2019 Constituency Polls Accuracy

How accurate were constituency polls in the 2019 UK Election?

Anthony B. Masters

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Before the 2019 UK General Election, research companies conducted over 30 constituency polls.

This article seeks to understand the methods of constituency polling, and their accuracy. The analysis finds a decline in mean absolute error as the election approaches. This is in line with national polling.

Methods

The British Polling Council said 2019 was “more accurate” than any election since 2005. This was for national polling. This analysis will look at constituency polling.

A constituency poll must meet the following criteria:

  • Target population: The target population must be one constituency.
  • British Polling Council: The company must be a British Polling Council member.
  • Fieldwork date: The survey fieldwork end-date must be after 1st October 2019.

This analysis does not look at constituency projections from national polls. Nor does it include MRP estimates.

Deltapoll

Deltapoll collected its responses by telephone, from landline and mobile numbers. The company calibrated responses to the profile of adults (18+) in each constituency. The weights were for gender, age, ethnicity, ward, a 2017 past vote recall target, and the 2016 EU referendum.

Deltapoll calculate weight targets by averaging actual and recalled 2017 vote shares. EU referendum recall targets come from areal interpolation estimated calculated by Prof Hanretty. Intention share estimates use self-reported likelihood to vote is on a 11-point scale (0 to 10) as a factor. These vote intention estimates exclude those who say they are 0 out of 10. Headline estimates exclude undecided responses. The question is:

In the upcoming general election, the following parties are standing in your constituency. If the general election were tomorrow, which candidate would you vote for?

Survation

Survation collected telephone responses, from a mix of landline and mobile numbers. The company weighted responses by six targets. These were: age, sex, ward, 2017 Election vote, 2016 EU referendum vote, and 2019 EP vote.

Self-reported likelihood to vote on a 11-point scale was then used to weight…

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Anthony B. Masters

This blog looks at the use of statistics in Britain and beyond. It is written by RSS Statistical Ambassador and Chartered Statistician @anthonybmasters.