An Introduction to Human Factors in Medical Devices

An Introduction to Human Factors in Medical Devices
An Introduction to Human Factors
in Medical Devices
By Dick Sawyer
Office of Health and Industry Programs
CDRH Work Group:
Kaiser J. Aziz, Office of Device Evaluation
Cathy L. Backinger, Office of Surveillance and Biometrics
Everette T. Beers, Office of Device Evaluation
Andrew Lowery, Office of Health and Industry Programs
Stephen M. Sykes, Office of Science and Technology
Alvin Thomas, Office of Health and Industry Programs
Kimberly A. Trautman, Office of Compliance
U.S. Department of Health and Human Services
Public Health Service
Food and Drug Administration
Center for Devices and Radiological Health
Do It By Design
FOREWORD
The Center for Devices and Radiological Health (CDRH), part of the Food and
Drug Administration (FDA), develops and implements national programs and
regulations to protect the public with respect to devices and radiological health. These
programs are intended to assure the safety, effectiveness, and proper labeling of
medical and radiation-emitting devices.
An emerging concern of great importance to the Agency is the implementation of
good human factors practices in the design of medical devices. If device operation is
overly complex or counter-intuitive, safe and efficient use of a medical product can be
compromised. Both CDRH databases and research findings indicate that lack of
attention to human factors during product development may lead to errors that have
the potential for patient injury, or even death. The application of user interface design
principles and participation of healthcare practitioners in design analyses and tests are
very important. In addition to increased safety, an added benefit of such practices is
the likelihood that good user interface design will reduce training costs to healthcare
facilities. This document offers guidance intended to increase the understanding of
human factors in device design.
The Center publishes the results of its work in scientific journals and in its own
technical reports. Through these reports, CDRH also provides assistance to industry
and to the medical and healthcare professional communities in complying with the laws
and regulations mandated by Congress. The reports are sold by the Government
Printing Office (GPO) and by the National Technical Information Service (NTIS). Many
reports are also available on the Internet/World Wide Web.
We welcome your comments and requests for further information.
D. Bruce Burlington, M.D.
Director
Center for Devices and Radiological Health
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PREFACE
Human factors is a discipline that focuses on those variables that affect the
performance of individuals using equipment. The subject of this primer is the impact of
design upon safe and effective use of medical devices. Errors in the use of such
devices often are caused, at least in part, by the design of the user interface, i.e., those
features with which healthcare practitioners and lay users interact. Mistakes made
during device operation not only can hamper effective patient treatment, monitoring, or
diagnosis but in some cases can lead to injury or death. It is important that medical
devices be designed with consideration of the impact of design on safe use. This
primer discusses human factors problems, general design principles, and human
factors engineering methods and uses examples and illustrations for clarification.
The Food and Drug Administration (FDA) believes that this information is important
because of its implications for patient and user safety. Reports received throughout
the Medical Device Reporting (MDR) system, recall data, and other postmarket
information indicate that device design and related use errors are often implicated in
adverse events. As implied in the language of the design control section of the Quality
System Regulation (“....design requirements relating to a device are appropriate and
address the intended use of the device, including the needs of the user and patient.”),
human factors is an important consideration in quality assurance programs.
Additionally, good human factors design is an important consideration in submissions
to the Agency prior to device marketing.
While this guidance represents a final document, comments and suggestions about
Do It By Design may be submitted at any time for Agency consideration by writing Dick
Sawyer, Office of Health and Industry Programs, HFZ 230, 1350 Piccard Drive,
Rockville, MD 20850. For inquiries about the Quality System Regulation, call Kimberly
A. Trautman, Office of Compliance, at 301-594-4648.
This guidance is available through Internet/World Wide Web at
http://www.fda.gov and after January, 1997, from the National Technical Information
Service, Springfield, Virginia 22161, telephone number 703-487-4650.
Lireka P. Joseph, Dr. P.H.
Director
Office of Health and Industry Programs
Center for Devices and Radiological Health
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ACKNOWLEDGMENTS
A wide range of human factors scientists, engineers, managers, and healthcare
professionals in FDA were invaluable for their contributions of time and expertise to
this document. The Agency acknowledges the following individuals for their efforts:
Marilyn Sue Bogner, Mary W. Brady, Peter B. Carstensen, Robert J.
Cangelosi, Art Ciarkowski, John J. Crowley, James E. Dillard, William D.
Galloway, Brenda A. Hayden, Ronald D. Kay, Patricia A. Kingsley, Michael C.
Long, Bonnie H. Malkin, Donald E. Marlowe, Jack McCracken, Susan K.
Meadows, Michael Mendelson, William H. Midgette, Gregory W. O’Connell,
Christine Parmentier, Jay A. Rachlin, Cornelia A. Rooks, Walter A. Scott,
Thomas B. Shope, Nancy Stade, Barbara Stratmore, Judy L. Strojny, Carol A.
Vetter, and Catherine P. Wentz. Many thanks also to Donna Castner, Nancy
Lowe, and Edie Seligson for their secretarial, editorial, and graphics support.
Finally, a large number of professionals with universities, healthcare facilities,
human factors and design firms, and the medical device manufacturing community
provided a great deal of expertise and support. We are unable to acknowledge them
individually but wish to thank them for their time and effort.
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TABLE OF CONTENTS
FORWARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ii
PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HUMAN FACTORS: AN HISTORICAL PERSPECTIVE
1
....................... 2
WHY HUMAN FACTORS ENGINEERING IS IMPORTANT
.................... 3
The Interaction of User characteristics, and the Operating Environment . . . . . . . .
Physical and Sensory Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Perceptual and Cognitive Abilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Home-use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Design Implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
3
3
4
4
THE USER INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
Control/Display Arrangement and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Examples of errors related to hardware design . . . . . . . . . . . . . . . . . . . . . . . . .
Rules of thumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
6
7
8
Device Logic and Microprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Characterizing the shift to software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Examples of errors related to software design . . . . . . . . . . . . . . . . . . . . . . . . . 9
Rules of thumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Component Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Problems and examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rules of thumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
11
12
13
Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Problems and examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Rules of thumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
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Other Important Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dimensions, forces, and angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transfer of training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Device maintainability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Device packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
14
15
15
16
16
HUMAN FACTORS ENGINEERING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Document Reviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Complaints and Recall Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Manuals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
18
19
19
19
20
Exploratory Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Why Do Such Studies? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Study Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conducting Focus Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Physical Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
20
21
21
22
22
23
23
Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functions and Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analyzing Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hazard Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Other Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
23
24
27
27
27
Usability Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Developing Prototypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Developing Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Requirements and Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conducting the Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Testing in the “Real” Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Simulating Actual Conditions in the Laboratory . . . . . . . . . . . . . . . . . . . . .
Simulations in Healthcare Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Simulations in Homes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clinical Trials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Field Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
28
28
29
29
30
30
31
31
31
32
32
32
32
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SPECIAL ISSUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
Initiating a Company Human Factors Program . . . . . . . . . . . . . . . . . . . . . . . .
Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Characterizing the Human Factors Efforts . . . . . . . . . . . . . . . . . . . . . . . . .
33
33
33
34
Advice to Healthcare Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Recognizing Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Evaluating Already-Purchased Devices . . . . . . . . . . . . . . . . . . . . . . . . . . .
Evaluating Devices Before Purchase . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analyze and Test the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Final Comment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Points to Consider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
35
36
37
37
38
39
GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
40
REFERENCES FOR FURTHER READING
vii
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
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The mention of commercial products, their sources, or their use in connection with
material reported herein is not to be construed as either an actual or implied
endorsement of such products by the Department of Health and Human Services.
Although this guidance document does not create or confer any rights for or on any
person and does not operate to bind FDA or the public, it does represent the agency’s
current thinking on guidance for medical devices.
Where this document reiterates a requirement imposed by statute or regulation, the
force and effect as law of the requirement is not changed in any way by virtue of its
inclusion in this document.
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INTRODUCTION
The purpose of this primer is to encourage manufacturers to improve the safety of
medical devices and equipment by reducing the likelihood of user error. This can be
accomplished by the systematic and careful design of the user interface, i.e., the
hardware and software features that define the interaction between users and
equipment. This document contains background information about human factors as a
discipline, descriptions and illustrations of device problems, and a discussion of human
factors principles and methods. In addition, the final section of this document contains
recommendations for manufacturers and healthcare facilities.
The primer is directed to the following audiences:
• Manufacturers
• Employees of the Food and Drug Administration (FDA)
• Healthcare professionals
Because many designers, engineers, scientists, and healthcare professionals may
be unfamiliar with human factors, this primer is written as a basic educational tool and
assumes little background in the subject. At the same time, much of the content may
serve as a resource for those individuals who have had experience with human factors
issues.
The information in this document will be useful in planning human factors programs
that involve testing, incident analysis, or staff training. In addition to providing technical
information, it also discusses various human factors resources.
Good user interface design is critical to safe and effective equipment operation,
installation, and maintenance. Human factors should be considered early in the design
process, and systematic analysis and hands-on testing should be conducted
throughout development stages and involve participants from the end-user population.
It is not simply a matter of “fine tuning.” Thorough attention to design will result in
safer, more usable devices and, correspondingly, fewer accidents, reduced training
costs, fewer liability problems, and less trial-and-error during device development.
Because poor user interface design greatly increases the likelihood of error in
equipment operation, Do It By Design encourages readers to think critically about the
impact of device design upon the ability of healthcare professionals to treat patients
safely and effectively . On a positive note, attention to human factors design principles
and methods will help greatly in the development of a product that meets the users’
needs. Consider this primer a starting point. One should supplement this information
with more detailed data, principles, and methodologies from guidelines, standards,
texts, and articles (some of which are listed in the References for Further Reading).
