more strongly supported. Seniors Case 1 An 83-year-old woman fell as she was going to get her mail. Although she typically used a walker to assist her with traversing long distances, she did not use it to negotiate the 15 ft to her mailbox. One day, as she set out to retrieve her mail, she did not notice that the water utility access hole in the driveway had its lid removed due to nearby construction. As she walked toward the mailbox, she accidentally stepped into the hole, fell, and broke her hip.
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A defense expert would be asked to evaluate whether the hole was open and obvious to all users of the driveway. A plaintiff’s expert would discuss the user population (senior housing) and the typical limitations for that age group. In this case, it was important to analyze the access hole as it was viewed by the victim at the time of the accident by considering how the physical limitations of the woman interacted with aspects of the environment. Despite the fact that she typically used her walker, she walked the length of her driveway daily without it. Was there a reason why she had difficulty that day? She was not taking any new medication that would have affected her balance or alertness. She was wearing her eyeglasses, which she wore daily. Was the time of day an issue? Perhaps there was a glare that she was not used to. Did her doctor recommend that she use her walker even for short trips like this one? If so, and she chose not to heed the doctor’s advice, she would bear some of the responsibility for this incident. This incident occurred in a retirement community in which the average resident was in his or her 70s. When maintenance was being done, the standard procedure was that the resident be notified about the scope and duration of the work. In this case, that did not occur. The woman did not know that work was being done in the community and that access to her water main was needed. If she had had prior notice about the nature of the hazard in her driveway and if the hazard had been marked with a good visual cue, she would have had the information necessary to avoid it. Case 2 A 37-year-old male was driving in an unfamiliar area at about 9:15 p.m. There was a light fog in the air. He was searching for a house that he was considering renting. He saw the street he was looking for as he passed it. There were curves in the road; therefore, before he could turn around to go back, he had to drive a distance until the road was straight and visibility seemed to be good. When the road appeared to be clear, he started to make a three-point turn. As he backed up during the second phase of the turn, he saw an oncoming car. He assumed that driver could see him, too. The oncoming car did not slow down, so he thought it was planning to go around him. The oncoming car took no evasive maneuver and plowed straight into the side of his car. The driver of the oncoming vehicle was a 75-year-old man who was taking five different medications and who had drunk an alcoholic beverage within an hour of this incident. For this type of incident, the plaintiff as well as defense experts would typically evaluate the perception-reaction time and visibility of the elderly driver. They would also determine whether the conduct of both drivers was reasonable. These experts would probably make different assumptions or weigh evidence differently in order to arrive at their opinions. Because of the degradation of perception and motor coordination often seen in older adults, a related decrease in driving ability occurs. Coupled with medications that may alter the functioning of the central nervous system and alcoholic beverages, it is not surprising that this older driver lacked the perception-reaction time necessary to perceive the stimulus of the car turning around in front of him and bring his vehicle to a safe stop before a collision occurred.
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Older drivers are more susceptible to intoxication from alcohol because they have reduced water content in their bodies. Therefore, a single dose of alcohol produces a higher concentration of alcohol in the person’s blood (Waller, 1992). In fact, older drivers have a steeper climb in crash risk at blood-alcohol levels under 0.10 than do middle-aged people. Alcohol also interacts with other bodily degradations normally seen in older people. For example, effects of alcohol such as increased night blindness and glare sensitivity, reduced glare recovery, narrow visual search, and altered contrast sensitivity interact with the normal degradation in these functions. Thus, when an older person gets behind the wheel after having only one drink, the risk increases (Vredenburgh and Zackowitz, 1998). Perhaps the visibility where the younger driver decided to attempt his turn was not as good as he had believed. If he had decided to make this turn where oncoming traffic did not have the viewing distance necessary to see the car and make the necessary allowances for it, this would support the defense expert’s opinions. If the younger driver had a taillight out or some other vehicular defect that reduced its visibility, these facts would negatively affect the reasonableness of his conduct.
Primary factor
35.5 Checklist of Main Factors to Consider Considerations
Accident Environmental or situational factors Individual differences investigations Reasonableness of Age Developmental level Physical limitations/abilities Cognitive conduct limitations/abilities Preschool-age School/daycare systems in place Well-developed motor skills Narrow focus of children attention Egotistic perspective Need adult help physically Judge distances poorly Do not understand mortality Poor memory Limited problem-solving skills Adolescents Impulsive Social pressures Abstract thought possible Do not always consider consequences Limit testing Males aggressive/competitive Personal fables expected Peer pressure “If…then” reasoning possible Older adults Physical and cognitive degradations More fall and car accidents Reduced vision Muscular weakness Medication side effects Cognitive impairment Increased perception-reaction time
Defining Terms Adolescence—A period of growth between childhood and adulthood, typically between the ages of 12 and 18. Age appropriate—Expected capabilities, limitations, and behaviors for a given cohort. Preschoolers—Children aged 3 to 6 years. Reasonableness of conduct—Behaviors consistent with societal norms for a given population. Seniors—Adults over 65 years of age.
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References Cowart, V. and Kandela, P. (1985). Prescription drugs and driving performance. JAMA, 254, 15– 24. Department of the Interior (1995). Children in Traffic . AAA Foundation for Traffic Safety. Elkind, D. (1985). Egocentrism redux. Dev. Rev. , 5, 218–226. Elkind, D. (1978). The Child’s Reality: Three Developmental Themes . Mahwah, NJ: Lawrence Erlbaum Associates. Gesell, A. and Ilg, F.L. (1949). Child Development: an Introduction to the Study of Human Growth . New York: Harper and Row. Hoffman, L., Paris, S., and Hall, E. (1994). Developmental Psychology Today (6th ed.). New York: McGraw-Hill. Klein, R. (1991). Age-related eye disease, visual impairment, and driving in the elderly. Hum. Factors , 33(5), 521–525. Olson, P.L. and Sivak, M. (1986). Perception-response time to unexpected roadway hazards. Hum. Factors , 28, 91–96. Ray, W.A., Gurwitz, J., Decker, M.D., and Kennedy, D.L. (1992). Medication and safety of the older driver: is there a basis for concern? Hum. Factors , 34(1), 33–47. Selman, R.L. (1980). The Growth of Interpersonal Understanding . New York: Academic Press. Stelmach, G.E. and Nahom, A. (1992). Cognitive-motor abilities of the elderly driver. Hum. Factors , 34(1), 53–65. Turnbow, C.E. (1996). Slip and Fall Practice . Costa Mesa, CA: James Publishing, Inc. Turner, J.S. and Helms, D.B. (1995). Lifespan Development (5th ed.). New York: Harcourt Brace. Vredenburgh, A.G. and Zackowitz, I.E. (2002). Playground safety: a forensic human factors analysis of fall injuries. Proc. 54th Annu. Meeting Am. Acad. Forensic Sci. , Atlanta, GA, 95– 96. Vredenburgh, A.G. and Zackowitz, I.E. (1998). Older drivers: a forensic human factors analysis. Proc. 50th Annu. Meeting Am. Acad. Forensic Sci. , San Francisco, CA, 91–92. Waller, J.A. (1992). Research and other issues concerning effects of medical conditions on elderly drivers. Hum. Factors , 34, 3–15. Zackowitz, I.E. and Vredenburgh, A.G. (2002). Applying a forensic human factors engineering analysis to falls in elderly people. Proc. 54th Annu. Meeting Am. Acad. Forensic Sci. , Atlanta, GA, 96–97. Zackowitz, I.E. and Vredenburgh, A.G. (1998). Preschoolers: a forensic human factors analysis. Proc. 50th Annu. Meeting Am. Acad. Forensic Sci. , San Francisco, CA, 90–91.
Further Information Elkind, D. (1978). The Child’s Reality: Three Developmental Themes . Mahwah, NJ: Lawrence Erlbaum Associates. Hoffman, L., Paris, S., and Hall, E. (1994). Developmental Psychology Today (6th ed.). New York: McGraw-Hill.
36 Sexual Harassment: A Forensic Human Factors Perspective Alison G.Vredenburgh Vredenburgh & Associates, Inc. Ilene B.Zackowitz Vredenburgh & Associates, Inc. 0–415–28870–3/05/$0.00+$ 1.50 © 2005 by CRC Press
36.1 Introduction to Human Factors Principles and Relevance to Standard of Care Traditionally, the study of human factors has focused on the interfaces of the individual with his or her work environment. This area of study includes workstation design, design of controls, protective safety gear, noise and vibration reduction, seating, temperature control, and lighting, as well as many others (Hendrick, 2000). These microergonomic principles (traditional ergonomics focusing on individual system components and subsystems) do not typically address system-wide human factors issues. For example, traditional microergonomic practices do not include intrinsic job satisfaction and jobrelated stress (Hendrick, 2000). Research indicates that it is possible to design subcomponents of a system employing ergonomics principles, yet fail to reach important systems’ effectiveness goals because of inattention to the design of the whole work system (Hendrick, 1984). From this realization, the subdiscipline of macroergonomics (design of the overall work system) was conceived. With the development of this discipline came the realization of a need to integrate organizational design and management practices into the study of human factors. Sexual harassment is an example of a human factors and workplace safety issue that is not addressed by traditional ergonomics or human factors study. Although many people view harassment as the result of one or a few chauvinistic employees and not as an organization-wide problem, harassment may create a fearful and unsafe work environment. If organizational policies, procedures, and practices do not prevent sexual harassment, an unsafe condition for employees may result and those organizations may be held liable for the damages. If victims do not follow the proper procedures in reporting harassment, their claims may be unsupported. Organizations must meet certain standards of care to prevent sexual harassment from occurring. Similarly, victims of harassment also have
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responsibilities in reporting alleged incidents to ensure that they will be able to continue working in safe, nonhostile environments. In order for employees to be properly motivated in the organizational setting, they require emotional and physical safety (Luthans, 1992). People need to feel that the world is organized and predictable and to feel secure in their environment. Sexual harassment has the potential of destroying the feeling of safety for victims. Physical safety can be compromised if the harassment involves assault, which may lead to injury. Emotional safety is also at stake as a result of harassment. If employees feel intimidated or threatened at work, or are so distracted that they cannot concentrate on work tasks, emotional safety has been compromised. From a human factors perspective, individuals, when threatened, may respond in any number of ways. Work performance may decrease when an individual is distracted, upset, or angry. An angry worker can affect organizational morale, which may have ramifications beyond the single employee. Harassment can affect a person’s career and lead to interpersonal problems or diverse emotional and physical reactions. All of these may interact with the work environment, leading to detrimental outcomes for all parties involved and may ultimately result in litigation. 36.2 Objective and Scope of the Chapter This chapter will illustrate that harassment is a workplace safety issue that can result in physical injury, emotional and professional damage to the victim, and negative consequences including legal liability to the organization. Because employees frequently spend most of their waking hours at work, their greatest opportunity to meet potential mates is on the job. If an organization prohibits all socializing of employees, they may feel stifled. Therefore, organizations must perform a balancing act: they must provide a safe climate, yet not create an oppressive environment. In order to ensure a satisfactory outcome, the victims of harassment and the organizations in which harassment occurs have certain responsibilities. We will discuss individual and organizational responsibilities and highlight these using actual examples of sexual harassment incidents. Furthermore, the principal forensic issues relevant to the discussion of harassment will be discussed. 36.3 Discussion of Principal Issues In the modern working world, few problems are as controversial as sexual harassment. It is controversial in part because it is not universally recognized as a problem. In addition, there is little agreement as to its definition. Central to all definitions is the abuse of actual or perceived power over another in a sexual context. However, sexual harassment is not about sex. It is about using sex as a vehicle for power over someone. In the workplace, this creates a fearful and unsafe working environment not only for those directly affected, but also for bystanders who observe these threatening behaviors to which co-workers are subjected.
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The definition of sexual harassment that will be used in this chapter is the one used by the American Psychological Association (provided by McKinney and Maroules, 1991): “deliberate or repeated comments, gestures or physical contacts of a sexual nature that are unwanted by the recipient.” This definition covers the issues without being gender or context specific. A sexual harassment event may be conceptualized as consisting of four basic elements: (1) the perpetrator intends to harass, (2) the perpetrator’s morals have been undermined, (3) the perpetrator’s social inhibitions have been undermined, and (4) the perpetrator overcomes the victim’s ability to avoid the harassment (Stawar, 1999). Sexual harassment has the added complication of involving differing perceptions from the victim’s and perpetrator’s points of view. In other words, what constitutes “unwelcome” advances maybe different for different people. It is easy to see how individual differences in perception can create a gray area where a question may arise as to what behaviors qualify as harassment. Some behaviors may seem clear-cut while others are not. Hypersensitivity is one personality trait that can exacerbate this complication. Take, for example, a sensitive female employee whom we will call Mary. Mary complained about the way a male co-worker, Steve, was looking at her. She construed this “look” to be harassment because she thought it was sexually based and it made her feel uncomfortable. On the other hand, the woman working at the desk next to Mary is Stacy. Stacy knows Steve pretty well and knows him to be very friendly and very happily married. Stacy knows Steve is the office “welcome wagon,” doing all that he can to make new employees feel comfortable. Because of Mary’s personality, interpersonal history, religious background, or prior harassment experiences, she may feel harassed. On the other hand, Stacy may enjoy Steve’s attention. This is one example in which a single behavior can be construed as harassment by one individual but not by another. Another example may be when someone invites another employee on a date. If Suzie receives the invitation and is interested, she may not consider this behavior harassment and may appreciate the offer. On the other hand, Cindy, who is not interested, may consider this behavior to be an unwelcome advance, or harassment. Sexual harassment occurs when one person seeks to abuse actual or perceived power over another in a sexual context. Though status and position are often the means of the party in power, it is also seen in force of numbers, such as when several male employees gang up on one female co-worker. Dependence can also be a vehicle of harassment, for example, when customers and clients harass a worker, often by threatening to take their business elsewhere if demands are not met (Backhouse and Cohen, 1981). Although the most commonly reported form of sexual harassment involves a male supervisor harassing a female subordinate, it is not limited to this form. In any case in which power can be abused, sexual harassment is possible. Thus, there have been cases of women harassing men as well as same-sex harassment scenarios. However, in our society, it is most common for men to be in a position of power over women, so that is the most common form of harassment (Meyer et al., 1981). Sexual harassment in an organizational setting can have detrimental human factors consequences. In addition to actual physical harm that may result from sexual harassment in the workplace, professional damage is another consequence. Because professionals
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move in smaller and more specialized circles, it is often more difficult for an upper- or middle-management-level sexual harassment victim to recover professionally from the damaging effects of harassment. If the rumor mill suggests that the victim has lost a job because of an inability to get along with co-workers, the damage can be irreparable. Some victims who choose to speak out are accused of inventing their stories and often retaliated against. The victims may lose their jobs if they have not quit already. Their names may become publicized, and they may gain a reputation as troublemakers, thus making it difficult to secure future employment (Backhouse and Cohen, 1981). The repercussions of sexual harassment do not end with the victim. There are also serious outcomes for organizations that employ harassers. A survey of 92 women who wrote to the Working Women’s Institute to complain about sexual harassment (Crull, 1979) found that as a result of the harassment, 83% of the respondents reported increased difficulty with job performance due to distraction, loss of motivation, or the time and energy needed to avoid the harasser. Seventy-one percent of the harassers had the power to promote or fire the target of their harassment. Only 34% of the respondents stayed with their job. The rest were fired or pressured into resigning, increasing turnover costs to the organization. Sexual Harassment Litigated Building on the concept of sexual discrimination, the issue of sexual harassment gained legal recognition as a problem contributing to inequity in employment in the mid-1970s (Sorenson et al., 1994). In response to this problem, the U.S. Equal Employment Opportunity Commission (EEOC) established guidelines in 1980 that placed sexual harassment within the purview of unlawful discrimination because of sex. This began a path of legal precedent that further clarified what constitutes sexual harassment. Several subsequent court decisions in the U.S. led to judgments that held employers responsible for preventing sexual harassment and for establishing effective grievance procedures (Sullivan, 1986). In 1991 the nation took a crash course on sexual harassment as it watched the confirmation hearings of Clarence Thomas. Professor Anita Hill’s testimony that she had been sexually harassed by Thomas generated a national dialogue on the subject and brought new attention to, understanding of, and energy to an old problem. The EEOC reported that the number of sexual harassment complaints rose by more than 50% in the aftermath of the hearings. When Anita Hill sat before the Judiciary Committee, sexual harassment claims were rare, even though harassment was not. Today, harassment claims are the most common form of employment litigation (Segal, 1996). The most widely cited legal protection from sexual harassment is Article VII of the Civil Rights Act of 1964, which prohibits employment discrimination on the basis of sex, race, color, religion, and national origin. Title VII covers all employers who employ 15 or more employees. Claims made through this medium make resources from the EEOC available, permitting monetary compensation for damages, back pay, lost benefits, and attorney’s fees. The plaintiff sues their employer, not the harasser. Claims can also be made as common law torts, which can be even more expensive because such suits can take punitive damages into account (Meyer et al., 1981).
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In 1980, the EEOC issued interpretive guidelines on sexual harassment under Title VII. These guidelines stated that Title VII prohibits the sexual harassment of employees. Employers are responsible for the actions of their agents and supervisors. Employers are responsible for the actions of all other employees if the employer knew or should have known about the sexual harassment. The guidelines state that an employer should take all necessary steps to prevent sexual harassment (Sorenson et al., 1994). The decision of whether the condition of employment has been changed (someone is being harassed) must be made using an objective perspective of an “average” or “reasonable” (not hypersensitive) person. However, this decision depends on whether this perspective is that of a “reasonable woman” or a “reasonable man.” Studies have indicated that men and women perceive behaviors differently. Therefore, the same act from a reasonable woman’s perspective may be judged quite differently from that of a reasonable man (Paludi and Barickman, 1998). The Supreme Court has not determined which perspective is to be used and thus has left this decision to the lower courts. Several cases have been decided in favor of the “reasonable woman” perspective (Ellison v. Brady; Lipsett v. University of Puerto Rico; Andrews v. City of Philadelphia’, Burns v. McGregor, and Robinson v. Jacksonville Shipyards). In a study using actual complaints to the Illinois Human Rights Office, Terpestra and Baker (1988) found that cash settlements for sexual harassment cases ranged from $100 to $15,000, with a mean of $3,234. A study was also done of the outcomes of federal court decisions on sexual harassment; Summers and Myklebust (1992) found that the severity of harassment behavior, presence of witnesses, and existence of notice to management were significantly related to the outcomes of cases. They also found that whether or not complainants had supporting documents and whether or not organizations had taken investigative or remedial action influenced the decision. The first major breakthrough in sexual harassment law came in 1986 when a unanimous Supreme Court ruled in Meritor Savings Bank v. Vinson that a sexually hostile work environment is illegal even if it does not cause economic harm to the victim. The second sexual harassment case to come before the Court was Harris v. Forklift Systems. This decision supported the notion that a discriminatorily abusive work environment— even one that does not seriously affect employees’ psychological well-being—can and often does detract from employees’ job performance, discourage employees from remaining on the job, or keep them from advancing in their careers. Because of these legal developments, organizations have been increasingly pressured to find methods to deal with sexual harassment, rather than face the high costs associated with increased legal fees, increased turnover, and decreased productivity. The courts’ primary recommendations for addressing sexual harassment have focused on encouraging organizations to establish policies, set up effective grievance channels within the organization, and educate employees about sexual harassment (Sorenson et al, 1994). These organizational responsibilities will be discussed in detail in the next section.
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Organizational Responsibilities Organizations are legally responsible to do all that is possible to avoid harassment and its negative consequences. Organizations should take several steps to create a harassmentfree environment; these will help the organization defend a claim if one is filed. A human factors expert can evaluate an organization’s sexual harassment program to determine whether it has met the following criteria. For organizations to prevent harassment before it occurs, to deal effectively with sexual harassment if it does occur, and to protect against litigation if a claim is filed, several harassment policy components are necessary. These include an effective policy statement, effective grievance procedures, and an education program for all organizational members (Levy and Paludi, 1997). The first component of the sexual harassment policy should be the organization issuing a strong statement condemning such behavior. The policy should include a definition of sexual harassment, describe possible actions against those who harass others, and make it clear that retaliatory action against an employee who makes charges will not be tolerated (Dessler, 1991). The existence of such a policy statement is not enough, however; the organization must ensure that all employees have read and understand it. This may be done effectively by requiring all employees to read and sign the statement upon hiring and keeping a signed copy in the employee file. In addition, a copy should be provided to the employee for his personal records. The components of an effective policy statement may incorporate the following (Paludi and Barickman, 1998): • A statement indicating that sexual harassment is illegal and won’t be tolerated • A definition of harassment that includes behaviors that constitute sexual harassment • The employee’s responsibility to report sexual harassment • The organization’s responsibility in responding to a report of harassment • A confidentiality statement • A description of the investigatory process • A description of sanctions for sexual harassment, retaliation, and false complaints • The identification of individuals responsible for hearing complaints Part of an organization’s sexual harassment policy should describe the procedures that will ensue if harassment occurs. The grievance procedure should outline specifically the steps a victim of harassment should take, how the organization should handle the investigation into a claim, and the consequences to harassers. The primary responsibility of the victim of harassment is record keeping. This will be discussed in detail in the next section. Several guidelines have been suggested when conducting an investigation into sexual harassment (Levy and Paludi, 1997). These include but are not limited to the following suggestions: • Every complaint must be kept confidential. • Determinations must not be made based solely on reputation of the individuals involved. • The harassment policy must be followed for every investigation and for the entire course of the investigation.
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• Every step of the investigation must be accurately documented. • Investigations must be completed promptly. • The complainant, the accused, and witnesses must be interviewed. • Every complaint against the same individual must be handled separately. • Closure must be provided for all parties involved. At the end of the investigation, a letter to this effect should be sent from the investigator to all involved parties, including the organizational CEO, who is typically involved in deciding appropriate sanctions for the perpetrator. Depending on the severity of the harassment, several remedial actions are recommended (Levy and Paludi, 1997). These include verbal or written reprimands, dismissal, suspension without pay, transfers, or demotions. In order for the sexual harassment policy to be recognized as an important component of an organization’s culture, organization leaders must demonstrate that the prevention of harassment is a high priority for them. It is unlikely that lower-level employees will buy into the harassment policy if organizational leaders are not committed. In addition, a training program should be designed to assist in the implementation of the policy. Thorough training programs send an unambiguous message to all individuals in the organization that the sexual harassment policy must be taken seriously and that harassment behaviors will not be tolerated (Dessler, 1991). The training program should ensure that all members of the organization understand their rights and responsibilities, help clarify the behaviors that constitute sexual harassment, describe how the organization will deal with an accusation if one occurs, and stress the importance of maintaining a work environment free of harassment and retaliatory behaviors (Paludi and Barickman, 1998). Individual Employee Responsibilities Employees also bear responsibility for preventing harassment. If someone is harassed, a human factors expert can evaluate whether the employee took the following steps. The first step victims of harassment should take is to confront his or her harassers so that it is absolutely clear that the specific behavior is unwanted. This notification, essentially a warning, is often effective in writing when it includes a factual account of the event, identification of the offending behavior, how this behavior affects the recipient, and the steps needed to avoid future conflict. Often this documentation is enough to get the perpetrator to stop the unwanted behavior (Dessler, 1991). The primary responsibility for employees who believe that they have been harassed is to keep accurate records of the alleged incident(s), including the date of the occurrence and details of the unwanted behavior. The date is especially important because if organization investigational outcomes are not satisfactory, there is a 180-day limit for a claim to be filed with the EEOC, counting from when the harassment occurred (Paludi and Barickman, 1998). It is also extremely important for the employee to report the incident to his or her immediate supervisor or a manager and to document this communication. This is absolutely necessary because the organization can only be held liable for harassment if it knew of or should have known about the incident. The individual should also report the unwelcome conduct to the harasser’s manager or the human resource director. This will leave no doubt that the employer has notice of the
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unwelcome nature of the conduct and create an obligation on the employer’s part to investigate and take warranted corrective actions (Dessler, 1991). If the employee feels that the organization has not met its duty and the standard required of it by law, the accuser may then file a claim with the local EEOC office. 36.4 Examples of Harassment Cases Researchers have found that, under certain circumstances, a victim of harassment is almost certain to win a case if it proceeds to litigation (Terpestra and Baker, 1988; Summers and Myklebust, 1992). If an individual has been the victim of severe harassment, has witnesses and documents to support the allegation, and has notified management of the harassment with no action taken by management upon notification, the victim is very likely to win the case. On the other hand, an organization fulfilling its responsibilities as discussed in the previous section may significantly decrease its likelihood of sexual harassment lawsuits and unfavorable settlements. Specifically, it should lessen the occurrence of the specific behaviors that tend to lead to a loss in court. These include sexual assault, unwanted physical contact, and sexual propositions intended to lead to a change in employment conditions (Terpestra and Baker, 1988). If an organization has followed the guidelines as outlined previously and stuck to its own written sexual harassment policy, the probability increases that the matter can be settled at the organizational level to the satisfaction of those involved. Unfortunately, incidents of sexual harassment typically are ambiguous. Either the victim did not follow all appropriate reporting and record-keeping procedures or the organizational safety climate failed to support the harassment policy. Organizations often stray from the procedures outlined in their written guidelines. The following subsection describes two examples of organizational sexual harassment illustrating that harassment situations are seldom straightforward and typically involve aspects favorable to the plaintiff as well as to the defendant organization. Case 1 This incident, which takes place in a restaurant, is unusual in that the person in the seemingly legitimate position of power is the victim. Here, a restaurant manager was the victim of harassment by a lower-level cook who had coercive power because he was good at his job. The harasser made lewd comments to the victim, touched her inappropriately, and made requests for sex. Although the victim was supposedly responsible for hiring and firing, she was told by higher-level management that the harasser was their only good cook. Therefore, she could not fire him. Despite her attempts to follow the proper corporate channels of documenting the harassment and reporting the transgressions to management, these measures were routinely ignored. Reprimands in the harasser’s employee file were regularly destroyed and disregarded. Safety culture describes the organizational attitude toward safety as proliferated by management. In this case, not only did the weak safety culture allow for this type of harassment but the management style also promoted it and prevented the victim from
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working in a safe, harassment-free environment. The victim in this case was fearful of retribution: she went through the appropriate procedures to discipline her harasser but still had to work close to him. The proximity of the harasser to the victim (especially after she tried to get him fired) left her in a vulnerable position. Case 2 A manager in the aerospace industry, “Mr. Slick,” had a series of women working for him, each leaving within a few years due to his harassment. However, employees hesitated to report Mr. Slick. His behavior was so blatant that the victims assumed that upper management had to be aware of his conduct. For example, in a large department meeting, he removed a chair from the room and told his employee that she had to sit in his lap. He assaulted her in his office another time with her knocking down furniture to escape him. When she opened his door, she ran into the division director, who must have heard the commotion. However, he walked by without question. This company lost productivity and, ultimately, several employees. Bystanders reported being very upset witnessing this harassment and were unable to focus on their work. The harasser’s behavior was so offensive that several people chose to leave the organization rather than stand by and watch what they perceived as permissive management. This case demonstrates the importance of documenting sexual harassment offenses. If these offenses are not reported through the appropriate channels, no record of the offensive behavior exists. Mr. Slick’s behavior was so blatant that employees assumed management was aware. Although formal policies addressing harassment were in place, management did not seek out the information; they relied on employees to report transgressions. Human factors experts would be called upon to evaluate the degree to which the plaintiff and the defendant organization fulfilled their respective responsibilities. Did the organization have an effective harassment program in place with a safety culture to back up the policies and procedures? Did the victim report and document the incidents properly? Because the organizations in both example cases ignored their own written policies and procedures regarding sexual harassment, this would increase their liability if these cases proceeded to litigation. In the first case, the plaintiff attempted to document and report the harassment; however, she failed to copy the complaint forms that she claimed she had submitted and that were destroyed by management. In the second case, the proper policies and procedures were also in place. The victim did not report the harassment because management observed it. Management clearly did not meet the standard of care: they did not take action after observing blatant harassment. The victim did not fulfill her responsibility; she did not file a complaint or report the problem to human resources.
Primary factor Macroergonomics
36.5 Checklist Considerations Management involvement Organizational design
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System design User-environment interaction System subcomponents Employee motivation Physical safety Emotional safety Organizational outcomes Decreased morale Increased turnover Reduced productivity Individual outcomes Decreased performance Interpersonal problems Emotional and physical reactions Individual differences Sensitivity Personality Religious beliefs Prior experiences Title VII compliance Prohibits sexual harassment Employers responsible for actions of employees Organizational responsibilities Establish written harassment policy Establish grievance procedures Educate and train employees about harassment Employee responsibilities Notify harasser in writing Document specifics about the incident Report incident to appropriate supervisor Microergonomics
Defining Terms Hostile environment sexual harassment—A situation created in the workplace that makes it difficult or impossible to work because the environment is perceived as threatening. Macroergonomics—Top-down sociotechnical systems approach to the design of organizations, work systems, jobs, and related human-machine, user-system, and humanenvironment interfaces. Microergonomics—The study of traditional human factors that focuses on the interfaces of the individual operator and his or her work environment. Physical harassment—Unwelcome patting, pinching, or brushing up against the body; coerced intercourse; assault; leering; or obscene gestures. Quid pro quo sexual harassment—An individual with organizational power who implies a condition dependent on the response to the sexual advance. Threats of being fired, failure to receive a promotion, or unjustified negative performance appraisals are examples of quid pro quo sexual harassment. Sexual harassment—Deliberate or repeated comments, gestures, or physical contact of a sexual nature that are unwanted by the recipient. Verbal harassment—Unwelcome sexual remarks, suggestive sounds, implied or overt threats, or pressure for sex.
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References Backhouse, C. and Cohen, L. (1981). Sexual Harassment on the Job . Englewood Cliffs, NJ: Prentice Hall, Inc. Crull, P. (1979). The impact of sexual harassment on the job: a profile of the experiences of 92 women. In Neutgarten, D.A. and Shafritz, J. (Eds.) (1981), Sexuality in Organizations: Romantic and Coercive Behavior at Work . IL: Moore Publishing Company, Inc. Dessler, G. (1991). Personnel/Human Resource Management . 5th ed. Englewood Cliffs, NJ: Prentice Hall. Hendrick, H.W. (2000). Introduction to macroergonomics. Proc. XIV Triennial Congr. Int. Ergonomics Assoc. 44th Annu. Meeting Hum. Factors Ergonomics Soc. , San Diego, CA, 539– 542. Hendrick, H.W. (1984). Wagging the tail with the dog: organizational design considerations in ergonomics. Proc. Hum. Factors Soc. 28th Annu. Meeting , Santa Monica, CA: Human Factors Society, 899–903. Levy, A. and Paludi, M.A. (1997). Workplace Sexual Harassment . Englewood Cliffs, NJ: Prentice Hall. Luthans, F. (1992). Organizational Behavior . 6th ed. New York: McGraw-Hill, Inc. McKinney, K. and Maroules, N. (1991). Sexual harassment. In Grauerholz, E. and Koralewski, M.A. (Eds.), Sexual Coercion . MA: Lexington. Meyer, M.C., Berchtold, I.M., Oesterich, J.L., and Collins, F.J. (1981). Sexual Harassment . New York: Petrocelli Books, Inc. Paludi, M.A. and Barickman, R.B. (1998). Sexual Harassment, Work and Education . 2nd ed. New York: State University of New York Press. Segal, J.A. (1996). Sexual harassment: where are we now? HR Mag. , October, 69–73. Sorenson, R.C., Luzio, R.C., and Mangione-Lambie, M.G. (1994). Perceived seriousness, recommended and expected organizational response, and effects of “bystander” and “direct” sexual harassment. Presented at the 23rd Int. Congr. Appl. Psychol. , Madrid, Spain, July. Stawar, T.L. (1999). Harassment: a model for sexual harassment behavior. Forensic Examiner , September/ October, 30–33. Sullivan, F.L. (1986). Sexual harassment: the Supreme Court’s ruling. Personnel , 83, 37–43. Summers, R.J. and Myklebust, K. (1992). The influence of a history of romance on judgments and responses to a complaint of sexual harassment. Sex Roles , 27, 345–357. Terpestra, D.E. and Baker, D.D. (1988). Outcomes of sexual harassment charges. Acad. Manage. J., March, 185–194.
Further Information Paludi, M.A. and Barickman, R.B. (1998). Sexual Harassment, Work and Education . 2nd ed. New York: State University of New York Press.
37 Health Care Forensics Christopher P.Nemeth University of Chicago 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
37.1 Introduction to Human Factors Principles and Standards of Care Health care is the work of providing services to a clientele that seeks “sound physical and mental condition” (Merriam-Webster, 1994:344), a $1.215 trillion a year business in the U.S. alone (HCFA, 2002). Health care in the U.S. is primarily provided through institutions, systems that amount to a collection of elements assembled and used in order to achieve an intended result. All systems in the operational (human-made) environment, including health care, are created through research and development (R&D) and are then operated and maintained. Woods and colleagues (1994) liken system performance to a wedge with sharp and blunt ends. At the sharp end of health care, practitioners apply expertise through actions in order to produce results. Health care organizations include tightly constrained teams of service providers who perform complex procedures that routinely have significant consequences. At the blunt end, policy, institutions, organizations, procedures, and practice guidelines provide resources and constraints for practitioners. Acutecare organizations such as hospitals typically offer a range of services that can include emergency care, surgery and critical care, rehabilitation, pediatrics, psychiatric, and drug and alcohol treatment. Some hospitals are teaching institutions that operate residency programs to educate physicians. Other health care organizations include outpatient clinics (offering such services as urgent, surgical, or rehabilitative services); extended care homes; physician offices; and visiting and remote-site services. Health care systems serve a population that has experienced a decline in infectious disease such as tuberculosis and a rise in chronic conditions such as heart disease. The latter tend to require more complex medical interventions. Those interventions, supported by technology, increase the risk of misadventures (Fagerhaugh et al., 1987:3–4). Health care, nuclear power generation, the military, and aviation are high-hazard applications that have extraordinary implications for the well-being of their workers and clients. Like these counterparts, health care organizations install defenses in order to avoid failure. For example, hardware mechanical fittings are intended to allow correct power, gas, and fluid connections and to prevent those that are inappropriate. Equipment and data system software interfaces are intended to guide practitioners through complex
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procedures. Training and supervision are intended to inculcate procedures that follow practice guidelines. Even with such defenses in place, the combination of human actions with latent hazards that exist in the organization as a whole or workplace in particular (Reason, 1990:208, 1997:12–17) cause significant morbidity (decline in health) and mortality (loss of life). One estimate puts the loss of life in the U.S. due to what is termed medical error at between 44,000 and 98,000 lives a year (Kohn et al., 2000:1). Those numbers, though, are a subject of continuing debate, as Brennan (2000) demonstrates. The Latent Failure Model Has Replaced the Individual Error Model Losses related to patient safety have been the focus of corrective efforts for many years. However, campaigns to improve patient safety in recent decades have had little lasting effect. Through that period, medical safety has been thought of as practitioner management: training those who practice to perform as needed. Practitioners who do not perform as needed are penalized. This notion of iatrogenic medical malpractice is based on a traditional model that emphasizes individual practitioner agency and accountability. In reality, practitioners act in comiogenic concert. As they do, they collectively cope with system defects that were “created by poor design, incorrect installation, faulty maintenance and bad management decisions” (Reason 1997:173). Multiple potential causes of an adverse outcome are usually present in a system as a characteristic of its routine operation. Poor system design, poor job design, and failed systems “contribute significantly to harmful error by providing the conditions under which error will thrive” (Sharpe and Faden, 1998:61–77, 138, 234). If a mistake is made, it is a “consequence and not a cause” because errors are “shaped and provoked by upstream, workplace and organizational factors” (Reason, 1997:126) such as limited or declining resources. As this chapter will show, health care is far more complex than simple matters of practice or malpractice. Concerns for well-being extend beyond the patient to include practitioners (physicians, nurses, technicians) and staff. Issues related to loss extend beyond procedures to policy, regulations, economics, management, hardware, software, facilities, and conditions. The chapter’s title, “Health Care Forensics,” reflects this scope. Remedies for Causes of Failure Are Now Sought beyond the Practitioner Blaming the operator is the normal organizational response to an incident (Reason, 1997:127–128), and the operator (in this case, practitioner) is the usual stopping point for forensic analyses (Rasmussen, 1986). A major reason for this is hindsight bias—the incorrect presumption that the chain of events that led up to an adverse outcome was foreseeable and that the event could have been prevented. The observation that such events are theoretically preventable is true but profoundly misleading. It diverts attention from the organizational causes and instead focuses it on the performance of individual practitioners. The importance of individual factors associated with an adverse outcome can only be appreciated in retrospect. High-hazard fields such as aviation and nuclear power generation have already realized that attaining high levels of performance would
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require them to evaluate their systems as causes of those failures. Health care forensics lags far behind these other domains in this respect. In addition to hindsight bias, other influences encourage the assignment of blame instead of looking for the actual cause. Operators are available to blame and tracing from an incident backward through the causal chain is difficult. A high level of human performance maintains system success as the norm rather than the exception (Cook and Woods, 1994:292–293). Such an inquiry also requires insight into how complex organizations function that few investigators demonstrate. Recent trends in health care safety have sought a more insightful response to incidents by shifting the focus away from blame and toward understanding health care practice and system design. In so doing, two distinct approaches have evolved that mirror the inherent separation between health care management and practitioner. Management. Management employs a quality improvement model in order to manage risk (Berwick et al, 1990:18–45). Risk management is a top-down process (Sedwick, 1997:25) that management uses “as a way to make decisions that will eliminate or minimize the consequence of accidental losses” (Hope, 1997:29). The approach relies on performance measurement, benchmarking, and tracking. One of the health care accrediting organizations, the Joint Commission on Accreditation of Healthcare Organizations (JCAHO), requires health care organizations to attend to issues of patient safety. Compliant organizations have an apparatus that typically includes the identification, reporting, and analysis of sentinel events, which are critical incidents that may result in loss of health or life. While reporting does identify events, event identification and reporting may not be connected to the actual underlying causes of accidents. Practitioner. Practitioner research into issues of patient safety takes a more “bottomup” approach. Authors, including Barley and Orr (1997); Cook and Woods (1996); Patterson et al. (2002); Xiao (1994); Nemeth (2003); Carthey et al. (2001); and Nunnally et al. (2002), strive to develop a deep and thorough grasp of health care as complex technical work. This approach seeks to understand the actual nature of health care practice and influences that act on it. Initiatives for change that are based on such understanding promise to remedy hazards directly. The needs to remedy issues in patient safety still exceed the means. Among 24 gaps in current U.S. patient safety research, Cooper (2000:5, 69) identified four that bear directly on human factors: 1. A “need for different research methodologies to overcome the barriers to access information about errors” (#1) 2. “…Research about communication and information-sharing among health care providers” (#3) 3. “Studies of work loads” (#6) 4. “Human factors” (#19)
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37.2 Objective and Scope of the Chapter This chapter: • Describes current issues with regard to patient safety • Discusses the principal issues that concern health care forensics • Provides an example to illustrate the principal issues • Identifies factors to consider when conducting a human factors forensic investigation in the health care field
37.3 Discussion of Principal Issues Among the issues that typify health care, ten should be considered when conducting a forensic review: uncertainty, complexity, constraints and control, adverse event investigation, standards of care, appropriate care, hardware and software, defenses and safety methods, documentation, and the limits and abilities of human performance. Uncertainty Aviation, the military, the nuclear power industry, and health care are considered highhazard sectors in which the potential loss of health, life, or property can have severe consequences. As a result, much effort is expended to erect defenses against hazards that could cause unrecoverable loss. However, health care is unique in a number of respects. Bosk (1979:23, 61) finds that “great uncertainty surrounds much medical behavior” because “medical decision-making is a probabilistic exercise. Presented with a patient with a set of symptoms, the physician makes a diagnosis and decides on an intervention.” Berg (1997:14) describes the practice of medicine as “applying scientific medical knowledge to individual patients with unique symptoms and complaints.” Only in health care do clients routinely undergo life-changing events that are highly emotionally charged. It is also difficult to know what to expect. Afflictions that are common in one location may be rare in another. Patients vary in their anatomy, in how they present, in the rate at which their health declines, and in how they react to treatments and medications. Although uncertainty is low in major trauma patients, it can be high in the instance of minor incremental trauma. For example, “going sour” is the term used to describe a series of negligible incidents that result in collective failure (Nicola, 2002). Each patient has a different history and condition requiring a unique course of treatment; patient willingness and ability to comply with courses of treatment can vary widely. Health care is event driven because patient type, needs, urgency, and timing vary a great deal. Numerous units, including patient wards, preoperative units, operating room, and postanesthesia recovery unit, bring together a variety of disciplines such as nurses, surgeons, and anesthesiologists to perform treatment. In order to cope with such variation, care providers configure equipment, supplies, and staff for each unique procedure adhoc.
