Dr.PeteFamMed said:

One practical note: write down what you did and when, before you need it.

Saving this. It is the first explanation that did not require me to already understand it.

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.

Moderator note: a couple of off-topic posts removed.

Dr.LeslieOBGYN 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 Dr.LeslieOBGYN’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.

The figures, for anyone assembling their own picture. One habit that pays for itself: post the method alongside the number. A figure without its method cannot be checked, and an unchecked figure is how this community accumulates folklore.

That is the short version; the long version is somebody else's post.