INCUMBENCY, NATIONAL CONDITIONS, AND THE 2008 PRESIDENTIAL ELECTION

Extract

The October 2008 issue of PS published a symposium of presidential and congressional forecasts made in the summer leading up to the election. This article is an assessment of the accuracy of their models.

The Incumbency and National Conditions Model predicted that John McCain would receive 44.3% of the two-party presidential vote; he ended up with 46.6% (at this writing, November 13, 2008), yielding a prediction error of 2.4 points. This error is slightly smaller than the mean absolute value of the out-of-sample forecasts from 1952 to 2004 (2.68), so the 2008 election result is not anomalous in the context of this model. The addition to the model of the 2008 outcome does not generate many important changes to the coefficients, except that the significance of incumbency interaction went from 0.08 to 0.02 and the standard error and adjusted R² of the model both indicate a slight improvement in fit.