View source for Instant-runoff voting

{{Short description|Single-winner ranked-choice electoral system}}
{{for|the proportional electoral system applying ranked ballots to multi-member constituencies|Single transferable vote}}
{{for|ranked methods in general|Ranked voting}}
{{Use dmy dates|date=April 2024}}
{{Use American English|date=May 2024}}
{{Electoral systems sidebar|expanded=Single-winner}}
'''Instant-runoff voting''' ('''IRV'''; {{abbr|[[American English|US]]:|United States and Canada|style=font-size:85%}} '''ranked-choice voting''' ('''RCV'''), {{abbr|[[Australian English|AU]]:|Australia|style=font-size:85%}} '''preferential voting''', {{abbr|[[British English|UK]]/[[New Zealand English|NZ]]:|United Kingdom and New Zealand|style=font-size:85%}} '''alternative vote''') is a single-winner [[ranked voting]] election system where [[Sequential loser method|one or more eliminations]] are used to simulate multiple [[runoff election]]s. In each round, the candidate with the fewest [[First-preference votes|first-preferences]] (among the remaining candidates) is eliminated. This continues until only one candidate is left. Instant runoff falls under the [[Plurality-rule family|plurality-with-elimination family]] of voting methods,<ref>{{Cite journal |last=Nurmi |first=Hannu |date=June 2005 |title=Aggregation problems in policy evaluation: an overview |url=http://dx.doi.org/10.1016/j.ejpoleco.2004.08.001 |journal=European Journal of Political Economy |volume=21 |issue=2 |pages=287–300 |doi=10.1016/j.ejpoleco.2004.08.001 |issn=0176-2680|url-access=subscription }}</ref> and is thus closely related to rules like the [[Runoff election|two-round runoff system]].<ref>{{Cite book |last1=Aubin |first1=Jean-Baptiste |url=https://hal.science/hal-04631154/ |title=A simulation-based study of proximity between voting rules |last2=Gannaz |first2=Irène |last3=Leoni-Aubin |first3=Samuela |last4=Rolland |first4=Antoine |date=July 2024}}</ref><ref>{{Cite journal |last1=Hyman |first1=Ross |last2=Otis |first2=Deb |last3=Allen |first3=Seamus |last4=Dennis |first4=Greg |date=2024-09-01 |title=A majority rule philosophy for instant runoff voting |url=https://link.springer.com/article/10.1007/s10602-024-09442-3 |journal=Constitutional Political Economy |language=en |volume=35 |issue=3 |pages=425–436 |arxiv=2308.08430 |doi=10.1007/s10602-024-09442-3 |issn=1572-9966}}</ref>

Instant-runoff voting has found some use [[History and use of instant-runoff voting|in national elections in several countries]], predominantly in the [[Anglosphere]]. It is used to elect members of the [[Australian House of Representatives]] and the [[National Parliament of Papua New Guinea]], and to elect the [[Heads of state|head of state]] in [[President of India|India]], [[President of Ireland|Ireland]], and [[President of Sri Lanka|Sri Lanka]].

