From polls to votes to seats: Forecasting the 2015 British general election

This paper develops a three-stage method to forecast parliamentary election results from vote preferences in British opinion polls: (1) adjusting and aggregating vote-intentions from different polling organizations; (2) forecasting how public support for parties will change in the period before election day; and (3) translating, through simulations, the forecast of election day vote shares into seat totals while incorporating constituency-level information, including local vote-intention polls. Overall, this approach seeks to combine relevant national, regional and local information, and uncertainty about that information, to better reflect the fragmentation and diversity of political contexts found in the new era of five/six-party British politics.