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 GoodTuring
and Normalization procedure as outlined by Lewis (2001)
and further discussed in (Turner, Lewis & Nielsen
2006).



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Quantifying the User Experience 2nd Ed.: Practical Statistics for User Research The most comprehensive statistical resource for UX Professionals Buy on Amazon  
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