Instant-runoff votingInstant-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.
Preferential votingPreferential voting or preference voting (PV) may refer to different election systems or groups of election systems: Ranked voting methods, all election methods that involve ranking candidates in order of preference (American literature) Optional preferential voting Instant-runoff voting, referred to as "preferential voting" in Australia and as "ranked choice voting" in United States, is one type of ranked voting method. Contingent vote (the top-two variant of IRV) Single transferable vote (referred to as "
History and use of instant-runoff votingInstant-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.
Ranked votingThe 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.
Supplementary voteThe supplementary vote (SV) is an electoral system used to elect a single winner, in which the voter ranks two of the candidates in order of preference. In an election, if no candidate receives an absolute majority of first-preference votes, then all but the two leading candidates are eliminated and there is a second count. In the second count, the votes of those who supported eliminated candidates are distributed among the two remaining candidates, so that one candidate achieves an absolute majority.
Electoral systemAn electoral system or voting system is a set of rules that determine how elections and referendums are conducted and how their results are determined. Electoral systems are used in politics to elect governments, while non-political elections may take place in business, non-profit organisations and informal organisations. These rules govern all aspects of the voting process: when elections occur, who is allowed to vote, who can stand as a candidate, how ballots are marked and cast, how the ballots are counted, how votes translate into the election outcome, limits on campaign spending, and other factors that can affect the result.
Vote splittingVote splitting is an electoral effect in which the distribution of votes among multiple similar candidates reduces the chance of winning for any of the similar candidates, and increases the chance of winning for a dissimilar candidate. This is commonly known as the spoiler effect, which can discourage minor party candidacies. Vote splitting most easily occurs in plurality voting (also called first-past-the-post) in which each voter indicates a single choice and the candidate with the most votes wins, even if the winner does not have majority support.
Independence of clones criterionIn voting systems theory, the independence of clones criterion measures an election method's robustness to strategic nomination. Nicolaus Tideman was the first to formulate this criterion, which states that the winner must not change due to the addition of a non-winning candidate who is similar to a candidate already present. To be more precise, a subset of the candidates, called a set of clones, exists if no voter ranks any candidate outside the set between (or equal to) any candidates that are in the set.
Spare voteThe spare vote is a version of single transferable voting applied to the ranking of parties, first proposed for elections in Germany in 2013. This preferential party system is a ranked proportional representation electoral system applying to political parties instead of individual candidates. The spare vote refers to a secondary vote (preference) of the voter, which only comes into play if the first preference for the political party preferred by the voter, is below the electoral threshold.
Two-round systemThe two-round system (TRS), also known as runoff voting, second ballot, or ballotage, is a voting method used to elect a single candidate, where voters cast a single vote for their preferred candidate. It generally ensures a majoritarian result, not a simple-plurality result as under first past the post. Under the two-round election system, the election process usually proceeds to a second round only if in the first round no candidate received a simple majority (more than 50%) of votes cast, or some other lower prescribed percentage.
