5.11 Aspirin and heart attacks. Can aspirin help prevent heart attacks? The Physicians’ Health Study, a large medical experiment involving 22,000 male physicians, attempted to answer this question. 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 explanatory variable and the values it can take, and the response variable.
(b) Use a diagram to outline the design of the Physicians’ Health Study. (When you outline the design of an experiment, be sure to indicate the size of the treatment groups and the response variable. The diagrams in Figures 5.2 and 5.3 are models.)
(c) What do you think the term “significantly” means in “significantly fewer heart attacks”?