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Quantifying the User Experience, 2nd Edition by James R Lewis, Jeff Sauro

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Chapter review questions

1. Assume you need to conduct a single-shot (not iterative) formative usability study that can detect about 85% of the problems that have a probability of occurrence of 0.25 for the specific participants and tasks used in the study (in other words, not 85% of ALL possible usability problems, but 85% of the problems discoverable with your specific method). How many participants should you plan to run?
2. Suppose you decide that you will maintain your goal of 85% discovery, but need to set the target value of p to 0.20. Now how many participants do you need?
3. You just ran a formative usability study with 4 participants. What percentage of the problems of p = 0.50 are you likely to have discovered? What about p = 0.01; ...

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