To examine the effect of exercise on body composition, healthy women aged 35 to 50 were classified as either
active (nine or more hours of physical activity per week) or sedentary.† Body fat percentage was measured, and
the researchers found that this percentage was significantly lower for women who were active than for sedentary
women.

(a) Is the study described an experiment?
Yes, the study is an experiment.
No, this is an observational study.

If the study was an experiment, what is the explanatory variable and what is the response variable? If not,
explain why it is not an experiment.

The study described is an experiment. The explanatory variable is the body fat percentage of the
women, and the response variable is the hours per week the women spent exercising.
The study described is not an experiment because there were no experimental conditions to which
study participants were randomly assigned.
The study described is an experiment. The explanatory variable is the hours per week the women
spent exercising, and the response variable is the body fat percentage of the women.
The study described is an experiment. The explanatory variable is the age of the women, and the
response variable is the body fat percentage of the women.
The study described is not an experiment because the researchers only used two classifications to
describe the participants.

(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.

No, it is not reasonable to conclude that physical activity is the cause of the observed difference in
body fat percentage. This experiment was not done on a sample that represents the population of
interest.
No, it is not reasonable to conclude that physical activity is the cause of the observed difference in
body fat percentage. This was an observational study, and cause-and-effect conclusions cannot
be drawn.
Yes, it is reasonable to conclude that physical activity is the cause of the observed difference in
body fat percentage. This was an observational study, so cause-and-effect conclusions can be
drawn.
Yes, it is reasonable to conclude that physical activity is the cause of the observed difference in
body fat percentage. This experiment was done on a randomized sample from the population of
interest.