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Complexity “Managing sophisticated technology and powerful, dangerous drugs alone poses a daunting challenge. Add our unique combination of diverse patients, multiple processes, and various professional disciplines, loosely organized along unclear lines of authority and major communication barriers and you have, to put it politely, a human factors design engineering nightmare” (Leape, 2000:xxii). In fact, “many authors argue that the problems modern doctors face are often too complex for ordinary humans to grasp comprehensively” (Berg, 1997:2). Medical knowledge has grown at a rate that has required differentiation into diverse practices (such as cardiac surgery) and specializations with those (such as pediatric cardiac surgery and anesthesia for pediatric cardiac surgery) and areas of expertise within each specialty. Eddy (1990a) contends, “Even if good evidence were available, it is unrealistic, even unfair, to expect people to be able to sort through it all in their heads.” Some have seized on this circumstance to advocate standardization and the automation of decision-making through computer-supported decision aids. A number of very real considerations make such general approaches difficult. Sharp-edge uncertainty and variety frustrate improvements through the application of global solutions. Most software support suffers from “clumsy automation” (Weiner, 1985), thus imposing a burden on practitioners who must operate software that meets only part of the procedure’s need. Practitioners must then develop coping skills including “work-around” procedures in order to adapt to the software’s shortcomings. Berg (1997) chronicles the failure of computer-based decision aids to assist medical choices. Cook and Woods (1994:266–268) explain the reasons why practitioners do not rely on formal decisionmaking. An optimal decision is often unattainable because medical knowledge is so complex and patient need proceeds on its more compelling schedule. Medical information is heterogeneous and imprecise. Embedded conflicts in the knowledge base call for trade-off decisions to be made at the point of delivery. Constraints and Control In addition to uncertainty in the type of demand for health care procedures, the timing and amount of demand for procedures also create uncertainty. Is the procedure elective, urgent, or emergent? Is the patient case mild, serious, or critical? Economic drivers force trade-offs as the physician is expected to meet a standard of medical expertise (SME) while at the same time satisfying requirements for efficiency imposed through a standard of resource use (SRU) (Sharpe and Faden, 1998:105). The confluence of these traits forms tight boundaries within which services are provided. Staff members have worked out complex means to evaluate and process decisions to best match widely varying demand with heavily constrained resources (Nemeth et al., 2002). Other elements constrain practice at the sharp end. For example, five sources of control influence bedside decisions: the physician and consultants, other health care providers such as nurses, the patient, the patient’s family, and third-party payers. Blunt end considerations such as finances and insurance inject issues that cut across the application of medical knowledge. Even if a practitioner performs flawlessly, failure can ensue from an unrelated cause, including disease, patient procrastination or
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noncooperation, nursing or support staff error, or machine malfunction (Bosk, 1979:67– 69). Adverse Event Investigation Agencies such as the National Transportation Safety Board (NTSB) exist to examine accidents and provide findings to the benefit of all concerned with transportation. Although opinions may vary regarding their methods, NTSB investigators are considered to be technically competent. Furthermore, NTSB investigators are not limited to the performance of practitioners surrounding the event. They account for all systems that may contribute to the cause of the events that they investigate, as their investigation into the Exxon Valdez grounding demonstrates. Health care organizations are deprived of similar resources to investigate adverse events. Each health care institution is responsible to develop its program. Programs are designed to meet the approval of the accrediting organization when it conducts a review. Investigators who manage such programs may not be technically qualified and can be driven by agendas other than deriving insights and improving health care practice. Standards of Care Practice guidelines are one means that the health care community uses to manage the performance expected among providers. For Eddy (1990b), guidelines “provide an intellectual vehicle through which the profession can distill the lessons of research and individual experiences and pool the knowledge and preferences of many people into conclusions about appropriate practice.” Guidelines are used to promulgate new knowledge and to establish the bounds of acceptable routine practice. Prior research by authors such as Lomas (1989) and Kanouse (1989) indicates that the intentions that bring about guidelines do not match the actual outcomes among U.S. physicians. Vang (1988) accounts for similar instances in European health care. Issues related to guidelines reflect issues embedded in health care practice: a lack of true consensus, complexity, cognition, conflict between practitioners and management, specificity, and compliance. • Lack of true consensus. Guidelines are issued as top-down mandates, the products of attempts among a cadre of experts to reach a consensus. Consensus (however tentative) among a handful of national experts does not represent a national consensus among practitioners. For example, the experience of computer-based decision support systems has demonstrated that little or no agreement about symptoms or disease categories exists among physicians (Berg, 1997:159). • Complexity. Health care is an amalgam of many elements including policy, people, hardware, software, procedures, and facilities that interact in complex ways in order to benefit the patient. Guidelines single out procedures and then reduce the concept of a procedure to a single new approach. This simplification and reduction ignores the complex interrelation among all health care system elements (Berg, 1997:177). • Cognition. Three cognitive factors influence practitioner performance: strategic factors, attentional dynamics, and knowledge factors. The effective use of knowledge to solve problems pivots on its content, organization, and activation. Guideline development
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may pay little or no attention to the four issues that influence knowledge application at the sharp end: mental models and knowledge flaws; knowledge calibration; inert knowledge; and the use of heuristics, simplifications, and approximations (Cook and Woods, 1994:258–262). Guidelines may introduce new knowledge content at the expense of the carefully worked-out equilibrium among many conflicting factors that a physician must establish. This can result in additional mental workload (cognitive overhead) with marginal improvement to actual practice. • Conflict between practice and management. Physicians are required to satisfy two standards of practice at the same time: a standard for medical expertise (SME) and a standard for resource use (SRU). Practice guidelines promulgate new SMEs but ignore SRUs, even through SRUs can exert an equal or greater force on a physician’s daily routine. As a result, “clinical standards may pit patient welfare against economic concerns” (Sharpe and Faden, 1998:102–105). • Specificity. National guidelines are necessarily universal and as a result are insensitive to individual patient care, which is necessarily particular. Guidelines are often vague and difficult to understand (Kanouse et al, 1989). In addition, each practice guideline addresses a single aspect of medical care. Most patients have more than one disease at a time, making a single diagnosis and treatment problematic (Berg, 1997:188). • Compliance. Guidelines do not describe an ideal model for practice. They are recommendations that physicians may or may not choose to follow. This can frustrate “…those individuals in public health, in the insurance fields, in health maintenance organizations and most surely and most terribly in the fields of law and government who will desire and will require strict conformity to the presumed ideal” (Elly, 1985). Practitioner initiative is often ahead of guidelines because guidelines use a deliberative consensusbuilding process to reflect best practices. As practice evolves, guidelines are frequently revised to reflect improvements. Thus, a forensic investigator must identify the guidelines that were in effect when the incident in a claim occurred. Sources for guidelines include: • Hospitals—Joint Commission on Accreditation of Healthcare Organizations (JCAHO) • Nurses—American Nursing Association (ANA) and nursing associations for each state • Physicians—American Medical Association (AMA) and professional associations for each type of medical practice Guidelines can also come from other sources. Organizations produce local guides such as standard procedure manuals. ECRI (formerly the Emergency Care Research Institute) issues health device and hazard alerts. The U.S. Food and Drug Administration (USFDA) issues reports on medical device performance (Ferguson, 1997:617). Information on drug indication and adverse reaction is available from the Physicians Desk Reference, The American Medical Association Drug Handbook, the U.S. Pharmacopoeia, and the American Society of Hospital Pharmacists. Because this variety of guideline sources can create circumstances in which guidelines from different organizations conflict, the practitioner who complies with the guidelines of one organization may fail to comply with those of another.
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Appropriate Care Even with the benefit of guidelines, clinical decisions are made case by case. In each case, points of view among four participants—the clinician, the patient, the third-party payer, and society—define appropriate care. Four interrelated clinical factors bear on the recommendation for a procedure: patient’s clinical profile, physician’s and team’s skill, quality of evidence supporting the procedure,
FIGURE 37.1 Clinical assessment. The decision to proceed with a certain treatment relies in part on the tradeoffs between what is known about certain courses of treatment and their anticipated harms and benefits. Strong evidence such as randomized clinical trials enables decisions to be made on the basis of results that are less subject to bias and inferential error. Weak
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evidence such as expert opinion leaves interventions unproven in their efficacy or effectiveness. (From Sharpe, V. and Faden, A., 1998, Medical Harm, Cambridge: Cambridge University Press, 219. Reprinted with the permission of Cambridge University Press.) and the procedure’s clinical benefit/harm ratio. Randomized clinical trials are considered the best method to determine whether an intervention is appropriate; however, most procedures do not have the benefit of large-scale trials. Instead, studies can be ranked according to those that are less subject to bias and inferential error (USPSTF, 1989). In descending order of strength, they include: randomized clinical trials (RCT), nonrandomized controlled trials, cohort studies, case-control studies, comparisons between time and place, uncontrolled experiments, and descriptive studies and expert opinion. Figure 37.1 depicts the relationship between quality of evidence and the harms and benefits that can be anticipated.
FIGURE 37.2 Sample cases. Sample interventions illustrate the areas
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described in Figure 37.1. Note that some procedures, such as radical prostatectomy, vary in their indications, based on the strength of evidence regarding harm and benefits for males over 75 and under 75 years of age. (From Sharpe, V. and Faden, A., 1998, Medical Harm, Cambridge: Cambridge University Press, 220. Reprinted with the permission of Cambridge University Press.) The lower portion of the diagram indicates areas in which study evidence is not strong. As a result, neither the efficacy nor the effectiveness of interventions is proven (Sharpe and Faden, 1998:214–220). Some practitioners contend that much of medical practice takes place at the lower center portion of the diagram, where there is little proven knowledge and anticipated harms/benefits are equivocal (O’Connor, 2002). Figure 37.2 illustrates the implications of treatment decisions. Certain procedures (such as the radical prostatectomy shown in the diagram) are assigned substantially different clinical recommendations on the basis of evidence quality and change in a single variable. Juhar (2002) notes that the roles involved in this decision regarding treatment flex in order to reconcile patient preference and practitioner expertise. This complex interplay of each participant’s point of view with clinical factors leads to the decision on what is to be done, how it will be done, and what is to be expected. Hardware and Software Protocols have been established to guide the development of health care equipment and supplies. In the U.S., the Food and Drug Administration requires compliance with design guidelines and certifies products only after rigorous evaluation to verify therapeutic benefit. The health care facility is the point of service provision. It is at the hospital and clinic, not the manufacturer, that hardware and software are brought together to comprise a system. This is because no single manufacturer can address the high rate of change in health care technology and/or the wide variation in patient needs and practitioner approaches. Staff members regularly assemble combinations of new and legacy equipment and software that are used across facilities and within departments. Growth in the complexity of diagnosis and treatment and in the sophistication of technology has led to increasing reliance on computer-supported equipment. This has led to practitioner exposure to the effects of clumsy automation (Woods and Patterson, 2002). Interfaces are difficult to understand. Many devices can be put into states that have not been anticipated by their programmers or understood by their users. This forces practitioners to develop mental models that are actually coping strategies that are designed to get the machine to do what needs to be done without understanding it. Nunnally and colleagues (2002) show how software interfaces for infusion pumps demonstrate this property.
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Defenses and Safety Methods Stable industries such as nuclear power generation employ engineered defenses and administrative controls. Health care defenses vary as widely as the types of practice. Some practices, such as anesthesi-ology, employ engineered defenses, while surgeons and nurses rely largely on skills. Health care organizations have developed safety methods, including morbidity and mortality (M&M) conferences, safety committees, and root cause analyses. The M&M conference was conceived as a means for practitioners to review and reflect on incidents and near-incidents in order to consider improvements to avoid future such events. M&Ms rarely meet that ideal. Even at its best, the M&M is a retrospective review of behavior (Bosk, 1979:184) that is subject to interpersonal dynamics of blame and defense. Driven by a need to comply with JCAHO accreditation, the process can be more oriented toward documentation and trend analysis than fact finding, understanding, and improvement. Health care organizations have sought to monitor sentinel events at the sharp end and to identify and remedy them through methods such as root cause analysis (RCA; Gertman and Blackman, 1994; JCAHO, 2001). JCAHO encourages the use of RCA by members of safety committees to identify the causes for sentinel events. Through this analysis, investigators try to trace a causal chain back from an event to a root cause. However, this does not take the latent failure model into account. Typically, multiple small failures contribute to an incident. Their causes may lie at multiple levels and in multiple locations and occur at varying points in time. Even when causes are known, it can be difficult to trace backward through the causal chain that led to the system failure (Rasmussen, 1986). That is because RCA collects data, not insights. Members of safety committees do not have the benefit of the same level of education, experience, training, and insight as the practitioners involved in an incident. For this reason, the RCA approach sheds more light on why institutions cannot deal with adverse outcomes than on the nature of the events that they seek to understand. Documentation Documentation related to health care claims includes medical records and incident reports. • Medical records. Medical records can serve as a source of information in the event of claims related to forensic investigation. Supporting documentation such as journal articles can expand on knowledge regarding procedures mentioned in the medical record. Such items should be from authoritative sources such as articles from the New England Journal of Medicine, the Journal of the American Medical Association, or professional specialty association journals. Kirby-Hall (1997:559) notes that “in reviewing any medical record, deviations from standards of care can be found. The important thing is to determine which deviation had an effect on the health outcome of the patient.” She poses eight questions that a medical record review should answer: • What is the investigation/review about? • What is the time frame for the event? • What information is sought?
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• What is the statute of limitations? • What records are available and needed? Who is involved? • What is the record reviewer’s role in the case? • Incident reports. Incident reports are a problematic source of information. Reports are intended for submission to an incident-reporting database, such as the U.S. FDA’s manufacturer and user device experience (MAUDE) reports. In their Patient Safety Foundation report, Cook and colleagues (1998:33) found that “…the view is widespread that less than 5% and perhaps less than 1% of incidents that might fit the criteria for reporting are actually reported.” Those who submit reports are often motivated by frustration over a particular piece of equipment. Manufacturer responses to such reports typically focus on the item (“device performed within specification”) instead of the use context. Report databases that are used to manage report submittal are made for various agendas, such as trend analysis, that do not serve the purpose of fact finding. Report submission typically relies on filling out forms that rarely get at the actual nature of what occurred. In addition, formatted reports do not allow for initiative because few submitters will initiate a balanced critique.
TABLE 37.1 Health Care Forensic Information Sources Patient medical record Can be used for initial Can be used to supplement May also be available, depending on review initial review case Physician’s orders, case entry notes Nursing notes Flow sheets Admission record and informed consent forms Discharge summary Medication records
Admission history and physical Physician’s progress notes Laboratory reports Radiology reports Electrocardiograph (EKG) strips and reports Vital sign graphic sheets
Consultation reports Operating room records Anesthesia records Intensive care records Recovery room records
Death certificate Autopsy report Therapy records (i.e., physical, occupational, speech) Note: Information on health care cases is typically complex and requires judgment based on experience to understand it and its implications. This table, drawn from Kirby-Hall (1997), recommends patient medical record information that may be used to develop an understanding of health care events. Source: Kirby-Hall, K., 1997, in Ciolino, P.J. and Castle, G.E., Eds., Advanced Civil Forensic Investigations. Tucson: Lawyers and Judges Publications, 552–553.
Table 37.1 through Table 37.3 summarize sources that Kirby-Hall (1997:552–553), Ferguson (1997:609–618), and Barton (1997:395) recommend for locating information that is related to a health care incident investigation. As large as it is, the patient record is not a complete account of what happened. Historically, the patient medical record contained comments that were highly informative because they reflected practitioner
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insights regarding what was or was not going on. Records have grown in size to the point that they have become unwieldy for practitioners to use. Records are also discoverable in an investigation, making practitioners increasingly reluctant to enter comments into them. Although practitioners continue to make comments, they no longer place them in the patient record; instead, they use informal means of documentation that are discarded. The practitioner constantly makes trade-off decisions in order to resolve conflicting pressures to the patient’s benefit. Thorough review and discussion among qualified medical experts can seek to discover the nature and causes of incidents. 37.4 Examples Geddes (2002) describes a variety of medical device accidents and provides illustrative cases. The following example shows the interrelationship among the issues that this chapter has described. Cardiac and Cerebral Catheterization Human factors professionals have a key opportunity to protect human safety in highstakes environments. Invasive surgical procedures that are performed in a hospital catheterization laboratory are such an opportunity, particularly when the potential exists for the procedure to inflict extraordinary patient trauma. Nemeth (2004) describes an occasion in which the operation of a contrast dye injector in cardiac catheterization labs resulted in patient morbidity and mortality. Cardiac and cerebral angiography is a diagnostic invasive procedure that is performed on patients who demonstrate symptoms of arterial disease and plaque build-up, which can lead to a heart attack or stroke. The cardiac catheterization lab where the procedure is performed can be considered a complex workstation. Although facilities vary in size and layout, the scenario is essentially the same at each location. The skin on the patient’s upper thigh is shaved to remove hair and then treated with povidone iodine in order to create a sterile field. A large bore needle is inserted into the femoral artery and a long catheter
TABLE 37.2 Health Care Forensic Information Sources Patient medical record Face sheet Progress notes Physicians’ orders Admission note Consultations Discharge summary Nursing notes Nursing admit and discharge notes Nursing flow sheets
Policy and procedure manuals Hospital privilege application Physician’s Desk Reference Professional organization guidelines Nursing manuals JCAHO standards Individual self-imposed standards Warning publications
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Care plan Operative reports Anesthesia records Postanesthesia recovery (PAR) room records Pathology report and samples Diagnostic testing Laboratory tests Blood bank records Emergency room records Ambulance reports Outside laboratory records Prescription information X-rays, CAT scans, MRIs, mammograms Fetal monitor strips Echocardiograms Correspondence Note: in addition to the patient medical record, Ferguson (1997) includes a number of sources to build an understanding of an adverse health care outcome. Source: Ferguson, L., 1997, in Ciolino, P.J. and Castle, G.E., Eds., Advanced Civil Forensic Investigations, Tucson: Lawyers and Judges Publications, 609–618.
TABLE 37.3 Health Care Forensic Information Sources Summaries of investigations by claims, risk-management personnel, and independent adjusters Summaries of interviews with involved staff and other parties Copies of statements by involved staff and other parties Medical records and other clinical reports Expert reports or report summaries Copies of pleadings Defense counsel reports Copies of correspondence with codefendants, insurers, excess carriers Copies of bills, invoices, records of payments Note: With regard to information sources, Barton (1997) takes an additional perspective by including legal documents as well as interviews. Interviews with qualified subjects will start to get at many of the issues related to actual conditions, appropriate care, and trade-offs with which practitioners were dealing. Source: Barton, E.L., 1997, in Carroll, R., Ed., Risk Management Handbook for Health Care Organizations. Chicago: American Hospital Publishing, 385–430.
is inserted through the needle via the thorax into the heart or carotid artery. Contrast dye is injected to show blood flow through arteries that feed the heart or brain. Strictures to blood flow, shown by x-ray images projected onto a video monitor, indicate clogged arteries that may need angioplasty or by-pass surgery. The patient, who must hold his or her breath in order to stop movement during image collection, receives local anesthesia and is awake during the procedure.
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During the process of patient catheterization, the potential exists for one or more air bubbles to be introduced into the patient bloodstream via the contrast dye. Free to travel through the patient’s body, a bubble may lodge in the nervous system or brain, causing paralysis or worse. Reports to the manufacturer that retained the investigator indicated that this had occurred in a number of instances. Because the cause was unknown, all of the equipment in use at the time was implicated, including the product made by the manufacturer who sponsored this research project. An equipment review showed certain pieces of equipment were individually well engineered but did not show the benefit of attention having been paid to issues such as user orientation or use in combination with other items. For example, controls on one item that were required to make gross and fine adjustment were located on the device housing. When the device was used, it was kept outside the sterile field. At the same time, the operator had to lean toward the sterile field to see clearly while operating the device. As a result, the operator had to reach back and adjust controls entirely by feel. In addition, the device was mounted on a fixed pedestal with casters. This prevented height adjustment, making it more difficult for nurses of short stature to see displays and operate controls. The potential existed for an incident to occur when circumstances coincided that were related to four elements: personnel, hardware/software, procedures, and total environment. The circulating nurse could be directed to operate ancillary equipment with little advance notice (personnel). With no self-monitor ing function, it was possible for a dye injector to be unprepared for use without the staff knowing about it (hardware/software). The rate of procedure could accelerate abruptly, posing the opportunity for oversight. In addition, no in-service training was provided for ancillary equipment operation after its initial installation, which resulted in instructions passed to new team members by word of mouth (procedures). The variety and number of collateral tasks distracted some staff members (total environment). The investigator’s report linked the source of the potential problem to the effect that it produced. The report then connected each of the effects to solution recommendations intended to prevent the problem. The manufacturer found the logic compelling and adopted the recommendations. The combination of poor design, clumsy software, and change in the distribution of workload made this incident inevitable. Practitioner actions were the least important contributing factor. 37.5 Main Factors to Consider Forensics is necessarily retrospective because it involves a search for information after a loss has been incurred. Section 37.3 identified influences on health care and its provision. This section outlines factors that the investigator of a health care incident should take into account. The nature of health care as it is has been described also makes claims related to the field complex and technically challenging. As a result, investigation into health care claims requires investigators qualified by virtue of experience in the field of practice. Four additional factors deserve consideration: the limits and abilities of human performance, incidence, prevention/audit, and process.
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Limits and Abilities of Human Performance This chapter’s inclusion in a human factors forensics handbook means that any investigation will be based on human performance limits and abilities: what people can and cannot do and will or will not do. Ramsey’s accident model, shown in Figure 37.3, demonstrates the connection between human performance and adverse outcomes. Perception precedes cognition, decision, and output. Any health care forensic investigation will necessarily reflect an understanding of human performance, as Nemeth (2004) describes, and its relation to the incident. Incidence Analysis of claims (Farraco and Spath, 2000:19) indicates that certain processes are associated with greater risk of patient injury: • Diagnostic and therapeutic decision-making • Physician, nurse, and other caregiver assessment and observation of patients
FIGURE 37.3 Accident sequence model. The limits and abilities of human performance bear on whether individuals are exposed to hazard, resulting in adverse outcomes. This
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figure demonstrates how sensory, cognitive, and physiomotor skills play a role in an individual’s exposure to hazard and subsequent results. (Reprinted from Safety Science, formerly Journal of Occupational Accidents, vol. 7, Ramsey, J. Ergonomic factors in task analysis for consumer products, 123–133. Copyright 1985, with permission from Elsevier.) • Transfer of patient care responsibilities between caregivers and facilities • Communication among caregivers and between caregivers and patients • Patient monitoring during and immediately after high-risk interventions • Administration of medications and monitoring of their effects Perper (1994:227) finds that elderly people in poor health and hospitalized over longer periods of time are at risk of therapeutic misadventures resulting in permanent disability or death. Prevention/Audit Effective patient safety relies on continuing attention to health care system elements, their interaction, and condition. Insightful observation by qualified practitioners is most likely to identify latent conditions. Forensic review of circumstances after the fact can begin with an audit of how well that observation was performed. • Health care organization • What was the dynamic condition of the organization over time? • What was the tempo of operations across the facility or in particular units? • Were there shortages of staff, supplies, equipment, rooms? • Did management policies direct procedures in a way that resulted in compromised care? • Were necessary education and training made available? • Was training adequate? • Hardware and software • What effort did the health care organization make to understand the nature of the systems/ components/utilities that already exist at the facility and those that are being introduced? • Do systems now in place serve their intended purpose? • Are they in need of repair…overhaul…replacement? • What are implications for the introduction of new systems? • What is the hazard inherent in their use? • Have necessary changes been made to allow for protection from these hazards?
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• Does use of the new systems pose conflicts when used in conjunction with existing systems? • Are multiple versions of the item (such as software) in use and, if they are, is it possible for individuals to know which version is in use? Similar questions can also be posed with regard to staff and procedures: • Personnel • Did patients and health care providers participate in the care process? • Patient • Did the patient misrepresent current condition or history? • Did the patient comply with prescription and directions? • Did the patient insist on a course of treatment and seek a provider who was willing to provide it? • Practitioners and staff • Was the practitioner or staff member qualified through education, training, and experience to perform the treatment? • Did any mitigating factors influence performance such as fatigue, illness, or reduced staff? • Procedures • What have others done in similar circumstances? • Was the result foreseeable? • External environment • Did elements from outside the health care system influence the provision of care? Process Cook and colleagues (1998) demonstrate the use of a parallel approach to understand the role that practitioners play in operating demand-driven complex technical systems. By describing celebrated (widely publicized) and uncelebrated cases, they lay the groundwork to understand that which is normal. By understanding the nominal, uncontroversial case as well as the recovery from near failure, the investigator can appreciate the actual nature of a case that involves loss. Reason (1997:18) describes a process of accident analysis for any complex system: • Begin with a bad outcome. • Consider how and when defenses failed. • Establish the active failures and latent conditions involved (for each defense that was bypassed or breached). • Consider the local conditions that could have shaped or provoked each unsafe act. • Ask what upstream factors could have contributed to each local condition.
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Barton (1997:392) describes a health care forensic investigation as a three-step process: • Discover the facts. • Determine the applicable standard of care. • Assess the applicable legal principles. Regardless of approach, the competent forensics investigation will discover: • Institutional factors that created the circumstances for failure • Design and technical factors that contributed to or caused failure • Important deviations from the standard of care • Actions of practitioners while providing care
37.6 Conclusion Discussions of adverse events in health care that centered on medical malpractice have discouraged medical professionals from the report or disclosure of bad outcomes (Sharpe and Faden, 1998:234). Recent studies of complex high-hazard technical systems, including health care, reveal that the cause for negative outcomes is more often embedded in many parts of the system that are upstream from the last individual in the chain of causation. For that reason, it is incumbent on the forensic investigator to account for health care’s uncertainty, complexity, constraints and control, methods of adverse event investigation, standards of care, appropriate care, hardware and software, defenses, and safety methods and documentation. Health care forensics exists to improve health care practice and to remedy loss. Shortterm progress in both areas relies on the evolution beyond “blame the operator” to understanding health care uncertainty, complexity, and scope. Long-term progress relies on the development of institutions, resources, and values that collaborate to the benefit of those who seek care. Acknowledgment The author gratefully acknowledges the generous assistance of Dr. Harold Wakeley, Dr. Richard Cook, and Dr. Michael O’Connor, who reviewed and commented on drafts of this chapter. Defining Terms Anamnestic—Information gained by questioning the patient; patient’s history. Care—The provision of accommodations, comfort, and treatment to an individual, implying responsibility for safety, that includes care, treatment, services, habilitation, rehabilitation, or other programs instituted by the organization for the individual (JCAHO, 2001:glossary 8).
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Cause—Something that brings about a result (Merriarn-Webster, 1994:130). Proximate (very near) cause may be most immediate and evident. Underlying (fundamental) cause is the primary reason. Claim—A formal notification, orally or in writing, that monetary damages are sought from the health care organization by a third party for an alleged injury (Barton, 1997:386). Defensive medicine—Instances in which a health provider’s practice decisions are motivated primarily by the desire to protect himself from the risk of legal liability (Sharpe and Faden, 1998:205). Error (conceptual)—The assumption that an actual or theoretical medical benefit justifies a specific therapeutic approach, resulting in a failure to foresee the nature of magnitude of possibly injurious effects (Perper, 1994:29). Error (technical)—Practitioner skills fall short of what the task requires even though performing a role conscientiously. Surgical service work is organized to suppress the absolute number of technical errors (Bosk, 1979:37, 41). Error (judgmental)—Choice of an incorrect treatment strategy. The two most common judgmental errors that attending surgeons make are overly heroic surgery and the failure to operate when the situation demands (Bosk, 1979:45–46). Error (normative)—Practitioner failure in the eyes of others to discharge role obligations conscientiously. Normative errors are breaches of standards of performance shared by all attending that indicate an error in the assumption of a role (Bosk, 1979:51, 61). Error (quasinormative)—Errors that are eccentric and specific to an individual attending practitioner (in contrast with normative error) (Bosk, 1979:61). latrogenic injury/illness—Adverse effects resulting wholly or in part from medical procedures or medication that are not a direct or indirect complication of the patient’s condition or disease (Perper, 1994:28). Illness induced by the physician and the physician alone (Sharpe and Faden, 1999:1). Illness—The human experience of sufferings and unwelcome symptoms associated with embodiment (Sharpe and Faden, 1998:122). JCAHO—Joint Commission on Accreditation of Healthcare Organizations. Latent system faults—Erroneous decisions and actions, often made by administration, that have a delayed impact on the function of the system (McClanahan et al, 2000:5). Medical mistake—A faulty human action made during the diagnosis or treatment of a patient that results in damage to, or death of, a patient (Ternov, 2000:98). Morbidity—Decline in health. Mortality—Loss of life. Nosocomial infection—An infection acquired by an individual when receiving care or services in a health care organization (JCAHO, 2001:glossary 19). Practitioner—Any individual qualified to practice a health care profession (e.g., physician, nurse) (JCAHO, 2001:glossary 33). Potentially compensable event—An incident in which there is neither an active claim nor institution of formal legal action (Barton,1997:387). Risk avoidance—Refraining from practices that are accompanied by a high degree of perceived malpractice risk (Sharpe and Faden, 1998:205).
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Risk reduction—The implementation of practice strategies intended to safeguard against litigation (e.g., more diagnostic tests, enhanced record-keeping, increased followup visits, and increased communication with patients regarding procedure risks and benefits) (Sharpe and Faden, 1998:205). Risk management—Protection of the health care organization against loss (HaggsRickert, 1997:38). Side effects—Effects of a selected medical approach that are accepted as reasonable therapeutic trade-offs (Perper, 1994:29). Therapeutic misadventure (also peritherapeutic adverse event)—Unexpected or unexplained medical care-related injury or adverse outcome. It is not an inherited disability, side effect or unpreventable natural complication of the involved procedure or medication, or a natural complication of the patient’s initial conditions (Perper, 1994:31). USFDA—United States Food and Drug Administration. References Barley, S.R. and Orr, J.E., Eds., 1997, Between Craft and Science: Technical Work in the U.S. Settings . Ithaca, NY: Cornell University Press. Barton, E.L., 1997, Claims and litigation management. In Carroll, R., Ed., Risk Management Handbook for Health Care Organizations . Chicago: American Hospital Publishing, 385–430. Berg, M., 1997, Rationalizing Medical Work . Cambridge, MA: The MIT Press. Berwick, D., Godfrey, A.B., and Roessner, J., 1990, Curing Health Care . San Francisco: JosseyBass. Bosk, C., 1979, Forgive and Remember . Chicago: The University of Chicago Press. Brennan, T.A., 2000, The Institute of Medicine Report on Medical Errors—could it do harm? New Engl. J. Med. , 343, 663–665. Carthey, J., Leval, M.R., Reason, J.T., Farewell, V.T., and Wright, D.J., 2001, Human factors research in cardiac surgery: opportunities and pitfalls, Clin. Risk , Royal Society of Medicine Press, 7(3), 85–90. Cook, R. and Woods, D., 1996, Adapting to new technology in the operating room, Hum. Factors , 38, 593–613. Cook, R., Woods, D., and Miller, C, 1998, A Tale of Two Stories: Contrasting Views of Patient Safety . National Health Care Safety Council of the National Patient Safety Foundation, Chicago: American Medical Association. Cook, R.I. and Woods, D., 1994, Operating at the sharp end: the complexity of human error. In Bogner, M.S., Ed., Human Error in Medicine , Hillsdale, NJ: Lawrence Erlbaum Associates, 255–310. Cooper, J.B., 2000, Current Research on Patient Safety in the United States . Chicago: National Patient Safety Foundation. Elly, W, 1985, Consensus or coercion? JAMA , 254, 1077. Eddy, D.M., 1990a, The challenge, JAMA, 263, 287–290. Eddy, D.M., 1990b, Practice obstacles: what are they? JAMA, 263, 877–880. Fagerhaugh, S.Y. et al., 1987, Hazards in Hospital Care . San Francisco: Jossey-Bass. Farraco, K. and Spath, P.L., 2000, Measuring performance of high risk processes. In Spath, PL., Ed., Error Reduction in Health Care . San Francisco: Jossey-Bass, 17–95. Ferguson, L., 1997, Medical malpractice. In Ciolino, P.J. and Castle, G.E., Eds., Advanced Civil Forensic Investigations . Tucson: Lawyers and Judges Publications, 609–618. Geddes, L.A., 2002, Medical Device Accidents and Illustrative Cases . Tucson: Lawyers and Judges Publications.
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Gertman, D. and Blackman, H., 1994, Human Reliability and Safety Analysis Data Handbook . New York: John Wiley & Sons. Haggs-Rickert, S.R., 1997, Elements of a risk-management program. In Carroll, R., Ed., Risk Management Handbook for Health Care Organizations . Chicago: American Hospital Publishing, 35–51. HCFA (Health Care Financing Administration), 2002, National Health Expenditures Aggregate and per Capita Amounts, Percent Distribution, and Average Annual Percent Growth, by Source of Funds: Selected Calendar Years 1980–2000, http://www.hcfa.gov/stats/nhe-oact/tables/tl.htm, 13 June. Hope, W, 1997, The risk management process. In Carroll, R., Ed., Risk Management Handbook for Health Care Organizations . Chicago: American Hospital Publishing, 29–34. (JCAHO) Joint Commission on Accreditation of Healthcare Organizations, 2001, Automated Comprehensive Accreditation Manual for Hospitals . Oakbrook Terrace, IL. Juhar, S., 2002, Advice rejoins consent, New York Times , 2 July, D5. Kanouse, D.E. et al., 1989, Changing Medical Practice through Technology Assessment: an Evaluation of the NIH Consensus Development Program . Health Administration Press. Kirby-Hall, K., 1997, Medical records investigation. In Ciolino, P.J. and Castle, G.E., Eds., Advanced Civil Forensic Investigations . Tucson: Lawyers and Judges Publications, 547–562. Kohn, L., Corrigan, J., and Donaldson, M., Eds., 2000, To Err Is Human . Washington: National Academy Press. Leape, L., Foreword. In Spath, PL., Ed., Error Reduction in Health Care . San Francisco: JosseyBass, xxi-xxiii. Lomas et al., 1989, Do practice guidelines guide practice? The effect of consensus statement on the practice of physicians, New Engl J. Med. , 321, 1306–1311. McClanahan, S., Goodwin, S.T., and Houser, F., 2000, A formula for errors: good people+bad systems. In Spath, PL., Ed., Error Reduction in Health Care . San Francisco: Jossey-Bass, 1–15. Nicola, T, 2002, 25 March, personal interview. Nemeth, C.P., Klock, PA., Daves, S., and Cook, R.I., 2002, A study of how cognitive artifacts affect distributed cognition in operating room management, Am. Soc. Anesthesiologists 2002 Natl. Conf. , 15 October, Orlando, FL. Nemeth, C.P. (in press), Human Factors Methods for Design . London: Taylor & Francis. Nunnally, M., Brunetti, V., O’Connor, M., Render, M., and Cook, R., 2002, Lost in menuspace: variability among users programming infusion devices under controlled conditions, Am. Soc. Anesthesiologists 2002 Natl Conf. , 15 October, Orlando, FL. O’Connor, M., 2002, 17 July, personal interview. Patterson, E., Cook, R., and Render, M., 2002, Improving patient safety by identifying side effects from introducing bar coding in medication administration. J. Med. Informatics Assoc. , 9(5), 540–553. Perper, J.A., 1994, Life threatening and fatal therapeutic misadventures. In Bogner, M.S., Ed., Human Error in Medicine . Hillsdale, NJ: Lawrence Erlbaum Associates, 27–52. Rasmussen, J.., 1986, Information Processing and Human-Machine Interaction . New York: Elsevier Science Publishing. Reason, J., 1990, Human Error . New York: Cambridge University Press. Reason, J., 1997, Managing the Risks of Organizational Accidents . Brookfield, VT: Ashgate. Sedwick, J., 1997, The risk manager role. In Carroll, R., Ed., Risk Management Handbook for Health Care Organizations . Chicago: American Hospital Publishing, 3–27. Sharpe, V. and Faden, A., 1998, Medical Harm , Cambridge: Cambridge University Press. Ternov, S., 2000, The medical side of human mistakes. In Spath, P.L., Ed., Error Reduction in Health Care . San Francisco: Jossey-Bass, 97–138. (USPSTF) U.S. Preventative Services Task Force, 1989, Guide to Clinical Preventative Services: an Assessment of 169 Clinical Interventions , Baltimore: Williams and Wilkins.
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Vang, J., 1988, The consensus development conference and the European experience, Int. J. Technol Assessment Health Care , 4, 65–76. The Merriam-Webster Dictionary , 1994, Springfield, MA: Merriam-Webster. Weiner, E., 1985, Beyond the sterile cockpit, Human Factors , 27(1), 75–90. Woods, D., Johannesen, L., Cook, R., and Sarter, N., 1994, Behind Human Error: Cognitive System, Computers, and Hindsight . Wright-Patter son AFB, OH: Crew Systems Ergonomics Information Analysis Center. Woods, D. and Patterson, E., 2002, How unexpected events produce an escalation of cognitive and coordinative demands, http://www.osu.edu/, 8 June. Xiao, Y, 1994, Interacting with complex work environments: a field study and planning model. Ph.D. dissertation, Graduate Department of Industrial Engineering, University of Toronto.
Further Information Chassin, M.R. and Becher, E.G., 2002, The wrong patient, Ann. Intern. Med. , 136, 826–833. Cook, R.I., 2002, A brief look at the new look in complex system failure, error, and safety. Cognitive Technologies Laboratory, University of Chicago,
, Chicago. Dekker, S., 2002, Field Guide to Human Error Investigations . Aldershot: Ashgate. Field, M.J. and Lohr, K.N., Eds. 1990, Clinical Practice Guidelines: Directions for a New Program . Washington, D.C.: National Academy Press. Heath, C. and Luff, P., 2000, Technology in Action , New York: Cambridge University Press. Hill, M.N. and Weisman, C.S., 1991, Physicians’ perceptions of consensus reports, Int. J. Technol. Assessment Health Care , 7 , 30–41. Hollinagel, E., 2004, Barriers and Accident Prevention . Aldershot: Ashgate. Kosecoff, J. et al., 1987, Effects of the National Institutes of Health Consensus Development Program on physician practice, JAMA , 258, 2708–2713. Ramsey, J., 1985, Assessment of warnings based on an ergonomic accident sequence model, Int. J. Ind. Ergonomics , Amsterdam: Elsevier Science Publishers, 195–199. Rasmussen, J., Duncan, K., and Leplat, J., 1987, New Technology and Human Error . New York: John Wiley & Sons. Svedung, I. and Rasmussen, J., 2002, Graphic representation of accident scenarios: mapping system structure and the causation of accidents, Saf. Sci. , 40, 397–417. Woods, D. and Cook, R.I., 1999, Perspectives on human error: hindsight bias and local rationality. In Durso, R.S. et al., Eds., Handbook of Applied Cognition . New York: John Wiley & Sons, 141–171.
