#25 - To test the claim that vitamin C is effective in treating acne, scientists

[Administrator]

Complete Question Explanation

Weaken. The correct answer choice is (A).

Answer choice (A): This is the correct answer choice.

Answer choice (B):

Answer choice (C):

Answer choice (D):

Answer choice (E):

This explanation is still in progress. Please post any questions below!

[sarah_tucker@alumni.brown.edu]

Hi, can someone walk through the reasoning behind A? I selected D as the right answer thinking that the vitamin C in food could account for similar results between people who knew which pill they were taking. I also understand how answer A could be correct, but it feels like it rests on similar assumption as D. Can you walk through why A is better than D?

[Luke Haqq]

Hi Sarah!

The key difference between answer choices (A) and (D) is that the former addresses the group that received vitamin C, while the latter addresses the group that received the placebo.

This seems to be an important difference, for the conclusion of the stimulus is, "Therefore, we can tentatively conclude that vitamin C has no real benefit in reducing the severity of acne." Given the question stem, we want to weaken this conclusion, that is, we want an answer choice indicating that vitamin C does have a benefit in reducing the severity of acne.

This is what answer choice (A) does. That answer choice states that "The subjects who were given vitamin C had a history of suffering from more severe acne than did the subjects receiving a placebo." If there was no difference in the severity of the acne between the two groups after the study, yet the group receiving vitamin C had much worse acne from the start, then this suggests that the vitamin C was beneficial in making their acne less severe.