HUMAN

FACTORS IN
ENGINEERING
AND DESIGN


HUMAN
FACTORS IN
ENGINEERING
AND DESIGN
SEVENTH EDITION

Mark S. Sanders,

Ph.D.

California State University, Northridge

Ernest J. McCormick,

Ph.D.

Late Professor Emeritus of Psychological Sciences,
Purdue University

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HUMAN FACTORS IN ENGINEERING

AND DESIGN

Copyright © 1993, 1987, 1982, 1976 by McGraw-Hili, Inc. All
rights reserved. Previously published under the following titles:
Human Factors Engineering, copyright © 1970, 1964 by McGrawHill, Inc., all rights reserved; and Human Engineering, copyright ©
1957 by McGraw-Hili, Inc., all rights reserved. Printed in the
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States Copyright Act of 1976, no part of this publication may be
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of the publisher.

12 13 14 15 16 17 DOC DOC 1 0
ISBN 0-07-054901-X
This book was set in Times Roman by Better Graphics,
The editors were Christopher
the production

supervisor

Inc.

Rogers and Tom Holton;


was Denise L. Puryear.

The cover was designed by Carla Bauer.
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& Sons Company was printer and binder.

Library of Congress Cataloging-io-Publication
Sanders, Mark S.
Human factors in engineering
J. McCormick.-7th

p.

and design / Mark S. Sanders, Ernest

ed.

em.

Includes bibliographical
ISBN 0-07-054901-X
1. Human engineering.
II. Title.
TA166.S33
620.8'2-dc20

Data


references

and index.

I. McCormick,

Ernest J. (Ernest James)

1993
92-194


DR. MARK S. SANDERS received his M.S. and Ph.D. degrees in human
factors from Purdue University. He is currently Professor and Chair of the
Human Factors Applied Experimental Psychology Graduate Program at California State University, Northridge. Also Dr. Sanders consults with various
organizations and serves as an expert witness in cases involving human factors
issues. He has executed or directed over 100 research and development contracts, subcontracts, and consulting activities. In addition, he has authored or
coauthored over 90 technical reports, journal articles, and professional presentations. He received the Human Factors Society's Jack A. Kraft Award for his
research on human factors issues in the mining industry. Dr. Sanders is a
member of the Ergonomics Society and Society of Automotive Engineers. He
is a fellow in the Human Factors Society and has served that organization as
president, secretary-treasurer,
and chair of the Education Committee and
Educators Professional Group. Dr. Sanders is also a fellow of Division 21
(Division of Applied Experimental and Engineering Psychologists) of the
American Psychological Association.
DR. ERNEST J. McCORMICK (deceased) was Professor Emeritus, Purdue
University. His academic career as an industrial psychologist covered a span of
30 years at Purdue. His first edition of this text (then titled Human Engineering) was published in 1957. Dr. McCormick's other major publications include
Industrial and Organizational Psychology (now in its eighth edition) and Job

Analysis: Methods and Applications. He was responsible for development of
the position analysis questionnaire (PAQ), a structured, computerized job
, v


vi

ABOUT THE AUTHORS

analysis procedure being used by numerous organizations; he was president of
PAQ Services, Inc. He has served on various advisory panels and committees,
including the Army Scientific Advisory Panel, the Navy Advisory Board for
Personnel Research, and the Committee on Occupational Classification and
Analysis of the National Academy of Sciences. His awards include the Paul M.
Fitts award of the Human Factors Society, the Franklin V. Taylor award of the
Society of Engineering Psychologists, and the James McKeen Cattell award of
the Society of Industrial and Organizational Psychology.


