Some doctors believe that a certain drug reduces the duration of episodes of vertigo, claiming that the average durat...

Farnoush on September 26 at 03:31PM

Why A and not C?

Hi could you explain why C isn’t the answer. I thought both strengthened it and then when I negated I thought C would make the answer choice fall apart. Thank you

1 Reply

on September 26 at 09:00PM

Hello @farnoushsalimian,

Keep in mind that a required assumption does not strengthen an argument. Rather, the argument depends entirely on this assumption. This is why the strategy of negating answer choices is effective.

Premise: During a three-month shortage of the drug, there was no significant change in the average duration of vertigo.

Conclusion: The drug has no effect on the duration of vertigo.

The author gives only one piece of evidence to support the conclusion, and that is the three-month window in which the shortage did not have a significant effect. We should know before even looking at the answer choices, that the author is assuming that this piece of evidence is sufficient to support the conclusion.

This is best reflected by answer choice A. It says that if the drug did work, then the three-month shortage would be enough time to see the positive effects of the drug diminish. This didn't happen, so the drug is ineffective. This is necessary for the success of the argument.

You are correct that C probably strengthens the argument. Let's negate it. Even if a shortage greater than three months would have given better information, that does not mean that the data from the three month shortage is worthless. It could still be strong enough to support the conclusion. The argument does not fall apart.