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This is a GMAT Prep question. So, if you haven’t gone through the Official practice tests yet, you might want to revisit this solution after you take those mock tests.

Question


A study followed a group of teenagers who had never smoked and tracked whether they took up smoking and how their mental health changed. After one year, the incidence of depression among those who had taken up smoking was four times as high as it was among those who had not. Since nicotine in cigarettes changes brain chemistry, perhaps thereby affecting mood, it is likely that smoking contributes to depression in teenagers. 

Which of the following, if true, most strengthens the argument?

(Because of copyrights, the complete official question is not copied here. You can access the question here: GMAT Club)

Difficulty: Medium

Accuracy: 77%

Based on: 3028 sessions

Solution


The Story

A study followed a group of teenagers who had never smoked and tracked whether they took up smoking and how their mental health changed.

  1. Researchers followed a group of teenagers who had never smoked.
  2. They tracked whether the teenagers took up smoking.
  3. They also tracked how their mental health changed.

After one year, the incidence of depression among those who had taken up smoking was four times as high as it was among those who had not.
The researchers tracked the teenagers for one year. After one year they found that the teenagers who had taken up smoking were four times more likely to be depressed than the teenagers who had not taken up smoking.

So, what exactly would have happened?

Say 80 teenagers did not take up smoking in that year. And out of those 80, 8 suffered from depression also. That would be a 10% likelihood of a non-smoking teenager getting (?) depression.

And say 60 teenagers took up smoking in that year. The likelihood of these smoking teenagers getting depressed would be 40% (“four times as high”). 
That would mean that 24 out of 60 teenagers suffered from depression.

Since nicotine in cigarettes changes brain chemistry, perhaps thereby affecting mood, it is likely that smoking contributes to depression in teenagers.
So the author is creating a causal link here. The author also supports her conclusion with some scientific evidence.

  1. Nicotine in cigarettes changes brain chemistry
  2. Changing brain chemistry perhaps affects mood
  3. So, smoking cigarettes  contributes to depression  (affects mood)

Gist:
Smoking cigarettes contributes to depression in teenagers (main point). 

This point has two bases:

  1. The study showed that the teenagers who took up smoking were four times as likely to be depressed as the teenagers who didn’t.
  2. The knowledge that nicotine in cigarettes changes brain chemistry. 
    • Smoking cigarettes —> brain chemistry
    • Brain chemistry —> mood affected

Gap(s) in logic:

  1. The study
    a. What if the reason for the difference in likelihoods between the two groups was not their taking up smoking?
    – What if depression made teenagers more likely to take up smoking? (reversed causal relation)
    – What if events in their lives make teenagers depressed and cause them to take up smoking? E.g. the teenagers who started studying engineering were more likely to suffer from depression and to start smoking? (Some third factor causing both these things)
    – What if it was a coincidence that the teenagers had such experiences?
    b. Can the results of the study be generalised for all teenagers?
  2. Does smoking cigarettes affect mood? Nicotine changes brain chemistry. And I’ll assume that with smoking I would ingest the harmful nicotine. Still, what part of brain chemistry does nicotine change? Maybe the brain chemistry impacted deals with memories, and not with mood.

There could be other gaps too. These are what I could think of. On to the question!

Question Stem


Which of the following, if true, most strengthens the argument?

Framework: We’re looking for an answer choice that would make us even more confident that smoking contributes to depression in teenagers.

Answer choice analysis


Answer Choice: A

Correct

Selected by: 77%

This answer choice talks about those teenagers in the study who were depressed at the start of the study. Remember, the study followed teenagers who were non-smokers at the start of the study. The study did not filter out participants based on whether they were depressed from before.

What does this answer choice give us? These teenagers were as likely (or less) to take up smoking as were the teenagers who were not depressed at the start.

Essentially, I now learn that depression did not cause these teenagers to take up smoking. Because if it did, the depressed-at-the-start teenagers would have been more likely to become smokers than the not-depressed-at-the-start teenagers.

