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Difficulty: MediumCausal Flaws and Confounding Variables

An urban planning committee observed that metropolitan neighborhoods with a high density of public community gardens reported significantly lower rates of stress-related cardiovascular conditions among residents than did neighborhoods with few or no community gardens. The committee concluded that exposure to community gardens directly reduces stress levels, thereby reducing the incidence of cardiovascular conditions among urban residents. Which of the following, if true, most seriously weakens the argument?

  1. A
    Community gardens in the metropolitan area produce organic vegetables that are distributed primarily to local food pantries.
  2. B
    Surrounding rural townships with vast natural open spaces report lower overall rates of stress-related illnesses than any neighborhood within the metropolitan area.
  3. The neighborhoods that established community gardens were also those selected for major municipal investments in extensive pedestrian walkways and cycling paths, which significantly increased regular physical exercise among residents.Answer
  4. D
    Stress-related cardiovascular conditions account for a substantial percentage of total emergency room visits throughout the entire metropolitan area.
  5. E
    Residents who actively work in community gardens report experiencing short-term spikes in physical exertion during intensive garden maintenance tasks.

Answer

The argument is most seriously weakened by the statement pointing out that neighborhoods with community gardens also received major municipal investments in pedestrian walkways and cycling paths, which significantly increased regular physical exercise among residents.
The correct answer identifies an alternative cause (a confounding variable) for the lower incidence of cardiovascular conditions in those specific neighborhoods. If the neighborhoods with gardens also received major infrastructure improvements that led to increased physical exercise among residents, the improved health outcomes may be due to exercise rather than exposure to community gardens. This severely weakens the claim of a direct causal link between gardens and reduced cardiovascular conditions.

Step-by-Step Solution

1
Identify the conclusion and premise
Premise: Neighborhoods with high garden density have lower rates of stress-related cardiovascular conditions. Conclusion: Exposure to community gardens directly reduces stress and cardiovascular conditions.
Understanding the precise causal claim (gardens cause lower cardiovascular illness) allows evaluation of logical vulnerabilities.
2
Identify the logical flaw
The argument assumes a correlation between community gardens and lower cardiovascular disease implies direct causation, ignoring potential confounding variables (third factors).
Causal arguments based on observational data are vulnerable to alternative factors that cause the observed effect.
3
Evaluate the answer choices for a confounding variable
The statement regarding new pedestrian walkways and cycling paths shows that increased physical exercise, rather than exposure to community gardens, could account for the reduced cardiovascular illness.
Providing a plausible third variable that accounts for the health outcome directly weakens the author's specific causal conclusion.

Key Concept

Causal Flaws and Confounding Variables
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Topics

Causal Flaws and Confounding Variables

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