[u320]

That gives us an upper bound but the real answer could be anything between that and harmless.

So I mean "we don't know" as in "we don't have the complete answer".

[TheRealPomax]

But that's not how that works? If there is no statistically significant effect, then whatever effect there might be is so small that it's part of the background noise: we have a complete enough answer to say "there is nothing that can be attributed to just this thing". And we can say that with certainty because of the statistics.