Intrade and the Dow Drop

With today’s snapback, the Dow lost 777 and regained 485.

As of this evening, Intrade says the probability of a bailout bill passing by Oct 31st is 85%.

(777-485)/​(1-.85) = 1,946. So a bailout bill makes an expected difference of 2000 points on the Dow.

Of course this is a bogus calculation, but it’s an interesting one. Not overwhelmingly on-topic for OB, but it involves prediction markets and I didn’t see anyone else pointing it out. I hope the bailout fails decisively, so this calculation can be tested.

PS: Bryan Caplan understands Bayes’s Rule: It’s not possible for both A and ~A to be evidence in favor of B. So which of the two possibilities, “unemployment stays under 8% following a bailout” and “unemployment goes over 8% following a bailout”, is evidence for the proposition “the bailout was necessary to prevent economic catastrophe”, and which is evidence against? Take your stand now; afterward is too late for us to trust your reasoning.