October 24, 2012
Brooks vs. Silver: The Limits of Forecasting Elections
Posted by John Cassidy
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http://www.newyorker.com/online/blo...te-silver-prediction-polls.html#ixzz2AiZDNYe6
As op-ed columnists often do, Brooks overstates his case. Up to a point, political outcomes are predictable. Sitting here today, I can forecast with certainty that neither candidate will win the popular vote by more than ten percentage points. History and common sense tells us this. Indeed, based on the opinion polls, I can predict with a good deal of confidence that neither candidate will win by more than five points. Voting patterns aren’t completely random. They reflect history, demography, sociology, economics—fundamental relationships exist that statisticians can, in principle, attempt to capture and turn into mathematical equations.
Unfortunately for forecasters, people aren’t interested in rough predictions, such as “it’s going to be close.” Especially in a tight contest, such as this year’s, they want to know who is going to win. And when it comes to answering this question, voting models based on fundamental factors don’t work very well. Years ago, I got interested in the work of Ray Fair, a Yale economist who pioneered the development of forecasting elections based upon a few simple economic statistics, such as G.D.P. growth, inflation, and unemployment. Fair’s record is mixed. He’s called most elections correctly, but he’s also got some wrong, notably 1992, when he predicted a Republican victory, and 2000, when he said that the Democrats would win. (In 2000, to give Fair his due, he correctly predicted that the Democrats would win the popular vote, which they did. But Al Gore lost the election in the electoral college.)
According to one expert who has looked closely at the record, “The ‘fundamentals’ models, in fact, have had almost no predictive power at all. Over this 16-year period, there has been no relationship between the vote they forecast for the incumbent candidate and how well he actually did—even though some of them claimed to explain as much as 90 percent of voting results.” The expert who wrote these words was Silver. If you want to learn about why most political predictions turn out to be wrong, I thoroughly recommend some of the posts he has written on the subject. And if you’ve got time, you should also consider reading his new book—“The Signal and the Noise: Why So Many Predictions Fail But Some Don’t,” which is largely devoted to the limits of forecasting in areas such as sports, finance, and business—as well as politics.
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http://www.newyorker.com/online/blo...te-silver-prediction-polls.html#ixzz2AiZ3nTDK