9.53 Clopidogrel and Aspirin A large study was con- ducted to test the effectiveness of clopidogrel in combina- tion with aspirin in warding off heart attacks and strokes. 19 The trial involved more than 15,500 people 45 years of age or older from 32 countries. These people had been diagnosed with cardiovascular disease or had multiple risk factors. The subjects were randomly assigned to one of two groups. After two years, there was no difference in the risk of heart attack, stroke, or dying from heart disease between those who took clopidogrel and low-dose aspirin daily and those who took low-dose aspirin plus a dummy pill. The two-drug combination actually increased the risk of dying (5.4% versus 3.8%) or dying specifically from cardiovascular disease (3.9% versus 2.2%).

a. The subjects were randomly assigned to one of the two groups. Explain how you could use the random number table to make these assignments.

b. No sample sizes were given in the article: however, let us assume that the sample sizes for each group were n = 7720 and n = 7780. Determine whether the risk of dying was significantly different for the two groups.

c. What do the results of the study mean in terms of practical significance?