[FoRK] Black Belt Bayesian vs. Authority, Fight!
<il.young.son at gmail.com> on
Thu Aug 9 11:21:22 PDT 2007
or you can get a free scan here:
e.t. jaynes is indeed one of the most lucid proponent of bayesian
logic. one can always make the case that even frequentists use priors
On 8/9/07, Matt Jensen <mattj at newsblip.com> wrote:
> Speaking of Bayesian statistics, run, don't walk, over to Amazon
> Canada. For some reason Jayne's monumental "Probability Theory : The
> Logic of Science" is priced at $4 (versus $49 in U.S., $80 list).
> Maybe that's why it's currently at #3 on the overall bestseller list!
> I just bought my copy...
> Matt Jensen
> Quoting Jeff Bone <jbone at place.org>:
> > BBB is quickly becoming one of my favorite blogs. This post from
> > earlier today is a perfect example, and a standalone gem. Anything
> > that begins with the lines "Tim is a famous geologist. Tom is a famous
> > clown." --- is a keeper. :-) (Despite the bit of naming confusion
> > that appears midway...)
> > Cf.
> > http://www.acceleratingfuture.com/steven/?p=33
> > --
> > (This post will be a more in-depth explanation of something I was
> > trying to get across in much of the Rapture of the Nerds essay.)
> > Tim is a famous geologist. Tom is a famous clown. Tim gives us a theory
> > about rocks. We judge it to be 90% probable. In a parallel universe,
> > Tom gives us the same theory about rocks. We judge it to be 10%
> > probable.
> > Jim gives us a theory about fish and presents a full technical case
> > that is good — the facts all fit. In a parallel universe, Jom gives
> > us a theory about fish and presents a full technical case that is
> > bad — it needs coincidences or leaps of logic. We judge Jim's theory
> > to be 90% probable. We judge Jom's theory to be 10% probable.
> > These two situations might seem the same. In the first case, we used
> > only indirect evidence — the theorist's credentials — to assess
> > probabilities. In the second case, we used only direct evidence —
> > the known facts of the matter — to assess probabilities. Both are
> > useful kinds of evidence. But there is an important difference.
> > Suppose we ask Tim and Tom to make a full technical case. Tim the
> > geologist gives us a full technical case that is, as expected, quite
> > good. Tom the clown, in his own parallel universe, gives us the
> > same full technical case — one much better than we expected from a
> > clown. Since a full technical case relies in no way on authority,
> > we put the same probabilities on Tim's claim and Tom's claim.
> > Anything else would be unreasonable.
> > Suppose we ask Jim and Jom about all of their credentials. It turns
> > out their credentials are exactly the same. Maybe they're both
> > equally famous clowns, who both took a course in marine biology once
> > — surprising in Jim's case, given that his arguments are so good.
> > Or maybe they're both famous marine biologists of exactly equal
> > fame and competence — surprising in Jom's case, given that his
> > arguments are so bad. None of this matters for our probabilities.
> > Again, we already have a full technical case, and a full technical
> > case relies in no way on authority. Jim's theory is still 90%
> > probable, Jom's theory still 10% probable.
> > So once we knew Tim and Tom's full technical arguments, their
> > credentials no longer mattered. But once we knew Jim and Jom's full
> > credentials, their technical arguments still mattered. Technical
> > arguments and credentials are useful types of information
> > individually, but when both types are available, one trumps the other.
> > If I'm not mistaken (but I need to read up on this!), what I've been
> > doing here is just repeating the definition of "screening off" from
> > the theory of causal diagrams. If we have three variables (A, B,
> > C), and A and C are independent conditional on the value of B, then
> > B screens off A from C, and A and C do not cause each other. In the
> > authority example of this post, you could see the causality running
> > as follows. If a theory is true, that causes the technical case for
> > it to be good. If people have good credentials, that causes them to
> > adopt theories for which the technical cases are good. But
> > causality does not run directly from truth to adoption by people
> > with good credentials, or from adoption by people with good
> > credentials to truth.
> > Maybe this all sounds like a complicated way to make a simple point,
> > but it matters, because people's intuitions sometimes get it all
> > wrong. If an idea is adopted by silly people, or is not adopted by
> > competent people, that is seen as a "bad point" that is weighed
> > against the "good point" of solid technical argumentation. But this
> > weighing makes no sense — to a rational thinker, the "bad point"
> > counts until the "good point" arrives, and is then annihilated. In
> > real life, everything interesting is a mix of things you'll always
> > have to take on authority and things you can check for yourself, but
> > you can still apply this insight.
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