PrepTest 157, Section 3, Question 25
To test the claim that vitamin C is(94 more words not shown)
Which one of the following,(7 more words not shown)
- AThe subjects who(20 more words not shown)
- BNone of the(15 more words not shown)
- CDuring the study,(12 more words not shown)
- DSome of the(17 more words not shown)
- ESome of the(16 more words not shown)
Reading the argument
Less severe acne in the vitamin C group initially sounds promising. But how severe was each group's acne before the experiment?
Suppose the vitamin C group started with much milder acne. It could finish with milder acne even if the pills did nothing. That is the first concern I'd have about the reported difference: were the groups comparable at the start?
Then we learn that half the participants knew which pills they received. The author turns to the people who couldn't tell. Within that group, the vitamin C and placebo recipients had equally severe acne during the study. That makes the apparent advantage look less convincing—but it still doesn't answer our starting-point question.
Now imagine the imbalance going the other way: the vitamin C recipients began with much worse acne. Finishing at the same level as placebo recipients could then mean they improved more. Equal results at the end aren't necessarily equal changes from the beginning.
What we’re looking for
To weaken the conclusion that vitamin C has no real benefit, I'd look for evidence of that kind of imbalance. We don't need to establish that vitamin C definitely works. We need a reason the equal acne levels among people unaware of their pill assignments may fail to show an absence of benefit.
Working the answers
- ACorrect
A history of more severe acne in the vitamin C group gives us reason to question whether the groups began on equal footing. If those recipients started worse off, matching the placebo group's later acne level could reflect greater improvement.
Imagine an illustrative severity scale on which the vitamin C group starts at ten and the placebo group at five. Both later reach four. The final levels match, but one group improved by six points and the other by only one. A doesn't give those exact starting scores or prove what caused the change. It does raise precisely the comparison problem that makes the no-benefit conclusion less secure.
- B
Not taking extra doses doesn't undermine the comparison or show that the prescribed vitamin C lacked a benefit. It simply rules out one variation in how much the treatment group took. We also can't infer that every possible dose would fail from the absence of additional doses.
- C
The national average isn't the relevant comparison. Both groups could have less severe acne than average and still differ in how much they improved. We need to compare the treatment and placebo groups, including their starting points, not compare the participants collectively with the country.
- D
Vitamin C from food could raise a concern about whether the control group really lacked the substance being tested. But this only tells us some placebo recipients ate vitamin-C-rich foods. We don't know the amount, whether it was enough to matter, or whether these were the people who couldn't identify their pills—the subgroup driving the conclusion. We also lack a useful comparison of total intake across the groups. A more directly identifies a reason equal later severity could conceal unequal improvement.
- E
These participants knew they had placebos. The argument's crucial comparison instead concerns participants who couldn't tell which pills they received. Whether some of the aware participants skipped their placebos doesn't explain away the equal acne levels in that other group.
More Weaken questions
Learn the LSAT our way
Our platform drills Weaken questions at your level and adjusts as you improve.