System Usability Scale – the universal marker of product usability
System Usability Scale, or SUS, provides a single score on a scale of 0–100, so it can be used even for systems that are quite different from one another.
Because it allows for comparisons on a relative rather than an absolute basis, it allows for UX professionals to quickly run a range of tests of different assets, or the same asset over a period of time, and compare the SUS score.
How does it work?
Participants are asked in a survey questionnaire to indicate their level of agreement or disagreement with a number of statements in relation to systems, websites, apps, or prototypes (“Please indicate how much you agree or disagree”).
Userlytics’ SUS activity is preformatted and automatically calculated. The questions are ordered in an alternating “positively framed’ and “negatively framed” manner, with slightly different wording that is related to the usability and user experience that the participant perceived. This makes it easy for you to add a SUS task to your study, and begin gathering key data.
How do I interpret System Usability Scale scores?
Interpreting the scores usually involves the following process: The participant’s scores for each question are converted to a new number, added together and then multiplied by 2.5 to convert the original scores of 0-40 to 0-100. These are not percentages and should be used in terms of their percentile ranking.
A SUS score above a 68 is normally considered above average and anything else below average, however, it is best to use the score to compare different iterations of a design, and/or compare against a production asset, and/or compare against a competitor asset or a “best practice” asset.
Benefits of the System Usability Scale
Because the SUS has become an industry standard, with references in over 1300 articles and publications, it provides a clear “standard” benefit in terms of comparisons.
It is also easy and simple to set up, as it is preformatted in the Userlytics dashboard and automatically calculated. The Userlytics system calculates the system usability scale (SUS) score automatically, and presents MIN, MAX AND AVERAGE results. All you need to do is fill in the blanks in terms of the asset being tested!
When used with small sample sets, SUS is historically shown to be very reliable.
SUS is also historically shown to be quite effective in differentiating between different test assets, and between good and bad usability.
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