Contingent vote

The contingent vote, also known as top-two IRV is an electoral system used to elect a single winner. It is a variation of instant-runoff voting (IRV), in which the voter ranks the candidates in order of preference. Under the contingent vote, there is a first round in which a candidate requires a majority of first preference votes to win. If no candidate has a majority, then all but the two leading candidates are eliminated and there is a second count, where the votes of those who supported eliminated candidates are distributed among the two remaining candidates. This ensures that one candidate achieves a majority. The contingent vote differs from IRV which allows for many rounds of counting, eliminating only one weakest candidate each round. The contingent vote can also be considered a compressed form of the two-round system (runoff system), in which both 'rounds' occur without the need for voters to go to the polls twice. Today, a special variant of the contingent vote is used to elect the President of Sri Lanka. Another variant, called the supplementary vote, is used to pick directly elected mayors and police and crime commissioners in England. In the past the ordinary form of the contingent vote was used to elect the Legislative Assembly of Queensland from 1892 to 1942. To date, this has been the longest continuous use of the system anywhere in the world. It was also used in the US state of Alabama in the 1920s. In an election held using the contingent vote the voters rank the list of candidates in order of preference. Under the most common ballot layout, they place a '1' beside their most preferred candidate, a '2' beside their second most preferred, and so on. In this respect the contingent vote is the same as instant-runoff voting.