COMMUNICATIONS OF THE ACM January 2005/Vol. 48, No. 1 71
U
sability is most often defined as the
ease of use and acceptability of a
system for a particular class of users
carrying out specific tasks in a specific environ-
ment. Ease of use affects the users’ performance
and their satisfaction, while acceptability affects
whether the product is used [1]. Thus, it is of
great importance that every software practitioner
not only be aware of various usability methods,
The human-computer interaction community aims to
increase the awareness and acceptance of established methods
among software practitioners. Indeed, awareness of the basic
usability methods will drive an Information Society for all.
USABILITY
ENGINEERING
METHODS FOR
S
OFTWARE
DEVELOPERS
By Andreas Holzinger

72 January 2005/Vol. 48, No. 1 COMMUNICATIONS OF THE ACM
but be able to quickly determine
which method is best suited to
every situation in a software
project.
One of the basic lessons we
have learned in human-computer
interaction (HCI) is that usabil-
ity must be considered before
prototyping takes place. There
are techniques (such as usability
context analysis) intended to
facilitate such early focus and
commitment [11]. When usabil-
ity inspection, or testing, is first
carried out at the end of the
design cycle, changes to the inter-
face can be costly and difficult to
implement, which in turn leads to usability recom-
mendations. These are often ignored by developers
who feel, “We don’t have usability problems.” The
earlier critical design flaws are detected, the more
likely they can be corrected. Thus, user interface
design should more properly be called user interface
development, analogous to software development,
since design usually focuses on the synthesis stages,
and user interface components include metaphors,
mental models, navigation, interaction, appearance,
and usability [6].
It is generally accepted that the following five
essential usability characteristics should be part of any
software project: learnability, so the user can rapidly
begin working with the system; efficiency, enabling a
user who has learned the system to attain a high level
of productivity; memorability, allowing the casual user
to return to the system after a period of non-use with-
out having to relearn everything; low error rate, so
users make fewer and easily rectifiable errors while
using the system, and no catastrophic errors occur;
and satisfaction, making the system pleasant to use.
There are trade-offs among these criteria, and some
are more important than others, although this rank-
ing depends on the situation. For example, long-term
efficiency may be sufficiently important for develop-
ers to be willing to sacrifice rapid learnability [10].
To ensure a software project has these essential
usability characteristics, we use methods we divide
into inspection methods (without end users) and test
methods (with end users). The accompanying figure
details these characteristics.
Usability Inspection Methods
This is a set of methods for identifying usability
problems and improving the usability of an interface
design by checking it against established standards.
These methods include heuristic
evaluation, cognitive walk-
throughs, and action analysis.
Heuristic evaluation (HE) is
the most common informal
method. It involves having usability specialists judge
whether each dialogue or other interactive element
follows established usability principles [8]. The origi-
nal approach is for each individual evaluator to
inspect the interface alone. Only after all the evalua-
tions have been completed are the evaluators allowed
to communicate and aggregate their findings. This
restriction is important in order to ensure indepen-
dent and unbiased evaluations. During a single evalu-
ation session, the evaluator goes through the interface
several times, inspects the various interactive ele-
ments, and compares them with a list of recognized
usability principles (for example, Nielsen’s Usability
Heuristics [7]). There are different versions of HE
currently available; for example, some have a cooper-
ative character. The heuristics must be carefully
selected so they reflect the specific system being
inspected, especially for Web-based services where
additional heuristics become increasingly important.
Usually 3–5 expert evaluators are necessary (increas-
ing the cost of this technique); less-experienced peo-
ple can perform an HE, but the results are not as
good. However, HE using non-experts is appropriate
at times, depending on who is available to participate.
Advantages include the application of recognized
and accepted principles; intuitiveness; usability early
in the development process; effective identification of
major and minor problems; rapidity; and usability
throughout the development process.
Disadvantages include separation from end users;
inability to identify or allow for unknown users’
needs; and unreliable domain-specific problem iden-
Heuristic
Evaluation
Applicably
in Phase
Required
Time
Needed
Users
Required
Evaluators
Required
Equipment
Required
Expertise
Intrusive
all
low
none
3+
low
medium
no
Cognitive
Walkthrough
Inspection Methods
all
medium
none
3+
low
high
no
Action
Analysis
design
high
none
1-2
low
high
no
Thinking
Aloud
design
high
3+
1
high
medium
yes
Field
Observation
Test Methods
final testing
medium
20+
1+
medium
high
yes
Questionnaires
all
low
30+
1
low
low
no
Comparison of Usability Evaluation Techniques
Comparison of
usability evaluation
techniques.