System Usability Scale

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 Corporation 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. Because it yields a single score on a scale of 0-100, it can be used to compare even systems that are outwardly dissimilar. This one-dimensional aspect of the SUS is both a benefit and a drawback, because the questionnaire is necessarily quite general.

It has been widely used in the evaluation of a range of systems.

References

* 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

* Tullis, T.S., and Stetson, J.N. A Comparison of Questionnaires for Assessing Website Usability, "Usability Professional Association Conference", 2004. [http://home.comcast.net/~tomtullis/publications/UPA2004TullisStetson.pdf]