Which of two widely prescribed drugs—Lipitor or Pravachol—helps lower “bad cholesterol” more? In an experiment, called the PROVE-IT Study, researchers recruited about 4000 people with heart disease as subjects. These volunteers were randomly assigned to one of two treatment groups: Lipitor or Pravachol. At the end of the study, researchers compared the proportion of subjects in each group who died, had a heart attack, or suffered other serious consequences within two years. For the 2063 subjects using Pravachol, the proportion was 0.263. For the 2099 subjects using Lipitor, the proportion was 0.224.15 

a. Does this study provide convincing evidence at the α = 0.05 significance level of a difference in the effectiveness of Lipitor and Pravachol for people like the ones in this study?

b. Based on your conclusion in part (a), which mistake—a Type I error or a Type II error—could you have made? Explain your answer.

c. Should you generalize the result in part (a) to all people with heart disease? Why or why not?