VII Human Factors Terminology
38 A Guide to Forensic Human Factors Terminology David A.Thompson Standford University H.Harvey Cohen Error Analysis, Inc. Donald P.Horst Private Consultant Daniel A.Johnson Daniel A Johnson Inc Richard A.Olsen Human Performance: Limited 0–415–28870–3/05/$0.00+$1.50 © 2005 by CRC Press
The following draft terminology is intended for use within the Human Factors and Ergonomics community. It consists of scientific and technical definitions used to describe events, behavior, objects, and environments used in the practice of forensic human factors. It is not intended to have legal meaning or to substitute for legal terminology. Variations from these definitions may be appropriate under certain circumstances. This terminology is primarily intended for use in civil litigation, but may be adaptable to criminal cases where appropriate. Abbreviations Adj.—(used as) an adjective Also—also known as or similar to (a term not in this glossary) Approx.—approximately Con.—contrast with, compare to (a related term listed in this glossary) n.—(used as) a noun Obs.—an obsolete or obsolescent term or unit to be avoided Opp.—as opposed to, the opposite of Pref.—a preferred term or unit in modern usage Roughly—approximately, colloquially, or loosely; not necessarily in a scientific sense See, see also—refer to (a related term listed in this glossary) Sl.—slang, jargon (may be widely used in some settings) Syn.—a synonym is
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v.—(used as) a verb 38.1 Introduction Human factors professionals who do litigation-related consulting, especially those serving as expert witnesses, face special terminology issues. This guide addresses two potential problem areas: • Scientific terms (as used by human factors/ergonomics professionals). The majority of terms in this guide fall into this category. Problems arise because: • Scientific terms may not be understood by the jury, judge, and lawyers (e.g., midsagittal, tribometry). • Lawyers may use different, nontechnical definitions for scientific terms (common examples: probability, statistical significance). • Two experts may use different definitions for a single term (common examples: risk, warning) • Terms with special meanings in litigation. There are many colloquial words that have formal definitions in the law or are used by lawyers in special ways. Others are widely used by lawyers to discredit the testimony of experts. Examples of these terms are discussed later. Such terms are included in this glossary to assist the forensic professional with understanding attorneys, but are not intended to thereby grant permission for their use as part of a scientist’s professional opinion. These terms are noted as “LEGAL TERM” in this glossary. Colloquial Terms with Special Definitions in Litigation Certain common words and phrases have special legal meanings. The human factors expert who uses these terms may inadvertently be stating legal opinions that he or she is not qualified to give. Alternately, because the terms usually have no operational definitions in the human factors or legal worlds, opinions incorporating the terms may be considered “junk science” by the court. Some common examples are 1 : Adequate Dangerous Defective (and unreasonably dangerous) Due care Duty Foreseeable Misuse Negligent/negligence Open and obvious Proper* Prudent* Responsible* Reasonable/unreasonable (care)
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Safe/unsafe Why Is Using These Terms a Problem? For scientific experts, legal terms present a serious problem that has several parts: 1. These terms are often very important in litigation. They may be at the heart of the ultimate jury decision. For example, a case may hinge on whether a manufacturer took “adequate” steps to ensure the safety of a product or on whether an injured person acted in a “prudent” manner. An expert who uses those terms is stating an opinion on the ultimate jury question of who is at fault. 2. The terms may have formal definitions in the law or have special connotations for lawyers. Although many of these terms are used in everyday conversation, the legal definitions and connotations may be different from those to which the expert is accustomed. Because they have special meanings in the law, an opinion that incorporates these terms may be a legal opinion that a human factors expert is not qualified to give. If a human factors expert does not have the appropriate legal qualifications, the judge may exclude the opinion. Judges’ rulings vary widely on this issue. 3. The legal definitions are often extremely vague by scientific standards. Lawyers typically choose their terms much more carefully than do people in other professions, and the lawyers are likely to insist 1
Boldface indicates the term is currently designated as a legal term in the main glossary (not appropriate for use by a scientific or technical expert). An asterisk (*) indicates that the term is not defined in the glossary.
on the exact definitions from the law or a legal dictionary. However, legal definitions often involve subjective judgments (e.g., what is “reasonable” or “ordinary”?) rather than spelling out objective criteria that can be addressed scientifically. In other words, the terms are not operationally defined. Without operational definitions, opinions that include these terms are often nothing more than subjective, personal value judgments that have no scientific basis or technical meaning. For example, two experts given the same facts can disagree on the ultimate legal issue of who is at fault. An activity that one expert considers “safe” may be considered “dangerous” by another. Behavior that one expert thinks is “reasonable” may be considered “unreasonable” by another. Because these opinions are value judgments, there may be no scientific way to resolve the disagreements. A judge may dismiss the opinions as “junk science.” 4. Lawyers often pressure expert witnesses to state opinions using the preceding terms. A client may refuse to hire an expert who will not give an opinion using terms from the preceding list. A crossexamining lawyer may argue that the expert is evasive if he or she will not use these terms. In short, the human factors expert maybe under great pressure to state opinions that are not scientific, human factors opinions.
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What Can the Human Factors Expert Do about Legal Terms? The authors recommend that human factors experts do not use some of the terms in the preceding list because they represent legal concepts with no direct counterpart in the science of human factors. However, for other legal terms, no consensus exists. Different experts deal with the terms in different ways. The possible approaches can be considered under two headings: 1. Refuse to use the terms. When asked for an opinion using a legal term, the expert can say it is a legal term that has no definition in the field of human factors. The expert may go on to provide a scientific opinion relevant to the ultimate assignment of fault, without actually making the subjective, legal judgment. For example, rather than testifying that a design is “safe” or “dangerous,” the expert could testify that accident rates are X with this design vs. Y and Z with other common designs. This approach lets the expert avoid giving legal opinions or stating personal value judgments in the guise of scientific opinions. However, some lawyers will refuse to hire an expert who will not answer the questions as the lawyers wish him to state them. Some judges will support this approach. That is, they will agree that answering the question would require (1) a legal opinion that the expert is not qualified to give; or (2) a nonscientific opinion that has no value to the court. Other judges may require an answer to the question. If so, the expert can explain what his or her personal opinion or value judgment is, while making clear that it is not a scientific, human factors opinion. 2. Redefine the terms using objective, measurable criteria. For certain terms, some experts prefer to provide their own operational definitions that include objective, measurable criteria. This approach permits the expert to use a legal term in giving a scientific opinion. However, redefining a term may create considerable confusion because the expert’s definition will almost certainly be different from the legal definition being used by the lawyers, judge, and jury. The expert may intend his or her opinion to mean one thing, but everyone else may interpret it to mean something quite different. Terms Used to Discredit Expert Testimony Some apparently innocuous words are frequently used by lawyers during crossexamination to discredit an expert’s testimony. Examples are: • Authority/authoritative*: Attorneys ask if an expert considers a text (or other source of information) to be “authoritative.” If the expert says “yes,” they try to find something in the text that contradicts the expert’s opinion and use that to discredit the entire opinion. • Rely*: Attorneys often ask if an expert “relies” on a piece of information for an opinion. Human factors experts may say “yes,” meaning only that they took the information into account. However, attorneys use the term to imply a logically necessary piece of
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information. If they can cast doubt on the accuracy of the information, they may claim that the expert’s entire opinion is invalid. For further discussion of all of the preceding terms, see the glossary that follows. Acknowledgments The authors are grateful to those who contributed to the review and editing of this document, including Rudolph Mortimer, Richard Pearson, Eric Olsen, Jake Pauls, and others. However, the responsibility for errors and omissions rests upon the Chapter Editor, David Thompson. Comments, suggestions, and corrections may be sent him at PO Box 6685, Incline Village, NV, 89451, or to [email protected]. Glossary Ability—Having the physical and/or mental capacity to perform a given task effectively. Also, a latent capacity to develop skills. See also skill. Acceleration—1. The rate of change of velocity. The acceleration of a falling body in a vacuum due only to gravity is 1 g, about 32.17 ft/sec/sec or 9.81 m/sec/sec. For vehicle braking, 1 g (seldom achieved) would reduce speed about 22 mph for each second. 2. A vector representing the rate of change of velocity with time: a=dv/dt where a represents acceleration; v is velocity; and t is time, all expressed in compatible units for a body initially at rest. Acceleration syndrome—Any change in physiological and/or perceptual-motorcognitive function due to the forces imposed on the body by changes in velocity. Syn. G-force syndrome. An older term. Accelerometer—A force transducer used in measuring acceleration. Syn. acceleration transducer, acceleration pickup. Accident—As used by lay persons, an unintentional, and typically unexpected and unpredictable, event that results in personal injury, illness, or property damage. Implies lack of causation, i.e., beyond control of any of the parties. Pref. collision, crash, injury event, loss event, incident. Accommodate—1. Adjust a sensory threshold or structure of a sense organ to best receive a signal of interest or not to perceive a continuous, constant stimulation; (n.) accommodation. 2. Change one’s activities to minimize the possibility of revealing a weakness or use another method or mechanism to achieve the same or similar effect. Accommodation—Unconscious changes in the eyes to attempt the clearest bifocal vision. Squinting (peering through almost closed eyelids) may improve focus slightly and temporarily when optical conditions are not correct. May be assisted by corrective lenses or contacts, if worn. Accuracy—A measure of the closeness with which an object or end product is located, placed, or represented in some dimension, compared to a desired, known, or believed
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point. Also, a measure of the extent to which a true or actual value of a measure is observed. Acoustic—Pertaining to sound. Action limit (AL)—A NIOSH guideline for the maximum load that should be lifted manually by a healthy person under given conditions to maintain acceptable injury incidence and severity rates. Active restraint—A restraining device that requires an action by an individual before it is effective (e.g., a manual seat belt). Opp. passive restraint. Activities of daily living (ADL)—Those functions normally performed on a daily or near daily basis that are involved in sustenance of the individual; examples include eating, grooming, urination/ defecation, dressing, and bathing. Acuity—The sharpness of a sense in resolving sensory stimuli. See also visual acuity. Acute—1. A dangerous condition or exposure, which generally has a rapid onset and is of short duration, yet may be life threatening. Opp. chronic. 2. Pertaining to a geometric angle less than 90°. Adaptation, visual—The visual system’s adjustment to operate and respond to contrasts and colors for any given overall level within a very wide range of luminance energy. See also dark adaptation. Syn. habituation. Comment. Adaptation levels vary continuously but are generally classified as photopic (high levels of lighting; late dawn to early dusk or brighter); scotopic (very low lighting; new moon light or star light levels); and mesopic (intermediate lighting level; dawn or dusk, night driving). Both the rods and the cones in the retina are used in mesopic vision; the cones predominate in photopic color vision (except in peripheral vision) and the rods (black and white) predominate in scotopic vision. Because rods are not present in the fovea, fine detail is reduced in scotopic vision. Adaption involves several mechanisms, e.g., pupil size, chemical pigments, neural effects. Adequate (Note: LEGAL TERM)—Meets or exceeds a generally recognized scientific criterion or standard. May involve subjective judgment. See also reasonable. Adhesion—The tendency of two surfaces in forceful contact, with or without the presence of a lubricating interface, to stick together. This tendency is related to residence time and, in general, becomes greater as residence time increases. See also stiction. Administrative control—Procedures and methods, set up by the employer, that significantly reduce exposure to risk factors by altering the way in which work is performed; examples include work/ rest cycles, employee rotation, job task enlargement, and adjustment of work pace. Agonistic muscles—Sets of muscles that act on the body or body part to achieve intended movements. See also antagonistic muscles. Air step—Stepping onto an unexpected depression or step down. Alarm—An indicator, usually visual or auditory, that a condition exists that may or will require human action to correct in order to prevent injury or loss of life, property, or equipment. Alternating tread type stair—Series of steps usually attached to a center support in an alternating manner so that a user of the stair normally does not have both feet on the same level. Ambient—Pertaining to the surrounding environment.
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Ambient vision—That sense, largely unconscious, derived from ocular stimulation, which forms concepts of self-locomotion and interaction with the environment. Con. focal vision. Ambinocular—The total field of view of both eyes. See also binocular. ANSI—American National Standards Institute. A private, nonprofit membership organization that coordinates voluntary standards activities. ANSI assists with standards developers and standards users from the private sector and government to reach agreement on the need for standards and to establish priorities. Antagonistic muscles—Sets of muscles that act on the body or body member, primarily in opposition to agonisti muscles, to control their displacement or speed of motion. See also agonistic muscles. Anthropometry—1. That field dealing with the physical dimensions, proportions, and composition of the human body, as well as the study of the related variables that affect them. Adj. anthropometries. 2. The technology of measuring human physical traits such as size, reach, mobility, and strength. Area of impact (AOI) —See point of impact. Associate Ergonomics Professional (AEP)—A certification for ergonomists established by the Board of Certification in Professional Ergonomics based on a practitioner’s extensive education and passing a basic examination. Considered to be an “ergonomist in training.” BCPE adheres to the criteria and policies for competency assessment set by the National Association for Compe- tency Assessment and is endorsed by the International Ergonomics Association as an accredited ergonomics certifying body. Equivalent to AHFP. See Certified Professional Ergonomist. Associate Human Factors Professional (AHFP)—A certification for human factors professionals established by the Board of Certification in Professional Ergonomics based on a practitioner’s extensive education and passing a basic examination. Considered to be an “ergonomist in training.” BCPE adheres to the criteria and policies for competency assessment set by the National Association for Competency Assessment and is endorsed by the International Ergonomics Association as an accredited ergonomics certifying body. Equivalent to AEP. See Certified Human Factors Professional. Assumption of risk (Note: LEGAL TERM)—The concept that an individual who is aware of the extent of some danger and still knowingly exposes himself or herself to that danger assumes all consequences and cannot recover any damages, even if injured through no fault of that person. Assured clear distance ahead (Note: LEGAL TERM)—The apparent available area on streets, roadways, etc. that would permit successful evasive actions in the event of a sudden hazard. Attention—The state of assessing the physical and information environment, including mental activities, and the selecting and processing aspects for conscious thought and the basis for further behavior. Comment: Attention is regularly shared among competing topics. The individual chooses to attend to each in varying degrees, depending on immediacy and relevance. This may be called “allocation of attention,” “paying attention,” “maintaining proper lookout,” etc. In interaction with the world, persons must select topics and shift among them appropriately to maintain performance and alertness. Although events or thoughts may attract attention
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(distractions), the person may need to assess quickly and ignore certain things and seek out less compelling but available information in order to perform the task at hand successfully. Attention span—The length of time that an individual can attend to a task, or the number of items to which an individual can respond before performance deteriorates. Attenuate—Reduce concentration, intensity, strength, force, or amplitude of some entity over time or space, n. attenuation. Syn. damp. Attribute—Some characteristic of an element or condition. Autonomic nervous system (ANS)—A generally efferent (i.e., from the brain or spinal cord) subdivision of the peripheral nervous system, which is distributed to and directs the function of smooth muscle and glands throughout the body, normally at a subconscious level. See also central nervous system, peripheral nervous system. Awareness device—A device that, by means of audible sound or visible light, warns an operator of a present or approaching hazard. Awkward posture—Posture is the position of the body while performing work activities. Awkward posture is associated with an increased risk for injury. It is generally considered that the more a joint deviates from the neutral (natural) position, the greater the risk of injury. Background noise—The total of all sources of sensation in a system, apart from the signal. Syn. noise (electrical, visual, vibratory, or auditory). Back injury—Any injury involving the spine, the spinal cord, the nerves exiting from the spinal cord through the spine, a rib-vertebral junction, or the muscles of the back. Balance—A state of static body equilibrium. Also, a generic term to describe the dynamics of body posture to prevent falling; related to the inertial forces acting on the body and the inertial characteristics of body segments and proprioceptive senses. Balance, standing—Quantified by measuring static postural oscillations (sway) in the antero-posterior and medio-lateral planes, and by recovery of posture on a moving platform. Ballistic movement—A rapid, gross, relatively smooth change in position of a bodily extremity initiated by one or more agonistic muscles that are active only during the initial phase of the motion. Syn. ballistic motion, preprogrammed movement. Opp. controlled movement. Barrier—1. An attachment that, by physical contact, warns an operator of an approaching or present hazard. 2. An object, such as a fence or bollard, that prevents movement in a certain direction. Base of support—The area in contact with the supporting surface within the outline of both feet. Also, the roughly trapezoidal contact area between the feet and the floor in which the resultant ground reaction force is located. Behavioral data—Data that show the effects of particular stimuli (such as warnings) on the behavior of exposed subjects. Bel (B)—A dimensionless measure of the intensity of some energy, corresponding to the ratio of two intensity or power levels. See also decibel. Benchmark—A thoroughly documented reference value or standard of measurement against which performance, response, or other characteristics may be compared with confidence.
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Binocular—The field of view that can be seen or is seen by both eyes simultaneously. The binocular field excludes the view of each eye that cannot be seen by the other eye. See also stereopsis, monocular, ambinocular. Bioengineering—The integration and application of knowledge in the fields of human biology, medicine, and engineering. Biofeedback—The use of instrumentation to provide information to a human, which enables that person to alter behavior accordingly. Biomechanics—The field of study involving classical mechanical principles and their relationships, as used by or applied to physical movements of the body and body members and other living organisms or biological tissues in motion. May also evaluate the effects of physical trauma to the body. See also occupational biomechanics. Blind spot—1. Any region on or around a vehicle at which another object may not be readily seen due to lack of mirror coverage or inability to view directly. 2. That region of the posterior eyeball where no photoreceptors are located due to the optic neural fibers exiting the eyeball. Body mass index (BMI)—A measure of physical condition calculated by dividing an individual’s weight in kilograms by his height in square meters. If an individual’s BMI exceeds 25 kg/m2, he is considered overweight; if his BMI exceeds 30, he is considered obese; if his BMI exceeds 35, he is considered grossly obese; and if his BMI exceeds 40, he is considered morbidly obese by WHO standards. Boredom—A form of mental fatigue generally due to lack of stimulation, lack of interest in the ongoing activity, isolation, performance of a monotonous task, other similar situations, or some combination of these situations. A mood state of disinterest; deterioration of alertness or mental functioning. Brightness—A subjective judgment of light intensity related to the amount of light projected onto or reflected from a surface or object; ranges from brilliant to dark. Opp. dimness. See also luminance, illuminance. Brightness contrast—The subjective difference between the brightness of an object and the background against which that object is located; may also be influenced by the larger local environment (the surround). See also contrast, luminance contrast. Bruise—An injury characterized by capillary or venous hemorrhaging beneath an unbroken skin. Built environment—Those areas, such as sidewalks, roadways, and structures, that have been built or maintained for use by people. Camouflage—A process (v.) or material (n.) on or near an object that, intentionally or not, has the effect of disguising or obscuring it or making it less conspicuous to an observer. Candela (cd)—1. A unit of luminous intensity equal to 1/60 of the luminous intensity per square centimeter of a black body radiating at the solidification temperature of platinum. Also called candle (obs.) or standard candle or new candle. It is that amount of light produced by a certain small candle. 2. An SI unit for luminous intensity; equal to the intensity of a 555-nm (5.40× 1014 Hz) point source radiating 1.464×10−3 W per steradian. Syn. new candle. Candlepower (cp)—Obs. An older measure of luminous intensity, generally equivalent to, and now stated in, candelas.
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Capacity—The upper limit of an individual’s ability to learn, understand, or perform through inherent ability, training, practice, or any other means. Carelessness—Behavior or mental functioning that does not exhibit adequate attention or concern for the task being performed to maintain the required level of performance (subjective). Carpal tunnel—An internal passage in the wrist between the extensor retinaculum and the carpal bones through which the median nerve, finger flexor tendons, and blood vessels pass from the arm to the hand. Carpal tunnel syndrome (CTS)—A painful disability in which the manipulative or gripping abilities of the hand and fingers are reduced due to median nerve compression injury within the carpal tunnel. See also repetitive motion injury, workrelated musculoskeletal disorders, cumulative trauma disorders. Comment. Generally caused by repetitive wrist motions, unusual wrist motions, or the use of awkward positions requiring maintained strength. May be caused by personal physical characteristics that are non-work-related. Cause—The factor or factors most responsible in precipitating an injury event. Of importance is the relative and absolute contribution of particular causal factors to a specific injury event, and whether reducing or eliminating a particular causal factor would have prevented the injury event. The relative importance of differing causal factors in a particular injury event may allow the determination of proportional fault (civil) or may assign all of it to a party (criminal) in litigation. State laws vary, and some police reports may assign a primary causal factor and associated or contributing factors to parties. Use with care. CAUTION—As a signal word in a warning sign or label (see ANSI Z535), indicates a potentially hazardous situation or unsafe practice that, if not avoided, may result in minor or moderate injury or damage. May be confused with Warning or Danger. See also WARNING, DANGER. Center of gravity (CG)—A point representing a body or system at which the force due to a uniform gravitational attraction acts. See also center of mass. Center of mass (CM)—1. A point equivalent of the total body mass in the global threedimensional special reference system with the gravitational vector as the primary reference. It is the weighted average of the center of mass of each body segment in that space. 2. That point of an object or system that may be treated as if the entire mass of the object or system were concentrated at that point, and any external translational forces appear to act through that point. For a standing person, the CM is approximately at the navel or 55% of stature. See also center of gravity. Center of pressure—The point location of the vertical ground reaction force vector. Central nervous system (CNS)—That portion of the nervous system comprising the brain and spinal cord; opp. peripheral nervous system. Central visual field—The portion of the visual field that falls on the foveal or macula lutea portion of the retina. Generally considered to be 1° (foveal) to 5° (macula) around the visual axis. See field of view, visual field. Opp. peripheral visual field. Certified Ergonomics Associate (CEA)—An entry-level certification for ergonomists established by the Board of Certification in Professional Ergonomics based on a practitioner’s education, experience, and an examination. BCPE adheres to the criteria and policies for competency assessment set by the National Association for
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Competency Assessment and is endorsed by the International Ergonomics Association as an accredited ergonomics certifying body. There is no CHFA. See also Associate Ergonomics Professional, Associate Human Factors Professional, Certified Human Factors Professional, Certified Professional Ergonomist. Certified human factors professional (CHFP)—A certification for human factors professionals established by the Board of Certification in Professional Ergonomics based on a practitioner’s extensive education, experience, and a rigorous examination. BCPE adheres to the criteria and policies for competency assessment set by the National Association for Competency Assessment and is endorsed by the International Ergonomics Association as an accredited ergonomics certifying body. Equivalent to CPE. See also Associate Ergonomics Professional, Associate Human Factors Professional, Certified Professional Ergonomist, Certified Ergonomics Associate. Certified Professional Ergonomist (CPE)—The highest level of certification for ergonomics professionals established by the Board of Certification in Professional Ergonomics based on a practitioner’s extensive education, experience, and a rigorous examination. BCPE adheres to the criteria and policies for competency assessment set by the National Association for Competency Assessment and is endorsed by the International Ergonomics Association as an accredited ergonomics certifying body. Equivalent to CHFP. See also Certified Ergonomics Associate, Certified Professional Ergonomist, Associate Human Factors Professional, Associate Ergonomics Professional. Certified Safety Professional (CSP)—One certified by the Board of Certified Safety Professionals (BCSP) as being competent in his field and having professional integrity. Change in level, abrupt—Any change in a walking surface level of 0.5 in. or more where the slope from the bottom level to the top level exceeds 1:8 (12.5%; 7.1°). Comment. An abrupt change in level of 0.5 in. or more can cause a foot to stop in flight, resulting in a trip and fall or a stumble. See step. Channel capacity—A concept pertaining to skilled human performance in which man is likened to a communication system depending, in effect, upon a single input channel of finite capacity, exceeding the limitations of which leads to deterioration in performance. Checklist—Any list in which items can be compared, scheduled, verified, or identified. Can be used to ensure that important features of a system are present or that specific activities have been accomplished. May also be utilized to evaluate elements of a system as a job performance aid. Chromatic contrast—That apparent contrast due to the presence of differing adjacent hues or colors. Syn. color contrast, hue contrast, simultaneous color contrast. See also color contrast, luminance contrast. Circadian rhythm—An innate physiological rhythm manifested by regular fluctuations in body chemistry or other indicators of the physiological state related to the 24-h or day-night cycle. Civil twilight—The period of twilight beginning (or ending) when the center of the (refracted) Sun is more than 6° below the horizon. Visual perception and sensitivity changes during this time. See dark adaption, light adaption. Closing rate (rate of closure) —See visual image distance.
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Clothing—light or dark (pedestrians)—The color of a pedestrian’s clothing may have an effect on the visibility distance in vehicle headlighting. Common clothing varies in reflectance units from about 70 (white) to less than 4 (dark blue or black). Comment. All-white clothing may allow detection at about 180 ft if in the headlight beams, while all black may be just visible at 55 ft or less. In a panic stop on a dry road, a driver may stop just in time from a speed of 42 mph for the white clothing and only 18 mph for the dark. Because headlights shine almost directly on them, white shoes without reflectors may increase the visibility to allow about 25 mph speed. Lights or reflectors on the pedestrian may enhance visibility where automobile headlights provide most of the illumination. Cluster workstation—A multiperson workstation built around a central core to provide some separation from co-workers. See also modular workstation. Coating—A substance intentionally or unintentionally applied to a surface that modifies some characteristic of the surface, such as slip resistance or appearance. The coating may improve or degrade the overall safety of the surface. Coefficient of dynamic or kinetic friction—The ratio of the magnitude of the sliding force to the magnitude of the perpendicular force between two objects or surfaces. The sliding force is measured parallel to the contact surfaces and is that force necessary to maintain movement between the objects or surfaces but not to commence that relative motion. Syn. coefficient of sliding friction. Coefficient of friction —Syn. friction coefficient. See coefficient of rolling friction, coefficient of dynamic or kinetic friction, coefficient of static friction. Coefficient of rolling friction—The ratio of the magnitude of the rolling force to the magnitude of the perpendicular force between two objects or surfaces at the point where their surfaces are parallel. Coefficient of static friction—The ratio of the magnitude of the static force to the magnitude of the perpendicular force between two objects or surfaces. The static force is measured parallel to the contact surface and is that force required to commence but not maintain movement between the objects or surfaces. Cognitive ergonomics—Concerned with mental processes, such as perception, memory, attention, motivation, reasoning, and motor response, as they affect interactions among humans and other elements of a system. The relevant topics include mental workload, decision-making, skilled performance, human-computer interaction, human reliability, work stress, and training as these may relate to human-system design. See also reaction time, perception-decision-response time. Cognitive reaction time—The temporal interval between the receipt of a stimulus and the initiation of a response in a task that requires some type of choice and is presumed to involve cognitive processing. Syn. decision time. See also response time, reaction time, perception-decision-response time, simple reaction time. Collision—The unintended contact among two or more objects or persons in which an injury or damage may occur. Most often applied in traffic or industrial incidents when causation or responsibility is at issue, making the term “accident” inappropriate. Syn. crash. See also impact, incident, accident. Color contrast—A difference in color between an object and its background which, if sufficiently great to be differentiated, enables an object to be detected even if there is
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no difference in luminance between the object and background. Syn. chromatic contrast. See also contrast. Common sense—(a) Colloquial: the sense that accumulated life experiences may prevent one from engaging in a certain activity or making performance errors, or may impel one to perform some action to achieve a desired goal. Includes community and cultural knowledge and experience. Preferred term: common knowledge. Highly subjective, (b) Technical: the knowledge, skills, and information gained in certain situations or activities that may assist a person in successfully performing related activities having common characteristics. The commonality of characteristics may be ambiguous, may or may not be obvious to an individual prior to engaging in the related activity, and may become apparent to an observer only after the fact. See transfer of training. Compatibility—1. A measure of how well spatial movements of controls, display behavior, or conceptual relationships meet human expectations. 2. The combination of characteristics that permits two or more individuals, groups, or systems to work together without significant interference or conflict. Compensation—1. A movement of a part of the body to restore or maintain equilibrium as another body part moves. 2. Any behavior that attempts to minimize the effect of weakness in one process by relying on another, stronger process or improving another process. Adj. compensatory. 3. A form of payment for work performed or for a disability incurred. Computer animation—A computer-generated series of computer models representing dynamic features of a system or phenomenon that accounts for its known characteristics. Computer animations can be used successfully to present critical dynamic information in automobile, industrial, construction, and other types of injury or loss events. The data, algorithms, and equations providing the basis for the computer animation must be disclosable, complete, accurate, and of the type reasonably relied upon for forming opinions or conclusions on the subject by experts in the field. Also called computer simulation or demonstration. The extent to which the entire situation is shown and the rigor employed vary. See also computer model, demonstrative evidence. Computer model—A computer-generated representation of a system or phenomenon that accounts for its known characteristics. Computer models include two-dimensional spreadsheets, charts, and diagrams, as well as three-dimensional graphic objects. Computer models can be used successfully to present critical information in automobile, industrial, construction, and other types of injury events. The data, algorithms, and equations providing the basis for the computer animation must be disclosable, complete, accurate, and of the type reasonably relied upon for forming opinions or conclusions on the subject by experts in the field. See also computer animation, demonstrative evidence. Cone—One of the somewhat conically shaped photoreceptors concentrated in the foveal region of the retina that provide for fine visual acuity and the detection of color under high (daylight) luminance levels. In the peripheral retina, cones are interspersed with rods up to about 10° off the central visual axis, and with few beyond that. See also rod. Consolidation (of memory)—Refers to the process or time required to convert shortterm memory (STM) into long-term memory (LTM) that can be recalled at a later
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time. Consolidation may be prevented by other events, trauma, or shock. Without consolidation, an item in STM (or working memory) will not be retained. See also short-term memory, long-term memory, working memory. Conspicuity—Refers to the characteristics of an object that attract visual attention. Objects readily visible when located and focused on may not be seen if not conspicuous because they do not attract attention or stimulate peripheral visual detection. See also visibility. Consultant—An individual or group who is qualified or claims expertise in a particular field and may be called upon to perform some specialized technical function on a onetime or an occasional basis. See also expert witness. Consumer product—A product intended for final use primarily by the general public, as opposed to industrial use. Contaminant—Any substance in or on a product, including a walking surface or shoe, that was not intended to be there by the designer, manufacturer, or builder. Contrast—Refers to the brightness difference between an object and its background. Contrast is perhaps the most important determinant of the visibility of an object. Visibility must take into account the brightness of the immediate, and often the extended, background. May be expressed as a contrast ratio of the brightness of the object and background. See also brightness contrast, chromatic or color contrast, conspicuity, and luminance contrast. Contrast threshold—The smallest difference between two visual stimuli perceptible to the human eye under specified conditions of adaptation, luminance, and visual angle on a certain proportion (often 50%) of a set of trials. May refer to brightness, color, saturation, or other contrasts. Syn. liminal. See also contrast, liminal contrast threshold, threshold. Control—1. Any device that enables a user to direct the action or operation of some equipment or system. 2. A condition or individual that serves as a reference to limit or test probable sources of error in an experiment. 3. A psychomotor skill involving fine positioning. 4. A state of being in charge, of having command or authority, and the ability to manage a situation. Control-display ratio—The ratio of movement of a control to the movement or change of an indicator on a display; also control display ratio. Syn. control-response ratio, control sensitivity. Control group—A group of individuals or items selected from what is believed to be the same population as an experimental group, but not exposed to the experimental treatment under consideration. Syn. comparison group. Control layout—The general grouping of controls within a location at a workplace. Syn. control arrangement. See also control location, control-display ratio. Control location—The general placement of controls for use by an operator; often evaluated with trade-off (compromise) analyses. See also control layout, controldisplay ratio. Control system—A system whose primary function is the monitoring of outputs from a given set of functions and using those data or information to regulate that set in some specified manner or to propose new rules or regulations. Controlled movement—Any controlled bodily movement in which prime mover agonistic and antagonistic muscles are integrated using muscle contraction throughout
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the range of the motion to generate a desired force precision, or velocity. Syn. nonballistic movement, tension movement. Opp. ballistic movement. Corrective lenses —See glasses. Cost-benefit analysis—The determination or estimation and evaluation of the weighted relative financial, social, or other costs to the same or other categories of rewards or compensation; also benefit-cost analysis. Comment. This analysis should be performed prior to undertaking the endeavor being considered. True costs, as opposed to out-ofpocket costs included for a specific endeavor, may be higher but may not be fully considered in decision-making. Cost of compliance—The amount of physical, mental, social, emotional, or financial effort involved in complying with safety instructions or warnings. May vary among different people in identical situations. Cost effectiveness—The relative financial or other benefits obtained compared to the costs of alternatives. Adj. cost-effective. Crash —See collision, incident. Crashworthiness—A measure of the capability of a vehicle to act as a protective container and energy absorber in order to reduce injury during impact and certain subsequent events. Critical confusion—When a symbol or stimulus elicits the opposite response from that desired, or a prohibited action; for instance, when a symbol intended to mean “no fires allowed” is misunderstood to mean “fires allowed here.” Crosswalk—Under most codes, a crosswalk exists wherever a sidewalk is interrupted by a roadway. It extends the sidewalk across the road, and it exists whether lines are marked or not, unless specifically marked to the contrary. Comment. Controversy continues as to whether marked crosswalks wrongly imply absolute safety and encourage careless use, especially in unfavorable conditions. Definitions at “t” intersections, private roadways, etc. are not clear. White lines are used, except for crosswalks near school zones, where they are yellow. Cumulative trauma disorders (CTDs)—Term used for injuries that occur over time because of repeated trauma or exposure to a specific body part, such as the back, hand, wrist, and forearm. CTDs occur when muscles and joints are stressed, tendons are inflamed, nerves are pinched, or the flow of blood is restricted. Common occupationally induced disorders in this class include carpal tunnel syndrome, epicondylitis, tendonitis, tenosynovitis, synovitis, stenosing tenosynovitis of the finger, Dequervian’s syndrome, and low-back pain. Similar to repetitive stress trauma (RST) and repetitive stress injury (RSI). See repetitive motion injury, work-related musculoskeletal disorders. DANGER—When used as a signal word in a warning sign, indicates an imminently hazardous situation that, if not avoided, will result in death or serious injury. This signal word is to be limited to the most extreme situations. See also WARNING, CAUTION. Dangerous—A personal judgment about a given level of risk. Objective measures of risk or relative risk are preferred. Dangerous condition (Note: LEGAL TERM) —See hazard, unsafe condition. Dark adaptation—The process of undergoing mechanical and neurochemical changes in the eye, after being placed in darkness or low light levels, during which the visual
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system becomes more sensitive to light. Syn. scotopic adaptation, dark adaption. Opp. light adaptation. See also night blindness. Comment. Adaptation enables the eye to see more detail and lower contrasts after a reduction of the total light energy observed. The visual system also changes when moving from darker into brighter areas (light adaptation). The adaptive process involves the iris (which opens and closes quickly to let in more or less light) and neural effects in the retina processing, which also operate fairly quickly to change the responses to visual stimuli. Photochemical changes in the visual receptors (rods and cones) also change in response to illumination levels to more slowly affect sensitivity to light. The total range of vision from high energy to low is a ratio of about 100 million to 1. Large changes in dark adaptation can take many minutes; light adaptation is generally faster. Dart—A sudden or unpredictable movement by a visible pedestrian from a neutral position to one in the path of a moving vehicle, usually at a very short range. Dash—A rapid, continuous movement by a pedestrian into the path of a vehicle from a position obscured for an oncoming vehicle driver, usually at a very short range. Date of loss (dol); date of incident (doi)—A reported date of primary incident, as defined by police or other authority (unless re-established by competent analysis). Daubert —Reference to a U.S. Supreme Court ruling in which the criteria for the admissibility of expert scientific testimony were broadened so that the general acceptance of the testimony by the scientific community was no longer needed. Under Daubert, admissibility of expert scientific testimony is based on testing or research that has been subjected to peer review, that follows good scientific protocol, and that can be replicated. General acceptance of the theory or technique is considered, but not required. Used to exclude expert testimony that is quasilegal, personal opinion, or other testimony that has no scientific basis. See Frye . Decibel (dB)—One tenth of a bel; a nondimensional logarithmic ratio of the measured quantity and a reference quantity for expressing power, intensity (I), pressure (P), or amplitude. P=10 log(I//I 0)or 20 log(P/P 0) Comment. the most common unit of sound is “sound pressure level” (SPL) expressed in decibels. It generally uses a standard reference level value (P 0=0.0002 dyn/cm2) unless another level is stated. For example, the sound level in a quiet office is 40 dB; a vacuum cleaner, 70 db; a loud motorcycle, 100 dB (which may damage hearing with repeated exposure). Decision sight distance—Distance needed for a driver to detect an unexpected or otherwise difficult-to-perceive information source or condition in a roadway environment that may be visually cluttered, recognize the condition or its potential threat, select an appropriate speed and path, and initiate and complete the maneuver safely and efficiently. Similar to the stopping sight distance appropriate for the conditions. See also direct field of view, field of view, line of sight, stopping sight distance. Defect—Any physical condition of a material or system, whether recognized or not, that is outside specifications or standards and affects function or appearance. Adj. defective.
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Defective (Note: LEGAL TERM) —A condition that exists when a product or device has a fault or imperfection that prevents it from functioning as intended. If that defect is not apparent to a reasonable user, it is a hidden defect. Also, a condition that exists when the risk of serious injury exceeds the benefit of the product or device. May be highly subjective. Use with care. See also hazard, risk. Demonstrative evidence—Representations of data used to illustrate the basis for the expert witness’ testimony. May include charts, diagrams, photographs, computer models, videotapes, computer animations, and courtroom experiments. Demonstrative evidence must fairly represent the testimony of the expert witness and accurately represent the event testified about. All data, algorithms, and equations supporting the demonstrative evidence must be disclosable, complete, accurate, and of the type reasonably relied upon for forming opinions or conclusions on the subject by experts in the field. Procedures for generating the demonstrative evidence also must be disclosable and of the type reasonably used by experts in the field. Depth perception—The ability to distinguish or infer the relative distances of two or more objects, or the distance of a single object from the observer. Cues used are stereopsis, interposed objects, gradients, relative size, and similar features. Design-induced error—An unintended action resulting in an injury or loss event that occurred at least in part due to the design of a product or the built environment. Detection—Refers to becoming aware of a sensory stimulation, although the object or phenomenon may not be yet identified or recognized. Direct field of view—The field of view that can be observed by the central and peripheral receptors of one or both eyes without the use of extraneous optical devices. Direct glare—A type of glare experienced when a relatively bright light source is within an individual’s field of view. See glare. Disability—1. Any restriction or lack of the ability to perform an activity in the manner or within the range considered normal. 2. Any reduction to normal capacity due to mental or physical factors that prevents an individual from experiencing or performing a full complement of activities. Adj. disabled. Obs. handicapped. Disability glare —See glare. Disabling injury—Any injury that prevents an individual from performing his normal job function for one or more days beyond the date of the injury. Discernibility—The ability to recognize or identify one object, individual, or event as separate or different from another. Implies more than simple perception. Discomfort—A state other than well-being due to the presence of one or more undesirable environmental stressors. Opp. comfort. Discomfort glare—A viewing condition in which glare from one or more relatively high-intensity sources within the field of view causes an observer to experience visual pain or annoyance. See glare. Disoriented—Loss of orientation; confusion as to location or motion brought on by inadvertent motion or relative motion not expected in an otherwise familiar, apparently stable environment. Display—The presentation of data or graphics from a system or device in a manner designed for human perception through one or more of the senses. Distal—Referring to a portion of the body or a body segment farther away from the central longitudinal axis than another part. Opp. proximal.
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Distraction—Reduction of the attention paid to a task (especially a vigilance task) due to environmental influences. Dorsiflexion—A motion involving raising the toes and upper part of the foot. Opp. plantar flexion. Dual task performance—Completing two or more tasks simultaneously. Also known as “task combination” or “dual tasking.” Due care—Legal term not appropriate for use by a scientific or technical expert. Duty—Legal term not appropriate for use by a scientific or technical expert. Dvorak keyboard (DSK)—A keyboard with a letter distribution pattern of AOEUIDHTNS on the home row. Syn. Dvorak-simplified keyboard. See also QWERTY keyboard. Dynamic equilibrium—The state of maintaining or controlling body position while in motion through the integrated involvement of the cristae in the semicircular ducts, vision, the cerebellum, and muscle activity, and proprioception. See also static equilibrium. Effort—The expenditure of physical or mental energy in the performance of some task. Emergency stop—1. A pushbutton, switch, or other control device installed in or on a piece of equipment that is capable of quickly cutting power to that equipment in an emergency. See emergency switch. 2. A rapid cessation of the motion of a machine part or the forward motion of a vehicle to avoid undesirable consequences. Emergency switch—A type of emergency stop consisting of a switch located in some readily accessible position for quickly shutting down a system in an emergency, or to prevent an injury or physical damage. Comment. May fail to prevent an injury if the device design does not account for human reaction time to the event. Engineer—An individual qualified by education, training, or experience to practice in one or more fields of engineering. Engineering—A discipline in which knowledge of the mathematical and natural sciences, gained by some combination of education, training, and practical experience, is integrated with various natural materials and forces to shape the environment. Engineering control—Physical changes that control exposure to risk. Engineering controls act on the source of the hazard and control user exposure to the hazard without relying on the user to take self-protective action or intervention. Examples include changing the handle angle of a tool, using a lighter-weight part, and providing a chair that has adjustability. Environment—The combination of all influences impinging on an entity. Adj. environmental. Epidemiology—A branch of public health dealing with the incidence, distribution, causes, and risk factors of disease and injury in a population. Equilibrium—A state in which the body maintains a desired posture or retains control in body movement through continuous sensory monitoring and the balancing of muscle tensions. See also static equilibrium, dynamic equilibrium. Ergonomics—The science that studies the physical and cognitive interactions between humans and their activities, equipment, and total environment. Ergonomists apply that information to the design of devices and systems that people use at work and in leisure, as well as to the tools they use and to the procedures and practices required for those devices and systems. The goal of this ergonomic application is to optimize
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human health, safety, and performance. Syn. human factors, human factors engineering. See forensic human factors. Obs. human engineering (military). Error—An inappropriate response by a human or system, whether of commission, omission, inadequacy, or timing. See also human error, system error. Exercise—The use of muscular exertion to maintain conditioning or health, or to train for an athletic event. Expectancy, expectation—The influence of a person’s past or recent experience in a similar situation. May be affected by information from any source as to the probability of encountering various hazards and cues. Has a strong influence on a person’s visual search patterns, focus of attention, and response to the immediate external situation. Expectation increases a person’s ability to detect potential hazards; for example, an expected object will typically be detected by an approaching motorist at about twice the distance of an unexpected object. Expert—An individual who (a) possesses certain knowledge, wisdom, and/or skills in a particular subject not likely to be possessed by ordinary persons; (b) acquired such knowledge, wisdom, and/or skills by study, investigation, and experience; (c) is capable of reasoning, inference, and drawing conclusions based on hypothetical facts relating to that subject; and (d) can offer reasonable opinions regarding one or more situations dealing with that particular subject. See expert opinion, expert testimony, expert witness. Expert opinion—A statement of belief by an expert witness, based on observations, measurements, calculations, evidence, testing, and the testimony of witnesses. See expert testimony, expert witness, expert. Expert testimony—One or more statements made by a witness containing opinions based on objective data or information, or information derived directly from such objective data or information. See expert opinion, expert witness, expert. Expert witness—An expert who is or may be accepted by the court as qualified to present certain testimony, opinions, or evidence in a court of law. See expert opinion, expert testimony, expert. Exposed—Unprotected from a hazard or potential hazard. Exposure—The presence of a substance, factor, or hazard in the environment external to the worker. Eye height, sitting—The vertical distance from the upper-seat surface to endocanthus (the inner corner of an eye). Comment. This is measured with the individual seated erect and looking straight ahead. Eye height, standing—The vertical distance from the floor or other reference surface to endocanthus (the inner corner of an eye). Eye height is 4.5 in. ±0.5 in. (11.4 cm±1.3 cm) less than stature. Comment. This is measured with the individual standing erect and looking straight ahead, with his weight balanced evenly on both feet. Eye movement—Any active or passive, conscious or unconscious movement of the eyeball relative to the orbit. It may be accompanied by head motion for a shift of more than a few degrees. Eye and head movements take time. Eye movements result in about three fixations per second in most settings. During any fixation, only the point focused upon is seen clearly. Perception of the environment results from the fixation of successive points or small areas. Syn. saccade.
