Bayesian Pop Quiz

From: Christian L. (
Date: Thu Aug 29 2002 - 14:54:02 MDT

Eliezer wrote:

>That's what the Bayesian Probability Theorem *is* - a *universal*
> >description of the way in which things can be evidence about other
> >things.

>It is not limited to any one domain. It is not limited to >deliberative or
>verbalizable thought.

>You must learn to see the BPT flowing underneath the surface of all
>cognition, like blood beneath skin.

Reading this, I looked up Bayes' theorem in my Probability Theory book, and
under the theorem itself, it was written: "Never has any theorem been
misused so much my so many".

I fail to see why anyone would hold this theorem so highly that he writes
poetry about it. In fact, I do not really think that you (Eli) really
understand the theorem. For instance, this example is given in my book on
elementary probability theory as a direct application of Bayes Th.:

In a land there lives two kinds of people: X and Y. Among the X:s, 80% are
tall. Among the Y:s, 1% are tall. The population in this country is 10% X:s
and 90% Y:s.

A tourist randomly meets a person, who happens to be tall. Use Bayes'
theorem to calculate the probability that this person is an X.

Can you (Eli) solve it? It ought not be a problem for someone who can "see
the BPT flowing underneath the surface of all cognition, like blood beneath



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