"The reason for this is that pundits (the better ones, anyway) don’t just predict election outcomes, they also tell you how confident they are in each of their predictions. For example, Silver gave Obama a 50.3% chance of winning in Florida. That’s pretty damn close to 50/50 or “even odds.” So if Romney had won Florida, Silver would have been wrong, but only a little wrong. In contrast, Silver’s forecast was 92% confident that Rick Berg would win a Senate seat in North Dakota, but Berg lost. For that prediction, Silver was a lot wrong. Still, predictions with 92% confidence should be wrong 8% of the time (otherwise, that 92% confidence is underconfident), and Silver made a lot of correct predictions. So how can we tell who did best? We need a method that accounts not just for the predicted outcomes, but also for the confidence of each prediction. There are many ways you can score predictions to reward accuracy and punish arrogance, but most of them are gameable, for example by overstating one’s true beliefs. The methods which aren’t cheatable — where you score best if you are honest — are all called “proper scoring rules.” One of the most common proper scoring rules is the Brier score. A Brier score is simply a number between 0 and 1, and as with golf, a lower score is better."
http://rationality.org/2012/11/09/was-nate-silver-the-most-a...
"Also note that Wang & Ferguson got a better Brier score than Silver despite getting Florida (barely) wrong while Silver got Florida right. The Atlantic Wire gave Wang & Ferguson only a “Silver Star” for this reason, but our more detailed analysis shows that Wang & Ferguson probably should have gotten a “Gold Star.”"