Dr.LeslieOBGYN said:

If two explanations both fit, the useful question is which one predicts something the other does not.

Adding the part of the answer the thread has not reached. 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.

One concrete data point for the thread. Give anything pharmacological four weeks before you judge it, and give anything measured weekly a four-point rolling average before you call it a trend.

Ask again with the specifics and you will get a better answer than this one.

A narrower follow-up, since the general answer is now clear:

Why calcitonin screening is not recommended when the label carries a thyroid warning, because those two facts look contradictory from the outside?

VendorMark said:

Give anything pharmacological four weeks before you judge it, and give anything measured weekly a four-point rolling average before you call it a…

This is where I part company with the consensus forming above. The counter-case has not been addressed. Somebody upthread described the situation that does not fit, and the thread moved on rather than engaging with it, which is the failure mode this board is supposed to avoid.

Closing the loop on my own question.

For the archive: it took about six weeks rather than the two I expected, and the difference between those two numbers was the whole of my problem.