Election Forecasting in the United Kingdom: A Two-Step Model

摘要

Election forecasting in the United Kingdom has been experiencing a renaissance, as work travels from popularity function to vote function models. One strain of recent work stresses political economy explanations, while another stresses parsimonious prediction. Both approaches have their strengths, and are combined here in a two-step approach. First, a prediction equation is offered, based on a powerful empirical proxy variable for the election outcome itself. Second, an explanatory equation is offered, accounting theoretically for that proxy variable. This recursive system of equations is estimated, evaluated and found, by various diagnostics, to be extremely robust. Then, forecasts are rendered for multiple measures of UK election outcomes, in order to bring together the various measures that have appeared in the literature: government vote (and seats) share, opposition vote (and seats) share, government vote (and seats) lead. Finally, as a test, the model is applied to forecast the next UK general election under two scenarios. Using poll data from August 2007 and May 2009, we conclude that Gordon Brown missed a golden opportunity when he became leader of his party. While a snap election at that time would have led the sitting government to another victory, an election in the autumn of 2009 would result in the worst score for the Labour Party since 1992 and a return to the opposition benches.