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The current fashion for BT really bugs me. BT inverts conditional probabilities. If you can estimate P(E), P(H) and P(E|H) better than P(H|E) it will give you

by sago 11y ago

The current fashion for BT really bugs me. BT inverts conditional probabilities. If you can estimate P(E), P(H) and P(E|H) better than P(H|E) it will give you a better result. It is one of many probability identities. But someone it has become 'the one', as if, say P(H|E) = P(H&E)/P(E) isn't much use, but put two of those together: world changing. I've seen so much crap come out of this fad. My particular favourite is in theology. William Lane Craig has demonstrated that Jesus raised from the dead, to a high probability. Richard Carrier has shown that there was no historical Jesus. Funny how few people ever run BT and find it contradicts their views. I think part of the problem comes from a lack of understanding of the difference between frequentist and bayesian interpretations of probability. I've yet to see these folks show BT working in anything but frequentist data. And then they'll switch and use it to demonstrate why their Bayesian situation is correct.

logfromblammo 11y ago
Bayes does more than just invert the conditional. Of P(x), P(y), P(x|y), and P(y|x), if you know any three, then Bayes will give you the fourth. It's just an equation. Garbage inputs will yield garbage outputs. In the realm of theology, it is of no more use than Pascal's Wager as an expected value calculation. All the input values are made up, so the output value is equally fabricated. If you're using it on real, verifiable statistics, such as verified spam in an e-mail corpus, you can use Bayes to make a classifier to automatically identify spam to a high degree of accuracy. But if you are estimating for any of the three numbers you need to know, the fourth that you calculate will also be suspect.
rcthompson 11y ago
Of course two people can come to different conclusions based on a Bayesian analysis of the same question, if their priors are different. The benefit of Bayes' Theorem is to make explicit the dependency of the result on the prior.

by sago 11y ago

logfromblammo 11y ago

Bayes does more than just invert the conditional. Of P(x), P(y), P(x|y), and P(y|x), if you know any three, then Bayes will give you the fourth. It's just an equation. Garbage inputs will yield garbage outputs. In the realm of theology, it is of no more use than Pascal's Wager as an expected value calculation. All the input values are made up, so the output value is equally fabricated. If you're using it on real, verifiable statistics, such as verified spam in an e-mail corpus, you can use Bayes to make a classifier to automatically identify spam to a high degree of accuracy. But if you are estimating for any of the three numbers you need to know, the fourth that you calculate will also be suspect.

rcthompson 11y ago

Of course two people can come to different conclusions based on a Bayesian analysis of the same question, if their priors are different. The benefit of Bayes' Theorem is to make explicit the dependency of the result on the prior.