The Bronze Medal

The Greens are unlikely to be third for vote intention share.

After two polls, there were claims the Greens are the “third largest political party”.

Surveys provide estimates, subject to many sources of potential error. A difference of one point between parties could be due to sampling error alone.

The two polls

A headline on The London Economic website asserts:

Greens replace Lib Dems as UK’s third largest political party

The article on 12th October begins:

The Greens are now the third most popular party in the UK, new polling has found, as support for the Liberal Democrats dwindles.

YouGov interviewed 1,673 GB adults via their internet panel, on 6–7th October. The Times and its sister Sunday paper sponsors that polling series.

The central vote intention estimate was the Greens had 6% share. In this survey, the Liberal Democrats had a share of 5%.

Later YouGov polls did not estimate the Greens ahead of the Liberal Democrats.

There were similar claims after a poll from Number Cruncher Politics. The online polls were for ITV’s Peston, of 2,088 UK adults on 9-17th October. Again, the survey estimated vote intentions of the Greens at 6%. The Liberal Democrat point estimate was 5%.

That Number Cruncher Politics poll led to similar claims on Twitter:

Errors and estimates

Up to 26th October 2020, those surveys are the only two polls estimating the Greens were third.

Polling is an imperfect instrument. Surveys provides estimates, subject to many sources of potential error.

There can be sampling error. This is the cost of not asking everyone. Beyond sampling error, there could be:

1. Specification error (validity): the question is not measuring what the researcher intended.