Logical reasoning PrepTest 124 · Section 2 · Question 13

Incorrect. This answer describes an ambiguous word usage flaw. However, there's no indication that there is a shift in the meaning of that phrase. While the premise talks about certain" personality disorders and the conclusion talks about them generally, that's not enough to make this answer correct for two reasons. First, if the risk of certain personality disorders increases, then the risk of personality disorders increases, all other risks being equal. Second, discussing different subsets of personality disorders isn't the same as using that phrase ambiguously, which would require a shift in meaning.

Incorrect. Not all phrases need to be defined—arguments would be insufferably long if that were the case. Only phrases whose definitions are key to the argument and whose definitions aren't clear or can be ambiguous need to be defined—and that's not the case here. Even if we don't know what theta brain waves are, they seem to be a set thing and wouldn't be misunderstood by someone who had that knowledge.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Theta waves increase while watching TV, and people with certain personality disorders have more theta waves, so TV increases the risk of personality disorders.

Answer Anticipation:
One of the most common flaws on the LSAT is the correlation/causation flaw, so you should start your work on any argument with a causal conclusion by seeing if this flaw is present.

Here, the premises are correlations. Personality disorders are correlated with more theta brain waves; theta brain waves increase while watching TV. These aren't causal statements—they establish that two things are correlated.

However, that can be a bit tricky because the conclusion and the second statement sound the same—they both talk about increases." The difference is that the premise talks about a number increasing, whereas the conclusion talks about one thing increasing another. When a number increases at a given time, something must be causing it, but not necessarily what it's correlated with. For example, if you watch TV only while exercising, it's true that your heart rate increases while watching TV, but TV isn't the cause. Compare this to the conclusion, where watching TV is the thing that is doing the increasing—since it's actively driving the change, that's a causal statement.

So since this argument takes two correlative statements and chains them together to get a causal one, we can look for an answer reflecting that correlation/causation flaw.

Answer Explanation:
This answer directly describes the jump from correlation to causation we anticipated, so it's the correct answer.

Key Takeaway:
Whenever an argument has a causal conclusion, your first thought should be that it might feature a correlation/causation flaw.

Incorrect. The premises are about individuals with personality disorders, and the conclusion is, as well, so there's no sampling flaw here.

Incorrect. This answer states the reverse relationship as the one established in the stimulus, so it's not something the argument infers. (Note that this could be a potential answer if it were brought up as a possibility the argument overlooks—one reason a correlation/causation jump is flawed is that it ignores the possibility of reversed causality.)