Re: Opinions as Evidence

Robin Hanson (
Wed, 26 Mar 1997 09:48:34 -0800 (PST)

Lee Daniel Crocker writes:
>> does this evidence lend support to one of these theories relative to
>> the others? If so, how much support? ...
>There are many complications here as well. What is the likelihood
>that /any/ theory of the set is correct? ...

This question is irrelevant to the question I posed.

>Doesn't this treat "evidence" as if it were a continuous quantity?
>As if it just piles up in front of each theory to give it weight (in
>fact, the very phrase "weight of evidence" assumes this). ...

Yes. Relative weight of evidence = log likelihood ratio, which adds.

These comments suggest to me that you are simply ignorant of the vast
literature on the relations between theory and evidence.

>and experience show us that not all evidence is created equal: one
>measurement outweighs 1000 expert opinions. If your mathematical
>model shows that generally taking seriously the opinions of others
>tends to reliably steer you toward theories supported by the most
>evidence, that is no use if the theory with centuries of history comes
>against a single experiment that not everyone has seen yet, but that
>inescapably discredits the majority.

Of course evidence varies in strength. If you happen to have
available a particularly strong peice of evidence which no one else
has yet seen, then of course this may outweigh all else. But what if
all those experts have seen this new experiment and their opinions
have not much changed. The question then is: how sure are you that
you have not missed or misunderstood some aspect of the experiment
that seems to you to offer such strong support?

>>... "paternalism" ... the experience of billions of parents, teachers,
>> employers, and local governments of thousands of years contains much
>> relevant information. Why do they continue in this practice if it is
>> worse than an obvious and widely tried alternative?
>They may keep practicing it out of fear, psychological predisposition,
>insufficient knowledge of available alternatives, incomplete
>understanding of the "evidence", predisposition to favor the status
>quo and ignore or deny its failures, and other reasons.

But you are just as likely to object to this common practice out of
fear, predispositions, etc. If anyone anywhere is actually looking at
relevant evidence with some understanding, why is it so much more
likely to be just you, rather than some influential fraction of these

>By your reasoning, nothing new and innovative would ever happen,
>because that /requires/ imagining that every other opinion on the
>planet might be wrong. Human progress depends on such precious

This is simply not true. Majority opinion can favor experimentation
and investigation into alternatives.

Robin D. Hanson