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Introduction to Human Factors I n a midwestern factory, an assembly-line worker had to reach to an awkward location and position a heavy component for assembly. Toward the end of a shift, after grabbing the component, he felt a twinge of pain in his lower back. A trip to the doctor revealed that t...

Introduction to Human Factors I n a midwestern factory, an assembly-line worker had to reach to an awkward location and position a heavy component for assembly. Toward the end of a shift, after grabbing the component, he felt a twinge of pain in his lower back. A trip to the doctor revealed that the worker had suffered a ruptured disc, and he missed several days of work. He filed a lawsuit against the company for requiring physical action that endangered the lower back. Examining a bottle of prescription medicine, an elderly woman was unable to read the tiny print of the dosage instructions or even the red-printed safety warning beneath it. Ironically, a second difficulty prevented her from potentially encountering harm caused by the first difficulty. She was unable to exert the combination of fine motor coordination and strength necessary to remove the “childproof ” cap. In a hurry to get a phone message to a business, an unfortunate customer found herself “talking” to an uncooperative automated voice response system. After impatiently listering to a long menu of options, she accidentally pressed the number of the wrong option and now has no clue as to how to get back to the option she wanted, other than to hang up and repeat the lengthy process. WHAT IS THE FIELD OF HUMAN FACTORS? While the three episodes described in the introduction are generic in nature and repeated in many forms across the world, a fourth, which occurred in the Persian Gulf in 1987, was quite specific. The USS Vincennes, a U.S. Navy cruiser, was on patrol in the volatile, conflict-ridden Persian Gulf when it received ambiguous information regarding an approaching aircraft. Characteristics of the radar system displays on board made it difficult for the crew to determine whether it was climbing or descending. Incorrectly diagnosing that the aircraft was de- From Chapter 1 of An Introduction to Human Factors Engineering, Second Edition. Christopher D. Wickens, John Lee, Yili Liu, Sallie Gordon Becker. Copyright © 2004 by Pearson Education, Inc. All rights reserved. Introduction to Human Factors scending, the crew tentatively identified it as a hostile approaching fighter. A combination of the short time to act in potentially life-threatening circumstances, further breakdowns in communication between people (both onboard the ship and from the aircraft), and crew expectancies that were driven by the hostile environment conspired to produce the captain’s decision to fire at the approaching aircraft. Tragically, the aircraft was actually an Iranian passenger airline, which had been climbing rather than descending. These four episodes illustrate the role of human factors. In these cases human factors are graphically illustrated by breakdowns in the interactions between humans and the systems with which they work. It is more often the case that the interaction between the human and the system work well, often exceedingly so. However, it is characteristic of human nature that we notice when things go wrong more readily than when things go right. Furthermore, it is the situation when things go wrong that triggers the call for diagnosis and solution, and understanding these situations represents the key contributions of human factors to system design. We may define the goal of human factors as making the human interaction with systems one that ■ ■ ■ Enhances performance. Increases safety. Increases user satisfaction. Human factors involves the study of factors and development of tools that facilitate the achievement of these goals. We will see how the goals of productivity and error reduction are translated into the concept of usability, which is often applied to the design of computer systems. In considering these goals, it is useful to realize that there may be tradeoffs between them. For example, performance is an all-encompassing term that may involve the reduction of errors or an increase in productivity (i.e., the speed of production). Hence, enhanced productivity may sometimes cause more operator errors, potentially compromising safety. As another example, some companies may decide to cut corners on time-consuming safety procedures in order to meet productivity goals. Fortunately, however, these tradeoffs are not inevitable. Human factors interventions often can satisfy both goals at once (Hendrick, 1996; Alexander, 2002). For example, one company that improved its workstation design reduced worker’s compensation losses in the first year after the improvement from $400,000 to $94,000 (Hendrick, 1996). Workers were more able to continue work (increasing productivity), while greatly reducing the risk of injury (increasing safety). In the most general sense, the three goals of human factors are accomplished through several procedures in the human factors cycle, illustrated in Figure 1, which depicts the human operator (brain and body) and the system with which he or she is interacting. At point A, it is necessary to diagnose or identify the problems and deficiencies in the human–system interaction of an existing system. To do this effectively, core knowledge of the nature of the physical body (its size, shape, and strength) and of the mind (its information-processing Introduction to Human Factors Performance Analysis Techniques A Identification of Problems Task Statistics Accident Brain Human System Body DESIGN Equipment Task Environment Selection B Implement Solutions Training FIGURE 1 The cycle of human factors. Point A identifies a cycle when human factors solutions are sought because a problem (e.g., accident or incident) has been observed in the human– system interaction. Point B identifies a point where good human factors are applied at the beginning of a design cycle. characteristics and limitations) must be coupled with a good understanding of the physical or information systems involved, and the appropriate analysis tools must be applied to clearly define the cause of breakdowns. For example, why did the worker in our first story suffer the back injury? Was it the amount of the load or the awkward position required to lift it? Was this worker representative of others who also might suffer injury? Task analysis, statistical analysis, and incident/accident analysis are critical