The Trial-Heat Forecast of the 2008 Presidential Vote: Performance and Value Considerations in an Open-Seat Election

Abstract

The trial-heat forecasting equation grew out of an examination of Gallup's trial-heat polls (“if the election were held today, who would you vote for?”) at various points in election years as predictors of the November vote (Campbell and Wink 1990). My co-author Ken Wink and I found, not surprisingly, that polls as literal forecasts were not very accurate until just before the election, that taking the historical relationship between the polls and votes into account through a bivariate regression significantly increased their accuracy, and that taking the contemporary context of the election as measured by economic growth in the election year into account increased their accuracy even further. Corroborating Lewis-Beck and Rice's earlier finding (Lewis-Beck 1985, 58), we found that an equation combining the Labor Day trial-heat poll standing of the in-party candidate and the second-quarter growth rate in the economy produced the most accurate forecast of the national two-party popular vote.