Doctor: In three separate studies, researchers compared children who

Question

Doctor: In three separate studies, researchers compared children who had slept with nightlights in their rooms as infants to children who had not. In the first study, the children who had slept with night-lights proved more likely to be nearsighted, but the later studies found no correlation between night-lights and nearsightedness. However, the children in the first study were younger than those in the later studies. This suggests that if night-lights cause nearsightedness, the effect disappears with age.

Which one of the following, if true, would most weaken the doctor’s argument?

(A) A fourth study comparing infants who were currently sleeping with night-lights to infants who were not did not find any correlation between night-lights and nearsightedness.
(B) On average, young children who are already very nearsighted are no more likely to sleep with night-lights than young children who are not already nearsighted.
(C) In a study involving children who had not slept with night-lights as infants but had slept with night-lights when they were older, most of the children studied were not nearsighted.
(D) The two studies in which no correlation was found did not examine enough children to provide significant support for any conclusion regarding a causal relationship between night-lights and nearsightedness.
(E) In a fourth study involving 100 children who were older than those in any of the first three studies, several of the children who had slept with night-lights as infants were nearsighted.

GMATNinja · Accepted Answer

The doctor cites three studies:

S1: Children who had slept with night lights as infants were more likely to be near-sighted. 
  S2 and S3: Older children who had also slept with night lights as infants showed no correlation between night-lights and nearsightedness.

The doctor concludes that the discrepancy between S1 and S2/S3 suggests that  if night-lights cause nearsightedness, the effect disappears with age.  The correct choice is the one that most weakens the conclusion.

The correct choice does NOT have to disprove the argument! It just needs to to a better job than any other choice at making us doubt that nearsightedness caused by night lights will disappear with age.

Comparing  infants  who sleep with night lights to  other infants  who don't tells us nothing about what happens to nearsightedness as children age. The information in choice (A) has no logical relevance to the doctor's conclusion, so eliminate it.

So what? Just as with choice (A), choice (B) compares children of the same age group. This has no bearing on the doctor's conclusion about the disappearance of nearsightedness as children age, so eliminate choice (B).

Choice (C) gives us a completely different premise from the three studies used to support the doctor's conclusion. The argument is not at all concerned with children who did NOT sleep with night lights as infants, so eliminate choice (C).

OK, here's an answer choice to keep! If S2 and S3  did not examine enough children  to support  any  conclusion regarding a causal relationship between night lights and nearsightedness, then a huge piece of evidence that the conclusion depends on can no longer be accepted.

This leaves us with a very incomplete picture:

S1: Children who had slept with night lights as infants were more likely to be near-sighted. 
  S2 and S3: Older children who had also slept with night lights as infants... were studied, but not enough of them were studied for us to learn anything about the impact of night lights on their eyesight. ¯\_(ツ)_/¯

This makes it much harder for us to believe that near-sightedness caused by night lights disappears with age. The evidence simply is no longer there. So let's keep (D) around and see if (E) is any better at shaking up the argument.

This choice does seem to weaken the argument, but by how much? Notice two things about the information here:

Several  children who had slept with night lights as infants were still nearsighted. This study involved 100 children, so the incidence of nearsightedness is very low. 
  If several children who had slept with night lights were nearsighted, then the rest of the children who had slept with night lights were NOT nearsighted. So we've got some data that weakens the conclusion AND some data that supports the conclusion. 
  This new study involves children who were older than any of those in S1, S2, or S3... but they're still children, and they're still aging. So it's entirely possible that the low number of near-sighted children may no longer be near-sighted as they get older. Nothing in this answer choice suggests that this will happen, but nothing in this answer choice suggests that it won't, either.

Choice (E) is a mixed bag that adds a little information to make us slightly doubt the doctor's conclusion.
Choice (D) tears down 2 of the 3 studies that the doctor directly depended on to reach that conclusion, raising major doubts about it.

Between these two options, (D) definitely does the most to weaken the doctor's argument. That's why we eliminate (E), stick with (D), and move on.

