Bunuel wrote:
Among people who have a history of chronic trouble falling asleep, some rely only on sleeping pills to help them fall asleep, and others practice behavior modification techniques and do not take sleeping pills. Those who rely only on behavior modification fall asleep more quickly than do those who rely only on sleeping pills, so behavior modification is more effective than are sleeping pills in helping people to fall asleep.
Which one of the following, if true, most weakens the argument?
(A) People who do not take sleeping pills spend at least as many total hours asleep each night as do the people who take sleeping pills.
(B) Most people who have trouble falling asleep and who use behavior modification techniques fall asleep more slowly than do most people who have no trouble falling asleep.
(C) Many people who use only behavior modification techniques to help them fall asleep have never used sleeping pills.
(D) The people who are the most likely to take sleeping pills rather than practice behavior modification techniques are those who have previously had the most trouble falling asleep.
(E) The people who are the most likely to practice behavior modification techniques rather than take sleeping pills are those who prefer not to use drugs if other treatments are available.
EXPLANATION FROM Fox LSAT
This is a classic flaw that gets tested over and over and over again on the LSAT. The basic problem here is that we don’t know how the people were divided into the two groups. We aren’t told that this is a scientific experiment, where people were randomly selected to be in one group or the other. Therefore, it’s possible that the people selected
themselves into their preferred group, which immediately means that you really can’t draw any sort of conclusion at all about one treatment vs. the other treatment. If you didn’t catch this flaw before looking at the answer choices, then one of two things must be true: 1) you’re not reading the arguments critically enough, or 2) you just haven’t practiced enough Logical Reasoning questions yet. This flaw has been tested many, many times before.
Watch out for it. I’m sure this flaw will be related in some way to the correct answer.
We’re asked to weaken the argument. So anything that points out the self-selection problem articulated above would be a great answer. Something like “the people who had the worst sleeping problems all used sleeping pills, and the people who had the most minimal sleeping problems all used only behavior modification” would be a perfect answer.
A) Is this answer choice even about people with sleeping problems? It may or may not be… since we don’t know, it can’t be the answer.
B) Again, what do people without sleeping problems have to do with anything? The conclusion was only about one sleeping treatment vs. another sleeping treatment. People who have no sleeping problems can’t possibly be relevant.
C) All this says is, “The two groups are separate.” So what? Wouldn’t that only make the study more valid (stronger) rather than weaker?
D) Boom. This is exactly what we were looking for. If this is true, then the study makes no sense because the two groups weren’t on even footing to begin with.
E) Nah. This says something like, “The people who chose behavior modification don’t like to take pills.” I don’t see how that weakens the idea that behavior modification is more effective than pills.
Our answer is D. It’s perfect.
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