Logical reasoning PrepTest 131 · Section 2 · Question 1

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
In a study, eating certain fruits was correlated with atypical Parkinson's, so these fruits probably cause that disease.

Answer Anticipation:
This argument starts by raising a study done by a researcher, so your thoughts should go directly to two flaws: sampling, and correlation/causation. By a wide margin, these two flaws are the most common when a study is done.

Here, the study looked at 100 people who both had and didn't have atypical Parkinson's. Those groups weren't randomly assigned, and 100 people isn't the largest sample, so a correct answer could bring up information that suggests these results are representative.

The study also used a correlation between eating these three fruits and developing atypical Parkinson's as being sufficient to prove that the fruits cause the disease. As with all correlation/causation jumps, that's flawed. To strengthen that relationship, we can look for one of the common answers—eliminations of an alternative cause; more examples where these two go together; more examples of the cause without the effect; an explanation of how the fruits cause atypical Parkinson's.

Either avenue could lead to a correct answer, so let's dive in and look for either.

Answer Explanation:
This answer choice shows that when the cause was removed, the effect also went away. That strengthens the causal relationship (no cause/no effect), so this is our answer.

Key Takeaway:
When an argument is based on a study, survey, poll, or research, your first thoughts should be sampling flaw and correlation/causation flaw. They're the most common flaws in questions that feature one of those elements, and if you can spot that flaw quickly, you'll be ahead of the game on the question and more likely to get it right.

Incorrect. This answer is too weak to have an impact on the argument, but even if it were stronger, it would cut against the argument, not support it, by showing examples of the cause being present without the effect.

Incorrect. By raising examples of the effect without the cause, this answer choice undermines the argument instead of supporting it.

Incorrect. If the examples with the most exposure to the cause didn't have the effect, that undermines the argument.

Incorrect. If anything, this answer suggests that the fruits are healthy ("essential" vitamins), not that it would cause a disease in a subset of the population. Without tying these vitamins into the disease somehow, this answer is out of scope.