Determining what individual SUS scores mean: adding an adjective rating scale

TLDR

The System Usability Scale (SUS) is a widely used, inexpensive tool that scores usability from 0 to 100 across various products, yet how these numeric scores map to absolute usability judgments remains unclear. The study aimed to clarify how SUS scores translate into absolute usability judgments. To do so, a seven‑point adjective‑anchored Likert scale was added as an eleventh question to nearly 1,000 SUS surveys. The Likert scale scores correlated strongly with SUS scores (r = 0.822), indicating that the added adjective rating can help practitioners interpret individual SUS scores and communicate results to non‑human‑factors professionals.

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.