Human Centered Design

Volume 5619 of the series Lecture Notes in Computer Science pp 94-103

The Factor Structure of the System Usability Scale

  • James R. LewisAffiliated withIBM Software Group
  • , Jeff SauroAffiliated withOracle

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Since its introduction in 1986, the 10-item System Usability Scale (SUS) has been assumed to be unidimensional. Factor analysis of two independent SUS data sets reveals that the SUS actually has two factors – Usable (8 items) and Learnable (2 items – specifically, Items 4 and 10). These new scales have reasonable reliability (coefficient alpha of .91 and .70, respectively). They correlate highly with the overall SUS (r = .985 and .784, respectively) and correlate significantly with one another (r = .664), but at a low enough level to use as separate scales. A sensitivity analysis using data from 19 tests had a significant Test by Scale interaction, providing additional evidence of the differential utility of the new scales. Practitioners can continue to use the current SUS as is, but, at no extra cost, can also take advantage of these new scales to extract additional information from their SUS data. The data support the use of “awkward” rather than “cumbersome” in Item 8.


System Usability Scale SUS factor analysis psychometric evaluation subjective usability measurement usability learnability usable learnable