Each of the following quotes is based on the results of an experiment or an observational study. Explain which was used. If an observational study was used, explain whether an experiment could have been used to study the topic instead.
a. “ A recent Stanford study of more than 6000 men found that tolerance for exercise (tested on a treadmill) was a stronger predictor of risk of death than high blood pressure, smoking, diabetes, high cholesterol and heart disease” (Kalb, 2003, p. 64).
b. “ In a three-month study, researchers randomly assigned 250 black men and women to one of four groups: one received a placebo and the others received 1000, 2000, or 4000 international units of vitamin D daily [to see if vitamin D helps reduce hypertension in African- Americans]. The effect was modest.” (New York Times, March 19, 2013, p. D4).