hard · GRE Verbal
Researchers evaluating a bus-lane pilot observed that travel times fell after a dedicated lane opened. They concluded that the lane caused the improvement. The observation is suggestive, but a major employer shifted to remote work 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 similar corridors with and without new lanes during the same employment shift.
- 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.
- Compare the intervention with an unrelated program used in a demographically different population.
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