Campaigns and the prediction of election outcomes: Can historical and campaign-period prediction models be combined?

► There are two approaches to predicting election outcomes: a historical one and a campaign-oriented one. ► We look at whether these two approaches can be usefully combined. ► We test whether prediction errors in historical models are related to trends during the campaign. ► That possibility is tested using 17 elections in the US, UK and Canada. ► Results suggest that campaigns account for prediction errors only indirectly.