Polls and votes: The trial-heat presidential election forecasting model, certainty, and political campaigns

This article revises, updates, and examines the background for a highly accurate model for forecasting the national two-party popular vote in presidential elections. The model provides a vote prediction in early September based on Gallup trial-heat or presidential preference polls and the (nonannualized) rate of economic growth in the second quarter of the election year. It is estimated over the 12 presidential elections from 1948 to 1992. The mean absolute error of the model's out-of-sample postdictions is less than 11/3 percentage point, and its actual error in predicting the 1992 vote was about half a percentage point. The article also assesses the reasons for confidence in the model, as well as an approach to gauging uncertainty in any specific forecast. The reasons presidential elections can be forecast at or before the beginning of the general election campaign also are explored. Finally, the forecasting model is applied to the 1996 presidential campaign between Clinton and Dole.