Adding the clinical framing, because it changes how the question reads. Whatever the answer turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, and invite the correction. That is slower than asserting, and it is the only version that survives being wrong.

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.

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

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

What did you change at the same time, and can you separate the two now?

BiostatsBrad 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. This treats a plausible mechanism as a demonstrated one. Plausible is where you start looking, not where you stop.

Moderator note: good thread. Keeping it here rather than moving it, because the question is general enough to be useful. Tagging this one for the weekly digest.