Single transferable vote

It has been suggested that Counting single transferable votes be merged into this article. (Discuss) Proposed since May 2024.

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The single transferable vote (STV), sometimes mistakenly conflated with proportional ranked choice voting (P-RCV),^[a] is a multi-winner electoral system in which each voter casts a single vote in the form of a ranked-choice ballot. Voters have the option to rank candidates, and their vote may be transferred according to alternate preferences if their preferred candidate is eliminated or elected with surplus votes, so that their vote is used to elect someone they prefer over others in the running. STV aims to approach proportional representation based on votes cast in the district where it is used, so that each vote is worth about the same as another.

STV is a weakly-proportional family of multi-winner electoral systems. They are a variation on the largest remainders method that uses solid coalitions rather than party lists. Votes belonging to winning candidates in excess of an electoral quota may be transferred to a voter's lower marked choices.

Under STV, no one party or voting bloc can take all the seats in a district unless the number of seats in the district is very small or almost all the votes cast are cast for one party's candidates (which is seldom the case). This makes it different from other commonly used candidate-based systems. In winner-take-all or plurality systems – such as first-past-the-post (FPTP), instant-runoff voting (IRV), and block voting – one party or voting bloc can take all seats in a district.

The key to STV's approximation of proportionality is that each voter effectively only casts a single vote in a district contest electing multiple winners, while the ranked ballots (and sufficiently large districts) allow the results to approach proportionality. The use of a quota means that, for the most part, each successful candidate is elected with the same number of votes. This equality produces fairness in the particular sense that a party taking twice as many votes as another party will generally take twice the number of seats compared to that other party.

Under STV, winners are elected in a multi-member constituency (district) or at-large, also in a multiple-winner contest. Every sizable group within the district wins at least one seat: the more seats the district has, the smaller the size of the group needed to elect a member. In this way, STV provides approximately proportional representation, ensuring that substantial minority factions have some representation.
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