SAT OwlQuestion bank / Evaluating statistical claims: observational studies and experiments
A researcher found that among randomly selected adults in a town, those who walk a dog daily had lower average blood pressure than those who do not. Which change to the study design would best allow the researcher to conclude that daily dog walking causes lower blood pressure?
Increasing the sample size to randomly selected adults
Measuring each participant's blood pressure twice instead of once
Selecting the adults from several towns instead of one
Randomly assigning participants to either walk a dog daily or not walk a dog, then comparing blood pressure
Show answer and explanation
Answer: D
The original study is observational: people chose whether to walk a dog, and those people might differ in other ways, such as overall activity level. Randomly assigning participants to the two conditions balances such factors between groups. That makes it possible to attribute a difference in blood pressure to dog walking.
Choice A increases precision, but a larger observational study still cannot rule out other explanations for the association.
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