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Eye movement analysis—The study of patterns, habits, and timing of eye movements in a situation that would require visual search. Object conspicuity and driver expectancy are especially impor-tant in determining eye movements and patterns, especially at night. Fatigue and drugs can strongly influence eye movement patterns. See field of view. Eye protection—Any device capable of shielding the eye in an environment containing one or more possible eye hazards. Eye scan—This occurs when the visual field is scanned by eye movement alone and head movement is not considered. See eye movement. Failure assessment—The process in which the cause, effect, responsibility, and cost of a failure are determined and reported. Failure mode and effects analysis (FMEA)—A methodology that attempts to identify the possible failures of each system component, the mode in which each might fail, the effects of that immediate failure, and the overall system effects on performance. See also failure assessment, fault tree analysis, risk analysis. Fail-safe—A design aspect of a product or system such that when some portion of it fails, the product or system will (a) retain operating capability due to sufficient redundancy or (b) fail in a nonhazardous manner and result in a nonhazardous condition, without injury or additional damage to itself or other systems; also failsafe, fail safe. Fall—An unintended impact between a person and a walkway or other surface caused by a loss of balance or support, misstep, or other physical or physiological condition. Also, an undesirable descent due to the force of gravity, usually from a standing posture or during ambulation, to a lower level, usually the ground or floor. Falls, causes of—(a) Environmental: some of the factors in a pedestrian’s environment that may trigger or contribute to the falls described earlier are listed here: Slippery surfaces. A slip can occur when friction between the walking surface and the bottom surface of the shoe (or footwear) is insufficient. The low friction may result from a lubricant on either or both surfaces. Under identical conditions, a slip is more likely to occur on a sloped rather than a flat surface. The degree of slipperiness or traction of a surface is defined by its coefficient of friction (COF). See also coefficient of friction, dynamic and static. Tripping hazards. Trips may be caused by abrupt and unexpected uplifts in the walking surface, including curbs, wheelstops, adjacent sidewalk slabs, or other uneven conditions that trap the unweighted foot during its normal swing to the next footfall. Unanticipated tripping hazards may be as low as 0.5 in. (13 mm). See change in level, abrupt; trip, trip hazard. Lighting or glare. Inadequate or uneven lighting or visual glare may account for the failure to observe and respond to potential walkway hazards as they are being approached. The adequacy of the lighting depends on the visibility and location of the potential hazard with respect to the pedestrian’s field of view and source of lighting. Visual glare or shadowing may also mask the visibility of the misstep hazard. Misstep hazards may also be unseen when an individual is entering or exiting a relatively dark room or area if he has had insufficient time for his eyes to adjust to the new light level. Signage or marking. Inadequately signed or marked walkway variations may contribute to the failure to observe and respond to potential falling hazards. Combinations of
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brightness and contrast enhance the visibility of unexpected hazards, and appropriate signing may alert pedestrians to their existence. (b) Biomedical: a few of the medical states that may create or contribute to a falling event are: dizziness, fainting, or seizure; hypoglycemia; poor, uncorrected eyesight; confusion; distraction; vestibular problems, vertigo; and impairment due to intoxication, drugs, or fatigue. (c) Behavioral: some of the personal characteristics that cause or contribute to falling events are: inattention to walkway or stairway characteristics, or the existing environmental conditions (rain, ice, etc.); inappropriate gait for conditions; inappropriate footwear; and inadequate concern for one’s medical condition. Falls, locations of—(a) Same-level fall: a fall occurring without a vertical change in elevation of the walking surface (e.g., from a rug onto the floor, or while walking on a sidewalk), (b) Fall on stairs, ramp, or ladder: a fall while climbing or descending a flight of stairs, a ramp, or a ladder. (c) Fall from elevation: a fall from an elevated height onto a lower surface or object. Falls, types of—(a) Stumbling: during a trip, the pedestrian’s recovery reflex allows a person to free the trapped foot and step quickly over or around the trip hazard, with partial recovery from the fall. A limited fall to the hands and knees or to a crouching posture may result rather than a complete fall to the walking surface, (b) Tumbling: while standing, walking, or rising from a seated or lying position, a person experiences a loss of balance and is unable to recover balance in sufficient time to prevent a fall. May include missteps. This loss of balance occurs when the pull of gravity and momentum through the person’s center of mass moves outside the person’s support centers (feet, handrails, wall, chair, bed). (c) Crumpling: while standing, walking, or rising from a seated or lying posture, the person collapses, often for some physiological reason. May be accompanied by loss of consciousness. The manner in which the person falls will be determined by his initial posture and which critical antigravity muscles fail, (d) Pushed or jostled: while standing or walking, a person may lose balance as result of the impact of another person or other external force, and tumble and fall. This loss of balance occurs when the pull of gravity and momentum through the center of mass move outside the person’s support centers (feet, handrails, wall). Fatigue—A subjective state characterized by aversion to continued work due to time on task. Not necessarily correlated with or predictive of future course of work. The effects may occur periodically or progressively. Con. work decrement. See also muscular fatigue. Fatigue-decreased proficiency—A decrease in performance due to prolonged exposure to whole-body vibration or other physically demanding activities. Fault—Any condition that may cause a system to fail. Syn. failure mechanism. See also cause. Comment. In police traffic collision reports (TCR), cause is often listed and attributed to one party, based on a conclusion related to the violation of a section of the Vehicle (or other) Code. These conclusions do not necessarily imply the party had a reasonable chance of avoiding the loss event, and a more complete investigation may result in other conclusions. Fault tree analysis—The development and examination of a tree-like structure in which all possible faults thought to occur within a system are given, with linkage of the
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lower-level to higher-level faults, and a description of the necessary and sufficient conditions for each failure. See also failure assessment, failure mode and effects analysis, risk analysis. Field of view—The width and height of unobstructed area, in degrees, over which an observer may see an object from a specified position. The total field maybe made up of several segments separated by obstructions, though this will slow visual search and efficiency. See visual field, line of sight, decision sight distance. Comment. Although an observer may have a wide field of view, detection is not equally likely throughout because of the size of the search cone by which the observer scans (often about 4 to 5°), the time required, the variation in objects of potential interest, and the conspicuity and expectancy of the target at various locations. Fixation (eye)—The period of time during which the eye examines a specific point, without moving, during visual search. Varies from about 0.3 sec to several seconds (with some tremor or smaller fixations in longer durations). See also saccade. Flammable—Pertaining to any substance that is readily ignited, burns rapidly, and is capable of rapid flame dissemination. Syn. inflammable. Opp. nonflammable. Floor hole—Opening measuring less than 12 in. (300 mm) but more than 2 in. (51 mm) in its least dimension in any floor. Floor opening—Opening measuring 12 in. (300 mm) or more in its least dimension, in any walking or working surface through which persons may fall, such as a hatchway, stair or ladder opening, trench, equipment, passageway, chute, or large manhole. Flowchart—A diagram consisting of standardized symbols that enclose text or other symbols and are governed by specific layout rules for describing the steps involved in a given operation; also flow chart. Focal vision—That sense, derived from ocular stimulation, that forms concepts of size, shape, color, texture, etc. The sense usually understood as “vision” but contrasted with environment or locomotion cues. Opp. peripheral vision. See eye movement analysis. Footcandle (fc)—A measure of the illuminance produced on a surface, all points of which are uniformly 1 ft from a point source of light with an intensity of 1 cd; a flux of 1 lm per square foot of surface; also foot candle. See also lux, footlambert. Footfall—The striking of the bottom of the foot or footwear on a surface in human gait. Foot Lambert (fL)—Obs. A unit of luminous intensity; the luminance of a surface emitting or reflecting 1 lm per square foot; also footlambert or foot-Lambert. Comment. Footlambert is an obsolete measure. Pref. candela/area (i.e., per square meters, square feet, square inches). Footwear—Wearing apparel or any external covering of the foot intended for ground contact during ambulation, such as shoes, boots, slippers, sandals, or overshoes, usually excluding hosiery. Force—1. The amount of muscular effort required to perform a task. Generally, the greater the force is, the greater is the degree of risk. High force has been associated with work-related musculoskeletal disorders at the shoulder or neck, the low back, and the forearm, wrist, or hand. 2. A vector of the amount of force applied on an object or surface, in newtons, and the direction in which the force is applied. Forensic human factors, ergonomics (HF/E)—In litigation settings: 1. The science of establishing the capabilities and limitations of people in the design and use of products, equipment, and facilities. 2. The science and technology of identifying and
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analyzing possible causes of human error, as opposed to system errors, in the design and use of products, equipment, and facilities that occurred in a given injury event. System errors are those potentially hazardous elements reflected in the design, management, maintenance, or operation of a system. See also error, human error, system error. Foreseeable (Note: LEGAL TERM)—When the appropriate use or misuse is reasonably anticipated by ordinary users or by a cognizant group, such as architects, design engineers, or facility managers. May be subjective and should be fully supported by physical and behavioral data from relevant populations and professional judgment. See expectation. Foreseeability (Note: LEGAL TERM)—A concept in which an individual may be held liable for actions resulting in injury or damage only if that person could reasonably have been expected to foresee the risk, misuse, or danger. Fovea—A depressed region within the macula lutea of the posterior retina at which cone density is highest and the greatest visual acuity occurs. Adj. foveal. Syn. fovea centralis. Foveal vision—The area of greatest visual resolution existing in an area at the center of the retina, named the fovea, about 1 to 2° of visual angle. Opp. peripheral vision. See also focal vision, eye movement. Fracture—A break or crack in a bone or other solid material; (v.) the process of cracking or breaking. Friction—The force acting at the interface of two contacting solid bodies that opposes relative motion between the bodies. Also, resistance to the relative motion of one body sliding, rolling, or flowing over another with which it is in contact. Available friction—The friction available at the walkway and shoe or foot interface. As long as the available friction exceeds the required friction, the pedestrian will not slip. Required friction—A baseline friction demand for safe gait, typically measured on dry nonslip surfaces. The friction required by the pedestrian for the maneuver being conducted. It is always greater than or equal to utilized friction. Utilized friction—The amount of friction on a surface brought into play while walking on a surface, independent of the relative motion in the shoe or floor interface. It is always less than or equal to required friction. Friction, coefficient of—A dimensionless number; the ratio of two forces acting at the interface of two contacting solid bodies. The force used in the numerator is parallel to the surfaces and the force used in the denominator is perpendicular (normal) to the surfaces. See also coefficient of friction, static and dynamic; stiction. Friction, dynamic coefficient of (DCOF)—1. The ratio of (a) the horizontal force required to continue a slipping action of an object along a surface; and (b) the vertical force on the surface. The higher or greater the DCOF is, the greater is the traction of the surface. 2. A coefficient of friction obtained during relative translation between two contacting solid bodies; used interchangeably with kinetic coefficient of friction. The coefficient of friction between surfaces in relative motion is not a constant, but a function of normal force and pressure, contact time, sliding velocity, and other parameters. See also stiction, friction. Friction, static coefficient of (SCOF)—The ratio of (a) the horizontal force required to initiate a slipping action of a stationary object along a surface; and (b) the vertical
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force on the surface. The higher or greater the SCOF is, the greater is the traction of the surface. SCOF is generally somewhat higher than DCOF. See stiction, friction. Frivolous (Note: LEGAL TERM)—Pertaining to a lawsuit with no basis in fact that is based on non-sensical legal theory or intended to harass the defendant or grandstand in court. Syn. nonmeritorious, punitive. Frontal plane—Any vertical plane at a right angle to the sagittal and horizontal planes and that divides the body into anterior and posterior portions. Syn. coronal plane. Fyre —Reference to a ruling defining the admissibility of expert scientific testimony based on scientific principles generally accepted by the scientific community. Also see Daubert . Fumble—An unintentional sensory-motor error. Functional impairment—A reduced ability to perform certain functions. Syn. functional limitation. Functional injury—A form of trauma not readily detectable by visual examination, but indicated by one or more variables measuring a functional limitation. Gait—1. In human gait, the equilibrium is lost and regained with each step—lost with takeoff of the propelling foot when the body’s center of mass momentarily lies beyond the anterior border of the supporting surface and regained as soon as the swinging leg is extended forward and its heel (on a flat surface) or the sole of the foot (on stairs) touches the ground or walking surface. Timing and placement of successive steps must be continuously adjusted in order to maintain dynamic equilibrium of the body during walking. This inherent instability of upright posture is exploited to assist in propelling the body forward by a forward orientation (leaning) of the body relative to the feet. 2. The mobility style using human or robotic legs. See walk, run, jog, limp, pedestrian gait patterns, walk cycle. Comment. There are many clinical types of gaits, depending on speed, weight carried, health, size, sex, age, and personal style of movement. Gait analysis—The study of gait. Comment. Gait analysis is usually conducted with the intent to determine mechanisms or quantify disorders. Gate—A swinging or portable member that acts as a safety barrier. It is commonly used at flooropenings, ladder openings, and hatchways through which people might fall. General duty clause—A statement in the Occupational Health and Safety Act of 1970 requiring that an employee be provided with a workplace free of recognized hazards, whether those hazards are specified in the OSHA standards or not. Glare—1. An uncomfortable visual sensation caused by a relatively large contrast or difference in brightness (related to veiling illumination). May consist of bright, large, or high-contrast light sources, reflections, or patterns. Generally will reduce an observer’s ability to detect visual signals of lower signal intensity in the vicinity of the source of the glare. Discomfort glare is a function of the adaptation luminance, the illumination at the eye from each source, and their glare angles. If discomfort glare is noted, it is almost always accompanied by disability glare. Glare sources can completely obscure a lower-contrast object because of an accommodation time delay in the visual system’s recovery once the glare source is no longer present. Coping with glare by looking away further reduces the chance of detecting signals in the direction of the glare. Ability to tolerate varies between people and may decrease with age. 2. An excessive luminance or reflection in the field of view, which is greater than that to
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which the eyes are adapted and may cause discomfort or interfere with visual performance. 3. Bright, large, or high-contrast light sources or patterns when viewed impair the eye’s ability to see other objects by changing the retina’s adaptation level or by completely swamping the retina’s ability to function at least for a time. Glare is related to the intensity of the glare source, the angular distance between the glare source and object, and the contrast of the object, as well as the point of visual fixation relative to the glare source. It is a function of the eye’s structure and internal reflections and cannot be photographically reproduced in many cases. Small sources of glare may affect parts of the retina while other parts retain some function. See also discomfort glare; glare resistance; direct glare; disability glare. Glare, disability—Light entering the eye of an observer that reduces the effective contrast of an object being viewed. The effect of the glare source is to act as a veiling luminance over the retina. The result is an increase in the threshold of visibility. It is a function of the illumination at the eye from each glare source and the inverse of its angle, raised to a power, from the object of regard. The effects on visibility vary among people. Older persons are more affected. Disability glare is not necessarily accompanied by discomfort glare. Glare resistance—The ability of an individual to tolerate glare sources in the visual field without serious interference with perception. Varies among people and tends to decline with age, visual defects, and corrective lenses. Glasses (corrective lenses)—A general term for optical lenses, including contact lenses, worn to correct refractive errors in the eye. Artificial lenses, such as those implanted after cataract surgery, are not included. Comment. The most common conditions that require correction via glasses are myopia (nearsightedness, in which objects at a distance are out of focus); hyperopia (or farsightedness, in which objects up close are out of focus); and astigmatism (a distortion which, for example, causes a circle to appear as an oval). Presbyopia is age-related reduction of the range of focus in the eye. The result is often hyperopia, which may require glasses used for reading, and often for intermediate or distant vision (reading glasses, bifocals, trifocals). Each eye may have its own combination of astigmatism and other refractive errors that may change over time. See accommodation. Grab bar—A bar to act as a safety or mobility aid located in or on a vehicle, toilet stall, bathtub, shower, or other location to furnish persons with a handhold, especially as they enter or leave. Syn. grab rail. Grasp—(v.) Position the required number of digits or the palm to enable an individual to move, pick up, or hold an object, (n.) Within one’s reach. Grip—(v.) Hold firmly. See also grasp. Grip diameter, inside—The diameter of the widest level of a cone that an individual can grasp with his thumb and middle finger (digit III) touching. See also grip diameter, outside. Comment. This diameter is measured at the level of the thumb crotch. Grip diameter, outside—The linear distance between the joint of the first and second phalanges of the thumb and the metacarpal-phalangeal joint of the middle finger (digit III). See grip diameter, inside. Comment. This diameter is measured with the hand held around a cone at the widest level at which the thumb and middle finger (digit III) can still touch.
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Grip strength—The amount of force that may be applied when grasping or squeezing an object under specified conditions. Guard—1. A protective barrier erected along exposed edges of stairways, balconies, and similar areas to prevent inadvertent, unintentional falls to a lower surface. Formerly referred to as guardrail. 2. A protective barrier to prevent inadvertent, unintended contact with moving machinery; sharp, hot, or high-voltage surfaces; or other hazardous locations. See also machine guard. Habituation—Decline in response of an organism to environmental or other stimuli with repeated or maintained exposure. Handhold—A structure consisting of a segment that normally is of elliptical- or rodshaped cross-section and of suitable outside perimeter and length to permit a hand to grasp it for carrying, for assistance in remaining in a desired position, or for mobility. Handicap—(n.) A physical or mental condition that prevents an individual from functioning at a normal performance level, especially referring to those functions such as activities of daily living. Adj. handicapped. See also disability. Handrail—A bar, pipe, or rail to furnish persons with a handhold for standing or moving stability, and with visual and tactual guidance, when using stairways, ramps, and walkways. Must be easy to grasp firmly by most users to be effective. See also guard. Haptic—Pertaining to the sensation of pressure, touch. Syn. tactile. See tactual. Hazard—Any physical condition or circumstance, or combination of physical conditions and circumstances, that has caused or could cause an injury event or property damage. May involve subjective judgment lacking relative data. Syn. unsafe condition. Adj. hazardous. Hazard analysis—A systematic analysis of a system or product to identify hazards. See risk analysis. Hazard area (zone)—An area or space that poses an immediate or impending hazard. Hazard control strategy—Combinations of control measures to (a) eliminate hazards by design when feasible; (b) reduce exposure to hazards through appropriate safeguarding; and (c) heighten safety awareness to hazards by procedures, training, warning devices, and signs. See safety hierarchy. Hazard elimination—The removal of a known hazard. Hearing—That specialized sense through which sound is perceived. Hearing impairment—A reduction in one’s hearing ability; the deviation of an individual’s absolute auditory threshold in decibels (dB) using a calibrated audiometer or by comparison to the absolute auditory threshold of a person with normal hearing. Often restricted to specific bands of the audible spectrum. Expressed in decibels of loss: 20 dB moderate loss, and 40 dB severe loss. Syn. hearing loss. Hearing protection device (HPD)—Any physical structure covering the auricle or inserted into the external auditory canal that is intended to reduce exposure (prevent hearing loss) in noisy environments. Hearing threshold—That sound intensity or pressure level at which an individual reports hearing test tones at a given frequency presented to the ear, and below which no indication is given that sound is detected. Syn. hearing level, hearing threshold level.
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Heat stress—The excessive cooling load imposed on the body by ongoing activity or simple presence in a hot and humid environment. Opp. cold stress. Heel scuff—A misstep occurring in stair descent when the rear of a person’s foot or shoe rubs or scrapes the riser or nosing of a stair. Horizontal plane—Pertaining to a plane through the body that runs horizontal to level ground. It is perpendicular to the frontal and sagittal planes. Human-computer interaction (HCI)—The total of the relationship and activities occurring between a human operator and a computer or terminal. Syn. man-computer interaction, user-computer interaction. Also computer—human interface (CHI). Human error—An inappropriate response by a human whether of commission, omission, inadequacy, or timing. Generally considered as an unintended action or one based on inadequate information or skill; information overload; or fatigue, alcohol, drugs, etc. In litigation settings, injury causation may involve assessing human error vs. system error. System error may include human error upstream in the system or process. Syn. operator error. See also error, system error. Human factors —See ergonomics. Human factors engineering—The use of information derived from human factors research, theory, and modeling for the specification, design, development, testing, analysis, and evaluation of products or systems for human use. See also ergonomics. Human factors specialist—An individual who has the necessary educational, training, and experiential background to have a working understanding of human factors principles and be capable of research or other work toward achieving human factors goals. Human-machine system—A system in which the interaction between a human and machine is necessary for proper system operation. Obs. man-machine interface. Human tolerance—The ability of the human body or psyche to withstand physical or mental stresses without permanent trauma or temporary loss of control. Human visual performance—Ability to see contrasts and colors, color vision deficiencies; ability to perceive and be influenced by patterns; ability to perceive distance and depth (how we perceive a three-dimensional world based on twodimensional retinal images); detection of low-brightness or low-contrast targets; characteristics of night vision vs. day vision; effect of glare sources on visual detection; characteristics of central vs. peripheral vision; eye movements; patterns in searching a visual scene; and the effects of attention and task requirements on visual detection of objects in the visual world. See visual field, field of view. Hyperopia—A refraction error in which parallel light rays from a close object are focused posterior to the retina under relaxed accommodation. Syn. farsightedness. Opp. myopia. See glasses. Illuminance—The luminous flux density incident per unit area at any point on a surface exposed to incident light; measured in units of lux (lumens per square meter), or foot candles (fc; lumens per square foot). See also luminance. Illumination—An alternative, less specific term for illuminance, the luminous flux incident on a surface; often measured in lux or footcandles. May be natural or artificial, including sun, moon, atmospherics, streetlights, area lighting, other vehicles, etc. See light.
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Image—A received sense experience, in the absence of sensory stimulation. The term “retinal image” refers to the optical image focused on the retina by the lens system of the eye. Impact—The contact between two objects, usually in a forceful manner. See collision, crash, point of impact, area of impact, loss event. Impaired—Performance decrement such as in range of motion, strength, motor skill, or lack of sensation due to a physical or mental handicap, or caused by environmental, physiological, or behavioral agents, e.g., noise, alcohol, stress, or physical and mental trauma. Inadvertent contact—When a person unintentionally contacts a power transmission apparatus or another hazard. Inattention—Lack of concentration on a task or search for relevant information that ordinarily would be expected of a person in a control situation. See also maintaining proper lookout. Comment. Inattention may include occupation with distractions or sources of information that, however compelling, are not of high priority or relevance for the task. Incident—Any distinct or definable event, or near-occurrence (“near-miss”) of such an event, that may disrupt normal procedure and that is recorded or observed. See also loss event, injury event, accident, collision. Indirect field of view—The field of view obtained by the use of extraneous optical devices (e.g., mirrors, video devices, periscopes) and that would not normally or readily be available by direct viewing (i.e., where gaze is unobstructed except perhaps by a transparent medium). See field of view, visual field. Industrial engineer—One who is qualified by education, training, and experience to practice the discipline of industrial engineering. Industrial engineering—The engineering discipline concerned with the design, development, installation, and improvement of integrated systems of people, materials, equipment, and energy in the industrial environment. Syn. production engineering. Industrial ergonomics—Human factors applied in an industrial setting. Industrial hygiene—That aspect of medicine generally promoting healthy conditions in the working environment, including attempting to prevent occupational diseases and accidents and developing or obtaining proper measures for any emergency treatment required. Industrial psychology—That field of study and practice involving the testing and development of criteria and predictors for personnel selection and human performance in the workplace. See psychologist. Informal experimental observation—Observations and subsequent conclusions that have the elements of a scientific study but are based on data gathered and recorded under less rigorous conditions. See also visibility study. Information overload —See load stress. Injury—An impaired physical or psychological condition that occurred as a result of an incident. Also, tissue damage caused by an excessive amount of energy released suddenly or over time. Injury event—An event in which one or more persons sustain an injury during exposure to a hazard or performing a hazardous act. May be classified as intentional or
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unintentional if the harmful outcome was not sought. Preferred to “accident.” See also loss event, incident. Instructions—A list or description of the manner in which a particular task or activity is to be performed safely and properly. May involve graphics. See also DANGER, WARNING, CAUTION. Intelligence—The ability to recognize, learn, understand, reason, create, and react appropriately to a given set of conditions. Intended use—The use for which a product or machine is suited according to the information provided by the supplier or that which is deemed usual by typical users according to its design, construction, and function. May be determined by the user. Intensity of light—The illumination on an object divided by the square of the distance between the object and the source, measured in candelas. Roughly, brightness or power of a light source. Pref. luminous intensity, radiant intensity. Interactive—Having the capability for one or more cycles of human input with rapid display feedback from a machine or system. Interface—A common boundary or point of connection between two or more parts of a system or between systems, whether physical or perceptual. See also human-machine system. Interlock—A mechanism that interacts with another mechanism to prevent operation of a device under certain circumstances for safety or other reasons. Internal clock—A hypothetical internal bodily mechanism responsible for maintaining biological rhythms. Invasive—Pertains to clinical or experimental procedures that result in the breaking of the skin, or insertion of an object into any body cavity except the mouth. These procedures may cause extreme discomfort. May include situations that attempt to change opinion or values, etc. purely for experimental purposes. Opp. noninvasive. Investigating officer (IO)—The police officer assigned to coordinate fact-finding and reporting efforts at the scene of a traffic or other loss incident. The role is often rotated among officers and is not necessarily given to the most senior or qualified person. Involved person —One who has suffered physical, psychological, or material damage in an incident or is otherwise a participant to an incident. Iris—The colored circular structure in the aqueous humor of the eye that encircles the pupil between the cornea and the lens and regulates the amount of light reaching the retina; p1. irides. Comment. Maximum pupil diameter and its range (about 2 to 8 mm) generally decrease with age. Although the pupil’s response to higher light levels is rapid, it can reduce retinal illumination by only a factor of about 16, so most of the range of useful vision is related to chemical adaptation in the retina. Irradiance (E)—The density of radiant flux per unit area on a specified surface. Iso-candela diagram—A set of closed lines, each of which describes a specific intensity of a light source in terms of its X-Y coordinates from the source. A means of describing the intensities to be found from street lamps, vehicle headlamps, brake lamps, etc. so that they can be superimposed on the environment. See candela. Job—1. The sum of all the tasks and duties assigned to and carried out by one or more workers toward the completion of some goal. 2. That work specified in a contract work order, usually to be performed by several people. 3. A position within a company serving one’s employment. See work environment.
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Job analysis—An evaluation of job requirements through an enumeration and description of the duties and tasks, facilities and working conditions, and worker qualifications and responsibilities necessary to perform a job. Syn. job study. Job description—A written general statement of the scope, duties, and responsibilities of a particular job. Job design—The process of determining what the job content should be for a set of tasks, how the tasks should be organised, and what linkage should exist between jobs. Syn. work design. Job enlargement—An increase in job scope, with the intent to make jobs more interesting, through the addition of more tasks of a similar nature to the duties or tasks currently performed. Syn. horizontal job enlargement. Job enrichment—An increase in the scope of a worker’s job, with the intent to increase variety and significance by adding additional duties such as planning, greater control over operations, and more interaction with others. Syn. vertical job enlargement. Job evaluation—The process of determining the relative worth, pay, salary, or utility of a job. Job restriction—A condition in which an individual returning to the workforce following an illness or occupational injury is not permitted to perform certain tasks that might aggravate that illness or injury. Job rotation—The assignment to or performance of different activities by a group of workers on a periodic basis. Job safety analysis—The division of any job into its components for the purpose of: (a) identifying possible hazards and the accidents that might be caused by the job, (b) developing solutions intended to eliminate or counteract such hazards, and (c) determining the qualifications or requirements for workers. Syn. job hazard analysis, safety job analysis. Job satisfaction—The degree to which the work environment provides such qualities as variety, comfort, compensation, and social expression to make a job meaningful in meeting an individual’s goals. See also morale, monotony. Job severity index (JSI)—A guideline for matching job design and employee placement such that an acceptable risk or injury potential is present. Jog—1. An intermediate gait between walking and running, or an alternating combination of continuous walking and running, used as a form of exercise. See also gait. 2. To nudge a control, as in momentary activation of a power press ram. Joint range of motion (JROM)—The angle through which a single joint can be flexed, extended, rotated, or otherwise normally moved without discomfort, pain, or injury. Syn. range of motion. Keyboard—A computer input device or typewriter keying mechanism consisting of a panel containing alphanumeric, grammatical, function, or other keys for typing information or data entry into a computer or onto hard copy. Keypad—A data entry pad consisting of the numeric keys 0 to 9, simple arithmetic function keys, a decimal key, and an enter key. Kinesiology—A discipline that studies human motions as a function of the construction of the musculoskeletal system. Syn. biomechanics. Lambert (L)—A unit of luminance; equals l/π cd/cm2. See luminance. Comment. An obsolete unit, similar to foot Lambert (fL), which equals 1/π×cd/t2. Pref. candela/area
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(i.e., square feet, square meters, square inches, etc.). Roughly, “brightness” of a surface. Landing—A walking surface at the top and bottom of a stairway or ramp. Intermediate landings may be located between upper and lower landings. Landings should have a slope in any direction of less than 1:48 (2%, or 1.2°). Latency—The time period from exposure to some event and the manifestation of an individual’s response to that exposure. See perception-decision-response time. Lateral—(Adj.) 1. Pertaining to, near, or toward the sides of the body or a symmetrical structure. 2. Away from the midline. Opp. medial. Learning curve—A concept, mathematical function, or graphical representation of performance vs. time in which performance generally improves with time as a result of learning and feedback. Syn. Learner’s curve, start-up curve. See also progress curve, plateau. Level of effort—The amount of physical or mental activity exerted or required to perform at a certain level. Level walkway surface —A walkway with a slope in the direction of travel less than or equal to 1:20 (5%, or 2.9°), or a cross slope not exceeding 1:48 (2%, or 1.2°). See also walkway surface. Life cycle cost—The total cost of an item over its useful life, including purchase, maintenance, and operations, less salvage. Life expectancy—The number of years a person may be expected to live from a given age, based on the mean length of life of persons of a similar age. Light—(n.) Radiation from that region of the electromagnetic spectrum of which an organism becomes aware through stimulation of the retina or other visual receptor; stimulation that excites visual receptors. See also illumination. Light adaptation—The physical and chemical adjustments of the eye and visual system that reduce sensitivity to light as levels of illumination are varied. Likelihood (probability)—As used in studies of participant behavior, the common perception of the odds of seeing a particular outcome in a specific situation. In general, an event is “unexpected” or has a low probability to an observer if that observer has never, or seldom ever, observed it to occur. See also statistics. Comment. Drivers’ expectations are based on probabilities. There is seldom a chance to be certain that a possible hazard will not appear at a given time. Generally, if a hazard has a low subjective probability, it will be considered as essentially having a zero probability (“impossible”) and the driver will make no preparation for the event’s occurrence; i.e., the event is unanticipated or unexpected. Liminal contrast threshold—At a just-detectable level, the threshold of perception. Opp. subliminal. See also contrast threshold. Limp—A type of gait in which steps are halting and the time spent on one leg is shorter than on the other. See also gait. Line of sight (LOS)—The continuous line from the observer’s eyes to a point of interest, generally assumed to be unobstructed. Does not presume visibility of an object. Syn. sight line, view. See field of view, decision sight distance. Load stress—That type of sensory overload caused by having too many channels of information to process effectively. May also be used to imply that too much
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information is flowing from one source. Syn. information overload. See also mental workload. Locus investigation—A site area visit for investigative purposes. May include event area approaches; participant sources and destinations; sight lines; information resources; and a variety of analytical or recording devices, reenactments, or visibility studies. Long-term memory (LTM)—A coded form of memory that apparently exists indefinitely. “Permanent” storage may fade after long periods, may be corrupted (unconsciously modified, “filled,” reconstructed, or intermingled with other memories), or may be lost because of trauma. See also short-term memory (STM), working memory, consolidation (of memory). Loss event—Similar to an injury event, except no human is injured. Property damage only (PDO). See also injury event, accident, crash, collision, incident. Luminaire—A complete lighting system, consisting of the lamps, positioners, protectors, and any required connections to a power supply. Luminance—The amount of light reflected from an object or surface. Measured in candelas per area (e.g., candelas per square meter, also known as the “nit”), or as foot Lamberts (fL) or millilamberts (mL), both obsolete. Roughly, brightness of a surface. 1 fL=3.426 cd/m2 (nits). See also illuminance. Luminance contrast (C L )—A measure of the physical relationship in luminance between two adjacent, nonspecular (i.e., not mirror-like) surfaces under the same general illumination and immediate surroundings, generally defined by an equation similar to the following form: C L =∆L/L where ∆L is the background’s luminance minus the object’s, divided by the background’s luminance. See also brightness contrast. Luminous flux (F)—The rate of visible light energy (radiant power) emitted from a source over time. Syn. light flux. Luminous intensity—A measure of the strength of a light source in terms of luminous flux per unit solid angle (lumens per steradian or in candelas). Syn. light intensity. Lux (lx)—The preferred SI or metric unit for illuminance (light hitting a surface). See footcandle . Conversion: 1 fc=10.76 lx. Common levels: dining room: 75 lx; reading: 300 lx. Machine—A mechanically or electromechanically powered device consisting of fixed and moving parts and having one or more specific functions. Machine guard—Any piece of equipment or device on a machine intended to reduce or eliminate the chance of injury through the use of that machine. See guard, hazard control strategy. Machine-paced work—That restricted or externally paced work in which machinery controls the rate at which the work cycle progresses. Syn. machine pacing, machinecontrolled work. See also selfpaced work. Maintaining proper lookout (Note: LEGAL TERM)—Relates to adequate allocation of attention and visual search sufficient to prevent an injury or damage incident. Failure does not assume that the involved operators or participants necessarily could have appreciated, processed, and handled all the visual aspects of the prevailing
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conditions leading up to the incident or at the time of the incident, but only that they appeared to fail to do so. Subjective term. See also inattention. Maintenance—The performance of those functions necessary to keep a machine, process, or system in, or return it to, a proper state of repair that will permit safe and efficient operation. Majority—More likely than not; the greater number or part of something; greater than 50%, more than half. Often confused with (or assumed to be) an overwhelming proportion, such as, perhaps, 75 to 99%. Manikin—1. An anthropomorphic dummy with joints or other simulated human physical characteristics, which may be used for a variety of biodynamic functions. 2. A twodimensional, scaled template of humans used for drafting and design work. Syn. dummy, mannequin. Mannequin —See manikin. Manual—1. Pertaining to an operation or set of operations performed solely by humans, rather than by machines or with machine assistance. 2. A document that provides instructions or other information for operation of some equipment. 3. Referring to the use of physical muscle activity, as in a manual lifting task. Manual dexterity—A measure of the ability to make rapid, coordinated, fine, or gross movements of the fingers, hands, or arms for handling independent objects. Manual materials handling—Lifting, carrying, and moving materials without mechanical aid. Materials handling—The study or actual movement of any substances, components, or products, whether in or out of containers or packaging. Maximal voluntary contraction (MVC)—The greatest force the muscle or muscle groups involved can develop under voluntary control when contracting against a resistance under specified conditions; also maximum voluntary contraction. Memory—The capacity for mental storage of feelings, sensations, information, movement patterns, and events. See also working memory, long-term memory, short-term memory. Mensuration (measurements)—The process of determining the dimensions and location of objects, features, and evidence. For objects with a substantial dimension (e.g., a wide line or a pool of liquid), locations and distances are based on the center of the objects and referenced to a permanent fixed object where practical. Reference lines (north/south) are perpendicular. Dimensions of the objects may also be listed in SI or inch-pound units. Mental health—A state in which an individual or population has accomplished a high degree of self-realization and integrated its own desires while successfully adapting to its environment. Mental workload—A measure of the amount of mental effort required to perform a task. Syn. mental load. See also load stress. Mesopic—Pertaining to relatively low-level illumination, such as occurs during twilight, in which vision is mediated by rods as well as cones. Vision for details is degraded compared to photopic visual conditions. See also glasses, night driving. Metabolic rate—The amount of chemical energy transformed into heat and work for the performance of bodily activities per unit time.
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Misstep—An unintentional departure from pedestrian gait appropriate for the walkway surface. If the misstep results in a loss of balance and the pedestrian does not recover that balance, a fall may result. Con. slip, trip, fall. Misuse—The utilization of a product or tool in a manner for which it was not designed or intended by the manufacturer, and in a manner that may not be in keeping with good safety practices. Requires clear understanding of appropriate use or attention to task that may not be appreciated by the user. Mobile—Having the freedom or ability to move about physically from one location to another through relatively independent means, (n.) mobility. Mobility aid—Any physical device that enhances one’s ability to move from one place to another, especially with regard to the handicapped. Mockup—A reduced- or full-scale, representative physical layout of a workstation, equipment, or situation used for training or as a design tool; also mock-up. Maybe two- or three-dimensional. Syn. service test model Model—(n.) A system for providing quantitative estimates of results under specified conditions. Cornment. A model may be physical, graphical, computer/electronic, or theoretical/abstract. Modular workstation—A workstation that may be assembled from modular components in a variety of different configurations. See also cluster workstation. Monocular—The field of view available to one eye. Also, the use of a single eye for a specific observing function. Opp. binocular. Syn. uniocular. See ambinocular. Monotony—The psychological state created by the lack of variety due to the repeated performance of a nonchallenging task or a long-duration task. Adj. monotonous. Morale—A measure of the level of confidence and enthusiasm of an individual or group. See also job satisfaction. Morbidity—The ratio of the number of individuals having some disease to the total population. Muscular fatigue—The reduction of performance or build-up of lactic acid (waste products) in muscle tissue due to prolonged heavy exertion. Syn. muscle fatigue. See also fatigue. Musculoskeletal disorders (MSDs)—Injuries and disorders of the muscles, nerves, tendons, ligaments, joints, cartilage, and spinal discs; examples include carpal tunnel syndrome, rotator cuff tendonitis, and tension neck syndrome. Musculoskeletal system—The integrated system of muscles, bones, and joints in the body. Myopia—A refraction error in which parallel light rays from a distant object are focused anterior to the retina under relaxed accommodation. Syn. nearsightedness. Opp. hyperopia. See also glasses. Nausea—A feeling of discomfort in the stomach region, accompanied by a food aversion and a possible tendency to vomit. Common in motion-induced sickness (seasickness) and in motion-vision perceptual conflicts. Highly variable across persons, but usually habituated with exposure. Negligent—(Note: LEGAL TERM, not a term that should be used by a scientific or technical expert; should not be operationally defined; should be left to the trier of fact to determine.) Implies lack of “ordinary care” compared to a related population.
