YouGov conducts its public opinion surveys online using something called Active Sampling for the overwhelming majority of its commercial work, including all nationally and regionally representative research. The emphasis is always on the quality of the sample, rather than the quantity of respondents.
When using Active Sampling, restrictions are put in place to ensure that only the people contacted are allowed to participate. This means that all the respondents who complete YouGov surveys will have been selected by YouGov, from our panel of registered users, and only those who are selected from this panel are allowed to take part in the survey.
Over the last eighteen years, YouGov has carefully recruited a panel of over 1 million British adults to take part in our surveys. Panel members are recruited from a host of different sources, including via standard advertising, and strategic partnerships with a broad range of websites.
When a new panel member is recruited, a host of socio-demographic information is recorded. For nationally representative samples, YouGov draws a sub-sample of the panel that is representative of British adults in terms of age, gender, social class and education, and invites this sub-sample to complete a survey.
To reiterate, with Active Sampling only this sub-sample has access to the questionnaire via their username and password, and respondents can only ever answer each survey once.
Once the survey is complete, the final data are then statistically weighted to the national profile of all adults aged 18+ (including people without internet access). All reputable research agencies weight data as a fine-tuning measure and at YouGov we weight by age, gender, social class, region and level of education. For political work we also weight by how respondents voted at the previous election, how respondents voted at the EU referendum and their level of political interest. Targets for the weighted data are derived from four sources:
1. The census
2. Large scale random probability surveys, such as the Labour Force Survey, The National Readership survey and the British Election Study
3. The results of the 2017 general election and 2016 referendum.
4. Official ONS population estimates
Active Sampling ensures that the right people are invited in the right proportions. In combination with our statistical weighting, this ensures that our results are representative of the country as a whole. Not just those with internet access, but everyone. While it is true that not everyone does have access to the internet, independent academic research shows that its widespread uptake means the views of those with access to the internet and now mostly indistinguishable from those without.
Obtaining good-quality samples is a challenge for all methodologies. Response rates for telephone polls for example, have been declining in recent years - to typically below 10% - and often much lower in inner city areas. The ability to extrapolate from the under 10% of telephone respondents that pollsters can get hold of, to the 90% that they cannot, is clearly a challenge - leading to concerns over the quality of achieved samples, whether telephone or face-to-face. There are, of course, some areas where an online approach is inappropriate, and we would always alert our clients to this. However, it would be unfair to say that online is ‘biased’ in a way that offline is not. The fact is, there are different biases for which all approaches have to account.
For Scottish polls we additionally weight by country of birth and vote at the 2014 referendum on Independence. For polls of Greater London we additionally weight by ethnicity.
When we ask voting intention for Westminster elections we prompt people with the names of the Conservatives, Labour, Liberal Democrats, Brexit party, Greens, the SNP, Plaid Cymru or "some other party". People selecting some other party are then shown a second screen offering the choice of other smaller political parties or "other".
The selection of which parties we prompt for is based purely upon what past research and comparison with election results has produced the most accurate results; there is no formal criteria or level of support at which a party is prompted for. This is kept under regular review to reflect changes in the party system.
Respondents are asked to say how likely they are to vote on a scale of zero to ten and their answers to voting intention questions are additionally weighted based on their answer and whether they report having voted at previous elections.
In designing our methodology, for Westminster, regional and European elections, our priority is always what our experience and research leads us to believe will produce the most accurate results.
YouGov has a strong history of accurately predicting actual outcomes across a wide range of different subjects, including national and regional elections, political party leadership contests and even the results of ITV talent show The X Factor.
YouGov is also a founder member of the British Polling Council and we abide by its rules.
YouGov is also a corporate member of ESOMAR - you can view full details of the YouGov answers to the ESOMAR 28 questions
For additional information on YouGov’s methodology see the research Q&A’s