System Usability Scale (SUS) is a 10 item questionnaire aimed for measuring the perceived ease of use.
SUS will provide a measure of usability and learnability, which can be compared to internal and industry benchmarks. It’s used to quickly identify areas that maybe affecting the experience.
The items of the SUS are phrased in a way that allows it to be administered on any type of system a user interacts with, resulting in a flexible internal benchmark.
Usability predicts customer loyalty. SUS scores predict around 40% of why customers recommend software and websites as measured by the Net Promoter Score. Detractors have an average SUS score of 67 (slightly below average usability) and Promoters have an average score of 82 (well above average usability). You cam estimate the ‘Likelihood to Recommend‘ question used in the Net Promoter Score (which is a 0 to 10 scale) by dividing the SUS by 10. For example, an SUS score of 72 would predict a LTR response of 7.2.
Even though SUS was intended to be a measure of just usability, two of the items can be used as a measure of learnability (items #4, #10).
#4
I think that I would need the support of a technical person to be able to use this system.
#10
I needed to learn a lot of things before I could get going with this system.
In general, learnability scores track higher than the usability scores and the original SUS score. Depending on the type of system being tested and its maturity, measures of learnability may be just as important as measures of usability.
Note: Question order and alternating item tone is intentional and should not be altered. The odd items are phrased positively, and the even items are negative phrases. The alternating tone is intended to reduce acquiescence and extreme response biases.
Data shows that SUS is a reliable and valid measure of perceived usability. It performs as well or better than commercial questionnaires and home-grown internal questionnaires.
Resources
Unmodified SUS
Modified SUS
Next Steps
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