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This paper describes recent research in subjective usability measurement at IBM. The focus of the research was the application of psychometric methods to the development and evaluation of questionnaires that measure user satisfaction with system usability. The primary goals of this paper are to (1) discuss the psychometric characteristics of four IBM… (More)

- James R Lewis, Unclassified Boca Raton, Florida
- 2001

Recently, Virzi (1992) presented data that support three claims regarding sample sizes for usability studies. The claims were (1) observing four or five participants will allow a usability practitioner to discover 80% of a product's usability problems, (2) observing additional participants will reveal fewer and fewer new usability problems, and (3) more… (More)

Factor analysis of Post Study System Usability Questionnaire (PSSUQ) data from 5 years of usability studies (with a heavy emphasis on speech dictation systems) indicated a 3-factor structure consistent with that initially described 10 years ago: factors for System Usefulness, Information Quality, and Interface Quality. Estimated reliabilities (ranging from… (More)

- Ed, Ahmet F Ozok, Gavriel Salvendy, James R Lewis
- 2000

usability studies, sample size, usability measurement Efficiency is an important consideration in the design of industrial usability studies. One way to reduce the cost of a usability study is to reduce its sample size. Small samples are not always appropriate, but in this paper I will describe a way to use binomial confidence intervals to determine rapidly… (More)

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 – Usability (8 items) and Learnability (2 items). These new scales have reasonable reliability (coefficient alpha of .91 and .70, respectively). They… (More)

- Carl W Turner, James R Lewis, Jakob Nielsen
- 2006

Correlations between prototypical usability metrics from 90 distinct usability tests were strong when measured at the task-level (r between .44 and .60). Using test-level satisfaction ratings instead of task-level ratings attenuated the correlations (r between .16 and .24). The method of aggregating data from a usability test had a significant effect on the… (More)

There are 2 excellent reasons to compute usability problem-discovery rates. First, an estimate of the problem-discovery rate is a key component for projecting the required sample size for a usability study. Second, practitioners can use this estimate to calculate the proportion of discovered problems for a given sample size. Unfortunately, small-sample… (More)

<i>"Really, how many users do you need to test? Three answers, all different."</i>---User Experience, Vol. 4, Issue 4, 2005

There is growing evidence that normal aging may produce declines in some motor tasks but not others. One account of the task-specific aging effects suggests that age-related differences will be evident in tasks that demand high-level processing but not in tasks that can be performed relatively automatically. To test this hypothesis we compared the… (More)