Since the EU referendum result was announced there have been questions about how individual constituencies voted. Up until now people have been reliant on the constituency estimates produced by Dr Chris Hanretty. Today, however, the BBC published new data on the results of the EU referendum for 1,283 of the 9,291 wards across the UK. From this it is possible to determine how people voted in the referendum by constituency, and compare this data against Dr Hanretty’s widely used estimates.

Why don’t we already know the results by constituency?

The results of the EU referendum were published across the UK by ‘counting area’, which in most cases were local authorities with electoral registration responsibilities (single tier authorities and lower tier authorities in two tier areas). Local authorities weren’t ever required to publish the results by Parliamentary constituency or by ward (whether this is even feasible for any given local authority depends on the particular arrangements on the day). In most cases local authorities sub-divided their count process into a ‘mini-counting model’, effectively jumbling the results up and removing the possibility to get ward or constituency breakdowns.

However, not all local authorities did the count this way. Some, like Birmingham City Council, counted the vote and published the results by ward and Parliamentary constituency. Northern Ireland was one counting area, but also published the results of the referendum for each of its 18 constituencies.

But I’ve already seen voting figures for my constituency

Because of the lack of local results for the EU referendum, many commentators have used estimates published by Dr Chris Hanretty of the University of East Anglia when talking about constituencies. Dr Hanretty used a model to estimate the results of the EU referendum for Parliamentary constituencies in England, Wales and Scotland. The model was built by first examining the relationship between the demographic characteristics of local authorities and their referendum results, and then estimating what the results may have been within each constituency given its demographic characteristics.

The estimates produced by Dr Hanretty are therefore an indirect way of estimating what the results by constituency may have been. The actual results at constituency level may have been different from what Dr Hanretty’s model predicts, in that the relationship observed between demographics and voting patterns at the local authority level may not hold for individual constituencies.

What does the BBC data add to our knowledge?

The BBC asked all local authorities in charge of counting the result in their area for voting figures broken down by ward. Of the 1,283 wards the BBC were able to collect data for, 857 of these can be transformed into 107 Parliamentary constituencies (constituencies with results for all of their wards). The results of 82 of these constituencies were previously largely unknown/not reported on.

In total we now know the result of the EU referendum for 169 Parliamentary constituencies (just over a quarter of the 650 constituencies in the UK).

How do the known results compare with Dr Hanretty’s estimates?

The graph below shows the number of constituencies by the differences between Dr Hanretty’s estimates and the known results:

The differences appear to be fairly evenly spread; there were 60 constituencies with known results lower than what Dr Hanretty had estimated and 55 higher than what Dr Hanretty estimated.

For 36 constituencies Dr Hanretty estimated the true result with a difference of less than 0.0% (effectively estimating the correct figure).

On average, the known result for constituencies is 0.1% lower than what Dr Hanretty had estimated.

The largest divergence from what Dr Hanretty estimated and the known result was in the Birmingham constituency of Hall Green. Dr Hanretty has estimated that 43.3% of the electorate had voted ‘leave’, although only 33.6% actually did so (a difference of 9.7%).

24 constituencies had a difference of 3% or more from their estimated result and known result.

In total 6 constituencies had their result outcome swapped. 4 constituencies had been estimated by Dr Hanretty to have voted remain (although their known result indicates that they voted leave) and 2 constituencies had been estimated to have voted leave (but their known result shows that they voted remain).

Where can I find data on the EU referendum by constituency?

You can view what the EU referendum result was in your constituency in this look up table we’ve produced. It collates the estimates by Dr Hanretty, those published by the BBC, and other known results for Parliamentary constituencies: Estimates of constituency-level EU Referendum result (Excel 56 KB)

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Image: Verification underway, by Epping Forest District Council, licensed under CC 2.0