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HUMAN FACTORS: AN HISTORICAL PERSPECTIVE
Human factors is a discipline that seeks to improve human performance in the use
of equipment by means of hardware and software design that is compatible with the
abilities of the user population. The terms "human engineering,” "usability
engineering,” and "ergonomics" are often used interchangeably for the process utilized
to achieve highly usable equipment.
Historically, human factors can be traced to early efforts by industrial engineers,
psychologists, and efficiency experts to streamline manufacturing operations and
equipment for better worker efficiency. In World War II, emphasis shifted from
production to personnel safety. A special focus was cockpit design of aircraft. Poor
design of controls and displays often induced pilot errors, sometimes leading to
crashes. Human factors analyses and tests became routine in the design of military
and commercial cockpits. Through the 1970s, the most notable applications of human
factors were highly costly, complex systems regulated by the Federal government,
such as military and transportation systems. Media coverage of user-related
accidents, like the Three-Mile Island nuclear power plant meltdown, has done much to
increase the recognition of human factors.
Such disaster stories are by no means a thing of the past. Recently, a nationally
aired television program presented findings related to a disastrous airline crash. The
investigators concluded that difficult-to-distinguish operating modes of the guidance
system and confusing data displays misled the pilots. They thought they were viewing
angle-of-descent information when, in fact, they were viewing vertical drop-in-altitude
data. The plane crashed short of the runway without the crew attempting corrective
action.
Human factors principles increasingly are being applied to commercial products.
Examples include "ergonomically-designed" automobiles and the development of
"user friendly" computer hardware, software, and communications products. Although
some manufacturers now integrate human factors design into their medical devices,
there exists a need for more widespread applications.
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WHY HUMAN FACTORS ENGINEERING IS IMPORTANT
Design-induced errors in the use of medical devices can lead to patient injuries and
deaths. A user’s behavior is directly influenced by operating characteristics of the
equipment; user interfaces that are misleading or illogical can induce errors by even
the most skilled users. A brief discussion of device users, operating conditions,
adverse events, and design implications will show the need for medical device designs
that accommodate the necessary range of user capabilities.
THE INTERACTION OF USERS, DESIGN, AND OPERATING ENVIRONMENT
Healthcare practitioners vary greatly in their physical, sensory, and mental abilities.
Lay people, who represent an increasing proportion of medical device users, are even
more variable. Medical devices are used in many environments, including operating
rooms, emergency rooms, patient units, x-ray departments, laboratories, emergency
vehicles, critical care facilities, clinics, and homes. Performance often is compromised
by noise, poor lighting, glare-producing surfaces, heat, dirt, improper cleaning
products, electrical interference, humidity, and moisture. Poorly written procedures,
stress, and fatigue can also degrade performance. Compounding the situation is the
wide array of equipment that a healthcare practitioner operates.
A medical device can be used safely and effectively only if the interaction between
the operating environment, user capabilities, stress levels, and device design is
considered when the manufacturer designs the device. The following dimensions of
human capability are basic to an understanding of human factors.
Physical and Sensory Characteristics
A person’s most basic physical and sensory capacities include vision, hearing,
manual dexterity, strength, and reach. A number of related design factors can interact
with them to influence human performance: the legibility and discriminability of
displayed symbols, audibility and distinctiveness of alarms, the strength required to
make connections, and the requirements for reaching controls.
Perceptual and Cognitive Abilities
Perception is the ability to detect, identify and recognize sensory input.
Understanding human limitations and exploiting human strengths in this area is crucial
for safe design of equipment. Perceptual characteristics are important in the design
and arrangement of controls, keypads, displays, information presentation, and alarms.
Cognition refers to higher level mental phenomena such as memory, information
processing, use of rules and strategies, hypothesis formation, and problem solving.
For example, the multiple hierarchical pathways and seemingly unlimited information
often found in computerized devices can rapidly exceed the user’s memory limits.
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Therefore, a designer should develop easy-to-use retrieval systems, taking advantage
of well-established semantic and symbolic techniques for screen and menu design.
Expectancies: People are predisposed to react to new situations according to
established habits. Designers can take advantage of existing conventions (“population
stereotypes” such as the color red equals danger) in the general population, as well as
the standards and conventions of the medical community. Designs consistent with
ingrained habits will facilitate performance and reduce training time. Designs that
conflict with such habits can lead to errors.
Mental Models: Based on experience, people form abstract concepts about how
complex phenomena actually work. For example, anesthesiologists, form mental
representations of patient status based on information about respiration, heart rate,
oxygen levels, and other bodily processes. Monitors should present such information
in a manner consistent with such models. There is a need for thorough assessment of
how users conceptualize device operation in patient treatment and monitoring. This is
a complex issue, because individuals differ in how they mentally integrate and
conceptualize data that change over time.
Home-use
Lay people increasingly use medical devices. Because of illness, poor reading
ability, inadequate facilities, insufficient assistance, and inexperience, this population
often represents a special challenge to designers. Decrements in vision, hearing,
strength, manual dexterity, and memory are to be expected with age and illness. Also,
many patients often are unfamiliar with automated devices and may be afraid to use
them. An additional concern is the potential effects of medications upon a patient’s use
of medical equipment. For these reasons, as well as lack of medical training, the lay
user’s operation of highly complex devices is problematic. Some devices that are
difficult for physicians and nurses to operate find their way into the home, where the
problems are further compounded by power outages, insufficient electrical outlets,
electromagnetic interference, narrow doors, the use of accessories (e.g., batteries),
and other factors.
DESIGN IMPLICATIONS
Obviously, completely “designing out” all problems associated with human
limitations, environmental factors, and stress is impossible. Regardless, the
cumulative and interactive effects of user errors can be serious and even disastrous.
Designing the interface with the user in mind usually will result in a device that:
•
accommodates a wide range of users working under variable,
often stressful conditions;
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•
is less prone to user error; and
•
requires less user training.
In general, human capability and limitations are extremely important considerations
in device design. The next section describes the kinds of user-interface issues
frequently encountered with medical devices.
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THE USER INTERFACE
This section describes and discusses problems related to human factors.
Hopefully, the material will foster an appreciation of the impact of considering the userinterface during design and provide the reader with the rationale and basic principles of
human factors. Brief summaries of serious incidents taken from the Food and Drug
Administration’s Medical Device Reporting (MDR) system illustrate the problems. The
summary principles found in the "Rules of Thumb" in each subsection are by no means
exhaustive, e.g., no detailed data on control dimensions and forces, body dimensions,
audition, vision, or menu and screen design are included. Consult guidelines,
textbooks, articles, and conference proceedings such as those listed in the References
for Further Reading. Finally, design principles alone do not solve every user interface
problem; the human engineering process, discussed later, is vital to such solutions.
CONTROL/DISPLAY ARRANGEMENT AND DESIGN
Many devices have large consoles with rows of mechanical controls and displays.
The designer should consider the ability of users to: quickly and properly identify
controls, switches, and displays; reach and accurately set controls; read displays
accurately; and associate controls with their related displays. Desirable features
include functional grouping of controls and displays, unambiguous labels, and easy-tooperate keys. Clear instructions and effective warnings also are important.
Examples of Errors Related to Hardware Design
The following three examples of problems were abstracted from the Medical Device
Reporting (MDR) system and FDA device recalls.
•
A physician treating a patient with
oxygen set the flow control knob, as
Figure 1 - Controls
show in Figure 1, between 1 and 2
With no flow
liters per minute, not realizing that the
between settings,
scale numbers represented discrete,
the user was
rather than continuous, settings.
“tricked” into
There was no oxygen flow between
dangerous
the settings, yet the knob rotated
errors!
smoothly, suggesting that
intermediate settings were possible.
The patient, an infant, became
hypoxic before the error was discovered. One solution would have been a
rotary control that snaps into a discrete setting. Some indication of flow also
should have been provided.
•
There have been numerous reports and recalls associated with
defibrillator design. These include paddles that are hard to remove from
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Do It By Design
their retaining wells and confusing arrays of poorly-labeled controls and
displays that inhibit safe, efficient use.
•
There have been cases in which patients were seriously injured when a
nurse over infused a patient after reading the number 7 as a 1. Because
the flow rate readout was recessed in the infusion pump display panel,
the top of the 7 was blocked from view by the display surface, even at
modest vertical viewing angles. There have been similar reports of flow
rates which had been misread when viewed from the side; for example,
355 ml read as 55 ml.
These few examples illustrate the fact that seemingly small design flaws can result
in serious problems. Tailoring a few general human factors guidelines, such as those
below, to particular devices will decrease the risk of such problems. Following are
some rules of thumb for designing the user interface.
Rules of Thumb
•
Make all facets of design as consistent with user expectations as possible. Both
the user’s prior experience with medical devices and well-established
conventions are important considerations.
•
Design workstations, controls, and displays around the basic capabilities of the
user, such as strength, dexterity, memory, reach, vision, and hearing.
•
Design well-organized and uncluttered control and display arrangements.
Ensure that the association between controls and displays is obvious. This
facilitates proper identification and reduces the user’s memory load.
•
Ensure that the intensity and pitch of auditory signals allow them to be heard
easily by device users. Consider the effects of ambient noise.
•
Ensure that the brightness of visual signals is sufficient to be perceived by
users working under various conditions of ambient illumination. Also, brightness
contrast and color contrast can help to optimize legibility.
•
Make labels and displays so that they can be easily read from typical viewing
angles and distances. Symbol size, contrast, color, and display depth are
important considerations.
•
Ensure that the abbreviations, symbols, text, and acronyms placed on, or
displayed by, the device are also used consistently in the instructional manual.
They also should correspond to standard nomenclature, if possible.
