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Problem-Solving and Data AnalysisHardRecognising the limits of a before-and-after comparison

Problem-Solving and Data Analysis practice question

A gym reports that members who joined its new fitness programme lost an average of 4 kilograms over three months. Which of the following would most strengthen the conclusion that the programme caused the weight loss?

  1. A. A comparison group of similar members who did not join the programme, and who lost little or no weight over the same three months.Correct
  2. B. Testimonials from members who enjoyed the programme.
  3. C. A larger number of members joining the programme.
  4. D. Weighing the members more precisely.

Answer: A. A comparison group of similar members who did not join the programme, and who lost little or no weight over the same three months.

A comparable group without the programme shows what would have happened anyway.

Why the other answers are wrong

B. Testimonials from members who enjoyed the programme.
Enjoyment doesn't show cause.
C. A larger number of members joining the programme.
More members with no comparison still can't separate the programme from other factors.
D. Weighing the members more precisely.
Precision doesn't address what caused the change.

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