Beyond the five-user assumption: benefits of increased sample sizes in usability testing

Behav Res Methods Instrum Comput. 2003 Aug;35(3):379-83. doi: 10.3758/bf03195514.


It is widely assumed that 5 participants suffice for usability testing. In this study, 60 users were tested and random sets of 5 or more were sampled from the whole, to demonstrate the risks of using only 5 participants and the benefits of using more. Some of the randomly selected sets of 5 participants found 99% of the problems; other sets found only 55%. With 10 users, the lowest percentage of problems revealed by any one set was increased to 80%, and with 20 users, to 95%.

MeSH terms

  • Consumer Behavior*
  • Data Collection / instrumentation
  • Data Collection / methods*
  • Humans
  • Internet
  • Product Surveillance, Postmarketing*
  • Sample Size
  • Software*
  • Task Performance and Analysis
  • User-Computer Interface*