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Neutral body posture—The posture that the body tends to assume when relaxed with the eyes closed or covered in a microgravity environment; the arms lie in front of the body with the elbows, neck, hips, and knees all somewhat flexed. New candle —See candela. Newton (n)—The SI unit of force; equal to that force resulting in an acceleration of 1 m/sec/sec to a 1-kg mass. This is the same as the force needed to just support 1 kg against gravity. In the inchpound system, the pound force is equal to that force resulting in an acceleration of 32.2 ft/sec/ sec to a 1-lb mass or the force needed to just support 1 lb against gravity. Conversion: 1 lbf equals 4.448 N. Newton’s laws of motion—Three physical laws that govern the basic interactions of physical objects and forces; see Newton’s first law of motion, Newton’s second law of motion, Newton’s third law of motion. Newton’s first law of motion—Every mass maintains its current state of motion unless acted on by one or more nonequilibrating forces. Syn. law of inertia. Newton’s second law of motion—The force required to impart a given acceleration to an object is proportional to the mass of that object. F=ma Newton’s third law of motion—For every action, there is an equal and opposing reaction. Night blindness—A reduced capability for night or low-light vision, regardless of the cause. Because of the headlighting of the road ahead, drivers usually operate in the mesopic range of vision. Syn. nyctalopia. See also glare; adaptation, visual. Night driving—A common experience when driving under artificial illumination in darkness using vehicle lighting, street lighting, and other light sources. Night myopia —See night blindness, night driving, night visual search. Night visual search—The process of examining the visual world at night by scanning with eye movements. Drivers generally search over a larger area during daytime than nighttime. At night, fixations tend to be more concentrated in the straight-ahead direction (ahead and nearer the right shoulder) and closer to one’s own vehicle because of the relatively impoverished visual scene at night and the extent of the useful view provided by headlighting. See also night blindness, night driving. Night walking—Refers to the pedestrian’s equivalent of a driver’s night driving. Without the headlights constantly in the field of view and without the constant straight-ahead gaze, the pedestrian’s eyes often can adapt to a higher level of sensitivity. This usually makes it inappropriate to compare a pedestrian’s ability to see other pedestrians or similar objects to that of a driver’s ability in the same environment. See also night blindness, pedestrian visibility. Comment. A useful rule of thumb is that pedestrians often estimate their visibility to drivers to be about three times the actual distance at which they will be seen. NIOSH—National Institute for Occupational Safety and Health, NIOSH is the institution that provides scientific data upon which OSHA makes recommendations. Nip point —The nearest point of intersection or near-contact of two oppositely rotating circular surfaces or a rotating circular surface and a planar surface. See also pinch point.
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Noise—1. Any undesired component of a measurement that accompanies a signal and interferes with signal clarity, usually of a wideband nature. 2. Any unwanted or undesirable sound. Adj. noisy. See also background noise. Noise exposure—The cumulative amount of acoustic stimulation that reaches the ear of an individual over some specified period of time. Unit: dBA-hours. Noise level—The intensity of unwanted sound in dB, dBA, etc. See decibel. Comment. Noise level is usually specified in decibels relative to some specified sound pressure level (SPL) or in dBA relative to some specified reference. A whisper is about 20 dBA; thunder or a jet on takeoff may be 120 dBA. Noise reduction—A decrease in the noise sound pressure level at a specific point using one or more devices or structures. Measured in decibels (ratio of after treatment to before) or “decibels down.” See also noise level. Noninvasive—Pertaining to those clinical or experimental procedures that do not require breaking the skin or insertion into any body cavity except the mouth, and do not cause extreme discomfort. May be used to indicate situations that do not attempt to change opinion, values, etc. purely for experimental purposes. Opp. invasive. Normal operator—An operator who is adapted to his position and attains normal performance when using prescribed methods and working at a normal pace and for a usual duration. Normal working posture—The typical posture assumed by a worker for a given task, generally taken as a standing or sitting position, with the upper arm hanging in a relatively stationary position close to the body and the elbow flexed at about 90°. Syn. normal working position. Nose (nosing)—The front edge of a step or landing near the intersection of the riser and tread. See stairway, step. Obesity—That condition resulting from a prolonged caloric energy intake exceeding energy output, with the excess energy converted to fat and deposited within the body. According to the World Health Organization, an obese person’s weight (in kilograms) divided by his height (in square meters) exceeds 30, e.g., a man of 6-ft stature weighing more than 220 lb. See body mass index. Occupational biomechanics—The study of the volitional acts of the individual in loading the musculoskeletal system in the working environment. See also biomechanics. Occupational ergonomics—The study or practice of human factors in the workplace. Original emphasis of the term “ergonomics” (“the study of working”). Occupational injury—Any injury such as a cut, fracture, sprain, or amputation that results from a work-related event or from a single instantaneous exposure in the work environment. Occupational stress—An internal condition resulting from any forces exerted on the individual as a result of performing some task in the work environment. Syn. work stress. Open and obvious (Note: LEGAL TERM)—A condition of a walkway, stair, product, or environment that is readily apparent to and identifiable by ordinary and expected users. It may result in an injury event if it represents a potentially hazardous condition that is not adequately observed or not observable by a user. May be subjective and should be fully supported by physical and behavioral data or professional judgment.
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Open riser—Space between the treads of stairs without upright or inclined members. See also stairway, step. Operate—Manipulate, support, and operationally maintain a system or piece of equipment; (n.) operation. Operation—The act of performing any planned job or task by one or more humans with or without machines or equipment in which value is added to a product or information is input, processed, or output. Operator—Person who has primary control of and responsibility for a vehicle (the driver), machine, or system of mechanical devices, or other equipment. Except in certain traffic incidents, the operator may or may not be at the control position and actively performing at the time of a loss incident. Optical axis—The central light path for a system of lenses and receptors, based on geometry and optical principles. Often the single path on which a light ray remains unchanged in transit. See also visual axis. Organization—That structure of people, concepts, or other entities that exist or are created to carry out or assist in one or more specific objectives. Organizational ergonomics—Concerned with the optimization of sociotechnical systems, including their organizational structures, policies, and processes. The relevant topics include communication, crew resource management, work design, design of working times, teamwork, partici-patory design, community ergonomics, cooperative work, new work paradigms, organizational culture, virtual organizations, telework, and quality management. Syn. macroergonomics. OSHA—Occupational Safety and Health Administration. Chartered by Congress with the mission of saving lives, preventing injuries, and protecting the health of America’s workers. To accomplish this, federal and state governments must work in partnership with the more than 100 million working men and women and their 6.5 million employers who are covered by the Occupational Safety and Health Act of 1970. Develops workplace safety guidelines based on scientific data provided by NIOSH. OSHA general industry standard (GIS)—Part 1910 of Chapter XVII of Title 29 of the Code of Federal Regulations dealing with OSHA occupational safety and health standards. Syn. general industry standard. OSHA reportable incident—Any incident resulting in a fatality, hospitalization, lost workdays, loss of consciousness, medical treatment, or job termination/transfer for one or more workers. Syn. reportable or recordable accident. Other involved person—A party who is not a passenger, operator, or rider in reference to a loss event but had some relationship to the incident or its consequences. Witnesses are not involved persons. Syn. party. Overstep —A misstep occurring when a pedestrian descending stairs places a foot on a stair tread or nosing of a landing such that the weight on the ball of the foot is not sufficiently supported by the tread or nosing, and the ball of the foot slips or rotates over the nose of the tread or landing. See also misstep. Pain threshold—The minimum level at which one perceives pain; also threshold of pain. Pan—(v.) Scan horizontally across the surrounding visual environment so that the center of the field of view changes. Panic—A behavioral response to an emergency situation. May consist of or become:
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1. Panic flight. Panic flight is always away from a danger perceived as life threatening and immediate. The subjective emotion is extreme fear. It occurs when escape is seen as possible but unlikely. Strong social bonds may be broken and others unintentionally injured. The panicky person, capable only of a low level of conscious thought, does not consider unusual solutions to avoid the danger. It is adaptive when escape occurs. Panic flight is more likely to occur when the participant is unaware of available escape routes. 2. Behavioral inaction (also known as “freezing,” “negative panic”) is virtually always maladaptive and occurs when a person does little or nothing to escape from, or resist, a danger. The person, who may sit in a burning facility without trying to escape, is aware of the danger and knows that if nothing is done, severe pain and even death will result. The subjective emotion is a blend of hopelessness and helplessness. Behavioral inaction is more likely when the participant has predefined the danger as always fatal (even if it is not), little or no warning is given, and adequate instructions on how to deal with it have not been provided. 3. Normal flight. Normal flight differs from panic flight in that social bonds are not broken and thinking is at a higher cognitive level. It is more likely to be an adaptive response than panic flight or behavioral inaction is. Appropriate warnings and instructions increase the probability of normal flight behavior. Party (in a loss event)—Any person involved in any aspects of a loss event who had or might have had an effect on its occurrence and immediate consequences. In a lawsuit, those named as plaintiffs or defendants. See also witness, other involved person. Passenger—Occupant, other than the operator, of any involved vehicle. May also refer to the “operator” of a parked or stopped vehicle. Passive restraint—Any type of restraint that does not require the individual to make a conscious effort to fasten, secure, or activate, such as an airbag. Opp. active restraint. Peak performance—A behavior that exceeds an individual’s expected or predicted level of ability; the best value observed. Pedestrian—1. A person using legs or leg surrogates (for example, prosthetic limbs, crutches) as the principal method of locomotion. 2. A person standing, sitting, or moving on, near, or toward a road or path and not in or on a motorized vehicle except a wheelchair or similar device. Comment. Pedestrians may be moving (in a “parallel conflict”) along the same path as a vehicle (same or opposite direction) or may be moving across the path of the vehicle (in a “crossing conflict”). Bicyclists are generally not included, unless they are walking the bike. Pedestrian gait patterns—level surfaces—The process of bipedal movement consisting of the pedestrian’s weight being supported primarily by alternate feet (see walk cycle). Interruptions of the regular pattern for any reason may result in the pedestrian losing his or her balance and falling. Pedestrian gait patterns—stairs ascending—The process of bipedal movement consisting of the pedestrian’s weight being supported primarily by alternate feet. As one foot begins to bear the full weight, the other begins to “unweight” and is lifted upward through the swing phase to its next position. This begins with the sole of the foot being placed and weight transferred to the surface through the metatarsal arch, the “ball” of the foot. Heel-strike may not occur.
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Pedestrian gait patterns—stairs descending—The process of bipedal movement consisting of the pedestrian’s weight being supported primarily by alternate feet. In normal descent, the ball of the metatarsal arch is placed on a lower step. The heel is then lowered to the tread so that the entire foot supports body weight during the stance phase. If the stairs have a very shallow pitch, the pedestrian gait will be similar to that which occurs on level surfaces in that the heel-strike occurs before the metatarsal arch is placed on the lower step. Comment. On toe-off, the heel of the trailing foot is the first part of the foot to be raised from the step and the metatarsal arch the last. At this moment, the toes are pointed in a downward direction. As the knee straightens and moves forward, dorsiflection of the ankle occurs and the toe-down orientation of the foot changes slightly. As the foot moves through the swing phase, the heel comes close to the nosing of the intermediate step on its path to the next-lowest step. Pedestrian visibility—The distance at which a pedestrian is detectable and perceptible as a person. Visibility depends on clothes worn (see clothing), the path relative to the observer, lighting, obstructions or distractions in the background, the surroundings and expectancy, and other factors. See also night walking. Perception-decision-response time (PDRT)—Sometimes termed “reaction time.” The time it takes to (a) search for a signal and detect it; (b) recognize it and interpret its meaning, significance, and importance; (c) decide what action, if any, to take; and (d) initiate some action. Includes nervous system latency time. PDRTs may range from less than 1 to 5 sec or more, depending upon numerous factors, including signal clarity or complexity; detection senses involved; expectancy; situational experience; workload; number of possible responses; response effort required; and the observer’s physical condition including age, fatigue, drive state or alertness level, and impairments, such as any alcohol or medication recently taken. See also response time, simple reaction time, reaction time, cognitive reaction time, decision sight distance. Perception of the environment—The process of building a strong mental sense of a stable, detailed visual world, even though the eyes are in constant motion. Wherever an individual looks at a given instant with his foveal vision, that area is perceived clearly. Each look is termed a fixation. Individuals’ brains process and compile this visual information, along with the input from other senses, to provide a continuous perception of an apparently continuous and detailed world, even when some parts of the complete field have not been examined. The resulting concept may be called a cognitive map. See also visual search, eye movement. Peripheral nervous system (PNS)—That portion of the nervous system outside the brain and spinal cord. See also autonomic nervous system, central nervous system. Peripheral vision—The ability to see or sense objects, motion, or light due to stimulation of the portions of the retina away from the fovea centralis while the gaze is directed at some fixed point. To be detected, an object in the periphery must have 5 to 10 times greater contrast and detail, or must be about 5 times as large compared to an object detected directly in central (foveal) vision. See also foveal vision, central visual field, focal vision. Peripheral vision (near periphery)—The area between about 2 and 5° off the visual axis. Visual resolution degrades and contrast necessary for detecting objects is increased with the angle. Syn. perifoveal vision.
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Peripheral vision (far periphery)—The area beyond about 5° off the central visual axis; the eye’s resolution degrades and contrast necessary for detection increases further up to the extremes of the visual field. However, the peripheral field sums energy over a larger area and does not require fine focus, so that large or high-contrast or flickering objects become conspicuous and can steer the gaze, causing their examination with central vision. Such objects may “demand” attention and eye fixation. This is useful when the information is important (e.g., a warning light) but may be an unnecessary distraction when the information is irrelevant. Personal protective equipment (PPE)—Worn to reduce the chance of user injury, includes such items as gloves, safety glasses or goggles, face shields, safety shoes, and fall-protection harnesses. Photometry—The measurement of the properties of light, especially those that have an effect on vision. Photopic—Related to daytime illumination levels in which the eye is adapted to light and vision is supported by the cone photoreceptors. Photoreceptor—A specialized nerve ending, such as a rod or cone cell in the retina of the eye, that is sensitive to light. Physical effort—1. The use of biomechanics, physiology, and body structures in carrying out some function. 2. Any measure of the physical labor or effort involved in some activity. Physical ergonomics—Concerned with human anatomical, anthropometric, physiological, and biomechanical characteristics as they relate to physical activity. The relevant topics include working postures, material handling, repetitive movements, work-related musculoskeletal disorders, workplace layout, safety, and health. Pinch point—A point at which two machine elements approach each other in such a manner that it is possible to nip, pinch, squeeze, or entrap a person or objects coming into contact with one of the two elements. Also nip point or shear point. Plateau (in learning curve)—A period in training or learning during which performance does not increase with time. Plateaus may be short or long and may repeat at different levels, presumably while the skill learning is assimilated. Platform—Any stationary or moving area where employees normally are positioned that is elevated above the surrounding floor or ground, such as a balcony or area specific for the operation of machinery and equipment. Point of impact (POI)—The point in space at which two objects first touch in a collision. The location stated on the traffic collision report (TCR) is the investigation officer’s (IO) assessment or estimate of the contact location. If the evidence does not suggest a specific point, an area of impact (AOI) is described. In either case, the evidence used to establish the location should be discussed. Comment. The points on the vehicles, persons, or other objects that touch and their heights above the ground may be described, but they are not labeled POI. In multiple impacts, each POI is listed and numbered in chronological order of occurrence, i.e., POI1, POI2, etc. Point of operation—The points at which cutting, stamping, forming, grinding, or other change in shape or appearance is accomplished by machinery or equipment upon a piece of work.
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Population stereotype—Spatial, movement, or conceptual features of stimuli and of responses, individually or in combination, that are most consistent with human expectations. Positive guidance—An approach to highway design and the use of traffic control devices developed within the Federal Highway Administration based on human factors principles. It involves a task analysis of information needed by a driver to recognize hazards, operate safely, and avoid incidents. Results provide highway design guidance to meet decision sight distance criteria and to enhance the probability of a driver’s effective speed and path decisions. Posture—Describes the orientation of any body segment relative to the gravitational vector or as an angular measure from the vertical. Power grip—A prehensile grasp by either hand, with the thumb opposing the fingers, of an object to control or manipulate it. It is the most powerful manual gripping method, with a 50th percentile grip strength of approximately 500 N for males and 270 N for females. Presbyopia —A refractive disability of accommodation of the eye due to the loss of lens elasticity with age, resulting in a focal point posterior to the retina and the inability to see near objects clearly or read small print. See glasses. Primary causal factor (PCF)—Police often report conclusions of the main reason a loss event occurred, usually related to an alleged vehicle code violation. Associated or contributing causes may also be reported. Probability —See likelihood, statistics. Progress curve —See learning curve. Property damage only (PDO)—Used to indicate that no person was injured or killed in a loss incident. Proprioception—The muscle senses; the sensing of limb position and motion by the nervous system. Protective device—A device (other than a guard) that reduces a risk alone or associated with a guard. Does not include personal protective equipment. See also guard, personal protective equipment. Protective measures—Design, safeguarding, administrative controls, warnings, training, or personal protective equipment used to eliminate hazards or reduce risks. Proximal—Referring to a portion of the body or a body segment that is closer to the central longitudinal axis than another part. Opp. distal. Psychologist—A professional who usually specializes in one area of psychology: Clinical psychologist: one who treats patients who have abnormal or distressing mental conditions; a clinician Experimental psychologist: one who works to determine how the mental and behavioral processes function; an experimentalist Engineering psychologist: one who expands and applies knowledge of how people interact with information, devices, and procedures; a human factors specialist or ergonomist. QWERTY keyboard—A keyboard with a letter distribution pattern of QWERTY on the left side of the top row of alphabetic characters. See also Dvorak keyboard. Ramp—1. A walkway surface having an incline in excess of 1:20 (2.9° or 5%). When designed for pedestrian use, ramp steepness is generally limited to 1:8 (12.5% or 7.1°)
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or less. 2. To be accessible and of use as a mobility aid for handicapped individuals, handrails are required. The ramp should have a maximum rise of 30 in. (762 mm). It should have a textured, slip-resistant surface and be limited to 1:12 (8.33% or 4.8°) or less. If the ramp has cross slopes that may be encountered by pedestrians walking on a path perpendicular to the ramp, they should be limited in steepness. Range of motion —See joint range of motion. Reaction time (RT) —See response time, cognitive reaction time, simple reaction time, perception-decision-response time. Reasonable—When behavior or conduct meets or exceeds the custom and practice of the majority of ordinary persons, the specific user group (e.g., elderly, children, disabled), or the standard of care of the industry (e.g., sweeps every 15 min in produce departments of supermarkets). If use of the term involves the value judgment only of the individual forensic expert, it may be considered the province of the jury and not appropriate for expression of expert opinion. If use of the term is based on the opinions of a sample of ordinary persons or the specific user group, or an analysis of the standard of care of the industry, then the term maybe an appropriate expression of expert opinion. Reasonable care—What an ordinary, prudent person would do under similar circumstances. See also reasonable, adequate. Reasonable degree of safety—Meets or exceeds generally recognized scientific criteria or standards in the presence of potential danger. Must be discussed along with level of risk and trained or informed parties. See also reasonable, adequate. Reasonable degree of scientific certainty (Note: LEGAL TERM) —A conclusion empirically determined to meet or exceed a specific statistical confidence level of probability, such as a Type I error with a probability of 5% or less (p≤0.05). (See statistics.) Otherwise, the conclusion may be promulgated based upon a reasonable degree of scientific judgment. See also reasonable degree of scientific judgment. Reasonable degree of scientific judgment (Note: LEGAL TERM)—A conclusion empirically determined beyond any reasonable scientific concern or question, and which the majority of the scientific facts support. See reasonable degree of scientific certainty. Reasonably foreseeable misuse (Note: LEGAL TERM)—The predictable use of a machine, tool, product, object, or procedure in a way or manner not intended by the supplier, designer, or user which may result from human accommodation to task demands. Examples: the use of a screwdriver to pry off paint can lids; use of a claw hammer with a chisel. See also foreseeable. Recognition—1. Refers to identifying a detected visual stimulus or assigning a meaning or interpretation to it. 2. The process in which an observer interprets or computer processor matches with data in memory the information available from a stimulus or object to arrive at a conclusion about the stimulus or object. Reflectance—1. The property of an object to reflect light. 2. The ratio of the energy reflected from a surface to the energy incident on that surface. The reflectance factor is usually expressed in percent. Syn. luminous reflectance. Reflected glare—That glare due to specular reflections from glossy or semiglossy surfaces within the field of view. See glare.
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Reflected light—Light that leaves an object or surface from the illuminated sides as opposed to being transmitted or absorbed. Reliability—The likelihood that a part, piece of equipment, or system will perform an intended function under certain conditions for a specified period of time or at a specified time. Repetition—The number of similar exertions performed during a task or a period of work. A warehouse worker may lift three boxes per minute from the floor to a countertop or an assembly worker may make more than 7200 repeated motions in a 4h period. Repetitive motion has been associated with injury and worker discomfort. See also repetitive motion injury. Repetitive motion injury (RMI)—Any of a class of pathologies created through excessively frequent use of a particular joint or tissue, especially in combination with awkward positioning, inadequate or no rest periods, or excessive loads. Syn. cumulative trauma disorder, repetitive strain injury, repetitive trauma disorder, repetitive stress injury, overuse syndrome. See work-related musculoskeletal disorders, cumulative trauma disorders. Repetitive stress injury (RSI) —See cumulative trauma disorders. Residence time—The period of time between initial shoe contact with the test surface and the instant that relative motion is initiated. Residence time produces stiction and adhesion. Slip meters, which apply the vertical and horizontal force components simultaneously, avoid stiction on wet or contaminated surfaces and adhesion on dry surfaces. Residual risk—The risk remaining after protective measures have been taken. Response time—The temporal interval between a stimulus onset and the completion of that motor activity required for the response. See also reaction time, perceptiondecision-response time, simple reaction time, cognitive reaction time. Responsibility (Note: LEGAL TERM)—An obligation incurred by, assigned to, or assumed by an individual or organization to perform at a certain level or within a certain time. Restraint—Any harness or other mechanical device used to prevent or restrict unintended movement of some object, body part, or the body as a whole, usually in response to vibration or rapid acceleration or deceleration. See also active restraint, passive restraint. Retention—The persisting trace left behind as an aftereffect by any experience, forming the basis of learning, memory, habit, and skill, and of all development, as far as it is based on experience. Retroreflectance—The property of an object to return light falling on it in the precise direction of the source. See also retroreflector. Retroreflector (reflector, retroflector)—A surface that efficiently redirects light back toward the source (headlights), providing a bright signal to indicate the presence of a person or object. Comment. The color seen in the reflection may be white, or have red, yellow, or other tints. Small areas of retroflectors may appear bright enough to be seen as active lamps or flashlights and often provide motion patterns’ that reveal pedestrians, bicycles, joggers, etc. The observer must be looking along or near the light source’s path toward the retroflector to see the reflection. When observed in
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normal lighting, the retroflector material may appear almost any color, from white to dark gray, and does not look bright. Rider—A person operating and carried by an animal, a bicycle, motorcycle, or other conveyance with fewer than four wheels. Additional persons are passengers. Rise—The vertical height of a step when measured from its nose to the nose of an adjacent step or level. Riser —The vertical (or nearly vertical) face of a step. See also stairway. Riser height—The vertical height of a stair tread from an adjacent tread or level. Should be between 4 in. (102 mm) and 7 in. (178 mm). Risk (objective)—1. In risk analysis, the product of the severity of injury times the probability of being injured. 2. Often used informally to mean simply the probability of injury. Risk may be compared with the benefit of using a product or device. Individual behavior may be risk adverse or risk preferring. The distinction may be made between “acceptable risk” in contrast to a risk considered “unacceptable” or “intolerable.” It is essential to understand who considers the risk “unacceptable” (an individual, a government agency, a population, etc.). Risk (subjective or perceived)—The participant’s estimate or impression of the chance of suffering a loss of a specific type when participating in a given activity. Comment: Individual assessments of risk, and acceptance or rejection of specific risk situations, vary widely across populations. Risk analysis (risk assessment)—1. An analysis of risk to a population. In an industrial setting, it is often conducted to provide guidance, plans, and programs to reduce risk around machines or the general working environment. Risk analysis generally involves (a) identification of tasks to be performed, (b) identification of the hazards associated with these tasks, and (c) assessment of risks posed by those hazards and means available to control those risks. 2. The process of determining the risk factors present, their characteristics, and estimating the probability of success or failure. See also failure mode and effects analysis, failure assessment, fault tree analysis. Risk factor—An aspect of personal behavior or lifestyle, substance, disability, environmental exposure, or inborn characteristic known to be associated with health or safety-related conditions. “Intermittent” risk factors are sometimes distinguished from “continuous” risk factors. Examples include forceful exertion, awkward postures, repetitive exertion, and physiological and environmental factors such as temperature and other ambient air conditions. Rod—A rod-shaped photoreceptor in the retina of the eye that responds to low levels of illumination. Rods do not convey color. They are located only outside the fovea in the peripheral retina, peaking in density at about 20° off axis, and are used in scotopic vision. Also see cone, photopic, mesopic, night blindness, scotopic. Rules—Authoritative regulations for action, conduct, method, procedure, or arrangement, usually for the safe and efficient conduct of work or other purposeful activity; an established practice. Run (of stairs)—The horizontal length of the tread in the direction of travel, which is measured horizontally between adjacent step nosings (i.e., the full horizontal tread dimension less the overlap of a projecting nosing). Also known as going outside North America. See tread width, rise.
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Run—A type of gait in which both feet may be off the ground simultaneously within a stride cycle, generally consisting of the following phases: (a) support phase: footstrike, midsupport, takeoff; (b) recovery phase: follow-through, forward swing, foot descent. See also gait. Runway—1. Elevated passageway or walking surface, such as a catwalk or walkway between buildings. Generally not intended for vehicle use. 2. Extended surface for the use of aircraft taking off and landing. Saccade—A quick eye movement (in milliseconds) used to shift visual fixation from one point to another. There is little or no useful vision during a saccade. See also visual search, eye movement. Safe (Note: LEGAL TERM)—A condition free of hazards that would harm users in its intended or foreseeable use. Typically used with a “level of risk” modifier, such as “reasonably safe” (lifting 5 lb) or “not considered safe” (e.g., walking on a wet floor or ice). (See the Introduction for a discussion of this term.) Safeguarding—Protection provided to people from a hazard by a guard, device, personal protective equipment, safe work procedures, or safe distance from the hazard. See machine guard. Safety—The practice of eliminating or minimizing the probability of injury or death to personnel, damage to or loss of equipment or property, or loss of time. See also hazard, hazard control strategy, risk. Safety engineering—That engineering discipline concerned with designing system components and processes so as to reduce risk. Safety hierarchy—A product or equipment design principle that holds that it should be: Designed to eliminate hazards, to the extent technically and economically feasible; if residual hazards exist, it should be: Guarded to prevent user injury, to the extent technically and economically feasible; if residual hazards still exist, it should contain: Warnings and instructions to prevent user injury that should be communicated to the extent technically and economically feasible; and, when appropriate, involve: User training, supervision, and personal protective equipment. The safety hierarchy is a mechanical design issue: one should design and guard machines and equipment for ultimate safety, and should not rely on warnings to make up for poor design. Warnings are generally appropriate only when they contain information of which the user was not otherwise aware and that is likely to assist the user in appreciating a hazard and thereby avoiding injury or causing damage. See WARNING. Sagittal —Pertaining to an anteroposterior (fore-aft) plane of the body (sagittal plane); parallel to the median vertical plane of the body, dividing it into right and left halves; it is the major plane for walking and running. It is perpendicular to the frontal plane and transverse (horizontal) planes through the body. Scene—Location of an incident. See also site. Scotopic—Pertaining to relatively low illumination levels in which the eye is adapted to the dark and at which vision is mediated primarily by the rods. Opp. photopic. See also mesopic, night blindness.
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Scotopic vision—Vision that occurs in low light levels or after dark adaptation using the retinal rods. Syn. night vision, low-light-level vision. Opp. photopic vision. See also night visual search, mesopic. Secondary task—A task that an operator is asked to do in addition to his primary task. The operator may attend to the secondary task as time is available or may share its priority with the primary task, possibly degrading the performance of both. Segmental vibration (hand-arm vibration)—Vibration applied to the hands or arms through a tool or piece of equipment. This can cause a reduction in blood flow to the hands and fingers (Raynaud’s disease or vibration white finger). Also, it can interfere with sensory receptor feedback, leading to increased handgrip force to hold the tool. Furthermore, a strong association has been reported between carpal tunnel syndrome and segmental vibration. See also whole-body vibration. Self-paced work—That work performed manually by a worker using simple tools or machines controlled by the worker so that the output rate or performance level is solely determined by the worker. Syn. internal-paced work man-paced work, effortcontrolled cycle, unrestricted work. Opp. external pacing, machine paced. Sense—Any system through which information is acquired about the environment, normally referring to human or robotic abilities. Adj. sensory. Sensitivity—The ability to detect a specific condition or stimulus, or distinguish differences between conditions or stimuli. High sensitivity is associated with low thresholds. Sensorimotor—Pertaining to sensory as well as motor capabilities, activities, or other interactions. Syn. sensory-motor. Sensory overload—A condition in which the sensory load is too great for the human to process effectively. See load stress, mental workload. Serious injury—Any disabling injury or a nondisabling injury of one of the following types: (a) an eye injury; (b) fractures (except to fingers, toes, or nose); (c) loss of consciousness; (d) any injury requiring admission to a hospital for observation; or (e) any injury that requires a work restriction or assignment to another job. Shear point —See pinch point, nip point. Ship stairs (ship ladders)—Typically, a series of steps angled at between 50 and 70° with open risers, often with compact or no handrails. Short-term exposure limit (STEL)—The OSHA-established maximum time-weighted average concentration of certain specific hazardous substances in the working atmospheric environment to which a worker should be exposed for a specified period of time during a workday—typically 15 min. Used with noise, vibration, and other hazards. Short-term memory (STM)—Used for recall of information recently presented; duration of memory ranges from a few seconds up to several minutes with rehearsal. STM may or may not be consolidated into permanent or long-term memory. Syn. working memory. See also long-term memory, consolidation (of memory). Sidewalk —See walkway. Sight distance—The length of the roadway ahead that is visible to the driver. The available sight distance should be sufficiently long to enable a below-average driver in a vehicle traveling at or near the design speed of the roadway to stop before reaching a stationary object in its path.
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Simple reaction time—The temporal interval required to initiate a single predetermined response to a single predetermined stimulus. See also reaction time, cognitive reaction time, perception-decision-response time, response time. Site—Geographic location of an incident at any time. Con. scene. Skill—An organized or coordinated activity pattern involving ability and proficiency that comes from practice, training, and experience. Slip—An event occurring when insufficient friction exists between a pedestrian’s foot and a supporting surface to prevent the foot from sliding. See also friction, slip resistance, slipping. Slip resistance—1. The relative force that resists the tendency of a shoe or foot to slide along the walkway surface. Slip resistance is related to a combination of factors including the walkway surface, the footwear or foot bottom, and the presence of foreign materials between them. 2. The tendency of two surfaces in forceful contact, with or without the presence of a lubricating interface of contaminant, to resist relative motion. See also coefficient of friction, friction. Comment. Slip resistance is dependent upon many factors, such as material and condition of the walkway surface, material and condition of the shoe sole and heel material, the physical abilities of the user, the attempted or proposed activities of the user, the slope of the surface, the angle at which the foot contacts the surface, the presence of contaminants on either of the surfaces, and other factors. A completely nonslip surface under all conditions is rare. Slip-resistant surface—A walkway surface that provides more than the required friction for the range of pedestrians who will be using it under the range of expected conditions, who are wearing the type of footwear expected for those conditions, and who are behaving in an expected and predictable manner. Slipperiness—1. Conditions underfoot that may interfere with human beings, causing a foot slide that may result in injury or harmful loading of body tissues due to a sudden release of energy. 2. The subjective perception of insufficient walking surface traction, i.e., “slippery.” Comment. Humans adapt to slipperiness through postural changes during early stance and midstance. The body’s center of mass is moved forward closer to the base of support; knee flexion is increased, facilitating a softer heel (sole) landing; and ankle plantar flexion is greater than during normal initial contact phase, thus reducing the heel (sole) contact angle with respect to the floor. Due to lower shear forces available in the shoe-floor interface, the ground reaction force profiles are altered for minimizing frictional utilization. These combined effects of force and postural changes seem to aim at reducing the vertical acceleration and forward velocity of the body. During safe locomotion, a dynamic interplay exists between the sensory systems that control posture, gait, and balance and the frictional surface phenomena between shoes and walkways. Slipping—A sudden loss of grip, often in the presence of liquid or solid contaminants and resulting in sliding of the foot on a surface due to a lower coefficient of friction than that required for the momentary activity. Comment. The risk exposure to slipping and falling hazards depends on the exposed person’s health status, anthropometry, perception and cognition of the hazards, and the ability to control his posture and regain perturbed balance. It also depends on the person’s activity and work task (walking, running, load carrying, lifting, pushing or pulling, etc.); the characteristics of
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the interacting surfaces (level or inclined surface, surface discontinuity, floor and footwear materials, etc.); and other adverse conditions that may reduce traction or cause interference (contaminants, obstacles, etc.). Slouched—Pertaining to a variant standing posture in which the shoulders and upper back are rotated anteriorly, with the neck slightly flexed. Slumped—Pertaining to a near-sitting posture in which the shoulders and back are rotated anteriorly, with the neck slightly flexed. Syn. slumping. Sound pressure level (SPL)—A measure of auditory noise. See also decibel, noise. Space perception—Perception of spatial order and spatial relationships of bodies, i.e., of position, direction, distance, form, and magnitude. Specular reflectance—The value of the ratio of the departing flux from a surface due to specular reflection to the incident flux. Syn. regular reflectance. Opp. diffuse reflectance. Speed—The rate of change of position, along any path, Con. velocity, a vector, which has a direction included in its definition. Units for both: miles per hour, kilometers per hour, feet per second. Conversion: z mph equals 1.4667z ft/s equals 1.609z km/h. See also too fast for conditions. Spiral stairs—One or more series of steps attached to a vertical pole and progressing from one level or floor to another in a helical fashion within a cylindrical space. See also winding stairs; stairway, spiral. Stability—That condition in which a position is maintainable, tends to be maintained, or is returned to after some movement. Adj. stable. Stabilize—Ensure that an individual will not be adversely affected by external forces while performing some function; (n.) stabilization. Also see disoriented. Stair—A change in elevation consisting of one or more risers. Stairway—One or more exterior or interior flights of stairs, with the necessary landings and platforms connecting them to form a continuous and uninterrupted passage from one level to another. Each riser should be between 4 in. (102 mm) and 7 in. (178 mm). Each tread in the direction of travel should be between 11 in. (279 mm) and 14 in. (356 mm). Stairway, interior—A stairway not meeting the definitions of an exterior stairway. Stairway, spiral—A stairway with a closed circular form in its plan view with uniform section-shaped treads attached to and radiating about a minimum-diameter supporting column. If limited to small areas such as catwalks, gridirons, etc. that serve few people, a lower standard of step geometry and stair width may be appropriate, according to common codes and standards. The minimum tread depth should not be less than 7.5 in. (190 mm) at a point not more than 12 in. (305 mm) from the narrow edge. Riser height should not be more than 9.5 in. (241 mm). Riser height should be sufficient to provide minimum headroom of 78 in. (1981 mm). Minimum stairway width should be 26 in. (660 mm). In all other cases, conventional limits on stair width and step geometry at the expected walking lines should be applied. See rise, run. Stairway, winding—A stairway with a curvature in the plan view that is not circular. The minimum tread depth should not be less than 6 in. (152 mm) and should be 11 in. (279 mm) at a point not more than 12 in. (305 mm) from the narrow edge. Stamina—The ability of the various bodily systems utilized in a given task to sustain efficient performance for long periods of time.
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Stance—That phase of a gait cycle during which at least one foot is in constant contact with the ground. Standard—Any statement of required quality or performance related to a product or process and promulgated by a recognized authority. Meeting a standard is not, in itself, always equivalent to adequate quality or performance. Standard of care—1. The design or maintenance of equipment or the built environment that provides an optimum level of user safety. 2. The minimum safety standards that manufacturers or builders must meet, by law or by common agreement within an industry through standardsetting organizations, e.g., ASTM, ANSI, and SAE. Startle—The physiological response to a sudden stimulus. Static equilibrium—The ability to maintain body posture or balance through a sense of position or motion of the head with respect to gravity from the integrated involvement of the inner ear, vision, the cerebellum, and muscle tension. See dynamic equilibrium, disoriented. Static friction —See friction, static coefficient of. Static strength—The force generated by a maximal voluntary isometric muscular exertion in a brief period of time. Syn. static ultimate strength. Static work—That manual work performed when muscles are isometrically contracted, but no readily observable motion occurs. Syn. static muscle work, isometric work, isometric muscle work, force. Statistical tests—Tests designed to analyze the difference between group means, taking into account the spread of mean scores. The tests determine if the difference in means is large enough to conclude that some treatment had a measurable effect or whether the difference was just due to chance (“error”). Statistical tests determine the probability that a difference between means could have occurred by chance if the experimental treatment had no effect. By convention, if the probability of the difference in means is such that it could be expected by chance to occur in only 5% of the times that such samples were tested (i.e., p<0.05), then the alternative conclusion, that the treatment did have an effect, can be drawn. If the mean difference were larger so that the chance of a difference that great would be expected in only 1% of the times such a test were conducted (p<0.01), then one would have more confidence in concluding the treatment had an effect. Statistical test errors—Two types of errors, Type 1 and Type 2, are possible in interpreting statistical tests. A Type 1 error occurs when a conclusion is made that the treatment had an effect when, in actuality, it did not. When the decision is made to accept the conclusion that the treatment had an effect based on the p<0.05 criterion, then Type 1 error can be expected 5% of the time. A Type 2 error occurs when the decision is made that the treatment had no effect when, in fact, it did. As the acceptance criterion moves from p < 0.05 to p<0.01, the chance of a Type 1 error decreases and that of a Type 2 error increases. Statistics —1. Descriptive statistics characterize a population or a sample from that population. These statistics include the average value (usually the arithmetic mean) of a variable of interest and the spread of scores. This spread may be based on a bellshaped curve and expressed in the form of a standard deviation (SD) around that average value. In a population where the distribution of the variable of interest lies on a Gaussian bell-shaped curve, 95% of that pop-ulation lies with 1.96 SD on either side
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of the average value. 2. Inferential statistics is used to make inferences about the populations from which two or more groups were drawn. Two samples randomly drawn from the same population will usually have, due simply to chance, somewhat different mean values. A third sample, drawn from a similar population but one that has been given some form of treatment that might affect the value of the variable under consideration, will also have a different mean value for that variable than did the first two groups. The difference in means of the first two groups is said to be due to randomness (also called “error”) rather than any causal factor. The difference between those two groups, when combined, and the third group would be due to random error plus any effect of the treatment. Step—A stair unit consisting of a single riser going from one level to another. See also stairway, riser, tread. Stereopsis—Perception of a three-dimensional world by virtue of the slightly different views of the two eyes as integrated by the brain. Requires good visual functioning of each eye. Observers may rely on other types of cues to depth and distance that exist in the visual field instead of or in addition to stereopsis. Stiction—The tendency of two surfaces in forceful contact to bond together if there is a period of time between initial contact and initiation of relative motion, as a result of residence time. A lubricating interface or contaminant may be present. See also adhesion. Stopping sight distance—The sum of two distances: (a) the distance traveled during the driver’s perception-decision-response time and (b) the distance needed to stop the vehicle from the instant that brake application begins. See also sight distance, line of sight, decision sight distance. Strain—1. An injury or disability involving overuse, overextension, compression, or twisting of a muscle, ligament, or joint. 2. The biomechanical, physiological, or psychological effects from one or more stressors on an individual. 3. A change in one or more dimensions of an object due to elongation, compression, or shear stressors. See also repetitive motion injury. Strength—The maximum capability of an individual to exert a brief force using only his muscles and body segments under specified conditions. Syn. muscular strength. Stress—The collective mental and physical conditions resulting when an individual experiences one or more biomechanical, physiological, or psychological stressors above comfortable levels or durations. Also, the force acting on an object. See also stress, strain. Stumble—Occurs when a person trips or missteps, and then takes one or more rapid steps forward in an attempt to recover balance. Balance may be recovered through reflex actions or by grasping a handrail or other object. A fall may or may not result. Surface characteristics—A set of terms considered to be the minimum needed to describe the condition of a surface precisely, especially regarding slip resistance (e.g., material, contamination, slope, texture, hardness, coating, temperature). System—An integrated collection of facilities, parts, equipment, tools, materials, software, personnel, or techniques that make an organized whole capable of performing or supporting some function. May be simple or highly complex. System error—Those potentially hazardous elements reflected in the design, management, maintenance, or operation of a system consisting of products,
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equipment, and facilities. Forensic human factors often involves the assessment of the possible role that system errors played in a specific injury event. See also error, human error. Tactile stimulus—Any mechanical stimulus that activates the touch or pressure receptors. See also haptic. Tactual—Causing a touch sensation. Tandem gait—A type of gait in which the individual places the heel of the advancing foot in line with and directly in front of the toes of the stationary foot. Threshold—The lowest level of a quality that has stimulus properties. Syn. limen. See also liminal contrast threshold, contrast threshold. Time of loss (TOL); Time of Incident (TOI)—A reported time of a primary incident, e.g., 1700 PDT (using military 24-h time), with zone and daylight or standard time indicated as defined by police or other authority unless re-established by competent analysis. Toeboard (also referred to as toeplate or kickplate)—Vertical barrier at floor level, erected along exposed edges of a floor or wall opening, platform/landing, runway, or ramp to prevent objects from falling over the edge. Tolerable risk—Risk that is accepted for a combination of a given task and hazard or for a hazardous situation. Too fast for conditions (Note: LEGAL TERM)—A speed greater than that which is reasonable or prudent with due regard for weather, visibility, traffic, and the surface or width of the roadway; a speed that endangers safety or property. An essential aspect of this as a causal factor must be that the driver ignored, failed to look for, or discounted available information or cues that a prudent driver would have utilized to avoid a loss or reduce a danger. Comment. The first sentence of this item (after ‘95 Cal. Veh. Code 22350, Basic Speed Law) specifies conditions to be considered, but it is commonly used more generally to cite any driver who has been involved in a crash, usually by striking an object. When information and expectancy concerning a hazard are lacking, there may be no fault if the driver was proceeding in a normal, lawful manner and reacted reasonably when the situation became apparent. Tool—Any device, piece of instrumentation, or machine used to perform an operation or to aid in the performance of an operation. Tool design—The part of engineering involved with the design of tools, especially of hand tools. Total disability—Any disability short of death that prevents an individual from following any gainful employment or includes the loss of use of (a) both eyes; (b) one eye plus a hand, arm, leg, or foot; or (c) any two members (hand, arm, foot, or leg) not on the same limb. Total stopping distance—That distance required for a vehicle to come to rest from the moment at which the necessity for braking is required; equal to the sum of the total reaction distance, brake reaction distance, and braking distance. Traction—The frictional force between a shoe, wheel, or other support and the supporting surface. See also friction. Train—(v.) To impart one or more particular skills to an individual via some combination of information, instruction, demonstration, and directed activity under controlled conditions.
