Researchers are investigating whether taking aspirin regularly reduces the risk of heart attacks. Four hundred men
participate in the study. The men are divided randomly into two groups: one group takes aspirin pills, and the other group
takes placebo pills (a pill with no aspirin in it). The men each take one pill a day, and they do not know which group they are
in. At the end of the study, researchers will count the number of men in each group who have had heart attacks.