Pundits versus probabilities

The misguided backlash against Nate Silver

Who will win the presidential election next Tuesday? Until recently, the market for analysis of questions like these has been dominated by mainstream political reporters and commentators. Their style leans heavily on qualitative impressions and hazy narratives. But as the audience for quantitative analysis of politics has grown, the establishment analysts have become increasingly defensive about their status.

The most well-known quantitative analyst of politics is Nate Silver, whose FiveThirtyEight blog now appears on the New York Times website. Even though his black box statistical models have not been publicly disclosed or scientifically validated, Silver’s analyses have acquired a talismanic quality among political junkies, particularly with nervous liberals who are reassured by his forecast of a likely Obama victory (current estimate: 72.9 percent).

Unfortunately, Silver has become the target of a vitriolic backlash from innumerate pundits whose market dominance is under threat as well as ill-informed conservative commentators who think Silver is somehow skewing the polls for partisan reasons.

The problem with these objections is best summarized by Elspeth Reeve’s headline at The Atlantic Wire: “People Who Can’t Do Math Are So Mad At Nate Silver”. Most amusingly, on PBS David Brooks said forecasting the expected outcome based on polls makes you some sort of “wizard”:

Because, if you tell me you think you can quantify an event that is about to happen that you don’t expect, like the 47 percent comment or a debate performance, I think you think you are a wizard. That’s not possible. The pollsters tell us what’s happening now. When they start projecting, they’re getting into silly land.

In his piece on the controversy, Politico’s Dylan Byers took the jeremiad against the laws of probability even further, suggesting that Silver would be discredited if Romney won:

So should Mitt Romney win on Nov. 6, it’s difficult to see how people can continue to put faith in the predictions of someone who has never given that candidate anything higher than a 41 percent chance of winning (way back on June 2) and—one week from the election—gives him a one-in-four chance, even as the polls have him almost neck-and-neck with the incumbent.

But as The Weekly Standard’s Jonathan Last pointed out, Silver’s estimate doesn’t mean that there is no chance Romney will win: “a .250 hitter [in baseball] gets on base once a game, so you’d never look at him in any given at bat and think there was no chance he’d get a hit.”

Ultimately, however, the debate over both Silver himself and the specifics of his model misses the point. The best available evidence from both statistical forecasting models and betting markets suggests that Obama remains the favorite in the election. These charts below, for instance, present the estimated probabilities of an Obama victory and current Electoral College forecasts (where available) from the political scientists Jay DeSart and Tom Holbrook, Stanford’s Simon Jackman, Emory’s Drew Linzer, Silver, Princeton’s Sam Wang, the British sports book Betfair, and the Intrade futures market (here and here):

The FiveThirtyEight forecast is not an outlier. Silver’s estimates are generally somewhat more conservative than the other statistical forecasting models and only moderately more confident in an Obama victory than the betting markets. Whatever objection pundits or conservatives may have is with the state of the publicly available evidence or the way in which forecasters and bettors translate that evidence into probabilities, not with Silver or his methods.

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Brendan Nyhan is an assistant professor of government at Dartmouth College. He blogs at brendan-nyhan.com and tweets @BrendanNyhan.