hard · GRE Verbal
Researchers evaluating a mobile-library service observed that book borrowing rose after weekly van visits began. They concluded that the service increased reading access. The observation is suggestive, but schools launched a reading contest that month; until that possibility is separated from the intervention, the causal interpretation remains provisional. Which additional study would most strengthen the researchers’ causal interpretation?
- Compare the intervention with an unrelated program used in a demographically different population.
- Compare districts with and without van service during the same contest.
- Repeat the same uncontrolled before-and-after comparison with a much larger collection of participant anecdotes gathered under unchanged conditions.
- Show that participants consider the intervention appealing and easy to understand.
- Document that policymakers regard the measured outcome as important.
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