The rule was first studied by the [[Marquis de Condorcet]], who was the first to analyze it and show it could eliminate the [[majority-preferred candidate]] ([[Condorcet winner]]).<ref name=":033">{{Cite book |last=Condorcet |first=Jean-Antoine-Nicolas de Caritat |title=Complete Works of Condorcet |date=1788 |volume=13 |publication-date=1804 |pages=243 |language=fr |chapter=On the Constitution and the Functions of Provincial Assemblies |quote=En effet, lorsqu'il y a plus de trois concurrents, le véritable vœu de la pluralité peut être pour un candidat qui n'ait eu aucune des voix dans le premier scrutin. |chapter-url=https://books.google.com/books?id=d0cwAAAAYAAJ&q=Oeuvres%20de%20Condorcet,%20Volume%2013&pg=PA243}}</ref><ref name=":032232">{{Cite journal |last=Nanson |first=E. J. |date=1882 |title=Methods of election: Ware's Method |url=https://archive.org/details/transactionsproc1719roya/page/206 |journal=Transactions and Proceedings of the Royal Society of Victoria |volume=17 |pages=206 |quote=The method was, however, mentioned by Condorcet, but only to be condemned.}}</ref><ref name=":2232232">{{cite journal |last1=Campbell |first1=D.E. |last2=Kelly |first2=J.S. |year=2000 |title=A simple characterization of majority rule |journal=[[Economic Theory (journal)|Economic Theory]] |volume=15 |issue=3 |pages=689–700 |doi=10.1007/s001990050318 |jstor=25055296 |s2cid=122290254}}</ref><ref name=":852232">{{Cite journal |last1=McGann |first1=Anthony J. |last2=Koetzle |first2=William |last3=Grofman |first3=Bernard |date=2002 |title=How an Ideologically Concentrated Minority Can Trump a Dispersed Majority: Nonmedian Voter Results for Plurality, Run-off, and Sequential Elimination Elections |url=https://www.jstor.org/stable/3088418 |journal=American Journal of Political Science |volume=46 |issue=1 |pages=134–147 |doi=10.2307/3088418 |issn=0092-5853 |jstor=3088418 |quote="As with simple plurality elections, it is apparent the outcome will be highly sensitive to the distribution of candidates."|url-access=subscription }}</ref> Since then, instant-runoff voting has been criticized for other [[Pathological (mathematics)#In voting and social choice|mathematical pathologies]] ([[Instant-runoff voting#Pathologies of instant-runoff voting|discussed below]]), including its ability to eliminate candidates for having [[Negative responsiveness|too much support]] or [[No-show paradox|too many votes]].<ref>{{Cite journal |last1=Doron |first1=Gideon |last2=Kronick |first2=Richard |date=1977 |title=Single Transferrable Vote: An Example of a Perverse Social Choice Function |url=https://www.jstor.org/stable/2110496 |journal=American Journal of Political Science |volume=21 |issue=2 |pages=303–311 |doi=10.2307/2110496 |issn=0092-5853 |jstor=2110496|url-access=subscription }}</ref> Like [[First-preference plurality|first-preference plurality (FPP)]], instant-runoff is vulnerable to a kind of [[spoiler effect]] called a [[center squeeze]],<ref name=":7332">{{Cite journal |last=Nurmi |first=Hannu |date=December 1996 |title=It's not just the lack of monotonicity1 |url=http://www.tandfonline.com/doi/abs/10.1080/00344899608522986 |journal=Representation |language=en |volume=34 |issue=1 |pages=48–52 |doi=10.1080/00344899608522986 |issn=0034-4893|url-access=subscription }}</ref><ref name=":032442">{{Cite web |last1=Atkinson |first1=Nathan |last2=Ganz |first2=Scott C. |date=2022-10-30 |title=The flaw in ranked-choice voting: rewarding extremists |url=https://thehill.com/opinion/campaign/3711206-the-flaw-in-ranked-choice-voting-rewarding-extremists/ |access-date=2023-05-14 |website=The Hill |language=en-US |quote=However, ranked-choice voting makes it more difficult to elect moderate candidates when the electorate is polarized. For example, in a three-person race, the moderate candidate may be preferred by a majority of voters to each of the more extreme candidates. However, voters with far-left and far-right views will rank the candidate in second place rather than in first place. Since ranked-choice voting counts only the number of first-choice votes (among the remaining candidates), the moderate candidate would be eliminated in the first round, leaving one of the extreme candidates to be declared the winner.}}</ref> which causes it to favor uncompromising alternatives over more-moderate ones,<ref name=":85242">{{Cite journal |last1=McGann |first1=Anthony J. |last2=Koetzle |first2=William |last3=Grofman |first3=Bernard |date=2002 |title=How an Ideologically Concentrated Minority Can Trump a Dispersed Majority: Nonmedian Voter Results for Plurality, Run-off, and Sequential Elimination Elections |url=https://www.jstor.org/stable/3088418 |journal=American Journal of Political Science |volume=46 |issue=1 |pages=134–147 |doi=10.2307/3088418 |issn=0092-5853 |jstor=3088418 |quote="As with simple plurality elections, it is apparent the outcome will be highly sensitive to the distribution of candidates."|url-access=subscription }}</ref><ref name="Merril 1985224223">{{Cite journal |last=Merrill |first=Samuel |date=1985 |title=A statistical model for Condorcet efficiency based on simulation under spatial model assumptions |url=http://dx.doi.org/10.1007/bf00127534 |journal=Public Choice |volume=47 |issue=2 |pages=389–403 |doi=10.1007/bf00127534 |issn=0048-5829 |quote=the 'squeeze effect' that tends to reduce Condorcet efficiency if the relative dispersion (RD) of candidates is low. This effect is particularly strong for the plurality, runoff, and Hare systems, for which the garnering of first-place votes in a large field is essential to winning |via=|url-access=subscription }}</ref><ref name="Merrill 1984223">{{Cite journal |last=Merrill |first=Samuel |date=1984 |title=A Comparison of Efficiency of Multicandidate Electoral Systems |url=http://dx.doi.org/10.2307/2110786 |journal=American Journal of Political Science |volume=28 |issue=1 |pages=23–48 |doi=10.2307/2110786 |issn=0092-5853 |jstor=2110786 |quote=However, squeezed by surrounding opponents, a centrist candidate may receive few first-place votes and be eliminated under Hare. |via=|url-access=subscription }}</ref><ref name=":24232">{{Cite journal |last=Robinette |first=Robbie |date=2023-09-01 |title=Implications of strategic position choices by candidates |url=https://doi.org/10.1007/s10602-022-09378-6 |journal=Constitutional Political Economy |language=en |volume=34 |issue=3 |pages=445–457 |doi=10.1007/s10602-022-09378-6 |issn=1572-9966|doi-access=free }}</ref> encouraging polarization.<ref name="a7902">{{cite journal |last=Atkinson |first=Nathan |last2=Ganz |first2=Scott |year=2024 |title=Robust Electoral Competition: Rethinking Electoral Systems to Encourage Representative Outcomes |journal=SSRN Electronic Journal |publisher=Elsevier BV |page= |doi=10.2139/ssrn.4728225 |issn=1556-5068}}</ref>

