Logical reasoning PrepTest 134 · Section 2 · Question 2

Incorrect. This answer highlights a sampling flaw, but it does so in a way that makes the answer incorrect. The argument doesn't assume ("presume, without providing justification") that university students are unrepresentative of the general public; it overlooks that possibility in using them as a sample to draw a general conclusion.

Incorrect. The argument concludes that insomnia causes napping, not that anyone who has insomnia must take naps or that only naps cause insomnia. In other words, the conclusion is that napping causes insomnia but leaves it open for other things to cause insomnia, as well.

Incorrect. A definition of every key term doesn't have to be provided, especially when there's a common definition that makes sense in context. Imagine how long an argument would be if every word needed a definition!

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Study 1 — Students who take naps are more likely to have insomnia
"Study" 2 — People who work on commercial fishing boats and thus nap frequently tend to have insomnia
Conclusion — Napping probably causes insomnia

Answer Anticipation:
There are two things that should jump out at you right away. First, there's a study mentioned, and studies tend to have sampling flaws, and correlation/causation flaws. Second, the conclusion is causal, so there's a good chance that there's a correlation/causation flaw.

First, let's consider a sampling flaw. The argument states that the sample size of one study was 436 students, which is large enough to draw valid conclusions from (generally, single—digit samples are where you are guaranteed to go wrong with sample size). And while university students aren't necessarily representative of people overall as far as sleep is concerned, the argument also brings up people who work on commercial fishing vessels who have a similar correlation between napping and insomnia. While this group isn't likely to be representative, in bringing together two disparate groups, the argument is more likely to have a valid sample. The correct answer could highlight this, but because the sample is large and somewhat varied, it's less likely.

What about the correlation/causation flaw? Well, the argument does establish that napping and insomnia are correlated in both university students and people on commercial fishing vessels. From that, it does conclude that there's a causal relationship. That's a correlation/causation flaw.

We could stop there and we'd probably find the right answer (if it deals with this flaw instead of the sampling flaw), but there are three common "reasons" that correlation doesn't equal causation on the LSAT. First, the correlation could be a coincidence—but that's rare, especially when one of the other two makes sense. The second is that there's a third cause that leads to both of the correlated phenomena—something that causes both insomnia and napping. While that's a potential answer, the third is usually the right answer when it makes sense—reversed causality. Is it plausible that it's not napping that causes insomnia, but rather insomnia that causes napping? Sure—if you can't sleep at night, there's a good chance you'll fall asleep during the day. Let's find that reversed causality answer (or one of the other two, though, again, they're less likely).

Answer Explanation:
This answer highlights the reversed causality that the argument overlooked. Napping and insomnia are correlated—it's just as possible that insomnia causes napping as that napping causes insomnia.

Key Takeaway:
On the LSAT, there are three common "reasons" that correlation/causation jumps are flawed that show up in correct answers:
(1) The correlation is a coincidence (rare, very rare)
(2) There is a third cause that is responsible for both correlated phenomena (common)
(3) The causal relationship is reversed (very common when it makes sense, especially in questions about medicine/health)

Incorrect. The irregular sleep pattern mentioned is brought up in contrast to what people who aren't on commercial fishing boats have, not in contrast to some other people on those boats who don't have a weird sleep schedule.