Vote Intention Poll Performance: General Election 2019

How accurate were the pre-election polls?

In the 2015 General Election, there was a systemic polling error which caused a large underestimation of the Conservative lead. In 2017, there was a wide spread of vote intentions — but, on average, underestimated Labour’s vote share by about five points.

This article looks at the final pre-election polling performance for the 2019 General Election.

Final Polls

Among the ten polling companies which conducted polling throughout the election campaign, estimates of the Conservative lead ranged from five points (Savanta ComRes) to 12 points (Kantar and Opinium). The only methodological change from prior polling was YouGov using the headline vote intention from their MRP model, instead of their traditional method.

According to my calculations based on the BBC results, the actual Conservative lead over Labour in Great Britain was 11.7 points¹.

In Great Britain, the Conservative vote share was 44.7%, and Labour had 33.0% of votes cast. Overall, the average Conservative vote intention share was 43.3% (a difference of 1.4 points) and Labour was 33.9% (a difference of 0.9 points).

In order to measure the accuracy of different polls, we are interested in:

• Lead error: the difference of Conservative and Labour vote intention share estimates minus the actual Conservative lead in…