Dedicated to the Memory of
Ernest J. McCormick


PREFACE

PART 1

INTRODUCTION

1


HumanFactors and Systems

2

HumanFactors ResearchMethodologies

PART 2

xi

3
23

INFORMATION INPUT

3

Information Input and Processing

47

4

Text, Graphics,Symbols,and Codes

91

5


Visual Displaysof DynamicInformation

132

6

Auditory, Tactual,and Olfactory Displays

160

7

SpeechCpmmunications

197

PART 3

HUMAN OUTPUT AND CONTROL

8

PhysicalWork and ManualMaterialsHandling

225

9

Motor Skills


273

HumanControl of Systems

301

10

ix


X

CONTENTS

11

Controls and Data Entry Devices

334

12

Hand Tools and Devices

383

PART 4

WORKPLACE DESIGN


13
14

15

PART 5

Applied Anthropometry, Work-SpaceDesign,
and Seating

415

Arrangement of Components
within a Physical Space

456

Interpersonal Aspects of Workplace Design

485

ENVIRONMENTAL CONDITIONS

16

Illumination

511


17

Climate

551

18

Noise

589

19

Motion

622

PART 6

HUMAN FACTORS APPLICATIONS

20

Human Error, Accidents, and Safety

655

21


Human Factors and the Automobile

696

22

Human Factors in Systems Design

726

APPENDIXES
A
8
C

List of Abbreviations
Control Devices
NIOSHRecommendedAction Limit Formula
for Lifting Tasks

759
764
769

INDEXES
Name Index
Subject Index

771
781



This book deals with the field of human factors, or ergonomics, as it is also
called. In simple terms, the term human factors refers to designing for human
use. Ten years ago, it would have been difficult to find very many people
outside the human factors profession who could tell you what human factors or
ergonomics was. Today, things are different. Human factors and ergonomics
are in the news. Visual and somatic complaints of computer terminal users
have been linked to poor human factors design. The incident at Three-Mile
Island nuclear power station highlighted human factors deficiencies in the
control room. The words human factors and especially ergonomics have also
found their way into advertisements for automobiles, computer equipment; and
even razors. The field is growing, as evidenced by the increase in the membership of human factors professional societies, in graduate programs in human
factors, and in job opportunities.
We intended this book to be used as a textbook in upper-division and
graduate-level human factors courses. We were also aware that this book has
been an important resource for human factors professionals over the last six
editions and 35 years. To balance these two purposes, we have emphasized the
empirical research basis of human factors, we have stressed basic concepts and
the human factors considerations involved in the topics covered, and we have
supplied references for those who wish to delve into a particular area. We have
tried to maintain a scholarly·approach to the field. Unfortunately, there are
times when our presentation may be a little technical or "dry," especially when
we are presenting information that would be more appropriate for the practicing human factors specialist than for students. For this we apologize, but we
hope the book will be one students will want to keep as a valuable reference.
For students, we have written a workbook to accompany this text (published
by Kendall-Hunt Publishing Co., Dubuque, Iowa). Included in the workbook,
for each chapter, are a list of key terms and self-contained projects that use
concepts and information contained in this book.
,.

XI


xii

PREFACE

There has been a virtual information explosion in the human factors field
over the years. The first edition of this book, published in 1957, contained 16
chapters and 370 references. This edition contains 22 chapters and over 900
references. In 1972, the Human Factors Society (HFS) first published a proceedings of their annual meeting. It contained 106 papers and was 476 pages
long. The proceedings for the 1991 HFS annual meeting contained over 350
papers and was 1600 pages long! In this book we have tried to cover both
traditional and emerging areas of human factors, but it was impossible to
include everything. The specific research material included in the text represents only a minute fraction of the vast amount that has been carried out in
specific areas. It has been our interest to use as illustrative material examples
of research that are relatively important or that adequately illustrate the central
points in question. Although much of the specific material may not be forever
remembered by the reader, we hope that the reader will at least develop a deep
appreciation of the importance of considering human factors in the design of
the features of the world in which we work and live. Appreciation is expressed
to the many investigators whose research is cited. References to their work are
included at the end of each chapter. To those investigators whose fine work we
did not include, we apologize and trust they understand our predicament. We
would also like to thank the following reviewers for their many helpful comments and suggestions: John G. Casali, Virginia Polytechnic Institute; Rick
Gill, University of Idaho; Martin Helander, SUNY, Buffalo; John Lyman,
University of California, Los Angeles; Joseph P. Meloy, Milwaukee School
of Engineering; Edward J. Rinalducci, University of Central Florida; and
William C. Howell, Rice University.
This edition represents some changes from the last edition. In addition to a

