Doctor: In Three Separate Studies, Researchers Compared Children who had Slept with Nightlights in their Rooms as Infants to Children Who had Not.

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?

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.

Doctor: In Three Separate Studies, Researchers Compared Children who had Slept with Nightlights in their Rooms as Infants to Children Who had Not. – is a topic in GMAT Critical Reasoning. This particular GMAT Critical Reasoning topic has been taken from the book ‘ GMAT Official Guide Verbal Review, 2022’. This is a version of “weaken” question, and that means that we must have a conclusion in here somewhere. The passage does not connect the evidence to the conclusion. We need to find out which of the options are true and weaken the doctor’s argument. GMAT critical reasoning tests the logical and analytical skills of the candidates. This topic requires candidates to find the strengths and weaknesses of the argument, or find the logical flaw in the argument. The GMAT CR section contains 10 -13 GMAT critical reasoning questions out of 36 GMAT verbal questions.

Answer: D
Solution and Explanation:

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

It has to do with the cause. We can see 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.
Now, let us consider each option one at a time.

1. 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. - This option merely fails to satisfy the condition presented in the original conclusion: "IF nightlights cause nearsightedness." It does not damage the conclusion itself. This states that the correlation between night-lights and nearsightedness could not be found.
2. 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. - Directly Irrelevant to the passage. 
3. 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. - Directly Irrelevant to the passage. 
4. 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. - This statement weakens the argument by disqualifying 2 of the 3 studies on which the actual conclusion is based. If we eliminate out those two, we will be left with the original, where a correlation was found.
5. 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. - This is closely related, 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.

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