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Do It By Design
•
Design control knobs and switches so that they correspond to the conventions
of the user population (as determined by user studies and existing medical
device standards).
•
Arrange and design knobs, switches, and keys in a way that reduces the
likelihood of inadvertent activation.
•
Use color and shape coding, where appropriate, to facilitate the rapid
identification of controls and displays. Colors and codes should not conflict with
universal industry conventions.
•
Space keys, switches, and control knobs sufficiently apart for easy
manipulation. This will also reduce the likelihood of inadvertent activation.
•
Make sure that controls provide tactile feedback.
Summary
In summary, the layout and design of controls and displays greatly affect the user’s
ability to successfully perform functions and extract information during operation of a
device, especially during critical events. The next section discusses the logic of such
user-device interactions.
DEVICE LOGIC AND MICROPROCESSING
With modern automation, the logical, temporal, and informational characteristics
provided via software are increasingly crucial and error-inducing. For instance, data
presented imprecisely, ambiguously, or in a difficult-to-read format are likely to be
misread. Examples are crowded CRT displays, cryptic abbreviations, or time lags
between user input and displayed feedback. Such design may overtax the user's
memory and decision-making capability.
Characterizing the Shift to Software
With a large number of controls and displays, the user must identify and integrate
spatially disparate information. Although such designs are still common, the trend is to
assign more functions to software. This reduces the number of controls and displays,
but it can increase the burden on the user in other ways. This is the case with with
many infusion pumps, as shown in Figure 2 on the following page. Although there are
few controls and displays, the large amounts of information impose heavy demands on
the user’s memory. Most information must be recalled in sequence, thereby precluding
simultaneous viewing of related data. Users can become lost in the system if sufficient
prompts and roadmaps are absent. Also, users may misinterpret displayed data and
respond inappropriately if not given precise feedback and indications of functional
status.
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Do It By Design
Product developers often incorporate multiple of functions into a device to provide
flexibility and to serve a wider user community. However, extensive functional
capability may well impose an unreasonable cognitive load on the user, unless
considerable effort is devoted to the design of the user interface. The following are
some problems that apply to many medical devices and can lead to errors:
Figure 2 - Infusion Pump
•
illogical or cumbersome control
sequences;
•
unfamiliar language, symbols, or codes;
•
inconsistencies among display formats;
•
conventions that contradict user
expectations;
•
uncertain or no feedback after input;
•
functions that are hidden from the user;
•
missing or ambiguous prompts, symbols,
or icons;
•
unsignalled resets or defaults;
•
no status information;
•
missing lock-outs or interlocks; and
•
requirements for complex mental calculations.
With current models, users often must
retrieve and remember large amounts
of information.
Examples of Errors Related to Software Design
Many use errors induced by software design are incorrectly attributed to other
factors, because such errors are not easily remembered or recreated for post hoc
analysis or correction. Also, software-related errors can be subtle. For example, users
become frustrated by cumbersome data entry steps and make errors not directly
related to those steps. Ambiguous acronyms or abbreviations used in the command
structure or on menus may also lead to serious errors. Below are examples gathered
from incident files, recalls, and analyses:
•
There have been incidents with radiation treatment devices because users
failed to enter dosage levels if the device software did not prompt the user for
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Do It By Design
the data. Instead, the device automatically defaulted to a given value without
signaling this value.
•
A cardiac output monitor alarm was disabled without the operator’s
knowledge when the control buttons were pushed in a specific sequence.
•
There have been serious infusion pump incidents and recalls involving such
deficiencies as poorly signaled operating modes, cumbersome operating
steps, and the presentation of unanticipated warning data on displays
normally reserved for other critical information.
Below are some general considerations that, if implemented, can prevent many
software-related design errors.
Rules of Thumb
•
Do not contradict the user’s expectation. Rather, exploit their prior experience
with computerized equipment and consider conventions related to language and
symbols.
•
Be consistent and unambiguous in the use and design of headings,
abbreviations, symbols, and formats.
•
Always keep users informed about current device status.
•
Provide immediate and clear feedback following user entries.
•
Design procedures that entail easy-to-remember steps.
•
Use prompts, menus, etc. to cue the user regarding important steps; do not
"strand” the user.
•
Give users recourse in the case of an error. Provide conspicuous mechanisms
for correction and troubleshooting guides.
•
Do not overload or confuse users with information that is unformatted, densely
packed, or presented too briefly.
•
Consider the use of accepted symbols, icons, colors, and abbreviations to
convey information reliably, economically, and quickly.
•
Do not over use software when a simple hardware solution is available, e.g., a
stand-alone push button for a high priority, time-driven function.
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Do It By Design
•
Consider using dedicated displays or display sectors for highly critical
information. In such cases, do not display other data in these locations.
Summary
Microprocessing offers outstanding capabilities – ready data access, manipulation,
computation, speedy accomplishment of functions, and information storage.
Technological sophistication, however, can work to the user’s disadvantage if the
software design is done without a thorough understanding of the user. At a minimum,
designers are advised to utilize guidelines for human computer interface (HCI), do a
thorough analysis, and conduct usability testing during software development. A
thorough knowledge of the user population is necessary. Finally, software designers
need to coordinate their efforts closely with hardware designers.
COMPONENT INSTALLATION
Among the most common errors reported to FDA are improper installations of
device accessories. Although erroneous installation often is not obvious before an
accident, design-related installation problems frequently can be detected upon
examination following an accident. Proper installation is critical to safe device
operation.
Problems and Examples
Some commonly reported errors are tubing connected to the wrong port; loose
connections; accidental disconnections; electrical leads inserted into an improper
power source; batteries or bulbs inserted incorrectly; and valves or other hardware
installed backward or upside-down. The following MDR reports are illustrative:
•
A component of an oxygen machine was installed upside-down, resulting in
a patient death because of impeded air flow.
•
A ventilator was recalled after a low-pressure alarm had short circuited on
several occasions. The failures were traced to misinstalled batteries
resulting from design of the battery ports.
•
Three deaths were reported due to the introduction of a feeding solution from
an enteral feeding tube into an IV tubing used for medication. This happened
because an adaptor intended to introduce medication from an IV tube into
the enteral feeding system permitted the reverse operation.
•
Several injuries and deaths occurred because users inserted a cassette from
one infusion pump model into a different model for which the set was not
compatible. The resultant medication volumes were incorrect, although
pump operation and data display did not reflect this error.
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Do It By Design
•
Numerous injuries, deaths, and "near-misses" with ventilators have occurred
because of disconnections of the breathing tubes due to poor tube and
connector design.
The situation is exacerbated because many manufacturers sell a wide range of
accessories for a given type of device. There are a great variety of cables, leads,
connectors, valves, and tubing on the market.
Accessories for different models are often similar in
Figure 3 - Connectors
appearance and/or difficult to install, leading to
misinstallations and disconnections. Figure 3
illustrates the kinds of confusion that can lead to
installation errors. However, such accidents can
often be prevented through design solutions. When
conducting user studies, tests, and simulations, it is
crucial that device components and accessories be
Improper connections are
regarded as part of a system, not isolated elements.
frequent causes of accidents.
Rules of Thumb
The following are general considerations for reducing the likelihood of confusion
between similar components and accessories and making improper connections.
•
Cables, tubing, connectors, leuers, and other hardware should be designed for
easy installation and connection. If properly designed, incorrect installations
should be impossible, extremely difficult, or so obvious that they can be easily
detected and remedied.
•
User instructions should be understandable, and warnings conspicuous.
•
If a hazard cannot be eliminated by a design solution, color codes or other
markings will help the user achieve proper connections and component or
accessory installation.
•
Positive locking mechanisms are desirable whenever the integrity of
connections may be compromised by such factors as component durability,
motion, or casual contact.
•
Protected electrical contacts (e.g., the conductors are recessed) are necessary
for body leads that can be inadvertently introduced into outlets, power cords,
extension cords, or other common connectors. If possible, exposed contacts
should be avoided.
•
Components and accessories should be numbered, so that defective ones can
be replaced with the proper items.
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Do It By Design
•
Textual complexity in maintenance manuals should be reduced by adding
graphics.
Summary
There is a variety of device components and accessories. Potential hazards should
be identified, and appropriate design and coding techniques should be used to prevent
misinstallation.
ALARMS
Alarms and related advisories are intended to alert device users about problems
with the patient and device status. This seemingly straightforward function often is
complex. In some environments, alarms sounding simultaneously or intermittently on
one or more devices make proper identification difficult, and staff may become
distracted. Alarms may be considered a nuisance or part of the background; they also
can induce stress. Ambient noise and numerous visual displays can mask the output
from a particular auditory or visual display; overly loud alarms can mask other alarms.
Compounding the above problems are alarm failures and false alarms due to electromagnetic interference (EMI), static electricity, or over-sensitivity. It is critical to test
alarms in the environments in which they will be activated.
Problems and Examples
Alarm problems include the following: false alarms, delayed alarms, too sensitive
or insensitive alarms, alarms drowned out by noise, ambiguous meanings,
inappropriate silencing, and accidental disabling. The two incidents below resulted
from relatively common problems.
•
A patient receiving oxygen died when a concentrator pressure hose loosened. The alarm was not loud enough to be heard over the drone of the
device.
•
A patient on a ventilator died following accidental detachment of the
breathing tube from the humidifier. The alarm did not sound, because the
pressure limit setting apparently was so low that it was essentially nonfunctional.
Variations of these scenarios are common. Low alarm intensity, high ambient
noise, low battery conditions, inappropriate alarm settings, and other factors combine
to create potentially dangerous situations.
Rules of Thumb
•
Consider the wide spectrum of operating environments when designing and
testing alarms, including other equipment in simultaneous use.
