ABSTRACT
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 needed to uncover a given proportion of problems in an interface during one test. The authors presented empirical evidence for the models and made several important claims:
O Most usability problems are detected with the first three to five subjects.
