For each problem, select the best response. (a) A marketing class designs two videos advertising an expensive Mercedes sports car. They test the videos by asking fellow students to view both (in random order) and say which makes them more likely to buy the car. Mercedes should be reluctant to agree that the video favored in this study will sell more cars because
A. results from students may not generalize to the older and richer customers who might buy a Mercedes.
B. this is an observational study, not an experiment.
C. the study used matched pairs design instead of a completely randomized design.
D. None of the above.
(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. one factor, the choice of diet.
B. two factors, normal/vegetarian diet and unrestricted/restricted salt.
C. four factors, the four diets being compared.
D. None of the above.
(c) 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.