Reading the 2019 Election Polls

The 2019 General Election is likely to be one of the most difficult to estimate in recent history.

At the London School of Economics, its Department of Methodology hosted an event on how to read the opinion polls for the upcoming General Election.

Polling stations open at 7am on Thursday 12th December, and postal voters have already received their ballots.

The Context

Prof. Patrick Sturgis (LSE), who led the inquiry into the 2015 polling miss, began by recounting the differing natures of errors in polls in the past two general elections.

In 2015, the two main parties appeared tied. A systematic overestimation of Labour vote intention share — coupled with a similarly-sized underestimation of the Conservative share — meant the impression of a close race was given. All final published polls from British Polling Council members estimated ties or leads for either party of under two points.

In 2017, there was a wide spread of Conservative leads in the final polls, ranging from one point (with Survation’s telephone poll) to 13 points (BMG Research’s mixed-mode sample).

A similar set of polling companies are conducting surveys this time. (Image: British Polling Council)

Even though the polls correctly averaged on the Conservative lead, Labour were substantially…