general updating of the material (almost 30 percent of the figures are new), a
new chapter on motor skills (Chapter 9) has been added. Several chapters have
been extensively revised and renamed, including: Chapter 8, Physical Work
and Manual Materials Handling; Chapter 20, Human Error, Accidents, and
Safety; Chapter 4, Text, Graphics, Symbols, and Codes; and Chapter 13,
Applied Anthropometry, Workspace Design, and Seating. We welcome comments and suggestions for making improvements in future editions.
It is with sadness that I report that Professor Ernest J. McCormick (Mac to
his friends) died on February 9, 1990. Mac's passing came as we were starting
to work on this edition of the book. I was deprived of a much admired colleague
and a wonderful writing partner. His input and critiques are missing from this
edition, but his contributions to the book over the last 35 years live on in every
chapter. When I was a graduate student at Purdue University, twenty-odd
years ago, I was asked to teach Mac's courses while he was in India. One of the
perks was being allowed to use his office. I remember sitting in his chair for the
first time. Although physically larger than Mac, I vividly recall feeling small
sitting there. As I worked on this edition without Mac's help, I had a similar
feeling. He has left an empty chair that will be hard to fill. Mac is, survived by


PREFACE

xiii

his wife Emily and two daughters Wynne and Jan. Mac was a model of
professionalism and integrity. He was a person of quiet wit, keen analytic
ability, and intellect. He will be missed.
Mark S. Sanders


HUMAN

FACTORS IN
ENGINEERING
AND DESIGN


1

Human Factors and Systems

2

Human Factors Research Methodologies


In the bygone millennia our ancestors lived in an essentially "natural" environment in which their existence virtually depended on what they could do directly
with their hands (as in obtaining food) and with their feet (as in chasing prey,
getting to food sources, and escaping from predators). Over the centuries they
developed simple tools and utensils, and they constructed shelter for themselves to aid in the process of keeping alive and making life more tolerable.
The human race has come a long way from the days of primitive life to the
present with our tremendous array of products and facilities that have been
made possible with current technology, including physical accoutrements and
facilities that simply could not have been imagined by our ancestors in their
wildest dreams. In many civilizations of our present world, the majority of the
"things" people use are made by people. Even those engaged in activities close
to nature-fishing,
farming, camping-use
many such devices.
The current interest in human factors arises from the fact that technological
developments have focused attention (in some cases dramatically) on the need
to consider human .beings in such developments. Have you ever used a tool,

device, appliance, or machine and said to yourself, "What a dumb way to
design this; it is so hard to use! If only they had done this or that, using it would
be so much easier." If you have had such experiences, you have already begun
to think in terms of human factors considerations in the design of things people
use. Norman (1988), in an entertaining book, provides numerous examples of
everyday things that were not designed from a human factors perspective,
including single-control shower faucets, videocassette recorders, and stove-top
controls. In a sense, the goal of human factors is to guide the applications of
3


4

PART 1: INTRODUCTION

technology in the direction of benefiting humanity. This text offers an overview
of the human factors field; its various sections and chapters deal with some of
the more important aspects of the field as they apply to such objectives.

HUMAN FACTORS DEFINED

Before attempting to define human factors, we should say a word about terms.
Humanfactors is the term used in the United States and a few other countries.
The term ergonomics, although used in the United States, is more prevalent in
Europe and the rest of the world. Some people have tried to distinguish
between the two, but we believe that any distinctions are arbitrary and that, for
all practical purposes, the terms are synonymous. Another term that is occasionally seen (especially within the U.S. military) is human engineering. However, this term is less favored by the profession, and its use is waning. Finally,
the term engineering psychology is used by some psychologists in the United
States. Some have distinguished engineering psychology, as involving basic
research on human capabilities and limitations, from human factors, which is

more concerned with the application of the information to the design of things.
Suffice it to say, not everyone would agree with such a distinction.
We approach the definition of human factors in terms of its focus, objectives, and approach.
Focus of Human Factors

Human factors focuses on human beings and their interaction with products,
equipment, facilities, procedures, and environments used in work and everyday living. The emphasis is on human beings (as opposed to engineering, where
the emphasis is more on strictly technical engineering considerations) and how
the design of things influences people. Human factors, then, seeks to change
the things people use and the environments in which they use these things to
better match the capabilities, limitations, and needs of people.

