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Problem-Solving and Data AnalysisHardWhat a randomised experiment supports

Problem-Solving and Data Analysis practice question

A hospital selected 200 of its patients at random and randomly assigned each of them to one of two post-surgery diets. Patients on diet A recovered significantly faster on average. Which conclusion is best supported?

  1. A. Among patients at that hospital, diet A causes faster recovery than diet B.Correct
  2. B. Diet A causes faster recovery for surgery patients in general.
  3. C. Diet A and faster recovery are associated, but the design can't support a causal claim.
  4. D. No conclusion is possible because only one hospital was involved.

Answer: A. Among patients at that hospital, diet A causes faster recovery than diet B.

Random ASSIGNMENT to the diets makes the groups comparable, so the difference in recovery can be attributed to the diet — a causal claim. Random SELECTION from the hospital's patients lets that claim be generalised to patients at that hospital, but not beyond.

Why the other answers are wrong

B. Diet A causes faster recovery for surgery patients in general.
The patients were randomly selected from ONE hospital. Nothing supports extending the result to surgery patients everywhere.
C. Diet A and faster recovery are associated, but the design can't support a causal claim.
Random assignment is exactly what makes a causal claim possible. This caution belongs to observational studies, not experiments.
D. No conclusion is possible because only one hospital was involved.
One hospital limits how far the result generalises; it doesn't prevent a conclusion within that hospital.

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