Dr.ReproEndo said:

Almost every unanswerable question in these threads is unanswerable because three things changed in the same fortnight, and no amount of subsequent…

This is exactly what I could not find anywhere else. Adding it to my notes with a link back to this thread.

Clinical perspective, offered as context rather than as advice. 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.

james_edin said:

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

Filing a mild objection. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. I think the framing smuggles in the conclusion. Ask it the other way round and the obvious answer reverses, which usually means the question is doing the work.

Adding the numbers, since they settle part of this. 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.

Moderator note: the sourcing question belongs in the vendor section and has been split out.