A tool for rapid assessment of product usability and universal design: Development and preliminary psychometric testing

Abstract

While there are many available tools and methods to evaluate product usability, few have been tested on user groups with disabilities and even fewer systematically consider universal design principles.
This paper describes the development and preliminary psychometric testing of the Rapid Assessment of Product Usability & Universal Design (RAPUUD), a 12-item user-report tool based on the seven principles of universal design.
A preliminary set of items was created to elicit ratings of diverse product characteristics (e.g., physical effort, cognitive effort, assistance required, safety). Data were gathered from 61 participants who rated the usability of products they use in their own environments.
Each item elicited a full range of responses, with no apparent floor or ceiling effects. Collectively, the 12 items achieved a high internal consistency (Cronbach's α=0.80). The data indicate that the tool was sensitive to differences in functional abilities, as well as differences in product characteristics. The instrument was usable for a range of consumer products, though not all items were appropriate for each and every product.
The results suggest that the instrument could become a pragmatic tool for designers to identify usability problems experienced by a diversity of user populations.

Full text

Work 39 (2011) 141–150 141
DOI 10.3233/WOR-2011-1160
IOS Press
A tool for rapid assessment of product
usability and universal design: Development
and preliminary psychometric testing
James A. Lenkera,∗, Mahiyar Nasarwanjib, Victor Paquetband David Feathersc
aDepartment of Rehabilitation Science, School of Public Health & Health Professions, University at Buffalo,
Buffalo, NY, USA
bDepartment of Industrial & Systems Engineering, School of Engineering and Applied Sciences, University at
Buffalo, Buffalo, NY, USA
cDepartment of Design and Environmental Access, College of Human Ecology, Cornell University, Ithaca, NY, USA
Received 30 October 2009
Accepted 19 December 2009
Abstract.Background: While there are many available tools and methods to evaluate product usability, few have been tested on
user groups with disabilities and even fewer systematically consider universal design principles.
Objective: This paper describes the development and preliminary psychometric testing of the Rapid Assessment of Product
Usability & Universal Design (RAPUUD), a 12-item user-report tool based on the seven principles of universal design.
Method: A preliminary set of items was created to elicit ratings of diverse product characteristics (e.g., physical effort, cognitive
effort, assistance required, safety). Data were gathered from 61 participants who rated the usability of products they use in their
own environments.
Results: Each item elicited a full range of responses, with no apparent floor or ceiling effects. Collectively, the 12 items achieved
a high internal consistency (Cronbach’s α=0.80). The data indicate that the tool was sensitive to differences in functional
abilities, as well as differences in product characteristics. The instrument was usable for a range of consumer products, though
not all items were appropriate for each and every product.
Conclusion: The results suggest that the instrument could become a pragmatic tool for designers to identify usability problems
experienced by a diversity of user populations.
Keywords: Universal design, usability, consumer products, measurement, special populations, disability
1. Introduction
The prevalence of disability is expected to increase
as the U.S. population ages. Although nearly 75% of
those over age 75 have a functionallimitation affecting
their ability to use products [12], product designers
∗Address for correspondence: Jim Lenker, 515 Kimball Tower,
3435 Main Street, University at Buffalo, Buffalo, NY 14214, USA.
Tel.: +1 716 829 6726; Fax: +1 716 829 3217; E-mail: lenker@
buffalo.edu.
do not routinely consider the impacts of disability and
aging on the usability of their products [18,23]. Older
adults and wheelchair users report numerous usability
challenges with products in their kitchens, bathrooms,
and home offices [15,16]. Thus, there is a need to
improve the usability of the products that are being
created and sold in the marketplace.
Universal design (UD) is one approach that has been
proposed to address this need. It has been defined as,
“...an approach to design that incorporates products as
well as building features which, to the greatest extent
feasible, can be used by everyone”[17]. Its seven prin-
1051-9815/11/$27.50 2011 – IOS Press and the authors. All rights reserved

