Ipsos political polling methodology in Scotland

Ipsos’s current political polling design in Scotland is based upon a telephone quota sample, using both landline telephone numbers (generated by random digit dialling) and mobile numbers (a mix of random digit dialling and targeted sample from a range of sources for some hard-to-reach groups), weighted to demographic population totals, aimed at achieving a representative sample of all Scotland residents aged 16+.

For Westminster General Election voting intention, a two-part question is used with prompting on major parties (Conservatives, Labour, Liberal Democrats, Scottish National Party or another party – if a respondent says they would vote for another party we ask which party that would be) and a follow-up “squeeze” question of those who were undecided or refused to the first question. Only those aged 18 and above are asked the voting intention questions. A turnout filter is used based on two questions (current stated likelihood to vote and previous voting behaviour).

For Scottish Parliament voting intention, a similar two-part question is used for both constituency and regional list voting intention, with prompting on major parties (the list of parties prompted for differs for constituency and regional list, as not all parties stand candidates on both) and a follow-up “squeeze” question of those who were undecided or refused to the first question. All those aged 16+ are asked the voting intention questions. A turnout filter is used based on two questions (current stated likelihood to vote and previous voting behaviour).

For independence referendum voting intention, a single question is asked to all those aged 16+, with the same wording as was used in the 2014 independence referendum. A turnout filter is used based on current stated likelihood to vote in an immediate referendum about Scotland’s constitutional future.

Quotas are set on gender, age, Scottish Parliament region, whether working full time and educational qualifications. Data are weighted to match demographic population targets from reliable sources (National Records of Scotland population estimates, Scottish Household Survey). Data are not weighted by how respondents tell us they voted at the most recent General Election or Scottish Parliament election, or in the 2014 independence referendum or 2016 EU referendum.

These demographic weights are applied simultaneously by rim weighting. Data are weighted by age within gender, work status within gender, Scottish Parliament region, social grade, work sector (public sector/other), housing tenure, educational qualifications and country of birth (Scotland/other).

Turnout correction: election voting intention

Respondents are included in the final totals if

1. They say they are at least 9 out of 10 certain to vote, and
2. Say that they “always” or “usually” vote in general elections (for General Election voting intention)/ Scottish Parliament elections (for Scottish Parliament voting intention) or that “it depends”.

In the final prediction poll of an election campaign, this is supplemented by including those who say they have already voted by post, and excluding those who say they are not registered to vote.

Remember that all polls are subject to a wide range of potential sources of error. On the basis of the historical record of the polls at recent general elections, there is a 9 in 10 chance that the true value of a party’s support lies within 4 points of the estimates provided by an individual poll, and a 2 in 3 chance that they lie within 2 points. This is especially important to keep in mind when calculating party lead figures.

We continually review our methods and may make further refinements and changes to our methodology in the future.

Article Updated 2024