A critique of how to specify the participant group size for usability studies: a practitioner's guide by Macefield

This critique addresses important issues overlooked by Macefield in his recent paper in JUS. The participant group size depends on the purpose of the test. It also depends on test quality---if poor methodology is used, participant group size is unimportant. Evaluator quality and number of involved evaluators affect usability studies more than participant group size. The Comparative Usability Evaluation (CUE) studies have shown that it is infeasible or impossible to find all serious usability problems on a typical website. This critique argues that five users are enough to drive a useful iterative cycle.