Instant-runoff Voting

Instant-runoff voting (IRV), alternative vote (AV), transferable voting, or preferential voting is an electoral system used to elect a single winner from a field of more than two candidates. It is a form of preferential voting (or ranked choice voting) in which voters rank the candidates in order of preference rather than simply selecting a single candidate.

Ballots are initially distributed based on each elector's first preference. If a candidate secures more than half of votes cast, that candidate wins. Otherwise, the candidate with the fewest votes is eliminated. Ballots assigned to eliminated candidates are recounted and assigned to one of the remaining candidates based on the next preference on each ballot. This process continues until one candidate wins by obtaining more than half the votes.

IRV has the effect of avoiding split votes and the need for electors to vote "strategically" for candidates who are not their first choice. For example, suppose here are two conservative candidates A & B, and a liberal candidate C, with raw popularity of 35%, 25% and 40% respectively. In a Plurality voting system, candidate C may win with 40% of the votes even though most electors prefer A or B. Alternatively, a conservative elector who likes B may decide to vote for A instead in order to prevent C from being elected. With IRV, the elector can allocate their preferences B, A, C and then A will win despite the split vote in first choices.

Instant runoff voting is used to elect members of the Australian House of Representatives and most Australian State Governments, the President of India, members of legislative councils in India, the President of Ireland, the National Parliament of Papua New Guinea, and the House of Representatives of Fiji. It is also used in Northern Ireland by-elections and for electing hereditary peers for the British House of Lords.

IRV is employed by several jurisdictions in the United States, including Portland, Maine; San Francisco, California; Oakland, California; Minneapolis, Minnesota; and Saint Paul, Minnesota.

It is used to elect the leaders of the Labour Party and the Liberal Democrats in the United Kingdom and will be used to elect the leader of the Liberal Party of Canada in a national primary and in the elections of city mayors in a number of countries. IRV is used to elect the mayor in cities such as London in the United Kingdom (in the variant known as supplementary vote) and Dunedin and Wellington in New Zealand.

Many private associations also use IRV, including the Hugo Awards for science fiction and the Academy of Motion Picture Arts and Sciences in selection of the Oscar for best picture.