dave_SLC said:

Practical: whatever you change, write down the date and the reason.

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.

dave_SLC said:

Practical: whatever you change, write down the date and the reason.

This answered a question I did not know how to ask. Printing the relevant bit and taking it with me.

Adding the clinical framing, because it changes how the question reads. 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 measure again under the same conditions.

traveltech_sara 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…

Same pattern here, and in the same order. Nothing to add that would improve it.

traveltech_sara 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…

Coming at traveltech_sara’s question from a different direction. There is a difference between no evidence and evidence of no effect, and this subject is one where the two get swapped freely in both directions.