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Chapter 7. What Sample Sizes Do We Need? > Chapter Review Questions

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 0.2. Now how many participants do you need?

3. You just ran a formative usability study with four participants. What percentage of the problems of p = 0.5 are you likely to have discovered? What about p = 0.01, p = 0.9, or p = 0.25?


  

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