An experiment to evaluate whether vitamins can help prevent recurrence of blocked arteries in patients who have had surgery to clear blocked arteries was described in the article “Vitamins Found to Help Prevent Blocked Arteries” (Associated Press, Sep tem ber 1, 2002). The study involved 205 patients who were given either a treatment consisting of a combination of folic acid, vitamin B12, and vitamin B6 or a placebo for 6 months.

a. Explain why a placebo group was used in this experiment.

b. Explain why it would be important for the researchers to have assigned the 205 subjects to the two groups (vitamin and placebo) at random.

c. Do you think it is appropriate to generalize the results of this experiment to the population of all patients who have undergone surgery to clear blocked arteries? Explain.