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Instant-runoff voting: Difference between revisions

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When the [[single transferable vote]] (STV) [[voting system]] is applied to a single-winner election it is sometimes called '''instant-runoff voting''' (IRV), as it is much like holding a series of [[runoff voting|runoff]] elections in which the lowest polling candidate is eliminated in each round until someone receives [[simple majority|majority]] vote. IRV is often considered independently of multi-winner STV because it is simpler and because it is the most widely advocated electoral reform in the United States.
 
Outside the USAUS, IRV is known as the '''[[Alternative Vote]]''', '''[[preferential voting]]''', '''single-winner STV''', or the '''[[Thomas Hare|Hare]] System''', though there is room for confusion with some of these terms, since they can also refer to STV in general. In the US, IRV is also known as '''Ranked Choice Voting''' ('''RCV'''), a term preferred by election officials in San Francisco in 2004 because election results were not instant, and voters are responsible for ranking candidates.<ref>As described on a [https://web.archive.org/web/20040514072509/http://www.ci.sf.ca.us/site/election_page.asp?id=24269 City of San Francisco election page in 2004] "''Is 'ranked-choice voting' the same as 'instant runoff voting'? In San Francisco, ranked-choice voting is sometimes called 'instant run-off voting.' The Department of Elections generally uses the term ranked-choice voting, because it describes the voting method—voter are directed to rank their first, second and third choice candidates. The Department also uses the term ranked-choice voting because the word 'instant' might create an expectation that final results will be available immediately after the polls close on election night. But the term 'instant run-off' does not mean instantaneous reporting of results—the term means that there is no need for a separate run-off election.''"</ref>
 
Instant-Runoff Voting was invented around 1870 by American architect [[William Robert Ware]], who simply applied Hare's method to single-winner elections.<ref>{{Cite book|url=https://books.google.com/books?id=W7QRAAAAYAAJ&pg=PA192|title=Application of Mr. Hare's system of voting to the nomination of overseers of Harvard College.|last=Ware|first=William R.|date=1871|publisher=|year=|isbn=|location=|pages=|oclc=81791186|quote=It is equally efficient whether one candidate is to be chosen, or a dozen.}}</ref><ref>{{cite web|url=http://archive.fairvote.org/articles/reilly.pdf|title=The Global Spread of Preferential Voting: Australian Institutional Imperialism|author=Benjamin Reilly|publisher=FairVote.org|accessdate=17 April 2011}}</ref> Ware was not a mathematician, thus never subjected his election method to any rigorous analysis. He evidently based IRV on the single winner outcome of the [[Single Transferable Vote]] or STV developed in 1855 originally by [[Carl Andrae]] in [[Denmark]]. It was introduced into [[England]] in 1857 by the [[barrister]] [[Thomas Hare]], where it earned public praise from [[John Stuart Mill]], an English philosopher, member of parliament, and employee of the [[British East India Company|East India Company]].
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=== Voting ===
 
Each voter ranks at least one candidate in [[Preferential_votingPreferential voting|order of preference]]. In most Australian elections, voters are required to rank all candidates. In other elections, votes may be "truncated", for example if the voter only ranks his first five choices.
 
=== Counting the votes ===
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*** Traditional rule; violates purity of one-person, one vote ideal
** ALL: Eliminate all tied candidates at once.
*** Good for weak candidates (with less than 5% of votes), but can lead to [[strategic nomination]]s, which cause IRV implementations using this method to not be [[Spoiler_effectSpoiler effect|spoiler proof]]
** RANDOM: Eliminate one randomly to break the tie.
** ORDER: If the order of the candidates on the ballot paper has been determined by lot, then ties can be eliminated by choosing say the top candidate.
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This failure mode occurs if the voter fears that their 1st-choice candidate (the 3rd party) might first win from his best-liked major party, then not get enough of the redistributed votes, and finally almost certainly lose to the other major party. The voter would wind up with his least-favored outcome. The voter may seek to prevent this by ranking the best-liked major party over their actual first choice.
 
This problem is known as "[[Favorite betrayal|favorite betrayal]]". A video which explains this problem more is [https://www.youtube.com/watch?v=JtKAScORevQ "How our voting system (and IRV) betrays your favourite candidate" by Dr. Andy Jennings at Center for Election Science], and an overall summary of [[Favorite betrayal criterion]] can be found on this wiki.
 
==== Failure to pick a good compromise ====
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Initially, in Australia, ballots are counted at the booth level, with first preference results reported to the Divisional Returning officer and then to the National Tally Room. If it is clear who the two leading candidates will be, a notional distribution of the preferences of the minor candidates may be made. Postal and absentee ballots are of course yet to be processed - that takes another week or two.
 
Over the next few weeks, ballots and matching documentation are concentrated in the offices of the Divisional Returning Officer, where aan actual distribution of preferences is made. This may be done by physically moving the ballots around, or by entering ballot data into a suitable computer.
 
If a candidate wins 51% of first preferences, a distribution of minor party preferences is strictly speaking not necessary, however the law now allows that such preferences be distributed to see what the "two-party preferred vote" actually is.
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Several variations of IRV have been proposed to meet the Condorcet and Smith criteria. The simplest of these are to eliminate everyone except the Condorcet winner (if they exist)/the candidates in the Smith Set, and then run IRV.
 
<br />
==See also==
*[[Australian electoral system]]
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*[[Table of voting systems by nation]]
*[[Bottom-Two-Runoff IRV]] - a variant that meets the Condorcet criterion
 
== References ==▼
<references/>▼
 
==External links==
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* Examples
** [http://www.mnip.org/caucusresults.htm Minnesota Independence Party 2004, IRV poll for U.S. President.]
** [http://www.OpenSTV.org/ OpenSTV] -- Software—Software for computing IRV and STV
** [http://www.aec.gov.au/ Australian Electoral Commission]
*Further Explanation
** [http://anewprogressiveamerica.blogspot.com/2004/11/what-is-instant-runoff-voting.html What is Instant Runoff Voting?]
 
{{fromwikipedia}}
▲== References ==
{{fromwikipedia}}[[Category:Single-winner voting methods]][[Category:Preferential voting methods]]▼
▲<references/>
▲{{fromwikipedia}}[[Category:Single-winner voting methods]][[Category:Preferential voting methods]]
[[Category:Plurality-runoff voting methods]]
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