Predictions and Confidence Values
When thinking of the increasing frequency with which pollsters fail to predict election outcomes (Modi in 2014, Kejriwal sweep of Delhi, Brexit, Trump), I’ve wondered whether the issue might be that no pollster wants to announce a radically -different-from-all-the-rest prediction. Does he feel it’s better to fail with the pack than to fail by being the outlier? If he fails with the pack, at least he can say, “Hey, nobody else got it either”. But is that what is really happening? Or is the problem that pollsters don’t bring out a fairly obvious point made by Elroy Dimson as part of their predictions: “Risk means more things can happen than will happen.” Put differently, it means that you can only assign probabilities to your predictions; almost nothing is a certainty. Since that’s obviously true, shouldn’t the pollster not just say that he believes that X will win, but also what his confidence in that prediction is? Nate Silver is a guy who has been assigning probabilitie...