Dr.ReproEndo said:

Most of what circulates confidently in this community traces back to one summary of one study, and the qualifier was dropped somewhere in the third…

Filing a mild objection. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. Pushing back on the anecdote-stacking. Twenty people reporting the same thing is twenty samples from the same self-selected pool, not twenty independent confirmations.

Adding the numbers, since they settle part of this. One habit that pays for itself: post the method alongside the number. A figure without its method cannot be checked, and an unchecked figure is how this community accumulates folklore.

FDA_TrackerJim said:

Twenty people reporting the same thing is twenty samples from the same self-selected pool, not twenty independent confirmations.

Coming at FDA_TrackerJim’s question from a different direction. 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.

Following on from COA_Karl — and this may be the naive question:

What would you measure differently if you were starting again?

OP back with an update, since a thread like this is useless without one.

Update: the thing I was blaming turned out not to be the cause. Leaving the original post as written rather than editing it, so the mistake stays visible for whoever searches this next.