Objectives

of Human Factors

Human factors has two major objectives. The first is to enhance the effectiveness and efficiency with which work and other activities are carried out.
Included here would be such things as increased convenience of use, reduced
errors, and increased productivity. The second objective is to enhance certain
desirable human values, including improved safety, reduced fatigue and stress,
increased comfort, greater user acceptance, increased job satisfaction, and
improved quality of life.
It may seem like a tall order to enhance all these varied objectives, but as
Chapanis (1983) points out, two things help us. First, only a subset of the
objectives are generally of highest importance in a specific application. Second,
the objectives are usually correlated. For example, a machine or product that is


CHAPTER 1: HUMAN FACTORS AND SYSTEMS


5

the result of human factors technology usually not only is safer, but also is
easier to use, results in less fatigue, and is more satisfying to the user.
Approach of Human Factors

The approach of human factors is the systematic application of relevant information about human capabilities, limitations, characteristics, behavior, and
motivation to the design of things and procedures people use and the environments in which they use them. This involves scientific investigations to discover relevant information about humans and their responses to things,
environments, etc. This information serves as the basis for making design
recommendations and for predicting the probable effects of various design
alternatives. The human factors approach also involves the evaluation of the
things we design to ensure that they satisfy their intended objectives.
Although no short catch phrase can adequately characterize the scope of the
human factors field, such expressions as designing for human use and optimizing working and living conditions give a partial impression of what human
factors is about. For those who would like a concise definition of human factors
which combines the essential elements of focus, objectives, and approach
discussed above, we present the following definition, modified slightly from
Chapanis (1985): Human factors discovers and applies information about
human behavior, abilities, limitations, and other characteristics to the design
of tools, machines, systems, tasks, jobs, and environments for productive,
safe, comfortable, and effective human use.
Discussion

There are several more or less established doctrines that characterize the
human factors profession and that together distinguish it from other applied
fields:
• Commitment to the idea that things, machines, etc. are built to serve
humans and must be designed always with the user in mind
• Recognition of individual differences in human capabilities and limitations
and an appreciation for their design implications

• Conviction that the design of things, procedures, etc. influences human
behavior and well-being.
• Emphasis on empirical data and evaluation in the design process
• Reliance on the scientific method and the use of objective data to test
hypotheses and generate basic data about human behavior
• Commitment to a systems orientation and a recognition that things, procedures, environments, and people do not exist in isolation
We would be remiss if we did not at least mention what human factors is not.
All too often, when people are asked what human factors is, they respond by
saying what it is not. The following are three things human factors is not.


6

PART 1: INTRODUCTION

Human factors is not just applying checklists and guidelines. To be sure,
human factors people develop and use checklists and guidelines; however,
such aids are only part of the work of human factors. There is not a checklist or
guideline in existence today that, if it were blindly applied, would ensure a good
human factors product. Trade-offs, considerations of the specific application,
and educated opinions are things that cannot be captured by a checklist or
guideline but are all important in designing for human use.
Human factors is not using oneself as the model for designing things. Just
because a set of instructions makes sense to an engineer, there is no guarantee
others will understand them. Just because a designer can reach all the controls
on a machine, that is no guarantee that everyone else will be able to do so.
Human factors recognizes individual differences and the need to consider the
unique characteristics of user populations in designing things for their use.
Simply being a human being does not make a person a qualified human factors
specialist.

Human factors is not just common sense. To some extent, use of common
sense would improve a design, but human factors is more than just that.
Knowing how large to make letters on a sign to be read at a specific distance or
selecting an audible warning that can be heard and distinguished from other
alarms is not determined by simple common sense. Knowing how long it will
take pilots to respond to a warning light or buzzer is also not just common
sense. Given the number of human factors deficiencies in the things we use, if
human factors is based on just common sense, then we must conclude that
common sense is not very common.
A HISTORY OF HUMAN FACTORS

To understand human factors, it is important to know from where the discipline
came. It is not possible, however, to present more than just a brief overview of
the major human factors developments. We have chosen to concentrate on
developments in the United States, but several sources trace the history in
other countries [see, for example, Edholm and Murrell (1973), Singleton (1982),
and Welford (1976)].
Early History

It could be said that human factors started when early humans first fashioned
simple tools and utensils. Such an assertion, however, might be a little presumptuous. The development of the human factors field has been inextricably
intertwined with developments in technology and as such had its beginning in
the industrial revolution of the late 1800s and early 1900s. It was during the
early 19OOs,for example, that Frank and Lillian Gilbreth began their work in
motion study and shop management. The Gilbreths' work can be considered as
one of the forerunners to what was later to be called human factors. Their work
included the study of skilled performance and fatigue and the design of workstations and equipment for the handicapped. Their analysis of hospital surgical


