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Difficulty: EasyCausal Flaws and Confounding Variables

A recent survey of urban professionals revealed that individuals who drink green tea every day report significantly lower stress levels than those who do not drink green tea. Based on this correlation, the researchers concluded that daily green tea consumption directly causes a reduction in psychological stress. Which of the following, if true, most seriously weakens the researchers' conclusion?

  1. Individuals who drink green tea daily are far more likely to engage in regular physical exercise, which independently lowers stress levels.Answer
  2. B
    Green tea contains natural chemical compounds that promote relaxation by interacting with brain receptors.
  3. C
    Many urban professionals who consume other types of herbal tea also report experiencing low stress levels.
  4. D
    Lowering psychological stress is widely recognized as a key intermediate goal for improving overall cardiovascular health.
  5. E
    Survey respondents with the lowest stress levels reported overall higher satisfaction with their career progression.

Answer

The argument is most seriously weakened by pointing out that green tea drinkers are also more likely to engage in regular physical exercise, introducing an alternate factor that accounts for the lower stress levels.
The correct answer identifies a classic confounding variable flaw. By pointing out that daily green tea drinkers are also significantly more likely to engage in regular exercise—a habit known to independently lower stress—it demonstrates that the observed lower stress levels could be caused by exercise rather than green tea, thereby severely undermining the researchers' causal conclusion.

Step-by-Step Solution

1
Identify the premise and conclusion of the argument.
Premise: Daily green tea drinkers report lower stress levels than non-drinkers. Conclusion: Daily green tea consumption directly causes a reduction in stress.
Understanding the logic structure reveals that the author assumes correlation implies direct causation without accounting for potential confounding variables.
2
Determine the weak point in the causal reasoning.
The argument commits a causal flaw by failing to rule out third-variable confounders that could cause the reduced stress instead of the green tea itself.
To weaken a causal conclusion based on correlation, look for an option showing an alternate cause for the effect.
3
Evaluate the answer choices for a confounding variable.
The choice noting that daily green tea drinkers also participate in regular exercise identifies a confounding factor that independently causes stress reduction.
If exercise is responsible for lower stress levels among green tea drinkers, the green tea itself may have no direct causal effect on stress.

Key Concept

Causal Reasoning and Confounding Variables
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Topics

Causal Flaws and Confounding Variables

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