Aspirin prevents heart attacks? During the 1980s approximately 22,000 physicians over the age of 40 agreed to participate in a long-term study called the Physicians’

Health Study. One question investigated was whether aspirin helps lower the rate of heart attacks. The physicians were randomly assigned to take aspirin or take a placebo.

a. Identify the response variable and the explanatory variable.

b. Explain why this is an experiment and identify the treatments.

c. There are other explanatory variables, such as the amount of exercise a physician got, that we would expect to be associated with the response variable.

Explain how such a variable is dealt with by the randomized nature of the experiment.