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Training time—The total amount of time involved in training a new worker or a worker being taught a new task. It may or may not be determined by achieving a criterion level. Transfer of training—The knowledge, skills, and information gained in certain situations or activities that may enhance or reduce one’s ability to be trained on, or perform, a task or activity with similar or common characteristics. The degree of commonality of characteristics should be apparent to the individual faced with the new task or communicated clearly to him. Positive transfer: when previous training assists in the learning or performance of another activity. Examples: 1. The operation of common sink faucets suggests the correct operation of outdoor water faucets. 2. Driving an automobile suggests the correct operation of an electric golf cart or tractor. Negative transfer: when previous training degrades the learning or performance of another activity. Examples: 1. The clockwise rotation of a hydraulic flow control generally decreases flow volume, whereas the clockwise rotation of an electrical control generally increases gain, or “volume.” 2. The sequence of key order on touchtone telephones is reversed from 10-key numeric keyboards. Trauma—Any physical or mental injury induced by an external force, agent, or event. (Adj.) traumatic. Tread—The horizontal (or nearly horizontal) surface of a step. Tread depth—Horizontal distance from front to back of treads NOT including nosing projection, if any. Should be no less than 11 in. (279 mm). Con. tread width. See also run, step, stairway. Tread width—Horizontal distance from front to back of tread including nosing, if any. Obs. Con. tread depth, run. Tribometry—The measurement of floor slip resistance or shoe traction properties on a walking surface, or of friction generally. See also friction, coefficient of friction. Trip—An event occurring when the toe or some other portion of the foot in the swing phase of the walk cycle contacts a surface, an obstruction, or a protrusion. The swinging foot may fail to clear the ground adequately or it may encounter an obstacle or an irregularity on the ground surface. May also occur when the bottom of the shoe locks on the surface with excessive friction. May involve unstable or erratic foot trajectories on uneven or discontinuous surfaces, or obstacles on the floor. Ground clearances generally decrease in older persons. Unless balance is recovered, may result in stumble or fall. See also misstep. Trip hazard—A protrusion above a walkway surface that causes a pedestrian to trip when using a gait appropriate to the prior conditions and using reasonable care. (ASTM F-1637–95). See falls, causes of; slip; reasonable. Trivial defect (Note: LEGAL TERM)—Defect in a walkway, such as a change in elevation, crack, or hole, that is not considered hazardous because of its size and therefore fails to present the property owner with a responsibility to repair the defect. Examples of defects can include a change in elevation, depression, crack, or hole. Many states have modified the concept of trivial defect so that the size of the defect is only one circumstance to be considered when determining whether a defect is trivial or dangerous. See trip hazard. Comment. In determining whether or not the condition is dangerous or defective, or merely trivial, all of the circumstances surrounding the
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condition must be considered. For example, height differentials of 0.5 in. (12.7 mm) or more between adjoining walking surfaces can readily produce a dangerous or defective condition, especially under adverse conditions such as poor lighting, unfamiliarity with the area, for older or handicapped pedestrians, or when it is necessary to be vigilant for traffic. Tunnel vision—A reduced ability to see toward the periphery of the normal visual field, i.e., substantially less than 180° width. A result of conditions such as glaucoma, stroke, etc. See also visual field. Underfoot accident—A fall-related or other unintentional injury in which the first unforeseen event was an interaction between the pedestrian’s foot and the substrate, including slipping, tripping, stumbling, missed footing, twisted foot or ankle, air step, and collapsed or moved surface. Understep—An event occurring when, in ascending stairs, a foot is not adequately placed on the nosing of a tread or landing to support the weight of the pedestrian. Unreasonably dangerous condition (Note: LEGAL TERM) —The presence of an unsafe situation that falls below an established standard of care. May involve subjective judgment lacking relevant data. See safe, reasonable. Unsafe act —1. Failure to follow a commonly accepted safe practice or procedure, thereby exposing oneself or another to a readily apparent danger. May involve subjective judgment. 2. Any departure from mandated, accepted, or standard practice, whether of commission or omission, which has caused or has the potential for causing personal injury or property damage. See also safe, hazard. Unsafe condition—A physical condition that creates a hazard that, if left uncorrected, may cause a specific injury event to occur. May involve subjective judgment lacking relevant data. Syn. dangerous condition. See also safe, hazard. Unstable footing—A walkway surface that is not sufficiently even, or which deforms under a pedestrian’s foot or footwear pressure, and which can result in a misstep. User-friendly—(Sl.) Designed according to human factors or ergonomic principles with claimed or demonstrated ease of use. User response time—The period required for or taken by a user to enter a command or reply to a display prompt. Vehicle code—The jurisdictional code regulating vehicle-owner and driver behavior and rules of the road. Velocity—The change in distance per unit time. Technically, a change in direction changes velocity because it is a vector quantity, defined by direction and magnitude. See speed (which is often intended when velocity is used). Vibration—Any mechanical oscillation of a structure or system. High frequencies may be heard; lower frequencies may also be felt; low (infrasonic) frequencies, especially about 3 to 6 Hz, are most disturbing to persons. Vibration syndrome—Any sign or symptom associated with the use of vibrating tools or equipment ranging from numbness, blanching, or tingling that can cause a recognized disease, including white finger disease and Raynaud’s syndrome. See also segmental vibration. Violation—A breach of one section of the Vehicle (or other) Code. A police report may include the officer’s assessment of the behavior that contributed to the loss event, with
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or without issuing citations or making arrests. Detailed investigations may confirm or alter these assessments. See cause, primary causal factor, fault. Visibility—1. Refers to the ability to see an object, given that conditions of location, contrast, glare, expectancy, meaning, and other factors are within acceptable ranges. 2. A measure of the capability of being seen through a combination of factors such as luminous intensity, contrasts, intervening conditions between the observer and objects, object size, visual noise, and distance from the observer. See also conspicuity, visual field. Visibility study—An investigation, often using film, video, or animation, that illustrates various visual aspects of a situation without necessarily being a full reconstruction of an event. See also informal experimental observation. Visual acuity—A measure of the ability to resolve distinct objects or fine detail with the eye. Normal acuity (20/20 or 6/6 metric, corrected or uncorrected) resolves about 1 min of arc (1/60 degree) under good conditions. Visual adaptation—A change in visual sensitivity over prolonged viewing of a particular intensity, color, or other aspect of light. See dark adaptation, light adaptation. Visual angle—The angle subtended at the eye (nodal point) by the linear extent of an object in the visual field. It determines linear retinal image size. A disc about 21 in. in diameter at 100 ft subtends 1°. Visual axis—An imaginary line, internal to the eye, projected from the point being fixated, through the lens, to the center of the fovea. Syn. visual line. See also optical axis. Comment. The visual axis is separated from the optical axis by about 4°; i.e., the fovea is used when a ray is about 4° inward from the midline (nose) compared to the optical axis. Visual comfort—The sense of having an adequately lighted visual environment, without glare. Opp. visual discomfort. Visual environment—That external physical and psychological volume having characteristics generated by all of the following: (a) the luminous environment, (b) the structure of the volume, and (c) any objects within that volume. Visual field—Refers to the angular dimensions of space over which a visual stimulus can be perceived. Common human ranges extend to about 160 to 185° horizontally, about 75 to 80° downward, and 50 to 60° upward unless blocked by the nose, other facial features, or corrective lenses and frames. See also field of view, central visual field, peripheral vision, monocular, binocular. Visual image distance, rate of change—In approaching a target, the rate of increase in the visual angle subtended by the target increases exponentially as the distance decreases. Detection and recognition of this change vary with the size of the target and the distance (interval) and relative speed between the target and the observer (closing rate, rate of closure). Example: A stationary sedan at 200 ft (73 m) may be perceived as stopped, but at greater distances it may be perceived (and assumed) to be moving. Visual noise—Patternless or irrelevant detail in the visual field or on a display such that salient cues may be missed or a sensory overload condition may exist. Syn. visual clutter. Visual performance—The ability to perceive and be influenced by patterns, colors, and color vision anomalies; ability to perceive distance and depth, including three-
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dimensional objects; detection of low-brightness and low-contrast targets; characteristics of night vs. day vision; effect of glare sources on visual detection; central vs. peripheral vision; patterns of eye movements in searching a visual scene; and the effects of attention and task requirements on visual detection of objects in the visual world. Visual search—The process of examining the visual world by scanning with eye and head movements. Not a random process, but rather based on intent, expectancy, peripheral field stimulation, conspicuity, recent and past experience, skill, and other factors. Comment. Through normal perception, we build a strong sense of a detailed visual world because our eyes are in constant motion. Vision involves rapidly looking at a series of individual points. Each look is termed a fixation separated by saccades, or jumps to a new fixation. Our brains process and compile this information to provide a continuous perception of an apparently unbroken and detailed world, termed a cognitive map. An area not specifically scanned (inspected) may contain information contrary to the “mapped” areas. The observer may not be aware of such omissions and assume the entire area is homogeneous (as happens in the blind spot.). Eye movements involve rotation of the eye or eyes within the head and may be accompanied by head motion for a shift of more than a few degrees. We make about three eye movements (involving a fixation and a saccade) per second in most settings. Visual search, night—Drivers generally search over a smaller area during nighttime than in daytime. Fixations at night tend to be more concentrated in the straight-ahead direction and closer to one’s own vehicle because of the relatively impoverished visual scene at night. Headlights and other lights or bright objects will attract the most attention. See visual search, eye movement. Walk—A type of gait in which each foot is normally placed sequentially along a line parallel to the direction of travel, with at least one foot on the ground at all times. See also gait. Walk cycle—Comprising “toe-off,” “swing phase,” “heel-strike,” and “stance phase” on level surfaces. In ascending and descending stairs, “toe-strike” may occur instead of “heel-strike.” See pedestrian gait patterns. Walkway—Walking surfaces constructed for pedestrian usage, including floors, ramps, walks, sidewalks, stair treads, parking lots, and similar paved areas that may be reasonably foreseeable as pedestrian paths. Natural surfaces such as fields, playing fields, paths, walks, or footpaths, or a combination thereof, are not included. (See ASTM F-1637.) Walkway surface—A structure intended to be used by a person attempting to walk. See also level walkway surface. Walkway surface hardware—Includes manhole covers, cellar doors used as walking surfaces, junction box covers, cleanout covers, hatches, sidewalk elevator covers, sewer gates, utility covers, and similar elements upon which pedestrians can reasonably be expected to walk. Wall hole—Opening measuring less than 30 in. (760 mm) and more than 2 in. (51 mm) in height and of unrestricted width in any wall or partition. Wall opening—Opening at least 30 in. (760 mm) in height and 18 in. (460 mm) in width, in any wall or partition, through which persons can fall to a lower level.
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WARNING—1. When used as a signal word, is specified in ANSI Z535 for potentially hazardous situations that, if not avoided, could result in death or serious injury. 2. Information about a possible negative consequence; a message that something undesirable may occur to someone or something as a result of taking (or failing to take) some action. 3. Any message intended by the sender to provide information about possible negative consequences of an action (or inaction). 4. Any message about possible negative consequences of an action (or inaction) that meets specified criteria of message content or form (e.g., a safety message that complies with ANSI Z535). 5. Any message interpreted by the receiver as providing information about possible negative consequences of an action (or inaction). A message may meet any or all of these definitions. These messages have the potential to change behavior and thereby prevent injury events, particularly by receivers who would not otherwise be aware of the specified hazard and its negative consequences. See also CAUTION, DANGER, safety hierarchy. An “audible warning” signals that a hazardous situation exists and that some corrective or evasive action may be required to avert possible loss of life and property. The audible warning may describe the corrective or evasive action if such an action is not obvious or has not been previously learned by the targeted audience. An audible warning has the advantage over a warning placard in that it can be dynamic—that is, present only when and where the hazard exists. It is also omnidirectional and, thus, a person must not be facing in a particular direction to receive the warning. However, audible warnings usually contain less information concerning the nature of the hazard and avoiding actions than does a warning placard. The audible warning needs to be provided in time so that the targeted audience has time to perform the required actions. A”warning placard” is used to visually alert or inform the user of a device, product, or environmental condition as to potential hazards, the risk and consequences of injury, and the ways to avoid injury. Message content and format are contained in ANSI Z535 and other standards. ANSI Z535 states that information about consequences and ways to avoid injury is optional when they are obvious to a target audience. See also CAUTION, DANGER. Safety sign. A visual alerting device in the form of a decal, label, placard, or other marking such as an embossing, stamping, etching, or other process that advises the observer of the nature and degree of the potential degree of the hazard. It can also describe safety precautions or evasive actions to take, or provide other directions to eliminate or reduce the hazard. It typically contains a signal word, symbol or pictorial, and a message panel. Signal word. A word or words used to call attention to the safety sign or label and designate a degree or level of hazard seriousness. The common signal words for product safety signs are DANGER, WARNING, and CAUTION. Symbol or pictorial A graphic representation used to convey a message without the use of words. It may represent a hazard, a hazardous situation, a precaution to avoid a hazard, a result of not avoiding a hazard, or any combination of these messages.
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Message panel. Area of the safety sign that contains the word messages that identify the hazard, indicates how to avoid the hazard, and advises of the probable consequence of not avoiding the hazard. Safety alert symbol. A symbol that indicates a potential personal injury hazard. It is composed of an equilateral triangle surrounding an exclamation mark. The safety alert symbol should not be used to alert persons to property-damage-only incidents. Safety instructions. Consists of information that tells what to do or how to do something. May or may not include safety signal words, descriptions of hazards, or consequence information. There may or may not be a clear distinction between instructions and warnings. In some situations, instructions can be more effective than warnings. Safety rules. Detailed statements to do or not to do something, issued by someone such as a legal authority, homeowner, or manufacturer. May be thought of as a warning wherein one of the negative consequences is offending whoever issues the rules. In some situations, rules can be more effective than warnings, especially when the rule is enforced by someone with the authority to impose penalties or when the rule is issued by someone (e.g., a homeowner) whom people wish not to offend. Warning barrier—A sign, pedestal, marker, or other object used to alert pedestrians to a hazardous area or warn them of a hazardous situation. Often used when mopping or waxing floors, or to block off a recent spill or wet area. Wet—An unbroken film of water covering the area of impending shoe contact. Whole-body vibration—Oscillation or rotation of a person’s body in one or more of the six degrees of freedom. Vibration may vary in frequency, direction, amplitude or intensity, and duration. The critical frequencies most likely to cause illness or injury are 4 to 8 Hz in the vertical direction when seated or standing and 1 to 2 Hz in a foreaft or lateral direction. Comfort, fatigue, and maximum tolerance boundaries are prescribed by ISO 2631. See also segmental vibration. Winding stairs —See stairway, winding. Witness—1. (n.) A person who saw, or can give a firsthand account of, individuals, events, or objects. 2. A person who testifies in court. 3. A person called upon to observe and verify a transaction or the signing of a document. 4. (v.) To give or serve as evidence; to testify. See also expert witness. Work design —See job design. Work environment—The total physical, physiological, social, and psychological environment within which a worker performs tasks. Syn. working conditions, working environment. See job. Workers’ compensation—An insurance system that provides for payment to employees or their families in the event of an occupational illness, injury, or fatality resulting in the loss of wages, regardless of any negligence. Syn. workman’s compensation, workmen’s compensation. Comment. Workers’ compensation is usually required by state law and financed by a tax on employers. Generally, payments preclude civil suits against employers for losses. Working memory—An intermediate-duration (generally of seconds to minutes) form of memory transferred or encoded from sensory memory and capable of manipulation; without rehearsal, the memory begins to fade after about 20 to 30 sec. Syn. short-term
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memory. See also long-term memory, consolidation (of memory), short-term memory. Workplace design—The process of developing a workplace, including accommodations and locations for the machines, materials flow, workers, tools, and other devices. Syn. workplace layout, motion efficiency principles, prerequisites of biomechanical work tolerance. Work-related musculoskeletal disorders (WMSD, WRMSD) —Injuries and disorders of the muscles, nerves, tendons, ligaments, joints, cartilage, and spinal discs due to physical work activities or workplace conditions in the job. Examples include carpal tunnel syndrome related to long-term computer data entry, rotator cuff tendonitis from repeated reaching, and tension neck syndrome associated with long-term cervical spine flexion. See also carpal tunnel syndrome, repetitive motion injury. Workstation—A single location within a workplace at which instrumentation or equipment is located and at which a worker might remain for extended periods of time to perform control, monitoring, processing, or other functions; also work station. Work tolerance—The length of time for which a worker can perform effectively at some task without a rest period or the onset of unnecessary discomfort, excessive fatigue, illness, or injury. Written standard practice—An outline of the methods for a worker to use in some operation, often including the tools and equipment used and a workplace layout diagram. Also standard practice sheet. Comment. This outline may be in hard copy or digital form. Abbreviations ANSI—
American National Standards Institute
ASTM—
American Society for Testing Materials
SAE—
The Society of Automobile Engineers
Index A Abbreviations, forensics terminology, 38-1 Abilities, health care, 37-12 Access to expert witnesses, 4-6 to 4-7 Accidental injury prevention application of principles, 25-12 to 25-13 basics, 25-1 to 25-2, 25-13 case study, 25-8 to 25-13 checklist, 25-14 compliance with regulations, 25-6 corrective action, 25-7 data sharing, 25-7 documentation, 25-6 to 25-7 identifying risks, 25-5 to 25-6 industry response, risk factors, 25-10 to 25-12 known risks, 25-8 to 25-10 manufacturing practices, responsible, 25-4 to 25-7 marketing practices, responsible, 25-4 to 25-7 overall policy, 25-4 to 25-5 product safety function, 25-5 quality control, 25-7 reasonableness vs. unreasonableness, 25-2 to 25-4 recall, 25-7 regulation compliance, 25-6 responsibility, 25-4 to 25-7 riding mower backover case studies, 25-8 to 25-13 risk factors, 25-10 to 25-12 usage considerations, 25-5 Accident analysis model, 5-11 to 5-14 Accidents, see also specific type avoidance, 8-4 product liability, 33-4 to 33-5 proneness, 1-3 “road map” for practice, 5-3 to 5-4, 5-8 to 5-9, 5-10 Accountability, safe practices, 6-3 Accumulated sleep loss, total, 17-8, 34-6 Acquisition, 12-1, see also Memory for conversation Active voice, 2-5 Activities, warning expert, 30-5 to 30-11 Actual risk doctrine, 9-5 Acuity, 32-4
Index
961
Acute exposures, shiftwork, 34-5 to 34-6 ADA (Americans with Disabilities Act), see Preplacement strength and capacity assessment Adequacy, warning expert, 30-9 Adolescents, 35-3 to 35-4, 35-7 to 35-8, see also Child pedestrians; Preschoolers Adversarial setting, 30-13 Adverse event investigation, 37-5 Affirmative role of experts, 7-5 to 7-6 Age human-centric approach, 28-8 motorcycle collisions, 18-3 to 18-4 Age and functioning attention, 11-17 to 11-18 basics, 11-1 to 11-2, 11-34 to 11-35 bias in interpretation, 11-18 checklist, 11-35 to 11-36 circadian patterns, 11-13 combining information, 11-30 to 11-31 decision processes, 11-30 to 11-34 earwitness identification, 11-27 encoding, 11-17 to 11-18, 11-24 to 11-27 estimating time, 11-16 eyewitness identification, 11-22 to 11-27 face perception, 11-22 to 11-27 gathering information, 11-30 to 11-31 hearing, 11-4 to 11-6 information processing, 11-28 to 11-30 inhibitory functions, 11-12 to 11-4 interpretation bias, 11-18 judgment processes, 11-30 to 11-34 jurors, 11-28 to 11-35 misinformation effect, 11-20 to 11-21 motion perception, 11-8 older drivers, 11-11, 11-12 own-age effect, 11-23 to 11-24 perception, 11-4 to 11-11, 11-16 to 11-17 peripheral vision, 11-9 to 11-10 processing speed, 11-10 to 11-11 retention failure, 11-18 retrieval, 11-18 to 11-27, 11-24 to 11-27 schematic processing, 11-31 to 11-34 source confusion, 11-21 source monitoring, 11-19 to 11-27, 11-29 to 11-30 sources of declines, 11-2 to 11-4 stereotypes, 11-14 to 11-15 therapeutic process, 11-21 victims, 11-16 to 11-27 vision, 11-6 to 11-10 vision acuity, 11-7 to 11-8 visual search, 11-9
Index
962
visuospatial processing, 11-16 to 11-17 voice perception, 11-27 witnesses, 11-16 to 11-27 working memory, 11-11 to 11-12 Age-appropriate thinking, 35-3 Age-related factors adolescents, 35-3 to 35-4, 35-7 to 35-8 basics, 35-1 to 35-2 checklist, 35-10 examples, 35-5 to 35-9 preschoolers, 35-2 to 35-3, 35-6 to 35-7 principal issues, 35-2 seniors, 35-4 to 35-5, 35-8 to 35 Alcohol and drugs alcohol, 13-44 to 13-54, 13-50 assessment, drug impairment, 13-45 to 13-48 basics, 13-53 to 13-55 benzodiazepines, 13-51 cannabis, 13-48, 13-52 to 13-53 checklist, 13-55 to 13-57 commercial motor vehicle collisions, 17-9 current evidence, 13-49 to 13-53 depressants, 13-48, 13-50 to 13-52 drugs, 13-44 to 13-54 hallucinogens, 13-48, 13-52 to 13-53 impairment, 13-50 to 13-52 LSD, 13-48, 13-53 mescaline, 13-48, 13-53 motorcycle collisions, 18-4 to 18-5 narcotics, 13-51 pedestrian accidents, traffic, 16-6 to 16-7 psilocybin, 13-48, 13-53 risk of collision involvement, 13-50 to 13-52 stimulants, 13-48, 13-52 therapeutic categorization, 13-48 Alexander v. Midland Bank PLC , 10-16 Allison v. McGhan Medical Corporation , 7-2 Alpha Gym, 24-7 to 24-8 Alsop v. Sheffield City Council , 10-16 Alternative facilities, lighting, 15-10 to 15-11 Alzheimer’s disease, 11-2 Ambient environment, 1-8 Ambient vision, 15-6 Ambiguity, pedestrian injuries, 15-8 Ambulance driver crash, 34-8 American slip meter, 20-10 Americans with Disabilities Act (ADA, see Preplacement strength and capacity assessment Amphetamines, 13-48, 13-52 Analogies, 2-5 Analysis, “road map,” 5-4, 5-9, 5-10 to 5-11, 5-11 to 5-15 Analytical process steps, crashes, 13-27 to 13-28 Andrews v. City of Philadelphia , 36-4
Index
963
Anthropometries, 28-4, see also specific type of injury Anxiety, memory effect, 12-4 to 12-5 A-pillar, 15-16 Approaching-turn collisions, 18-10 to 18-11 Appropriate care, health care, 37-6 to 37-7 Area lighting, 15-11 “Arising out of,” 9-4 Asian standards, 1-16 Askren studies, 5-1 to 5-15 Assessment, drug impairment, 13-45 to 13-48 Assumptions, warning expert, 30-8 Attention age and functioning, 11-17 to 11-18 commercial motor vehicle collisions, 17-2 driver response time, 14-2 to 14-5 encoding, 11-25 memory, 12-2 to 12-5 pedestrian falls, 19-7 Attention maintenance, consumer product warnings, 31-6 to 31-7 Attention switch, consumer product warnings, 31-6 Attitudes, consumer product warnings, 31-7 to 31-8 Attorney’s qualities, 4-2 to 4-4 Auditory factors, 13-17 to 13-18, 28-4, see also Human-centric approach (HCA), system liability Australian standards, 1-16 Available data not noticed, 8-5 to 8-6 Aviation example, 6-20 to 6-21 Avoidance of accident, 8-4 B Backing-type crashes, 13-21 Bakken studies, 28-1 to 28-19 Balcony falls balcony issues, 21-2 balustrades, 21-5 to 21-6 Barbados, 21-8, 21-10 to 21-12 basics, 21-1 to 21-2, 21-2, 21-13 British regulations, 21-9 center of gravity, 21-2 to 21-4 checklist, 21-13 to 21-14 codes of practice, 21-6 to 21-9 contributing factors, 21-6 Crete, 21-12 to 21-13 European regulations, 21-8 examples, 21-9 to 21-13 guard rails, 21-5 to 21-6 handrails, 21-5 to 21-6 height of fall, 21-5 Ibiza, 21-12 injury severity, 21-5 legislation, 21-6 to 21-9
Index
964
London, 21-9, 21-9 to 21-10 moments of inertia, 21-2 to 21-4 principle issues, 21-2 to 21-9 standards, 21-6 to 21-9 U.K. regulations, 21-7 U.S. regulations, 21-7 to 21-8 Ward v Ritz Hotel (London) Limited , 21-9 to 21-10 Balustrades, 21-1, 21-5 to 21-6 Bankstown Foundry Pty Ltd. v. Braistini , 10-4 Barbados, 21-8, 21-10 to 21-12 Barriers, 21-1, 26-4, see also Balcony falls Bath Iron Works v. Director, Office of Workers’ Compensation Programs , 9-3 Behavior, see also Accidental injury prevention breaks, 34-8 consumer product warnings, 31-8 expectations, 26-5 to 26-6 pedestrian accidents, traffic, 16-3 to 16-4 pedestrian injuries, 15-11, 15-13 to 15-14 product liability, 26-7 reconstructed situated performance, 8-5 to 8-6 Behavioral science data basics, 3-1 to 3-2, 3-8 Daubert-Joiner-Kumho trilogy, 3-5 to 3-7 evidence, 3-3 expert witnesses, qualifying, 3-7 Federal Rules of Evidence, 3-3 to 3-5 FRE Rules, 3-3 to 3-5 Frye v. United States , 3-2 Jenkins v. United States , 3-3 presentation, 3-7 to 3-8 psychological theory and data, 3-7 validity, 3-8 Behavioral sequences, reconstructing, 8-7 to 8-13 Being current, warning expert, 30-12 Beliefs, consumer product warnings, 31-7 to 31 Benzodiazepines, 13-51 Beta Center, 24-8 to 24-9 Bias in interpretation, 11-18 Bicycle crashes, see Pedestrians and bicycle crashes Biomechanical capabilities, 28-7, see also Pedestrian falls, perceptual-cognitive and biomechanical factors Biorhythm, 34-6 to 34-7, see also Circadian rhythm Blame, safe practices training, 6-3 Bolton v. Stone , 10-5 Boundaries, lighting, 15-10 to 15-11 Boundaries, warning expert, 30-12 Brakes, 14-1, 18-7 Breach, statutory duty, 10-10 Breach of warranty, 27-2 to 27-3 Breaks during work, 23-7 Bricio studies, 9-1 to 9-9
Index
965
British regulations, 21-9 Bronstein studies, 2-1 to 2-7 Brungraber, Mk II, 20-12 Burke studies, 6-1 to 6-25 Burns v. McGregor , 36-4 Busses, see Commercial motor vehicle (CMV) collisions Bux v. Slough Metals Limited , 10-10 C Cadger v. Vauxhall Motors , 10-13 Caffeine, 13-48, 13-52 Camouflaged tread nosings, 20-13 Cannabis, 13-48, 13-52 to 13-53 Capabilities of humans, 17-4 Capacity (workload), 18-6 to 18-7 Cardiac catheterization, 37-10 to 37-12 Cardiopulmonary system, 28-5, see also Human-centric approach (HCA), system liability Cardiovascular system, 28-5, see also Human-centric approach (HCA), system liability Car following, 14-15 14-16 Carpal tunnel syndrome (CTS), 23-3, see also Upper limb disorders (ULDs) Carpeted stairs, 20-17 to 20-18 Car-truck collision example, 13-9 to 13-10 Cartwright v. G-K-N- Sankey Ltd. , 10-4 Cases closure, 4-10 initiation, 5-2 to 5-3, 5-8, 5-9 to 5-10 presentation, 4-10 Case studies and examples accidental injury prevention, 25-8 to 25-13 age-related factors, 35-5 to 35-9 balcony falls, 21-9 to 21-13 commercial motor vehicle collisions, 17-15 to 17-18 exercise injuries, 24-6 to 24-11 health care, 37-10 to 37-12 human-centric approach, 28-12 to 28-14 legibility of color warnings, 32-4 to 32-13 pedestrian falls, 19-11 to 19-18 pedestrian injuries, 15-17 to 15-19 pedestrians and bicycle crashes, 13-28 to 13-31 preplacement strength and capacity assessment, 22-4 to 22-5 product liability experts, 26-6 to 26-9 reconstructed situated performance, 8-13 to 8-16 “road map” for practice, 5-8 to 5-11 safe practices training, 6-20 to 6-21 sexual harassment, 36-6 to 36-8 shiftwork, 34-8 to 34-9 traffic crashes, 13-9 to 13-10 worker’s compensation causation issues, 9-7 to 9-8 work-related musculoskeletal disorders (U.K.), 10-16 to 10-18, 10-20 to 10-21
Index
966
Casual analyses, 13-26 to 13-27 Caswell v. Powell Duffryn Associated Collieries Lit- , 10-17 Categories, humans, 28-7 Causation issues products liability law, 27-8 warning expert, 30-9 to 30-10 work-related musculoskeletal disorders (UK.), 10-3 Causation issues, worker’s compensation basics, 9-1 causation, 9-4 to 9-5 checklist, 9-8 to 9-9 discussion of principal issues, 9-2 to 9-7 disease, 9-2 to 9-4 ergonomic principles, 9-5 example, 9-7 to 9-8 experts, 9-5 to 9-7 historical perspectives, 9-2 injury, 9-2 to 9-4 CDL licensing system, 17-3 to 17-5 Center of gravity (CG or COG) balcony falls, 21-2 to 21-4 pedestrian falls, 19-2 Cerebral catheterization, 37-10 to 37-12 Cervical spondylosis, 23-5 CG, see Center of gravity (CG or COG) Changes, upper limb disorders, 23-11 to 23-12 Channel, consumer product warnings, 31-4 to 31-5 Checklists accidental injury prevention, 25-14 age and functioning, 11-35 to 11-36 age-related factors, 35-10 alcohol and drugs, 13-55 to 13-57 balcony falls, 21-13 to 21-14 commercial motor vehicle collisions, 17-18 exercise injuries, 24-19 to 24-20 human-centric approach, 28-15 to 28-17 motorcycle collisions, 18-16 pedestrian falls, 19-18 to 19-19 pedestrian falls, measurement, 20-24 pedestrian injuries, 15-19 to 15-21 preplacement strength and capacity assessment, 22-5 product liability experts, 26-10 reconstructed situated performance, 8-16 to 8-17 “road map” for practice, 5-11 safe practices training, 6-22 to 6-23 sexual harassment, 36-8 shiftwork, 34-9, 34-10 to 34-11 upper limb disorders, 23-19 to 23-20 worker’s compensation causation issues, 9-8 to 9-9 work-related musculoskeletal disorders (U.K.), 10-18 to 10-19 Cherry picking, 8-3 to 8-4 Child pedestrians, 16-7 to 16-8,
Index
967
see also Adolescents; Preschoolers C-HIP, see Communication-human information processing (C-HIP) model Choices, pedestrian injuries, 15-13, 15-14 to 15-15 Chronic exposures, 34-5 to 34-6, 34-7 Chronic fatigue syndrome, 34-7 Circadian rhythm, see also Biorhythm age and functioning, 11-13 commercial motor vehicle collisions, 17-2, 17-7 shiftwork, 34-6 to 34-7 Citations, pedestrian injuries, 15-17 Claims, health care, 37-6 Clay v Ford Motor Co- , 27-5, 27-8 Clear language, products liability law, 27-8 to 27-9 Client consultation, pedestrian falls, 19-7 to 19-8 Clifford v. Charles H- Challen and Son Ltd. , 10-7 Clothing, 2-6, 15-14 to 15-15 CMV, see Commercial motor vehicle (CMV) collisions Cocaine, 13-48, 13-52 Codes and laws, 19-9 Codes of practice, 21-6 to 21-9 Coefficient of friction (COF), 19-8, 20-9 COF, see Coefficient of friction (COF) COG, see Center of gravity (CG or COG) Cognitive factors, see also Physical and cognitive factors health care forensic, 37-6 human-centric approach, 28-6 pedestrian injuries, 15-13 safe practices training, 6-5 training, 6-18 Cohen studies, 19-1 to 19-20, 38-1 to 38-46 Cole v. De Trafford , 10-8 Colfar v. Coggins and Griffiths (Liverpool) Ltd. , 10-7 Collins v. Harker Heights , 6-20 Colloquial terms, 38-2 Color warnings, see also Warnings basics, 32-1 to 32-2 color, 32-2 to 32-3, 32-8, 32-14 to 32-15, distance threshold, 32-4, 32-7 to 32-8 examples, 32-4 to 32-13 graphics, 32-9 to 32-10, 32-12 to 32-13 issues, 32-2 to 32-4 measuring legibility, 32-2 motorcycle collisions, 18-13 recommendations, 32-15 retinal image, 32-3 to 32-4 standards, 32-13 to 32-14 tobacco warnings-1991, 32-2 to 32-7 tobacco warnings-1999 (revised), 32-10 to 32-13 Commercial motor vehicle (CMV) collisions alcohol equivalence, 17-9
