SAT OwlQuestion bank / Evaluating statistical claims: observational studies and experiments
A company gave its new sports drink to volunteer runners every day for weeks while the runners continued their usual training. At the end of the weeks, the runners' average time in a -kilometer race had improved by seconds. The company claims that the drink caused the improvement. Which of the following is the strongest reason the claim is not supported?
The study included only runners, and a study needs at least participants to support any conclusion.
The study had no comparison group, so the improvement could have come from the training or other factors.
The runners were volunteers, so the results can't apply to any runners.
The runners' times were measured only at the start and end of the study instead of every week.
Show answer and explanation
Answer: B
Without a comparison group that didn't get the drink, there's no way to separate the drink's effect from the effect of weeks of training. A better design would randomly assign runners to get either the new drink or a similar drink without the new ingredients.
Choice C points to a real limit of using volunteers, but it overstates it; the bigger problem is that nothing rules out other causes of the improvement.
Why the other choices are wrong
- A. There is no rule that a study needs 100 participants. The bigger problem is the missing comparison group.
- C. Volunteers limit how far results can be generalized, but the main flaw is that training could explain the improvement.
- D. Measuring more often wouldn't separate the drink's effect from the effect of training.
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