Smoking affects lung cancer? You would like to investigate whether smokers are more likely than nonsmokers to get lung cancer. From the students in your class, you pick half at random to smoke a pack of cigarettes each day and half not ever to smoke. Fifty years from now, you will analyze whether more smokers than nonsmokers got lung cancer.

a. Is this an experiment or an observational study? Why?

b. Summarize at least three practical difficulties with this planned study.