System Usability Scale
Encyclopedia
In systems engineering
, 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:
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 text editor. 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.
Recently, Lewis and Sauro suggested a two-factor orthogonal structure, which practitioners may use to score the SUS on independent Usability and Learnability dimensions. At the same time, Borsci, Federici and Lauriola by an independent analysis confirm the two factors structure of SUS, also showing that those factors (Usability and Learnability) are correlated.
The SUS has been widely used in the evaluation of a range of systems. Bangor, Kortum and Miller have used the scale extensively over a ten year period and have produced normative data that allow SUS ratings to be positioned relative to other systems. They propose an extension to SUS to provide an adjective rating that correlates with a given score.
Systems engineering
Systems engineering is an interdisciplinary field of engineering that focuses on how complex engineering projects should be designed and managed over the life cycle of the project. Issues such as logistics, the coordination of different teams, and automatic control of machinery become more...
, the system usability scale (SUS) is a simple, ten-item attitude Likert scale
Likert scale
A Likert scale is a psychometric scale commonly involved in research that employs questionnaires. It is the most widely used approach to scaling responses in survey research, such that the term is often used interchangeably with rating scale, or more accurately the Likert-type scale, even though...
giving a global view of subjective assessments of usability
Usability
Usability is the ease of use and learnability of a human-made object. The object of use can be a software application, website, book, tool, machine, process, or anything a human interacts with. A usability study may be conducted as a primary job function by a usability analyst or as a secondary job...
. It was developed by John Brooke at Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
in the UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
in 1986 as a tool to be used in usability engineering
Usability engineering
Usability engineering is a field that is concerned generally with human-computer interaction and specifically with making human-computer interfaces that have high usability or user friendliness...
of electronic office
Electronic office
The electronic office, or e-office, was a term coined to cover the increasing use of computer-based information technology for office work, especially in the 1980s...
systems.
The usability of a system, as defined by the ISO standard ISO 9241
ISO 9241
ISO 9241 is a multi-part standard from the International Organization for Standardization covering ergonomics of human-computer interaction. It is managed by the ISO...
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 text editor. 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.
Recently, Lewis and Sauro suggested a two-factor orthogonal structure, which practitioners may use to score the SUS on independent Usability and Learnability dimensions. At the same time, Borsci, Federici and Lauriola by an independent analysis confirm the two factors structure of SUS, also showing that those factors (Usability and Learnability) are correlated.
The SUS has been widely used in the evaluation of a range of systems. Bangor, Kortum and Miller have used the scale extensively over a ten year period and have produced normative data that allow SUS ratings to be positioned relative to other systems. They propose an extension to SUS to provide an adjective rating that correlates with a given score.
Further reading
- 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
- Bangor, A., Kortum, P.T. and Miller, J.A. (2008) An empirical evaluation of the System Usability Scale (SUS). International Journal of Human-Computer Interaction 24(6). 574–594
- Lewis, J.R. & Sauro, J. (2009). The factor structure of the system usability scale. international conference (HCII 2009), San Diego CA, USA. http://www.measuringusability.com/papers/Lewis_Sauro_HCII2009.pdf
- Sauro, J. (2011). Measuring Usability with the System Usability Scale (SUS) http://www.measuringusability.com/sus.php