Are the proportion of HIV patients who take AZT less likely to develop AIDS than a placebo group?
In a study, 870 HIV patients were randomly assigned to two treatment regimes with 435 patients in each group. the first group received AZT while the second received a placebo. After a period of years, 17 individuals in the AZT group develop AIDS as compared to 38 individuals in the placebo group. • Hypothesis Tests. The previous problem may be tested formally with a statistical procedure called a hypothesis test. Begin by assuming that the probability of developing AIDS is the same for each group. This is our null hypothesis. The alternative hypothesis is that the probability of developing AIDS is smaller in the AZT group. We see an observed difference of 21 individuals. The basic question is, if the two population proportions were equal, would a difference this large likely occur by chance alone? We can measure the difference between what actually occurs and what we expect to occur by calculating the probability of seeing an outcome at least as extreme as what actually occurs if we we