142 J.A. Lenker et al. / A tool for rapid assessment of product usability and universal design
ciples [5] and overarching philosophy have been en-
thusiastically received by academics and advocates in
the rehabilitation technology and environmental design
communities. Accessibility considerations are relevant
at each step in the product development process, includ-
ing conceptualization, design, evaluation, and manu-
facture [9]. Universal design is intended to improve the
lives of people with disabilities by providing guidelines
for product developers [4].
Unfortunately, current UD resources are insufficient
to meet the needs of product designers and develop-
ers. Law et al. [14] reviewed eight UD and accessi-
bility resources and identified five common problems:
(a) UD resources do not consistently define their tar-
get audience or its needs; (b) the terminology used for
accessible and universal design is imprecise; (c) there
are no accepted standards for measurement and com-
pliance; (d) standards and guidelines are not enforce-
able because of their ambiguity; and (e) the usability
of the UD resources is compromised. In effect, most
UD resources are not made to support the cognitive
processes of designers [3]. These shortcomings cre-
ate confusion, frustration, and misinterpretation among
product developers who are attempting to implement
such guidelines. Thus, the UD philosophy is perceived
by product developers as a special interest that slows
down the time-to-market and increases costs [11,18,
23].
One approach for achieving more inclusive designs
is disability simulation. Disability simulation is a dis-
count method for evaluating the usability flaws in a
product [12]. The tests are inexpensive and easy to im-
plement. They are not intended to replicate the expe-
rience of living with a disability, but may help identify
difficulties that those with disabilities experience when
using products. Although many descriptions of simula-
tion tests have appeared in the literature, there has been
only one published validation study, involving partici-
pants who were college students [13]. Therefore, the
effectiveness of this method remains unproven.
Another option is for product developers to conduct
usability tests using older adults and people with dis-
abilities [6]. While this approach yields valuable in-
formation, it can become time intensive and financially
expensive. While there are many available tools and
methods to evaluate usability, few have been tested on
user groups with disabilities and even fewer system-
atically consider universal design principles [2,24,25].
Collectively, these factors are a disincentive for design-
ers who might otherwise embrace the universal design
philosophy [11,18]. There remains a clear need for
efficient usability testing methods that support those
who want to consider UD principles in their product
designs.
This paper describes the development and prelimi-
nary testing of the Rapid Assessment of Product Us-
ability & Universal Design (RAPUUD), a 1 2-item user-
report tool based on the seven principles of universal
design. The goal was to create a succinct, psychometri-
cally sound tool that (a) embodies traditional usability
principles, as well as UD principles, (b)lends itself to a
continuum of consumer products, (c) is amenable to a
diversity of user populations, including older adults and
persons with disability, (d) differentiates products hav-
ing different usability strengths and weaknesses, and
(e) reveals product features requiring re-design.
2. Method
2.1. Study design
The validity of product usability research conducted
in controlled laboratory settings is often threatened by
several factors: (a) the product types and models being
tested are typically identified by the investigator and
may have little relevance and meaning for some par-
ticipants; (b) products are often tested using contrived
tasks chosen by the investigator to exemplify ‘typical
product usage’, which may or may not reflect the task
cycles that participants enact in their daily lives; (c)
products are tested in settings that are unfamiliar to
participants and lack the affordances present in partici-
pants’ everyday environments; and (d) participants are
asked to provide usability ratings based on a relatively
short interval of product exposure. To circumvent these
potential threats to validity, the current study employed
a cross-sectional design in which participants provid-
ed one-time usability ratings on products that they had
been using regularly in their everyday living environ-
ments. These ratings were gathered during nine focus
groups that were conducted for a related study.
2.2. Participants
It was hoped that the RAPUUD could distin-
guish persons having demonstrable impairments from
those having no ostensible limitations. Thus, par-
ticipants were sought from four demographic groups:
healthy young adults, adults with vision impairment,
wheelchair users, and older adults. The young adult
group was chosen as a control group. The vision im-

