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Comment by marcosdumay | Hacker News Reader

> Yeah, but we shouldn't take absence of evidence as evidence of absence.

That's wrong. Yes, we should.

Each and every study that doesn't find evidence for what they are looking for is evidence for its absence.

That’s wrong. Only if the studies are powerful enough and are looking at the right stuff can you make any reasonable conclusions.

If the studies are powerful enough then that absolutely isn’t evidence of absence at all.

Evidence can be strong or weak. Every positive study result is evidence of presence, usually strong evidence. Every negative study result is evidence of absence, usually very weak evidence.

And yet, people can be extremely vigilant about a positive correlation when it doesn’t fit their personal agenda, going as far as questioning methodology in even the least pragmatic ways possible; or, become accepting of the absence of evidence as evidence of absence when weak/no correlation is convenient to their own biases.

I'd say it's very sensible to assume absence up front before there's convincing evidence of presence. Sure, personal biases influence our evidence thresholds a lot, and often people demand unfair rigor that cannot be practically met. But the opposite is also true - sometimes people will believe in presence with zero evidence if they like it enough. The latter is far, far more dangerous than the former.

It’s one thing to believe in presence with zero evidence, and another to _withhold_ judgment when there’s zero evidence. I think you may be conflating the two.

Then again, perhaps we are simply two different types of people. I don’t believe that a complex system can be expected to stay the same when you introduce a new factor into it, while you prefer to adjust much later when effects appear or when evidence achieves total infallibility up to the academic level. I am risk-averse, you like taking it; I’d rather prevent, you’d rather cure. Stating that the former is “far, far more dangerous” is just begging the question though.

That's not right, a negative study often still can give evidence that something is true, but it just didn't meet the p=.05 threshold.

p<=0.05 is so easy to achieve for actual positive results (just increase sample size) that I don't think it's productive to treat any result with p>0.05 as positive evidence for any purpose other than deciding to rerun the study with a bigger sample size.

That's not true at all, that's a weird generalization that's patently false.

Take things like even certain physics propositions (e.g. discovering new particles) -- can take billions of dollars building a new reactor and years of experiments to find a result.

Anything medical or psychological also can take this result. If a chemical reduces your iq by 5 points over 10 years, it might not be able to do a study that finds that result on an academic budget.

Absence in the results of whatever we measured for. Just take the sheer hybris of "junk DNA": We don't understand this, so it's probably junk.

Note that we didn't call it junk DNA until we learned a whole lot about how DNA works and formulated a theory in which junk DNA doesn't do anything for good reasons. In a way, lack of understanding prevented us from calling it junk DNA earlier.

Of course it's still possible for the theory to be wrong and the so-called junk DNA being actually important. It's only junk according to our classical, non-quantum and non-relativistic theory of junkiness.

> Note that we didn't call it junk DNA until we learned a whole lot about how DNA works and formulated a theory in which junk DNA doesn't do anything for good reasons. In a way, lack of understanding prevented us from calling it junk DNA earlier.

Thanks for noting that, you totally caught me since I actually don't even really remember the stuff I read about that, which was probably false to begin with: https://en.wikipedia.org/wiki/Junk_DNA#Junk_DNA_and_non-codi...

So upon further consideration, since I don't really know anything about the research of the impact of microplastics, I'll apologize for speaking of scientific hybris so flimsily, that was really the hybris of the layman (me).

I'm still skeptical, not of science but of the harmlessness of microplastics. Not because of any evidence I have, but because it's just so us... this cycle of putting something everywhere before we even know it exists, finding out it exists, going "nahhh it's probably fine" for years, decades or centuries, and then "oh shit". Which I'll admit is not scientific and not really a useful contribution to this conversation, either :P

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