As we reach the halfway mark in primary season, PredictWise is pausing to take stock of our predictions so far and how effective the political markets have been in forecasting the winner. We've made calls at least a week in advance for 26 primary contests so far—every matchup, excluding territories and nontraditional matchups in Missouri and Wyoming. Our predictions, which are based on data from the gambling markets at Intrade and Betfair, were correct in 18 of those seven days before the election. At five days out, the odds rose to 21 in 26. Interestingly, they were equally accurate one day ahead of time.
It's easy to assume that the reason we—or anyone else—got some of those predictions incorrect is that our methods are flawed. But one of the principal lessons of this campaign cycle, so far, is that in fact elections are subject to the fall of the dice, and that no model for predicting them can ever be correct in every instance. In other words, we don't want to be right all of the time. That is why we attach likelihoods to all of our forecasts. When we say Rick Santorum has a 50 percent likelihood of winning a state, we literally mean he will win every other time. When we say 20 percent likelihood, we mean it will happen 1 out of 5 times.