Confounding the commentators : how the 2010 exit poll got it (more or less) right

Curtice, John and Fisher, S and Kuhai, J; Fisher, Justin and Wlezien, Christopher, eds. (2011) Confounding the commentators : how the 2010 exit poll got it (more or less) right. In: The UK General Election of 2010. Routledge, London. ISBN 9781315868059

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An exit poll conducted on behalf of the three main UK broadcasting organizations for the 2010 general election predicted that the Liberal Democrats would win fewer seats than in 2005, a suggestion that was met with widespread disbelief amongst commentators. Not only did this forecast prove correct, but the poll’s prediction that the Conservatives would be the largest party in a hung parliament with 307 seats also proved to be spot on. This paper describes and evaluates the methodology of the poll. The key features were a focus on changes in party vote shares facilitated by conducting the poll in the same places as at the previous election, modelling of the variation in those estimated changes, and a probabilistic approach to identifying the likely outcome in seats. All three features contributed to the accuracy of the 2010 poll. The data provided a highly accurate estimate of the change in the Liberal Democrat vote. Meanwhile, a slight overestimation of the swing from Labour to the Conservatives was corrected by the modelling of changes in vote shares and the use of a probabilistic approach to seat prediction.