Doctor: In three separate studies, researchers compared children who had slept with night–lights in their rooms as i...

Shiyi-Zhang on May 21, 2019

Why is D correct?

Victoria on May 21, 2019

Hello @Shiyi-Zhang,

This is a tricky one! Let's go through the passage first.

The passage states that researchers compared children who slept with night-lights as infants with children who had not in three separate studies.

The first of these studies found that the children who had slept with night-lights as infants were more likely to be nearsighted than those who had not.

The later two studies found no correlation between night-lights and nearsightedness.

The doctor explains this discrepancy by suggesting a possible explanation for it. The doctor shares that the children in the first studies were younger than those in the later studies. They state that this suggests that, if it is true that night-lights cause nearsightedness, that this effect disappears with age.

We are looking for the answer choice that, if true, most weakens the doctor's argument.

A is incorrect because it presents a study which compares infants who were currently sleeping with night-lights to infants who were not. The doctor's argument is based on studies which compared children and suggests that, if night-lights do cause nearsightedness, the effect disappears with age. We cannot determine whether the effect disappears with age based on studies comparing infants. Therefore, this answer choice is irrelevant because it does not affect the doctor's argument and overall conclusion.

D is the correct answer because it weakens the doctor's argument by eliminating as credible two of the three studies upon which the doctor's conclusion is based. If these two studies failed to examine a sufficient number of children to provide support for any conclusion regarding this causal relationship, then their results which demonstrated no correlation between the two are not valid. This leaves the first study as the sole evidence supporting the doctor's argument and this study found that there is a correlation between sleeping with a night-light as an infant and nearsightedness. This weakens the doctor's argument and calls into question their conclusion that the effects of night-lights on vision likely disappear with age.

Hope this is helpful! Please let us know if you have any further questions.

SarahA on May 26, 2019

very helpful. thank you, victoria!