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Do It By Design
•
Be sure that visual and auditory alerts and critical alarms are included in the
design requirements for the device.
•
Carefully consider the effects of over-sensitivity, electromagnetic interference,
and static electricity on alarm functioning.
•
Design alarms so they meet or exceed normal hearing and visual limits of the
typical user.
•
Make sure that both brightness contrast and color contrast are sufficient for
legibility under a variety of lighting conditions.
•
Use codes, such as color, that correspond to established conventions.
•
Design alarms to be distinguishable from one another and, to the extent
possible, from alarms on other devices used in the same setting.
•
Design alarms to activate immediately following the onset of a critical problem.
It is important that alarms identify the source of the problem.
•
Consider giving a priority status to critical alarms. Critical alarms should provide
redundant auditory and visual signals.
•
Design alarms so that when they are silenced, they remain silent temporarily.
They ideally will have visual indicators to indicate status and a mechanism for
querying the reason for the alarm.
OTHER IMPORTANT ISSUES
Dimensions, Forces, and Angles
Workstations, seating, and consoles associated with medical devices should fit the
user population. Data on body dimensions of various populations, including arm
length, body height, leg length, and numerous other bodily specifications, are collected
and published in a variety of documents. Such data, in conjunction with dynamic fitting
trials, are important in designing equipment, so that controls are within reach and
seating arrangements are comfortable. There are important implications for anesthesia
workstations, prosthetics, and rehabilitative devices; these data apply to many homeuse devices, such as wheelchairs, in which portability, compatibility with structures,
and compactness are important. Knowledge of the clinical or home use environments
is extremely important.
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Do It By Design
Important, but more elusive, are the
biomechanical characteristics of tools such as
hammers, dental tools, surgical instruments, control
knobs, keyboards, and other devices that require
substantial dexterity or strength and/or involve
repetitive motions. For example, instruments such
as those shown in Figure 4 can be difficult to use if
they are not tested with users. Physicians and
dentists often must precisely manipulate instruments
in limited spaces. There may be problems
associated not only with demands on dexterity and
strength but those related to visibility, reach, and
compatibility with other equipment.
Figure 4 - Medical Tools
Design for fine
manipulations is very
important.
Transfer of Training
Product developers often are encouraged to design products that incorporate
unique, distinctive features. These can have performance and training impacts upon
users in hospital units, where physicians and nurses have become accustomed to a
particular device model. For example, if two models have very similar (“look-alike”)
user interface configurations but require conflicting operator actions, habits established
with one device can interfere with user performance on the other. This greatly
increases the likelihood of errors. For example, if the ON/OFF switch positions are
reversed on two very similar devices, a user transferring from one to the other could
easily revert to the switch operation habits learned with the first device. The same
concern applies to a device that is retrofitted or redesigned. This discussion is not
intended to discourage innovation but rather to encourage designers to carefully
evaluate the impact of user interface changes on user performance.
Device Maintainability
Medical devices should be designed for simple maintenance, because poor
maintenance can hinder safe, reliable operation. Maintenance personnel often
encounter the following problems:
•
poor component labeling, coding, or numbering;
•
inadequate self-diagnostic capability;
•
parts that are hard to locate visually or by touch;
•
screws and other parts that are difficult to reach or manipulate;
•
confusing component arrangements;
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Do It By Design
•
requirements for difficult-to-find tools;
•
inadequate design for easy cleaning; and
•
materials that are not durable and degrade the user interface.
Possible signs of inadequate attention to human factors include improperly
connected wires, stripped threads, unreliabe operation, dirty displays, and sticking
keys. Not only are devices that are difficult to maintain usually out of use for long
periods of time, but maintenance personnel may modify the devices to compensate for
deficiencies, possibly creating new problems for the user.
Device Packaging
Packaging sometimes affects operation of a device. For example, there have been
incidents resulting from packaging materials enclosed in such a way that users failed to
detect and remove them. In some cases, this impaired functioning of the device. With
one infusion pump, serious accidents occurred when unremoved packaging materials
increased flow rates. On the other hand, packaging also can be designed to facilitate
removal of devices or accessories and/or to make storage easier.
Sometimes, package design can reduce the likelihood of error. For example,
catheters and compatible guide wires usually are packaged together. The same is true
of needles and syringes, some infusion pumps and dedicated administration sets, and
various contact lens accessories. A unique example is a customized container cover
having an integral spacer that separates heart valve leaflets. Originally, cotton was
used to accomplish this separation, but in a number of instances surgeons had
neglected to remove the cotton spacer prior to installing the heart valve. There were
several deaths due to the formation of massive clots associated with residue from the
cotton. The integral spacer precludes such accidents.
Summary
Implicit in the discussion of errors is the importance of implementing good design
principles. Rarely do human factors principles fully cover all design situations. Good
design practice entails the involvement of medical device users in studies, analyses,
and tests to achieve optimal design. The next section, on human factors engineering
discusses these methods.
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HUMAN FACTORS ENGINEERING
Human factors engineering is a methodology that is crucial to effective userinterface design; it entails the iterative application of various procedures and tools
throughout the design cycle, as illustrated in Figure 5. Participation of individuals from
the user population is integral to this process. The developers of high technology
products have adopted and refined such methods, calling their approach usability
engineering. Of particular note is their emphasis on user studies and computerized
testing prototypes.
Figure 5 - Human Factors Engineering Process
Conduct
Exploratory
Studies
Develop
Concept &
Requirements
Analyze
Tasks,
Hazards, &
Functions
Design
User
Interface
Perform
Usability
Tests
Develop
Final
Specification
Resources & Tools
Literature
Guidelines
Device Data
Device Users
Subject-MatterExperts
Consultants
Drawings
Mock Ups
Predicate Devices
Storyboards
Prototypes
Usability Labs
Medical Facilities
The rationale embodied in Figure 5 may be characterized as “designing in the
user”. Designers usually are too familiar with, and too close to, their designs to
understand all of the potential impacts upon users. Early consultation with the user
population is necessary for assessing needs and developing requirements. Users also
are critical for analytical work and testing throughout product development. With
marketed products, field testing and feedback to manufacturers are highly desirable.
Ideally, hardware and software designers, engineers, human factors practitioners,
document writers, and clinical staff coordinate their efforts to achieve a user interface
design that lends itself to safe device assembly, installation, operation, and
maintenance. The following factors will influence the flow of a given project:
• pre-existing data;
• complexity of the device;
• criticality of errors;
• human factors expertise;
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• experience with other devices ;
• similarity of a product to an existing one;
• organizational culture; and
• competitive market pressures.
When developing a device that automates previously manual tasks, one might start
by analyzing the performance of such tasks by healthcare professionals in a clinical
setting. A competitive “benchmark” test of already-marketed models also might be
conducted to uncover strengths and weaknesses of existing designs. Or, a project
could start with an examination of existing devices and manuals for design
modifications, markings, or notations. These may indicate that users attempted to
compensate for design deficiencies.
Sometimes, a new design represents a small departure from an existing one, as in
many product improvement efforts. However, even small hardware or software
changes may have substantial impacts on the user interface. Therefore, potential
impacts of change are important, even when the use history of the predecessor device
is indicative of good design.
Although there is latitude with respect to what analyses, tests, and tools are
implemented, the process should not be haphazard. The rationale for human factors
engineering lies in the repetitive analysis, testing, and refinement of design concepts –
all with input from users. There is some trial-and-error, but the bigger problems are
detected and eliminated during the earlier stages before the design is "frozen."
Finally, information collected during these efforts can help reduce errors, time, and
costs in future projects involving similar products. The development of an in-house
human factors guidance notebook for a family of devices should be considered.
The remainder of this section describes methods used by human factors
professionals in designing user interfaces for equipment.
DOCUMENT REVIEWS
Studying documents about human factors and related device issues is valuable
early in the development of a product. Such information is easy to obtain and is useful
in understanding user interface issues and human factors methods.
The Literature
Human factors articles, technical reports, and textbooks offer substantial
information. Numerous journals, magazines, and newsletters report studies and
surveys on the combined effects of design, environment, and work conditions upon
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device operation. Also of value are design case studies and product evaluations.
Research, design, and conceptual articles of value also can be found in such human
factors publications as: Human Factors, Ergonomics, Ergonomics in Design, The
Journal Of Applied Ergonomics, and the Proceedings of the Human Factors and
Ergonomics Society (HFES) Annual Meetings. The proceedings of sessions
conducted by the Human Factors and Ergonomics Society (HFES) Medical Systems
and Rehabilitation Technical Group are especially relevant, as are those of the Human
Engineering Division (#21) of the American Psychological Association. Textbooks
offer a broader view of human factors principles, design process, environmental
factors, and humans as device operators. Finally, technical reports, standards, and
guidelines from government and military agencies are useful.
Complaints and Recall Data
A company’s recall and device experience data can provide historical information
that may lead to important insights about potential problems and design solutions
relevant to new product development. Reports in FDA’s MDR system about problems
across a device area may also be enlightening. Although use errors and design
traditionally have been treated as separate issues, one can glean substantial
information from this source via careful analysis. Such information may identify
potential problems during the feasibility phase of a new development project.
Guidelines
Guidelines provide principles, data, and human factors engineering methods. An
example of a principle might be the following: "There usually should be feedback
displayed immediately following a user input via a control, key, switch, or other input
device." Data may include anthropometric, dimensions, visual and auditory limits, etc.
The most widely recognized guidelines in the medical device community are the
ANSI/AAMI Human Factors Engineering Guidelines and Preferred Practices for the
Design of Medical Devices (1993). Other guidelines published by government
agencies include guidelines and military standards. They contain useful information
about principles and methodology. Many textbooks on human factors, usability testing,
and human-computer interface (HCI) design also are applicable.
