From my understanding, the prior probability/distribution is assigned based on previous data/experiments. And the statistician would consult previous literature or talk with an expert in the field about this. And since none of this really exists in this case I haven't read much into this post. Jabba cannot convince me unless he shows me data!

This is the case sometimes. Priors can also be purely subjective, or just assume a state of ignorance.

Quick sum-up:

To apply Bayes theorem to the testing of an hypothesis you need three inputs:

P(H), the prior probability that the hypothesis (e.g., that reincarnation exists) is true

P(D|H), the probability of the observed data if the hypothesis were true

P(D|~H), the probability of the observed data if the hypothesis were false

It is

*sort of* acceptable to just make up a number for P(H); this is the subjective mode of Bayesian inference, where you report a posterior that is transparently contingent on a particular subjective specification of the prior probability.

However, scientists base the likelihood terms P(D|H) and P(D|~H) on actual empirical data and fitted statistical models. Jabba argues that P(D|~H), the probability of him existing, would be some

**small **number if reincarnation does not exist, and that's intuitively reasonable, but he has no actual empirical data or statistical model to put a number on

*how *small. Even worse, he has absolutely no way of putting

*any *kind of number on P(D|H), the probability that he would be here if reincarnation does exist. We have no idea of knowing what that probability would be without some detailed specification of how reincarnation might work, how many times people are reincarnated, etc. Without this input, we cannot calculate a posterior probability, and the whole exercise is doomed.

The net effect is that Jabba does not have appropriate inputs to solve this problem using Bayes theorem, even if he understood the theorem properly, which I'm not convinced of. I'm not interested in further back and forth about this with Jabba; there is simply no way that he can demonstrate what he wants to.