[Diabetes-talk] Article -- The Role of Human Factors in the Design and Development of an Insulin Pump.

[eileen scrivani]

I thought some of you who are interested in pumps may find this article interesting.  It specifically is for the Tandum T. Slim pump, but still interesting to read the considerations that should go into design. 

look for the link that says Journal of Diabetes Science & Technology The original .PDF can be found at: 
http://www.tandemdiabetes.com/Products/t-slim-Insulin-Pump/

VOL-6-2-SYM7-SCHAEFFER.pdf
Schaeffer
The Role of Human Factors in the Design and Development of an Insulin Pump
J Diabetes Sci Technol Vol 6, Issue 2, March 2012
www.journalofdst.org
261
260
Journal of Diabetes Science and Technology
Volume 6, Issue 2, March 2012 
© Diabetes Technology Society
SYMPOSIUM
The Role of Human Factors in the Design and Development 
of an Insulin Pump
Noel E. Schaeffer, Ph.D.
AbstractThis article discusses human factors (HF) processes and how they are applied during the development of a medical device to minimize the risk that
the user interface design could lead to patient errors, adverse events, and product recalls. This process is best defined as “prevention through design.”
The HF design process is exemplified by three distinct phases: (1) preliminary analysis, (2) formative design evaluation and modification, and (3) design
validation. Additional benefits of employing HF principles during medical device development are briefly reviewed, including reduced patient risk by eliminating
design flaws, increased patient adherence through the reduction in the complexity of therapeutic regimes, and reduced likelihood for product recalls.J
Diabetes Sci Technol 2012;6(2):260-264
Introduction
There are approximately 450,000 people in the United 
States who use insulin pumps to manage their diabetes. 
All these people interact with their pumps several 
times every day to administer insulin into their bodies 
to manage their blood glucose levels. If you have ever 
interacted with a piece of technology regularly—for 
example, the automated ticket machine for the train, a 
smart phone, or the check-in kiosk at the airport—and 
you have thought to yourself, if only the designers and 
engineers had done something a little differently, it would be 
so much easier to use, then you would have been thinking 
in terms of how people interact with technological 
systems and of how important it is (especially with 
medical devices) that those interactions are consistently 
safe, error free, and efficient.
Human Factors Defined
Human factors (HF) is a unique field because it draws 
from a variety of disciplines, including psychology, 
engineering, design, statistics, ethnography, and anthro-
pometry. Specifically, a human factor is any physical, 
perceptual, cognitive, or behavioral aspect of a human 
being that impacts a technological system or environment. 
The most important aspect of HF is that it is truly an 
empirical science, which means it is based almost entirely 
on observation. The power of the HF discipline is that 
its process can be wielded to collect information on how 
humans interact with technology, and that knowledge 
can be applied to the design and development of 
technologies that better fit human behaviors, needs, and limitations. The focus of HF is expressed by the seminal 
work of Sanders and McCormick:
Human factors focuses on human beings and 
their interaction with products, equipment, facilities, 
procedures, and environments, used in work and 
everyday living. The emphasis is on human beings 
(as opposed to engineering, where the emphasis is 
more strictly technical engineering considerations) and 
how the design of things influences people. Human 
factors, then, seeks to change the things people use 
and the environments in which they use these things 
to better match the capabilities, limitations and needs 
of people.1
A common misperception is that HF research is similar 
or related to market research. Market research typically 
utilizes methodologies such as focus groups, customer 
preference surveys, or executive reviews to gather data that
center on opinions, attitudes, and speculation about a
product. Focus groups and other kinds of market research 
methodologies are not specific tests of medical device 
use or risks in medical device interaction. They provide 
a different kind of information, which can be useful 
during the very early stages of product development when 
developing user profiles, creating device-use scenarios, 
and better understanding use environments.
The Human Factors Process and Medical 
Device Development
The health care field has come under major scrutiny 
because of poorly designed medical systems and devices 
with inherent design flaws that induce user errors. 
There have been numerous examples of infusion pump 
recalls due to poor designs. For example, in August 2004, 
the N’Vision® Clinical Programmer was recalled by the 
Food and Drug Administration (FDA) because users 
were able to enter infusion times with incorrect units. 
Minutes were entered into the hours field, which caused 
patient overdose.2 The Colleague® IV infusion pump 
could shut down while delivering critical medication to 
patients. The reason for this was that the “on/off” key 
was so close to the “start” key that nurses would often 
inadvertently turn the pump off when they intended to 
start delivery. Over 206,000 Colleague infusion pumps, 
used mostly in hospitals, were recalled by the FDA.3,4
The HF process in the medical device field takes a very 
risk-centric approach, generally referred to as a “prevention 
through design” strategy. The primary objective is to 
design out characteristics of a system or device that 
could lead to human error. The HF process generally 
includes three primary phases: (1) preliminary analysis, 
(2) formative evaluation and design modification, and 