Advocates of instant-runoff voting often argue these properties are positive, as voting rules should encourage candidates to appeal to their [[core support]] or political base rather than a broad coalition.<ref>{{Cite journal |last1=Hyman |first1=Ross |last2=Otis |first2=Deb |last3=Allen |first3=Seamus |last4=Dennis |first4=Greg |date=September 2024 |title=A Majority Rule Philosophy for Instant Runoff Voting |journal=Constitutional Political Economy |volume=35 |issue=3 |pages=425–436 |arxiv=2308.08430 |doi=10.1007/s10602-024-09442-3 |issn=1043-4062}}</ref> They also note that in countries like the [[United Kingdom|UK]] without [[Primary election|primaries]] or [[Two-round system|runoffs]], instant-runoff voting can prevent [[Spoiler effect|spoiler effects]] by eliminating minor-party candidates, because it [[Mutual majority criterion|avoids some kinds of vote-splitting]] by [[Independence of clones criterion|nearly identical (clone) candidates]]. IRV has also been described as a natural extension of the two-round system or [[Primary election|primary elections]] that avoids multiple rounds of voting.<ref name=":03223b">{{Cite journal |last=Nanson |first=E. J. |date=1882 |title=Methods of election: Ware's Method |url=https://archive.org/details/transactionsproc1719roya/page/206 |journal=Transactions and Proceedings of the Royal Society of Victoria |volume=17 |pages=206 |quote=This method is a perfectly feasible and practicable one for elections on any scale ... [i]t is a simple and obvious extension of the French system...}}</ref>

== Election procedure ==
[[File:IRV_counting_flowchart.svg|thumb|Flowchart of instant-runoff voting]]
In instant-runoff voting, as with other [[ranked voting]] rules, each voter orders candidates from first to last. The counting procedure is then as follows:

# If there is more than one candidate left, eliminate the one with the fewest voters ranking them first.{{efn|This procedure can be sped-up by eliminating more than one candidate if their combined top preferences are less than the next-lowest remaining candidate; this process is sometimes called batch elimination. When batch elimination is used, the procedure can terminate if some candidate has a majority.}}
# Reassign votes held by the eliminated candidates to the next-highest preference on each ballot paper (setting aside any with no remaining preferences). Return to Step 1.

