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).



Getting Started Finding the Right Sample Size
The Essentials of a Contextual Inquiry
8 Ways to Show Design Changes Improved the User Experience
How to Conduct a Usability test on a Mobile Device
How common are usability problems?
Confidence Interval Calculator for a Completion Rate
What five users can tell you that 5000 cannot
Should you use 5 or 7 point scales?
Why you only need to test with five users (explained)
10 Things to Know about Usability Problems
The Five Most Influential Papers in Usability
5 Examples of Quantifying Qualitative Data
97 Things to Know about Usability
A Brief History of the Magic Number 5 in Usability Testing
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Excel & R Companion to Quantifying the User Experience Detailed Steps to Solve over 100 Examples and Exercises in the Excel Calculator and R Buy on Amazon  Download  
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