Researchers took a group of teenagers who had never smoked and for one year tracked whether they took up smoking...
GMAT Critical Reasoning : (CR) Questions
Researchers took a group of teenagers who had never smoked and for one year tracked whether they took up smoking and how their mental health changed. Those who began smoking within a month of the study's start were four times as likely to be depressed at the study's end than those who did not begin smoking. 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?
Passage Analysis:
| Text from Passage | Analysis |
| Researchers took a group of teenagers who had never smoked and for one year tracked whether they took up smoking and how their mental health changed. |
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| Those who began smoking within a month of the study's start were four times as likely to be depressed at the study's end than those who did not begin smoking. |
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| Since nicotine in cigarettes changes brain chemistry, perhaps thereby affecting mood, it is likely that smoking contributes to depression in teenagers. |
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Argument Flow:
The argument starts with study methodology, presents correlation data showing smoking teens have much higher depression rates, then uses biological reasoning about nicotine's brain effects to conclude that smoking causes depression.
Main Conclusion:
Smoking contributes to depression in teenagers.
Logical Structure:
The argument uses correlation data (4x higher depression in smoking teens) plus a biological mechanism (nicotine changes brain chemistry and mood) to support a causal claim that smoking leads to depression.
Prethinking:
Question type:
Strengthen - We need to find information that makes the conclusion more believable. The conclusion is that smoking contributes to depression in teenagers.
Precision of Claims
The argument claims a causal relationship (smoking contributes to depression) based on correlation data (4x more likely to be depressed) and a proposed mechanism (nicotine changes brain chemistry and mood).
Strategy
To strengthen this causal argument, we need to rule out alternative explanations and support the proposed mechanism. We should look for evidence that:
- eliminates reverse causation (depression causing smoking)
- eliminates third variables that could cause both smoking and depression
- supports the nicotine-brain chemistry mechanism
This directly strengthens the argument by eliminating reverse causation. The argument's main weakness is that correlation doesn't prove causation - maybe depressed teens are more likely to start smoking, not the other way around. If depressed participants at the study's start were no more likely to become smokers than non-depressed participants, this rules out the possibility that depression causes smoking. This supports the conclusion that smoking contributes to depression.
This talks about quitting rates among early vs. mid-study smokers, which doesn't address the core issue of whether smoking causes depression. Whether people who started smoking early were more or less likely to quit compared to those who started later is irrelevant to the causal relationship between smoking and depression.
The fact that few participants were friends or relatives doesn't strengthen the smoking-depression link. While this might address some potential confounding variables (like shared environments), it's too indirect and doesn't tackle the main alternative explanations we need to rule out.
Knowing that some participants had temporary depression episodes doesn't help establish that smoking causes depression. This information about the timing and duration of depression doesn't address whether smoking was the cause or just correlated with it.
Not tracking alcohol use actually weakens the argument slightly, as alcohol could be a confounding variable that affects both smoking and depression. This choice points out a limitation in the study design rather than strengthening the conclusion.