hard · GRE Verbal
Researchers studying soil inoculant observed that inoculated seedlings grew faster. They concluded that the inoculant accelerated growth. The result is suggestive, but those seedlings also received more sunlight; unless that possibility is addressed, the causal claim remains provisional. Which additional study would most strengthen the researchers’ causal interpretation?
- Randomly place inoculated and control seedlings across light conditions.
- Repeat the original uncontrolled comparison while collecting a much larger number of participant anecdotes.
- Show through a separate opinion survey that the intervention is unusually popular with the participants.
- Document in detail that the measured outcome matters to policymakers responsible for the program.
- Compare the intervention with an unrelated program administered to a demographically different population.
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