Vasectomies and Prostate Cancer. Refer to the vasectomy/

prostate cancer study discussed in Example 1.5 on page 28.

a. How could the study be modified to make it a designed experiment?

b. Comment on the feasibility of the designed experiment that you described in part (a).

In Exercises 1.17–1.22, state whether the investigation in question is an observational study or a designed experiment. Justify your answer in each case.