Problem-Solving and Data AnalysisVery hardFlaw in comparing completers with dropouts
Problem-Solving and Data Analysis practice question
In a trial of a new medicine, patients who completed the full course recovered faster on average than patients who dropped out partway through. The researchers concluded that the medicine speeds recovery. Which of the following is the best reason the comparison is flawed?
- A. Patients who dropped out may differ from those who finished — for instance, those feeling worse may have been more likely to quit — so the two groups are not comparable.Correct
- B. The medicine was never actually given to anyone.
- C. Recovery time cannot be measured.
- D. The trial lasted too long.
Answer: A. Patients who dropped out may differ from those who finished — for instance, those feeling worse may have been more likely to quit — so the two groups are not comparable.
Dropping out wasn't random. If sicker patients quit, the completers were healthier to begin with, and the medicine gets credit that belongs to that difference.
Why the other answers are wrong
- B. The medicine was never actually given to anyone.
- The medicine was given; the problem is who was compared with whom.
- C. Recovery time cannot be measured.
- Recovery time was measured; the issue is the groups being compared.
- D. The trial lasted too long.
- Trial length isn't the flaw.
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