System Usability Scale
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The System Usability Scale (SUS) is a simple, ten-item attitude (Likert) scale giving a global view of subjective assessments of usability. It was developed by John Brooke at Digital Equipment Company in the UK in 1986 as a tool to be used in usability engineering of electronic office systems.
The usability of a system, as defined by the ISO standard ISO 9241 Part 11, can be measured only by taking into account the context of use of the system – i.e., who is using the system, what they are using it for, and the environment in which they are using it. Furthermore, measurements of usability have several different aspects
- effectiveness (can users successfully achieve their objectives)
- efficiency (how much effort and resource is expended in achieving those objectives)
- satisfaction (was the experience satisfactory)
Measures of effectiveness and efficiency are also context specific. Effectiveness in using a system for controlling a continuous industrial process would generally be measured in very different terms to, say, effectiveness in using a word processor. Thus, it can be difficult, if not impossible, to answer the question “is system A more usable than system B”, because the measures of effectiveness and efficiency may be very different. However, it can be argued that given a sufficiently high-level definition of subjective assessments of usability, comparisons can be made between systems.
SUS has generally been seen as providing this type of high-level subjective view of usability and is thus often used in carrying out comparisons of usability between systems.
It has been widely used in the evaluation of a range of systems.
References
The System Usability Scale is described in:
- Brooke, J. (1996) SUS: a "quick and dirty" usability scale. In P W Jordan, B Thomas, B A Weerdmeester & A L McClelland (eds.) Usability Evaluation in Industry. London: Taylor and Francis.
Bibliography
A comparison among diverse psychometric questionnaires can be found at:
- Tullis, T.S., and Stetson, J.N. A Comparison of Questionnaires for Assessing Website Usability, Usability Professional Association Conference, 2004 [link]
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