Logical reasoning PrepTest 140 · Section 1 · Question 13

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
Rats fed GMO potatoes: Intestinal deformities; weakened immune system
Rats fed normal diet (no GMOs): None of those health problems
Conclusion: Don't feed animals GMOs

Answer Anticipation:
There are a couple issues here that suggest specific flaws.

First, there's a study, so we should consider a sampling flaw. However, there's no indication that these rats weren't randomly selected, or that the sample size was too small. However, the argument uses a study about rats to draw a conclusion about animals generally, so there could be an answer stating rats are unrepresentative.

Second, studies generally try to prove causality, so they're rife with correlation/causation flaws. Here, the conclusion does rely on a causal assumption—that the GMO potatoes caused the health problems—and it's based on the correlation found in the premises. This argument does commit a correlation/causation flaw, and so we can look for the normal answers that weaken an argument committing that flaw:

(1) ID an alternative cause
(2) Find counterexamples (cause without effect; effect without cause)
(3) Reversed causality

Reversed causality doesn't make sense here because of the timeline (the health issues developed during the study). However, not only is IDing an alternative cause the most common answer, but there's a suggested alternative cause in the stimulus—potatoes. Maybe it's potatoes themselves that contributed to these issues, whether they were GMO or not. We should look for answers suggesting the potatoes (or another cause) resulted in the health issues.

Answer Explanation:
The argument compares the diets of two groups of rats. One difference is the presence of GMOs in the diet; this answer tells us that the presence of potatoes was also a difference. If potatoes aren't a normal part of the rat diet, then only the first group was eating them, and there's as much evidence potatoes cause health issues in rats as there is GMOs. This answer suggests potatoes as an alternative cause, weakening the argument.

Key Takeaway:
Studies always suggest sampling flaws and usually have correlation/causation flaws. They also frequently have percent/amount flaws, when the stimulus discusses those concepts. Every time you see a study in a question with a flaw, start there!

Incorrect. That would make sense as they developed intestinal abnormalities and a weakened immune system, thus they probably weren't feeling that good. At best, this answer is trying to get you to believe that this is a counterexample (as the effect got worse, the cause lessened), but we're talking about serious health problems over a 30-day period, so this answer doesn't provide a counterexample.

Incorrect. The stimulus specifically notes that the intestinal deformities in question developed during the study, so this answer doesn't address the stimulus.

Incorrect. This answer doesn't distinguish between the two rat groups because we don't know the second ate potatoes.

Incorrect. The ability to explain a phenomenon will not weaken an argument—things can be connected without scientists being able to explain it.