In the Physician’s Health Study, introduced in Data 1.6 on page 37, 22,071 male physicians participated in a study to determine whether taking a daily low-dose aspirin reduced the risk of heart attacks. The men were randomly assigned to two groups and the study was double-blind. After five years, 104 of the 11,037 men taking a daily low-dose aspirin had had a heart attack while 189 of the 11,034 men taking a placebo had had a heart attack.52 Does taking a daily low-dose aspirin reduce the risk of heart attacks? Conduct the test, and, in addition, explain why we can infer a causal relationship from the results. 

Data 1.6 on page 37

Does anyone you know regularly take a low-dose aspirin? If so, it may be because of a randomized experiment conducted in the 1980s, the Physicians’ Health Study. The study recruited 22,071 male physicians and randomly assigned half of them to take an aspirin every other day for about five years and the other half to take a fake aspirin pill instead. They found that the physicians who took the real aspirin had 44% fewer heart attacks than those taking the fake aspirin.