Liberal Democrat Letters and House Effects

A letter from the leader of the Liberal Democrats claims the party is ahead of Labour in “many polls”.

This article examines this claim about opinion polling, and looks at house effects.

“Winning up and down”

As part of their leafleting campaign, Jo Swinson MP (East Dunbartonshire, Liberal Democrats) claimed that:

In many polls, we are now ahead of Jeremy Corbyn’s Labour Party.

Using the BBC’s poll tracker, we can look at published vote intention polls for general elections in Westminster.

As at 21st October 2019, the central estimate for Liberal Democrats is 18%. (Source: BBC)

In the 80 published polls with fieldwork ending between 1st June and 21st October 2019, covering either Great Britain or the United Kingdom:

• Eight estimated that the Liberal Democrats were ahead of Labour;
• Two showed ties in the vote intention share estimate;
• The remaining 70 polls estimated Labour were ahead.

All eight of the estimated Liberal Democrat leads and both ties were from YouGov polls. In this period, the largest estimated lead was four points.