It is possible for a candidate to win an instant-runoff race without any support from more than half of voters, even if there is an alternative majority-approved candidate; this occurs when some voters [[Exhausted vote|truncate their ballots]] to show they do not support any candidates in the final round. (In practice, candidates who do not receive a majority of votes in the first round usually do not finish with a majority, i.e. IRV does not prevent most majority failures.)<ref name=":5342">{{cite arXiv |eprint=2301.12075 |class=econ.GN |first1=Adam |last1=Graham-Squire |first2=David |last2=McCune |title=An Examination of Ranked Choice Voting in the United States, 2004-2022 |date=2023-03-06}}</ref><ref name=":12322">{{Cite SSRN |ssrn=1858374 |first=Kathy Anne |last=Dopp |title=Realities Mar Instant Runoff Voting Flaws and Benefits of IRV |date=2011}}</ref>

==Properties and pathologies==
=== Wasted votes and Condorcet winners ===
Compared to a plurality voting system that rewards only the top vote-getter using non-transferable votes, instant-runoff voting mitigates the problem of [[Wasted vote|wasted votes]].<ref name="chamberlin23">{{cite journal |last1=Chamberlin |first1=John R. |last2=Cohen |first2=Michael D. |year=1978 |title=Toward Applicable Social Choice Theory: A Comparison of Social Choice Functions under Spatial Model Assumptions |journal=American Political Science Review |publisher=Cambridge University Press (CUP) |volume=72 |issue=4 |pages=1341–1356 |doi=10.2307/1954543 |issn=0003-0554 |jstor=1954543 |quote=A long-established response to the 'wasted vote' problem is the method advocated by Hare...}}</ref> However, it does not ensure the election of a [[Condorcet winner criterion|Condorcet winner]], which is the candidate who would win a direct election against any other candidate in the race. 

Some advocates of instant-runoff voting argue that the failure to elect a Condorcet winner is positive, as it enables instant-runoff voting to pass [[later-no-help]] and [[later-no-harm]], which together render the method immune to [[Strategic voting#Common types of strategic voting|burying strategy]]. FairVote, in particular, has stated that they "believe [later-no-harm] is necessary in the context of high-stakes, competitive elections".<ref name="d912">{{cite web | title=How is RCV better than Approval, Score or Condorcet voting methods? | website=FairVote | date=2018-10-23 | url=https://fairvote.org/how_is_rcv_better_than_approval_score_or_condorcet_voting_methods/ | access-date=2025-03-01}}</ref>

=== Resistance to strategy ===
Instant-runoff voting has notably high resistance to [[Strategic voting|tactical voting]] but less to [[strategic nomination]].

==== Party strategizing and strategic nomination ====
In Australia, preference deals (where one party's voters agree to place another party's voters second, in return for their doing the same) between parties are common. This is also sometimes called “cross-endorsing” in the United States. Parties and candidates often encourage their supporters to participate in these preference deals using [[How-to-vote card|How-to-vote cards]] explaining how to use their lower rankings to maximize the chances of their ballot helping to elect someone in the preference deal before it may exhaust.<ref>{{cite web |date=20 May 2022 |title=Explained: What are 'preference deals' and how do they influence my vote? |url=https://www.9news.com.au/national/explainer-preference-deals-and-how-australias-voting-system-works/7078d92b-d6a6-4b37-919a-3aad0a13e873 |website=[[Nine News|9News]]}}</ref>

