Contingent vote

The contingent vote electoral system (also known as supplementary voting) elects a single representative through a two-stage process, in which the winner receives a majority of votes. It uses ranked voting. The voter ranks candidates in order of preference, and when the votes are first counted, only first preferences are counted. If no candidate has a majority (more than half) of the votes cast, then all but the two leading candidates are eliminated and the votes that had been received by the eliminated candidates are transferred to whichever of the two remaining candidates are marked as the next preference.

The contingent vote can be considered a compressed or "instant" form of the two-round system (runoff system), in which the second "round" is conducted without the need for voters to go to the polls a second time. For this reason, the term instant-runoff voting has been used for this system, though this conflicts with the more common use of that term.

The contingent vote election system also is similar to other ranked-vote systems. Unlike the contingent vote, other ranked-vote systems – such as single transferable voting (STV), instant-runoff voting (IRV), Coombs' method, and Baldwin's method – allow for many rounds of counting, often eliminating only one candidate, the weakest, each round. STV may be thought of as the multi-winner version of contingent voting. IRV is a single-winner election system and thus is similar to contingent voting except, unlike contingent voting, IRV may elect a candidate other than one of the two who led in the first count.