Instant-runoff voting (IRV) is a voting method used in single-seat elections with more than two candidates. Instead of voting only for a single candidate, voters in IRV elections can rank the candidates in order of preference. Ballots are initially counted for each elector's top choice, losing candidates are eliminated, and ballots for losing candidates are redistributed until one candidate is the top remaining choice of a majority of the voters. When the field is reduced to two, it has become an "instant runoff" that allows a comparison of the top two candidates head-to-head.
IRV more commonly known outside the US 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 and elections with only a single winner (such as elections for the President of Ireland) in 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 many ranked (or preferential) voting systems.
This method was considered by Condorcet as early as 1788, though only to condemn it, for its ability to eliminate a candidate preferred by a majority of voters.
Instant-runoff voting is based on the Single Transferable Vote electoral system, developed by Hill in 1819, Hare in 1857, and Andrae in 1855.
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Instant-runoff voting (IRV) is an electoral system that uses ranked voting. Its purpose is to elect the majority choice in single-member districts in which there are more than two candidates and thus help ensure majority rule. It is a single-winner version of single transferable voting. Formerly the term "instant-runoff voting" was used for what many people now call contingent voting or supplementary vote.
The term ranked voting, also known as preferential voting or ranked choice voting, pertains to any voting system where voters use a rank to order candidates or options—in a sequence from first, second, third, and onwards—on their ballots. Ranked voting systems vary based on the ballot marking process, how preferences are tabulated and counted, the number of seats available for election, and whether voters are allowed to rank candidates equally.
The contingent vote is an electoral system used to elect a single representative in which a candidate requires a majority of votes to win. It is a variation of instant-runoff voting (IRV). Under the contingent vote, the voter ranks the candidates in order of preference, and the first preference votes are counted. If no candidate has a majority (more than half the votes cast), then all but the two leading candidates are eliminated and the votes received by the eliminated candidates are distributed among the two remaining candidates according to voters' preferences.
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