J.A. Lenker et al. / A tool for rapid assessment of product usability and universal design 143
pairment and wheelchair user groups were chosen be-
cause they are among the largest groups having sensory
limitations and physical disabilities. The older adults
group was chosen because it was hoped that the RA-
PUUD would be responsive to the declines in phys-
ical, sensory, and cognitive function that are natural
components of the aging process.
A convenience sample of each was recruited using
flyers distributed to multiple locations, including: uni-
versity programs in occupational therapy and human
factors engineering, two offices of state vocational reha-
bilitation, a university-based assistive technology cen-
ter, an assisted living facility, and two senior centers.
Participants received a $50 honorarium in consideration
of their time, which involved participation in a three-
hour focus group, during which data for the current
study were also collected.
The recruitment methods and experimental proce-
dures were approved by the University at Buffalo’s
Social and Behavioral Sciences Institutional Review
Board. Informed consent was obtained from all partic-
ipants.
2.3. Instrument
The tool was developed by a four-person team of
experts, all having doctoral preparation in human fac-
tors engineering. One team member is also a licensed
occupational therapist, and another has a background
in anthropology. Collectively, the team has extensive
experience conducting research involving persons with
disabilities.
2.3.1. Item development and response scaling
Item creation was based on the Principles of Uni-
versal Design [5], factors identified in a related study
by Beecher and Paquet [2], usability heuristics from
the human factors literature [19], and the clinical and
research experiences of the co-authors. The goal was
to produce a parsimonious appraisal of usability that
captures product usability characteristics (e.g., physi-
cal effort, cognitive effort, visible information, safety)
and elements of the task cycle (e.g., set-up, ease of use,
clean-up and storage). The team followed principles
of survey development suggested by DeVellis [7] and
Fink [8].
For six items, the usability term was worded in a
negative sense (e.g., poses a safety risk,draws unwant-
ed attention). This was done for two reasons. First,
surveys having a preponderance of positively worded
items can convey the false impression that the survey-
or is interested in receiving only positive feedback [7].
In addition, a mix of negatively and positively word-
ed items can also help researchers identify respondents
who provide categorically positive or negative respons-
es.
The team considered a range of response options
(e.g., visual analog, semantic differential, categorical),
ultimately settling on 5-point Likert scale of endorse-
ment (e.g., strongly agree, somewhat agree, etc.) in
order to lessen respondent burden and enhance reliabil-
ity. The response options also included a “not applica-
ble” choice, since it was anticipated that not all items
would be relevant for all products. The preliminary
item set was iteratively refined and informally pilot test-
ed within the development group. Ultimately, the team
arrived at a 12-item version of the Rapid Assessment
of Product Usability and Universal Design (RAPUUD;
see Fig. 1). The content validity of RAPUUD was
assessed by comparing the instrument’s items to three
other tools intended to aid the usability or universal
design of consumer products [2,5,19].
2.4. Procedure
Each focus group included participants representing
one of the target demographic groups. One moderator
and one observer were present for each group. Within
each group, the moderator used a four-step procedure
to facilitate an ordered discussion of products used in
the kitchen, home office and bathroom environments:
(1) The participants were asked to list the three prod-
ucts that were most challenging for them in the
environment being discussed;
(2) Participants independently completed the RA-
PUUD tool for the product in that environment
that was most challenging for them to use. The
moderator and observer were available as need-
ed to answer participant questions regarding the
meaning of individual items and response op-
tions;
(3) The focus group discussion commenced, empha-
sizing the most frequently identified products;
(4) Participants were asked to provide comments re-
garding products that had not been covered dur-
ing the main discussion.
The analysis discussed in this paper reflects the us-
ability data collected during Step 2 of the above proce-
dure. Each participant was asked to rate the usability
of three products (one each for the kitchen, home of-
fice, bathroom environments) that were challenging to

144 J.A. Lenker et al. / A tool for rapid assessment of product usability and universal design
Fig. 1. Rapid assessment of product usability and universal design (RAPUUD).