(3) validation testing. The t:slimTM insulin delivery system 
(t:slim pump) user interface was developed with this process. 
This process resulted in a pump that utilizes a touch screen 
to facilitate data entry, along with a home screen to 
display critical information users need to manage their 
diabetes. The home screen displays critical information 
such as the amount of insulin in the cartridge, battery 
life, time and date, and insulin on board, as well as 
provides direct access to bolus functions and pump 
system functions (“options”).
Preliminary analysis started prior to the design of the 
t:slim and sought to better understand who the users are, 
what their needs are, what kind of environment they use 
the device in, what their limitations are, what specific 
tasks they need to accomplish, and a risk analysis of 
those tasks as they related to device use. This phase also 
included analysis of the user interface designs of products 
already in use. The methodologies, study focus, and 
outcomes that occurred during the preliminary analysis 
phase are summarized in Table 1. From the data collected 
in the preliminary analysis, an early interface design 
was developed, as shown in Figure 1.
The next phase of t:slim pump development involved 
HF activities that included formative evaluation and 
design modification. This phase of the process was 
accomplished via risk-based iterative usability testing. 
The primary focus of this testing was on safety and 
usability of the product’s design. A typical usability study is relatively small (5–8 participants), with actual 
users being observed by a researcher in a controlled 
environment. The participants go through a set of task-
based scenarios that are representative of real device 
use. The researcher observes each participant’s behavior 
as they are going through the tasks and records data on 
their interactions.5,6 Data collected are used to inform the 
next iteration of the design. Table 2 shows a summary 
of the formative studies that were conducted during the 
development of the t:slim pump.
During several of the early usability tests, it was revealed 
that participants struggled with data entry, navigation, 
and information retrieval tasks. One example of design 
improvements to the home screen that occurred as a 
result of this iterative usability testing is exemplified 
in Figure 2.
Modifications were continually made to the user interface 
based on observations made during the formative design 
evaluation phase. At the end of the development process 
and formative tests, a HF validation test was conducted 
to prove that the t:slim pump was safe and effective for 
human use.
The purpose of the validation study was to confirm that 
the t:slim pump could be used safely and effectively by 
representative users in the intended use environment. 
Study participants included both people with diabetes 
who were insulin pump users and people with diabetes 
being treated with multiple daily injections. Participants 
performed a comprehensive, realistic set of basic and 
advanced task-based scenarios with the t:slim pump. 
Data were collected via a software data log, participant 
journals, follow-up interviews, and video/audio tape 
recordings. The results indicated that, during certain 
tasks, participants made programming errors when 
inputting information into the pump. To mitigate 
potential programming errors, a software solution was 
developed that forced users to actively confirm their 
inputs before continuing through the workflow. In order 
to prevent automaticity7,8 or response chaining, in which 
users could act habitually in an automatic fashion and 
tap through confirmation screens that were presented 
too frequently, the confirmation screens appear only 
when users make changes to settings that impact insulin 
delivery, such as delivering a bolus or setting a basal 
rate. A revalidation study was conducted to evaluate the 
effectiveness of the active confirmation screens. The goal 
was to demonstrate and validate the effectiveness of the 
active confirmation screens on the t:slim pump with a 
sample of representative users.
There were several events that occurred during the 
revalidation study that revealed that the active confirmation 
screens did prevent incorrect entries. The reason the active 
confirmation screens may have impacted participant 
behavior is likely due to several related factors, including 
the unique screen layout, a summary of all critical 
information in one location, and the active confirmation 
required from the participant. The home screen of the 
validated design is shown in Figure 3.
The improvement in the usability of the interface was 
further substantiated through a system usability scale 
(SUS) questionnaire that participants completed after their
sessions. The SUS yields a single number which represents 
the overall usability of the system.9 Figure 4 shows 
higher SUS scores for the new interface versus the old.
The results of these validation studies were the culmination 
of successful HF/usability design efforts, which included 
preliminary analysis, iterative formative evaluations, and 
design modifications. The current regulatory environment 
has required an increased focus on the application of 
the HF process to the development of medical devices in 
order to eliminate design flaws that could lead to unsafe 
behavior. These studies exemplified how applying that 
process helped create a user-centric system that reduced 
risk, increased effectiveness, and improved ease of use.
Human Factors Standards
There are several HF standards that practitioners and 
companies can use to guide them through the practical 
application of HF processes. The Association for the 
Advancement of Medical Instrumentation is an organization 
that brings together experts in order to create standards that are widely recognized by other organizations, including the 
