EXPLANATION FROM POWER SCORE

Strengthen. The correct answer choice is (C)

Whenever the author begins her argument by stating the position of "many" ("many studies have suggested that..."), you should anticipate that her conclusion will be in direct disagreement with that position. Even though the studies suggest that melatonin induces sleep, the author argues that melatonin is not necessarily helpful in treating insomnia. Why? Because (1) most of the studies examined only people without insomnia (which presumably makes them unrepresentative), and (2) in many of these studies, only a few of the subjects appeared to be significantly affected by the substance.

Generally speaking, if an author uses data from a survey to substantiate her claims, her argument is only as good as the validity and applicability of that survey. For instance, what if every single one of the few subjects who were significantly affected by melatonin also suffered from insomnia? This would be consistent with both of the premises stated above but not with the conclusion. To strengthen the argument, we must therefore look for an answer choice that explicitly states that few, if any, of the subjects affected by melatonin were themselves victims of insomnia. Only then would the conclusion be fully supported by the studies.

Answer choice (A): This is an attractive, but incorrect answer. Even though the study that included insomniacs showed a weaker correlation between taking melatonin and the inducement of sleep, we have no idea whether this weakness is attributable to the insomniacs themselves or to other members of the group. Further, we do not know how many people with insomnia participated and what was the ratio of insomniacs vs. healthy subjects among those who were helped by melatonin.

Let's imagine that both studies include 10 people:

Study #1: participants include 8 healthy subjects and 2 subjects with insomnia

Study #2: participants include 10 healthy subjects

Result: In study #1, the correlation between melatonin and inducement of sleep was 0.3, i.e. 3 out of 10 subjects were helped to fall asleep. In study #2, the correlation was 0.4.

Does that strengthen the argument that melatonin is not helpful in treating insomnia? Not necessarily. It is entirely possible that the 3 subjects in Study #1 who were affected by the use of melatonin included both of the insomniacs along with one healthy subject. The results would therefore be consistent with the hypothesis that melatonin helps both the healthy and those suffering from insomnia.

Answer choice (B): Whether the sample examined is fully representative of the human population is irrelevant to the author's conclusion.

Answer choice (C): This is the correct answer choice. In our example above, if none of the 3 people affected by the use of melatonin in Study #1 suffers from insomnia, this would provide significant support for the hypothesis that melatonin only helps those not suffering from insomnia and has no effect on those who do.

Answer choice (D): Since this answer does not differentiate between insomniacs and non-insomniacs, it provides no support for the author's conclusion.

Answer choice (E): This statement is consistent with the results of the studies and provides no additional support for the author's conclusion. It is entirely possible that every single person with insomnia who took melatonin was affected by it: if established, this fact would significantly weaken the author's conclusion. This answer choice is incorrect.
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EXPLANATION FROM Fox LSAT

Hmm. I think the logic here sounds better than it actually might be. To summarize, it goes like this: Melatonin studies have only studied subjects without insomnia. And in many of those studies, only a few of the subjects were significantly affected by it. Therefore, the fact that many scientific studies have suggested that melatonin tablets can induce sleep does not mean that melatonin is helpful in treating insomnia.

Wait, what? First of all, the studies have shown that melatonin can induce sleep. Isn’t insomnia a lack of sleep? The studies seem like, if anything, they at least suggest that melatonin can fix insomnia. The fact that most of the studies haven’t actually used insomniacs as test subjects doesn’t really help much. The fact remains that melatonin did induce sleep in the subjects who were tested. And some of the studies did include insomniacs!

With all that said, we’re then asked to strengthen the argument. No problem. Since we know what some of the holes in the argument might be, we can look for an answer that would plug one or more of those holes. If we can’t find an answer that would plug an obvious hole, then we’ll just pick the one that seems to strengthen the most, while eliminating anything that’s irrelevant or actually weakens the argument.

A) I think this weakens the argument. Imagine if I said, “Cigarette smoking has been shown to have a weaker correlation with cancer than rolling naked in a big pile of decaying uranium shavings does.” Would that help my case, if my goal was to prove that cigarette smoking does not cause cancer? Nah, didn’t think so. If this answer is true, then it admits that melatonin is correlated with inducing sleep in insomniacs. So it’s actually a weakener.

B) Meh. I don’t think this could ever be the answer, unless the conclusion of the argument had specifically been about “the entire human population.” Random sampling is good, but there are limits to how “fully representative” your sample can ever actually be.

C) Yep. If this is true, then it says that the insomniacs who were actually tested did not respond significantly to melatonin. That’s the best evidence so far that melatonin isn’t going to alleviate insomnia.

D) This is always going to be true, and does not indicate that melatonin doesn’t work. It could only be used to prove that melatonin isn’t the only thing that works, or perhaps that melatonin doesn’t work more than a placebo works. But even if a placebo works, melatonin could also work. So this is out.

E) This might have actually happened in the given studies! We weren’t given enough information to know what happened to the insomniacs who were included in the tests.

Our answer is C, because if it’s true it plugs one of the holes in the argument.
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