Single transferable vote: Difference between revisions
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{{Wikipedia}}
The '''Single Transferable Vote''', or '''STV''', is a [[preferential voting|preferential]] [[voting system]] designed to minimise
When promoted as a [[proportional representation]] method in multi-party multi-seat elections, it is generally known as '''Proportional Representation through the Single Transferable Vote''' or '''PR-STV'''. When a similar method is applied to single-seat elections it is sometimes called ''[[instant-runoff voting]]'' or the ''alternative vote'', and has different proportionality implications for a similar ballot.
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Within a constituency, however, STV can be said to be proportional for whatever characteristics the voters valued. For example, if 60% of voters put all the female candidates first, and 40% put all the male candidates first, 60% of the winners would be female and 40% would be male. (Assuming there are sufficient candidates of each gender to make up the numbers.)
STV provides this proportionality simply by wasting as few votes as possible. A vote is a "
The degree of proportionality nationwide is strongly related to the number of seats to be filled in each constituency. In a three-seat constituency, using the Droop quota, about a quarter of the vote is "wasted". These votes may be for minor candidates that were not eliminated, or elected candidates' surplus votes that did not get redistributed. In a nine-seat constituency, only a tenth of the vote is wasted, and a party needs only 10% of the vote in a constituency to win a seat. Consequently, the best proportionality is achieved when there are a large number of representatives per constituency.
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However, in older STV systems there is a loophole:
candidates who have already been elected do not receive any more votes, so there is incentive to avoid voting for your top-ranked candidate until after they have already been elected. For example, a voter might make a tactical decision to rank their top-place candidate beneath a candidate they know will lose (perhaps a fictional candidate). If the voter's true top-place candidate has not been elected by the time their fake top candidate loses, the voter's full vote will count for their true top-place candidate. Otherwise, the
voter will have avoided having had their ballot in the lottery to be "
Note that in more modern STV systems, this loophole has been fixed. A vote receives the same fractional weighting regardless of when it arrives at the successful candidate. This modernisation has not been adopted in all STV systems.
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