Beyond the Five-User Assumption: Benefits of Increased Sample Sizes in Usability Testing    

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%.

Faulkner, Laura. Behavior Research Methods, Instruments and Computers (2003). Articles>Usability>Testing

Take Breaks! A Simple Way to Improve Your Heuristic Evaluation Results

As primary tools in the usability field, heuristic or expert evaluations can be rich areas for methods studies and improvement. Early results of one methods study suggest that performing evaluations in limited segments, with breaks between each segment, may increase the effectiveness of the evaluator in identifying usability problems.

Faulkner, Laura. Usability Professionals Association (2005). Articles>Usability>Methods>Heuristic Evaluation