Making sense of the predictions

I absolutely agree that Sam Wang and the Princeton Election Consortium have a good argument for there being a 99+% chance of Clinton winning. Unfortunately, I think there’s only about a 50% chance of his argument being right. It could also be that Nate Silver is right, that there is a 65% chance. Putting that all together, I come down right about where the NY Times is, at about an 85% chance of escaping apocalypse.

I’ve written a bit more about how I think about the likelihoods here. But a fundamental problem with the PEC estimate is that it clearly puts very little weight on the possibility of model failure. A fundamental problem with the 538 estimates is that they are very clearly not martingales. That is, they are not consistent predictions of the future based on all available information. One way of saying this is to note that a few weeks ago Clinton had close to a 90% estimated victory probability. Now it’s 65%. That seems like a modest change, but if the first estimate was correct, the current estimate reflects an event that had less than a 1 in 3 chance of happening. So we’re more than halfway there. But does anyone really think that the events of the past month have been that unlikely?