sean_dublin said:

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.

There is a second half to this that has not been said yet. Order of operations matters more than any single choice here: establish a baseline, change one thing, wait long enough for it to express itself, then measure again under the same conditions.

If somebody has the primary source to hand I would rather cite it than paraphrase it.

The figures, for anyone assembling their own picture. For anyone reading later: the numbers in this thread are worth checking against a primary source before you act on them, including mine. Half the figures circulating in this community trace back to a secondary summary that dropped a qualifier.

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

Was that from a primary source or from a summary of one?

jason_paloalto said:

For anyone reading later: the numbers in this thread are worth checking against a primary source before you act on them, including mine.

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.

jason_paloalto said:

For anyone reading later: the numbers in this thread are worth checking against a primary source before you act on them, including mine.

Agreeing with jason_paloalto, and the qualification matters more than the agreement. Yes, and the corollary is less popular: if the reasoning holds, it also holds where it produces an answer we do not like.