Logical reasoning PrepTest 117 · Section 2 · Question 20

Incorrect. First, the adults in the stimulus were engaged in thrill—seeking behavior, not impulsive behavior. Second, since the stimulus is dealing with likelihood, some examples ([M]any") of the effect without the cause doesn't undermine it. Especially since there's no claim that the gene is the exclusive cause of the behavior.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
Research — Kids that are impulsive/thrill—seeking are twice as likely to have a gene variant
Conclusion — The gene variant causes people to be thrill—seeking

Answer Anticipation:
Weaken questions tend to have correlation/causation flaws, and when they do, we have common answers we can look for. When we're dealing with a Weaken question, we should be on the lookout for correlative and causal language.

Here, we get both. Statements about likelihood (twice as likely") are correlative (unless there's a causal verb, e.g., "increase the likelihood"), so we have a correlation in the premises. (The observations of research/studies are also almost always correlations.) And the conclusion is causal—as highlighted by the Scientist using the word "causal" in the conclusion.

So we have a correlation/causation flaw, and we should look for a standard answer:
(1) ID an alternative cause (something that results in both this gene variant and impulsive/thrill—seeking behavior)
(2) Counterexamples (however, since this stimulus is about a likelihood of the effect appearing, counterexamples are unlikely to be correct since a few people with the gene variant who don't demonstrate that behavior won't weaken the argument)
(3) Reversed causality (though this answer doesn't make much sense, as it's hard to see how impulsive/thrill—seeking behavior would cause someone's genes to change)

So we're left with looking for an alternative cause!

Answer Explanation:
This answer has nothing to do with our anticipation of an answer that raises an alternative cause, but it does call into question the reliability of the observations in the study. If it's impossible to observe children and determine which of them are engaged in impulsive behavior, then the scientist couldn't actually determine that the children being observed were engaged in such behavior. By undermining the research that the conclusion is based on, this answer undermines the argument. It's not what we were expecting, but it is correct.

Key Takeaway:
Rules of thumb we have for the LSAT are helpful because they usually lead us to the ballpark of the correct answer. Here, however, the correct answer had nothing to do with our anticipation, which was based on our rule of thumb for Weaken questions with correlation/causation flaws. When this happens, be sure to learn from it—when does the rule of thumb break down?

There are generally two categories of a rule of thumb breaking down. The first is an exception to the rule—it's when the rule of thumb doesn't actually apply. That's not what happened here—there is a correlation/causation flaw, and an answer proposing an alternative cause would have been correct. The other is when a rule of thumb is a red herring—as it was here. In this case, learn what else to look out for—here, the argument was weakened by calling the experimental design into question. We now have another thing we can anticipate in Weaken questions!

Incorrect. The Scientist is very clear that the behavior she witnessed is impulsive behavior similar to adult thrill—seeking behavior, so the Scientist isn't an adult who's making this mistake, and thus this answer doesn't weaken the argument.

Incorrect. First, what is true for [m]any people" won't weaken a statistical argument, as we have here ("twice as likely"). Second, the argument is based on observation of kids who do exhibit impulsive behavior, so it'd have more of an effect on the argument if this relationship were reversed (kids show behavior that they grow out of as they become adults).

Incorrect. By showing more correlations between this gene variant and behavior changes, this answer—if anything—aligns with the argument's assumed causality.