Guidelines must be used judiciously. They are not intended as "cookbooks." The
effectiveness of a guideline is in part determined by the education and skill of the
person using it. Understanding the rationale behind principles is important, because
the applicability of some principles may depend in part on the specific design in
question, as well as analytical, research, and test data.
Manuals
Review of user instruction manuals may provide information about pitfalls to avoid
and possible features to include when considering the development of a new product.
For example, a warning such as "be careful of automatic flow rate defaults" may
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indicate that such defaults are not clearly signaled or, possibly, may not be desirable in
the first place. The review and comparison of the written operating procedures and
control panel illustrations may also point to a number of strengths or weaknesses in
key layout, operating logic, and other user interface concerns during new product
development.
Ideally, once the user interface concept begins to take shape, concurrent work on
the instruction manual should begin. Manual development should not be delayed until
after the design effort is well under way or completed. If manual development is
coordinated closely with the design effort, the very process of developing the new
manual may uncover design problems.
Summary
Review of the above types of documents can provide a clearer picture of the
following:
•
sensory, perceptual, physical and cognitive capabilities and limitations of
individuals;
•
environmental interactions with human performance, especially as mediated by
user interface design;
•
human factors principles and methods;
•
generic problems associated with types of devices; and
•
strengths and weakness of existing devices and the one under development.
Document reviews help one to ask the right questions, avoid pitfalls, and get the
product design process off on the right track.
EXPLORATORY STUDIES
Obtaining first-hand information from physicians, nurses, and lay-users is important
in assessing the strengths and weaknesses of a device design. Other potential
participants to consider are risk managers, clinical engineers, maintenance personnel,
trainers, and supervisors. Questionnaires, on-duty observations, interviews, and focus
groups are ways to assess design concepts, mockups, or predicate devices.
Why Do Such Studies?
Direct contact with the user population is essential for good human factors work. It
should be initiated in the earliest stages of product design. Observations, remarks,
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and anecdotal comments about existing devices, desirable design features, and
working conditions can provide the following:
•
a snapshot of how healthcare professionals use devices;
•
a picture of how operating conditions, including the multi-device environment,
affect use;
•
a snapshot of what problems are encountered;
•
anecdotal reports or comments;
•
a sampling of the user population with respect to individual differences;
•
ideas for new designs and reactions to design concepts; and
•
information necessary for establishing performance test protocols and
performance criteria.
Early studies, along with document reviews and task analyses, are very important.
They engender creative thinking and reduce the likelihood of major mistakes in the
design process.
Study Methods
Below are some techniques frequently used in early studies. They are not
independent of one another, and techniques discussed elsewhere, such as task
analysis, may also be integrated into these approaches.
Observations: In a medical facility, the operating rooms, emergency rooms, and
critical-care units are fertile areas for observational studies of associated devices.
These include the observation of ongoing operations and the inspection of devices
following operation, especially after prolonged use. There are implications for areas
such as maintenance, cleaning, installation, and the effects of environmental conditions
upon the user interface. In the operating environment, substances such as dirt, water,
saline solutions, alcohol, blood, and coffee often impede proper use of a device, as
well as its functioning.
Non-intrusive and systematic observations are best. They can be recorded as
narrative descriptions and/or as entries on data sheets formatted with predetermined
data categories. Demographic and device information are desirable. When
videotaping a session, the tapes can be indexed by critical events and times in order to
avoid a time-consuming review. Another issue is the sampling of participants and
operating conditions. Within the scope of time and resources available, observing
different users under varying work conditions is desirable to ensure the generality of
the observations.
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Interviews: Interviewing is a flexible way of obtaining opinions about specific
devices, problems, and user preferences and ideas about improving user-interface
design. Interviews also can be conducted quickly and in conjunction with
observations. Below are a few ideas about interviewing personnel in medical facilities.
Interviewing Users: Healthcare practitioners and lay users often hold perceptions
that differ greatly from those of the designer. Valuable data can be obtained by having
physicians, nurses, or home users do the following:
•
walk through the operational steps;
•
compare relative strengths and
weaknesses of different models;
•
describe "critical incidents" involving
a device;
•
if needed, recommend device changes;
and
•
assess a new device concept.
Figure 6 - Blood Glucose Monitor
•
•
•
•
Are displays and labels legible?
Are strips easy to clean and insert?
Is device compact and durable?
How difficult are timing operations?
Remember that interviewees usually will not be
able to visualize design concepts in the abstract.
They react best to existing devices, mockups, or pictorial drawings of a device
interface. In the latter instance, the operational logic should be clear. Allowing people
to react to something tangible will provide a wealth of ideas. Questions, such as those
in Figure 6, can help target problems with design.
Interviewing Supervisors, Trainers, and Risk Managers: Most healthcare
supervisors have fairly broad views of device strengths and weaknesses. They are
aware of serious incidents and device characteristics that are substantial impediments
to productivity. Training staffs often have detailed knowledge of the effects of design
on training time, as well as recommendations for instructional manuals. Risk
managers document incidents that can shed light on specific design problems.
Interviewing Maintenance Personnel: Maintenance personnel may have a
unique perspective about device problems. Users often bring to them “broken” devices
that, in fact, are functional but difficult to use. For example, poor design-for-installation
and examples of misinstalled componen ts may come to light. In addition, a damaged
device may signal a user-related problem. Finally, since recalled devices often are
modified on site, technicians will know of both hardware and software fixes related to
deficiencies in the user interface.
Conducting Focus Groups: Focus group sessions are group interviews of a few
individuals from a specified population. The sessions are conducted to obtain opinions
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Do It By Design
and ideas regarding a product concept. A focus group typically consists of about six to
eight healthcare practitioners or lay users. These individuals should be prospective
users of the new device under consideration. Such sessions are best conducted by
experienced moderators working from scripts prepared in concert with the design
team. Well-conducted sessions yield numerous ideas about user-interface design
alternatives and user requirements. Remember that users generally have limited
knowledge of design alternatives and principles. Thus, the best approach is to weigh
subjective data against known interface characteristics, human factors expertise, and
user performance data. Finally, because dominant individuals can bias findings, it may
be wise to also consider one-on-one sessions.
Physical Measurements: Measuring sound and light will help in the assessment
of such design-moderated factors as glare, contrast, and masking by ambient noise.
Also, measurements of both physical reach and visual envelopes are necessary in
workstation design. Samples from different facilities will produce data to profile typical
work environments.
Summary
Observational studies and interviews can pay handsome dividends. The design
team gains a better appreciation of the user population, the working environment,
potential hazards, problems with predicate devices, and viable alternatives for new
designs.
ANALYSES
Analyses of functions, tasks, and hazards are important to good design and will
help shape the user interface by providing information about:
•
user requirements and usability goals;
•
other devices in the users’ environment;
•
bottlenecks to potential performance and error-inducing factors;
•
possible hazards;
•
device impact on user training; and
•
device operating logic.
Analyses merit careful attention and should be woven into the development
process.
Functions and Tasks
The user and a finished device work together as a system. Primary functions are
device installation, maintenance, operation, and monitoring. The user’s functional
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Do It By Design
contributions are referred to as tasks. Increasingly, devices are multi-functional in
order to accommodate a wider range of users and to increase the flexibility of
applications of the device. Such increased capability can impede ease of use, unless
the respective assignments of functions to the device and tasks to the user are
carefully weighed. Machines are good at storage and retrieval of coded data, rapid
computation, timing, and deductively-based activities. People perform better in
sensory, judgmental, interpretative, and non-routine tasks. The number of functions
and relative device/user allocations have important implications for the user interface.
As a hypothetical example, suppose that an infusion pump designer decided to
provide the user with the capability to "stack" flow rates, i.e., to program a sequence of
rates that will apply to successive patient administrations. A number of questions
arise: Should flow rate retrieval and administration functions be automatic or manual?
What happens if one of the queued flow rates is accidentally deleted, defaulting to the
next flow rate? How does the user identify and track the flow rates? How does the
user access and change a specific flow rate? If
such questions are addressed early in the
Figure 7 - Ventilator Alarm
product’s development, the answers will help
Control
shape the functional design, which in turn will help
determine the user-interface alternatives.
Some functional issues are complicated by
medical practice, operating conditions, and the
preferences of individual healthcare practitioners.
An example is the degree to which ventilator or
anesthesia machine pressure-limit alarm settings,
illustrated in Figure 7, should be under the user’s
control. Many practitioners prefer a wide latitude in
setting alarms. However, a very low alarm setting
permits the user to effectively disable the alarm.
Safety implications should be carefully weighed
against the user’s preferences.
How much discretion should the user
be permitted in setting limits?
In summary, too many functions or too much/little automation can be problematic,
depending upon the user population and working environment. The appropriate
tradeoffs should be considered at an early stage in the evolution of the design concept.
Analyzing Tasks
Task analysis is critical to good human-factors engineering and can be performed
throughout the development phase. At various points, the design team should perform
detailed sequential analyses of those tasks that comprise assembly, installation,
operation, and maintenance. In the early conceptual stages, critical tasks can be
identified and described by observing and/or questioning healthcare professionals who
use the type of device under development. When design concepts are initially
formulated, the analyses should be conducted as paper-and-pencil exercises. As
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Do It By Design
development progresses, analyses can be performed with such tools as device
descriptions, drawings, existing devices and prototypes. There are many
methodological variations, but task analysis is basically straightforward. Depending
upon the scope and purpose, the analyst usually will do some, or all, of the following:
•
list the major tasks, such as calibration, entering operating parameters,
attaching the device to patient, and cleaning parts;
•
describe the necessary information for each task, user actions, required
decisions, and related accessories;
•
describe the device response for each action or step;
•
record observations and inferences about design factors which potentially
impact the user;
•
list the effects of environmental conditions and other devices on the user
interface and performance; and
•
list the impact of the user interface on training requirements.