Instant runoff may be manipulable via strategic candidate entry and exit, reducing similar candidates' chances of winning. Such manipulation does not need to be intentional, instead acting to deter candidates from running in the first place.<ref name="d138">{{cite journal | last=Robinette | first=Robbie | title=Implications of strategic position choices by candidates | journal=Constitutional Political Economy | publisher=Springer Science and Business Media LLC | volume=34 | issue=3 | date=2023-02-02 | issn=1043-4062 | doi=10.1007/s10602-022-09378-6 | doi-access=free | pages=445–457}}</ref> Spatial model simulations indicate that instant runoff rewards strategic withdrawal by candidates.<ref name="Armytage 2014">{{cite journal | first=James|last=Green-Armytage | title=Strategic voting and nomination | journal=Social Choice and Welfare | publisher=Springer | volume=42 | issue=1 | year=2014 | issn=0176-1714 | jstor=43663746 | pages=111–138 | doi=10.1007/s00355-013-0725-3 | s2cid=253847024 | url=http://www.jstor.org/stable/43663746 | access-date=2024-02-23}}</ref>{{efn| name="ExitIncentive"|Figure 4 on page 137 shows instant-runoff voting having exit incentive despite being clone independent.}}

==== Tactical voting ====
{{See also|Tactical voting#Instant runoff voting}}
[[Gibbard's theorem]] demonstrates that no (deterministic, non-dictatorial) voting method can be entirely immune from tactical voting. This implies that instant-runoff voting is susceptible to tactical voting in some circumstances. In particular, when there exists a [[Condorcet winner]] who instant-runoff voting fails to elect, voters who prefer the Condorcet winner to the instant-runoff voting winner have an incentive to use the [[Tactical voting#Types of strategic voting|compromising]] strategy.<ref name="Armytage 2014" />{{rp|at=proposition 17}} instant-runoff voting is also sometimes vulnerable to a paradoxical strategy of ranking a candidate higher to make them lose, due to instant-runoff voting failing the [[monotonicity criterion]].<ref>{{cite web |title=Monotonicity and instant-runoff voting – Why the Monotonicity Criterion is of Little Import |url=http://archive.fairvote.org/?page=2261 |access-date=17 April 2011 |website=archive.fairvote.org}}</ref>

Research suggests that instant-runoff voting is highly resistant to strategic voting. In a test of multiple methods, instant runoff was found to be the second-most-resistant to tactical voting, after a class of instant runoff-[[Condorcet method|Condorcet]] hybrids.<ref name=":0">{{Cite journal |journal=[[Voting matters]] |title=Four Condorcet-Hare Hybrid Methods for Single-Winner Elections |url=https://www.votingmatters.org.uk/ISSUE29/I29P1.pdf |year=2011 |access-date=2024-10-25|first=James|last=Green-Armytage|quote=HRSV and HRSN are abbreviations for ‘highly resistant to strategic voting’, and ‘highly resistant to strategic nomination’. (Of course, reducing the simulation results to a binary score requires the imposition of a somewhat arbitrary cut-off, but in general, the methods deemed ‘highly resistant’ in each category perform substantially better than the others.)}}</ref> Instant-runoff voting is also completely immune to the ''burying'' strategy: ranking a strong opposition candidate lower can't get one's preferred candidate elected.<ref name="Armytage 2014" />{{rp|at=proposition 3}}

Tactical voting in instant-runoff voting seeks to alter the order of eliminations in early rounds, to ensure that the original winner is challenged by a stronger opponent in the final round. For example, in a three-party election where voters for both the [[Left-wing politics|left]] and [[Right-wing politics|right]] prefer the [[Centrism|centrist]] candidate to stop the opposing candidate from winning, those voters who care more about defeating the opposition than electing their own candidate may cast a tactical first-preference vote for the centrist candidate.

