Logical reasoning PrepTest 121 · Section 4 · Question 2

Incorrect. This answer weakens the argument with a counterexample—a group without the cause but with the effect.

Incorrect. This answer connects dreams with stress. Since dreams happen during REM sleep, this answer would establish that REM sleep can cause stress. That runs directly counter to the conclusion.

Incorrect. This answer is more of a weakener, establishing reversed causality (stress interrupting REM sleep).

Incorrect. First, the argument doesn't connect dreams to stress/irritability, but rather it connects REM sleep independently to both dreams and stress. Second, remembering the dream is out of scope since that isn't connected in any way with stress.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
Research - Those who are deprived of REM sleep are irritable
Conclusion - REM sleep relieves stress

Answer Anticipation:
Strengthen questions will frequently have correlation/causation flaws. Arguments relying on research/studies will frequently have correlation/causation flaws. Strengthen questions with studies/research in the stimulus are very likely to have a correlation/causation flaw!

And this one does. The research shows that being deprived of REM sleep is correlated with being irritable. From that, it concludes that REM sleep causes ("relieves") stress levels to decrease.

Whenever a Strengthen question has a correlation/causation flaw, we should look for answers that:
(1) Eliminate alternative causes (here, maybe a lack of sleep causes irritability, not specifically REM sleep)
(2) More examples of cause and effect going together
(3) A control - those in the study without interruptions in their REM sleep weren't stressed out/irritable

One more note before heading to the answers—the argument does jump from a correlation involving irritability and a conclusion about stress. There is a jump there, but it's unlikely that the LSAT is going to test that jump on question #2 since irritability and stress are generally accepted as being related.

Answer Explanation:
This answer brings up more examples of cause and effect going together, while also providing evidence against alternative causes. If controlling for other facts (removing other causes) sees a general, direct correlation between shorter REM sleep and higher stress levels, then the causal connection between the two is strengthened.

Key Takeaway:
Strengthen questions frequently have correlation/causation flaws. Arguments that rely on studies/research also tend to have that flaw (as well as sampling flaws). Knowing these trends can make it a lot easier to spot flaws in arguments!