Doctor: In three separate studies, researchers compared children who

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!