PrepTest 124, Section 1, Question 13
Some doctors believe that a certain drug reduces(61 more words not shown)
Which one of the following(7 more words not shown)
- AIf a drug(26 more words not shown)
- BIf there were(29 more words not shown)
- CA period of(25 more words not shown)
- DChanges in diet(21 more words not shown)
- EThere are various(18 more words not shown)
Reading the argument
What if the drug keeps working after people stop taking it?
The doctors' initial evidence isn't conclusive: vertigo episodes became shorter after the drug appeared, but perhaps patients also began another treatment or changed their sleep habits. The timing alone doesn't prove the drug caused the improvement.
The author's reply has a problem too. During a three-month shortage, average episode duration didn't change. That would be useful evidence against the drug if a genuinely effective drug's absence would show up within those three months. But what if its earlier use had lasting benefits? Then the shortage could leave the average unchanged even though the drug had helped.
What we’re looking for
We're asked for an assumption the argument requires. My prediction is that the shortage would have revealed a real effect if the drug had one. Otherwise, the unchanged average doesn't justify concluding that the drug has no effect.
Working the answers
- ACorrect
If the drug affected duration, the three-month shortage would have produced a significant change in the average. We observed no such change, so this assumption lets the author rule out an effect.
Our lingering-benefits possibility shows why the assumption matters. If an effective drug could leave the average unchanged during the shortage, the author's evidence would fit both an effective drug and an ineffective one. The author needs the absence of a change to tell those possibilities apart.
- B
This would support the doctors' original claim. The passage says average duration fell after the drug was introduced; B says a change after introduction would demonstrate the drug's effect. That points against the author's conclusion that the drug has no effect, rather than supplying an assumption that conclusion requires.
- C
Three months needs to be informative enough for the author's inference. It doesn't have to be the best possible observation period. A longer study might offer more information or more confidence even if three months were already enough to detect an effect. C rules out a possible improvement the argument doesn't need to rule out.
- D
The author needn't rule out diet or smoking as explanations for the earlier improvement. Those factors could explain the change while the drug did nothing, which is entirely compatible with the author's conclusion. What the argument relies on is the significance of the shortage result, not eliminating these alternative causes.
- E
The author doesn't have to establish several other ways to shorten vertigo episodes. Showing that this drug has no effect would not require identifying replacement treatments or multiple causes of improvement. E could be true, but the shortage argument doesn't depend on it.
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