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?

A. Participants who were depressed at the start of the study were no more likely to be smokers after one year than those who were not depressed.
B. The study did not distinguish between participants who smoked only occasionally and those who were heavy smokers.
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.

This is how I have it: Because those who took up smoking were 4x more depressed than those who hadn't, then smoking contribute to depression.
I chose C because I thought no genetic background or family history of depression, then the results are genuine.
Can someone please help me understand why A is the correct answer and c is incorrect?

cheers!!!

If you negate Option A, it becomes
Participants who were depressed at the start of the study were more likely to be smokers after one year than those who were not depressed
The sentence above weakens the argument by providing an alternate cause - "Depression causes Smoking".
Option A strengthens the argument by closing the weakness "Depression does not cause Smoking" and is the correct answer.

Excellent!

Yes, beware of these causal arguments. You can recognize them when you see the author present that A and B happen together to therefore A caused B. To properly conclude that A caused B you have to rule out the possibility that B may have actually caused A. Doing so will strengthen the potential causality.

In this case, we see that smoking and depression occur together. It was then concluded that smoking caused the depression. To conclude this we have to rule out the possibility that being depressed causes people to smoke, which answer choice A does. I also like how this poster uses negation, which can be very valuable on questions involving assumptions.

_________________
Jamie Nelson
ManhattanGMAT Instructor

Thanks a lot Murali and Jamie,

Now I think I misinterpreted Answer choice A.

What does this part mean, 'were no more likely to be smokers'? I thought it means participant who were depressed at the beginning of the study stopped smoking!

i think I need help seriously, I misinterprete these type of statements most of the time. Please someone simplify these type of wording for me.

Cheers

aaaaahh, i see what you did there. (i find these kinds of errors absolutely fascinating -- because no native speaker would ever think to interpret the words in this way, yet i can totally see the logic behind your interpretation.)

you are (mistakenly) reading the sentence as equivalent to one of these:
... those participants were no longer likely to be smokers
... those participants were not likely to be smokers anymore
these two constructions mean that these particular participants were unlikely to be smokers by the time of the study's conclusion.

that's not what the construction in this sentence means, though.
the construction here is “no more likely”, which is, from a mathematical standpoint, like saying “current likelihood < original likelihood”.



the problem with this request -- even though it's a perfectly reasonable request -- is that it's essentially impossible for us to answer, for the same reason i pointed out above: we native speakers don't make these mistakes, and so we aren't aware of them (and can't enumerate them) until we actually see them in the speech/writing of a non-native speaker.
in other words, it's impossible for us to anticipate these errors until we actually see posts like this one. so, unfortunately, we can't give you “preventive medicine” here; we will just have to explain things after you've actually made an error.

I do not agree that we use negation test for strengthening question. This technic is used for assumption question.

in causal argument, look for something which said that there is no other cause,or that causal relation is not reversed- A said this and is correct.

pls, comment on my thinking. Thank you.

well, both of you are correct, each of you in your own way.

yes, "the negation test" is a tool primarily used on assumption questions. but it's also certainly true that ruling out a possible objection or shortcoming is a very effective way to strengthen an argument.