I hope this helps!

KaranB1 · Answer

Difficult one, although very sound in logic. It is a typical LSAT question.

colinlin1 · Answer

It needs second thought after getting the answer, the answer does not weaken the conclusion directly.

manass · Answer

GMATNinja   daagh   VeritasKarishma  please help

PallabiKundu · Answer

I think E is the answer.
The conclusion states "if night-lights cause nearsightedness, the effect disappears with age."
However in E they say that in the fourth study,the observed children who were much older and had slept with night-lights on were nearsighted.(opposite to our conclusion).
 can someone explain?

akela · Answer

Manhattanprep explanation

We must first closely consider the logic of the original argument.

It has to do with CAUSE. Notice the conditional nature of the conclusion, also. "IF night-lights CAUSE nearsightedness, the effect disappears with age."

This is based on the evidence that:
1. Studies compare children who sleep w/nightlights to those who don't
2. In first study, children w/nightlight = more likely nearsighted
3. Next two studies, no correlation.
4. Children in first study = younger than those in other two

Focus on weakening the conclusion when you consider answers.

(A) This answer merely fails to satisfy the condition presented in the original conclusion: "IF nightlights cause nearsightedness." It does not damage the conclusion itself.

(B) irrelevant.

(C) irrelevant.

(D) directly weakens the argument by essentially disqualifying 2 of the 3 studies on which the conclusion is based. Throw out those two and all you're left with is the original, where a correlation was found.

(E) is close, but ultimately doesn't really weaken the conclusion that IF the nightlight CAUSES the nearsightedness, it disappears with age. Why? Because we don't know what caused the nearsightedness of the "several children" cited.

user8275 · Answer

although D seems to be the closest to the right answer, " not enough children" simply sounds not convincing enough ...

SameerJain2705 · Answer

I think E should not be the answer because of words "100 children". How do we know that these numbers are significantly smaller or large than previous 3 studies. This option seems like a trap.  PallabiKundu

YashYashkratos · Answer

The conclusion that correlation shown in first study is wrong is proven by the second and third studies.
D) says those studies were not accurate. Making the final conclusion weak.

Raman109 · Answer

Doctor: In three separate studies, researchers compared children who had slept with nightlights in their rooms as infants to children who had not. - Background Info

In the first study, the children who had slept with night-lights proved more likely to be nearsighted, but the later studies found no correlation between night-lights and nearsightedness. - Premise

However, the children in the first study were younger than those in the later studies. - Premise

This suggests that if night-lights cause nearsightedness, the effect disappears with age. - Conclusion. Based on the other 2 studies in which there was no correlation.

Which one of the following, if true, would most weaken the doctor’s argument?

(A) A fourth study comparing infants who were currently sleeping with night-lights to infants who were not did not find any correlation between night-lights and nearsightedness. - Strengthener.

(B) On average, young children who are already very nearsighted are no more likely to sleep with night-lights than young children who are not already nearsighted. - strengthener.

(C) In a study involving children who had not slept with night-lights as infants but had slept with night-lights when they were older, most of the children studied were not nearsighted. - different set of students. out of scope.

(D) The two studies in which no correlation was found did not examine enough children to provide significant support for any conclusion regarding a causal relationship between night-lights and nearsightedness. - if the other 2 studies were not credible, then we can't conclude. ok.

(E) In a fourth study involving 100 children who were older than those in any of the first three studies, several of the children who had slept with night-lights as infants were nearsighted. - But the conclusion is still true. May in years to come the effects will disappear.

gurugmat · Answer

The doctor's argument depends on the later studies to support the idea that the effect of night-lights causing nearsightedness disappears with age. If these studies lacked sufficient data (i.e., they didn’t examine enough children), then their findings are not statistically significant and cannot be used to draw any reliable conclusions. This significantly weakens the doctor’s argument. Thus D is the right answer.

Doctor: In three separate studies, researchers compared children who

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