may be tested by only five users, when the method is properly applied, the parts of the design that worked in that initial test will go on to be tested by 50 to 100 people.

Limitations of participant sampling

Statistical critiques of small sample testing

The widely cited claim that five participants are sufficient to identify 85% of usability problems has been subject to significant academic scrutiny. The underlying mathematical model assumes a constant probability of problem discovery across all users and all problems.

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