The following table shows a few steps from an analysis of a marketed infusion
pump conducted by FDA. The analysts were “troubleshooting” the user interface
design.
In this example, the human factors team found that performing the initial setup
steps was quite easy; but, shortly into the exercise, problems arose. First, the team
had been operating on the assumption that the pump was plugged in when, in fact, it
was not. Because the battery and AC power icons were poorly located and very small,
they appeared as tiny “dots” at normal viewing distances and angles. Therefore, they
were easily overlooked. The team also discovered that users could miss important
status information and prompts due to a very brief display of data. When the keys for
entering flow rates were depressed for more than a fraction of a second, the values
scrolled past the desired one. In addition, there was auditory feedback only after the
initial key press, not following each of the scrolled values. Inconsistencies across
operating modes in the operation of a double function key were found, and these could
be very confusing to the user.
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Sample of Task Analysis Steps from Analysis
of an Actual Pump: Troubleshooting the User Interface
User Action
1. Push “On” button.
Device Response
If unplugged, battery light (icon) glows.
If plugged in, power light glows.
“Select Mode” message appears for brief
interval of 3 seconds
Flow rate and volume displays show “0"
even if there is a default value.
Observed Problem
Battery and power lights are so small and
poorly positioned that the user probably
will not notice power status.
User likely will miss mode indication and
leave device in previous (default) mode.
Many other pumps show default value from
last use. User may assume no default
value with this pump (see step #3).
2. Press pump mode
button.
Mode light glows.
Mode lights do not blink, are small, and can
easily be missed. Each is close to a key
with no functional relationship. Incorrect
association is very possible.
3. Press rate
button.
Flow rate displays default value from
previous administration.
User experienced with another pump may
assume a “0" value by this point and miss
default value (see step # 1).
4. Enter flow rate
values in
ml per hour.
As first value (e.g., 100 ml) is entered,
device “beeps” and 100 is displayed. User
can scroll in increments of 100, and
successive values are displayed - but no
more “beeps”. With constant pressure on
key, values may scroll up to 300 ml, for
example, in 1 sec.
A distracted user, not observing display,
may intentionally or accidentally enter
more values without any auditory feedback
to indicate entry.
The research team visited a hospital after performing this analysis, and, by chance,
this pump was used in the unit visited. The head nurse stated that she had selected it
because it seemed "user friendly." Unfortunately, the unit staff found it so difficult to
use that the head nurse now considers the pump not only an inconvenience to users
but an impediment to safety and effectiveness.
If task analyses had been performed in the preceding example, a set of guiding
principles for pump setup might have emerged, such as the following:
•
Status indication and feedback should be precise and unambiguous.
•
Displayed alerts should be attention-getting and in view until an action is taken.
•
Flow rate and volume-entry mechanisms should be convenient for the user,
without sacrificing accuracy (e.g., over-scrolling).
•
Specific keys should operate in a consistent manner across modes.
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Hazard Analyses
Human factors should be integrated into procedures used to isolate hazardous
device failures. Although these analyses conventionally deal with electrical and
mechanical problems, potential hazards associated with the user also should be
evaluated. One should assume that if errors can occur, they will occur and that design
may be a factor. Hazard analysis meetings provided an excellent collection point for
possible hazards uncovered from complaint files during earlier studies, as well as from
tests, user studies, and task analyses. As a first step, by considering errors as
“failures” analysts can hypothesize what errors are possible. Then, they can
analytically pinpoint potential causes and draw conclusions about consequences and
appropriate design solutions. This information may be tabulated to provide a concise
overview for further analysis and/or input into the design concept and requirements.
The utility of such an approach is
illustrated by electrocutions of infants
resulting from the insertion of patient
electrode leads into AC power cords
by parents, siblings, and healthcare
professionals (see Figure 8). If
analysts had considered the use
environment, user populations, and
potential errors, the hazard probably
would have been identified and the
appropriate solution, such as
recessed body leads, implemented.
One should note that hazard
analyses may pinpoint low-frequency
errors not discovered in prototype
tests involving users.
Figure 8 - Electrical Leads &
Hazard Analysis
Some hospitals have many unprotected body
leads in inventory. Hazard analyses can
identify the hazards and their solutions.
Other Analyses
Other techniques include time lines and workload analysis. Time lines represent
sequential and simultaneous responses required of the user which are graphed over
time. Workload analysis can produce measures ranging from estimated expenditures
of energy for physical tasks to subjective and performance measures of the
performance requirements imposed on operators. Both of these methods are useful in
multi-task situations which involve the use of more than one device by the user.
Summary
Thorough and continuous analysis is a powerful tool and is necessary throughout
the design process. Overall, the findings can be combined with drawings, diagrams,
user profiles, and various other data summaries to help shape alternative user-
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Do It By Design
interface designs, elucidate flaws in design, and provide the focus for human-factors
tests.
USABILITY TESTING
Testing for ease and accuracy of use is the only way to ensure that users can
safely and effectively operate, install, and maintain devices. By means of iterative
prototyping, individual concepts of design can be tested, refined, and retested
throughout the development process. This process culminates with full testing of a
model embodying all the user-interface characteristics for both hardware and software
of a fully functioning device.
Developing Prototypes
Prototypes simulate the user interface as defined by both the hardware and
software; they are used to select alternative designs and uncover problems. A
prototype’s fidelity, or resemblance to a working device, is determined by it’s physical
and/or conceptual attributes. If installation, control and display layout, or manual
operation (e.g., of surgical tools) are of special interest, mock-ups should be used for
physical simulations, or “games playing”. Users can perform the procedural steps to
confirm or repudiate the design or layout details. If underlying machine logic and
information presentation are of concern, story boards, screen prints, interactive
computer models, and working models can be used to evaluate user efficiency with a
given interface design. An early test might consist of users completing tasks by
performing data entry operations on a sequence of screen prints. The test participants
would indicate their selected keys, while verbally describing each action. Each user
input is followed by the presentation of a new print showing the appropriate feedback,
prompts, or status change.
With more sophisticated, computerized prototypes, key panels and controls are
represented graphically on a computer with the program having limited functionality.
Thus, for example, a finger press on a specific "button" simulated on a touch screen
results in apparent button movement, followed by displayed feedback. The program
then sets up the contingencies for the next operator response. "Horizontal" prototypes
present an overview of top-level features but do not permit much operational depth.
"Vertical" approaches allow more in-depth operation of fewer functions and greater
data access. “Scenario” prototypes combine features of both approaches, allowing
test participants to perform a limited number of tasks of particular interest at a given
point in development. Based on the findings, the design is refined, and the prototype is
then retested. Such prototypes permit a great deal of flexibility in evaluating alternative
designs prior to the final stages of development.
Developing Scenarios
Written scenarios help provide the structure for what test participants actually will
do. A scenario generally is a written description of what the participants are expected
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Do It By Design
to accomplish and may be narrow or broad in focus, depending upon the purpose of
the test and the functionality of the prototype. For example, the participant might be
asked to turn on an infusion pump and set it up for drug administration by keying in the
appropriate flow rate and volume-to-be-infused parameters. A more advanced
scenario might include other tasks, such as installing the administration set, performing
primary and secondary infusion, changing parameters, and reacting to an emergency.
In all cases, scenarios should be clearly written to help ensure consistency across
participants and test conditions. Healthcare professionals are of great use in creating
scenarios and checking them for realism and accuracy.
Requirements and Measures
User requirements are based primarily on earlier interviews, observations,
manufacturer’s experience, analyses, and literature reviews. Some requirements are
specific, such as "installation should take no more than 30 minutes." At the conclusion
of the test, the actual performance times can be compared to these criteria. In other
instances, initial requirements will be broader, such as "novice users should reach high
levels of efficiency after a few hours of training." Efficiency, in terms of errors and
time, can be hard to determine while the design concept is in flux. At some point in
development a clearer picture of expected performance levels will emerge, and
detailed performance criteria need to be defined. If possible, these should be
quantitative and should be linked to safe use and any other goals important to the
manufacturer and user population. In addition to specific strengths and weakness in
device operation, a number of other design-related measures may be important, such
as calibration time, accuracy, changes in error probability, and other measures.
Various measures are used in testing. Errors may be recorded by direct
observation, videotaping, or electronic data logging. Speed of operation is based on
completion times of tasks, and other objective measures may be used, such as the
number of times the user must refer to the device manual. Verbal responses also are
important and can be obtained by interviews or by having users state the rationale for
their actions as they progress through task sequences. Also, subjective impressions
of usability and potential safety problems are important.
Facilities
Depending on resources and the nature of the test, a modest usability laboratory
may suffice. A limited facility might consist of a room containing a table, chairs,
electrical outlets, and adequate lighting. An increasingly elaborate setup would include
a one-way mirror, observation room, video camera(s), adjustable lighting, tape player
for noise presentation, an automated data-logging system, a microphone, and other
medical equipment. Finally, testing in medical facilities is another possibility.
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Test Participants
In the case of small, iterative, prototype evaluations conducted throughout
development, two or three participants per test may be sufficient. Employees such as
clinical staff may be used, although repeated use of the same individuals can bias the
findings. Full usability tests require larger samples drawn directly from the user
population. If a device is intended for a fairly homogenous population, data obtained
with about 10 individuals representative of that population may be sufficient to eliminate
most problems. However, it is important to note that the cumulative number of
participants over the course of development can be substantial, given the iterative
small tests mentioned earlier.
