To examine the effect of exercise on body composition, healthy women age 35 to 50 were classified as either active (9 hours or more of physical activity per week) or sedentary (“Effects of Habitual Physical Activity on the Resting Metabolic Rates and Body Composition of Women aged 35 to 50 Years,” Journal of the American Dietetic Association [2001]: 1181–1191). Percent body fat was measured and the researchers found that percent body fat was significantly lower for women who were active than for sedentary women.

a. Is the study described an experiment? If so, what are the explanatory variable and the response variable? If not, explain why it is not an experiment.

b. From this study alone, is it reasonable to conclude that physical activity is the cause of the observed difference in body fat percentage? Justify your answer.