Adverse Drug Reactions The drug Viagra has become quite well known, and it has had a substantial economic impact on its producer, Pfizer Pharmaceuticals. In prelim-

inary tests for adverse reactions, it was found that when 734 men were treated with Viagra, 16% of them experienced headaches. (There’s some real irony there.) Among 725 men in a placebo group, 4% experienced headaches (based on data from Pfizer Pharmaceuticals).

a. Using a 0.01 significance level, is there sufficient evidence to support the claim that among those men who take Viagra, headaches occur at a rate that is greater than the rate for those who do not take Viagra?

b. Construct a 99% confidence interval estimate of the difference between the rate of headaches among Viagra users and the headache rate for those who are given a placebo. What does the confidence interval suggest about the two rates?