Adding the clinical framing, because it changes how the question reads. The honest answer is that the effect is real, the magnitude is contested, and the individual variation is larger than either. Those three things can all be true at once, and most arguments here are two people holding different parts of that.

Correct me if the detail matters more than I have assumed.

Dr.SleepRoch said:

The honest answer is that the effect is real, the magnitude is contested, and the individual variation is larger than either.

Filing a mild objection. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. I would resist the confidence. Half of what this board was certain about two years ago has since been quietly dropped, and nobody went back to correct the threads.

Dr.SleepRoch said:

The honest answer is that the effect is real, the magnitude is contested, and the individual variation is larger than either.

Dr.SleepRoch has the substance of this right. The condition it depends on is worth stating. Yes, and the corollary is less popular: if the reasoning holds, it also holds where it produces an answer we do not like.

Dr.SleepRoch said:

The honest answer is that the effect is real, the magnitude is contested, and the individual variation is larger than either.

This answered a question I did not know how to ask. Printing the relevant bit and taking it with me.

Moderator note: good thread. Keeping it here rather than moving it, because the question is general enough to be useful.