quinn_sf said:

The boring version of this is the one that works, and the boring version is: measure a baseline, change one variable, wait, measure again under the…

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

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.

jim_asheville said:

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

Same experience, arrived at from the opposite direction.

jim_asheville 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.

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

Closing the loop on my own question.

Resolved, and the thing that resolved it was the least interesting suggestion in the thread. Writing that down for the next person who wants the interesting answer.