(1) Suppose you want to estimate a mean with a margin of error d. What additional information do you need to know before determining the sample size requirements of the study?
(2) You want to calculate a proportion so that the margin of error is .025 (2.5%). An educated guess of the proportion is 0.10. How large a sample is needed?
(3) You are looking for a mean difference of 5 and assume that the standard deviation of the variable is about 20. How many observations do you need to test the data for a difference with a = .05 (two-sided) and 1 - b = .8?
(4) A case-control study is looking to detect an odds ratio of 1.5. It uses a ratio 1:1 for cases: controls. The prevalence of exposure in the source population is 20%. How many cases and controls do you need to study assuming a = .05 (two-sided) and 1 - b = .8?
(5) Redo the sample size calculation for #4 now assuming an odds ratio of 2.0.
(6) You are planning a cohort study in which the expected incidence proportion in the exposed is 20% and the expected incidence proportion in the nonexposed is 10%. You want to test H0: RR = 1. Group sample sizes will be equal. How many people should you study?
Key to Odd Numbered Problems Key to Even Numbered Problems (may not be posted)