J.A. Lenker et al. / A tool for rapid assessment of product usability and universal design 145
use in everyday routines at home. The self-selection of
products was a deliberate choice intended to minimize
the potentially biasing influence of investigator-chosen
products and task cycles.
2.5. Analysis
A number of psychometric and administrative prop-
erties of the tool were evaluated, including: (a) content
validity, (b) item acceptability, (c) completion time, (d)
internal consistency, (e) the measurement model, in-
cluding item dispersion and missing data, (f) ability to
distinguish user populations, and (g) ability to distin-
guish product types. These reflect conventional cri-
teria for evaluating measurement tools [1,10,21]. To
facilitate statistical analysis, the ordinal scale response
for each item was numerically coded on a 1-to-5 scale,
with higher values denoting ‘better’ usability than low-
er values. For the positively worded items (i.e., #1–
3, 7, 9, and 10), “strongly disagree” was assigned a
value of 1, and “strongly agree” assigned a value of
5. For the six negatively worded items (i.e., 4–6, 8,
11, 12), “strongly disagree” was assigned a value of
5, and “strongly disagree” assigned a value of 1. The
internal consistency of the tool was evaluated using the
Cronbach’s αstatistic. Differences among user groups
were evaluated using Kruskal-Wallis non-parametric
analysis of variance. Post-hoc multiple comparison
tests were performed to determine between-group dif-
ferences once statistical significance across all groups
was found. Readability statistics were calculated us-
ing a standard utility within Microsoft Word 2007 (Mi-
crosoft Corp., 2009). All other statistical analyses were
completed using Minitab, v. 15.1.3.
3. Results
A total of 61 adults were recruited, representing four
demographic groups: young adults (n=17), older
adults (n=22), persons with vision impairment (n=
12) and wheelchair users (n=10). Participant de-
mographics (sex, age, and self-reported impairments)
are summarized in Table 1. All participants rated three
products, with two exceptions. One participant rated
all items “not applicable” for all three products, and
one participant submitted a blank rating form for the
home office product. Thus, usable data were obtained
on 179 products.
3.1. Content validity
An instrument is considered to have content validity
to the extent that its items represent the construct be-
ing measured [20,22]. Table 2 compares the RAPUUD
items to the principles articulated in three related con-
ceptual frameworks: the Principles of Universal De-
sign [5], Nielsen’s usability heuristics [19], and factors
identified by Beecher and Paquet [2]. The RAPUUD’s
items appear to embody the core concepts articulated in
all three frameworks. In terms of clarity, the RAPUUD
items are succinct (9.5 words per item), worded in the
active voice (0 passive sentences), and written using
plain language (4.5 characters per word; reading grade
level =6.1).
3.2. Item acceptability and completion time
Most participants completed the tool independently
in 3 to 5 minutes. Participants occasionally requested
clarification about the intent of individual items, most
frequently item # 7 (I get the information I need to use
the product efficiently).
3.3. Internal consistency
Collectively, the RAPUUD items achieved high in-
ternal consistency (Cronbach’s α=0.80), which is
well within the 0.70–0.90 range that is considered ac-
ceptable [22].
3.4. Measurement model
All 12 items elicited a full range of responses, with
no apparent floor or ceiling effects. Figure 2 depicts
the dispersion of responses for items 2, 3, 4, and 12.
Several items elicited greater than 10% Not Applicable
responses, including: set-up,clean-up and storage,in-
formation,safety,draws unwanted attention,andem-
barrassment. These responses are somewhat explained
by the products being rated. Several product types (e.g.,
kitchen cabinets, desks, filing cabinets, grab bars) are
typically anchored to one location and have no asso-
ciated set-up or clean-up tasks. Many of these same
products do not have written information or pictorial
icons, in which case labeling information is also irrel-
evant as a usability consideration. Given that partici-
pants rated consumer products that they were regularly
using at home, it is unsurprising that many participants
indicated that embarrassment and unwanted attention
were not applicable to their product rating.

