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Difficulty: MediumWeaken

Agricultural scientist: Over the past year, many farmers in the Oakhaven region transitioned to using a newly developed pest-control spray on their apple orchards. A recent survey shows that orchards using the new spray suffered, on average, a 15 percent higher rate of crop damage from insects compared to orchards that continued using the traditional pesticide. Therefore, the new pest-control spray must be less effective at repelling insects than the traditional pesticide.

Which of the following, if true, most seriously weakens the agricultural scientist's argument?

  1. A
    In controlled laboratory settings, the traditional pesticide has been proven to eliminate a significantly broader variety of crop-damaging insects than the new spray.
  2. B
    The recent survey that measured crop damage was conducted during a brief period and did not accurately reflect the true damage rates for the entire year.
  3. Farmers in Oakhaven generally switch to alternative pest-control methods only after their orchards suffer insect infestations that the traditional pesticide has failed to manage.Answer
  4. D
    The newly developed pest-control spray is formulated to be non-toxic to beneficial pollinating insects, whereas the traditional pesticide eliminates all insects indiscriminately.
  5. E
    The overall number of apples lost to insects this year in orchards using the new spray was smaller than the overall number of apples lost in orchards using the traditional pesticide.

Answer

The statement indicating that farmers generally switch to alternative pest-control methods only after their orchards suffer insect infestations that the traditional pesticide failed to manage.
The correct answer introduces a selection bias, which serves as an alternative explanation for the observed correlation. If farmers only use the new spray when their orchards are already suffering from severe infestations that the old pesticide could not handle, then the new spray is being tested exclusively on the most heavily infested orchards. This underlying condition explains the higher rate of crop damage and completely severs the assumed causal link that the new spray itself is less effective.

Step-by-Step Solution

1
Identify the conclusion of the argument.
The conclusion is: 'Therefore, the new pest-control spray must be less effective at repelling insects than the traditional pesticide.'
Understanding the main point the author is trying to prove is the first step in evaluating any argument.
2
Identify the premise supporting the conclusion.
The evidence is that orchards using the new spray suffered a 15 percent higher rate of crop damage than those using the traditional pesticide.
This establishes the correlation used to justify the causal conclusion.
3
Locate the logical flaw or gap in the reasoning.
The scientist assumes that the higher damage rate was caused by the new spray's ineffectiveness, ignoring other possible causes like selection bias (i.e., perhaps only the worst-off orchards switched to the new spray).
In causal arguments based on correlation, there is often a failure to consider alternative explanations or reverse causation.
4
Evaluate the options to find one that exploits this gap.
The option stating that farmers only use the new spray when traditional methods fail provides a reason why those specific orchards would have higher damage regardless of the new spray's effectiveness.
This directly undermines the causal relationship claimed in the conclusion, effectively weakening the argument.

Key Concept

Identifying alternate causes for an observed correlation (Selection Bias)
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