If #AE17 had been fought on the proposed new electoral boundaries

Unless there is a snap Assembly or Westminster election called within the next 18 months, this month’s Assembly Election will be the last Northern Ireland election to be fought under the existing 18 constituency map.

Under the Parliamentary Voting System and Constituencies Act of 2011, the number of Westminster constituencies will fall from 650 to 600, and as a result of this there will be a reduction in the number of Northern Ireland constituencies by one, from 18 to 17. An interactive map of the proposed new constituencies, with the ability to superimpose the existing constituency map, can be viewed on the spatialni.gov.uk website.

I built a model to try and work out what the results of the 2017 Assembly Election would have been if they had have been fought on the new boundaries. This is obviously a (very) inexact science. I apportioned the number of Sinn Féin and SDLP votes to each 2011 Census Ward by the estimated number of Catholic adults in each ward.

I extrapolated that there were 670,224 Catholic adults in Northern Ireland on election day, compared with 605,001 in 2011. Unionist parties and the Alliance Party have had their vote apportioned to wards on the basis of the non-Catholic vote in each ward. I appreciate that distributing Alliance votes in this way is dumb, and that treating the vote as nothing more than a sectarian headcount is depressing, but I couldn’t think of a better methodology.

Using this method, I estimated that the number of first preference votes for each party under the new 17 constituencies would have been as follows.

In a Westminster election, the DUP would expect to win eight of the new seats; West Antrim, Dalriada, Strangford, North Down, West Down, East Antrim, South Antrim and Belfast East. Unless they are assisted by a Unionist pact, the UUP don’t appear to be close enough to the DUP to win any of these.

Nationalists will win easily in Glenshane, North Tyrone, Newry and Armagh, South Down, Foyle and Belfast South West. Under present form Sinn Féin would win all of these, but the fact that Foyle and South Down have relatively unchanged boundaries might help the SDLP to cling on at a Westminster election.

The remaining three seats of Fermanagh and South Tyrone, Belfast North West, and Upper Bann and Blackwater are all Nationalist majority constituencies that could conceivably be won by a Unionist unity candidate. However, Sinn Féin would be the narrow favourite to win all of these, even against a Unionist unity candidate.

A Westminster election would expect to see the DUP winning eight seats and Nationalists winning nine, however with a Unionist pact and a reversion to the sort of turnout differential seen in 2016, it is possible that Unionists could win as many as eleven seats.

In terms of an Assembly election, the number of estimated quotas for each party in each constituency is as follows.

In terms of seat estimates, I guessed the following.

Of course, much of the final seat projection is complete guesswork, and there are a number of very marginal seats. For example, the fifth seat in Belfast South West would be expected to be a close contest between Sinn Féin, Alliance, and People Before Profit. Also, the reduction in the number of seats makes it harder win three of the five seats, and the DUP could struggle to win three seats in any constituency, unless of course there is some sort of merger with the UUP.

The redrawing of Northern Ireland’s electoral map is unlikely to produce much in the way of immediate benefits to either Nationalist or Unionist parties. However, the reduction in seats from 90 to 85 could throw up more marginal contests than exist under the current boundaries. There are likely to be some very close electoral calls over the coming years.

A qualified accountant and data analyst, interested in politics, economics and data. Twitter: @peterdonaghy