A study found that towns with more ice-cream shops per resident have higher rates of sunburn. A journalist concludes that ice-cream shops cause sunburn. Which of the following, if true, best explains the association without ice-cream shops causing sunburn?

Question

Accepted Answer

A. Both ice-cream shops and sunburn are more common in towns with hotter, sunnier weather.. A third factor — sunny weather — would independently raise BOTH the number of ice-cream shops and the sunburn rate, producing the association with no causal link between them.

Answer

B. The study included only towns with at least one ice-cream shop. — Restricting the sample to towns with a shop doesn't explain why more shops go with more sunburn.

Answer

C. Sunburn rates were measured from hospital records, which are very accurate. — Accurate measurement makes the association more credible; it does nothing to explain it away.

Answer

D. Most ice-cream shops also sell sunscreen. — If shops sold sunscreen, that would if anything REDUCE sunburn near them, making the association harder to explain, not easier.

Problem-Solving and Data Analysis practice question

Answer: A. Both ice-cream shops and sunburn are more common in towns with hotter, sunnier weather.

Why the other answers are wrong

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