pete_nash said:

Order of operations matters more than any single choice here: establish a baseline, change one thing, wait long enough for it to express itself, then…

Adding the part of the answer the thread has not reached. Most of what circulates confidently in this community traces back to one summary of one study, and the qualifier was dropped somewhere in the third retelling.

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

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.

One thing that is still open after pete_nash’s answer:

What did you change at the same time, and can you separate the two now?

hank_denver said:

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

I do not accept the framing. The question has been narrowed to the version that has a tidy answer, and the part that was dropped is the part the OP actually asked about.

hank_denver said:

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

Fair, and it stops being fair at the extremes. The middle of the range is well understood; the ends are where the honest answer is that nobody knows.