Objective: The goal of the research presented in this paper was to determine if the positively worded System Usability Scale (SUS) can be used in place of the positively and negatively worded standard SUS instrument for the subjective assessment of usability, and whether the results found here replicate those of Sauro and Lewis.
Background: Sauro and Lewis' previous study found no evidence that responses to SUS items differed across the standard SUS and the modified, positively worded version of the SUS when participants assessed websites. This study replicates and extends this work by examining a large number of different systems with larger sample sizes to add to the generalizability of previous findings.
Methods: So that participants could retrospectively assess 20 products, the standard SUS was administered to 268 participants and the positive SUS to 698 participants. SUS scores were computed and the data analyzed using psychometric methods to explore how the two versions of the SUS differed.
Results: The standard and positive versions of the SUS yielded similar SUS scores. In addition, both versions of the scale demonstrated evidence in support of reliability and validity.
Conclusion: Either version of the SUS can be used with confidence to measure subjective usability. Furthermore, the scores generated from both versions of the SUS can be directly compared.
Applications: In situations where cognitive load, participants' spoken language, or item consistency with other surveys being given may be a factor, the positive SUS is a viable alternative to the standard SUS.
Keywords: SUS; acquiescence bias; measurement; systems usability scale; usability.