In general, the test team should consider the extent to which additional problems
are uncovered as more participants are added and/or as more tests are run. With a
more heterogenous population or in competitive device testing, larger samples are
desirable. The user interface can be maximally stressed by using new healthcare
practitioners. However, the preexisting habits of experienced individuals also may be
an important concern, depending on the type of device and target population. With
home-use devices, participants should be sampled from the lay-user population. In
some cases, the effects of medication should be considered, provided that safety and
ethical standards are met.
Conducting the Test
Below is a scenario that might be used
in a fairly comprehensive assessment of the
user-interface design of the arrhythmia
monitor. It consists of narrative that
requests the participants to perform various
tasks. This will help the test team obtain
data on errors, performance times, and
impressions of device design features.
Evaluation of the data will answer the
kinds of questions listed under the monitor
in Figure 9. The participants might be given
instructions such as the following:
Figure 9 - Monitor Interface
Are alarms distinctive and obvious;
waveforms accessible and clear; and
screens and menus well-formatted? What is
the likely impact of the user interface on
training requirements?
“Turn on the monitor and perform the basic setup tasks, such as checking and
adjusting the calibration, amplitude, gain, and alarm limits. When prompted, retrieve
waveforms and trend data as specified. Report any visual alarms such as
disconnected lead wires or a low battery.”
Generally, the device users selected as test participants should be healthcare
professionals who are not trained on the specific model. After participants become
familiar with the monitor, the test team might have them run through the operations at
their own pace, at any point probing with questions about bottlenecks or apparent
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Do It By Design
problems. If critical issues arise, the test can focus on these and less on others. In
addition, because devices are often used in very intensive, novel situations, users can
be stressed by minimizing their familiarization with the device and limiting the use of
instruction manuals, which often are not readily available in real world situations. Also,
consider the possibility of testing novice device users, in order to impose a greater
burden on the interface.
Possible performance measures in the sample scenario include set-up times,
number of errors, type of errors, changes in error raters, failures to detect and
discriminate alarms, task completion time, and any observations that indicate
performance obstacles. In addition, if the participants are asked to "think aloud" as
they proceed through the tasks, it is important to develop a record of their remarks.
Finally, pre- and post-testing questionnaires or interview comments, likes and dislikes
about user interface elements, and other comments about overall device safety and
usability are valuable. One caveat, however, is that users generally are inexperienced
with design principles. Although their opinions generally are valuable, the subjective
preferences of device users for various interface designs are most valuable when
assessed in conjunction with performance data and expert opinion.
Testing in the "Real" Environment
The user interface should be tested under conditions that are as realistic as
possible. Participants should be reminded that it is the device, not themselves, being
tested.
Simulating Actual Conditions in the Laboratory: Some aspects of actual use
conditions are relatively easy to simulate. For example, adjustable lighting and
individual lamps of varying wattage and direction will produce variable levels of
illumination and glare. Likewise, tape recordings from emergency rooms, operating
rooms, and critical care facilities will reproduce decibel and frequency levels that
challenge alarm audibility and the user's concentration. With home-use devices, it is
important to simulate environmental constraints (e.g., space) that pertain to such
device characteristics as placement and portability.
It is more difficult to simulate patient and device status, as well as the interactive
effects of multiple devices. In the monitor example, changes in patient and device
status could be simulated by programming in ECG changes and alarms. In multiple
device scenarios, test participants might alternate between different devices they
typically use on the job. Variables might include conflicting user-interface designs and
problems associated with device attachments.
Simulations in Healthcare Facilities: Even without patients, performance testing
in healthcare facilities adds substantial realism. If on-duty physicians and nurses are
tested on devices that effectively simulate device interfaces and functions, the effects
of stress and fatigue on use of the device can be assessed, especially if the tests are
conducted at the end of shifts. Testing in emergency rooms, operating rooms, or
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critical care facilities is difficult, if not impossible. Testing in many cases should be
performed during breaks and be limited to especially problematic design issues. The
exception would be a study in which a medical team performs a lengthy, simulated
procedure. Then, the facility essentially becomes a laboratory.
Simulations in Homes: Medical devices intended for home use should be tested
in that environment. This can be especially useful in assessing devices that pose
problems associated with space, portability, availability of electrical outlets, lighting,
noise, and operational complexity. Lay users should participate if possible.
Clinical Trials: Ideally, one could do full testing during clinical trials; however,
there are definite limits. First, manipulating the healthcare practitioner’s behavior by
running scenarios would be disruptive and could endanger patients. Second, the userinterface design should be at least adequate prior to clinical trials. However, these
factors do not preclude additional evaluation at this stage. Physicians and nurses can
be alerted to design issues of special interest and interviewed after the completion of
procedures. Likewise, observations by trained observers are valuable.
Field Studies: Studies of devices already in use offer an excellent opportunity to
obtain valuable information once a device is marketed. Because there are few time
constraints, data can be obtained from a wide variety of settings and user groups.
Such studies can be modified at any point to accommodate changing circumstances.
The findings will supplement and clarify complaint data, as well as provide
unanticipated information pertinent to marketing and new development efforts. This
data should be documented for current and future use.
Summary
Obtaining performance data from actual users is crucial. If test participants cannot
safely and effectively use a device under test conditions, healthcare professionals
definitely will have problems with it under actual conditions of use. Finally, the
development of user requirements and thorough testing helps ensure that the final
product addresses the needs of healthcare professionals and patients.
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SPECIAL ISSUES
INITIATING A COMPANY HUMAN FACTORS PROGRAM
Personnel
No two product development projects are identical, and the same can be said of
corporations. Size, organization, and culture vary from firm to firm; all will affect the
implementation of a human-factors program. Whether relying primarily on consultants
or staff experienced with human factors engineering, integrating them into project
design teams is crucial.
Educating both technical and managerial staff about human factors also provides
long-term benefits to the organization. The target audience for training should include
engineers, designers, manual and training developers, risk managers, quality
managers, and corporate executives. Staff should know what a human-factors
program is and why it is important. One should consider having a human-factors
professional give seminars which would include one or more of the following: (1)
discussion of human factors principles, problems, and methods, (2) demonstrations, or
(3) case studies. Involving a company’s own designers and products will greatly
increase the effectiveness of seminars. Likewise, the first-hand experience of humanfactors practitioners with development efforts, design principles, liability issues, and the
literature is valuable. There also are established professional short courses in human
factors, and many universities offer degree programs in this discipline. There is a
caveat, however: casual “armchair” approaches do not work; training and experience
are necessary. Effective human factors programs consist of ongoing training that
provides feedback for continuous improvement. Finally, depending on the
manufacturer’s capabilities and corporate resources, management should consider
hiring human-factors staff. Trained human factors practitioners can expand solutions
to problems in ways that others would not anticipate.
Resources
Some resources already have been discussed: the literature, guidelines, and expertise
of current staff. Many manufacturers may also need a consultant’s help in establishing a
human-factors program. There are many highly qualified human-factors consultants
available for such purposes. They currently apply their expertise to areas ranging from
military systems, air-traffic control, and nuclear power plants to office equipment and,
increasingly, medical devices. The basic rationale and methodology is the same in all
of these areas. The societies listed below are clearing houses for consultants.
Ergonomics Society
University of Technology
Loughborough, LEIC LE11 3TU
England
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Do It By Design
Human Factors and Ergonomics Society (HFES)
P.O. Box 1369
Santa Monica, CA 90406
IEEE Systems, Man, and Cybernetics Society
345 East 47th Street
New York, NY 10017
Industrial Designers Society of America
1142-E Walker Road
Great Falls, VA 22066
Society for Information Display
8055 W. Manchester Avenue
Suite 615
Playa del Rey, CA 90293
Society for Technical Communications (STC)
Suite 904
901 North Stuart Street
Arlington, VA 22203
Special Interest Group on Computer
and Human Interaction (SIGCHI)
Association for Computing Machinery
P.O. Box 12115
Church Street Station
New York, NY 10249
Usability Professionals Association
American Airlines/STIN
P.O. Box 619616 MD 4230
DFW Airport, TX 75261-9616
Characterizing the Human Factors Effort
Despite substantial variability in human-factors engineering efforts, the following are
essential:
•
a designated individual in the design effort who is responsible for user-related
issues;
•
participants from the user population;
•
requirements that the product be designed for safe use;
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•
studies, analyses, and tests that assess user performance and identify hazards;
and
•
data indicating whether or not the user interface meets requirements.
The best “advocate” for the device user is someone who works integrally with the
design team. They participate in the planning and implementation of the appropriate
studies, analyses, and tests. Test participants can be drawn from the company’s pool
of clinical staff and outside healthcare professionals. Potential hazards, errors, and
broader usability issues normally are defined from device records, user studies, and
analyses. They will help shape initial requirements of the user, which will be refined
throughout development and will help determine the test criteria and measures.
Although there is no formula for deciding how extensive a human-factors effort
should be, consideration of some basic variables will help in making decisions. Weigh
the following: the nature of the user-device interaction, the user population and use
environment, the likelihood and criticality of errors, the feasibility of alternative user
interfaces, and the company’s experience with predecessor devices.
In the unlikely case that a device has virtually no user interface or functional
integrity precludes interface design options, a substantial human engineering effort
would not be warranted. However, most devices require substantial user/device
interaction, and the complexity of the interface usually is an issue. The greater the
impact of errors upon the health and safety of patients, the greater the need for
thorough analysis and testing. If the user interface is similar to that of a previous
model, the use history of the latter model and the potential impacts of any changes to
the new model merit attention.
The Appendix offers points to consider regarding human factors engineering efforts.
