Does aspirin prevent strokes and heart attacks? The Bayer Aspirin Web site claims, "Nearly five decades of research now link aspirin to the prevention of strokes and heart attacks." The most important evidence for this claim comes from the Physicians' Health Study, a large medical experiment involving 22,000 male physicians. One group of about 11,000 physicians took an aspirin every second day, while the rest took a placebo. After several years the study found that subjects in the aspirin group had significantly fewer heart attacks than subjects in the placebo group.
(a) Identify the experimental subjects, the factor and its levels, and the response variable in the Physicians' Health Study.
(b) Use a diagram to outline a completely randomized design for the Physicians' Health Study
(c) What does it mean to say that the aspirin group had "significantly fewer heart attacks"?