Is this your prediction for the election?
No – this is not a prediction. It is our estimate of what the range of possible results would be if the election took place today and the voting intention was showing what it currently shows, based on our current data. It is not a prediction of where we will be on 4th July. We don’t know how things will change between now and polling day, but it would be surprising if things didn’t alter – one way or the other – before then.
Is this a poll?
No – it is a Multi-level Regression and Post-stratification (MRP) model that uses polling data. Polls aim to ask a representative sample of people a question and then show the results to that question, broken down by demographics. Our model uses a large sample of data collected from our panel to discover relationships between people’s characteristics and their answers to the voting intention question. It then combines these relationships/patterns with information about the characteristics of people living in different constituencies to construct estimates of how vote intention would look in each constituency, if we were able to do very large polls in every constituency. The sample sizes involved mean we speak to many different voters from many different places and across all constituencies in Great Britain.
What is the model and how does it work?
MRP (multi-level modelling and post-stratification) constituency projection models first estimate the relationship between a wide variety of characteristics about prospective voters and their opinions – in this case, which party they will vote for at the general election – in a ‘multilevel model’. It then uses data at the constituency level to predict the outcomes of seats based on the concentration of various different types of voters who live there, according to what the multilevel model says about their probability of voting for various parties (‘post-stratification’). The precise multilevel model equation has been benchmarked to correctly estimate the 2019 General Election to within a couple of seats of each party’s actual performance in that election, and the overall approach to MRP by YouGov has been used to successfully predict elections as recently as Spain in July 2023.
Have you assessed every local variable?
No, but we have used a very wide variety of variables that might capture different voting patterns. These include socio-demographic characteristics of individuals and the constituencies they live in, past vote choices of individuals and shares for various parties within each constituency, and information about the candidates standing for different parties. While we cannot reliably capture every factor specific to every single seats, but our large model sample sizes will help us get close to understanding how voters are behaving in different places up and down the country.
Who made the model?
The model has been designed and tested by members of the YouGov political team, headed by Dr Patrick English. The same team has recently successfully designed MRP model projections for the Spanish 2023 general election, the 2024 Catalonian parliament election, and battleground races across England in the 2023 and 2024 local authority elections. YouGov MRP models are written and fit with the open-source software Stan. Stan was developed at Columbia University by Andrew Gelman and his colleagues, with support from YouGov and other organisations.
Are you saying these numbers are exactly right?
Both the seat and voting intention estimates have uncertainty, as does any measurement using survey data. For each party in each seat, as well as the seat total for each party overall, we report ‘credible intervals’ which represent the range of data we believe the ‘true’ shares (and seat totals) have a 90% chance of lying within, The specific number presented for each party is the most likely value, which is typically very close to the middle of that range. So when assessing the data it is best to remember that both the seat and voting estimates for all parties projected could very well be higher, or lower, than this midpoint.
How have you accounted for turnout?
We estimate voter turnout probability from a range of sources, including voter demographics, previous patterns of turnout among different voter groups (from the British Election Study), and self-reported likelihood to turn out at this coming election
How many people have you polled in my constituency?
It varies from seat-to-seat, but a minimum of 35 in each constituency. Naturally, we cannot ask everyone in a constituency how they would vote, and a model cannot produce as accurate a result as a full-scale poll in each seat. However, the sample size in each constituency is not all that important given that the demographics of each constituency – based on census data – are what is actually used to map voter data into each constituency.
Why are you doing this?
Elections are becoming more difficult to assess and so, as well as running traditional polls, we are looking at new ways to meet the challenge. We know we run a risk publishing so much data in the heat of a campaign but as data scientists we are committed to innovating, to increase both accuracy and specificity. We hope that voters, campaigners, and the media are able to form an accurate picture of the current state of the election as a result and make the decisions that each of those groups make in a campaign based on more accurate information, rather than less accurate, information.
Why should I trust you over other research companies?
There are other seat-level estimates being published and reported on during this campaign. YouGov has the strongest track record of applying these methods successfully in US, Spanish, Australian, and UK elections. Nonetheless, we recognise that these methods are relatively new, and that each election can present new challenges. Methods which have worked well in the past may no longer do so. We are committed to constantly improving our methods and we make every effort to ensure that our work represents our best estimation of what the world thinks.
What impact will new boundaries have?
The 2024 election will be the first since the 2023 parliamentary boundary review, in which wholesale changes were made to the constituency map up and down the country. Only around 80 constituencies are left unchanged since 2019. This creates a modelling challenge for MRP, which relies on constituency-based information to work. Most importantly - party shares in each constituency at the previous election. While notional results have been produced by experts such as Colin Rallings and Michael Thrasher, no official data exists for how each party would have performed in 2019 if the constituencies used then were the same ones we will be using now. This is an important source of potential error for the model as it tries to accurately and best-reflect the shape of British electoral geography in 2024.
We acknowledge and appreciate the use of data sourced from Democracy Club, available at Democracy Club.
Specifically, our polling data by candidate name in our General Elections page is sourced from the platform provided at "Who Can I Vote For?."
