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Difficulty: Very hardLogical Arguments and Causal Relationships

A municipal environmental agency conducted a study across 50 comparable mid-sized cities over a four-year period. The study observed that cities that introduced a mandatory pay-as-you-throw (PAYT) unit-pricing system—charging households per bag of municipal solid waste disposed—experienced a 35 percent decrease in landfilled waste and a 20 percent increase in curbside recycling rates. The environmental director concluded that the financial burden of the PAYT fees directly caused households to adopt waste-minimization habits and actively divert recyclable materials from the waste stream.

Which two of the following statements, if true, most strongly support the environmental director's causal conclusion?

  1. In the cities implementing PAYT, the reduction in landfilled waste began immediately following the introduction of per-bag fees rather than during prior years when public awareness campaigns were active.Answer
  2. Similar mid-sized cities in the same geographic region that did not implement a PAYT system experienced no significant change in landfilled waste volumes or recycling rates over the four-year study period.Answer
  3. C
    Cities with residents who already exhibited above-average baseline recycling rates and high environmental consciousness were significantly more likely to adopt the PAYT pricing system.
  4. D
    Concurrently with the introduction of PAYT, the participating cities enacted strict municipal bans on single-use commercial plastic packaging.
  5. E
    Municipalities that increased municipal trash collection frequency saw a temporary 10 percent rise in total waste volume handled by private waste management contractors.

Answer

The two statements that most strongly support the causal conclusion are: (1) the statement indicating that waste reduction began immediately after per-bag fees were introduced rather than during prior awareness campaigns, and (2) the statement showing that control cities without PAYT experienced no significant changes in waste or recycling levels.
To strengthen a causal claim of the form 'X caused Y', an argument must demonstrate that Y occurred specifically following X (temporal precedence) and that Y does not occur in the absence of X (control comparison), while eliminating alternative explanations. The statement noting that waste reduction began immediately after per-bag fees were introduced establishes clear temporal precedence, ruling out earlier public awareness campaigns as the cause. The statement confirming that control cities without PAYT saw no changes in waste or recycling rules out broader regional macro-trends.

Step-by-Step Solution

1
Identify the director's core causal claim
The core claim is that mandatory per-bag PAYT fees directly caused households to decrease landfilled waste and increase recycling.
Evaluating causal arguments requires isolating the proposed cause (unit-pricing fees) and effect (waste reduction/recycling increase).
2
Evaluate potential strengtheners for temporal precedence and control group validity
The statement showing that waste reduction immediately followed fee implementation demonstrates temporal precedence over alternative factors like public awareness campaigns. The statement establishing that non-PAYT cities saw no changes provides a control group ruling out regional trends.
Showing that the effect occurs specifically when and where the cause is present (and not when/where it is absent) reinforces the causal link.
3
Identify and eliminate weakeners and irrelevant statements
The option describing pre-existing high recycling rates suggests selection bias (reverse/alternative causation). The option mentioning single-use plastic bans introduces a confounding variable. The option regarding collection frequency is irrelevant.
Alternative explanations and confounding variables undermine the claim that PAYT fees were the primary driver of the observed outcome.

Key Concept

Causal Argument Evaluation: Establishing Control Groups and Temporal Precedence
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Topics

Logical Arguments and Causal Relationships

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