ADVICE TO HEALTHCARE FACILITIES
Recognizing human-factors design problems with already purchased devices is
important. The selection of new equipment that staff can operate safely and effectively
also is important. This section deals with these issues.
Recognizing Problems
Healthcare professionals are more likely to blame themselves for errors than they
are to blame the equipment. User interface flaws can be subtle, and a physician’s or
nurse’s attention is focused on the patient, not the device. Also, a sense of
professional responsibility often precludes healthcare practitioners from "blaming" the
device; as a consequence, practitioners are often blamed for design-induced errors.
Although problems with user interface do not negate one's responsibility for proper
training and careful operation of a device, poor design can greatly increase the
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likelihood of errors. Such errors can have serious consequences and
trained away.
cannot simply be
If there are serious flaws with the design of a device, patterns may emerge. Ask
users about operational problems they have experienced with a given device. Try to
determine how widespread the problem is. Biomedical engineers and other
maintenance personnel constitute a valuable source of information. In addition to
individual interviews, try a focus group or questionnaire approach.
Evaluating Already-Purchased Devices
Below are some indications of problems.
Observations:
•
Training has been slow and arduous.
•
Only a few staff members seem able to use the device.
•
Staff tends to modify the equipment or takes shortcuts.
•
Staff refuses to use the device.
Installation Problem:
•
Staff finds installation of accessories difficult, confusing, or overly timeconsuming.
•
Alarms and batteries often fail.
•
Incorrect accessories sometimes are installed.
•
Parts often become detached.
Complaints :
•
Displays are difficult to read or understand.
•
Controls are poorly located or labeled.
•
Alarms are difficult to hear or distinguish.
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•
Device alarms are very annoying.
•
Device operation is illogical and confusing.
Incidents :
•
Accidents or “near-misses” can be a warning, especially if there are highly
competent individuals involved. When questioning staff and examining
implicated devices, look for types of problems mentioned above.
The December 1995 coding manual for Medical device reporting using mandatory
MedWatch FDA Form 3500A contains a number of codes having implications for user
interface design. These are found under the “Device-Related Terms”, “Results of
Evaluation Codes”, and “Conclusion Codes.” They are valuable not only for devicereporting purposes but also for sensitizing staff to important human factors design
issues.
Evaluating Devices Before Purchase
Before buying a new model, consider the means of assessing its usability,
especially if it is a life-sustaining or life-supporting device. Following are some steps to
consider:
•
Determine whether or not the manufacturer conducted human factors/usability
testing of the device in question.
•
Check with staff, and possibly other facilities, about predecessor models made
by the manufacturer.
•
Check with other facilities that may also be using the new model.
•
Check published evaluations of the new model.
•
Request a trial period prior to the actual purchase of a new device.
Analyze and Test the Model
When doing analyses and tests on devices being considered for purchase or
already in use, there are a few guidelines to keep in mind. Be careful not to bias the
users. Staff should be told that it is the device, not the users, being tested. If this is
not made clear, users may feel that their performance will be discussed with their
superiors, and thus they will not be forthcoming about errors and deficiencies related to
interface design. Also, should a device be evaluated during actual use on patients,
data should be collected over a reasonable length of time, not just a day or two. In real
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Do It By Design
world settings, actual problems often emerge slowly and require repeated observations
for identification. Findings may prove of great value to both healthcare facilities and
manufacturers.
Final Comment: There is much one can do to assess devices already in use, as
well as those being considered for purchase. Let the manufacturer know of uncovered
strengths and weaknesses. Companies not only are responsive to their customers,
but they want to market medical devices that meet customers’ needs for functionality,
safety, and effectiveness.
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Do It By Design
APPENDIX
Points to Consider
In considering the need for, and conduct of, human factors analysis and testing,
there are a number of issues and questions to ask.
1. Does the device require user interaction with respect to operation, maintenance,
cleaning, or parts installation? If so, do the technology and device functions
permit alternative user interface designs?
2. Given the combination of user interface, user population, and operating
conditions, are errors likely?
3. Could the consequences of error be serious for the patient or user?
4. In doing actual testing:
•
Is someone integral to the design team focusing on the user-related issues?
•
Are users involved?
•
Are hardware and software designers, technical writers, and others
coordinating their efforts with respect to human factors?
•
Has a test plan been developed?
•
Have user requirements been developed, and are they being updated?
5. Has the design team checked the literature and company files for useful human
factors information?
6. What studies, analyses, and test steps are being performed? Are staff
examining all relevant issues related to the installation of accessories and
operation of the device?
7. Has the project team done testing in simulated and/or actual environments?
8. Have user requirements been met?
9. User interface changes can be inadvertantly introduced into production models
during manufacturing. Have they been accounted for?
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Do It By Design
GLOSSARY
The definitions in this section are pertinent to this document. In some cases they
are general and may not coincide with a specific usage or application.
Administration set (intravenous): A device used to administer fluids from a
container to a patient’s vascular system through a needle or catheter inserted into a
vein. The device may include the needle or catheter, tubing, flow regulator, drip
chamber, filter, stopcock, fluid delivery tubing, connectors, capped side tube to serve
as an injection site, and hollow spike to penetrate and connect the tubing to an I.V. bag
or other infusion fluid container.
Anthropometry: The field that involves the measurement of the dimensions and
other physical characteristics of people and the application of this information to the
design of things they use.
Blood glucose monitor: A device that quantitatively measures glucose
concentrations in the blood.
Calibration: To check, adjust, or standardize systematically the graduations of a
quantitative measuring instrument.
Cardiac monitor (including cardiotachometer and rate alarm): A device used to
measure the heart rate from an analog signal produced by an electrocardiograph,
vector cardiograph, or blood pressure monitor. This device may sound an alarm when
the heart rate falls outside preset upper and lower limits.
Catheter: A tubular medical device for insertion into canals, vessels, passageways,
or body cavities, usually to permit injection or withdrawal of fluids or to keep a passage
open.
Coding: Identifying objects or events with the use of recognizable symbols, typically
visual or auditory, utilizing readily apparent variables such as color, shape, size,
direction, pitch, or duration.
Cognition: Processing information about the environment and oneself in conscious
intellectual activity, as in thinking, reasoning, remembering, and imagining.
Default: Parameters that are automatically selected by a machine in case deliberate
actions by the user do not occur.
DC-Defibrillator: A device that delivers an electrical shock for defibrillating (restoring
to normal heart rhythm) the atria or ventricles of the heart or to terminate other cardiac
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Do It By Design
arrhythmias. The device delivers the electrical shock through paddles placed directly
across the heart or on the surface of the body.
Enteral Feeding Tube: A tube for passing of food or medicines into the stomach.
Function: The action or accomplishment intended of a system where the system
consists of a device and a user. Alternatively, individual primary functions, such as
installation, maintenance, operation, and monitoring, are needed to accomplish the
intended use of the user-device system.
Guide wire: A catheter guide wire is a coiled wire that is designed to fit inside a
percutaneous catheter for the purpose of directing the catheter through a blood vessel.
Human Factors: In the broadest sense, a discipline devoted to the effects of user
interface design, job aiding, and personnel training in the operation, maintenance, and
installation of equipment.
Heart valve leaflets: Any of the leaf-like flaps of the bicuspid or tricuspid valves of
the heart.
Infusion pump: A device used to pump fluids into a patient in a controlled manner.
The device may use a piston pump, roller pump, or a peristaltic pump and may be
powered electrically or mechanically. The device may include means to detect a fault
condition, such as air in, or blockage of, the infusion line and to activate an alarm.
Infusion pump cassette: That part of the set of intravenous tubing that fits into an
infusion pump. Each cassette is “dedicated” or designed to fit a specific pump.
Iterative Prototyping: Successive small-scale tests on variations of a limited
function prototype. Such tests permit continual design refinements based upon human
performance.
Interlock: To prevent initiation of new operations until current operations are
completed (computer science). To connect in such a way that no part can operate
independently.
MedWatch Form 3500A: A form that must be completed by user facilities and
manufacturers to report device-related adverse events to FDA under the medical
device reporting (MDR) system (21 CFR, Parts 803 and 804).
Mockup: Usually a full-sized scale model of a structure, used for demonstration,
study, or testing.
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Do It By Design
Negative transfer: Transfer of training that results in increased likelihood of human
error, due to changes in the user interface or situations that are not obvious to the
user.
Oxygen concentrator: A device that produces a high concentration of oxygen (85%
to 95%) at clinically useful flow rates (up to 5 L/min) by physical separation of oxygen
from ambient air. Oxygen concentrators are commonly used in home healthcare and
occasionally in general anesthesia.
Screen print: A static image, represented on paper, which is used to show how a
computer program will appear on a monitor.
Storyboard: One page in a series of paper representations of the sequence of
actions possible in a system. Story boards representing a computer program could
show keys, prompts, and changes in status.
Task: The steps or work activities required of the user in order to perform functions.
Task analysis: Identification and analysis of the key user tasks and steps for a
device. The analysis may be conducted as a paper-and-pencil exercise for a device
concept, or by running through the procedures on a prototype or actual device.
Transfer-of-training: The automatic application of skills, habits, or expectations to a
new situation that appears similar to the one in which the skills and expectations were
originally developed.
Usability Test: A test of either an actual device or an advanced prototype with a fully
functional user interface. Data obtained includes user performance (time, errors, and
accuracy) and subjective responses of test participants.
User performance data: Information describing human behaviors and responses
during task performance. Examples of the criteria measured are frequency of
accomplishing a task, time required for task accomplishment, and changes in
performance with practice.
Ventilator: A continuous ventilator (respirator) is a device intended to mechanically
control or assist patient breathing by delivering a predetermined percentage of oxygen
in the breathing gas.
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Do It By Design
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