DataDave said:

Practical: whatever you change, write down the date and the reason.

Thank you — that is the clearest version of this I have read, and I have read a lot of them. Adding it to my notes with a link back to this thread.

Adding the clinical framing, because it changes how the question reads. Worth answering the question that was asked rather than the one behind it. The narrow version usually has an answer; the broad version usually does not, and answering the broad one is how a thread stops being useful.

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

ingrid_STO said:

Worth answering the question that was asked rather than the one behind it.

There is a second half to this that has not been said yet. 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.

The figures, for anyone assembling their own picture. Say what you would expect to see if you were wrong, before you look. It is a small discipline and it changes what you notice.

If somebody has the primary source to hand I would rather cite it than paraphrase it.