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# Researchers took a group of teenagers who had never smoked and for one

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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
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definitely (A).

(A) says that the people who started smoking are mentall/biologically same as those who did not smoke.
Infact (A) is an assumption.
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
I still don;t understand how A is the answer.
All it says is - depression is not the reason for smoking.

And as per the argument, we have to prove that smoking contributes to depression. This can not be proved on the basis of A.

But, except A, nothing comes close and hence I select A.
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
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Cause (Smoking for 11 months) ---> Effect (Depression at the end of 11 months)
Now, we need to strengthen this causal relation; So, any wened to eliminate reverse causation or alternate causation.
A. This option says: teenagers already depressed (effect) ---->NOT started smoking during the study (cause)
This option shows "effect" doesn't cause the "cause" . So the causality is srengthened.
Always remember whenever a causality is ecountered we check 3 basic causality rules.
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
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 studyâ€™s start were four times as likely to be depressed at the studyâ€™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?

A. Participants who were depressed at the studyâ€™s start were no more likely to be smokers at the studyâ€™s end than those who were not depressed.
B. Participants who began smoking within a month of the studyâ€™s start were no more likely than those who began midway through to have quit smoking by the studyâ€™s end.
C. Few, if any, of the participants in the study were friends or relatives of other participants.
D. Some participants entered and emerged from a period of depression within the year of the study.
E. The researchers did not track use of alcohol by the teenagers.

My 2 cents.

Conclusion : smoking causes depression

A. So this is saying that at the start of the depression, there were some participants who were depressed. And these depressed participants were no more likely to be smokers than those who were not depressed. So this is trying to establish that depression does not cause smoking. So, by shooting down alternative explanation, the argument is strengthened.

Not an easy question but if you are aiming high on gmat, you need to see why A is correct answer.
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
It Says that both Depressed and Non-depressed people are equally predisposed to smoke in the defined period. Only then is the result of the study accurate and can be considered true. It defies the circular reasoning that X causes Y as well as Y causes X.
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
GMATNinja VeritasPrepKarishma

Smoking (which contains nicotine) -> Depression in Teenagers

To strengthen: we need to prove reverse causation in not possible

Depression in Teenagers -> Smoking (which contains nicotine) in not feasible

This is what (A) does on negation

But correct strengthener can also be: Eliminating any alternate causes for stated effect.

Why (E) incorrect?
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
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GMATNinja VeritasPrepKarishma

Smoking (which contains nicotine) -> Depression in Teenagers

To strengthen: we need to prove reverse causation in not possible

Depression in Teenagers -> Smoking (which contains nicotine) in not feasible

This is what (A) does on negation

But correct strengthener can also be: Eliminating any alternate causes for stated effect.

Why (E) incorrect?

If at all, (E) weakens the argument. It says that the study was limited in its scope and did not track drinking. Perhaps the teens who started smoking started drinking too and actually that caused depression, not the smoking. It doesn't make our argument stronger i.e. it doesn't make the conclusion of our study more likely to be true.

Knowing that A and B are linked and by saying that B is not the cause of A, we make it more likely that A is the cause of B. So option (A) is correct.
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
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Let’s look at the details of the argument.

Premises
1) 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.
2) 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.
3) nicotine in cigarettes changes brain chemistry, perhaps thereby affecting mood

Conclusion-

It is likely that smoking contributes to depression in teenagers.

We need to find an option that strengthens the conclusion.

A) Participants who were depressed at the study's start were no more likely to be smokers at the study's end than those who were not depressed.

Let’s try and negate this- participants who were depressed at the start of the study were more likely to be smokers at the study's end than those who were not depressed. This reverses the cause and effect sequence in the argument. This would mean that they took to smoking because of depression and not vice versa. This would seriously weaken the conclusion that smoking contributes to depression.
Option A says that people who were depressed and who were not depressed at the start of the study were equally likely to start smoking. This supports the conclusion that smoking contributes to depression. Hence A is correct.

(B) Participants who began smoking within a month of the study's start were no more likely than those who began midway through to have quit smoking by the study's end.

The comparison is only between the mental state of the participants who began smoking and that of participants who did not. This is not relevant to the conclusion of the argument. Eliminate B

(C) Few, if any, of the participants in the study were friends or relatives of other participants.

This is totally irrelevant to the conclusion- It is likely that smoking contributes to depression in teenagers- Eliminate C

(D) Some participants entered and emerged from a period of depression within the year of the study.

Emerging from depression is not relevant to the conclusion. Eliminate D

(E) The researchers did not track use of alcohol by the teenagers.

Out of scope. The argument only talks about the relation between smoking and depression. Eliminate E

Vishnupriya
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
Hi, please explain the option choice. I marked correct answer A on the basis of elimination as other options were not contenders
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
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.

Nicotin causes depression

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

(A) Participants who were depressed at the study's start were no more likely to be smokers at the study's end than those who were not depressed.
Depression does not lead to smoking habit (nicontin)

(B) Participants who began smoking within a month of the study's start were no more likely than those who began midway through to have quit smoking by the study's end.
Irrelevant to "Nicotin causes depression"

(C) Few, if any, of the participants in the study were friends or relatives of other participants.
Irrelevant to "Nicotin causes depression"

(D) Some participants entered and emerged from a period of depression within the year of the study.
Irrelevant to "Nicotin causes depression"

(E) The researchers did not track use of alcohol by the teenagers.
Irrelevant to "Nicotin causes depression"
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
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Re: Researchers took a group of teenagers who had never smoked and for one [#permalink]
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