CHAPTER 1: HUMAN FACTORS AND SYSTEMS


7

teams, for example, resulted in a procedure used today: a surgeon obtains an
instrument by calling for it and extending his or her hand to a nurse who places
the instrument in the proper orientation. Prior to the Gilbreths' work, surgeons
picked up their own instruments from a tray. The Gilbreths found that with the
old technique surgeons spent as much time looking for instruments as they did
looking at the patient.
Despite the early contributions of people such as the Gilbreths, the idea of
adapting equipment and procedures to people was not exploited. The major
emphasis of behavioral scientists through World War II was on the use of tests
for selecting the proper people for jobs and on the development of improved
training procedures. The focus was clearly on fitting the person to the job.
During World War II, however, it became clear that, even with the best
selection and training, the operation of some of the complex equipment still
exceeded the capabilities of the people who had to operate it. It was time to
reconsider fitting the equipment to the person.
1945 to 1960: The Birth of a Profession

At the end of the war in 1945, engineering psychology laboratories were
established by the U.S. Army Air Corps (later to become the U.S. Air Force)
and U.S. Navy. At about the same time, the first civilian company was formed
to do engineering psychology contract work (Dunlap & Associates). Parallel
efforts were being undertaken in Britain, fostered by the Medical Research
Council and the Department of Scientific and Industrial Research.
It was during the period after the war that the human factors profession was
born. In 1949 the Ergonomics Research Society (now called simply the
Ergonomics Society) was formed in Britain, and the first book on human
factors was published, entitled Applied Experimental Psychology: Human Factors in Engineering Design (Chapanis, Garner, and Morgan, 1949). During the

next few years conferences were held, human factors publications appeared,
and additional human factors laboratories and consulting companies were
established.
The year 1957 was an important year, especially for human factors in the
United States. In that year the journal Ergonomics from the Ergonomics
Research Society appeared, the Human Factors Society was formed, Division
21 (Society of Engineering Psychology) of the American Psychological Association was organized, the-first edition of this book was published, and Russia
launched Sputnik and the race for space was on. In 1959 the International
Ergonomics Association was formed to link several human factors and
ergonomics societies in various countries around the world.
1960 to 1980: A Period of Rapid Growth

The 20 years between 1960 and 1980 saw rapid growth and expansion of human
factors. Until the 1960s, human factors in the United States was essentially
concentrated in the military-industrial complex. With the race for space and


8

PART 1: INTRODUCTION

staffed space flight, human factors quickly became an important part of the
space program. As an indication of the growth of human factors during this
period, consider that in 1960 the membership of the Human Factors Society
was about 500; by 1980 it had grown to over 3000. More important, during this
period, human factors in the United States expanded beyond military and space
applications. Human factors groups could be found in many companies, including those dealing in pharmaceuticals, computers, automobiles, and other consumer products. Industry began to recognize the importance and contribution
of human factors to the design of both workplaces and the products manufactured there. Despite all the rapid growth and recognition within industry,
human factors was still relatively unknown to the average person in the street
in 1980.

1980 to 1990: Computers,

Disasters, and Litigation

Human factors continued to grow with membership in the Human Factors
Society reaching almost 5000 in 1990. The computer revolution propelled
human factors into the public limelight. Talk of ergonomically designed computer equipment, user-friendly software, and human factors in the office seems
to be part and parcel of virtually any newspaper or magazine article dealing
with computers and people. Computer technology has provide I new challenges
for the human factors profession. New control devices, information presentation via computer screen, and the impact of new technology on people are all
areas where the human factors profession is making contributions.
The 1980s was, unfortunately, also a decade marred by tragic, large-scale,
technological disasters. The incident at Three Mile Island nuclear power station in 1979 set the stage for the 1980s. Although no lives were lost and the
property damage was confined to the reactor itself, the incident came very
close to resulting in a nuclear meltdown. The 1980s would not be so fortunate.
On December 4, 1984, a leak of methyl isocyanate (MIC) at the Union Carbide
pesticide plant in Bhopal, India, claimed the lives of nearly 4000 people and
injured another 200,000. Two years later, in 1986, an explosion and fire at the
Chernobyl nuclear power station in the Soviet Union resulted in more than 300
dead, widespread human exposure to harmful radiation, and millions of acres
of radioactive contamination. Three years later, 1989, an explosion ripped
through a Phillips Petroleum plastics plant in Texas. The blast was equivalent
in force to to tons of TNT. It killed 23 people, injured another tOo workers, and
resulted in the largest single U.S. business insurance loss in history ($1.5
billion). Meshkati (1989, 1991) analyzed several of these disasters and found
that inadequate attention to human factors considerations played a significant
role in contributing to each disaster he studied.
Another area that saw a dramatic increase in human factors involvement
was forensics and particularly product liability and personal injury litigations.
Courts have come to recognize the contribution of human factors expert

