Suppose we wish to conduct a clinical trial to study the association between ASA and colon cancer. We will enroll 50,000 women in the study, half of whom will be assigned to ASA and half to placebo. Each woman is followed for 5 years. The expected incidence rate of colon cancer in the ASA group = 70/105 person-years and in the placebo group = 100/10⁵ person-years. If we conduct a two-sided test with α = 0.05, how much power will the study have? 

Most risk factors seem of comparable magnitude for men and women. However, one exception is cigarette smoking.