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- James R. Lewis
- Int. J. Hum. Comput. Interaction
- 1995

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, Jeff Sauro
- HCI
- 2009

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)

- James R. Lewis
- Int. J. Hum. Comput. Interaction
- 2002

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)

- James R. Lewis
- SGCH
- 1991

A three-item after-scenario questionnaire was used in three related usability tests in different areas of the United States. The studies had eight scenarios in common. After participants finished a scenario, they completed the After-Scenario Questionnaire (the ASQ). A factor analysis of the responses to the ASQ items revealed that an eight-factor solution… (More)

Virzi (1992), Nielsen and Landauer (1993), and Lewis (1994) have published influential articles on the topic of sample size in usability testing. In these articles, the authors presented a mathematical model of problem discovery rates in usability testing. Using the problem discovery rate model, they showed that it was possible to determine the sample size… (More)

- James R. Lewis
- Interactions
- 2006

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

- Conal Quah, Girish Nanjunda Swamy, James R. Lewis, John Kendrew, Nitin P. Badhe
- The Knee
- 2012

INTRODUCTION
Stiffness following total knee arthroplasty (TKA) is a disabling problem resulting in pain and reduced function.
OBJECTIVE
The aim of our study was to evaluate the natural course of fixed flexion deformity (FFD ) following primary total knee arthroplasty.
METHODS
Prospective review of 1626 patients undergoing primary TKA from 2001 to 2006… (More)

- Jeff Sauro, James R. Lewis
- CHI
- 2009

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)

- Jeff Sauro, James R. Lewis
- CHI
- 2010

The distribution of task time data in usability studies is positively skewed. Practitioners who are aware of this positive skew tend to report the sample median. Monte Carlo simulations using data from 61 large-sample usability tasks showed that the sample median is a biased estimate of the population median. Using the geometric mean to estimate the center… (More)

- Daud Tai Shan Chou, Girish Nanjunda Swamy, James R. Lewis, Nitin P. Badhe
- The Knee
- 2012

Recent reports suggest good outcome results following unicompartmental knee replacement (UKR). However, a number of authors have commented on the problem of osseous defects requiring technically difficult revision surgery. We reviewed clinical outcomes following revision total knee replacement (TKR) for failed UKR and analysed the reasons for failure and… (More)