[extropy-chat] Bayes, crackpots and psi

[Hal Finney]

Michael Kinsley's column this weekend had a tongue in cheek comment
about the nature of disagreement:

: Like you, I'm sure, I try to be a good sport about the inexplicable
: fact that other people sometimes disagree with me. What other choice is
: there? The nonsense that other people think is often amazing and always
: disappointing -- but at this late date it's not really surprising,
: is it? And other people are disappointing in so many ways. What's one
: more? For all I know, you yourself may even disagree with me about this
: or that, and I may disagree with you about the other. It's everywhere.
:
: And other people are so stubborn! Possibly unlike you, I actually get
: paid to try to convince people that I am right and they are wrong,
: and thank goodness I'm not paid on the basis of results. It's almost
: enough to make you consider the possibility that other people are right
: and you are wrong. Merely considering this possibility is therapeutic,
: if you don't make a habit of it.

The analysis Damien posted of disagreement about psi on the basis
of Bayesian reasoning is OK as far as it goes, but it stops with the
assumption that people have different priors.  Where did those priors
come from?  Robin Hanson argues that we shouldn't assume people are born
with different priors: we are all descendents of a common ancestor and in
that sense we all have the same priors, with our different paths through
time and evolution being mere information added to that original set of
prior beliefs.

We see here a good example of apparent sharp disagreement, between
Damien and Eliezer for example; two people who probably respect each
other and see each other as making a good faith attempt at being rational
in their beliefs.  How can they disagree?  Doesn't Damien's deep study
of the issues lend credibility to his relatively favorable assessment?
And yet doesn't Eliezer's reputation for careful reasoning give credit
to his own skepticism?  Like the irresistable force meeting the immovable
object, it's a paradox.  It can't happen.  One side or the other finally
has to say, you're being irrational (or at least think it; they may be
too polite to say it out loud).

Another possibility is that they don't really disagree as much as
they seem to.  It could be that if they were forced to come up with a
percentage estimate for the probability that psychic powers exist, they
wouldn't be that far off.  Maybe it is merely a matter of perspective,
the glass being half full or half empty.  So I'd be interested to
hear estimates of the probability, from those who are willing to make
a serious, unbiased and rational analysis based on the information
available to them, including (of course) knowledge of other people's
opinions on the subject.

Hal