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Why people prefer inaccurate forecasts of the U.S. Presidential Election

There are at least seven ways to forecast political elections. The most popular among the public is polling of likely voters. As it happens, polls are the least accurate method to predict election outcomes. We could combine all of the many polls to improve accuracy, but that brings the polls only up to a tie with econometric models as the least accurate method.

The solution is PollyVote.com. Launched in 2003, PollyVote conducts real time forecasts to demonstrate simple well-tested methods designed to improve forecast accuracy in virtually any area. PollyVote uses the powerful method of combining forecasts. In the case of the polls, combining can be used within a method, which typically reduces forecast error by one-eighth. But it is most powerful when combining across methods. When there are many methods, such as six methods used for U.S. presidential elections, forecast errors .

The benefits of combining have been known for over a century, and the evidence has mounted over time. However, it is resisted by governments and corporations.

So why is the combining method resisted and why do people choose less accurate methods?

One reason is that combining seems counterintuitive. Intelligent people think that if you combine forecasts you get only average accuracy, so they attempt to pick what they believe to be the best method. However, the result of combining is never worse than the typical error, which means there is little risk in using it. Thus, New York City would have saved money in January 2015 by —they used the least accurate forecast.

Because forecasts from different methods often bracket the true value, combining is more accurate than the typical forecast. Most surprising, combined forecasts are sometimes more accurate than the best component forecast.

Another reason is that forecast many people who commission or use forecasts are not interested in accuracy. They want forecasts that support a decision that they want to make or an outcome that they prefer. In the case of political election forecasts, voters are looking for hope and entertainment. They get this from individual polls. On this basis, the PollyVote is boring. Polly’s forecast is stable and has very little error, as you can see from the . She has been correct about who would win for each of the last 100 days of the last six U.S. Presidential elections.

J. Scott Armstrong, Professor
The Wharton School, JMHH 747
U. of Pennsylvania, Phila., PA 19104
Home Phone 610-622-6480
homepage:

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