SYSTEM USABILITY SCALE (SUS)

If you are not measuring it,
you are not managing it

Usability testing and user experience research are built upon a key ingredient: integrating real user and customer feedback into the design, development and optimization process.

As such, for many decades usability and user experience optimization of desktop, website and mobile app software have been predicated upon observing real people, the target Persona for each studied feature, functionality or use case, as they interact with an existing or proposed user interface (UI).

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If you are not measuring it, you are not managing it
High-level subjective view of usability

High-level subjective view of usability

SUS is generally 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 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.

In particular, 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.

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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”):

The SUS of Userlytics: 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.

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How does it work?
System Usability Scale (SUS) Score Interpretation

System Usability Scale (SUS) Score Interpretation

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.

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Benefits of the System Usability Scale (SUS) for User Experience Optimization

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.

Additional benefits include:

Easy and Simple to Set Up

preformatted in the Userlytics dashboard, and automatically calculated, so all you need to do is fill in the blanks in terms of the asset being tested

Reliable

when used with small sample sets

Effective

in differentiating between different test assets, and between good and bad usability

The Userlytics system calculates the system usability scale (SUS) score automatically, and presents Min, Max and Average results.

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68 separates an above average result from a below average result. If you receive an 80 or higher that means you are at the top of the class.

However the best way to apply the System Usability Scale is not to use the score in an absolute sense, but on a relative basis, either comparing different assets against each other (different designs, a production asset and a competitor or best practice asset, etc) or comparing the evolution of your website, desktop application or mobile app over time, to see if your SUS score is trending upwards or downwards with your visitors or target Personas.

At Userlytics we generally recommend our clients always include an SUS in every test, since it is so easy; the questions are integrated into our platform, pre-formatted and the calculations are automatic.

Other special types of questions that are preformatted and automatically calculated in the Userlytics system include the Net Promoter Score (NPS) and the SEQ, used to gauge the usability of a specific task, rather than an entire system.

All of the above, as well as time on task and success/failure rates can be downloaded from the Userlytics Dashboard as excel files.

System Usability Scale (SUS)