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The Factor Structure of the System Usability Scale

  • James R. Lewis
  • Jeff Sauro
Part of the Lecture Notes in Computer Science book series (LNCS, volume 5619)

Abstract

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.

Keywords

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

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Copyright information

© Springer-Verlag Berlin Heidelberg 2009

Authors and Affiliations

  • James R. Lewis
    • 1
  • Jeff Sauro
    • 2
  1. 1.IBM Software GroupBoca RatonUSA
  2. 2.OracleDenverUSA

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