Hi,
This question is from Critical Reasoning, Third Edition, page 133.
The question is as follows:

Scientists: An experimental technique for combating severe depression, deep-brain stimulation (DBS) demonstrates much promise for the long-term treatment of chronic depression. In a recent experiment, electrodes were implanted into the brains of six patients who had not responded to any currently approved treatment for depression. When an electrical current to the electrodes was stwitched on, four of the patients reported feeling a dramatic reduction of depressive symptoms. The depressive symptoms returned when the current was switched off.

Which of the following, if true, best supports the scientist's claim of the promising potential usage of DBS?

A. The electored implanted during deep-brain stimulation can only be activated in a hospital setting.
B. The other two patients reported a slight reduction of depressive symptoms when the current on their electrodes was activated.
C. The operation to implant the electrodes poses a high risk of brain hemorrhage, infection or seizure.
D. In a subsequent experiment, a one hour treatment the electrodes produced sustained remission from depression in the four patients for six months.
E. Deep-brain stimulation relies on the expertise of highly skilled physicians.

The answer is given as D. I brought the choices down to B and D.
My question here is that how can we avoid the result of rest two patients out of 6? If for example, those two patients died, then this argument fails. I am not saying that D does not strengthen the argument.
B is infact given as irrelevant in the explanation. In my opinion, both B and D are strengthening the argument.
Also, in question it is given "scientist's claim of potential usage of DBS". Can this technique be potentially used if the results with rest two patients show that the condition becomes worse for them? So in my view, I thought that knowing the results of rest two patients is equally important as knowing the result of four patients.

Please help me in understanding this question.

Thanks.

Bump!!!

Hello Ritesh,

Look again at the conclusion made:
An experimental technique for combating severe depression, deep-brain stimulation (DBS) demonstrates much promise for the long-term treatment of chronic depression

Notice the key word 'long term'. So we cannot conclude anything from this one experiment. SO even if the other two patients had remission from depression, we still do not know whether the effects will last for a 'longer term'. The proof that the effects are long term is provided in (D) there is sustained remission from depression for 6 months which strengthens the conclusion

Hope this helps

ganeshram's explanation is excellent. The key point is that the conclusion is looking at long-term treatment, and (D) is the only one related to treatment for an extended amount of time.

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Ben Ku
Instructor
ManhattanGMAT