Index
968
attention, 17-2 basics, 17-1, 17-2, 17-3 capabilities of humans, 17-4 CDL licensing system, 17-3 to 17-5 checklist, 17-18 circadian rhythms, 17-2 cumulative fatigue, 17-7 to 17-9 decision-making, 17-2 driver errors, 17-10 examples, 17-15 to 17-18 expert opinions, organization and communication, 17-15 fatigue, 17-2, 17-6 to 17-9 findings, organization and communication, 17-15 forensic analysis, 17-9 to 17-15 foundations, 17-3 to 17-9 hours-of-service regulations, 17-6 to 17-9 irregular schedules, 17-7 to 17-9 knowledge requirements and tests, 17-2, 17-5 limitations of humans, 17-4 Model Driver’s Manual , 17-4 to 17-5 motor response, 17-2 muscular reaction, 17-2 operational requirements, 17-3 to 17-4 perception, 17-2 personnel selection, 17-2 skill requirements and tests, 17-2, 17-5 standard of care, 17-12 to 17-14 tests, 17-5 time-of-day effects, 17-7 training, 17-2 vehicle groups, 17-3 work-rest history, 17-10 to 17-12 Communication-human information processing (CHIP) model, 31-2 to 31-8 Competence, 4-4 to 4-6, 15-7 Complexity, health care, 37-4, 37-5 to 37-6 Compliance, 25-6, 37-6 Comprehension, consumer product warnings, 31-7 Compress, heating, 26-8 to 26-9 Computational analysis, traffic crashes, 13-8 to 13-9 Computer equipment, see Upper limb disorders (ULDs) Concealed targets, 13-25 Conceptual description, 8-11 to 8-13 Conduct of pedestrian, 15-16 to 15-17 Confidentiality, expert witnesses, 4-7 Conflict, practice and management, 37-6 Conflict of interest, expert witnesses, 4-2 Consensus, 37-5 Consistency, warning expert, 30-12 Conspicuity motorcycle collisions, 18-12 to 18-13 pedestrians and bicycle crashes, 13-24 to 13-25 Constraints, health care, 37-5
Index
969
Construction, positive guidance principles, 13-40 Construction zones pedestrian accidents, traffic, 16-13 traffic crashes, 13-42 to 13-44 Consultative stage, expert witnesses, 4-6 to 4-10 Consumer product accidents, 5-12 to 5-13 Consumer Product Safety Act, 25-3 to 25-4 Consumer Product Safety Commission (CPSC) pedestrian injuries, 16-14 riding mower case study, 25-8 to 25-13 Consumer product warnings, see also Warnings attention maintenance, 31-6 to 31-7 attention switch, 31-6 attitudes, 31-7 to 31-8 basics, 31-1 to 31-2, 31-9 behavior, 31-8 beliefs, 31-7 to 31-8 channel, 31-4 to 31-5 C-HIP model, 31-2 to 31-8 comprehension, 31-7 motivation, 31-8 receiver, 31-5 to 31-8 source, 31-4 Content, memory, 12-8 to 12-9, 12-9 to 12-10 Context, memory, 12-6, 12-22 Context-specific language, 8-8 to 8-9 Contingency fees, 4-6 Contributions, memory for conversation, 12-10 to 12-11 Contributory negligence, 10-6 Control, 13-33, 37-5 Conversation, see Memory for conversation Coronal plane, 21-3 Corpus callosum, 11-3 Corrective action, 25-7 Cost of compliance, 26-5 Courtroom behavior, 2-5 to 2-6 Courtroom testimony, see Testimony Court’s judgment, warning expert, 30-5 Crashes, 34-8, see also Commercial motor vehicle (CMV) collisions; Motorcycle collisions; Pedestrians and bicycle crashes Credentials, witnesses, see Expert witnesses; Qualifications, warning expert Crete, balcony fall, 21-12 to 21-13 Critical incidents technique, 6-17 Cross-examination, 2-6 to 2-7 Crosswallks, 15-10, 15-15, see also Pedestrian accidents, traffic Cryptomnesia, 12-15 to 12-16 CTS, see Carpal tunnel syndrome (CTS)
Index
970
Culture, safe practices training, 6-16 Cumulative fatigue, 17-7 to 17-9 Cumulative sleep loss, 17-8, 34-6 Cumulative trauma disorder, see Upper limb disorders (ULDs) Current evidence, 13-49 to 13-53 D Darkness, 15-8 to 15-9, 15-15, see also Nighttime conditions Dartout-type crashes, 13-21 Data, product liability experts, 26-3 to 26-4 Data-gathering, expert witnesses, 4-6 to 4-10 Data not noticed, 8-5 to 8-6 Data sharing, 25-7 Daubert v. Merrell Dow Pharmaceuticals affirmative role of experts, 7-5 to 7-6 basics, 7-1, 7-10 to 7-11 behavioral science data, 3-5 to 3-7 evidence preparation and presentation, 2-1 experts, 7-5 to 7-10 Federal Rules of Evidence, 7-2 to 7-4 Frye , 7-2 to 7-4 impact, 7-4 to 7-5 misapplication of literature, 7-8 to 7-9 mischaracterization of literature, 7-7 to 7-8 misinterpretation of findings, 7-10 outside area of expertise, testimony, 7-9 rationale, 7-1 to 7-2 rebuttal role of experts, 7-6 to 7-10 Davidson v. Handley Page Limited , 10-8 Davis studies, 11-1 to 11-37, 12-1 to 12-23 Day shift, 34-8, see also Shiftwork Decision-making age and functioning, 11-30 to 11-34 commercial motor vehicle collisions, 17-2 human-centric approach, 28-6 pedestrian falls, 19-6 to 19-7 Defects, 27-2, 27-4 to 27-6, 29-3 Defenses, health care, 37-8 to 37-9 Definitions, 38-1 to 38-46, 38-2 Dekker studies, 8-1 to 8-18 Demonstrations, evidence, 2-1 to 2-2 Dempsey studies, 22-1 to 22-5 Deposition testimony “road map” for practice, 5-5 to 5-6, 5-9, 5-11 warning expert, 30-10 to 30-11 Depressants, 13-48, 13-50 to 13-52 Design accident analysis model, 5-12 to 5-14 defects, products liability law, 27-5 to 27-6 positive guidance principles, 13-40
Index
971
product liability, 29-5 Design activity analysis, 1-13 to 1-14 Designers, product liability, 29-4 to 29-6 DETECT computer program, 14-6 Devereux studies, 10-1 to 10-19 Dewar studies, 16-1 to 16-15 Differential source monitoring, 12-14 to 12-15 Digestive system, 28-5, see also Human-centric approach (HCA), system liability Dillingham v. Yeargin Construction Co- , 9-3 Disease human-centric approach, 28-8 worker’s compensation causation issues, 9-2 to 9-4 Display screen equipment, 10-13 to 10-15, see also Visual display units (VDUs) Distance threshold, 32-4, 32-7 to 32-8 Documentation accidental injury prevention, 25-6 to 25-7 health care, 37-9 to 37-10 product liability, 29-4 Driver errors, 17-10 Driver response time, estimating attention, 14-2 to 14-5 basics, 14-1 to 14-2, 14-18 to 14-19 car following, 14-15 to 14-16 gaps in traffic, 14-14 green traffic signals, 14-14 inattention, 14-2 to 14-5 limb movement, 14-16 to 14-18 objects not easily identified, 14-5 to 14-7 operationalization of terms, 14-24 to 14-25 path intrusions, 14-14 to 14-15 perception-response time, 14-10 to 14-16 previous results, research methods, 14-8 to 14-10 rule of thumb estimates, 14-14 transition time, 14-16 to 14-18 urgency, 14-16 vehicle latency, 14-16 to 14-18 vehicles changing lanes, 14-14 Drivers, traffic crashes, 13-3 to 13-19 Driving environments commercial motor vehicle collisions, 17-1 to 17-19 motorcycle collisions, 18-1 to 18-16 pedestrians, 15-1 to 15-21, 16-1 to 16-15 response time estimation, 14-1 to 14-19 traffic crashes, human factors, 13-1 to 13-57 DRM paradigm, 11-21 Drugs, 35-5, see also Alcohol and drugs Dunton v. County of Suffolk , 6-3 Dupuytren’s contracture, 23-3
Index
972
Duty of employer, 10-6 to 10-10 Dynamic coefficient of friction, 20-9 E Earwitness identification, 11-27 Ecological approach, behavioral reconstruction sequence, 8-8 Education, professionals, 1-4 Edwards v. National Coal Board , 10-5 Egregious conduct, 9-2 Elderly pedestrians, 16-8 to 16-9, see also Age and functioning; Age-related factors; Seniors Electronic level, measurement, 20-8 Elevation changes, 19-15 Ellison v. Brady , 36-4 Emotion, memory, 12-4 to 12-5 Empirical study, pedestrian falls, 19-10 to 19-11 Employee responsibilities, sexual harassment, 36-6 Employer-determined irregular hours, 34-7 Encoding age and functioning, 11-17 to 11-18, 11-24 to 11-27 memory, 12-2 to 12-8 Energy of walking, 19-4 to 19-5 Enforcement, pedestrian injuries, 15-11 Engineering, human-centric approach, 28-20 to 28-21 Engineering experts, see Products liability law Engineering impact, products liability law, 27-6 to 27-9 Environment human-centric approach, 28-8 to 28-9 human factors and ergonomics, 1-8 Epicondylitis, 23-4 Episodes, creating, 8-9 to 8-10 Episodic memory, 11-3 Equipment, 10-8, 28-9 Ergonomics upper limb disorders, 23-14 to 23-16 worker’s compensation causation issues, 9-5 Errors reconstructed situated performance, 8-16 to 8-17 reporting, 6-17 to 6-18 safe practices training, 6-8 to 6-9 Estimating time, 11-16 Ethics, expert witnesses access to expert, 4-6 to 4-7 attorney’s qualities, 4-2 to 4-4 basics, 4-1 case closure, 4-10 case presentation, 4-10 competence, 4-4 to 4-6 confidentiality, 4-7 conflict of interest, 4-2 consultative stage, 4-6 to 4-10
Index
973
data-gathering, 4-6 to 4-10 expertise, 4-4 to 4-6 forensic referral acceptance, 4-1 to 4-6 information, obtaining, 4-9 junk science, 4-8 to 4-9 legal knowledge, 4-5 to 4-6 money matters, 4-6 personal skills, 4-4 pretrial meetings, 4-9 to 4-10 privacy, 4-7 privilege, 4-7 to 4-8 record keeping, 4-9 research, conducting, 4-9 standards of practice, 4-5 testifying, 4-10 time table and scheduling, 4-8 warning expert, 30-11 Ethics, language, 2-5 European standards and regulations, 1-15 to 1-16, 21-8 European Union directives, 10-15 Evaluation of training, 6-11 to 6-14 Evasive maneuvers, 15-13 Event rate, 18-10 Evidence, behavioral science data, 3-3 Evidence, preparation and presentation basics, 2-1, 2-7 courtroom behavior, 2-5 to 2-6 cross-examination, 2-6 to 2-7 demonstrations, 2-1 to 2-2 exhibits, 2-1 to 2-2 expert witness role, 2-4 to 2-5 language usage, 2-5 learned treatises, 2-2 to 2-3 testimony organization, 2-3 to 2-4 Exact content, memory, 12-9 to 12-10 Examples, see Case studies and examples Excusing vs. explaining, 8-12 to 8-13 Exercise-ergonomic dichotomy, 24-5 to 24-6 Exercise injuries Alpha Gym, 24-7 to 24-8 basics, 24-1 to 24-2, 24-14 Beta Center, 24-8 to 24-9 case studies, 24-6 to 24-11 checklist, 24-19 to 24-20 emergent standard of practice theme, 24-10 to 24-11 exercise-ergonomic dichotomy, 24-5 to 24-6 fitness industry overview, 24-2 to 24-3 Gamma Studio, 24-9 to 24-10 human factors/ergonomics approach, 24-13 legal context, 24-3 to 24-5 safe practice model, 24-11 to 24-14, 24-19 to 24-20 standards of care, 24-6 to 24-11
Index
974
Exhibits, evidence, 2-1 to 2-2 Exit ramps, 13-35, see also Ramps Expectancy mother/doctor example, 12-7 positive guidance principles, 13-34 to 13-37 traffic crashes, 13-12 to 13-13 training, 6-18 Experience, see “Road map” for practice Expert witnesses, see also Product liability experts; Warning experts affirmative role of experts, 7-5 to 7-6 commercial motor vehicle collisions, 17-15 discrediting, 38-3 to 38-4 ergonomics, 23-14 to 23-16 legal terms, 38-3 outside area of expertise, 7-9 qualifying, behavioral science data, 3-7 rebuttal role of experts, 7-6 to 7-10 role, evidence, 2-4 to 2-5 worker’s compensation causation issues, 9-5 to 9-7 Expert witnesses, Daubert influence affirmative role of experts, 7-5 to 7-6 basics, 7-1, 7-10 to 7-11 experts, 7-5 to 7-10 Federal Rules of Evidence, 7-2 to 7-4 Frye , 7-2 to 7-4 impact, 7-4 to 7-5 misapplication of literature, 7-8 to 7-9 mischaracterization of literature, 7-7 to 7-8 misinterpretation of findings, 7-10 outside area of expertise, testimony, 7-9 rationale, 7-1 to 7-2 rebuttal role of experts, 7-6 to 7-10 Expert witnesses, ethics access to expert, 4-6 to 4-7 attorney’s qualities, 4-2 to 4-4 basics, 4-1 case closure, 4-10 case presentation, 4-10 competence, 4-4 to 4-6 confidentiality, 4-7 conflict of interest, 4-2 consultative stage, 4-6 to 4-10 data-gathering, 4-6 to 4-10 expertise, 4-4 to 4-6 forensic referral acceptance, 4-1 to 4-6 information, obtaining, 4-9 junk science, 4-8 to 4-9 legal knowledge, 4-5 to 4-6 money matters, 4-6
Index
975
personal skills, 4-4 pretrial meetings, 4-9 to 4-10 privacy, 4-7 privilege, 4-7 to 4-8 record keeping, 4-9 research, conducting, 4-9 standards of practice, 4-5 testifying, 4-10 time table and scheduling, 4-8 Explaining behavior and performance, 8-5 to 8-6 Explaining vs. excusing, 8-12 to 8-13 Express warranty, product liability, 29-2 External factors, safe practices training, 6-14 to 6-20 Eye movements, 15-6 Eyewitness identification, 11-22 to 11-27 F Face perception, 11-22 to 11-27 Facets of humans, 28-8 to 28-9 Facility issues, 15-9 to 15-11 Fact of the conversation, 12-8 Falls, 5-14, 20-3, see also Balcony falls; Pedestrian falls, perceptual-cognitive and biomechanical factors Farm equipment, 5-9 to 5-11 Farm laborer, 9-7 to 9-8 Fatigue, see also Sleep disturbance and deprivation commercial motor vehicle collisions, 17-1 to 17-2, 17-6 to 17-9 shiftwork, 34-7 Federal Rules of Evidence (FRE) behavioral science data, 3-3 to 3-5 Daubert v. Merrell Dow Pharmaceuticals , 7-2 to 7-4 Rule 403, 30-3 Rule 701, 3-3 to 3-4 Rule 702, 3-4, 7-6, 7-8, 30-3, 30-4 Rule 703, 3-4, 30-3 Rule 704, 3-4 Rule 705, 3-4 Rule 706, 3-5 Field research, 34-6 Findings commercial motor vehicle collisions, 17-15 misinterpretation, 7-10 “road map” for practice, 5-4, 5-9, 5-10 to 5-11, 5-11 to 5-15 Finger-pull slipmeter, 20-10 Fitness facilities, see Exercise injuries Fitness industry overview, 24-2 to 24-3 Fixed objects, positive guidance principles, 13-38 Flextime, 34-7 Focal vision, pedestrian injuries, 15-6
Index
976
Follette studies, 12-1 to 12-23 Force, upper limb disorders, 23-8 to 23-9 Forces of movement, 19-3 to 19-4 Foreseeability engineering experts, 27-5 pedestrian falls, 19-15 product liability, 26-1, 29-5 work-related musculoskeletal disorders (U.K.), 10-3 Foster v. British Gas PLC , 10-15 Foundations, commercial motor vehicle collisions, 17-3 to 17-9 Franklin v. Gramophone Company Limited , 10-10 FRE, see Federal Rules of Evidence (FRE) Frontal lobes, 11-3 Front-end vehicle design, 15-16 Front plane, 21-3 “Frozen” shoulder, 23-4 to 23-5 Frye v. United States , 3-2, 7-2 to 7-4 Functional limits, 18-10 Function/event sequence, 13-20 G Gait cycle, 19-3, 19-5 Galley studies, 21-1 to 21-15 Gamma Studio, 24-9 to 24-10 Ganglion, 23-5 Gaps in traffic, 14-14 Garcia v. Hartland and Wolfe Limited , 10-8 Gender, motorcycle collisions, 18-3 to 18-4 General Cleaning Contractors Ltd. v. Christmas , 10-7 General Electric Co- v. Joiner , 3-3, 3-5 to 3-7 Gilligan v. Morgan , 6-20 Ginsburg, Ruth Bader, 12-13 Glare, see also Headlights pedestrian injuries, 15-16, 16-10 to 16-11 traffic crashes, 13-7 to 13-8 Glasgow Corporation v. Muir , 10-3 Glossary, 38-1 to 38-46 Goals ergonomics, 1-9 to 1-11 reconstructed situated performance, 8-10 to 8-11 training, 6-18 Government standards, 27-7, see also Standards Graphics, color warnings, 32-9 to 32-10, 32-12 to 32-13 Green traffic signals, 14-14 Green v. Smith & Nephew AHP, Inc- , 27-4, 27-5 to 27-6 Grossly negligent conduct, 9-2 Guard, accident analysis model, 5-12 to 5-14 Guarding against hazards, 26-8 to 26-9 Guard rails, 21-5 to 21-6 Guidance, see Positive guidance principles;
Index
977
“Road map” for practice H Hallucinogens, 13-48, 13-52 to 13-53 Hancock studies, 18-1 to 18-16 Handicapped pedestrians, 16-9 Handicap work schedule accommodation, 34-8 Handrails balcony falls, 21-5 to 21-6 pedestrian falls, measurement, 20-19 to 20-20 Hardware, health care, 37-8 Harris v. Forklift Systems , 36-4 Hats (white), 15-17 Hawkes v. London Borough of Southwark , 10-15, 10-13 Hayes v. Pilkington Glass Limited , 10-4 Hazard control hierarchy, 26-4 to 26-6 Hazards, see also Accidental injury prevention elimination, 31-1 examples, 28-12 to 28-14 positive guidance principles, 13-37 to 13-40 HCA, see Human-centric approach (HCA), system liability Headlights, see also Glare HID type, 15-16 pedestrian injuries, 15-5, 15-11, 15-12 traffic crashes, 13-3, 13-4 to 13-5 Health care forensics abilities, humans, 37-12 adverse event investigation, 37-5 appropriate care, 37-6 to 37-7 basics, 37-1 to 37-3, 37-15 cardiac and cerebral catheterization, 37-10 to 37-12 complexity, 37-4 constraints, 37-5 control, 37-5 defenses, 37-8 to 37-9 documentation, 37-9 to 37-10 examples, 37-10 to 37-12 hardware, 37-8 incidence, 37-12 to 37-13 individual error model, 37-2 latent failure model, 37-2 limitations, humans, 37-12 main factors, 37-12 to 37-15 prevention/audit, 37-13 to 37-14 principal issues, 37-3 to 37-10 process, 37-14 to 37-15 remedies, 37-2 to 37-3 safety methods, 37-8 to 37-9 software, 37-8 standards of care, 37-5 to 37-6
Index
978
uncertainty, 37-4 Health issues, shiftwork, 34-3 to 34-4 “Healthy worker effect,” 34-4 Hearing, age and functioning, 11-4 to 11-6 Heat stress, 9-5 Height, trip hazards, 20-3 to 20-4 Helander studies, 1-1 to 1-16 Helmet usage, motorcycle collisions, 18-5 to 18-6 Hely studies, 24-1 to 24-16 Hess studies, 3-1 to 3-8, 4-1 to 4-10 Hewett v. Alf Brown’s Transport Limited , 10-10 HFE, see Human factors and ergonomics (HFE) High-beam headlights pedestrian injuries, 15-12 traffic crashes, 13-3 Highway conditions, positive guidance principles, 13-38 Hindsight bias memory, 12-21 reconstructed situated performance, 8-2, 8-3 to 8-7 Historical developments and perspectives human factors and ergonomics, 1-1 to 1-6 worker’s compensation causation issues, 9-2 Hobscheid studies, 27-1 to 27-9 Horizontal pull slipmeter, 20-9 to 20-10 Horizontal (transverse) planes, 21-3 Hormonal system, 28-5, see also Human-centric approach (HCA), system liability Hormone replacement therapy, 11-30 Hormone replacement therapy, example, 11-30 Horst studies, 38-1 to 38-46 Hours-of-service regulations, 17-6 to 17-9 Howard studies, 5-1 to 5-15 Hudson v. Ridge Manufacturing Company Ltd. , 10-6 Human-centric approach (HCA) capabilities of humans, 28-3 to 28-7 categories, humans, 28-7 facets of humans, 28-8 to 28-9 Human-centric approach (HCA), system liability basics, 28-1 to 28-3 checklist, 28-15 to 28-17 environment, 28-10 to 28-12 examples, 28-12 to 28-14 principal issues, 28-3 to 28-12 system safety engineering, 28-20 to 28-21 technology, 28-9 to 28-10 Human errors, see also Errors; Situated performance, reconstructing medical, 6-21, 37-2 product liability, 33-4 to 33-5 safe practices training, 6-2 to 6-3 Human factors and ergonomics (HFE)
Index
979
accident proneness, 1-3 Asian standards, 1-16 Australian standards, 1-16 basics, 1-1 to 1-2, 1-16 design activity analysis, 1-13 to 1-14 education, professionals, 1-4 effects of stress, 1-8 environment, 1-8 European standards, 1-15 to 1-16 exercise injuries, 24-1 goals, 1-9 to 1-11 historical developments, 1-1 to 1-6 International Ergonomics Association, 1-4 to 1-5 international proliferation, 1-3 to 1-4 International Standards Organization, 1-14 to 1-15 machine subsystem, 1-9 measurement problem, 1-11 to 1-12 methods, measurements, and procedures, 1-11 to 1-12 modulating variables, 1-7 to 1-8 New Zealand standards, 1-16 operator satisfaction, 1-10 to 1-11 productivity goal, 1-10 productivity/safety trade-off, 1-10 safety goal, 1-9 standards, 1-14 to 1-16 systems approach, 1-6 to 1-9 Taylorism, 1-3 United States standards, 1-15 Human factors applications age-related factors, 35-1 to 35-10 health care, 37-1 to 37-16 sexual harassment, 36-1 to 36-9 shiftwork, 34-1 to 34-13 Human factors approach and perspective, 18-13 to 18-15, 33-4 Human factors/ergonomics approach, 24-13 Human factors practitioners, 29-4 to 29-6, see also Expert witnesses; Product liability Human performance, legal context age and functioning, 11-1 to 11-37 causation, worker’s compensation, 9-1 to 9-9 memory, 12-1 to 12-23 reconstructing situated performance, 8-1 to 8-18 work-related musculoskeletal disorders, 10-1 to 10-19 I Ibiza, balcony fall, 21-12 Ice cream vendor crashes, 13-23, 13-28 to 13-31 Identifiable changes, walking surface, 19-13 Identifying risks, accidental injury prevention, 25-5 to 25-6 IEA, see International Ergonomics Association (IEA) Illusion of control, 18-7 Immune system, 28-5,
Index
980
see also Human-centric approach (HCA), system liability Impairment, alcohol and drugs, 13-50 to 13-52 Implied warranty, 29-2 Inattention driver response time, 14-2 to 14-5 pedestrian falls, measurement, 20-13 to 20-14 IN CAR CREED, 14-2 to 14-4 Incidence, health care, 37-12 to 37-13 Inclinometer method, 20-8 Increased risk doctrine, 9-5 Individual employee responsibilities, sexual harassment, 36-6 Individual error model, 37-2 Individuals, see also Person analysis focus of attention, 8-10 to 8-11 goals, 8-10 to 8-11 knowledge active/available, 8-10 to 8-11 safe practices training, 6-18 Industrial example, safe practices training, 6-20 Industrial machine accidents, 5-13 to 5-14 Industry custom and practice, 19-10 Industry response, risk factors, 25-10 to 25-12 Industry standards, products liability law, 27-7 Inferential questions, 11-30 Inferred meaning, 12-9 to 12-10 Information age and functioning, 11-28 to 11-30 combining, age and functioning, 11-30 to 11-31 expert witnesses ethics, 4-9 gathering, age and functioning, 11-30 to 11-31 human-centric approach, 28-6 positive guidance principles, 13-34 review, 19-8 warning expert, 30-7 to 30-8 Information-processing model, 19-5 to 19-7 Informing parties, 15-9 to 15-10 Inhibitory functions, 11-3 to 11-4, 11-12 to 11-14 Initial contact, warning expert, 30-6 Injury, see also Accidental injury prevention; specific type human-centric approach, 28-8 severity, balcony falls, 21-5 worker’s compensation causation issues, 9-2 to 9-4 In-line skates, 16-13 to 16-14 Inside out perspective, 18-6 to 18-8 Instructional strategies, safe practices training, 6-6 to 6-10 Instructions defects, 27-6 Interactions, system liability, 28-1 Interfaces, system liability, 28-1 International Ergonomics Association (IEA), 1-4 to 1-5 International proliferation, 1-3 to 1-4
Index
981
International Standards Organization (ISO) human factors and ergonomics, 1-14 to 1-15 standards issued, 1-19 to 1-24 International trends, 29-3 to 29-4 Interpretation, memory, 12-5 to 12-8 Interpretation bias, 11-18 Interviewing procedures, 11-26 to 11-27 “In the course of employment,” 9-5 to 9-6 Irregular schedule and working hours, 17-7 to 17-9, 34-1, 34-7 Irregular stair geometry, 19-17 to 19-18 ISO, see International Standards Organization (ISO) J Jackson v. Deft, Inc- , 27-6 Jargon, 2-5 Jenkins v. United States , 3-3 Jensen studies, 9-1 to 9-9 Job analysis, safe practices training, 6-4 to 6-5 Job rotation, 23-8 Job tenure, 34-4 Johnson studies, 20-1 to 20-27, 38-1 to 38-46 Johnstone v. Bloomsbury Health Authority , 10-9 Joiner, see General Electric Co. v. Joiner Jones v. Livox Quarries Limited , 10-6 Joseph v. Ministry of Defence , 10-4 Judgment pedestrian falls, 19-11 pedestrian injuries, 15-14 processes, age and functioning, 11-30 to 11-34 reconstructed situated performance, 8-5 to 8-7 Junk science, 4-8 to 4-9, see also Pseudoscience Jurors, 11-28 to 11-35, see also Age and functioning K Kaiserman studies, 32-1 to 32-16 Keen and Nettlefold (Bolts and Nuts Ltd.) , 10-3 Kelley v. American Heyer-Schulte Corporation , 7-7 Kelly studies, 10-1 to 10-19 Kemmelmeier studies, 12-1 to 12-23 Keyboard (computer), see Upper limb disorders (ULDs) King v. RCO Support Services Limited , 10-13 King v. Sussex Ambulance NHS Trust , 10-15, 10-17 Knott v. Newham Health Care NHS Trust , 10-17 Knowledge commercial motor vehicle collisions, 17-2, 17-5 human-centric approach, 28-8 work-related musculoskeletal disorders (U.K.), 10-3 to 10-4 Knowledge active/available, 8-10 to 8-11 Known risks, 25-8 to 25-10
Index
982
Koonjul v. Thameslink Health Care Trust , 10-11, 10-16 Kumho Tire Company v. Carmichael , 3-5 to 3-7, 7-3, 7-5 Kurke studies, 33-1 to 33-9 L Laboratory research, shiftwork, 34-6 Landy studies, 7-1 to 7-11 Lane changes, 15-13 Language usage, evidence, 2-5 LaRue studies, 19-1 to 19-20 Latent failure model, 37-2 Latex allergy, 26-9 Laughery studies, 30-1 to 30-14, 31-1 to 31-9 Law and visibility, 13-18 to 13-19 Law enforcement example, 6-20 Learned treatises, 2-2 to 2-3 Learning phases, 6-13 to 6-14 Left-turn problem, 18-9 to 18-12 Legal analyses, pedestrians and bicycle crashes, 13-26 to 13-27 Legal context, exercise injuries, 24-3 to 24-5 Legal environment, product liability, 33-2 Legal issues, shiftwork, 34-3 Legal knowledge, expert witnesses, 4-5 to 4-6 Legal system, work-related musculoskeletal disorders (U.K.), 10-3 to 10-15 Legal theories, products liability law, 27-2 to 27-3, 27-7 Legibility of color warnings, see Color warnings Leukoaraiosis, 11-2 Level-and-ruler method, 20-7 Lighting human-centric approach, 28-12 pedestrian falls, measurement, 20-12 to 20-13 pedestrian injuries, 15-10 to 15-13 Lights (retroreflectors), 15-17 Limb movement, driver response time, 14-16 to 14-18 Limitations, commercial motor vehicle collisions, 17-4 Limitations, health care, 37-12 Line operations safety audit, 6-14 Lineup procedures, age and functioning, 11-25 to 11-26 Lipsett v. University of Puerto Rico , 36-4 Literature, misapplication, 7-8 to 7-9 Literature, mischaracterization, 7-7 to 7-8 Local-haul drivers, 7-8, see also Commercial motor vehicle (CMV) collisions Local rationality, 8-7 Locus of work schedule, 34-6 Loftus studies, 11-1 to 11-37 London (U.K.), balcony falls, 21-9, 21-9 to 21-10 Long-distance (long-haul) drivers, 7-8, see also Commercial motor vehicle (CMV) collisions Low-beam headlights pedestrian injuries, 15-11 traffic crashes, 13-4 to 13-5
Index
983
LSD, 13-48, 13-53 Lubricants, pedestrian falls, 20-12 M Machines, 1-9, 28-9 Macroergonomic principles, 1-8, 36-1 Magnetic compass, 20-22 Management and practice, conflict, 37-6 Management of Health and Safety at Work Regulations 1999, 10-10 to 10-11 Manual handling regulations, 10-11 to 10-13 Manual materials handling jobs, see Preplacement strength and capacity assessment Manufacturing defects, 27-4 to 27-5 Manufacturing practices, responsible, 25-4 to 25-7 Manufacturing workers, see Shiftwork Marjiuana, see Cannabis Marketing practices, responsible, 25-4 to 25-7 Marshal v. Gotham Company Limited , 10-10 Masters v. Hesston Corp. , 27-7 Materials handling jobs, see Preplacement strength and capacity assessment McCaffery v. Datta , 10-17 McCann v. J-R- McKeller (Alloys) Ltd. , 10-9 McKeown studies, 23-1 to 23-22 McPherson v. London Borough of Camden , 10-16 McQuilter v. Gouldandris Bros- Ltd. , 10-8 McSherry v. British Telecommunications PLC , 10-4, 10-9 Mearns v. Lothian Regional Council , 10-17 Measurements, 1-11 to 1-12 Median plane, 21-3 Medical equipment, plaintiff, 5-8 to 5-9 Medical example, safe practices training, 6-21 Memory consumer product warnings, 31-5 pedestrian falls, 19-6 pedestrian injuries, 15-14 Memory for conversation anxiety, 12-4 to 12-5 attention, 12-2 to 12-5 basics, 12-1 to 12-2, 12-22 to 12-23 content, 12-8 to 12-9, 12-9 to 12-10 context, 12-6, 12-22 contributions, 12-10 to 12-11 cryptomnesia, 12-15 to 12-16 differential source monitoring, 12-14 12-15 emotion, 12-4 to 12-5 encoding failures, 12-2 to 12-8 exact content, 12-9 to 12-10 fact of the conversation, 12-8 inferred meaning, 12-9 to 12-10 interpretation, 12-5 to 12-8 medium, 12-16 order, 12-20 to 12-21
Index
984
participants, 12-12 to 12-16, 12-21 perception, 12-2, 12-5 to 12-6 personal determinants, 12-8 reality monitoring, 12-18 to 12-19 retention, 12-8 to 12-22 schematic processing, 12-7 to 12-8, 12-13 to 12-14 social categorization, 12-12 to 12-13 source confusion, 12-12 to 12-13 source monitoring, 12-11 to 12-22 space, 12-19 to 12-20 speech features, 12-6 to 12-7 target, 12-16 to 12-18 time, 12-19 to 12-20 unconscious plagiarism, 12-15 to 12-16 varying conversational roles, 12-14 to 12-15 Meritor Savings Bank v. Vinson , 36-4 Mescaline, 13-48, 13-53 “Method of limits,” 32-5 Methods, measurements, and procedures, 1-11 to 1-12 Mexican farm laborer, 9-7 to 9-8 Microergonomic principles, 36-1 Microsoft Streets and Trips software, 17-12, 17-17 MICTO, see Model Ice Cream Truck Ordinance (MICTO) Midblock crossing, 15-15 Midblock rideout bicycle-type crashes, 13-21 Misapplication of literature, 7-8 to 7-9 Misattribution, 12-11 to 12-22 Mischaracterization of literature, 7-7 to 7-8 Misinformation effect, 11-20 to 11-21 Misinterpretation of findings, 7-10 Misrepresentation, product liability, 29-2 Missteps, 19-14 to 19-15 Model Driver’s Manual 17-4 to 17-5 Model Ice Cream Truck Ordinance (MICTO), 13-28 to 13-29 Modulating variables, 1-7 to 1-8 Moll studies, 27-1 to 27-9 Moments of inertia, 21-2 to 21-4 Monell v. Department of Social Services of the City of New York , 6-20 Money matters, expert witnesses, 4-6 Monitors (computer), see Upper limb disorders (ULDs) Moonlighting, 34-8, see also Fatigue Morbidity, 37-2 Morris v. West Hartlepool Steam Navigation Co- Ltd. , 10-5 Mortality, 37-2 Motion perception, 11-8 Motivation age and functioning, 11-34 consumer product warnings, 31-8 memory, 12-21 safe practices training, 6-5, 6-18 to 6-19 Motor carriers, 17-2, 17-12 to 17-14,
Index
985
see also Commercial motor vehicle (CMV) collisions Motorcycle collisions age, 18-3 to 18-4 alcohol, 18-4 to 18-5 analysis, 18-6 to 18-8 basics, 18-1 to 18-2, 18-15 to 18-16 capacity (workload), 18-6 to 18-7 checklist, 18-16 conspicuity, 18-12 to 18-13 gender, 18-3 to 18-4 helmet usage, 18-5 to 18-6 human factors approaches, 18-13 to 18-15 human factors issues, 26-6 to 26-7 inside out perspective, 18-6 to 18-8 left-turn problem, 18-9 to 18-12 outside in, 18-8 to 18-13 passive safety, 18-5 to 18-6 rider licensing, 18-5 riding demands, 18-6 to 18-7 risks, 18-7 to 18-8 scale of problem, 18-2 to 18-6 scope of problem, 18-2 to 18-6 size of motorcycle, 18-5 unfamiliar vehicle perception, 18-12 to 18-13 Motorcycle crashes, 13-15 to 13-16 Motor-pull slipmeter, 20-10 Motor response (muscular reaction), 17-2 Motor vehicle accidents, 5-13 Mouse (computer), see Upper limb disorders (ULDs) Mughal v. Reuters Litd- , 10-16 Mugshots, 11-26 Munrow v. Plymouth Health Authority , 10-8, 10-17 Muscular reaction, commercial motor vehicle collisions, 17-2 Musculoskeletal disorders (U.K.), work-related basics, 10-1 to 10-3 breach, statutory duty, 10-10 case law examples, 10-16 to 10-18 cases, 10-20 to 10-21 causation, 10-3 checklist, 10-18 to 10-19 consultation, 10-15 contributory negligence, 10-6 display screen equipment, 10-13 to 10-15 duty of employer, 10-6 to 10-10 equipment provision, 10-8 European Union directives, 10-15 examples, 10-16 to 10-18 knowledge, 10-3 to 10-4 legal system, 10-3 to 10-15 Management of Health and Safety at Work Regulations 1999, 10-10 to 10-11 manual handling regulations, 10-11 to 10-13
Index
986
reasonable foreseeability, 10-3 reasonable practicability, 10-5 to 10-6 safe systems, 10-7 to 10-8 staff, 10-8 to 10-10 statutory duty, 10-10 to 10-15 vicarious liability, 10-6 visual display unit, 10-13 to 10-15 work equipment regulations, 10-13 workplace safety, 10-8 work systems, 10-7 to 10-8 Muttart studies, 14-1 to 14-19 N Narcotics, 13-51 National Coal Board v. England , 10-10 Navigation, positive guidance principles, 13-33 Necessity, warning expert, 30-9 Negligence, product liability, 27-3, 29-2, 33-2 to 33-3 Nemeth studies, 37-1 to 37-16 Neurological system, 28-5, see also Human-centric approach (HCA), system liability New Zealand standards, 1-16 Nicotine, 13-48 Night driving, traffic crashes, 13-8, see also Glare Night photography, 13-5 Night shift, see Shiftwork Nighttime conditions pedestrian accidents, traffic, 16-9 to 16-11 pedestrian injuries, 15-8 to 15-9, 15-15 Nilsson studies, 32-1 to 32-16 No-fault systems, 9-8, 29-2 Nose-to-nose method, 20-16 to 20-17 Nosings, 19-8, 20-16 O Objects not easily identified, 14-5 to 14-7 Occupational biomechanics, see Pedestrian falls, perceptual-cognitive and biomechanical factors Occupational cerviobrachial disorder (OCD), 23-5 O’Connor, Sandra Day, 12-13 Older drivers, 11-11, 11-12, see also Age and functioning; Age-related factors; Seniors Olfactory stimuli, 28-5, see also Human-centric approach (HCA), system liability Olsen studies, 15-1 to 15-21, 38-1 to 38-46 O’Neill v. DSG Retail Limited , 10-17 On-the-job training, 6-10 to 6-11 Operationalization of terms, 14-24 to 14-25
Index
987
Operational requirements, commercial motor vehicles, 17-3 to 17-4 Operator satisfaction, human factors and ergonomics, 1-10 to 1-11 Opinions pedestrian falls, 19-8 to 19-11 “road map” for practice, 5-4, 5-9, 5-10 to 5-11, 5-11 to 5-15 warning expert, 30-8 to 30-9 Order, memory, 12-20 to 12-21 Organization, testimony and evidence, 2-3 to 2-4 Organizational analysis, safe practices training, 6-4, 6-16 to 6-18 Organizational environment, 1-8 Organizational responsibilities, sexual harassment, 36-5 to 36-6 Oron-Gilad studies, 18-1 to 18-16 Osteoarthritis, 23-5 Outside in, motorcycle collisions, 18-8 to 18-13 Overall policy, accidental injury prevention, 25-4 to 25-5 Overhead illumination, 15-12 Overshadowing (verbal), effect, 11-26 Overtaking and passing, 13-12 Own-age effect, 11-23 to 11-24 Owner-operators, see Commercial motor vehicle (CMV) collisions P Papinkchock studies, 7-1 to 7-11 Parallel situation, 15-3 to 15-5 Paris v. Stepney Borough Council , 10-9 Participants, memory, 12-12 to 12-16, 12-21 Passing, 13-12 Passive safety, 18-5 to 18-6 Passive voice, 2-5 Path intrusions, driver response time, 14-14 to 14-15 Paxton v. County of Alameda , 24-13 PCDETECT computer program, 14-6 PC Miler software, 17-12 Pease v Sinclair Refining , 26-2 Pedestrian accidents, traffic alcohol, 16-6 to 16-7 basics, 16-1 to 16-2, 16-14 behavior, 16-3 to 16-4 child pedestrians, 16-7 to 16-8 elderly pedestrians, 16-8 to 16-9 handicapped pedestrians, 16-9 in-line skates, 16-13 to 16-14 nighttime conditions, 16-9 to 16-11 pedestrian traffic control devices, 16-12 to 16-13 perception-response time, 16-6 roadway design, 16-11 to 16-12 scooters, 16-13 to 16-14 skateboards, 16-13 to 16-14 turning accidents, 16-2 to 16-3 walking speed, 16-4 to 16-6 weather conditions, 16-11
Index
988
work zones, 16-13 Pedestrian falls, measurement American slip meter, 20-10 basics, 20-2 Brungraber, Mk II, 20-12 camouflaged tread nosings, 20-13 carpeted stairs, 20-17 to 20-18 causes of fall, 20-3 checklist, 20-24 cleaning surfaces, 20-12 coefficient of friction, 20-9 design of stairs, 20-14 dynamic COF, 20-9 electronic level, 20-8 finger-pull, 20-10 handrails, 20-19 to 20-20 height, 20-3 to 20-4 horizontal pull slipmeter, 20-9 to 20-10 importance, 20-2 inattention, 20-13 to 20-14 inclinometer method, 20-8 level-and-ruler method, 20-7 lighting, 20-12 to 20-13 location of sun, 20-21 to 20-22 lubricants, 20-12 magnetic compass, 20-22 motor-pull, 20-10 nose-to-nose method, 20-16 to 20-17 nosing profile, 20-16 optimal methods, 20-4, 20-6, 20-8, 20-10 to 20-12, 20-16 to 20-17, 20-20 to 20-21 perceptual inadequacy, 20-12 to 20-14 photographic approaches, 20-22 to 20-24 pin-to-pin method, 20-18 profile measurement, 20-18 profile tool, 20-4, 20-6 ramps, 20-6 to 20-8 rise, 20-3 to 20-4, 20-14 to 20-18 run, 20-16, 20-17 to 20-18 shadows, 20-21 slip-resistance, 20-9 to 20-10 slips and falls, 20-8 to 20-12 stair nosings, 20-12 to 20-13 stairs, falls, 20-12 to 20-18 standards, international, 20-24 to 20-27 static COF, 20-9 steepness, 20-6 to 20-8 straightedge ruler method, 20-14 to 20-16 sunlight, 20-21 sun location, 20-21 to 20-22 tread nosings, 20-13 trip hazards, 20-3 to 20-6 types of falls, 20-2 to 20-3
Index
989
