Here’s how to predict the outcome of the presidential election

By Ezra Klein, The Washington Post
Posted April 24, 2012, at 6:04 a.m.

“To see what’s in front of one’s nose requires a constant struggle,” George Orwell wrote. But the problem for those of us paying attention to the 2012 election is rather the opposite: To ignore what keeps being thrust in front of one’s face requires its own sort of struggle.

Here is a partial list of “scandals” that have grabbed hold of the news cycle in past weeks: “Rosengate,” in which a Democratic operative and CNN contributor named Hilary Rosen said something dismissive about Ann Romney’s work history; “Dog-gate,” in which conservatives pretended to be outraged that President Barack Obama, as a 7-year-old living in Indonesia, had been fed dog meat; and “Cookiegate,” in which Mitt Romney asked if cookies he was offered were from 7-Eleven and inadvertently insulted a local baker.

I could go on. But I won’t. It’s too depressing. The good news, however, is that the tornado of idiocy that seems to accompany modern presidential campaigns — remember “lipstick on a pig”? — doesn’t much matter.

Political scientists have long known that you can predict most of what will happen in a presidential election with just a few key pieces of information: how the economy does, for instance, and the incumbent’s approval ratings in the summer. If you have those two numbers — even before you know the opponent, the campaign strategies or the issues — you can usually call the winner.

What these models suggest, in other words, is that the ephemera of elections aren’t that important. Not that this stuff doesn’t matter at all: Elections are often close, and a few percentage points can mean the difference between defeat and victory. But these micro-scandals mostly serve to distract us from the things that really do matter. And I don’t want to spend the next seven months distracted.

So I asked three political scientists — Seth Hill of Yale, John Sides of George Washington University and Lynn Vavreck of UCLA — to help me create an election forecasting model. And when I say “help me,” I mean that they did all the work and then sat me down and explained, slowly and using small words, what they had done.

The model uses just three pieces of information that have been found to be particularly predictive: economic growth in the year of the election, as measured by the change in gross domestic product during the first three quarters; the president’s approval rating in June; and whether one of the candidates is the incumbent.

That may seem a bit thin. But it calls 12 of the past 16 elections right. The average error in its prediction of the two-party vote share is less than 3 percentage points.

Then I started playing with the model. And frankly, it just looked wrong. If GDP is flat — that is to say, if the economy doesn’t grow at all this year — and Obama’s approval rating is 45 percent, he wins 49 percent of the time. If you boost growth to a still-anemic 1.5 percentage points, he wins 74 percent of the time. That seems a little unlikely.

That, the political scientists said, is the point of a model such as this one.

“There’s this moment where you go, ‘Whoa, that’s a high number,’ ” Vavreck says. ” ‘Something must be wrong.’ But what it forces you to do is … to divorce yourself from contemporary context. You can’t go in thinking, ‘But, oh, this president is black,’ or ‘Gas prices are high,’ or ‘We just had the tea party.’ You have to strip all that away and say: ‘Incumbent parties, in growing economies, almost always win in contemporary American history.’ ”

She’s right. Since 1948, only three incumbent presidents have lost re-election campaigns: Gerald Ford, Jimmy Carter and George H.W. Bush. Carter and Bush both ran in very bad economies. Ford was a bit of an odd case, as he took office after Richard Nixon resigned over Watergate, and even so, the election was extremely close. This is the way models discipline your thinking: They force you to see relationships and patterns that conflict with your intuition.

The question is what happens when you add contemporary context back in. The model, for instance, assumes that voters will have the same reaction to slow economic growth in 2012 that they would have had in 1996 or 1964. But the past four years have seen the worst financial crisis since the Great Depression. Voters might be much less willing to forgive slow growth. Or, since many place the bulk of the blame for the crisis on George W. Bush, perhaps they’ll grade Obama on a kind of curve. The model can’t tell us.

And, sadly, neither can the past. Since 1948, there have been only 16 presidential elections. Which is another limit of models like this one: a relatively thin data set spread over a relatively long time. It would be nice to have more examples of presidential elections conducted during once-in-a-generation crises, in the Internet era, with serious third parties, with African American incumbents, with Mormon challengers, etc. And as Nate Silver, a statistician and blogger at the New York Times, points out, these models often do much worse when tested against new elections that are not in the original sample.

The three contests that the model was worst at calling were the 2008 race, where it predicted that Obama would get an additional 3.7 percentage points; the 1992 election, where it forecast that the elder Bush would win easily; and the 1972 election, where it foretold an even larger victory for Nixon. Perhaps race depressed Obama’s numbers, Ross Perot hurt Bush, and Nixon hurt Nixon. But those are just hypotheses. We have no way of knowing whether they’re right. We can’t rerun the elections under different conditions.

So sure, perhaps this year will be different — that’s what my gut tells me, and the model has me thinking about the ways in which that could be true. But the reality is, everyone always thinks “this year” will be different, and they’re usually wrong. That’s what the model tells me.

I am, however, confident that if this year really is different, it won’t be because of “Dog-gate.”

There’s no reason we should have all the fun. So we’ve opened the model for you to play around with at our Election Predictor. Put in your best guess for economic growth this year and Obama’s approval rating in June. Or rerun previous elections and see how the model performs. At the very least, it’ll be a nice distraction from, well, all the distractions. printed on July 22, 2014