SAT OwlQuestion bank / Evaluating statistical claims: observational studies and experiments
A researcher recruited adult volunteers through a newspaper ad. The researcher randomly assigned of them to take a new herbal sleep supplement each night and the other to take a placebo. After one month, the supplement group averaged significantly more hours of sleep per night than the placebo group. Which of the following conclusions is best supported?
The supplement causes an increase in nightly sleep for all adults.
The supplement is associated with more sleep, but no cause-and-effect conclusion can be drawn.
The supplement likely causes an increase in nightly sleep for adults similar to the volunteers, but the results may not generalize to all adults.
No conclusion can be drawn because the volunteers were not randomly assigned to groups.
Show answer and explanation
Answer: C
Because the volunteers were randomly assigned to groups, the study supports a cause-and-effect conclusion. However, the participants were volunteers, not a random sample of all adults, so the conclusion should be limited to people similar to those in the study.
Choice A is tempting because random assignment supports causation, but generalizing to all adults would require random selection from that population.
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