Statin drugs are used to decrease cholesterol levels and therefore hopefully to decrease the chances of a heart attack. In a British study (“MRC/BHF Heart Protection Study of Cholesterol Lowering with Simvastin in 20,536 High-Risk Individuals: A Randomized Placebo-Controlled Trial,” Lancet 2002: 7–22) 20,536 at-risk adults were assigned randomly to take either a 40- mg statin pill or placebo. The subjects had coronary disease, artery blockage, or diabetes. After 5 years there were 1328 deaths (587 from heart attack) among the 10,269 in the statin group and 1507 deaths (707 from heart attack) among the 10,267 in the placebo group.

a. Give a 95% confidence interval for the difference in population death proportions.
b. Give a 95% confidence interval for the difference in population heart attack death proportions.
c. Is it reasonable to say that most of the difference in death proportions is due to heart attacks, as would be expected?