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Difficulty: HardRuling Out Alternate Explanations (Defender)

In a recent decade-long study of 50 agricultural regions, researchers found that the regions that had adopted a newly developed soil conservation technique experienced a significantly lower rate of topsoil erosion than the regions that continued to rely on traditional methods. Based on this data, the researchers concluded that the adoption of the new technique was responsible for the disparity in erosion rates between the two groups.

Which one of the following is an assumption on which the researchers' argument depends?

  1. A
    Any agricultural region that adopts the new soil conservation technique will experience a lower rate of topsoil erosion than it would have using traditional methods.
  2. The agricultural regions that adopted the new technique did not experience significantly less severe rainfall—a primary driver of erosion—than the regions using traditional methods over the past decade.Answer
  3. C
    Regions that did not adopt the new soil conservation technique experienced an overall increase in their rate of topsoil erosion over the past decade.
  4. D
    A reduction in topsoil erosion causes farmers to be more willing to adopt newly developed agricultural techniques.
  5. E
    The new soil conservation technique is no more expensive to implement than the traditional methods previously used in these regions.

Answer

The assumption that the regions adopting the new technique did not also experience significantly less severe rainfall, which rules out an alternate cause for the lower erosion.
This option provides a necessary 'defender' assumption by ruling out a critical alternate explanation. The conclusion claims a causal relationship based on a correlation between the new technique and lower erosion. However, if the regions with the new technique also happened to experience significantly less severe rainfall, then this weather discrepancy—rather than the farming technique—could be the actual cause of the lower erosion rates. By stating this confounding variable was not present, the option defends the argument's causal claim. Negating this option destroys the argument.

Step-by-Step Solution

1
Identify the argument's core conclusion.
The adoption of the new soil conservation technique was responsible for the disparity in erosion rates.
This is the causal claim the researchers make based on their observations.
2
Identify the argument's premise.
Regions using the new technique had significantly lower erosion rates than regions using traditional methods.
This is the correlational evidence provided to support the conclusion.
3
Analyze the logical gap (Correlation to Causation).
The argument assumes that because the new technique and lower erosion occurred together, the technique caused the lower erosion. It fails to consider alternate explanations for why those specific regions might have had less erosion.
To prove a causal claim, one must rule out third-variable confounders (like weather, geography, or other practices) that could have independently caused the effect.
4
Apply the Negation Test to the options.
Negating the correct option yields: 'The regions that adopted the new technique DID experience significantly less severe rainfall... than the regions using traditional methods.'
If this negated statement is true, the less severe rainfall (a known driver of erosion) easily explains the lower erosion rates, entirely undermining the claim that the new technique was responsible. Therefore, the original statement is a logically necessary assumption.

Key Concept

Ruling Out Alternate Explanations (Defender Assumptions)
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Ruling Out Alternate Explanations (Defender)

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