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Published online by Cambridge University Press: 08 January 2009
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.
On September 8, 2008, the Trial-heat Forecasting Model predicted that in-party candidate Senator John McCain would receive 52.7% of the national two-party popular presidential vote. The forecast of a victory of modest proportions for Senator McCain reflected his having a five-percentage-point lead over Senator Barack Obama in Gallup's early September, post-convention poll (49% to 44%) and the Bureau of Economic Analysis' August report of a 3.3% GDP growth rate in the second quarter of the year, about average for a second quarter election year economy.
1 Gallup's poll of registered voters is used throughout and in the estimation of the models. However, to check on the robustness of the forecast, I also examined RealClearPolitics' poll averages. The two series were substantively similar. Using the RealClearPolitics' poll average in the forecast models produced a forecast of 51.7% for McCain in the main model and 51.3% in the Convention Bump Model.
2 This is based on incomplete and unofficial returns as of November 19, 2008.