typical methods, 20-4, 20-7, 20-9 to 20-10, 20-14 to 20-16 variable incident tribometer, 20-10 to 20-12 variables, slip resistance, 20-12 visibility, 20-12 to 20-13 walk cycle phases, 20-3 wooden stairs, 20-16 to 20-17 Pedestrian falls, perceptual-cognitive and biomechanical factors attention, 19-7 basics, 19-1 to 19-2 case studies, 19-11 to 19-18 center of gravity, 19-2 checklist, 19-18 to 19-19 client consultation, 19-7 to 19-8 codes and laws, 19-9 decision-making, 19-6 to 19-7 elevation changes, 19-15 empirical study, 19-10 to 19-11 energy of walking, 19-4 to 19-5 forces of movement, 19-3 to 19-4 forensic process, 19-7 to 19-9 foreseeable changes, 19-15 gait cycle, 19-3 guidelines, professional, 19-10 identifiable changes, walking surface, 19-13 incidents, 19-11 to 19-18 industry custom and practice, 19-10 information-processing model, 19-5 to 19-7 information review, 19-8 irregular stair geometry, 19-17 to 19-18 judgment, professional, 19-11 memory, 19-6 missteps, 19-14 to 19-15 opinions, 19-8 to 19-11 perception, 19-5 to 19-6 principle issues, 19-2 to 19-11 response execution, 19-7 scientific literature, 19-10 sensory processing, 19-5 site inspection, 19-8 slips, 19-11 to 19-13 trips, 19-15 to 19-17 unexpected changes, 19-11 to 19-15, 19-17 to 19-18 unexpected impediments, 19-15 to 19-17 visible impediment, 19-16 to 19-17 voluntary consensus standards, 19-9 walking biomechanics, 19-2 to 19-5 Pedestrian injury issues alternative facilities, lighting, 15-10 to 15-11 ambient vision, 15-6 ambiguity, 15-8 A-pillar, 15-16 area lighting, 15-11
Index basics, 15-1, 15-1 to 15-2 behavior, 15-11, 15-13 to 15-14 boundaries, lighting, 15-10 to 15-11 case studies, 15-17 to 15-19 checklist, 15-19 to 15-21 choices, 15-13, 15-14 to 15-15 citations, 15-17 clothing, 15-14 to 15-15 cognitive map, 15-13 competency, 15-7 conduct of pedestrian, 15-16 to 15-17 darkness, 15-8 to 15-9, 15-15 enforcement, 15-11 evasive maneuvers, 15-13 expectancy, 15-14 eye movements, 15-6 facility issues, 15-9 to 15-11 focal vision, 15-6 front-end vehicle design, 15-16 glare, 15-16 high-beam headlights, 15-12 informing parties, 15-9 to 15-10 judgment, pedestrian, 15-14 lane changes, 15-13 lighting, 15-10 to 15-13 low-beam headlights, 15-11 memory, 15-14 midblock crossing, 15-15 night, 15-8 to 15-9, 15-15 overhead illumination, 15-12 parallel situation, 15-3 to 15-5 pedestrian collisions, 15-3 to 15-5 perception, 15-5 to 15-6 peripheral vision, 15-6 to 15-7 police, 15-17 populations, 15-7 to 15-8 principle issues, 15-2 to 15-19 provisions for needs, 15-9 to 15-10 recall, 15-14 responsibility of pedestrian, 15-16 to 15-17 search, visual, 15-6 situational issues, 15-8 street lighting, 15-12 tinted glass, 15-16 transverse situation, 15-3 to 15-5 vehicle design, 15-15 to 15-16 visibility devices, 15-16 to 15-17 vision and visibility, 15-5 to 15-7 vulnerability, 15-7 to 15-8 warnings, lighting, 15-10 to 15-11 weather, 15-8 to 15-9, 15-15 Pedestrians and bicycle crashes
990
Index
991
analytical process steps, 13-27 to 13-28 bicycle crashes, 13-19 to 13-31 casual analyses, 13-26 to 13-27 conspicuity, 13-24 to 13-25 crash types, 13-19 to 13-25 examples, 13-28 to 13-31 function/event sequence, 13-20 legal analyses, 13-26 to 13-27 pedestrians, 13-19 to 13-31 police crash report, 13-25 to 13-26 precipitating factors, 13-20 to 13-21 results usage, 13-28 Pedestrian traffic control devices, 16-12 to 16-13 Perception age and functioning, 11-4 to 11-11, 11-16 to 11-17 commercial motor vehicle collisions, 17-2 memory, 12-2, 12-5 to 12-6 motorcycle collisions, 18-12 to 18-13 pedestrian falls, 19-5 to 19-6 pedestrian injuries, 15-5 to 15-6 Perception-reaction time driver response time estimation, 14-1 positive guidance principles, 13-34 seniors, 35-5 Perception-response time driver response time, 14-1, 14-10 to 14-16 pedestrian accidents, traffic, 16-6 Perceptual-cognitive and biomechanical factors pedestrian falls, attention, 19-7 case studies, 19-11 to 19-18 center of gravity, 19-2 checklist, 19-18 to 19-19 client consultation, 19-7 to 19-8 codes and laws, 19-9 decision-making, 19-6 to 19-7 elevation changes, 19-15 empirical study, 19-10 to 19-11 energy of walking, 19-4 to 19-5 forces of movement, 19-3 to 19-4 forensic process, 19-7 to 19-9 foreseeable changes, 19-15 guidelines, professional, 19-10 identifiable changes, walking surface, 19-13 incidents, 19-11 to 19-18 industry custom and practice, 19-10 information-processing model, 19-5 to 19-7 information review, 19-8 irregular stair geometry, 19-17 to 19-18 judgment, professional, 19-11 memory, 19-6 missteps, 19-14 to 19-15 opinions, 19-8 to 19-11
Index
992
perception, 19-5 to 19-6 principle issues, 19-2 to 19-11 response execution, 19-7 scientific literature, 19-10 sensory processing, 19-5 site inspection, 19-8 slips, 19-11 to 19-13 standard of care, 19-1 to 19-2 trips, 19-15 to 19-17 unexpected changes, 19-11 to 19-15, 19-17 to 19-18 unexpected impediments, 19-15 to 19-17 visible impediment, 19-16 to 19-17 voluntary consensus standards, 19-9 walking biomechanics, 19-2 to 19-5 Perceptual inadequacy, 20-12 to 20-14 Performance after paid work hours, 34-8 to 34-9 Performance issues, shiftwork, 34-4 to 34-5 Peripheral vision age and functioning, 11-9 to 11-10 pedestrian injuries, 15-6 to 15-7 Personal determinants, memory, 12-8 Personal skills, expert witnesses, 4-4 Person analysis, 6-5, see also Individuals Personnel selection, commercial motor vehicles, 17-2 Photographic approaches, 20-22 to 20-24 Physical and cognitive factors, see also Cognitive factors balcony falls, 21-1 to 21-15 biomechanical factors, 19-1 to 19-20 exercise injuries, 24-1 to 24-16 measurements, pedestrian falls, 20-1 to 20-27 pedestrian falls, 19-1 to 19-20, 20-1 to 20-27 perceptual-cognitive factors, 19-1 to 19-20 preplacement strength and capacity assessment, 22-1 to 22-5 upper limb disorders (work-related), 23-1 to 23-22 Pin-to-pin method, 20-18 Planning, positive guidance principles, 13-40 Police, pedestrian injuries, 15-17 Police crash report, 13-25 to 13-26 Policies and procedures accidental injury prevention, 25-4 to 25-5 safe practices training, 6-17 Populations, pedestrian injuries, 15-7 to 15-8 Positional risk doctrine, 9-5 Positive guidance principles construction, 13-40 control, 13-33 design, 13-40 expectancy, 13-34 to 13-37 fixed objects, 13-38 guidance, 13-33, 13-37 to 13-39
Index
993
hazards, 13-37 to 13-40 highway conditions, 13-38 information handling, 13-34 navigation, 13-33 perception reaction time, 13-34 planning, 13-40 positive guidance principles, 13-31 to 13-44 primacy, 13-33 to 13-34 railroad crossings, 13-40 to 13-42 roadway design, 13-34 to 13-35 roadway environment, 13-37 situations, 13-38 strategic improvements, 13-38 to 13-39 task complexity, 13-33 traffic, 13-37 traffic control devices, 13-35 to 13-36, 13-37 urban intersection work zone, 13-42 to 13-44 Post-training environment, 6-19 to 6-20 Posture, 23-9 to 23-11 Practicability, reasonable, see Reasonable practicability Practice and experience, see “Road map” for practice Practice and management, conflict, 37-6 Precipitating factors, pedestrians and bicycle crashes, 13-20 to 13-21 Preliminary feedback, attorney, 30-10 Preplacement strength and capacity assessment basics, 22-1 to 22-2 checklist, 22-5 examples, 22-4 to 22-5 principle issues, 22-2 to 22-4 Presbycusis, 11-4 Preschoolers, 35-1 to 35-3, 35-6 to 35-7, see also Adolescents; Child pedestrians Presentations, behavioral science data, 3-7 to 3-8, see also Evidence, preparation and presentation Pretraining environment, 6-15 to 6-16 Pretrial meetings, 4-9 to 4-10 Prevention/audit, health care, 37-13 to 37-14 Priest studies, 6-1 to 6-25 Primacy, positive guidance principles, 13-33 to 13-34 Principal issues age-related factors, 35-2 balcony falls, 21-2 to 21-9 health care, 37-3 to 37-10 human-centric approach, 28-3 to 28-12 pedestrian falls, 19-2 to 19-11 pedestrian injuries, 15-2 to 15-19 preplacement strength and capacity assessment, 22-2 to 22-4 product liability experts, 26-2 to 26-4 reconstructed situated performance, 8-3 to 8-13 “road map” for practice, 5-2 to 5-8 safe practices training, 6-2 to 6-20
Index
994
sexual harassment, 36-2 to 36-6 shiftwork, 34-3 to 34-7 worker’s compensation causation issues, 9-2 to 9-7 Privacy, 4-7, 30-13 Privilege, 4-7 to 4-8 Proactive practices, product liability, 29-4 to 29-5 Procedures, 1-11 to 1-12 human-centric approach, 28-10 reconstructed situated performance, 8-5 Process accidents, 5-13 to 5-14 Processes, human-centric approach, 28-9 to 28-10 Processing speed, 11-9, 11-10 to 11-11 Product design, 26-6 to 26-7 Productivity goal, 1-10 Productivity/safety trade-off, 1-10 Product liability basics, 29-1, 29-6 defects, 29-3 designers, implications for, 29-4 to 29-6 express warranty, 29-2 human factors practitioner, implications for, 29-4 to 29-6 implied warranty, 29-2 international trends, 29-3 to 29-4 misrepresentation, 29-2 negligence, 29-2 no-fault compensation, 29-2 proactive practices, 29-4 to 29-5 reactive approaches, 29-5 to 29-6 strict liability, 29-2 theories, 29-1 to 29-2 Product liability, human factors view accidents, 33-4 to 33-5 basics, 33-1 forensic task analysis, 33-6 to 33-9 human errors, 33-4 to 33-5 human factors perspective, 33-4 legal environment, 33-2 negligence, 33-2 to 33-3 product liability theory, 33-2 to 33-3 reliability, human, 33-5 to 33-6 Product liability and warnings accidental injury prevention, 25-1 to 25-14 color warnings, 32-1 to 32-16 engineering experts, 27-1 to 27-9 human-centric approach, 28-1 to 28-19 human factors view, 33-1 to 33-9 liability law, 27-1 to 27-9 product liability experts, 26-1 to 26-10, 29-1 to 29-6 system liability, 28-1 to 28-19 warning experts, 30-1 to 30-14 Product liability experts, see also Expert witnesses
Index
995
basics, 26-2 behavioral expectations, 26-5 to 26-6 case studies, 26-6 to 26-9 checklist, 26-10 data, 26-3 to 26-4 guarding against hazards, 26-8 to 26-9 hazard control hierarchy, 26-4 to 26-6 principal issues, 26-2 to 26-4 product design, 26-6 to 26-7 qualifications, 26-3 standard of care, 26-1 to 26-2 standards familiarization, 26-3 warnings about hazards, 26-9 Product risks, see Accidental injury prevention Product safety function, 25-5 Products liability law basics, 27-1 to 27-2, 27-9 breach of warranty, 27-2 to 27-3 causation issue, 27-8 clear language, 27-8 to 27-9 defective products, 27-2 defects, types, 27-4 to 27-6 design defects, 27-5 to 27-6 engineering impact, 27-6 to 27-9 government standards, 27-7 industry standards, 27-7 instructions defects, 27-6 legal theories, 27-2 to 27-3, 27-7 manufacturing defects, 27-4 to 27-5 negligence, 27-3 standards, 27-7 strict liability in tort, 27-3 to 27-4 warnings defects, 27-6 Professional issues behavioral science data, 3-1 to 3-8 Daubert , 7-1 to 7-11 evidence, 2-1 to 2-7 expert witness ethics, 4-1 to 4-10 human factors engineering and ergonomics, 1-1 to 1-16 “road map,” 5-1 to 5-15 safe practices training, 6-1 to 6-25 Profile measurement, 20-18 Profile tool, 20-4, 20-6 Proprioceptive sensory capability, 28-5, see also Human-centric approach (HCA), system liability Provisions for needs, 15-9 to 15-10 Pseudoscience, 8-2, 8-11 to 8-12, see also Junk science Psilocybin, 13-48, 13-53 Psychological theory and data, 3-7, 28-6
Index
996
Q Qualifications, warning expert, 30-4 to 30-5 Quality control, 25-7 R Railroad crossings positive guidance principles, 13-40 to 13-42 traffic crashes, 13-16 to 13-18 Ramps, 20-6 to 20-8, see also Exit ramps Reactive approaches, product liability, 29-5 to 29-6 Reality monitoring, memory, 12-18 to 12-19 Rear-end collisions, 13-10 to 13-12 Reasonable foreseeability, 10-3, see also Foreseeability Reasonableness, 27-5 Reasonableness of conduct, 26-2, 35-1 Reasonableness vs. unreasonableness, 25-2 to 25-4 Reasonable practicability, 10-5 to 10-6 Rebuttal role of experts, 7-6 to 7-10 Recall, 15-14, 25-7 Receiver, consumer product warnings, 31-5 to 31-8 Reconstructing situated performance, see Situated performance, reconstructing Record keeping, expert witnesses, 4–9 Recovery, shiftwork, 34-5 Reed v. Ellis , 10-8 Referral acceptance, 4-1 to 4-6 Regrouping evidence, 8-3 to 8-4 Regulations, compliance, 25-6 Regulatory issues, shiftwork, 34-3 Relative legibility, 32-6 Reliability, human, 33-5 to 33-6 Remedies, health care, 37-2 to 37-3 Remove, accident analysis model, 5-12 to 5-14 Repetition, 23-6 23-8 Repetitive strain injury (RSI), 23-5 Reports and reporting pedestrians and bicycle crashes, 13-25 to 13-26 “road map” for practice, 5-4 to 5-5, 5-9, 5-11 safe practices training, 6-17 to 6-18 warning experts, 30-10 Research, conducting, 4-9 Response execution, 19-7 Response time, drivers, 13-14 to 13-15 attention, 14-2 to 14-5 basics, 14-1 to 14-2, 14-18 to 14-19 car following, 14-15 to 14-16 gaps in traffic, 14-14 green traffic signals, 14-14 inattention, 14-2 to 14-5 limb movement, 14-16 to 14-18 objects not easily identified, 14-5 to 14-7
Index
997
operationalization of terms, 14-24 to 14-25 path intrusions, 14-14 to 14-15 perception-response time, 14-10 to 14-16 previous results, research methods, 14-8 to 14-10 rule of thumb estimates, 14-14 transition time, 14-16 to 14-18 urgency, 14-16 vehicle latency, 14-16 to 14-18 vehicles changing lanes, 14-14 Responsibility, accidental injury prevention, 25-4 to 25-7 Responsibility of pedestrian, 15-16 to 15-17 Rest, shiftwork, 34-5 The Restatement of the Law Second, Torts: Products Liability , 30-2 The Restatement of the Law Third, Torts: Products Liability engineering experts, 27-3 to 27-6 human factors issues, 26-4 to 26-5 warning expert, 30-2 Results usage, 13-28 Retention, memory, 12-8 to 12-22 Retention failure, 11-18 Retinal image, 32-3 to 32-4 Retrieval, age and functioning, 11-18 to 11-27, 11-24 to 11-27 Retroreflectors, 15-17 Retrospective bias, 12-20 Retrospective outsider, 8-2 Rider licensing, motorcycles, 18-5 Riding demands, motorcycles, 18-6 to 18-7 Riding mower backover case studies, 25-8 to 25-13 Riser height basics, 20-3 to 20-4 carpeted stairs, 20-17 to 20-18 site inspection, 19-8 stairway design, 20-14 to 20-16 unexpected change, walking surface, 19-14 Risks accidental injury prevention, 25-5 to 25-6, 25-8 to 25-12, 25-10 to 25-12 collision involvement, alcohol and drugs, 13-50 to 13-52 management, 37-3 motorcycle collisions, 18-7 to 18-8 “Road map” for practice accident analysis model, 5-11 to 5-14 accident scenario, 5-3 to 5-4, 5-8 to 5-9, 5-10 analysis, 5-4, 5-10 to 5-15 basics, 5-1 to 5-2 case examples, 5-8 to 5-11 case initiation, 5-2 to 5-3, 5-8, 5-9 to 5-10 checklist, 5-11 consumer product accidents, 5-12 to 5-13 deposition testimony, 5-5 to 5-6, 5-9, 5-11 fall accidents, 5-14 farm equipment, 5-9 to 5-11 farm equipment, defense, 5-9 to 5-11
Index
998
findings, 5-4, 5-9 to 5-15 industrial machine accidents, 5-13 to 5-14 medical equipment, plaintiff, 5-8 to 5-9 motor vehicle accidents, 5-13 opinions, 5-4, 5-9 to 5-15 principle issues, 5-2 to 5-8 process accidents, 5-13 to 5-14 reports, 5-4 to 5-5, 5-9, 5-11 slip accidents, 5-14 trial testimony, 5-5, 5-6 to 5-8, 5-9, 5-11 trip accidents, 5-14 Roadways pedestrian accidents, traffic, 16-11 to 16-12 positive guidance principles, 13-34 to 13-35, 13-37 Robinson studies, 27-1 to 27-9 Robinson v. Jacksonville Shipyards , 36-4 Rodriguez v. Suzuki Motor Corp- , 27-4 Rogers v. Raymark Industries , 2-2 Rotating hours, 34-6, see also Shift work RSI, see Repetitive strain injury (RSI) Rule of thumb estimates, 14-14 Rules, warning expert, 30-1 to 30-3 Run, pedestrian falls, 20-16, 20-17 to 20-18 Russel v. Criterian Film Productions Limited , 10-8 S Safe practice model, 24-2, 24-11 to 24-14, 24-19 to 24-20 Safe practices training accountability, 6-3 aviation example, 6-20 to 6-21 basics, 6-1 to 6-2, 6-21 to 6-22 benefits, 6-3 to 6-4 blame, 6-3 checklist, 6-22 to 6-23 cognitive task analysis, 6-5 culture, 6-16 designing training, 6-5 to 6-11 development steps, 6-22 to 6-23 error reporting, 6-17 to 6-18 error training, 6-8 to 6-9 evaluation of training, 6-11 to 6-14 examples, 6-20 to 6-21 external factors, 6-14 to 6-20 human error, 6-2 to 6-3 individual trainee characteristics, 6-18 industrial example, 6-20 instructional strategies, 6-6 to 6-10 job analysis, 6-4 to 6-5 law enforcement example, 6-20 line operations safety audit, 6-14 medical example, 6-21
Index
999
motivation, trainees, 6-18 to 6-19 needs analysis, 6-4 to 6-5 on-the-job training, 6-10 to 6-11 organizational analysis, 6-4 organizational characteristics, 6-16 to 6-18 person analysis, 6-5 policies and procedures, 6-17 post-training environment, 6-19 to 6-20 pretraining environment, 6-15 to 6-16 principle issues, 6-2 to 6-20 scenario-based training, 6-6 to 6-8 stress exposure training, 6-9 task analysis, 6-4 to 6-5 team training, 6-9 to 6-10 trainees, 6-18 to 6-19 Safe systems, work-related musculoskeletal disorders (U.K.), 10-7 to 10-8 Safety critical conditions, 25-3 to 25-4 culture, 6-16 exercise injuries, 24-1 goal, human factors and ergonomics, 1-9 health care, 37-8 to 37-9 hierarchy, 31-1 productivity trade-off, 1-10 product liability, 29-5 shiftwork, 34-4 to 34-5 work-related musculoskeletal disorders (U.K.), 10-8 Sagittal plane, 21-3 Salas studies, 6-1 to 6-25 Sampson v. City of Schenectady , 6-3 Scenario-based training, 6-6 to 6-8 Scheduling, expert witnesses, 4-8 Schematic processing age and functioning, 11-31 to 11-34 memory, 12-7 to 12-8, 12-13 to 12-14 Schwalb v. H- Fass & Son Ltd. , 10-5 Schwoerer v. Union Oil Co- , 27-6 Scooters, 16-13 to 16-14 Screens (computer), see Upper limb disorders (ULDs) Search, visual, 15-6 Second jobs, 34-8, see also Shift work Self-efficacy, 6-18 Seniors, 35-4 to 35-5, 35-8 to 35-9, see also Age and functioning; Age-related factors Sensory processing, 19-5 Sequence of events, see Situated performance, reconstructing Sexual harassment basics, 36-1 to 36-2 checklist, 36-8 examples, 36-6 to 36-8
Index individual employee responsibilities, 36-6 litigation, 36-3 to 36-5 organizational responsibilities, 36-5 to 36-6 principal issues, 36-2 to 36-6 Shadows, 20-21 Shift tenure, 34-6 Shiftwork acute exposures, 34-5 to 34-6 basics, 34-1 to 34-2, 34-9 biorhythms, 34-6 to 34-7 case examples, 34-8 to 34-9 cautions, 34-6 checklist, 34-9, 34-10 to 34-11 chronic exposures, 34-5 to 34-6, 34-7 chronic fatigue syndrome, 34-7 circadian rhythms, 34-6 to 34-7 fatigue, 34-7 field research, 34-6 flextime, 34-7 handicap work schedule accommodation, 34-8 health issues, 34-3 to 34-4 irregular hours (employer-determined), 34-7 laboratory research, 34-6 legal issues, 34-3 moonlighting ambulance driver crash, 34-8 performance issues, 34-4 to 34-5 pitfalls, 34-6 principal issues, 34-3 to 34-7 regulatory issues, 34-3 rest and recovery issues, 34-5 safety issues, 34-4 to 34-5 sleep disturbance and deprivation, 34-7 stress, 34-7 well-being issues, 34-3 to 34-4 working beyond paid hours, 34-8 to 34-9 Shoes (white), 15-17 Site inspection, 19-8 Situated performance, reconstructing accident avoidance, 8-4 basics, 8-1 to 8-2 behavioral sequences, 8-7 to 8-13 checklists, 8-16 to 8-17 cherry picking, 8-3 to 8-4 conceptual description, 8-11 to 8-13 context-specific language, 8-8 to 8-9 data, 8-5 to 8-6 episodes, creating, 8-9 to 8-10 errors, 8-16 to 8-17 example, 8-13 to 8-16 explaining behavior and performance, 8-5 to 8-6 explaining vs. excusing, 8-12 to 8-13 focus of attention, individual, 8-10 to 8-11
1000
Index
1001
goals of individual, 8-10 to 8-11 hindsight bias, 8-3 to 8-7 judgments, 8-5 to 8-7 knowledge active/available, 8-10 to 8-11 local rationality, 8-7 principal issues, 8 -3 to 8-13 procedures, 8-5 pseudoscience, 8-11 to 8-12 regrouping evidence, 8-3 to 8-4 rules, 8-16 standards not met, 8-6 steps, 8-8 to 8-11, 8-17 Situational issues, 15-8 Situations, positive guidance principles, 13-38 Skateboards, 16-13 to 16-14 Skill requirements and tests, commercial motor vehicles, 17-2, 17-5 Sleep disturbance and deprivation, see also Fatigue misapplications, 7-8 to 7-9 shiftwork, 34-7 Sleep inertia, 34-6 Slip accidents, 5-14 Slip-resistance, 20-9 to 20-10 Slips, 19-11 to 19-13 Slips and falls, see Pedestrian falls, measurement Smith v. Cammell Laird and Company Limited , 10-10 Smith v. Leech Brain and Co- Limited , 10-9 Social categorization, memory, 12-12 to 12-13 Software, health care, 37-8 Source, consumer product warnings, 31-4 Source confusion age and functioning, 11-21 memory, 12-12 to 12-13 Source monitoring age and functioning, 11-19 to 11-27, 11-29 to 11-30 memory, 12-11 to 12-22 Sources of declines, 11-2 to 11-4 Space, memory, 12-19 to 12-20 Special definitions, 38-2 Specificity, health care, 37-6 Speech features, memory, 12-6 to 12-7 Springfield v. Kibbe , 6-20 Staff, work-related musculoskeletal disorders (U.K.), 10-8 to 10-10 Stairs carpeted, 20-17 to 20-18 design, 20-14 falls, 20-12 to 20-18 nosings, 20-12 to 20-13 Standard deviation, center of gravity, 21-4 Standard of practice theme, 24-10 to 24-11 Standards balcony falls, 21-6 to 21-9
Index
1002
ergonomics and human factors, 1-14 to 1-16 expert witnesses, 4-5 legibility of color warnings, 32-13 to 32-14 pedestrian falls, measurement, 20-24 to 20-27, product liability, 29-5 product liability experts, 26-3 products liability law, 27-7 reconstructed situated performance, 8-6 Static coefficient of friction, 20-9 Static muscle work, 23-11 Statler studies, 25-1 to 25-14 Statutory duty, 10-10 to 10-15 Staveley Iron and Chemical Co- Ltd. v. Jones , 10-9 Steepness, 20-6 to 20-8 Stereotypes, 11-14 to 11-15 Stimulants, 13-48, 13-52 Stokes v. Guest , 10-3 Storage, 12-2, see also Memory for conversation Stories, evidence presentation, 2-5 Straightedge ruler method, 20-14 to 20-16 Strain, 9-5 Strategic improvements, positive guidance principles, 13-38 to 13-39 Street lighting, 15-12 Stress causation, worker’s compensation, 9-5 exposure training, 6-9 human factors and ergonomics, 1-8 shiftwork, 34-7 traffic crashes, 13-13 to 13-14 Strict liability, 29-2 Strict liability in tort, 27-3 to 27-4 Structural limits, 18-10 Studies, see Case studies and examples Subthreshold targets, 13-25 Sudden change, upper limb disorders, 23-12 Sullivan v. Young Brothers & Co- , 27-3 to 27-4 Sunlight, 20-21 Sun location, 20-21 to 20-22 Supervision, upper limb disorders, 23-12 Suprathreshold targets, 13-25 Surfaces, cleaning, 20-12 System liability, see Human-centric approach (HCA) system liability, System safety engineering, 28-20 to 28-21 Systems approach, human factors and ergonomics, 1-6 to 1-9 T Tactile stimuli, 28-4, see also Human-centric approach (HCA), system liability Target, memory, 12-16 to 12-18 Task analysis, 6-4, 6-4 to 6-5, 33-6 to 33-9 Task complexity, positive guidance principles, 13-33
Index
1003
Taste, sense of, 28-5, see also Human-centric approach (HCA), system liability Taylorism, 1-3 Team training, 6-9 to 6-10 Technology, human-centric approach, 28-9 to 28-10 Temperature, upper limb disorders, 23-12 Tendinitis, 23-4 Tenosynovitis, 23-2 Tepas studies, 34-1 to 34-13 Terminology, 38-1 to 38-46 Testimony expert witnesses ethics, 4-10 organizing, evidence, 2-3 to 2-4 outside area of expertise, 7-9 “road map” for practice, 5-5, 5-6 to 5-8, 5-9, 5-11 warning expert, 30-10 to 30-11 Tests, commercial motor vehicle collisions, 17-5 Therapeutic categorization, 13-48 Therapeutic misadventures, 37-13 Therapeutic process, age and functioning, 11-21 Thompson studies, 38-1 to 38-46 Thompson v. Smiths Ship Repairers Northshields Limited , 10-4 Thom studies, 18-1 to 18-16 “Three witches,” 9-2 Threshold, distance, 32-2, 32-4, 32-7 to 32-8 Time, 11-16, 12-19 to 12-20 Time, estimation, 11-16 Time-of-day effects, 17-7 Time table and scheduling, 4-8 “Time to contact,” 18-11 to 18-12 Tinted glass, 15-16 Tobacco warnings-1991, 32-2 to 32-7 Tobacco warnings-1999 (revised), 32-10 to 32-13 Toronto Power Co- Ltd. v. Paskwan , 10-8 Torrington Co- v. Stutzman , 27-5 Total accumulated sleep loss, 17-8, 34-6 Tracking speed, 11-8 Tractor-trailers, 13-9 to 13-10, 17-15, see also Commercial motor vehicle (CMV) collisions Traffic, positive guidance principles, 13-37 Traffic control devices, 13-35 to 13-36, 13-37 Traffic crashes alcohol, 13-44 to 13-54, 13-50 analytical process steps, 13-27 to 13-28 assessment, drug impairment, 13-45 to 13-48 auditory factors, 13-17 to 13-18 basics, 13-1 to 13-3, 13-53 to 13-55 benzodiazepines, 13-51 bicycle crashes, 13-19 to 13-31 cannabis, 13-52 to 13-53 car-truck collision example, 13-9 to 13-10 casual analyses, 13-26 to 13-27
Index
1004
checklist, 13-55 to 13-57 computational analysis, 13-8 to 13-9 conspicuity, 13-24 to 13-25 construction, 13-40 control, 13-33 crash types, 13-19 to 13-25 current evidence, 13-49 to 13-53 data gathering, 13-2 to 13-3 depressants, 13-48, 13-50 to 13-52 design, 13-40 drivers, 13-3 to 13-19 drugs, 13-44 to 13-54 examples, 13-9 to 13-10, 13-28 to 13-31 expectancy, 13-12 to 13-13, 13-34 to 13-37 fixed objects, 13-38 function/event sequence, 13-20 glare, 13-7 to 13-8 guidance, 13-33, 13-37 to 13-39 hallucinogens, 13-48, 13-52 to 13-53 hazards, 13-37 to 13-40 high beam, 13-3 highway conditions, 13-38 impairment, 13-50 to 13-52 information handling, 13-34 law and visibility, 13-18 to 13-19 legal analyses, 13-26 to 13-27 low beam, 13-4 to 13-5 LSD, 13-53 mescaline, 13-53 motorcycles, 13-15 to 13-16 narcotics, 13-51 navigation, 13-33 night driving, 13-8 night photography, 13-5 overtaking and passing, 13-12 pedestrians, 13-19 to 13-31 perception reaction time, 13-34 planning, 13-40 police crash report, 13-25 to 13-26 positive guidance principles, 13-31 to 13-44 precipitating factors, 13-20 to 13-21 primacy, 13-33 to 13-34 psilocybin, 13-53 railroad crossings, 13-16 to 13-18, 13-40 to 13-42 rear-end collisions, 13-10 to 13-12 response time, 13-14 to 13-15 results usage, 13-28 risk of collision involvement, 13-50 to 13-52 roadway design, 13-34 to 13-35 roadway environment, 13-37 situations, 13-38 stimulants, 13-48, 13-52
Index strategic improvements, 13-38 to 13-39 stress, 13-13 to 13-14 task complexity, 13-33 therapeutic categorization, 13-48 traffic, 13-37 traffic control devices, 13-35 to 13-36, 13-37 traffic crashes, 13-3 to 13-19 urban intersection work zone, 13-42 to 13-44 visibility, 13-3 to 13-10, 13-17 to 13-19 Traffic signals, green, 14-14 Trainees, 6-18 to 6-19 Training accident analysis model, 5-13 to 5-14 commercial motor vehicle collisions, 17-2 outcomes, 6-14 training objects, 6-4 upper limb disorders, 23-12 Training, safe practices accountability, 6-3 aviation example, 6-20 to 6-21 basics, 6-1 to 6-2, 6-21 to 6-22 benefits, 6-3 to 6-4 blame, 6-3 checklist, 6-22 to 6-23 cognitive task analysis, 6-5 culture, 6-16 designing training, 6-5 to 6-11 development steps, 6-22 to 6-23 error reporting, 6-17 to 6-18 error training, 6-8 to 6-9 evaluation of training, 6-11 to 6-14 examples, 6-20 to 6-21 external factors, 6-14 to 6-20 human error, 6-2 to 6-3 individual trainee characteristics, 6-18 industrial example, 6-20 instructional strategies, 6-6 to 6-10 job analysis, 6-4 to 6-5 law enforcement example, 6-20 line operations safety audit, 6-14 medical example, 6-21 motivation, trainees, 6-18 to 6-19 needs analysis, 6-4 to 6-5 on-the-job training, 6-10 to 6-11 organizational analysis, 6-4 organizational characteristics, 6-16 to 6-18 person analysis, 6-5 policies and procedures, 6-17 post-training environment, 6-19 to 6-20 pretraining environment, 6-15 to 6-16 principle issues, 6-2 to 6-20 scenario-based training, 6-6 to 6-8
1005
Index
1006
stress exposure training, 6-9 task analysis, 6-4 to 6-5 team training, 6-9 to 6-10 trainees, 6-18 to 6-19 Trains, see Railroad crossings Transition time, 14-16 to 14-18 Transportation workers, see Shiftwork Transverse (horizontal) planes, 21-3 Transverse situation, 15-3 to 15-5 Tread, 19-8, 20-13 Treatises, see Learned treatises Trial testimony “road map” for practice, 5-5, 5-6 to 5-8, 5-9, 5-11 warning expert, 30-11 Trips pedestrian falls, 19-15 to 19-17 pedestrian falls, measurement, 20-3 to 20-6 “road map” for practice, 5-14 walking energy, 19-5 Truck drivers, see Commercial motor vehicle (CMV) collisions Turning accidents, 16-2 to 16-3 U Uncertainty, health care, 37-4 Unconscious plagiarism, 12-15 to 12-16 Unexpected changes, 19-11 to 19-15, 19-17 to 19-18 Unexpected impediments, 19-15 to 19-17 Unfamiliar vehicle perception, 18-12 to 18-13 “Unholy trinity,” 9-2 United Kingdom regulations, 21-7 United States regulations, 21-7 to 21-8 United States standards, 1-15 United States v. Rincon , 7-7 United States v. Virginia , 6-20 Unpaid work hours, 34-8 to 34-9 Upper limb disorders (ULDs) basics, 23-1 carpal tunnel syndrome, 23-3 causes, 23-5 to 23-13 cervical spondylosis, 23-5 checklist, 23-19 to 23-20 designing the workplace, 23-13 to 23-14 Dupuytren’s contracture, 23-3 epicondylitis, 23-4 ergonomics expertise, 23-14 to 23-17 force, 23-8 to 23-9 “frozen” shoulder, 23-4 to 23-5 ganglion, 23-5 nonwork factors, 23-13 organizational factors, 23-12 osteoarthritis, 23-5
Index
1007
posture, 23-9 to 23-11 repetition, 23-6 to 23-8 static muscle work, 23-11 sudden change, 23-12 supervision, 23-12 symptoms, 23-2 to 23-5 temperature, 23-12 tendinitis, 23-4 tenosynovitis, 23-2 to 23-3 training, 23-12 VDUs, 23-17 to 23-18 vibration, 23-11 to 23-12 vibration white finger, 23-3 working within industry, 23-18 to 23-19 workload peaks, 23-12 Urban intersection work zone, 13-42 to 13-44 Urgency, driver response time, 14-16 Usage considerations accidental injury prevention, 25-5 product liability, 29-4 to 29-5 User behaviors, see Accidental injury prevention V Validity, behavioral science data, 3-8 Variable incident tribometer, 20-10 to 20-12 Variables, slip resistance, 20-12 Varying conversational roles, 12-14 to 12-15 Vassallo v. Baxter Healthcare Corp- , 27-6 Vehicle design, 15-15 to 15-16 Vehicle groups, 17-3 Vehicle latency, 14-16 to 14-18 Vehicles changing lanes, 14-14 Vendor crashes, 13-23, 13-28 to 13-31 Verbal overshadowing effect, 11-26 Vestibular sensory capability, 28-5, see also Humancentric approach (HCA), system liability Vibrations, 23-11 to 23-12 Vibration white finger, 23-3 Vicarious liability, 10-6 Victims, 11-16 to 11-27, see also Age and functioning Vigilance, 17-6, see also Fatigue Visibility pedestrian falls, measurement, 20-12 to 20-13 traffic crashes, 13-3 to 13-10, 13-17 to 13-19 Visibility devices, 15-16 to 15-17 Visible impediment, 19-16 to 19-17 Vision, age and functioning, 11-6 to 11-10 Vision and visibility, 15-5 to 15-7 Visual acuity, 11-7 to 11-8, 32-4 Visual data, 28-4,
Index
1008
see also Human-centric approach (HCA), system liability Visual display units (VDUs) upper limb disorders, 23-17 to 23-18 work-related musculoskeletal disorders (U.K.), 10-13 to 10-15 Visual marking, 11-8 Visual-motor useful field of view (VM-UFOV), 11-10 Visual search, 11-9 Visuospatial processing, 11-16 to 11-17 Voice perception, 11-27 Voluntary consensus standards, 19-9 Voluntary reporting systems, 6-17 to 6-18 Voyager software program, 20-21 Vredenburgh studies, 26-1 to 26-10, 35-1 to 35-10, 36-1 to 36-9 Vulnerability, pedestrians, 15-7 to 15-8 W Walk cycle phases, 20-3 Walker v. Wabco Automotive U-K- Limited , 10-4 Walking, 19-2 to 19-5, 19-4 to 19-5 Walking speed, 16-4 to 16-6 Wanton disregard for employee safety, 9-2 Wardell studies, 29-1 to 29-6 Ward v. Ritz Hotel (London) Limited , 21-9 to 21-10 Warning experts, see also Expert witnesses activities, 30-5 to 30-11 adequacy, 30-9 adversarial setting, 30-13 analysis, 30-7 to 30-10 assumptions, 30-8 basics, 30-1, 30-13 to 30-14 being current, 30-12 boundaries, 30-12 causation, 30-9 to 30-10 consistency, 30-12 court’s judgment, 30-5 deposition testimony, 30-10 to 30-11 ethics, 30-11 formal role, 30-3 functions, 30-5 to 30-11 informal role, 30-3 to 30-4 information analysis, 30-7 to 30-8 initial contact, 30-6 necessity, 30-9 opinions, 30-8 to 30-9 preliminary feedback, attorney, 30-10 privacy, 30-13 qualifications, 30-4 to 30-5 reports, 30-10 role, 30-3 to 30-4 rules, 30-1 to 30-3 testimony, 30-10 to 30-11
Index
1009
trial testimony, 30-11 Warnings, see also Color warnings; Consumer product warnings accident analysis model, 5-13 to 5-14 defects, products liability law, 27-6 hazards, product liability experts, 26-9 human factors issues, 26-5 to 26-6 lighting, pedestrian injuries, 15-10 to 15-11 product liability, 26-1, 29-5 traffic crashes, 13-36 Warranty, 29-2 Watergate Hearings, 12-1, 12-10 to 12-11 Weather conditions human-centric approach, 28-10 to 28-12 pedestrian accidents, traffic, 16-11 pedestrian injuries, 15-8 to 15-9, 15-15 Well-being issues, 24-3, 34-3 to 34-4 White apparel, 15-17 White matter hyperintensities (WMHs), 11-2 White v. Hallbrook Precision Castings Limited , 10-4 Wilsons and Clyde Coal Co- Ltd. v. English , 10-6, 10-8, 10-9 Wilson studies, 6-1 to 6-25 Wilson v. Tyneside Window Cleaning Co- , 10-6 Witnesses, see also Age and functioning; Expert witnesses age and functioning, 11-16 to 11-27 conditions, 11-24 Wogalter studies, 30-1 to 30-14, 31-1 to 31-9 Wooden stairs, 20-16 to 20-17 Work equipment regulations, 10-13 Worker’s compensation (WC), causation issues basics, 9-1 causation, 9-4 to 9-5 checklist, 9-8 to 9-9 disease, 9-2 to 9-4 ergonomic principles, 9-5 example, 9-7 to 9-8 experts, 9-5 to 9-7 historical perspectives, 9-2 injury, 9-2 to 9-4 principal issues, 9-2 to 9-7 Working beyond paid hours, 34-8 to 34-9, see also Shiftwork Working memory, 11-3 to 11-4, 11-11 to 11-12 Workload peaks, upper limb disorders, 23-12 Workplace, 10-8, 23-13 to 23-14 Work-related musculoskeletal disorders (U.K.) basics, 10-1 to 10-3 breach, statutory duty, 10-10
Index
1010
case law examples, 10-16 to 10-18 cases, 10-20 to 10-21 causation, 10-3 checklist, 10-18 to 10-19 consultation, 10-15 contributory negligence, 10-6 display screen equipment, 10-13 to 10-15 duty of employer, 10-6 to 10-10 equipment provision, 10-8 European Union directives, 10-15 examples, 10-16 to 10-18 knowledge, 10-3 to 10-4 legal system, 10-3 to 10-15 Management of Health and Safety at Work Regulations 1999, 10-10 to 10-11 manual handling regulations, 10-11 to 10-13 reasonable foreseeability, 10-3 reasonable practicability, 10-5 to 10-6 safe systems, 10-7 to 10-8 staff, 10-8 to 10-10 statutory duty, 10-10 to 10-15 vicarious liability, 10-6 visual display unit, 10-13 to 10-15 work equipment regulations, 10-13 workplace safety, 10-8 work systems, 10-7 to 10-8 Work-related upper limb disorders (ULDs) basics, 23-1 carpal tunnel syndrome, 23-3 causes, 23-5 to 23-13 cervical spondylosis, 23-5 checklist, 23-19 to 23-20 designing the workplace, 23-13 to 23-14 Dupuytren’s contracture, 23-3 epicondylitis, 23-4 ergonomics expertise, 23-14 to 23-17 force, 23-8 to 23-9 “frozen” shoulder, 23-4 to 23-5 ganglion, 23-5 nonwork factors, 23-13 organizational factors, 23-12 osteoarthritis, 23-5 posture, 23-9 to 23-11 repetition, 23-6 to 23-8 static muscle work, 23-11 sudden change, 23-12 supervision, 23-12 symptoms, 23-2 to 23-5 temperature, 23-12 tendinitis, 23-4 tenosynovitis, 23-2 to 23-3 training, 23-12 VDUs, 23-17 to 23-18
Index
1011
vibration, 23-11 to 23-12 vibration white finger, 23-3 working within industry, 23-18 to 23-19 workload peaks, 23-12 Work-rest history, 17-10 to 17-12 Work schedule accommodation, handicap, 34-8 Work systems, 10-7 to 10-8 Work zones pedestrian accidents, traffic, 16-13 traffic crashes, 13-42 to 13-44 Wright v. Dunlop Rubber Co- Ltd. and ICI Ltd. , 10-4 Wylie studies, 17-1 to 17-19 Wyong Shire Council v. Shirt , 24-13 Z Zackowitz studies, 26-1 to 26-10, 35-1 to 35-10, 36-1 to 36-9
