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homunq comments on What Can We Learn About Human Psychology from Christian Apologetics? - Less Wrong
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Sure, but it's utterly unsurprising that there exists a B such that P(A&B)<P(A). That there exists a B such that P(A&B) > P(A) is more surprising, which is why I'd asked for an example of what DanielLC had in mind by it.
Your probability theory here is flawed. The question is not about P(A&B), the probability that both are true, but about P(A|B), the probability that A is true given that B is true. If A is "has cancer" and B is "cancer test is positive", then we calculate P(A|B) as P(B|A)P(A)/P(B); that is, if there's a 1/1000 chance of cancer and and the test is right 99/100, then P(A|B) is .99.001/(.001.99+.999.01) which is about 1 in 10.
Can anyone explain why the parent was downvoted? I don't get it. I hope there's a better reason than the formatting fail.
I suppose, given the context, I should say out loud that it wasn't me, both because I don't find it downvoteworthy and because I make a practice of not downvoting comments that reply to mine or that I reply to.
I endorse not trying to read much into one or two downvotes... the voting behavior of arbitrarily selected individuals in a group like this doesn't necessarily mean much.
The way to fix the formatting is to use a \ in front of the asterisk whenever you want to actually display it. This is also necessary for underscores, which some people use in their usernames.
I didn't downvote it, and don't have interesting speculation as to why it was downvoted.
That's fair.