GMAT Focus EditionVerbal ReasoningMedium
A recent study found that individuals who regularly consume blueberries score significantly higher on cognitive function tests than those who do not. Researchers conclude that including blueberries in one's diet directly enhances cognitive function. Which of the following, if true, would most seriously weaken the researchers' conclusion?
- ASome participants in the study reported a dislike for blueberries and rarely consumed them.
- BThe cognitive function tests used in the study primarily measured short-term memory, not overall cognitive ability.
- CIndividuals who regularly consume blueberries are also more likely to follow a generally healthy diet and lifestyle.
- DBlueberries contain antioxidants known to support brain health.
Show answer & explanationAnswer & explanation
Correct answer: C. Individuals who regularly consume blueberries are also more likely to follow a generally healthy diet and lifestyle.
The conclusion draws a direct causal link between blueberries and cognitive function. If blueberry consumers also engage in other healthy behaviors (a confounding variable), then it's possible these other behaviors, not just the blueberries, are responsible for the improved cognitive function, thus weakening the direct causal conclusion.
Why the other options are wrong
- A. This represents normal variation in dietary habits within a population and does not, on its own, weaken the conclusion about those who *do* regularly consume blueberries.
- B. This questions the *scope* of cognitive function measured, but doesn't weaken the causal link between blueberries and *some* aspect of cognitive function.
- D. This suggests a plausible mechanism, which would strengthen, not weaken, the conclusion.
Confounding Variables
An extraneous variable that correlates with both the dependent and independent variables, potentially leading to a spurious correlation or misleading causal inference.
- Can create false causal links.
- Must be controlled for in studies.
- Often related to lifestyle or environment.
Memory trick: When a cause is claimed, seek out the hidden hand, or the link will be unchained!