From probability theory of course! And you haven't specified what standards a belief has to meet before you "believe in them"
In that case, it's still a question of fact, on which reasonable people can disagree.
As for what standards need to be met before I believe in them, now that's an interesting question. My first instinct is to say that I don't know what the standards are, and it does not matter, because I have no control over whether I believe something or not. But this is probably not true.
--
Congratulations to SuperNiceDog, Guru Winner, who was smart enough to pick
your 7 time champion, Link.