(a) The Nurses' Health Study has interviewed a sample of more than 100,000 female registered nurses every two years since 1976. The study finds that " light-to-moderate drinkers had a significantly lower risk of death" than either nondrinkers or heavy drinkers. The Nursers' Health Study is A. an experiment. B. an observational study. C. Can't tell without more information.
(b) Can changing diet reduce high blood pressure? Vegetarian diets and low-salt diets are both promising. Men with high blood pressure are assigned at random to one of four diets: (1) normal diet with unrestricted salt; (2) vegetarian with unrestricted salt; (3) normal with restricted salt; and (4) vegetarian with restricted salt. This experiment has A. four factors, the four diets being compared. B. one factor, the choice of diet. C. two factors, normal/vegetarian diet and unrestricted/restricted salt. D. None of the above.
(c) What electrical changes occur in muscles as they get tired? Student subjects hold their arms above their shoulders until they have to drop them. Meanwhile, the electrical activity in their arm muscles is measured. This is A. an observational study. B. a randomized comparative experiment. C. an experiment with no control group. D. None of the above.
You can earn partial credit on this problem.