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Difficulty: MediumWeakening Arguments

A municipal public health board recently introduced a high-dose vitamin D supplementation campaign aimed at reducing winter absenteeism among public transit workers. During the six months following the campaign's launch, sick leave days taken by transit employees declined by 22 percent compared to the same period in the previous year. Consequently, the health board concluded that the vitamin D campaign was directly responsible for the decrease in worker absenteeism. Which of the following statements, if true, most seriously weakens the public health board's argument?

  1. During the same six-month period, the transit authority instituted a strict new attendance policy requiring a physician's verification for any absence, which caused a citywide reduction in reported sick days.Answer
  2. B
    Laboratory evaluations confirmed that over 80 percent of participating transit workers achieved optimal blood vitamin D levels by the conclusion of the six-month campaign.
  3. C
    Private corporations operating in neighboring municipalities noted negligible fluctuations in overall employee productivity over the identical timeframe.
  4. D
    Routine vitamin D supplementation has been shown in clinical trials to improve bone mineral density and long-term cardiovascular functioning in working-age adults.
  5. E
    Surveys indicated that transit workers who consistently consumed the provided supplements also reported elevated subjective energy levels during their work shifts.

Answer

The argument is most seriously weakened by the statement that the transit authority instituted a strict new attendance policy requiring a physician's verification for any absence, which caused a citywide reduction in reported sick days.
The correct answer undermines the argument by introducing a confounding variable that serves as an alternative explanation. If the transit authority introduced a strict attendance policy requiring physician verification at the same time as the campaign, the drop in reported sick leave can be attributed to administrative deterrence rather than improved health from vitamin D. This undermines the conclusion that the health campaign was the direct cause.

Step-by-Step Solution

1
Deconstruct the argument into premise and conclusion.
Premise: Sick leave decreased by 22% following the launch of a vitamin D campaign. Conclusion: The campaign was directly responsible for the reduction in absenteeism.
Isolating the causal claim is necessary to understand how to challenge it.
2
Identify the underlying logical vulnerability.
The author assumes a causal relationship purely based on temporal sequence (correlation vs. causation) and assumes no external confounding factors influenced employee attendance.
Causal claims in critical reasoning are most effectively weakened by demonstrating an alternative cause for the outcome.
3
Evaluate the choices for an alternative cause or confounding variable.
The implementation of a strict new attendance policy requiring doctor notes provides an alternative reason why workers took fewer reported sick days.
If administrative policy changes caused the attendance change, the health board cannot validly claim that vitamin D was the direct cause.

Key Concept

Causal Fallacy and Alternative Explanations in Critical Reasoning
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Topics

Weakening Arguments

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