single transferable vote

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A system of proportional representation in use in Ireland, Malta, for some elections in Australia, and since 2007 for local elections in Scotland; also popular among clubs and societies. A number (usually between three and seven) of seats are filled simultaneously. Each voter lists the candidates in order of preference. First preferences are counted. Those candidates who have achieved at least the Droop quota (v/(n + 1), rounded up to the next integer, for an n‐member seat in which v valid votes have been cast) are elected, and their ‘surplus’ votes are transferred to the next candidate, if any, on those voters' lists. Surplus votes are weighted: thus, if the Droop quota was 1,200 and a candidate obtained 1,400 first preference ballots, each of those is assigned to the second preference named on it with a weight of 200/1,400. When no further candidates can be elected by this route, the candidate with the fewest first preferences is eliminated and his or her second preferences transferred with a weight of one. The process continues through redistribution of surpluses where possible and eliminations otherwise, until n candidates have been elected. (The process of vote transfers is similar to the alternative vote system used in single‐member constituencies.)

The main property of STV is that each faction or party is guaranteed as many seats as it has Droop quotas of first preference votes. A secondary property, in evidence in Ireland, is that it encourages candidates of the same party to compete against each other; as they cannot normally compete on ideology, they tend to compete on the conspicuous provision of local services. STV is more popular among electoral reformers than among social choice theorists. The latter complain that the concept of ‘wasted vote’, on which the rationale of transfers depends, is ill‐defined, and that the elimination process is arbitrary and non‐monotonic.

Subjects: Politics.

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