Net, not individual, movements
In a Twitter post shared over a thousand times, a user stated:
In approximate terms Labour lost 2 million votes at the election to pro-Remain parties and 400,000 votes to pro-Brexit Parties.
Let us look at an illustrative election to show the problem with this reasoning. Imagine a prior election with three parties. 45% voted Blue, 40% chose Red, and 15% backed Green.
The same voters cast ballots again, but there is switching.
5% of the electorate voted Blue last time, but now voted Green. 5% went from Red to Blue. Also, Red and Green swapped 5% of voters in both directions.
Blue: 45 (=);
Red: 35 (-5);
Green: 20 (+5).
The net change between Red and Green was zero. Red lost voters to Blue.
We cannot draw inferences about switching by individual voters from the total votes for each party. We need surveys to understand how individual voters changed.
The latest YouGov Blumenau-Lauderdale model of vote intention was based on surveys from 5th — 11th December 2019. Here, 2017 Labour voters were estimated to defect at roughly even rates to the Conservatives and the Brexit Party (13%, in the ‘Leave’ bloc), and the Liberal Democrats, Greens and the Scottish National Party (12%, in the ‘Remain’ bloc).
Another example of the ecological fallacy at work in British politics is the belief that most Labour voters (in the 2017 General Election) backed Leave in the 2016 EU referendum.
Lord John Mann, formerly the Labour MP for Bassetlaw, claimed:
Most Labour Party members are middle-class Remainers. Most Labour voters are working-class Leavers.
This is untrue. Most Labour voters, in both 2015 and 2017, backed Remain in the 2016 EU referendum.
If a constituency elects a Labour MP and was estimated to vote Leave, it does not follow that most Labour voters in that seat also voted Leave.
There are other voters in that constituency. Disproportionately, it was the Conservative and UKIP voters in those constituencies that backed Leave. As an analysis of YouGov data on behalf of Best for Britain found:
However, the research suggested there were “only a handful” of seats where more Labour voters backed leave than remain, and that many of these would support the party at a general election irrespective of its position on Brexit.
Not everything is a fallacy
It is important to remember that constituency-level associations can provide indications of individual movements.
As John Burn-Murdoch (Financial Times) highlights, there is a reduced association between the type of jobs in constituencies and the difference between Labour and Conservative vote share:
This is reflective of the reduced importance of social grade in vote choice.
People seeking to understand election results should be aware of the ecological fallacy. The siren call of seemingly clear conclusions muffles more complicated electoral rhythms.