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

What would you measure differently if you were starting again?

VendorMark said:

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

Pushing back on VendorMark here. This treats a plausible mechanism as a demonstrated one. Plausible is where you start looking, not where you stop.

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

VendorMark said:

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

That is right for the common case. Whether it is right for the case being asked about depends on a detail that has not been given.

Old thread, but it comes up first when you search for this, so it is worth updating. 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.

Clinical perspective, offered as context rather than as advice. Worth answering the question that was asked rather than the one behind it. The narrow version usually has an answer; the broad version usually does not, and answering the broad one is how a thread stops being useful.