Clinical perspective, offered as context rather than as advice. The version of this that has an answer is narrower than the version being asked. Narrow it and it becomes tractable; leave it broad and the thread will produce nine confident and incompatible replies.

DataDave said:

If you are going to change something, change one thing and give it long enough to express itself.

Thank you — that is the clearest version of this I have read, and I have read a lot of them. Sending this to two other people who asked me the same thing last week.

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.

SleepDoc_PDX 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…

This is my experience too, for whatever a second data point is worth. Posting only so the count is not one.

Moderator note: two posts asking for a source have been merged into one. Please search the thread before asking again. No action needed from anybody.