Now, how does this knowledge impact the argument?

Let me explain this using a simplistic example.

Yesterday,

  1. John waved at Ramesh.
  2. Ramesh smiled at John.

You have to figure out: Did Ramesh smile at John because John waved at him? (In other words, did John’s wave lead to Ramesh’s smile?)

Then you learn: Well, John didn’t wave at Ramesh because Ramesh smiled at him. (Ramesh’s smile did not lead to John’s wave.)

By learning this, in which direction does your belief go about whether John’s action caused Ramesh’s?

The belief should increase. 

Q. Did John’s action lead to Ramesh’s? 

Ans. At least Ramesh’s didn’t lead to John’s.

So, my belief goes up. I now believe more than before that John’s action led to Ramesh’s.

Jargon alert! By eliminating the reverse causal relationship, the belief goes up in the established causal relationship.

The same concept applies to this answer choice. The information that at least depression did not make the participants more likely to take up smoking strengthens the argument.


Answer Choice: B

Incorrect

Selected by: 7%

What impact does the following option have on the argument?

(B’) Occasional smokers were less likely to be depressed than heavy smokers.

B’ strengthens the argument. It further strengthens the link that smoking leads to depression. 

B’ talks about the difference in the likelihood of getting depressed between different categories of smokers. Such an answer choice could have been relevant.

The original answer choice, however, only tells us that the study did not distinguish between these two categories of smokers. That information on its own has no bearing on the argument.

No impact.


Answer Choice: C

Incorrect

Selected by: 2%

So pretty much none of the participants followed each other on Instagram. That has no impact on the argument. The passage never indicates that presence of / interaction with fellow participants could affect smoking behaviour or depression.


Answer Choice: D

Incorrect

Selected by: 13%

As soon as I read this answer choice, I wondered whether the study was about which teenagers were depressed at the end of the year. I went back to the passage, and found the phrase “incidence of depression”. 

My understanding is that the study followed and tracked the teenagers for the year. They did not just measure mental health at the end of the year, but tracked it throughout. So, this answer choice has no impact on the argument.

Now, what if the researchers did not follow the participants throughout the year; they simply noted the participants’ smoking behaviour and mental health status at the end of the year?

Even then this answer choice would have no impact on the argument. I can think of three reasons:

  1. The answer choice just states ‘some participants’. We don’t learn whether these participants had taken up smoking or not. 
  2. The answer choice does not establish any link between smoking and how quickly someone may emerge from a period depression.
  3. Still, at the end of the year, those who took up smoking were four times as likely to be depressed as those who did not take up smoking. Was that difference caused by smoking? That is the question to answer. This answer choice does not help with answering that question.

Answer Choice: E

Incorrect

Selected by: 1%

What if we had the following answer choice?

E’. Those teenagers who had taken up smoking and then experienced depression in that year had also taken up drinking in that year. 

This answer choice would weaken the argument. It gives us an alternative possible cause for depression. In that case, maybe alcohol consumption causes depression and not smoking.

How about:
E’’. Alcohol did not cause depression among the participants.

By learning this, I believe more than before that smoking contributes to depression in teenagers. This answer choice strengthens the argument.

How about the original answer choice now?

The option states that the use of alcohol was not tracked. That’s it. Sure, had the use of alcohol been tracked, perhaps the researchers could have made a more informed argument. (This is assuming that alcohol can cause depression.) So from that perspective, this answer choice has a very (very) mild negative impact on the argument.

If you have any doubts regarding any part of this solution, please feel free to ask in the comments section.

Anish Passi

GMAT Coach

With over a decade of GMAT training experience, top 1 percentile scores on the CAT and GMAT, and a passion for teaching, I’d like to believe I am quite qualified to be a GMAT coach. GMAT is learnable, and I help students master the GMAT through a process-oriented approach based on logic and common sense. I offer private tutoring and live-online classroom courses. My sessions are often sprinkled with real-world examples, references to movies, and jokes that only I find funny. You’ve been warned 🙂

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