146 J.A. Lenker et al. / A tool for rapid assessment of product usability and universal design
Tab le 1
Participant demographics
Demographic Gender Self-reported impairments (n) Mean age
group (Males / Females) Vision Hearing Physical (Years, SD)
Young adults 7 / 10 4 0 1 26.7 (3.8)
Older adults 5 / 17 10 5 8 73.4 (5.9)
Wheelchair users 5 / 5 2 0 10 48.3 (9.9)
Visually impaired 7 / 5 12 0 4 48.4 (10.4)
Tab le 2
Comparison of RAPUUD items to related conceptual frameworks
RAPUUD, v.1 7 Principles of universal design Nielsen [19] Beecher and Paquet [2]
Set-up Size and space for approach and use. Reach and access for use
Ease of use Simple and intuitive use Flexibility and efficiency of use. Adaptability to user pace
Clean up & storage
Safety Tolerance for error Secure, safe and private use
Tolerance for error.
Assistance Flexibility in use User control & freedom
Flexibility and efficiency of use
Flexibility in use
Mistakes and errors Tolerance for error Error prevention Tolerance for error
Information Perceptible information Visibility of system status
Help users recognize, diagnose, and
recover from errors.
Help and documentation
Perceptible information
Time Flexibility and efficiency of use.
Physical effort Flexibility in use
Low physical effort
Low physical effort
Size for use
Mental effort Simple and intuitive use Match between system & real world.
Consistency and standards;
Recognition rather than recall;
Intuitive use
Simple use
Unwanted attention Equitable use Esthetic and minimalist design Equitable use
Secure, safe and private use
Embarrassment Equitable use Esthetic and minimalist design Equitable use
3.5. Ability to distinguish user populations
Among the four participant groups, RAPUUD scores
were compared in order to assess the tool’s ability to
distinguish differences in usability that reflect user abil-
ities and limitations, irrespective of product. Figure 3
summarizes the median scores on each of the RAPU-
UD’s 12 items for the four participant groups. The
shaded area of each polar graph is indicative of over-
all product usability. Thus, the smaller shaded areas
for the wheelchair user and vision impairment groups
indicate diminished usability for the assorted products
rated by each of these groups.
Closer inspection reveals that individual items were
also sensitive to group differences (Fig. 4). For item
#5 (need for assistance) wheelchair users reported sig-
nificantly lower scores then the young and older adults
groups. For item #9 (physical effort) wheelchair users
reported significantly lower (p<0.001) scores than
the other three groups. These findings would seem
to reflect impairments in physical capacity that affect
product usability. For item #10 (mental effort), the
vision impairment group reported significantly lower
scores than older adults (p=0.002) and young adults
(p=0.018). The latter perhaps reflects the increased
demands on memory, spatial awareness, and concen-
tration that are needed to compensate for diminished
visual capacity. The ratings for item #2 (ease of use)
were significantly lower for the vision impairment and
wheelchair user groups than for young adults (p<
0.001). Again, this suggests that substantial physical
or sensory impairments can cause diminished product
usability. The scores for item #8 (takes more time than
it should) were equivalently low across the four groups,
suggesting that this factor is common to sub-optimal
product usability.
3.6. Ability to distinguish product types
Although participants were free to rate products of
their own choosing, a number of them rated products
that could be grouped into common product types (e.g.,

J.A. Lenker et al. / A tool for rapid assessment of product usability and universal design 147
Fig. 2. Dispersion of responses for four RAPUUD items.
can openers, microwave ovens, filing cabinets, medi-
cation bottles). The four most frequently rated product
types were: cabinets, showers/tubs, stoves/ovens, and
computers/laptops. For each product type, the RAPU-
UD data were aggregated. Items having high (median
score 4) and low (median score 2) usability ratings
were identified in order to evaluate the RAPUUD’s sen-
sitivity to different product types. As summarized in
Table 3, the RAPUUD scores appear to vary in accord
with the demands of contrasting product types. For ex-
ample, cabinets received low ratings (i.e., lower scores)
for the required physical effort, safety, and amount of
assistance required, which is consistent with anecdotal
comments made during the focus groups. In contrast,
laptop and desktop computers received high ratings in
the same three areas, which is consistent with the low
physical demands and risks inherent in these products.
Stoves/ovens and computers/laptops received low rat-
ings for mental effort and mistakes & errors, which
is in accord with the high cognitive demands experi-
enced by everyday users of these products. Stove/oven
and shower/tub products received low ratings for safe-
ty, which is consistent with risks that are commonly
acknowledged for these product types.
4. Discussion
The promising findings suggest that the RAPUUD
could become a pragmatic, informative tool for re-
searchers and designers. The data indicate that the tool
was sensitive to differences in functional abilities of
respondents, as well as differences in characteristics
of product usability. The instrument was usable for a
range of consumer products, though, as expected, not
all items were appropriate for each and every product.
There were four principal limitations to this study:
1. Assessment of content validity did not include
review by outside experts, which may have re-
sulted in differences among the 12 items and
response options. Nonetheless, the tool clearly

148 J.A. Lenker et al. / A tool for rapid assessment of product usability and universal design
Fig. 3. Median item ratings across the four participant groups.
Fig. 4. Median item scores for each item and group (∼indicates significant differences between groups at α=0.05).

