adam_van said:

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

That is right, and it stops being right at the edges. The general case is well behaved; the interesting cases in this thread are all at the boundary where the general case breaks.

Reporting back.

Reporting back for the archive rather than for the thread: I did the narrow version of what was suggested, gave it the full interval, and it settled. Posting it because threads without a follow-up are half a thread.

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.

Dr.PathRoch said:

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

Same experience, arrived at from the opposite direction. Posting only so the count is not one.

Dr.PathRoch said:

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

There is a second half to this that has not been said yet. It helps to ask what evidence would change your mind before you look at any. If nothing would, the discussion is not about evidence, and it is better to say so early than to spend nine posts discovering it.