Northern Irish well-represented
The Northern Ireland Assembly, re-elected last week, is one of the most representative legislatures in the world, with over 82% of those who voted represented by their preferred political party.
Both the UK province of Northern Ireland and the Republic of Éire to the south adopted the single transferable vote (STV) early in the 20th century.
The use of the STV voting system in Ireland – at the time only the second place in the world after Tasmania to adopt it – was seen by the UK Government as a means of managing the Irish ‘home rule’ issue by allowing both the nationalist/catholic and unionist/protestant communities a fair share of political representation.
Traditional single-member voting had been shown to result in widespread exclusion of representation of the minorities in each of the catholic and protestant zones of the island.
Éire has kept the STV voting system for the near-century that has followed. In the 1950s and ‘60s governments in Dublin twice tried to convince Irish voters to remove the STV voting system and use single-member districts and plurality voting (i.e.: first-past-the-post), but the electorate refused both times to approve proposed changes to the Irish Constitution.
In the North, the first two elections for the House of Commons of Northern Ireland in 1921 and 1925 were conducted using STV, but thereafter the unionist majority legislated (as it had been empowered to do by the UK Parliament) for the use of single-member district plurality. This change still left nationalists winning seats where they were strong, but permanently in the minority, while voters who supported minor parties became almost effectively unrepresented. This approach persisted for ten elections until the House was abolished in 1972. [Note: preceding two paras revised from initial post following comment from Reg Jones (below).]
STV was then restored to Northern Ireland when the Assembly was established in 1998.
With currently five significant political parties in Northern Ireland, each of which has voter support concentrated in particular localities, the more representative voting system is helping to ensure that a very high proportion of Northern Irish voters are politically represented.
There were five seats available in each electoral division in last week’s vote, causing over 82% of those who voted to send a representative to the Stormont Assembly from their preferred political party.
In single-member division voting systems the percentages of voter representation are dramatically lower.
In the 2015 elections for the UK House of Commons, the average rate of representation in the nation’s constituencies was just 50% of those voting.
In the 18 Northern Irish House of Commons constituencies – the same as used last week to elect the Assembly – the average rate of representation in 2015 was just 43%, barely half of the representation that voters have in the newly-elected local Assembly.
The previous Northern Ireland election in 2016, when there were six seats in each division, also saw a province-wide representation rate of 82%.
The 2017 election results show very similar party delegations to the 2016 election results from most electoral divisions, despite the shrinkage of the chamber. The the supporters of the Ulster Unionists (UUP) – the minor of the two unionists parties – have suffered an outright loss of representation in a small number of electoral divisions, as have supporters of the SDLP and PBP parties in one division where they were previously represented.
In the election aftermath some commentators have called for the two unionist parties to merge in the face of their recent losses. In fact, had they formed one party at last weeks polls and had their voter support been 100% aggregated, they would likely have picked up another seat in two electoral divisions, but lost one in a third. (With STV voting, in the race for the final seats in any electoral division it is often advantageous for a party to have two candidates with similar vote totals, rather than have the party’s vote concentrated on a single strong candidate.)
Nationalists Sinn Féin came very close to the psychological shock of claiming the right to appoint the provinces’ first nationalist First Minister to lead the government.
If Sinn Féin had won one more seat they would have tied with the Democratic Unionist Party on 28 seats, and if they had won 1,200 more votes across the province (around 70 votes per electoral division) they would have exceeded the DUP total and become entitled to the position.
Even after 19 years of peaceful joint government, not all have given up a willingness to fight physically over the province’s identity. A Sinn Féin First Minister-ship could have dramatically heightened sensitivities.
As it is, the unusual constitutional arrangements in Northern Ireland will oblige both parties to work together. A new government can only be formed if the two leading parties put aside antagonism and join in a coalition. Other parties are also entitled to participate.
Stormont, home of the Northern Ireland Assembly. A government can only be formed if the largest unionist and nationalist political parties cooperate
In addition, both nationalists and unionists still have the necessary 30 seats in the Assembly (although not held by one party alone) to insist that parliamentary majorities from both communities must be achieved to pass controversial laws.
Whilst the unusual power-sharing system has brought stability and economic recovery to the province, the events of recent weeks have shown that the system is less able to cope with partisan acrimony over more mundane political events, such as how to determine the appropriate accountability of former First Minister Arlene Foster for a renewable energy policy debacle.
On Elections 
Think your line “Government in Northern Ireland has been suspended at various points, but the UK Parliament which establishes the province’s constitutional system has also stuck with STV.” needs to be checked.
Wikipedia (https://en.wikipedia.org/wiki/Parliament_of_Northern_Ireland) says:
House of Commons of Northern Ireland
The House of Commons had 52 members, of which 48 were for territorial seats and four were for graduates of Queen’s University, Belfast (until 1969, when the four university seats were replaced by an additional four territorial seats). The Government of Ireland Act prescribed that elections to the House of Commons should be by single transferable vote (STV), though the Parliament was given power to alter the electoral system from three years after its first meeting. The STV system was the subject of criticism from grassroots Unionists but because the three-year period ended during the Labour government of 1924, the Stormont government decided not to provoke the known egalitarian sympathies of many Labour backbenchers and held the second election on the same basis. The loss of eight Unionist seats in that election caused great acrimony and in 1929 the system was changed to first-past-the-post for all territorial constituencies, though STV was retained for the university seats.
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