tools for gaining such an understanding. Having identified the problem, the five different approaches shown at point B may be directed toward implementing a solution (Booher, 1990, 2003), as shown at the bottom of the figure. Equipment design changes the nature of the physical equipment with which humans work. The medicine bottle in our example could be given a more readable label and an easier-to-open top. The radar display on the USS Vincennes might be redesigned to provide a more integrated representation of lateral and vertical motion of the aircraft. Task design focuses more on changing what operators do than on changing the devices they use. The workstation for the assembly-line worker might be redesigned to eliminate manual lifting. Task design may involve assigning part or Introduction to Human Factors all of tasks to other workers or to automated components. For example, a robot might be designed to accomplish the lift of the component. Of course, automation is not always the answer, as illustrated by the example of the automated voice response system. Environmental design implements changes, such as improved lighting, temperature control, and reduced noise in the physical environment where the task is carried out. A broader view of the environment could also include the organizational climate within which the work is performed. This might, for example, represent a change in management structure to allow workers more participation in implementing safety programs or other changes in the organization. Training focuses on better preparing the worker for the conditions that he or she will encounter in the job environment by teaching and practicing the necessary physical or mental skills. Selection is a technique that recognizes the individual differences across humans in almost every physical and mental dimension that is relevant for good system performance. Such performance can be optimized by selecting operators who possess the best profile of characteristics for the job. For example, the lower-back injury in our leading scenario might have been caused by asking a worker who had neither the necessary physical strength nor the body proportion to lift the component in a safe manner. The accident could have been prevented with a more stringent operator-selection process. As we see in the figure, any and all of these approaches can be applied to “fix” the problems, and performance can be measured again to ensure that the fix was successful. Our discussion has focused on fixing systems that are deficient, that is, intervening at point A in Figure 1. In fact, the practice of good human factors is just as relevant to designing systems that are effective at the start and thereby anticipating and avoiding the human factors deficiencies before they are inflicted on system design. Thus, the role of human factors in the design loop can just as easily enter at point B as at point A. If consideration for good human factors is given early in the design process, considerable savings in both money and possibly human suffering can be achieved (Booher, 1990; Hendrick, 1996). For example, early attention given to workstation design by the company in our first example could have saved the several thousand dollars in legal costs resulting from the worker’s lawsuit. Alexander (2002) has estimated that the percentage cost to an organization of incorporating human factors in design grows from 2 percent of the total product cost when human factors is addressed at the earliest stages (and incidents like workplace accidents are prevented) to between 5 percent and 20 percent when human factors is addressed only in response to those accidents, after a product is fully within the manufacturing stage. The Scope of Human Factors While the field of human factors originally grew out of a fairly narrow concern for human interaction with physical devices (usually military or industrial), its scope has broadened greatly during the last few decades. Membership in the pri- Introduction to Human Factors mary North American professional organization of the Human Factors and Ergonomics Society has grown to 5,000, while in Europe the Ergonomics Society has realized a corresponding growth. A survey indicates that these membership numbers may greatly underestimate the number of people in the workplace who actually consider themselves as doing human factors work (Williges, 1992). This growth plus the fact that the practice of human factors is goal-oriented rather than content-oriented means that the precise boundaries of the discipline of human factors cannot be tightly defined. One way of understanding what human factors professionals do is illustrated in Figure 2. Across the top of the matrix is an (incomplete) list of the major categories of systems that define the environments or contexts within which the human operates. On the left are those system environments in which the focus is the individual operator. Major categories include the industrial environment (e.g. manufacturing, nuclear power, chemical processes); the computer or information environment; healthcare; consumer products (e.g., watches, cameras, and VCRs); and transportation. On the right are those environments that focus on the interaction between Contextual Environment of System Nature of Human Components Individual Group Computer & Health Consumer Products Transportation Manufacturing Information Care Team Organization Human Components Visibility Sensation Perception Communications Cognition & Decision Motor Control Muscular Strength Other Biological Factors Stress Training Individual Differences Task Analysis FIGURE 2 This matrix of human factors topics depicts human performance issues against contextual environments within which human factors may be applied. The study of human factors may legitimately belong within any cell or combination of cells in the matrix. Introduction to Human Factors two or more individuals. A distinction can be made between the focus on teams involved in a cooperative project and organizations, a focus that involves a wider concern with management structure. Figure 2 lists various components of the human user that are called on by the system in question. Is the information necessary to perform the task visible? Can it be sensed and adequately perceived? These components were inadequate for the elderly woman in the second example. What communications and cognitive processes are involved in understanding the information and deciding what to do with it? Decisions on the USS Vincennes suffered because personnel did not correctly understand the