Many scientific studies have suggested that taking melatonin tablets

 

Don't get lost in the quantifiers - keep it simple. 

Premises: 
Many scientific studies have suggested that taking melatonin tablets can induce sleep.
Most of the studies examined only people without insomnia, and in many of the studies, only a few of the subjects given melatonin appeared to be significantly affected by it.

Conclusion: But this does not mean that melatonin is helpful in treating insomnia.


Here is the thing - the premises do not tell us why and how can we say that ­melatonin may not be helpful in treating insomnia. They give some data abotu what happens in studies which examined people without insomnia. How melatonin affects them is irrelevant to our argument. Focus on the conclusion. Point is the impact it has in people with insomnia. 

(A) A weaker correlation between taking melatonin and the inducement of sleep was found in the studies that included people with insomnia than in the studies that did not.

Weaker correlation does not mean no correlation. Even if it does not affect people with insomnia as much as others, if it does affect them to some extent, it could still be used to treat insomnia. 

(B) None of the studies that suggested that taking melatonin tablets can induce sleep examined a fully representative sample of the human population.

No study by itself is fully representative but we are considering many studies here. Also, our conclusion is about people with insomnia. We are not trying to establish something about the entire population.

(C) In the studies that included subjects with insomnia, only subjects without insomnia were significantly affected by doses of melatonin.

Exactly what we needed. What happens when these tablets are given to people with insomnia? This is our point of focus. It tells us that the tabs do not impact them. The ones who are significantly affected were all without insomnia. So then it doesn't seem to be a possible treatment for insomnia. Correct. 
Note that "significantly" means "statistically relevant". So the effects on people with insomnia were not statistically relevant.

(D) Several people who were in control groups and only given placebos claimed that the tablets induced sleep.

Perhaps placebo effect in play? We don't know. Ignore anyway. 

(E) If melatonin were helpful in treating insomnia, then every person with insomnia who took doses of melatonin would appear to be significantly affected by it.

It doesn't tell us what happens actually when people with insomnia are given melatonin. We need that info to strengthen our argument. 
There really isn't a gap between 'helpful in treating insomnia' and 'significantly affected' so this statement is not adding anything. If a medicine has no significant impact on a person, it means it is not helping treat the person. Also, it seems to be too restrictive logically. Every person may not be significantly affected. Even if many or some people are, it could be helpful in treating insomnia. 
This statement does not strengthen that 'melatonin is not helpful in treating insomnia' because it doesn't tell us whether it affects people with insomnia or not. 

Answer (C)­

 

­An inference is a statement that MUST BE TRUE.

Passage: Most of the studies examined only people without insomnia.
Most = more than half.
This could mean 99 of 100 studies.
Thus, the following inference is valid:
AT LEAST ONE study did not examine only people without insomnia.

Note:
did not examine only people without insomnia = included AT LEAST ONE person with insomnia.
We do not know whether any studies examined ONLY people with insomnia.

Passage: in many of the studies, only a few of the subjects given melatonin appeared to be significantly affected by it.
The passage does not state whether, among the subjects in blue, any had insomnia.
In a study that included insomniacs, it is possible that none of the subjects in blue had insomnia, that all of the subjects in blue had insomnia, or that it was a mix.
As a result -- when we evaluate the contrapositive of E -- there is no support for the premise that at least one insomniac was unaffected by melatonin.­­

This discussion is far more relevant to the LSAT than to the GMAT.
When it comes to quantifiers such as most and many, the LSAT is much more exacting.­­

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.­

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.­

Hi GMATNinja KarishmaB GMATGuruNY ReedArnoldMPREP AjiteshArun

I found this one difficult. I was wading through options and then narrowed them down to (C) and (E).
Please help me to understand why (C) is better than (E).
Also, I would request you review elimination process for the rest of the options.

Why i found this option weird is that it says ONLY normal dudes were ''significantly affected'', but insomniacs CANBE somewhat affected, right?
So does this option assumes that ''only significant affected'' is ''HELPFUL'' and nothing else is HELPFUL?

Earlier, i found this option better because it bridged the GAP between ''HELPFUL'' and ''SIGNIFICANTLY AFFECTED''.
NOW, i think this one is a TRAP, because stimulus goes from ''SIGNIFICANTLY AFFECTED'' to ''HELPFUL'', not the other way round.

Comparison is a red-herring. Correlation doesn't prove causation. Weaker correlation can be caused by Several other factors.
Maybe guys had coffee before the study?

If we are questioning the study, then we are actually questioning the conclusion. If Study was faulty, then we can't say that Melatonin is NOT helpful. Maybe Melatonin is helpful, maybe it is NOT.

Several can be 3,4. Also, how many of these several were insomniac? Not really touches the conclusion.­­­­

Hi ReedArnoldMPREP

I am glad that i got this question wrong, otherwise i wouldn't have noticed the deep layers of the argument. Never have been happier getting one wrong!

Above text forced me to think what happens if ''Many of the studies'' WERE  a SUBSET of ''MOST OF THE STUDIES, and how this info relates to option (C):

ALL STUDIES related to MELATONIN: 10000
MOST STUDIES without INSOMANIACS: 6000
MANY STUDIES in which only a few of the subjects given melatonin appeared to be significantly affected: 500

So, we are still left with 4000 MELATONIN STUDIES, which MAY have all INSOMANIACS. And this is where (C) comes into play and calms us down saying that none of the INSOMANIACS from those 4000 studies were affected.

I am not sure, whether my logic is sound, but thankyou for the detailed explanation. It really helped me and pressed me think more!
 




 ­

 

­Hi GMATGuruNY I can see, why (E) adds nothing to the argument.

I think, rather the contrapositive of (E) CAN BE INFERRED from ''Most of the studies examined only people without insomnia, and in many of the studies, only a few of the subjects given melatonin appeared to be significantly affected by it.''

If ''Many studies'' are the subset of ''Most of the studies'', then we still will be left with ''Many studies'' in which at-least 1-guy was significantly affected by Melatonin.

As in: ALL STUDIES related to MELATONIN: 10000
MOST STUDIES without INSOMANIACS: 6000
MANY STUDIES in which only a few of the subjects given melatonin appeared to be significantly affected: 2000
Remaining studies: 4000. 
Out of this 4000 studies, 1 guy was significantly affected, yet we can say that ''Melatonin wasn't helpful''­