If the results of yesterday's Westminster election are compared with the most recent Assembly election in 2007, it is possible to estimate the scale of tactical voting. In 2007 it is unlikely that many voters voted tactically with their first preferences, as in a PR-STV election this is unnecessary. So the 2007 results can be seen as a close approximation to the voters' 'true' political adherence. In 2010, though, because of the 'winner-takes-all' nature of the voting system used, there is greater incentive on voters to vote tactically where they know their preferred candidate has no hope, and where they have a strong preference (positive or negative) between the candidates with a realistic chance.
This blog will look at several of the constituencies where tactical voting probably happened, to estimate its extent. Firstly, Foyle.
In 2007, on a 62.7% turnout, unionism got 8,788 votes (21.4%).
In 2010, on a 57.5% turnout, unionism got 5,710 votes (15.1%). If the 2007 turnout had been repeated, this would have been 6,222, so 512 unionists failed to vote due to apathy or demographic decline. But another 2,566 disappeared from the 2007 unionist total (8788-6222) – where did they go?
The clear beneficiary seems to have been the SDLP. In 2007 it got 15,182 votes (37.0%), on a turnout of 62.7%, equivalent to 13,930 votes on a turnout of 57.5% as yesterday.
But the SDLP actually received 16,922 votes (44.7%) yesterday – almost 3,000 more than the 2007 experience would have led us to expect. The electorate in Foyle has slightly increased (though this was slowed down by the loss, due to boundary changes, of some territory to East Derry). The absence of Green and independent candidates yesterday may have slightly boosted the SDLP's total, but the inescapable conclusion is that, not for the first time, a large number of voters (around 2,500) who are unionists in local and Assembly elections voted tactically for Durkan yesterday.