LSAT 55 - Section 3 - Question 09

The question stem reads: Which one of the following, if true, most weakens the argument? This is a weaken question.

The author describes two groups of people who have chronic trouble falling asleep. One group relies only on sleeping pills, while another relies only on behavior modification to treat their maladies. The group that relies on behavior modification falls asleep more quickly than the group that relies on sleeping pills. The author concludes from this that behavior modification is more effective than sleeping pills in helping people fall asleep.

The author has made the causal claim: the author argues that behavior modification is causing that group to fall asleep faster than the group who uses sleeping pills. In the curriculum, we covered how the tool science uses to identify causes is the Ideal Experiment. One of the requirements of the Ideal Experiment is that we randomly assign the samples into experimental and control groups. Random assignment of the groups helps isolate the hypothesized cause by controlling for other causes.

The author has provided the hypothesis that behavior modification is causing that group to fall asleep faster than the sleeping pill group. If this were an ideal experiment, we would expect to see a large sample size of people who had chronic trouble falling asleep assigned into a behavior modification group, a sleeping pill group, and a control group. However, what we find in the stimulus is not an experiment with randomly assigned groups. Instead, we find an observation that people who use behavior modification tend to fall asleep faster than those who use sleeping pills. By failing to assign groups randomly, we fail to isolate for other causes, such as self-selection. What does self-selection mean in this case? Let me ask you, “Why might it be that some people use sleeping pills (a medical intervention) and others use behavior modification (a change in habits)?” If you think that people who use sleeping pills might have a more severe case of insomnia than those who use behavior modification, you are spot on. The individuals who have a less severe case of insomnia might have simply self-selected into using behavior modification. The fact they fall asleep quicker might not be caused by their treatment. Instead, they simply have a less severe form of the disease.

Our job is to weaken the argument. So a good answer choice will illustrate the problem we just identified.

Answer Choice (A) is irrelevant to the argument. The argument is about the time it takes to fall asleep, while (A) speaks to the amount of sleep different groups get over the course of a night.

Answer Choice (B) fails to weaken the argument by comparing the behavioral modification group to a newly introduced group: one that has no trouble falling asleep. We can rule this answer choice out because the argument is solely concerned with individuals who need help falling asleep. The conclusion is a comparative claim between behavior modification and sleeping pills, so the comparison between behavior modification and people who do not have trouble falling asleep is irrelevant.

Answer Choice (C) fails to weaken because the argument is already explicitly concerned with the group that uses behavioral modification and does not use sleeping pills. Whether or not people have or have not used sleeping pills in the past is arbitrary.

Correct Answer Choice (D) is exactly what we prephrased. (D) States that the people who are most likely to use sleeping pills are those who have the most trouble falling asleep. So those who use sleeping pills could be falling asleep slower because they initially had much more trouble falling asleep than those who decided to use behavioral modification.

Answer Choice (E) is incorrect. While it does expose a self-selection bias (Those who choose the behavior modification prefer it to medication), it is unclear exactly how that would affect the time it takes to go to sleep. (D) provides a much clearer reason as to why the pill group takes longer.

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