Jeff Sauro • October 1, 2006
Sample Size from an estimate of Problem Occurrence (p)
If the probability of detecting a UI problem is known in advance, use this portion of the calculator to estimate the total number of users needed to uncover on average the specified percentage of problems (e.g. 90%). The calculator is based on the binomial probability formula.
Estimate Problem Occurrence (p) then Sample
Size
This portion of the calculator first builds
an estimate of the probability of detecting a UI problem (from sample
data). It then produces an estimate of the number of users needed
to discover the specified percent of total problems. It uses the Good-Turing
and Normalization procedure as outlined by Lewis (2001)
and further discussed in (Turner, Lewis & Nielsen
2006).
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Jeff Sauro is the founding principal of Measuring Usability LLC, a company providing statistics and usability consulting to
Fortune 1000 companies.
He is the author of over
15 journal articles and 3 books on statistics and the user-experience.
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