A recent study found that individuals who regularly consume blueberries score significantly higher on memory tests than those who do not. Researchers concluded that regular blueberry consumption enhances cognitive function. Which of the following, if true, would most seriously weaken the researchers' conclusion?
- AIndividuals who regularly consume blueberries are also more likely to engage in other healthy lifestyle choices, such as regular exercise and a balanced diet.
- BThe study was funded by a major blueberry growers' association.
- CThe memory tests used in the study primarily assessed short-term recall, not other aspects of cognitive function.
- DA separate study found that the antioxidants in blueberries are poorly absorbed by the human brain.
Show answer & explanationAnswer & explanation
Correct answer: A. Individuals who regularly consume blueberries are also more likely to engage in other healthy lifestyle choices, such as regular exercise and a balanced diet.
The researchers draw a causal conclusion (blueberry consumption enhances cognitive function) based on correlation. Option B introduces a confounding variable: other healthy lifestyle choices. If these choices, rather than blueberries themselves, are responsible for higher memory scores, then the causal link between blueberries and cognitive function is weakened.
Why the other options are wrong
- B. Funding source can suggest bias, but doesn't directly weaken the observed correlation or provide an alternative explanation for the results themselves.
- C. This suggests the conclusion might be too broad (cognitive function vs. short-term recall), but doesn't weaken the claim that blueberries *do* enhance short-term recall.
- D. Poor absorption of antioxidants might prevent a *mechanism* for enhancement, but doesn't directly disprove the observed *correlation* or offer a better alternative explanation for it.
Confounding Variable
An unmeasured variable that influences both the supposed cause and the supposed effect, creating a spurious correlation between them.
- Distorts the true relationship between variables.
- Can lead to incorrect causal conclusions.
- Must be controlled for in experimental design.
Memory trick: Just because two trains run on parallel tracks, doesn't mean one pushes the other.