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Table 13.1 Heuristic basis for user interface evaluation (adapted from http://www.nngroup.com/
articles/ten-usability-heuristics )
1.
The current system status should always be readily visible to the user
2.
There should be a match between the system and the user's world: the system should speak
the user's language
3.
The user should have the control and freedom to undo and redo functions that they
mistakenly perform
4.
The interface should exhibit consistency and standards so that the same terms always mean
the same thing
5.
Errors should be prevented where possible
6.
Use recognition rather than recall in order to minimize the mental workload of the users
7.
The system should have flexibility and efficiency of use across a range of users, e.g., through
keyboard short-cuts for advanced users
8.
The system should be esthetic and follow a minimalist design, i.e., do not clutter up the
interface with irrelevant information
9.
Users should be helped to manage errors: not all errors can be prevented so make it easier for
the users to recognize, diagnose, and recover
10.
Help and documentation should be readily available and structured for ease of use
make judgments, based on a set of guidelines or principles together with their own
knowledge, about a particular design. The individual results are then aggregated
together. In this way it is possible to overcome the inherent inaccuracy of indi-
vidual evaluations.
In the ideal world all of the evaluators would use the same (standard) set of
criteria for judging what is good or bad. In reality, most people tend to rely on
intuition and common sense, partly because most usability guidelines tend to be
excessively large, often having many tens or even hundreds of rules (e.g., Brown
1988 ; Mosier and Smith 1986 ). Molich and Nielsen ( 1990 ), however, suggested
that a relatively simple set of guidelines can be used as the basis for evaluation.
Initially they used nine guidelines, but over the years, these have been refined and
the number increased to ten, as shown in Table 13.1 .
Each expert works their way through the user interface design individually
noting compliance with the heuristics. Note that the user interface may just be a
paper-based prototype, because the experts are not being asked to carry out tasks
using the system. Problems that are detected can either be written down or
recorded verbally (e.g., by taking verbal protocols). The individual results are then
aggregated to highlight the detected problems.
Typically, only three to five experts are required to carry out a heuristic eval-
uation and generate useful results. Many people have taken this to be a hard and
fast rule for all types of evaluation, however, which can be a serious mistake. The
requisite number, to a large extent, depends on the diversity of the eventual user
population. So, for example, if you were designing an on-line population census,
then it would not make sense to just use three to five users, since such a small
sample is very unlikely to be truly representative of the diversity inherent in a
nation's general population.
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