GMAT and Flu Season: Making Assumptions

by , Feb 19, 2018

flu_vitaminsI thought this question would be apropos for this time of year. :)

Assumption questions are common on the Critical Reasoning section of the GMAT, and assumptions in general form the basis of several other CR question types (including Strengthen and Weaken), so its crucial to master this topic.

Try this problem from the free questions that come with the GMATPrep software and then well talk about how Assumption questions work!

Until now, only injectable vaccines against influenza have been available. Parents are reluctant to subject children to the pain of injections, but adults, who are at risk of serious complications from influenza, are commonly vaccinated. A new influenza vaccine, administered painlessly in a nasal spray, is effective for children. However, since children seldom develop serious complications from influenza, no significant public health benefit would result from widespread vaccination of children using the nasal spray.

Which of the following is an assumption on which the argument depends?

(A) Any person who has received the injectable vaccine can safely receive the nasal-spray vaccine as well.

(B) The new vaccine uses the same mechanism to ward off influenza as injectable vaccines do.

(C) The injectable vaccine is affordable for all adults.

(D) Adults do not contract influenza primarily from children who have influenza.

(E) The nasal spray vaccine is not effective when administered to adults.

[Note: the question is reproduced faithfully from the software, including nasal-spray vaccine in answer (A) and nasal spray vaccine (no hyphen) in answer (E). One must be a typo, but I dont know which. Im going to go with nasal-spray vaccine.]

Lets start by talking about what you need to do for Assumption questions in general. Then well tackle the problem.

Any arguments in the Assumption Family (Assumption, Strengthen, Weaken, Evaluate, or Flaw) will provide you with some kind of premise(s) and conclusion. The argument will be making at least one assumptionsomething the author assumes to be true in drawing her conclusion even though she doesnt explicitly state this assumption in the argument.

For example, if I argue the following, what am I assuming to be true?

Our stores revenues increased by 10% last month. Our profits must have increased by 10% as well.

Im assuming a whole lot of things that may or may not be true! Profit doesnt necessarily correlate directly with revenue. For example, maybe we put some items on sale at a steep discountreducing the profit margin. And maybe those items accounted for most of the revenue increase. If so, our profits wouldnt have increased by the same percentage as our revenues.

Turn that into an assumption: Im assuming that the average profit margin didnt decrease.

But lets say that our average profit margin stayed the same. Does that mean our profits did go up by 10%?

Not so fast. Im also assuming that our costs didnt go up for some reason. If they did, then that would eat into our profits.

Lets see how this plays out in the flu problem.

Step 1: Identify the Question

How do you know that this is a Find the Assumption question in the first place?

The word assumption in the question stem is a pretty good clue. :D Most Assumption questions actually do include some form of that word in the question stem, though you can also see variations that dont include that word.

For instance, a question might ask you what is required or necessary in order to draw the given conclusion. That still gets at this idea that an assumption is something that the author of the argument must believe to be true in drawing her conclusion.

Step 2: Deconstruct the Argument

Parents are reluctant to give their kids flu injections because the shots hurt. Adults are at serious risk from the flu, so they do tend to get vaccinated. A nasal-spray vaccine has been invented, so that doesnt hurt the kidsbut, according to this author, there isnt a great reason to give even the nasal spray to all kids because they dont usually have serious complications from the flu.

Heres what I jotted down as I read and processed the argument:

Hmm. The author concludes that theres no great reason to vaccinate most kids because theyre at low risk for serious complications. What is the author assuming to be true in drawing this conclusion? Maybe theres some other reason or benefit that doesnt have to do with complications of the flu?

By the way, the nasal-spray flu vaccine has been in the news lately. I was fascinated to learn that studies of the nasal spray in the US have shown very low effectiveness, so it hasnt been recommended for anyone, but studies in Canada have shown that the nasal-spray vaccine has been effective in that country. Each country studied the effectiveness among its own populationbut they havent figured out why the outcomes are so different between the two countries. Im really curious what it will turn out to be!

Okay, back to our argument

Step 3: State the Goal

On Assumption questions, the goal is to find the answer that reflects something the author must believe to be true in drawing that conclusion. In other words, the assumption is necessary for the author to believe. (Note that it might not actually be true. The author just has to believe it is in order to draw the conclusion.)

Step 4: Work from Wrong to Right

All right, lets dive in.

(A) Any person who has received the injectable vaccine can safely receive the nasal-spray vaccine as well.

The argument doesnt focus on the safety of the nasal-spray vaccine. I certainly believe that thats an important factor in the real worldand that makes this one a good trap answer. Our task, though, is to focus on the specific argument made, and this argument does not hinge on the safety of the vaccine.

(B) The new vaccine uses the same mechanism to ward off influenza as injectable vaccines do.

The author doesnt discuss how either vaccine works. The author does establish that the nasal-spray vaccine is effective for children. As long as that's true, it doesnt matter whether the nasal spray uses the same mechanism or a different one.

(C) The injectable vaccine is affordable for all adults.

This choice is like answer (A): while we might care about this in the real world, the argument doesn't hinge on the cost of either vaccine.

(D) Adults do not contract influenza primarily from children who have influenza.

Im going to give it away: This is the correct answer. I think its really easy to read right over this answer and not realize its significance. The author argues that its not necessary to vaccinate kids because the kids are at low risk of serious complications. But adults are at much higher risk (as the argument also states)and the flu is a communicable disease. The more people in a community who have the flu, the more likely it is to spread to other people. So if a bunch of kids get the flu (because they werent vaccinated!), then theyre more likely to infect adults, and those adults are more likely to have serious complications. Thats the very definition of a public health issue. So, if it is the case that adults get the flu from kids, then there could be a significant public health benefit to vaccinating those kids.

The author, then, is assuming that most adults are not getting the flu from sick kids.

I think this choice is especially tricky because it is negatively worded (Adults do not contract). So Im going to show you a little trick you can use on Assumption questions (and only on Assumption questions) to better avoid traps in negatively-worded answers.

Take the answer and flip it around to be positive: Adults do contract influenza primarily from children who have influenza. What happens to the argument?

It falls apart. I conclude, Theres no public health benefit to vaccinating the kids and you say, Wait a second! Most of the time, adults get the flu from kids who have the flu! There goes my argument.

Remember when I said assumptions were necessary to the argumentthe author has to believe the assumption is true? If you take an assumption and flip it around, then, the argument should fall apart, because you took away something that was necessary to make the argument work.

(E) The nasal spray vaccine is not effective when administered to adults.

If thats true, its a great reason not to give the nasal spray to adults, but the argument only talks about giving that vaccine to the kids. The argument never says anything about needing or even just wanting to give that form of the vaccine to the adults.

The correct answer is (D).

What did you learn on this problem? Come up with your own takeaways before you read mine below.

Key Takeaways for Assumption Problems:

(1) Know how to identify the question type. On CR, this usually means some form of the word assumption or something that is required for or necessary to the argument.

(2) Lay out the premises and the conclusion so that you can think about the gap between them. The assumption lives in that gapits something the author didnt say but nevertheless must believe in order to get from the premises to the conclusion.

(3) If you get a negatively-worded answer and youre not sure how to think about it, try flipping it around. If that answer is the correct answer, the argument will fall apart. (If that answer is not the correct answer, then the argument wont fall apart.)

* GMATPrep questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.