instantrunoff

Instantrunoff, commonly known as instant runoff voting (IRV) or preferential voting, is an electoral method for single-winner elections in which voters rank candidates in order of preference. The ballot records a ranking rather than a single choice, and a winner is determined through iterative transfers of votes.

Counting begins with first-choice votes. If a candidate secures more than half of the active ballots, they win. If no candidate reaches a majority, the candidate with the fewest first-choice votes is eliminated. All ballots for that candidate are transferred to the next preferred candidate still in the race, and this process repeats until a candidate has a majority or only one candidate remains. Ballots that do not provide a further preference for any remaining candidate become exhausted and are no longer counted in later rounds.

IRV is used in some national and subnational elections, most notably in Australia for the House of Representatives (where it is called preferential voting), and in many cities and jurisdictions in North America and elsewhere for municipal elections. It is distinct from the single transferable vote, which is designed for multi-seat elections and proportional representation; IRV is typically applied to single-seat districts.

Advantages include avoiding a separate runoff election, allowing voters to express sincere first choices without fearing wasted votes, and often producing a winner with broad support among active voters. Criticisms include voter confusion, the potential for strategic ranking, the possibility that the IRV winner is not the Condorcet winner, and the issue of exhausted ballots reducing the effective electorate during later rounds.