The Physicians’ Health Study, a large medical experiment involving 22,000 male physicians, attempted to determine whether aspirin could help prevent heart attacks. In this study, one group of about 11,000 physicians took an aspirin every other day, while a control group took a placebo. After several years, it was determined that the physicians in the group that took aspirin had significantly fewer heart attacks than the physicians in the control group. Which of the following statements explains why it would not be appropriate to say that everyone should take an aspirin every other day? I. The study included only physicians, and different results may occur in individuals in other occupations. II. The study included only males and there may be different results for females. III. Although taking aspirin may be helpful in preventing heart attacks, it may be harmful to some other aspects of health