New technical advances in diagnosis and screening are often expensive, and so their benefits must be evaluated. A study of a new screening procedure for heart disease, computerized tomographic angiography (CTA), examined 4146 patients who had stable chest pains (The SCOT-HEART Investigators 2018). All patients received standard tests for coronary heart disease, but 2073 of the patients, randomly assigned, were additionally screened with CTA which improves detection of heart disease. After 5 years, 81 of the 2703 patients receiving standard tests had a “major event” (death or major heart attack), whereas 48 of the 2703 patients who also received CTA had a major event.

a. Calculate the relative risk of a major event for the CTA screening group compared to the group without this screening. 

b. Interpret this result. Does CTA screening seem to increase or decrease the rates of major events?

c. Do an appropriate hypothesis test to determine whether these data support an effect of CTA screening on the risk of major events.