SAT Math · Evaluating statistical claims: observational studies and experiments · medium
A researcher observes that, among adults who were not randomly assigned to groups, those who exercise regularly have lower rates of a…
A researcher observes that, among adults who were not randomly assigned to groups, those who exercise regularly have lower rates of a certain illness than those who do not exercise regularly. The researcher concludes that exercise directly prevents the illness. Which factor, if true, would most weaken this causal conclusion?
Answer and explanation
Answer: A: People with greater access to healthcare and healthier diets are also more likely to exercise regularly.
Because people were not randomly assigned to exercise or not, the groups may differ in other ways. Choice A names such a confounding variable: access to healthcare and healthier diets are linked to both exercise and lower illness rates, so they could explain the results instead of exercise. That directly weakens the claim that exercise prevents illness, making A correct. Choice B is expected in any study and does not undermine a statistical trend. Choice C, a large sample, would strengthen the reliability of the pattern, not weaken the causal claim. Choice D is about recommendations and says nothing about whether this study shows cause.
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