In her speech to the DUP party conference today, First Minister Arlene Foster called attention to the narrowness of the margin between her party and Sinn Féin:
A swing of only two votes in every hundred from the DUP to Féin would see Martin McGuinness become the next First Minister.
In the last Assembly election in 2011, the DUP won 38 seats with 30.0% of first preferences, and Sinn Féin won 29 seats with 26.9%. At a first glance, that 3.1% margin between the two parties’ vote shares is even closer than the First Minister claimed; a uniform swing of a mere 1.6% would be enough to make SF the largest party by votes, and as we all know the largest party by seats gets to choose the First Minister.
But there’s an important difference between seats and votes.
Looking at the 2011 results for each constituency, and applying a (highly improbable) uniform shift of votes from the DUP to Sinn Fein while keeping the votes for other parties at the 2011 levels, it seems that the real figure required to give SF more seats than the DUP is more like 5% than 2%; the DUP could actually trail SF by more than 6% in first preferences overall, and still win more seats. This is partly because the DUP’s stronger constituencies have smaller electorates, and partly because in the last election the DUP tended to get elected with votes to spare while a number of successful SF candidates had tighter squeaks to get in.
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