Logical reasoning PrepTest 137 · Section 3 · Question 4

Incorrect. Those with insomnia are known to be relevantly different from people without insomnia as far as sleep is concerned, so there's no guarantee that they'd react in the same way to peppermint as far as sleep is concerned.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
Study sample – People enrolled in a sleep clinic for insomnia
Group 1 – Inhaled peppermint
Group 2 – Inhaled bitter orange
Results – Group 1 were more likely to have trouble falling asleep
Bonus premise – Bitter orange doesn't help insomnia
Conclusion – Peppermint makes insomnia worse

Answer Anticipation:
There's actually a lot going on in this argument for a question #4, but it does fall into some common patterns. It's a Weaken question with a study, so a sampling flaw or a correlation/causation flaw should top your list of potential issues with this argument we can attack to weaken it.

Let's start with the sample—is it large and representative/random? There's no indication of the size, so it's unlikely the LSAT will weaken the argument using that (though it's possible, so don't completely eliminate it as a possibility). The premises are about people with insomnia and the conclusion is about insomnia, so there's not a huge jump there. However, the argument doesn't establish that the insomniacs were randomly split between the peppermint and bitter orange group, so the correct answer could highlight a key difference in the group that undermines the results—some other factor that was different between the groups that could explain the difference in difficulty falling asleep.

We have a potential answer due to the sampling flaw, but we should also check for a correlation/causation flaw. While the stimulus does feature a causal premise (well, anti-causal—bitter orange doesn't cause easier sleep), that statement simply sets a baseline that allows the comparison in the conclusion to be drawn, not the causality. That causal relationship—peppermint worsens insomnia—is based on a correlation ("more likely to"). So we can weaken this argument using our common answers in Weaken questions with correlation/causation flaws—alternative causes; counterexamples; reversed causality. Reversed causality seems unlikely (why would worse insomnia cause people to end up in the peppermint group?), but the other two are possible. And we'd like to point out the alternative cause—that aligns with our anticipation for the sampling flaw in that a non-random sample means there might be an alternative factor (i.e., cause) in that first group that made their insomnia worse. Since both flaws lead to that same place, it's likely the correct answer.

Answer Explanation:
This answer highlights a relevant difference between the groups that calls the randomness of the sample into question and provides a different explanation for the results. It wasn't the bitter orange/peppermint split that resulted in the peppermint group having a harder time falling asleep—it was the more serious cases of insomnia that led to that difference. Since this answer calls the sample split into question and provides an alternative explanation, it weakens the argument.

Key Takeaway:
Weaken questions frequently feature sampling flaws and correlation/causation flaws. When one features a study, explore both!

Incorrect. The patients knowing they were being studied would have affected both groups equally, so it can't serve as an alternative explanation for the discrepancy in their insomnia. Additionally, the subjects knowing they're in a study doesn't undermine the study itself, as valid studies can have subjects who are aware of the study.

Incorrect. First, this answer about "some" patients is unlikely to have much of an effect on a probabilistic stimulus ("more likely"). Second, the study always talks about falling asleep, not staying asleep. While both may be relevant to insomnia, without knowing if there was a difference between the two groups in staying asleep, it's impossible to know what effect this answer has on the argument.

Incorrect. First, there's no indication that either or both of these scents are pleasant, or whether peppermint is one of the ones that affects insomnia. Second, even if peppermint is one of these scents (bitter orange is stated to not be in the stimulus), this answer doesn't state whether it positively or negatively affects the ability to sleep. Third, if anything, this answer aligns with the argument in stating that scents can cause differing levels of insomnia.