LSAT Question Explanation
PT 108, Section 2, Question 15
Necessary AssumptionArgument structure
Society has a tough decision to make: should we pay the $240,000 it would cost to use drug T to save 1 additional patient?
Drugs S and T both work quite well in reducing fatalities, but a study shows that drug T can save an additional 1 patient per 120. Drug T costs $2,000 more than drug S.
Explanation
My first thought here was whoa, where is the $240,000 figure coming from? On re-reading I realized that the author is assuming drug T would have to be administered to every single patient to save the extra life. Because T is $2,000 more expensive, so multiplied by 120 patients (because T saves an additional 1 in 120) the additional life saved would cost $240,000.
But what if we knew which drug to give? If a doctor could tell whether or not a patient would survive with just drug S, which it seems that many patients would, then we wouldn't actually spend the extra $2,000 for every patient. So each additional life saved might cost far less than $240,000.
The author's assumption is just that we would have to administer drug T to every patient to save the additional life.
Answer choices
This doesn't need to be true. The author concludes that we have to decide about spending $240,000 to save 1 life based on the efficacy and price of drug T, it doesn't matter if the drugs have the same or different side effects.
This has nothing to do with the conclusion. It could be a possible explanation as to why drug T saves 1 more patient per 120, but it's not needed to make the conclusion about spending $240,000 to save another life.
Similar to (B) this could be an explanation as to why T saves an additional 1 in 120 patients. But it's irrelevant to and not necessary for the conclusion.
This is needed for the conclusion to hold. If this weren't true, and there was a way to determine which drug is needed for a given case, then we wouldn't always have to spend the extra $2,000 to administer drug T. We could save the additional 1 in 120 patients without spending an extra $240,000 per 120 patients.
Again, similar to (B) and (C). Maybe this explains how drug T works to save more people than drug S, but this is absolutely not needed for the conclusion to be valid.