FDA. Many of these documents contain comprehensive 
information that covers HF design processes as well as 
HF design principles.10–12
Conclusion
There are several primary benefits to employing a HF 
process during the design of medical devices. The most 
important benefit is increased patient safety. This safety 
comes in the form of reduced patient risk through a 
design that has been heavily tested with representative 
users in its intended use environment in order to 
eliminate design flaws. Another benefit may be increased 
patient adherence. There is evidence indicating that reducing
the complexity of therapeutic regimes may increase 
patient adherence.13–16 Reduced therapeutic complexity, 
in part, can be derived from improved device usability. 
Secondary benefits of a systematic HF process may include 
reducing or eliminating the need for costly modification(s) 
after product launch, reducing the likelihood of product 
recalls due to design flaws, improving overall ease of 
use (improved ease of use is a byproduct of good HF 
practices, not the sole outcome), and enhancing look and 
feel. There is also evidence to suggest that patients may 
pay a higher premium for more usable products.17 All of 
the benefits resulting from the systematic implementation 
of a sound HF process will converge to generate a 
medical product that creates a patient experience that is 
safer, more efficient, and more satisfactory.
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Funding:
This work was funded by Tandem Diabetes Care Inc., San Diego, CA.
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Disclosure:
Noel E. Schaeffer, Ph.D., is a full-time employee at Tandem Diabetes 
Care.
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Acknowledgments:
I thank all the HF practitioners and user-experience designers who 
contributed their time, energy, and expertise to the development of 
the t:slim pump, including Kathryn Rieger-King, Ph.D., Brian Bureson, 
and Jason Farnan.
N’Vision® is a registered trademark of Medtronic Inc. Colleague® is a 
registered trademark of Baxter Healthcare Corp.
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References:
1. Sanders MS, McCormick EJ. Human factors in engineering and 
design. 7th ed. New York: McGraw-Hill; 1993.
2. Food and Drug Administration. Medtronic 8870 Software 
Application Card Version AAA 02: class I recall. http://www.fda.
gov/MedicalDevices/Safety/RecallsCorrectionsRemovals/ListofRecalls/
ucm064764.htm. Accessed October 31, 2011.
3. Food and Drug Administration. Baxter Healthcare Corp. 
COLLEAGUE® Volumetric Infusion Pumps: class 1 recall. http://
www.fda.gov/MedicalDevices/Safety/RecallsCorrectionsRemovals/
ListofRecalls/ucm063713.htm. Accessed October 31, 2011.
4. Reuters. F.D.A. orders Baxter recall of IV pumps. New York Times; 
July 14, 2010. 
5. Tullis T, Albert B. Measuring the user experience: collecting, 
analyzing, and presenting usability metrics. Amsterdam: Elsevier; 
2008.
6. Kuniavsky M. Observing the user experience: a practitioner’s 
guide to user research. San Francisco: Morgan Kaufmann; 2003.
7. Schneider W, Shiffrin RM. Controlled and automatic human 
information processing. I. Detection, search, and attention. Psychol 
Rev. 1977;84(1):1–66.
8. Shiffrin RM, Schneider W. Controlled and automatic human 
information processing. II. Perceptual learning, automatic attending 
and a general theory. Psychol Rev. 1977;84(2):127–90.
9. Brooke J. SUS: a “quick and dirty” usability scale. In: Jordan PW, 
Thomas B, Weerdmeester BA, McClelland AL. Usability evaluation 
in industry. London: Taylor and Francis; 1996.
10. Association for the Advancement of Medical Instrumentation; 
American National Standards Institute. Human factors engineering: 
design of medical devices. ANSI/AAMI HE75:2009. www.aami.
org/publications/standards/HE75_Ch16_Access_Board.pdf. Accessed 
January 31, 2012.
11. Association for the Advancement of Medical Instrumentation; 
American National Standards Institute. Medical devices: application 
of usability engineering to medical devices. ANSI/AAMI/IEC 
62366:2007.
12. Food and Drug Administration. Applying human factors and usability 
engineering to optimize medical device design. http://www.fda.gov/
MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/
ucm259748.htm. Accessed January 31, 2012.
13. Paes AH, Bakker A, Soe-Agnie CJ. Impact of dosage frequency on 
patient compliance. Diabetes Care. 1997;20(10):1512–7.
14. Viller F, Guillemin F, Briançon S, Moum T, Suurmeijer T, 
van den Heuvel W. Compliance to drug treatment of patients with 
rheumatoid arthritis: a 3 year longitudinal study. J Rheumatol. 
1999;26(10):2114–22.
15. Cramer JA, Gold DT, Silverman SL, Lewiecki EM. A systematic 
review of persistence and compliance with bisphosphonates for 
osteoporosis. Osteoporos Int. 2007;18(8):1023–31.
16. Zahn JD. Analysis: desirable attributes of insulin injection pens 
that drive patient preference and compliance. J Diabetes Sci 
Technol. 2011;5(5):1210–1.
17. Cambridge Consultants. Patients prescribe ease-of-use for the 
medical device industry. http://www.cambridgeconsultants.com/news_
pr296.html. Accessed October 31, 2011.
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Author Affiliation:
Tandem Diabetes Care, San Diego, California
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Abbreviations: (FDA) Food and Drug Administration, (HF) human factors, (SUS) system usability scale
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Keywords: engineering psychology, human factors, human factors engineering, human factors research, usability
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Corresponding Author: Noel E. Schaeffer, Ph.D., Tandem Diabetes Care, 11045 Roselle St., Suite 200, San Diego, CA 92121; email address 
noel.schaeffer at tandemdiabetes.com
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Figure 1. Early home screen design.

