Small magnets were applied to one group. Most of them reported significant improvement.
No treatment was given to the other group. Very few reported improvement.

Conclusion: This shows that magnetic fields are probably effective at relieving some back pain.

We need to weaken the conclusion. The conclusion certainly seems reasonable, right? Those with magnet reported less pain while others didn't so it seems magnets helped. But we need to weaken the conclusion. Something should say that it may not have been the magnets that helped but something else that happened in group 1.

(A) A patient’s merely knowing that a treatment has been applied can lead to improvement in his or her condition.

This could be the "something else" that helped group 1 people. If merely knowing that a treatment has been applied (placebo effect) can reduce the sensation of pain, the magnets may have had nothing to do with the improvement. It may be the impact of knowing that they were treated. While group 2 people did not get any treatment and hence did not get this psychological reassurance that they were treated. Hence they did not claim a reduction in pain.

(B) Most physicians believe that medication relieves chronic back pain more effectively than magnets do.

What is more effective than magnets is irrelevant. Our conclusion just says that magnets have some impact.

(C) No other experiments have been done showing that magnetic fields reduce pain in any area other than the back.

Areas other than the back are irrelevant. The conclusion only talks about back pain.

(D) Some of the scientists who helped design the experiment believed even before the experiment that magnetic fields relieve back pain, but they were not directly involved in conducting the experiment.

Scientists involved are irrelevant.

(E) There was wide variation in the specific causes of the chronic back pain suffered by the patients in the experiment.

Causes of back pain does not matter. Most people claimed a reduction in pain so whatever worked, worked for most people.

Answer (A)
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Physician: In an experiment, 50 patients with chronic back pain were divided into two groups. Small magnets were applied to the backs of one group; the other group received no treatment. Most of the patients in the first group, but very few in the second group, reported a significant reduction in pain. This shows that magnetic fields are probably effective at relieving some back pain.

Which one of the following, if true, constitutes the logically strongest counter to the physician’s argument?
Conclusion- magnetic fields are probably effective at relieving some back pain

Pre-thinking- As with many causal relationships, the easiest way to weaken the conclusion is by recognizing an alternate cause. We want to think of a reason, other than the magnates, that the two groups differ. A key factor may be the fact that this was not a blind study. Participants knew if they were receiving the magnet treatment or no treatment by the nature of the study. After all, it would be hard not to notice a magnet on your back.


(A) A patient’s merely knowing that a treatment has been applied can lead to improvement in his or her condition.- Correct; the patient’s knowledge of the fact he or she is receiving treatment can impact subjective levels of pain
(B) Most physicians believe that medication relieves chronic back pain more effectively than magnets do.- incorrect; the causal argument was comparing magnet use to a complete lack of treatment. The argument does not attempt to compare types of treatment, but rather a type of treatment versus no treatment at all. The study was not attempting to determine what type of treatment is best to manage back pain, but rather could magnets work as a type of treatment to manage back pain.
(C) No other experiments have been done showing that magnetic fields reduce pain in any area other than the back.- Out of scope; the conclusion is specifically focused on “some back pain
(D) Some of the scientists who helped design the experiment believed even before the experiment that magnetic fields relieve back pain, but they were not directly involved in conducting the experiment.- incorrect; This answer choice attacks those who created the study. It sounds plausible that the developers’ beliefs could impact the results of the study. However, as we read through this answer choice, we realize that those researchers with a bias were not actually involved in carrying out the study.
(E) There was wide variation in the specific causes of the chronic back pain suffered by the patients in the experiment.- incorrect; It does not tell us, for example, that the first group consisted of patients with low back pain, while the second group consisted of patients with neck pain. It merely states that there were different types. Since it does not allow us to draw a new distinction between the two groups, it is not the correct answer choice.

Answer A


Hi janadipesh,

Hope this helps!

Please read Magoosh blog in the following link for a better understanding

https://magoosh.com/gmat/2013/medical-t ... reasoning/
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