General Election 2019 Stat Checks: Week One

Parliament has been dissolved, and the campaign formally starts.

This article looks at the various statistics and claims I have checked in the first formal week of campaigning for the 2019 General Election. A letter from Sir David Norgrove, chair of the UK Statistics Authority, was sent to all party leaders:

I would ask that statistical sources should be clear and accessible to all; any caveats or limitations in the statistics should be respected; and campaigns should not pick out single numbers that differ from the picture painted by the statistics as a whole.

5m Labour Leave voters?

Claim: 5m people voted Leave in 2016 and Labour in 2017.
Rating: Needs clarification.
Reasoning: Nigel Farage MEP, Brexit Party leader, has repeated his claim that 5m people voted Leave in 2016 and Labour in the 2017 General Election:

Those five million are the most vulnerable group of voters to the Brexit Party in this country.

Various survey estimates suggest this figure is less than four million. Moreover, not all of these voters will reside in Labour-held constituencies.

We can look at what estimated proportion of Labour voters in 2017 also voted Leave in 2016. In the British Election study face-to-face survey: about 30% of Labour voters backed Leave, or 3.9m voters. Sampling error means this…