table with 4 columns and 7 rows
Table 1.Preliminary Analysis Phase 
Study methodology
Sample description
Study focus
Outcomes 
Web-based survey
350 patients, 125 clinicians
Focus on touch screen concept
Participants preferred touch screen interface 
Web-based survey
45 patient insulin pumpers
Prioritization of information to be included on the graphical user interface home screen
Initiated design based on user feedback of home screen function priorities 
Web-based survey
116 patients, 31 diabetes educators
Prioritization of all user tasks, including critical tasks, beyond the graphical user interface home screen
Used to select the architecture of the user task workflows 
Focus group
40 patients
Focus on various options for terms and icons in the user interface workflow
Used to select specific terms and icons for user workflows that minimize confusion 
Web-based survey
61 patients
Study color schemes used within the graphical user interface that maximize user recognition and minimize confusion
Selection of color scheme used throughout the graphical user interface
table end

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Figure 2. Design iteration of the home screen.

table with 4 columns and 9 rows
Table 2.Formative Evaluation Phase 
Study methodology
Sample description
Study focus
Outcomes 
Usability study
21 representative users
Workflow testing for completing critical tasks and for ease of use
Identified improvements required on critical tasks 
Usability study
30 representative users
Focus on detailed critical task list and user errors and other HF
Usability errors identified and mitigated through changes to the graphical user interface 
Usability study
33 representative users
Focus on test to ensure design changes made to the graphical-user-interface-mitigated errors
Design changes to increase task success rate 
Usability study
15 representative users
Collect end user feedback on design changes made to user interface based on previous outcomes
Usability issues identified and design improvements implemented 
Usability study
9 representative users
Graphical user interface navigation and presentation, software control usage and hardware control usage
Usability issues identified and design improvements implemented 
Usability study
5 representative users
Graphical user interface navigation and presentation, software control usage and hardware control usage
Usability issues identified and design improvements implemented 
Usability study
7 representative users
Graphical user interface navigation and presentation, software control usage and hardware control usage
Usability issues identified and design improvements implemented
table end

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Figure 3. Validated home screen design.
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Figure 4. Mean SUS score across all participants.

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