History and use of instant-runoff voting
Instant-runoff voting, more commonly known outside the USA as the alternative vote or preferential voting, was devised around 1870 by the US architect W. R. Ware. Today it is in use at a national level to elect the Australian House of Representatives, the National Parliament of Papua New Guinea, the President of Ireland and President of India. In Australia it is also used for elections to the legislative assemblies (lower houses) of all states and territories except Tasmania and the Australian Capital Territory, and for the Tasmanian Legislative Council (upper house).
IRV is also used a number of municipal elections in Australia, the United States, United Kingdom and New Zealand. Because of its relationship to the Single Transferable Vote (STV) system, IRV is used for by-elections in a some jurisdictions that use STV for ordinary parliamentary elections, such as the Republic of Ireland and Scotland.
IRV is known by different names in the various countries in which it is used. It is also known as the 'Alternative Vote', 'Ranked Choice Voting', and 'Preferential Voting', although IRV is only one of a number of forms of preferential voting systems.
Instant-runoff voting is based on the Single Transferable Vote electoral system, invented independently by Thomas Hare in 1857 and Carl Andrae in 1855. Unlike IRV, the Single Transferable Vote was designed as a form of proportional representation involving multi-seat constituencies, and today STV is used in a number of countries, including Australia, the Republic of Ireland and Malta.
William Robert Ware, the founder of the schools of architecture at the Massachusetts Institute of Technology (MIT) and Columbia University, invented IRV around 1870 by applying the Single Transferable Vote system to single winner elections. IRV was adopted for the Australian House of Representatives in 1918 and has been used to elect the President of Ireland since the office came into being in 1937. It was introduced in Fiji in 1999 and in Papua New Guinea in 2007.
Use by country
In Australia IRV has been used to elect the members of the lower house of Parliament since 1918, using a form of IRV where voters must rank every candidate. Voters are required to rank all candidate to cast a valid ballot. Preferential voting is used for most state and local elections in Australia, but sometimes with optional preferential voting where voters are allowed to limit their number of rankings.
In 2007, the Australian Labor Party won a majority of seats and a majority of votes in the final round of counting. Every House race had at least four candidates, and the average number of candidates was seven, yet every race was still won with a majority of the vote in the final instant runoff. The number of candidates who depended on preferences to win was 76 – more than half of the 150 winners.
Under the name 'preferential' or 'elimination ballot', IRV was used in the British Columbia's general elections of 1952 and 1953. IRV was initially brought in by the governing coalition consisting of the Liberal and Conservative parties to try to prevent a left-wing government under the Co-operative Commonwealth Federation as voters could then choose one of the governing parties as their first choice and the other as their second choice. However, IRV backfired on the Liberals and Conservatives when many CCF supporters chose the relatively unknown Social Credit Party, a minor party that had never held any seats in the British Columbia legislature, as their second choice. The Social Credit Party achieved an upset victory in the 1952 election, winning 19 seats in the 48-member legislature to 18 for the CCF, 6 for the Liberals and 4 for the Conservatives. The Socreds formed a short-lived minority government until the 1953 election, in which they won a majority of seats (28 of 48). After the 1953 election, the Liberal and renamed Progressive Conservative Parties were reduced to third parties in the province, and first-past-the-post was reinstated by the government.
Today IRV is used for certain party and private elections in Canada, including such large-scale elections at the Canadian Wheat Board, the Progressive Conservative Association of Alberta leadership election, 2006, where it has generated high turnout, and the British Columbia Liberal Party leadership election, 2011. The Liberal Party of Canada had adopted IRV with a national primary for its leadership elections.
The President of India is chosen by an electoral college consisting of the elected members of both houses of the Parliament and the elected members of the State Legislative Assemblies (Vidhan Sabha). The election is held with IRV, which in the Indian Constitution (Article 55) is called single transferable vote.
The single transferable vote (STV), a multi-seat variation of IRV, is used for all district health board elections. Starting in 2004, several New Zealand cities and local authorities began to use STV for their elections—including the nation's second largest city and capital Wellington and its fifth largest city Dunedin  Where electing a mayor directly, these cities used instant runoff voting. In 2007, for example, Wellington's mayor Kerry Prendergast defeated her 10 rivals on the 9th round of counting. Other contested IRV races have included the Dunedin mayoral election, 2010 and Wellington City mayoral election, 2010.
As of September 2013, seven authorities are elected with STV: Dunedin City Council, Greater Wellington Council, Kapiti Coast District Council, Marlborough District Council, Palmerston North City Council, Porirua City Council, and Wellington City Council. Wellington upheld STV in a 2008 ballot measure.
Papua New Guinea
A form of IRV has been used to elect members of parliament since last plurality voting election in 2002. Called "limited preferential voting" because voters are limited to ranking three candidates, the system has been credited with reducing election violence in a highly fractured political system.
