Information Technology Reference
In-Depth Information
can range from a set of sketches on paper or screen-shots giving an
overview, and perhaps its functionality, to a fully functioning system in
use in the field [24].
According to Nielsen [4][24], about five evaluators are sufficient to
conduct an evaluation study. These evaluators are usability experts. One
evaluator will not be able to find all problems, and it has been shown that
different evaluators tend to find different problems. The number of five
evaluators is based on a statistical formula that claims that five evaluators
will discover about 80% of the overall usability problems, whereas one
evaluator will find around 30%. With this recommendation, one does not
gain much extra information to justify using more people, considering the
resources needed (15 evaluators are needed to find 95%) [24].
Heuristic evaluation has been, and is, a well-used and valuable
method. For further details see [2][4] for how it is used in human-
computer interaction. The method's disadvantage is that the standard
approach is not really successful for evaluation in information
visualization [6]. It primarily assesses issues related to a graphical user
interface and control of a system. It is not designed to deal with the way
information is represented or the complex interaction between these two
important aspects (i.e. graphical interface and control of system). Thus, it
fails to capture important aspects, such as how well users are supported in
exploration and analysis of the data represented. Further, experts in
usability perform the evaluation, rather than experts in the actual data
domain visualized by the system, or real users in a specific context. These
other groups may not experience some problems found by usability
experts as real difficulties. Experts in usability will fail to capture aspects
of use, since these are not covered by the method.
The next two sections describe efforts undertaken to modify the
method to be more suitable for information visualization and thus
improve the validity and reliability of its results. In the next section, a
number of heuristic sets proposed in information visualization literature
are presented. Some of these sets have been used in evaluations and
others have been presented as potential candidate sets. The section
discusses issues to consider when applying Heuristic Evaluation in
information visualization and presents recommendations on how to
proceed.
Heuristic Sets
In heuristic evaluation, the evaluator uses a set of heuristics, usability
principles or guidelines for good design, to judge whether the system
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