The Twilight of the Polls? A Review of Trends in Polling Accuracy and the Causes of Polling Misses

Polls have had a number of high-profile misses in recent elections. We review the current polling environment, the performance of polls in a historical context, the mechanisms of polling error, and the causes of several recent misses in Britain and the US. Contrary to conventional wisdom, polling errors have been constant over time, although the level of error has always been substantially beyond that implied by stated margins of error. Generally, there is little evidence that voters lying about their vote intention (so-called ‘shy’ voters) is a substantial cause of polling error. Instead, polling errors have most commonly resulted from problems with representative samples and weighting, undecided voters breaking in one direction, and to a lesser extent late swings and turnout models. We conclude with a discussion of future directions for polling both in terms of fixing the problems identified and new approaches to understanding public opinion.