J.A. Lenker et al. / A tool for rapid assessment of product usability and universal design 149
Tab le 3
Low- and high-rated RAPUUD items across different product types
Product type Most problematic usability areas
(RAPUUD items with median scores 2)
Least problematic usability areas
(RAPUUD items with median scores 4)
Cabinets
(n=22)
Assistance
Mistakes & errors
Physical effort
Safety
Set-up
Time
Embarrassment
Mental Effort
Shower & tub
(n=19)
Ease of use
Safety
Set-up
Time
Assistance
Information
Stove & oven
(n=14)
Mental effort
Mistakes & errors
Safety
Embarrassment
Set-up
Computers & laptop
(n=12)
Mental effort
Mistakes & errors
Set-up
Time
Assistance
Embarrassment
Physical effort
Safety
embodies traditional usability heuristics and the
principles of universal design.
2. The test-retest reliability of the RAPUUD was
not evaluated. The circumstances of data col-
lection made it infeasible to collect a second set
of usability ratings from each participant. Al-
though it is sometimes suggested that evaluation
of reliability should precede evaluation of va-
lidity, the order is not essential as long as both
properties are ultimately demonstrated [10].
3. The small sample size for each of the four par-
ticipant groups constrains the statistical power,
limiting the strength of our conclusions and mut-
ing effect sizes that might have emerged with a
larger sample.
The data comparing product types and disability pop-
ulations were potentially confounded by participant
self-selection of products from each of the three envi-
ronment categories. However, self-selection of prod-
ucts circumvented the potentially biasing influences of
investigator-determined products and task cycles, en-
hancing the validity of the data in at least three ways:
(a) participants rated products that had relevance in
their daily lives; (b) their usability ratings reflected
real-world task cycles completed in familiar environ-
ments; and (c) usability ratings reflected multiple task
cycles occurring over an extended period of time. Self-
selection of products also fostered a diversity of ratings,
which enabled identification of potential floor and ceil-
ing effects. Lastly, self-selection of products helped
assure that the RAPUUD is, in fact, a viable tool for a
variety of consumer product types.
4.1. Future research
Additional studies are needed in order to substan-
tiate the reliability and validity of the RAPUUD, in-
cluding evaluations of: (a) test-retest reliability, (b)
responsiveness for additional user groups (e.g., those
with hearing impairment) and populationswith specific
disabling conditions (e.g., persons with arthritis, stroke
survivors), and (c) ability to discriminate usability con-
cerns for novice product users. The RAPUUD must
also be tested by product design teams to determine
if it helps identify usability problems during product
development.
Some items and response options may also benefit
from modest refinement. A number of items (e.g.,
items 1, 4–6, and 8–10) may not truly need a “not
applicable” option, since these indicatorsare applicable
to virtually all products. In addition, some items (e.g.,
items 4, 6, and 12) may only require a 3-point ordinal
response since safety risk, mistakes and errors, and
embarrassment are factors that are either present to
varying degrees or absent entirely.
5. Conclusion
This research is based on the premise that product
developers already possess the technical and creative
skills needed to produce accessible, usable consumer
products. What they lack is insight and perspective –
not for lack of caring or commitment, but for lack of ex-
posure to the impact of functional limitations on prod-
uct usage and usability. The RAPUUD tool described

150 J.A. Lenker et al. / A tool for rapid assessment of product usability and universal design
here offers a practical, cost-effective technique for eval-
uating product usability in a manner that is consistent
with the tenets of universal design and traditional us-
ability heuristics. The RAPUUD will hopefully sup-
port product designers and developers to identify prod-
ucts and product features that are problematic for those
with physical, sensory, and/or cognitive impairments
due to aging and/or disability.
Acknowledgments
This work was conducted at the Center for Inclu-
sive Design and Environmental Access, University at
Buffalo. The research was supported in part by Grant
#H133E050004-07 from the U.S. Department of Ed-
ucation, National Institute on Disability and Rehabil-
itation Research (NIDRR). The contents of this paper
reflect the views of the authors and do not necessarily
reflect the views of the U.S. Department of Education
or NIDRR.
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