By James Kwak
There’s been a minor controversy in the blogosphere not about whether Obama or Romney should be president, and not about whether Obama or Romney is ahead in the polls, but about the esoteric question of whether one should interpret the polls to mean that Obama is the favorite or that the race is a “tossup.” This debate has largely swirled around Nate Silver, who aggregates polling data, recalculates confidence intervals, and incorporates other factors (drawn from analysis of previous elections), and for the past few weeks has rated Obama as having about a 60–80% chance of winning the election. In response, various members of the pundit class have argued that the national polls show a tied race, polls can’t predict the future, or even that since both sides (supposedly) think each has a 50.1 percent chance of winning, their chances must be equal. (See Felix Salmon for a summary.)
Silver has responded to all of the coherent objections that might be made to his forecast, in detail. But what’s at work here isn’t a reasoned debate about how to interpret polls. It’s sheer innumeracy, pure and simple. The statement that Obama has about a 75–80 percent chance of winning is roughly equivalent to the statement—which no one contests—that his average lead in Ohio is about 2–3 points, once you take the confidence interval into account. As Silver has said, it’s analogous to the statement that a team that’s ahead by a field goal deep in the fourth quarter has a better chance of winning than the team that’s behind; no one would call that game a “tossup,” even though either team could win. Even if you can’t predict the next turnover or breakaway running play, that wouldn’t lead you to believe the three-point lead is irrelevant.
It’s the same thing we saw in Moneyball—people who can’t understand numbers claiming that numbers have no practical value. Unfortunately, in political journalism the sample size is so small and the monetary stakes are so low that the incoherent innumerates will never be drummed out of the marketplace.