PT157 S3 Q25 ExplanationTo test the claim that

Answer choices, explained

1. A

   Correct49% picked this

   The subjects who were given vitamin C had a history of suffering from more severe acne than did

   Why this is right

   If the vitamin C subjects started with more severe acne than the placebo subjects, then the study results look very different. The vitamin C group had less severe acne during the study despite starting with worse acne -- suggesting vitamin C actually reduced their acne enough to surpass the control group. Even among those who did not know which pill they received, having "no difference" in severity is significant if the vitamin C subgroup began with worse acne. Equal outcomes from unequal starting points suggest the treatment was effective. This undermines the conclusion that vitamin C provides no real benefit.

   Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

   49%
2. B

   No Impact5% picked this

   None of the subjects who were given vitamin C took additional doses of vitamin C

   This answer rules out a potential confounding factor -- vitamin C subjects secretly taking extra vitamin C. But ruling out this possibility does not change the study's findings or the argument's reasoning. The study already showed the vitamin C group had less severe acne overall but no difference among subjects who did not know their pill. Whether anyone took extra doses does not affect this comparison. Even if they did take extra, we would need to know whether those subjects were in the knowing or unknowing subgroup to evaluate the impact.

   5%
3. C

   No Impact6% picked this

   During the study, the severity of the subjects’ acne was lower than

   Whether all subjects had milder acne than the national average is irrelevant to the argument. The argument compares groups within the study -- vitamin C versus placebo, knowing versus unknowing. External comparisons to the national average do not affect whether vitamin C was responsible for the differences observed within the study. Both groups could have below-average acne and the argument's reasoning would be unchanged.

   6%
4. D

   Strengthens31% picked this

   Some of the subjects who were given placebos consumed foods during the study that are naturally

   If placebo subjects consumed foods naturally rich in vitamin C, this muddies the distinction between the two groups. The control group was effectively getting some vitamin C through diet, which could have reduced their acne. If the placebo group's acne was already being reduced by dietary vitamin C, then the absence of a difference between groups does not prove vitamin C is ineffective -- it suggests both groups were receiving some vitamin C. However, this actually supports the argument's conclusion more than it weakens it: if both groups got vitamin C and there was no difference, then additional vitamin C through pills provides no extra benefit.

   31%
5. E

   No Impact9% picked this

   Some of the subjects who knew their pills were placebos did not actually take the

   Some subjects who knew they had placebos did not take them. This does not meaningfully affect the argument. Those subjects are in the placebo group regardless -- they were not receiving vitamin C whether or not they swallowed their placebo pills. A placebo contains no active ingredient, so not taking it produces the same pharmacological result as taking it. At most, this introduces a minor methodological concern, but it does not provide any evidence that vitamin C actually reduces acne severity.

   9%