With Sinn Féin set to become the biggest party at Stormont for the first time, O’Neill says the results mark a ‘new era’ for ‘our politics and for our people’

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The elections to the Northern Ireland assembly are quite different to most UK elections. Members of the assembly are elected to 18 multi-member constituencies by single transferable vote.

Each constituency has five representatives, totalling 90 overall. Voters assign preferences to candidates on a ballot slip. If a candidate gets enough first-preference votes, they win a seat, and if not, second and then third preferences – and so on – are counted until all seats are filled.

Because of this, multiple counts are needed in each constituency, which means results can take a while to compile. It is possible for the first count not to result in the award of a seat. Another consequence is that it is not clear whether a party has increased or decreased its total seats in a constituency or overall, until all seats have been awarded.

By the terms of the Good Friday agreement the government of Northern Ireland is shared between the two main communities: nationalists, who favour closer ties with the Republic of Ireland, and unionists, for whom Northern Ireland’s position in the UK is more important. The largest party in the assembly appoints the first minister, and the largest party from the other community appoints the deputy first minister.

Some parties with cross-community support or whose supporters do not identify strongly with either community think this arrangement perpetuates divisions, but in practice since 1998 the largest party has always been from the unionist community and the second-largest from the nationalist.