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Problem-Solving and Data AnalysisVery hardConclusion from a self-selected diet study

Problem-Solving and Data Analysis practice question

A researcher compared two groups of volunteers: those who had chosen a vegetarian diet and those who had not. The vegetarians had lower cholesterol on average. Which conclusion is best supported?

  1. A. Among these volunteers a vegetarian diet is associated with lower cholesterol, but because the groups chose their own diets the study cannot show that the diet caused the difference, and the result may not extend beyond volunteers.Correct
  2. B. A vegetarian diet lowers cholesterol in the general population.
  3. C. People with low cholesterol tend to become vegetarians.
  4. D. The study proves nothing at all.

Answer: A. Among these volunteers a vegetarian diet is associated with lower cholesterol, but because the groups chose their own diets the study cannot show that the diet caused the difference, and the result may not extend beyond volunteers.

Association, self-selection, and a volunteer sample.

Why the other answers are wrong

B. A vegetarian diet lowers cholesterol in the general population.
Claims cause and generalises beyond volunteers.
C. People with low cholesterol tend to become vegetarians.
Assumes the reverse cause without evidence.
D. The study proves nothing at all.
The association is a real finding.

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