>But within the context of Bayes rule, the modeler must have made an
>assessment of P(B | A) where A = "tooth fairy exists" and B = "I am thinking
>about the tooth fairy." This is a 2x2 matrix of values. That assessment
>requires the modeler to consider not only the probability that he would be
>thinking about the tooth fairy when the tooth fairy exists, P(B=T|A=T), but
>to also consider the probability of not thinking about the tooth fairy when
>the tooth fairy exists, P(B=F|A=T), or why p(B=T|A= T) is less than one.
>In addition the assessment requires thinking about the tooth fairy when the
>tooth fairy doesn't exists P(B=T!A=F) . And that requires the modeler to
>consider all the other possible causes. He doesn't have to make the other
>causes an explicit part of his model. They are in there implicitly and the
>use of Bayes rule requires that they be part of the calculation. The values
>of the terms in the likelihood matrix p(B | A) are not implicit assumptions.
>The modeler is required to make an assessment. This is not a closed world
>modeling environment.
Remember that the starting point for this was the modeler's seemingly
innocent assumption that the tooth fairy would predispose people think
about the tooth fairy more than they would otherwise do, i.e. P(B|A) >
P(B|~A). So, I agree; the modeler's disregard for other hypotheses is
coded directly into the model. I see all of this as supporting my claim
that the tooth fairy believer is not making a scientific assessment.
--
Ron Parr email: [EMAIL PROTECTED]
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Home Page: http://robotics.stanford.edu/~parr