Republic of Ireland
In the Republic of Ireland IRV is used for presidential elections and for by-elections to the Dáil (the lower house of parliament). Most elections in the Republic use the Single Transferable Vote, STV. The STV system was first introduced for a national election when the abortive Parliament of Southern Ireland was elected in 1921. It was provided, at the same time, that by-elections for the body would occur under IRV. When what is now the Republic seceded from the United Kingdom in 1922 STV was adopted for ordinary elections to Dáil Éireann and IRV for by-elections, and this combination has been used ever since. STV is also used for local and European elections, but in these cases by-elections do not occur. Instead local council vacancies are filled by co-option and European vacancies by an individual from a list of replacements nominated by the MEP at the time of his election.
The office of President of Ireland has existed since the adoption of the current Constitution of Ireland in 1937, which provided that the President would be elected by IRV. However the first election did not occur until 1945. This is because the constitution also allows that, where there is agreement among political parties, a consensus candidate can come to office without the occurrence of an election. The President occupies a largely ceremonial position, as real power is exercised by the Taoiseach (prime minister) and Dáil.
On the island of Ireland IRV is not referred to as 'instant-runoff voting' and only rarely as the 'Alternative Vote', the name popular in Great Britain. Instead it is usually called the 'Single Transferable Vote' or, sometimes, incorrectly, 'proportional representation'. The name Single Transferable Vote is used because when the rules of STV are applied to a single-winner election, such as a presidential election or by-election, STV becomes one and the same as IRV. However this can be confusing because there are many important differences between the use of STV for multi-seat elections and IRV. For this reason many scholars regard STV as a separate system from IRV, and that is the convention followed in this article. It is incorrect to refer to IRV as 'proportional representation' because the term proportional representation can only meaningfully be applied to an election in which more than a single candidate is returned.
IRV is currently used in the United Kingdom for by-elections to the Northern Ireland Assembly and to local assemblies in Scotland, both of which use the single transferable vote method of proportional representation in regularly scheduled elections. It is used in its contingent vote form (also called the supplementary vote), for all direct elections for mayor in England, including in London. It is used to fill vacancies within the House of Lords, to elect the leaders of the Liberal Democrats  and the Labour Party  and for many private elections, including for Chancellor of Oxford University  and rectorial elections at the University of Edinburgh. IRV was the electoral method available to select a replacement MEP by election for the Northern Ireland constituency of the European parliament, however now a party can co-opt a replacement without the need for a by-election.
IRV has been debated vigorously in the country since the early 20th century. In 1917, for example, the Speaker's Conference advocated the adoption of IRV for 358 of the 569 constituencies in the UK, and STV for the rest; its intention was that STV would be used in densely populated urban areas but, in order to keep constituencies from being too large, IRV would be used in more sparsely populated rural areas. Although the House of Commons voted in favour of the proposals five times, the House of Lords rejected it until the nationwide effort was ultimately abandoned in parliament.
In 1921 the Government of Ireland Act established two home rule parliaments in Ireland–the Parliament of Northern Ireland and the Parliament of Southern Ireland–and while STV was used for regular elections to these bodies IRV was used for by-elections. This combination of IRV and STV has been used in what is now the Republic of Ireland ever since. The Northern Ireland Parliament continued to use the combination until the late 1920s when it switched to the 'first past the post' plurality system. However STV for regular elections, and IRV for by-elections, has been reintroduced and used there to elect devolved assemblies since the 1970s.
IRV is usually referred to in the UK as the 'Alternative Vote' or 'AV'. In 1998 the Jenkins Commission, charged by the government with suggesting an alternative system to plurality, devised a new system called the Alternative Vote Plus (AV+) for elections to the British Parliament. This involved a combination of party-list proportional representation and single seat constituencies elected under IRV. However no action has been taken on the Commission's report.
In March 2009 the government announced that it would run an inquiry into the use of IRV at future general elections, and in February 2010 the House of Commons voted to hold a national referendum on AV. The government's term expired before this legislation was approved, but in July 2010, newly elected Deputy Prime Minister Nick Clegg announced a referendum on AV. On May 5, 2011, the referendum was defeated by 68% to 32%, as detailed in United Kingdom Alternative Vote referendum, 2011.
Since 1917, IRV has been used in various United States jurisdictions. Since 2002, IRV has been adopted by more than a dozen cities, with some adoptions pending implementation. As of September 2013, American cities currently using IRV to elect at least one office include Minneapolis, Minnesota; Oakland, California; Portland, Maine; St. Paul, Minnesota; San Francisco, California; Takoma Park, Maryland; Berkeley, California; San Leandro, California; and Telluride, Colorado. Since 1941, the single transferable vote, a multi-seat variation of IRV, has been used to elect the city council and school committee in Cambridge, Massachusetts.
San Francisco's system of IRV was challenged in federal court, but a unanimous panel of the US Court of Appeals for the 9th Circuit upheld San Francisco's IRV law, finding that the plaintiff failed to establish that the City's chosen electoral system was unconstitutional. 
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