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Difficulty: MediumRuling Out Alternate Explanations (Defender)

A recent workplace study found that employees who regularly use standing desks report 30 percent fewer instances of lower back pain than employees who use traditional sitting desks. Based on this study, a workplace consultant concluded that using a standing desk instead of a sitting desk reduces the risk of developing lower back pain.

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

  1. Employees who chose to use standing desks did not already have a significantly lower incidence of lower back pain before they began using standing desks.Answer
  2. B
    Everyone who uses a standing desk will experience fewer instances of lower back pain than they would if they used a sitting desk.
  3. C
    Standing desks provide more overall health benefits to office workers than traditional sitting desks do.
  4. D
    There is no correlation between the number of hours an employee works per week and the likelihood of developing lower back pain.
  5. E
    No employees who use sitting desks are entirely free from lower back pain.

Answer

The assumption that employees using standing desks did not already have a lower incidence of back pain before using them.
The argument observes a correlation between standing desks and reduced back pain, then concludes that the desks caused the reduction. For this causal claim to be true, it is logically necessary to assume that the lower incidence of back pain in the standing desk group wasn't already present before they started using the desks. If they were already healthier before the intervention, that pre-existing condition—rather than the desk—would explain the study's results. By ruling out this alternate explanation, this choice successfully defends the argument.

Step-by-Step Solution

1
Identify the argument's premises and main conclusion.
Premise: Standing desk users report 30% less back pain than sitting desk users. Conclusion: Using a standing desk reduces the risk of back pain.
Deconstructing the argument structure is the first step in evaluating any LSAT Logical Reasoning question.
2
Determine the gap in the reasoning.
The argument assumes that a correlation between desk type and back pain implies that the desk type caused the reduction in back pain.
Identifying the logical gap reveals what the argument is taking for granted without explicitly stating it.
3
Anticipate the type of necessary assumption required.
Because this is a causal argument based on an observational study, a necessary assumption must defend the causal claim by ruling out an alternate cause, such as a pre-existing baseline disparity.
Knowing that causal conclusions are vulnerable to alternate explanations helps identify the correct defender assumption.
4
Apply the negation test to the correct option.
Negating the correct option yields: 'Employees who chose standing desks DID already have a lower incidence of back pain.' This provides an alternate cause for the study's results, destroying the argument.
The negation test is the definitive method to confirm if an assumption is truly logically necessary for the conclusion to hold.

Key Concept

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

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