The Physician's Health Study was a randomized clinical trial, one of whose goals was to effect of cigarette smoking on the development of myocardial infarction preventing myocardial infarction (MI).
Suppose that the incidence of MI is 0.005 per year among subjects who are actually take placebo and that aspirin prevents 20% of MIs (i.e. relative risk=p1/p2=0.8). We also assume that the duration of the study is 5 years, and during study, there is neither drop out nor drop in.
How many subjects need to be enrolled in each group to achieve 80% power using two-sided test with significance level=0.05?