witnesses for explaining human behavior and expectations, defining issues of


CHAPTER 1: HUMAN FACTORS AND SYSTEMS

9

defective design, and assessing the effectiveness of warnings and instructions.
Approximately 15 percent of Human Factors Society members are involved in
expert-witness work (Sanders, Bied, and Curran, 1986).

1990 and Beyond

What does the future hold for human factors? We, of course, have no crystal
ball, but it seems safe to predict continued growth in the areas established
during the short history of human factors. Plans for building a permanent space
station will undoubtedly mean a heavy involvement of human factors. Computers and the application of computer technology to just about everything will
keep a lot of human factors people busy for a long time. The National Research
Council (Van Cott and Huey, 1991) estimates that the demand for human
factors specialists will exceed supply well into the 1990s.
Other developments should also increase the demand for human factors. For
example, the U.S. Occupational Safety and Health Administration (OSHA)
will be formulating ergonomic regulations for general industry during the 1990s.
A law passed by the U.S. Congress in 1988 ordered the Federal Aviation
Administration (FAA) to expand its human factors research efforts to improve
aviation safety. Two other area where human factors should expand are in the
design of medical devices and in the design of products and facilities for the
elderly. We hope that in the future human factors will become more involved
and recognized for its contribution to the quality of life and work, contributions
that go beyond issues of productivity and safety and embrace more intangible

criteria such as satisfaction, happiness, and dignity. Human factors, for example, could play a greater role in improving the quality of life and work in
underdeveloped countries.

HUMAN FACTORS

PROFESSION

We offer here a thumbnail sketch ofthe human factors profession in the United
States as depicted from surveys and from an analysis of human factors graduate
education programs in the United States and Canada.

Graduate Education in Human Factors

The Directory of Human Factors Graduate Programs in the United States and
Canada (Sanders and Smith, 1988) lists 65 programs. The programs (with but a
few exceptions) are housed in engineering departments (46 percent) or psychology departments (42 percent) with an additional 6 percent being joint programs.
From 1984 through 1987, engineering programs accounted for 55 percent of the
master's degrees granted but only 42 percent of the doctoral degrees. In 1987
there were about 1000 students in graduate programs in the United States and
Canada (MuckIer and Seven, 1990).


10

PART 1: INTRODUCTION

Who Are Human Factors People?

It is not entirely fair to assume that membership in the Human Factors Society
defines a person as a human factors specialist. Nonetheless, an analysis of the

backgrounds of its membership should give some insight into the profession as
a whole. Table 1-1 shows the composition of the Human Factors Society
membership by academic specialty and highest degree held. Psychologists
comprise almost half of the membership and account for 66 percent of all
doctoral degrees but only 40 percent of the master's degrees. More than half of
the members do not possess doctoral degrees. The number of different academic specialties in Table 1-1 attests to the multidisciplinary nature of the
profession.
Where Do Human Factors Specialists

Work?

The National Research Council (Van Cott and Huey, 1991) conducted an
extensive survey of members and colleagues of members from 11 professional
societies (including the Human Factors Society). These societies were thought
to contain people doing human factors work even though they might not call
themselves human factors specialists. The principle workplace of the respondents was in private business or industry (74 percent). In addition, 15
percent worked for government agencies and 10 percent worked in academia.
(The percentage in academia is an underestimate because only those academicians engaged in outside consulting work were included.)

TABLE 1-1
ANALYSIS OF HUMAN FACTORS SOCIETY MEMBERSHIP
AND HIGHEST DEGREE HELD

BY ACADEMIC

SPECIALTY

Highest degree held (%)
Academic


specialty

Psychology
Engineering
Human factors/ergonomics
Medicine, physiology, life sciences
Education
Industrial design
Business administration
Computer science
Other
Total degrees
Students
Not specified
Total
Source:

permission.

