A Methodological Summary of 2019 Election Polls

This is how each polling company estimates vote intentions.

In order to assist public understanding of opinion polling in the 2019 General Election, this article will outline the basic method undertaken by the companies. This article is based on their public methods and data tables.

Survey mode, target population, weightings, turnout model, and vote intention questions are shown for each company.

The Common Method

Polling companies generally use either opt-in internet panels or computer-assisted telephone interviews. For internet panels, the respondent administers the questionnaire themselves, ticking boxes or clicking radio buttons. For telephone interviews, an interviewer asks the survey questions and responses are recorded.

Across both types of polls, demographic population totals — such as ONS estimates of the numbers of men and women — are used to set quota targets. A minimum sample size is specified, usually based on price and time. If a poll of 1,600 adults requires 790 men and 810 women, the survey continues until these quotas are ‘filled’.

Once the sample is gathered, weights are applied. Typical weights are for age, gender, and region.

All members of the sample are asked how likely they are to vote, and which party (or candidate) they intend to vote for. This is typically the first pair of questions asked in each vote…