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.

lisa_labSD said:

Say what you would expect to see if you were wrong, before you look.

This is exactly what I could not find anywhere else. I will report back once I have actually tried it.

Clinical perspective, offered as context rather than as advice. It is worth asking what the claim would look like if it were false. If nothing would look different, it is not a claim about the world and no amount of discussion will settle it.

sophie_paris said:

It is worth asking what the claim would look like if it were false.

This is my experience too, for whatever a second data point is worth.

Moderator note: good thread. Keeping it here rather than moving it, because the question is general enough to be useful. Thread quality here is what the rules are for. Keep it up.