situation due to ambiguous communications. How are actions to be carried out, and what are the physical and muscular demands of those actions? This, of course, was the cause of the assembly-line worker’s back injury. What is the role of other biological factors related to things like illness and fatigue? As shown at the far left of the figure, all of these processes may be influenced by stresses imposed on the human operator, by training, and by the individual differences in component skill and strength. Thus, any given task environment listed across the top of the matrix may rely upon some subset of human components listed down the side. A critical role of task analysis that we discuss is to identify the mapping from tasks to human components and thereby to define the scope of human factors for any particular application. A second way of looking at the scope of human factors is to consider the relationship of the discipline with other related domains of science and engineering. This is shown in Figure 3. Items within the figure are placed close to other items to which they are related. The core discipline of human factors is shown at the center of the circle, and immediately surrounding it are various subdomains of study within human factors; these are boldfaced. Surrounding these are disciplines within the study of psychology (on the top) and engineering (toward the bottom) that intersect with human factors. At the bottom of the figure are domain-specific engineering disciplines, each of which focuses on a particular kind of system that itself has human factors components. Finally, outside of the circle are other disciplines that also overlap with some aspects of human factors. Closely related to human factors are ergonomics, engineering psychology, and cognitive engineering. Historically, the study of ergonomics has focused on the aspect of human factors related to physical work (Grandjean, 1988): lifting, reaching, stress, and fatigue. This discipline is often closely related to aspects of human physiology, hence its closeness to the study of biological psychology and bioengineering. Ergonomics has also been the preferred label in Europe to describe all aspects of human factors. However, in practice the domains of human factors and ergonomics have been sufficiently blended on both sides of the Atlantic so that the distinction is often not maintained. Engineering psychology is a discipline within psychology, whereas the study of human factors is a discipline within engineering. The distinction is clear: The ultimate goal of the study of human factors is toward system design, accounting for those factors, psychological and physical, that are properties of the human Introduction to Human Factors Experimental Psychology Statistics Social Psychology Displays Training Decision Making Communications Personality Psychology Cognitive Science Workload Biological Psychology ENGINEERING PSYCHOLOGY Stress Selection COGNITIVE ENGINEERING ERGONOMICS Industrial Psychology Bioengineering Biomechanics HUMAN FACTORS Management Job Design Industrial Engineering Workplace Layout Aeronautical Industrial Design Anthropometry Computer Science Operations Engineering Artificial Intelligence Nuclear Information Transportation Systems FIGURE 3 The relationship between human factors, shown at the center, and other related disciplines of study. Those more closely related to psychology are shown at the top, and those related to engineering are shown toward the bottom. component. In contrast, the ultimate goal of engineering psychology is to understand the human mind as is relevant to the design of systems (Wickens & Hollands, 2000). In that sense, engineering psychology places greater emphasis on discovering generalizable psychological principles and theory, while human factors places greater emphasis on developing usable design principles. But this distinction is certainly not a hard and fast one. Cognitive engineering, also closely related to human factors, is slightly more complex in its definition (Rasmussen et al., 1995; Vicente, 1999) and cannot as easily be placed at a single region of Figure 3. In essence, it focuses on the complex, cognitive thinking and knowledge-related aspects of system performance, whether carried out by human or by machine agents, the latter dealing closely with elements of artificial intelligence and cognitive science. Introduction to Human Factors The Study of Human Factors as a Science Characteristics of human factors as a science (Meister, 1989) relate to the search for generalization and prediction. In the problem diagnosis phase (Figure 1) investigators wish to generalize across classes of problems that may have common elements. As an example, the problems of communications between an air traffic control center and the aircraft may have the same elements as the communications problems between workers on a noisy factory floor or between doctors and nurses in an emergency room, thus enabling similar solutions to be applied to all three cases. Such generalization is more effective when it is based on a deep understanding of the physical and mental components of the human operator. It also is important to be able to predict that solutions designed to create good human factors will actually succeed when put into practice. A critical element to achieving effective generalization and prediction is the nature of the observation or study of the human operator. Humans can be studied in a range of environments, which vary in the realism with which the environment simulates the relevant system, from the laboratory for highly controlled observations and experiments, to human behavior (normal behavior, incidents, and accidents) of real users of real systems. Researchers have learned that the most effective understanding, generalization, and prediction depend on the combination of observations along all levels of this continuum. Thus, for example, the human factors engineer may couple an analysis of the events that led up to the USS Vincennes tragedy with an understanding, based on laboratory research, of principles of communications, decision making, display integration, and performance degradation under time stress to gain a full appreciation of the causes of the Vincennes’ incident and suggestions for remediation. OVERVIEW Several fine books cover similar and related material: Sanders and McCormick (1993), Bailey (1996), and Proctor and Van Zandt (1994) offer comprehensive coverage of human factors. Norman (1988) examines human factors manifestations in the kinds of consumer systems that most of us encounter