Measuring Usability

Administration

The SUS should be administered intermittently during task performance or as soon as possible afterwards. Instruct the respondent to read each statement carefully and indicate the extent to which they agree or disagree using the scale provided.

Survey

Scoring

Interpretation

Higher scores indicate better usability. Scores below 68 indicate poor usability, while scores above 68 indicate good usability. However, it is important to note that scores should be considered in the context of the specific system being evaluated, as well as the user population and the task being performed.

Bangor, Kortum, & Miller (2009) offer intuitive labels for SUS scores:

References for All-Positive Scale

Sauro, J., & Lewis, J. R. (2011). When designing usability questionnaires, does it hurt to be positive? Conference on Human Factors in Computing Systems — Proceedings, 2215–2223.

Kortum, P., Acemyan, C. Z., & Oswald, F. L. (2021). Is It Time to Go Positive? Assessing the Positively Worded System Usability Scale (SUS). Human Factors, 63(6), 987–998. 

Reference for Original Scale

Brooke, J. (1986). SUS: a “quick and dirty” usability scale. In P. W. Jordan, B. Thomas, B. A. Weerdmeester, & A. L. McClelland (eds.). Usability Evaluation in Industry. London, England: Taylor and Francis.

Administration

Administer immediately after the respondent uses the product. Instruct the respondent to read each statement carefully and indicate the extent to which they agree or disagree using the scale provided. It is acceptable to administer multiple UMUX-LITE scales for components of a system under test

Survey

Item		Strongly Disagree                              Strongly Agree
1	[This system’s] capabilities meet my requirements.	1          2          3          4          5         6         7
2	[This system] is easy to use.	1          2          3          4          5         6         7

Scoring

The overall score is the average of the two item responses. This process can be expressed formulaically as:

Interpretation

Higher scores indicate greater usability.

UMUX-LITE scores can also be interpreted in comparison to the SUS 0 to 100 scale. More information about the correspondence between UMUX-LITE and SUS can be found in:

Lewis, J.R., Utesch, B.S., Maher, D.E. (2015). Investigating the Correspondence Between UMUX-LITE and SUS Scores. In: Marcus, A. (eds) Design, User Experience, and Usability: Design Discourse. Lecture Notes in Computer Science, vol 9186. Springer. https://doi.org/10.1007/978-3-319-20886-2_20 

The linear regression formula for transforming UMUX-LITE scores to a SUS scale is:

Note: If using this format note that the UMUX-LITE’s two questions do not cover the full range of the SUS. The range of the UMUX-LITE for comparison to the SUS is [22.9, 87.9].

Reference for UMUX-LITE

Lewis, J.R., Utesch, B.S., & Maher, D.E. (2013). UMUX-LITE: When there’s no time for the SUS. In Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. Chicago, IL (pp. 2099 - 2102).

Administration

Administer immediately after the respondent uses the product. Instruct the respondent to read each statement carefully and indicate the extent to which they agree or disagree using the scale provided.

Survey

Scoring

The Items 2 and 4 are reverse coded, meaning that high responses on these items correspond to low Usability. All item responses are then converted onto a 0 to 6 scale for scoring.

To allow for comparison to SUS scores, divide the summed total by the maximum total score (24) and multiply by 100.

Interpretation

Higher scores indicate greater usability.

References For UMUX

Finstad, K. (2010). The usability metric for user experience. Interacting with Computers, 22, 323-327.