Bachelor's

6.8
4.9
1.3
0.8
0.2
1.6
0.5
0.5
2.1


Total (%)

Master's

Doctoral

12.0
8.1
3.8
1.1
0.9
0.7
1.3
0.5
4.1

26.3
6.1
2.6
1.1
1.5
0.1
0.1
0.3
2.1

45.1
19.1
7.7

3.0
2.6
2.4
1.9
1.3
8.3
91.4
8.2
0.4

-

-

-

18.7

32.5

40.2

-

-

-

--


100.0
Human Factors Society, 1991. Copyright by the Human Factors Society, Inc. and reproduced by


CHAPTER

1:

HUMAN FACTORS

AND SYSTEMS

11

The respondents were asked to identify the principle area in which they
worked. Six areas accounted for 83 percent of the respondents as shown in
Table 1-2.
In an earlier survey of Human Factors Society members, Sanders, Hied, and
Curran (1986) found that a majority (57 percent) of the respondents reported
working for a "large" organization, yet 49 percent indicated that their immediate work groups consisted of 10 or fewer people. For most of the respondents,
the number of human factors people in their work group was small. Some
24 percent reported no other human factors people in their work group besides themselves, and 25 percent reported only one or two others besides
themselves. Such a situation can get a little lonely, but it can also be quite
challenging.
What Do Human Factors People Do?

As part of the survey of Human Factors Society members, Sanders, Hied, and
Curran provided a list of 63 activities and asked respondents to indicate for
each activity whether they performed it rarely (if ever), occasionally, moderately often, or frequently. Table 1-3 lists all the activities for which 30 percent
or more of the respondents indicated they performed moderately often or

frequently in their work. The activities group nicely into four major areas:
communication, management, system development, and research and evaluation.
How Do Human Factors People Feel about Their Jobs?

Sanders (1982), in another survey of the Human Factors Society membership,
found that respondents rated their jobs especially high (compared to other
professional and technical people) on skill variety (the degree to which the job
requires a variety of different activities, skills, and talents) and autonomy (the
degree to which the job provides freedom, independence, and discretion to the

TABLE 1-2
PERCENTAGE OF HUMAN FACTORS SPECIALISTS
WORKING IN VARIOUS AREAS OF WORK
Principal area of work

Percentage

of respondents

Computers
Aerospace
Industrial processes
Health and safety
Communications
Transportation
Other
Source: Van Cott and Huey, 1991, Table 3-1.

22
22

17

9
8
5
17


12

PART 1: INTRODUCTION

TABLE 1·3
ACTIVITIES PERFORMED MODERATELY OFTEN OR FREQUENTLY
PERCENT OF HUMAN FACTORS SOCIETY RESPONDENTS

Activity
Communication
Write reports
Conduct formal briefing and presentations
Edit reports written by others
Write proposals
Evaluate relevance, worth, and quality of reports written
by others
Review and summarize the literature

BY OVER 30

Percentage responding
moderately often or frequently


80
59
54
52
47
35

Management
Schedule project activities
Manage and supervise others
Prepare budgets and monitor fiscal matters

53
49
38

System development
Determine system requirements
Verify system design meets human factors standards
Write system goals and objectives
Perform task analysis
Specify user requirements for hardware and software

43
43
40
37
31


Research and evaluation
Develop experimental designs to test theories or evaluate
systems
Design data collection instruments and procedures
Determine proper statistical test for particular data set
Plan and conduct user-machine evaluations
Collect data in controlled laboratory setting
Develop criterion measures of human-system
performance

44
39
38
36
32
31

worker in scheduling and determining the procedures used to carry out the
work). Sanders also assessed job satisfaction among his respondents and found
them especially satisfied (compared to other professional and technical people)
with their pay, security, and opportunities for personal growth. Their overall
general level of satisfaction was also very high.
Human Factors beyond the Human Factors Society

We have emphasized the Human Factors Society and its membership because
it is the largest human factors professional group in the world and because a lot
of interesting data are available about its membership. There are, however,
other human factors groups in other countries, including Great Britain, Germany, Japan, Indonesia, the Netherlands, Italy, France, Canada, Australia,
Norway, Israel, Poland, Yugoslavia, Hungary, Belgium, China, Soviet Union,



