This is an effective counter to the physician's argument. Magnets are a placebo. It's possible that if the other group had had some kind of \"treatment\" administered, they also would have reported less pain. Thus, the physician’s conclusion that magnets probably reduce back pain seems less likely.

This is irrelevant. The stimulus doesn't talk about medication versus magnets. We just want to know whether magnets can effectively relieve back pain or not--it doesn't matter if medication can do so even more effectively.

This doesn't weaken the argument, which is only focused on back pain, not other types of pain. Notice also that \"no other experiments have been done\" is different from \"no other experiments have shown\". The second phrase would tell us that other experiments have been done, and potentially found results undermining the ones from the experiment in the stimulus. This might weaken the argunment. But if no other experiments have been done, this experiment could still be valid.

This is trying to suggest that the experiment was biased. But most scientists who have a hypothesis might be somewhat in favor or against it before starting an experiment, and if these scientists--notice that we don't know how many there were--didn't directly conduct the experiment, it's unclear how they could have compromised the results.

Irrelevant. We don’t care what caused the pain in the first place. We care how well, if at all, the magnets relieved it.