Electoral Forecasting from Poll Data: The British Case

Abstract

Forecasting elections has long been regarded by political scientists as an interesting problem in its own right. But it assumes special importance for those countries that do not have fixed election dates. In Britain, for example, it is up to the prime minister to choose the date, within the statutory five year limit. Correct timing can clearly be crucial to the outcome, and the prime minister can be expected to go to considerable lengths to ensure that the election is called for the date most favourable to his party. But there lies the prime minister's problem: elections must be called three to four weeks before polling day. With what degree of accuracy can the result be forecast at the time the election is called? A small but interesting literature on election forecasting has emerged in recent years. The forecasting techniques used in this literature vary widely, from crude extrapolation to sophisticated model building. Up to now the emphasis has been on election night forecasting, in which the basic problem involves extracting the maximum amount of information from electoral returns, in order to forecast the outcome a few hours before it is finally known. For obvious reasons the techniques utilized in this context are of little use prior to election day.