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Among the satisfaction tests, we particularly like the SUS. This test was created by John Brooke in 1986 and has the great virtue of balancing accuracy and not being too long for the user and researcher. What SUS intends to evaluate:
• Effectiveness
• Efficiency
• Satisfaction
To this end, using a scale: 1 - Completely Disagree to 5 - I agree completely,
and 10 questions:
In odd answers, we subtract a point from the answer given by the user.
For even answers, remove the user's answer from 5.
We will thus have answers between 0 and 4.
After the previous calculation, we add the scores of the 10 questions and multiply by 2.5 which will reflect a score that can go from 0 to 100 (instead of 0 to 40, if we did not multiply by 2 ,5).
Sauro (2011) states that although SUS is widely used, there are few guidelines on the interpretation of its results. Based on his experience with more than 5000 users and 500 usability evaluations, this author argues that SUS have reliable metrics, being a reliable and valid measure of perceived usability.
The average obtained in the 500 evaluations was 68. The result of the SUS is not a percentage. The best way to interpret your score is to convert it to a percentile rank through a process called normalization. Created a calculator and guide that gets raw SUS scores and generates percentage ratings and grades (from A+ to F) for eight different types of apps.
The following chart shows how percentile rankings are associated with SUS scores and grades.
Examples:
74, would correspond to 74%, something like a B-
80.3 would already allow you to reach an A (the highest 10%), the equivalent of “I would recommend the product to a friend”. In contrast, a score of 68 would correspond to a 51 and an F (the bottom 15%).
The average obtained in the 500 evaluations was 68. The result of the SUS is not a percentage. The best way to interpret your score is to convert it to a percentile rank through a process called normalization. Created a calculator and guide that gets raw SUS scores and generates percentage ratings and grades (from A+ to F) for eight different types of apps.
The following chart shows how the percentile ratings are associated with the SUS scores and grades. Examples:
74, would correspond to 74%, something like a B-
80.3 would already allow you to reach an A (the highest 10%), the equivalent of “I would recommend the product to a friend”. In contrast, a score of 68 would correspond to a 51 and an F (the bottom 15%).
Although SUS only intended to measure perceived ease of use (a single dimension), more recent studies (Lewis, R., Sauro, J.) show that it provides an overall measure of system satisfaction and usability and learning subscales. Of the 10 SUS questions, 4 and 10 provide the learning dimension and the rest provide the usability dimension.
As Sauro points out, the size and reliability of the sample are not related, and therefore SUS can be used in very small sample sizes (up to two users) and still generate reliable results, although in this case it may allow for scoring estimates. inaccurate.
Users can encounter (even serious) problems with an application and still provide apparently high SUS scores. Post-test SUS scores should be correlated with task performance. Although the correlation is modest (around r = 0.24 for rates and time to completion), which means that only about 6% of SUS scores are explained by what happens in usability testing. This is the same level of correlation found with other post-test questionnaires.
Thus, we developed our SUS document.
References:
Sauro, J. (2011, February 2). Measuring usability with the System Usability Scale (SUS). MeasuringU. Retrieved from https:// measuringu.com/sus/ [Access 2019/09/27].
Sauro, J. (2016, December 28). 50 UX metrics, methods & measurement articles from 2016. MeasuringU. Retrieved from https://measuringu.com/2016-review/ [Access 2019/09/24].
Sauro, J. (2016, June 14). 5 common mistakes in UX benchmark studies. MeasuringU. Retrieved from https://measuringu.com/benchmark-mistakes/ [Access 2019/09/24].
Sauro, J. (2016, May 17). Combining UX research with market research. MeasuringU. Retrieved from https://measuringu.com/ux-market-research/ [Access 2019/09/24].
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