CHAPTER 1: HUMAN FACTORS AND SYSTEMS

13

Austria, Brazil, and Mexico. In addition, other professional organizations have
divisions or technical groups dealing with human factors. Such organizations
include the American Industrial Hygiene Association, American Psychological
Association, Institute of Electrical and Electronics Engineers, Society of Automotive Engineers, American Society of Mechanical Engineers, Association for
Computing Machinery, Aerospace Medical Association, American Institute of
Industrial Engineers, American Nuclear Society, American Society of Safety
Engineers, Environmental Design Research Association, and the Society for
Information Displays.
THE CASE FOR HUMAN FACTORS

Since humanity has somehow survived for these many thousands of years
without people specializing in human factors, one might wonder why-at the
present stage of history-it
has become desirable to have human factors
experts who specialize in worrying about these matters. As indicated before,
the objectives of human factors are not new; history is filled with evidence of
efforts, both successful and unsuccessful, to create tools and equipment which
satisfactorily serve human purposes and to control more adequately the environment within which people live and work. But during most of history, the
development of tools and equipment depended in large part on the proc~ss of
evolution, of trial and error. Through the use of a particular device-an ax, an
oar, a bow and arrow-it was possible to identify its deficiencies and to modify
it accordingly, so that the next "generation" of the device would better serve
its purpose.
The increased rate of technologic:ll development of recent decades has
created the need to consider human fat;tors early in the design phase, and in a

systematic manner. Because of the complexity of many new and modified
systems it frequently is impractical (or excessively costly) to make changes
after they are actually produced. The cost of retrofitting frequently is exorbitant. Thus, the initial designs of many items must be as satisfactory as possible
in terms of human factors considerations.
In effect, then, the increased complexities of the things people use (as the
consequence of technology) place a premium on having assurance that the item
in question will fulfill the two objectives of functional effectiveness and human
welfare. The need for such assurance requires that human factors be taken into
account early in the (usually long) design and development process. In Chapter
22 we discuss the development process in more detail and the role of human
factors in it.
SYSTEMS

A central and fundamental concept in human factors is the system. Various
authors have proposed different definitions for the term; however, we adopt a
very simple one here. A system is an entity that exists to carry out some


14

PART 1: INTRODUCTION

purpose (Bailey, 1982). A system is composed of humans, machines, and other
things that work together (interact) to accomplish some goal which these same
components could not produce independently. Thinking in terms of systems
serves to structure the approach to the development, analysis, and evaluation
of complex collections of humans and machines. As Bailey (1982) states,
The concept of a system implies that we recognize a purpose; we carefully analyze
the purpose; we understand what is required to achieve the purpose; we design the
system's parts to accomplish the requirements; and we fashion a well-coordinated

system that effectively meets our purpose. (p. 192)

We discuss aspects of human-machine systems and then present a few characteristics of systems in general. Finally, we introduce the concept of system
reliability.

Human-Machine

Systems

We can consider a human-machine system as a combination of one or more
human beings and one or more physical components interacting to bring about,
from given inputs, some desired output. In this frame of reference, the common
concept of machine is too restricted, and we should rather consider a "machine" to consist of virtually any type of physical object, device, equipment,
facility, thing, or what have you that people use in carrying out some activity
that is directed toward achieving some desired purpose or in performing some
function. In a relatively simple form, a human-machine system (or what we
sometimes refer to simply as a system) can be a person with a hoe, a hammer,
or a hair curler. Going up the scale of complexity, we can regard as systems the
family automobile, an office machine, a lawn mower, and a roulette wheel,
each equipped with its operator. More complex systems include aircraft, bottling machines, telephone systems, and automated oil refineries, along with
their personnel. Some systems are less delineated and more amorphous than
these, such as the servicing systems of gasoline stations and hospitals and other
health services, the operation of an amusement park or a highway and traffic
system, and the rescue operations for locating an aircraft downed at sea.
The essential nature of people's involvement in a system is an active one,
interacting with the system to fulfill the function for which the system is
designed.
The typical type of interaction between a person and a machine is illustrated
in Figure I-I. This shows how the displays of a machine serve as stimuli for an
operator, trigger some type of information processing on the part of the operator (including decision making), which in turn results in some action (as in the

operation of a control mechanism) that controls the operation of the machine.
One way to characterize human-machine systems is by the degree of manual
versus machine control. Although the distinctions between and among systems
in terms of such control are far from clear-cut, we can generally consider
systems in three broad classes: manual, mechanical, and automatic.