The ‘magic number 5’

Common practice holds that 80% of usability findings are discovered after five participants. Recent findings from web testing indicate that a much larger number of participants is required to get results and that independent teams testing the same web-based product do replicate results. Other findings suggest that results improve when testing teams work closely with developers in planning the test. This paper presents an insider view of the CUE-2 evaluation that may stimulate further debate regarding the results, plus two cases in which different teams uncovered the same usability issues, working independently but closely with the sponsor.