josh_phd_bmore 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…

Correct as far as it goes. The part it does not cover is what to do when the honest answer is "not enough data", which is more often than anyone likes.

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

josh_phd_bmore 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…

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. 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.

james_edin said:

It helps to ask what evidence would change your mind before you look at any.

Same pattern here, and in the same order.

Closing the loop on my own question.

Closing the loop. The answer turned out to depend on the detail I had left out of the opening post, which is a lesson about how to ask rather than about the subject.