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
Abstract
The System Usability Scale (SUS) is an inexpensive, yet effective tool for assessing the usability of a product, including Web sites, cell phones, interactive voice response systems, TV applications, and more. It provides an easy-to-understand score from 0 (negative) to 100 (positive). While a 100-point scale is intuitive in many respects and allows for relative judgments, information describing how the numeric score translates into an absolute judgment of usability is not known. To help answer that question, a seven-point adjective-anchored Likert scale was added as an eleventh question to nearly 1,000 SUS surveys. Results show that the Likert scale scores correlate extremely well with the SUS scores (r=0.822). The addition of the adjective rating scale to the SUS may help practitioners interpret individual SUS scores and aid in explaining the results to non-human factors professionals.
Practitioner’s Take Away
This research examined the addition of an adjective rating scale to the System Usability Scale (SUS) and found the following:
- The SUS is an effective, reliable tool for measuring the usability of a wide variety of products and services.
- The 0 to 100 scale is intuitive to understand, yet raises many questions about what a single SUS score means in an absolute sense.
- Analysis of nearly 1,000 SUS scores has shown that an adjective rating is highly correlated with SUS scores.
- The addition of an adjective rating scale to the SUS can help practitioners interpret individual SUS scores, and aid in explaining the results to non-human factors professionals.
- The SUS score associated with the mid-point adjective of OK is consistent with previous adjective rating scale research, but the connotation of OK may suggest an acceptable product. We present alternative adjectives that have similar ratings but that suggest a more accurate connotation of the product’s actual usability.
- Using a letter grade scale in lieu of an adjective scale could be an alternate way to understand the absolute meaning of a SUS score.
Article Contents
Download Article
Determining What Individual SUS Scores Mean: Adding an Adjective Rating Scale