Cytomegalovirus and coronary restenosis. Each year, cardiologists surgically repair thousands of clogged coronary arteries only to have many of these arteries narrow again (restenose) soon after surgery. A study sponsored by the NIH was conducted to help determine whether infection with a common type of virus, cytomegalovirus

(CMV), contributed to coronary restenosis. Forty-nine of the subjects showed serological evidence of CMV infection, while 26 showed no such evidence. In the CMV+ group, 21 individuals restenosed within 6 months of atherectomy. In the CMV− group, 2 individuals restenosed.e

(a) Calculate the risk difference of restenosis associated with seropositivity.

(b) Calculate a 95% confidence interval for p1

− p2

. Explain the meaning of this confidence interval in terms a layperson can understand.

(c) Optional: Use WinPepi Compare2.exe to calculate 95%

confidence intervals for p1

− p2

. How do WinPepi’s calculations compare with the confidence interval calculated by hand in part

(b)?