Are opinion polls biased towards leave?

Online polling is the most common way of gauging public opinion. But are people recruited to polling sites truly representative?

In this article for the LSE Brexit blog, Thiemo Fetzer investigates how the nature of online polling could be biasing opinion polls. Online surveys require members to sign up to the service and they are sometimes paid for taking part in a poll. He reveals how lack of regulation regarding who can participate, and the propensity of certain types of people to sign up to polling sites, can create an unrepresentative opinion pool.

He illustrates some of the technical issues that arise using the example of the British Election Study, which is an important point of reference for much UK political science research. The analysis suggests that repeat participation in the BES panel may systematically skew the implied Leave/ Remain split in favour of Leave. While there are many reasons behind this, the industry should increase transparency and develop access protocols for underlying micro-data. This could be a positive turn in industry self-regulation and spur innovation and development in the sector.

Read the research

Fetzer, Thiemo, Are opinion polls biased towards leave? LSE Brexit blog, 19th October, 2019

Find out more

Fetzer, Thiemo, Did Austerity Cause Brexit?, CAGE working paper no. 389, 2019

Eleonora Alabrese and Thiemo Fetzer, Who is Not voting for Brexit anymore?, CAGE working paper no. 394, 2019

Eleonora Alabrese, Sascha O. Becker, Thiemo Fetzer and Dennis Novy, Who Voted for Brexit? Individual and Regional Data Combined, CAGE working paper no. 384, 2018