Revitalizing SUS, the System Usability Scale
Jens Meiert, April 23, 2007 / March 2, 2008.
This entry is filed under Usability.
About 20 years ago, John Brooke published the concept of a “System Usability Scale”, a reliable, low-cost usability scale that can be used for global assessments of systems usability
. SUS is based on a Likert scale questionnaire with standardized content that results in an overall usability and user satisfaction index (ranging from 0 to 100).
Figure: Sample statement from SUS.
Serco Usability Services once published a good description of SUS that is now gone; I saved and converted that document to PDF (150 KB): SUS – A quick and dirty usability scale.
While there’s no need to repeat everything written in that PDF, I may cite some important paragraphs from it:
In response to these requirements, a simple usability scale was developed. The System Usability Scale (SUS) is a simple, ten-item scale giving a global view of subjective assessments of usability.
[…]The technique used for selecting items for a Likert scale is to identify examples of things which lead to extreme expressions of the attitude being captured.
[…]It can be seen that the selected statements actually cover a variety of aspects of system usability, such as the need for support, training, and complexity, and thus have a high level of face validity for measuring usability of a system.
[…]The SU scale is generally used after the respondent has had an opportunity to use the system being evaluated, but before any debriefing or discussion takes place. Respondents should be asked to record their immediate response to each item, rather than thinking about items for a long time.
[…]To calculate the SUS score, first sum the score contributions from each item. Each item’s score contribution will range from 0 to 4. For items 1,3,5,7,and 9 the score contribution is the scale position minus 1. For items 2,4,6,8 and 10, the contribution is 5 minus the scale position. Multiply the sum of the scores by 2.5 to obtain the overall value of SU.
[…]
Please note that feedback from John Brooke, Hewlett-Packard (that once indirectly acquired the original copyright holder Digital Equipment Corporation), and Serco Usability Services is still missing. However, SUS has been made freely available for use in usability assessment
. And should be used more often.
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Comments
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On April 30, 2007, 14:49 CEST, Jan said:
I came across “SUS” a while ago and like to apply it in my diploma thesis.
Do have any experience using it?
How would you rate the results? -
On May 1, 2007, 10:25 CEST, Jens Meiert said:
Hi Jan – unfortunately, I may not publish any results of SUS applications, and instead I still hope to use this method in large-scale projects (this “missing large-scale implementations” problem also appears to be popular, as far as I remember Tom Tullis, for example). So far it’s quite insightful, though.
By the way, please also see UPA’s “A Comparison of Questionnaires for Assessing Website Usability” (PDF, 273 KB).
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On August 18, 2007, 15:45 CEST, John Brooke said:
What feedback were you hoping for? Anybody who wants to get in touch with me about SUS is welcome to do so (mail john.brooke at contingent-solutions.com). SUS seems to have taken on a life of its own, and as your comment notes, it’s 20 years old. I think it still meets its original goal of being system-independent and giving a simple, reliable global assessment of subjective usability (despite various attempts to rewrite it to make it more “relevant”, which I would have to point out effectively invalidates it).
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On August 19, 2007, 20:38 CEST, Jens Meiert said:
Hi John, really great to receive your feedback! I once wasn’t sure if it’s really okay to publish the Serco paper here, so I tried to contact you and others involved … without success, until now.
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On October 26, 2007, 13:22 CEST, John Brooke said:
I wrote a chapter on SUS in a book published in 1996 (Brooke, J. (1996). “SUS: a ‘quick and dirty’ usability scale”. In P. W. Jordan, B. Thomas, B. A.
Weerdmeester & I. L. McClelland, (Eds.) “Usability Evaluation in Industry”, pp. 189-194. London: Taylor & Francis.).There are a number of interesting comparative studies that have been done by Thomas Tullis and others that show that SUS tends to give a reliable result even when used with small samples. Jurek Kirakowski in Cork also found that there’s a very high correlation between SUS scores and general usability scores on the SUMI scale that was developed as part of the MUSiC project, and there is a high level of reliability for both questionnaires.
There are various electronic copies knocking about the Internet, and it continues to be used - Google Scholar has about 150 citations of its use, many in last couple of years. And if anybody can’t find one out there, I can let them have a copy of the chapter if they want to drop me an email.
Anyway, I appreciate the fact that you’re encouraging its use, and hope that people find it useful for many years to come. It seems to have stood the test of time….
