ABSTRACT
Q1 Two hundred and twenty-eight of 1320 patients with moderate to severe congestive cardiac failure who received placebo treatment died, as did 156 of 1327 who received bisoprolol. What was the relative risk of dying? A 17% B 12% C 68% D 53% E 22%
A1 C In clinical trials subjects with different characteristics are followed up to see whether an outcome of interest occurs. The proportions having the outcomes in each group is calculated and so the ratio of these two proportions is a measure of the raised risk in one group compared with the other. This ratio is termed the relative risk. Under the null hypothesis the expected value of RR is 1. In the above example, the risk of death in the placebo group is 0.1727272 (228/1320) and the risk in the treated group is 0.1175584 (156/1327) making the RR of dying (if untreated) 0.1727272/0.1175584 or 68.06%.
