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Determining What Individual SUS Scores Mean: Adding an Adjective Rating Scale

Aaron Bangor, Philip Kortum, and James Miller

Journal of Usability Studies, Volume 4, Issue 3, May 2009, pp. 114-123

Article Contents

Adding an Adjective Scale

Having a large database of SUS scores to use as a benchmark is useful because it allows the practitioner to make relative judgments of product usability, either from iteration-to-iteration or to comparable applications. However, one question that is often asked by project team members, as well as other usability practitioners, remains: “What is the absolute usability associated with any individual SUS score?” In order to help answer this question, a study was conducted that added an eleventh question to the SUS. However, instead of following the SUS format, a seven-point, adjective-anchored Likert scale was used to determine if a word or phrase could be associated with a small range of SUS scores. A subjective image quality rating scale (Bangor, 2000; Olacsi, 1998) was adapted, with the terms Marginal and Passable dropped as being too similar to OK for the diverse user population that participate in our studies.

The phrasing of the prompt has three components. First, it preserves the overall wording from the original rating scale. Second, it uses the term user-friendliness because it is a widely known synonym for the concept of usability. Finally, the term product is used consistently with our version of the SUS. Figure 2 shows the adjective rating scale.

Figure 2. The adjective rating scale added to the SUS.

Figure 2. The adjective rating scale added to the SUS.

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