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Difficulty: EasyWeaken

Agricultural Advisor: A regional coffee farming cooperative recently reported that member farms using a newly introduced organic compost experienced a twenty percent decrease in crop-damaging beetle infestations compared to the previous year. Because no other new pest control products were distributed to these farms during that period, the cooperative's directors concluded that the compost itself produces compounds that actively repel these beetles.

Which of the following, if true, most seriously weakens the directors' argument?

  1. A
    Laboratory tests confirm that chemical compounds released by the decaying compost are toxic to crop-damaging beetles.
  2. B
    The cooperative's record-keeping system experienced data entry errors during the harvest season that led to inaccurate beetle damage reports.
  3. An unseasonable regional cold snap caused a similar decrease in beetle infestations on neighboring coffee farms that did not apply the compost.Answer
  4. D
    Organic compost is significantly more labor-intensive and expensive to apply across large acreage than conventional chemical fertilizers.
  5. E
    Beetle infestations always cause catastrophic financial losses for coffee farmers whenever any agricultural innovation is implemented.

Answer

The argument is most weakened by evidence that an unseasonable regional cold snap caused a similar decrease in beetle infestations on neighboring coffee farms that did not apply the compost.
The correct answer provides an alternative explanation for the observed reduction in beetles. By demonstrating that a regional cold snap caused an identical decrease on farms that never used the compost, it shows that the decline in beetle infestation was likely due to weather rather than any chemical property of the compost.

Step-by-Step Solution

1
Identify the premises and the main conclusion.
Premises: Farms using new compost had 20% fewer beetles, and no other new pest products were used. Conclusion: The compost itself produces compounds that repel beetles.
Isolating the argument structure reveals the causal inference made by the directors.
2
Identify the underlying assumption and logical vulnerability.
The directors assume that no external or environmental factor accounted for the drop in beetle numbers.
Causal claims based on simple before-and-after observations are vulnerable to alternative explanations.
3
Evaluate the choices to find the one that undermines the causal link.
Showing that untreated control farms experienced the same reduction due to cold weather demonstrates that the compost was not the cause.
Providing a plausible alternative cause that explains the observed correlation effectively weakens the argument.

Key Concept

Weaken a causal argument by providing an alternative explanation for an observed correlation
Estimated Time:50s
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