jason_paloalto said:

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

Saving this. It is the first explanation that did not require me to already understand it. Sending this to two other people who asked me the same thing last week.

From the other side of the consultation, briefly. 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.

I would rather be corrected than agreed with, if it comes to it.

NurseLeah_Nash said:

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

This is my experience too, for whatever a second data point is worth. The detail I would add is minor and it is already implied above.

NurseLeah_Nash said:

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

Coming at NurseLeah_Nash’s question from a different direction. The useful move here is to separate what is established from what is widely repeated. Those two sets overlap less than the confident tone of most write-ups suggests, and the second set is where nearly all the disagreement on this board comes from.

Adding the numbers, since they settle part of this. For anyone reading later: the numbers in this thread are worth checking against a primary source before you act on them, including mine. Half the figures circulating in this community trace back to a secondary summary that dropped a qualifier.