Moderator note: good thread. Keeping it here rather than moving it, because the question is general enough to be useful.

SarahChen_PharmD said:

The distinction that resolves most of these threads is between what is true on average and what is true for one person.

Coming at SarahChen_PharmD’s question from a different direction. The useful move here is to separate what is established from what is widely repeated. Those two sets overlap less than the confident tone of most write-ups suggests, and the second set is where nearly all the disagreement on this board comes from.

One concrete data point for the thread. 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 same conditions. Nobody wants that answer and it is still the answer.

Happy to go further on any of that.

One thing that is still open after SarahChen_PharmD’s answer:

How would you tell the difference between that and the alternative explanation?

bri_stats 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…

This is where I part company with the consensus forming above. Filing an objection on the n=1 problem. Personal experience is genuine evidence about one person and very weak evidence about anybody else, and this thread keeps promoting the first into the second.