medium · GRE Verbal
Researchers studying language course observed that students using an app retained more vocabulary. They concluded that the app improved retention. The result is suggestive, but app users practiced twice as long; unless that possibility is addressed, the causal claim remains provisional. Which choice most accurately identifies the weakness in the researchers’ reasoning?
- It treats a before-and-after association as causal without ruling out a simultaneous change.
- It cites an observation relevant to the issue and therefore proves that the intervention can never work under any conditions.
- It assumes without evidence that every participant responded identically to both the intervention and the simultaneous change.
- It relies entirely on a sample that the passage explicitly describes as too small for any statistical analysis.
- It confuses the definition of the intervention with an empirical prediction while never defining the disputed term.
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