Single transferable vote

Single transferable vote (STV) is a ranked-choice electoral system that elects multiple representatives in each district. Candidates win seats by reaching a quota, while surplus and eliminated-candidate votes transfer according to voters’ rankings.

Droop quota: A threshold of votes used in proportional elections; under the Droop formula, it is the total valid votes divided by one more than the seats, plus one. STV commonly uses this threshold to determine when a candidate has enough votes to win.
Ranked ballot: A ballot on which voters order candidates by preference rather than selecting only one. STV uses each voter’s ordered preferences to decide where a vote transfers.
Thomas Hare: An English lawyer and electoral reformer who proposed a system of proportional representation using ranked ballots in the nineteenth century. His proposal helped establish the intellectual foundations of STV.
Irish electoral system: Ireland’s system of parliamentary elections, which uses multi-member constituencies and proportional representation by single transferable vote. Ireland is a prominent national example of STV in regular legislative elections.
Party-list proportional representation: A family of electoral systems that allocates legislative seats to political parties in proportion to their vote totals. Unlike party-list systems, STV lets voters rank individual candidates within and across parties.
Surplus transfer: The redistribution of votes received by an elected candidate beyond the quota needed to win. It lets ballots for an already elected candidate help choose remaining representatives.
Proportional representation: Electoral systems designed to make the distribution of seats reflect the distribution of votes. STV is a candidate-centered form of proportional representation.
Carl Andræ: A Danish mathematician and politician who devised a form of proportional representation using transferable votes. His independent proposal was implemented in Denmark before STV spread elsewhere.
Malta electoral system: Malta’s electoral system, which uses STV in multi-member districts to elect its parliament. Malta illustrates STV’s use in a small state with strongly organized parties.
First-past-the-post voting: An electoral system in which the candidate with the most votes wins, without requiring a majority. Its single-winner districts contrast with STV’s multi-member proportional representation.

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