==== Spoiler effect ====
{{main|Spoiler effect}}
Proponents of instant-runoff voting claim that instant-runoff voting eliminates the spoiler effect, since instant-runoff voting makes it safe to vote honestly for marginal parties. Under a plurality method, voters who sympathize most strongly with a marginal candidate are strongly encouraged to instead vote for a more popular candidate who shares some of the same principles, since that candidate has a much greater chance of being elected, and a vote for the marginal candidate will not result in the marginal candidate's election. Instant-runoff voting reduces this problem, since the voter can rank the marginal candidate first and the mainstream candidate second; in the likely event that the fringe candidate is eliminated, the vote is not wasted but is transferred to the second preference.

However, when the third-party candidate is more competitive, they can still act as a spoiler under instant-runoff voting,<ref name=":043">{{Cite book |last=Borgers |first=Christoph |url=https://books.google.com/books?id=u_XMHD4shnQC |title=Mathematics of Social Choice: Voting, Compensation, and Division |publisher=SIAM |year=2010 |isbn=9780898716955 |quote=Candidates C and D spoiled the election for B ... With them in the running, A won, whereas without them in the running, B would have won. ... Instant runoff voting ... does ''not'' do away with the spoiler problem entirely, although it ... makes it less likely}}</ref><ref name=":723">{{Cite book |last=Poundstone |first=William |url=https://books.google.com/books?id=_24bJHyBV6sC |title=Gaming the Vote: Why Elections Aren't Fair (and What We Can Do About It) |publisher=Farrar, Straus and Giroux |year=2009 |isbn=9781429957649 |quote=IRV is excellent for preventing classic spoilers-minor candidates who irrationally tip the election from one major candidate to another. It is not so good when the 'spoiler' has a real chance of winning}}</ref><ref name="Burlington23">{{cite journal |author=Bristow-Johnson, R. |year=2023 |title=The failure of Instant Runoff to accomplish the purpose for which it was adopted: a case study from Burlington Vermont |url=https://doi.org/10.1007/s10602-023-09393-1 |format=PDF |journal=Const Polit Econ |volume=34 |issue=3 |pages=378–389 |doi=10.1007/s10602-023-09393-1 |s2cid=255657135 |access-date=9 January 2024|url-access=subscription }}</ref> by taking away first-choice votes from the more mainstream candidate until that candidate is eliminated, and then that candidate's second-choice votes helping a more-disliked candidate to win. In these scenarios, it would have been better for the third party voters if their candidate had not run at all (spoiler effect), or if they had voted dishonestly, ranking their second-favorite first and their favorite second, rather than first (favorite betrayal).<ref>{{Cite SSRN |last=O'Neill |first=Jeffrey C. |date=2006 |title=Everything That Can be Counted Does Not Necessarily Count: The Right to Vote and the Choice of a Voting System |page=340 |ssrn=883058 |quote=With instant runoff voting ... The strategy for the liberal voter is the same as for plurality voting: Her favorite candidate cannot win, so she casts her vote for her favorite candidate with a realistic chance of winning}}</ref>{{Better source needed|reason=The current source is insufficiently reliable ([[WP:NOTRS]]).|date=September 2024}} This is the same bracketing effect exploited by Robinette and Tideman in their research on strategic campaigning, where a candidate alters their campaign to cause a change in voter honest choice, resulting in the elimination of a candidate who nevertheless remains more preferred by voters. This occurred in the [[2022 Alaska's at-large congressional district special election]]. If Republican [[Sarah Palin]], who lost in the end, had not run, the more centrist Republican candidate, Nick Begich, was expected to have defeated the winning Democratic candidate, [[Mary Peltola]], because the expectation was that the votes for the two Republican candidates would have been combined behind Begich and would have exceeded those of Peltola. This did not happen in the IRV election due to the way 15,000 Begich supporters marked their back-up preferences across party lines.<ref>{{cite arXiv |eprint=2209.04764v1 |class=econ.GN |first1=Adam |last1=Graham-Squire |first2=David |last2=McCune |title=A Mathematical Analysis of the 2022 Alaska Special Election for US House |date=2022}}</ref>

This may be observed when a candidate leads in the first count but is in the end unsuccessful. For example, in the [[2009 Burlington, Vermont mayoral election|2009 Burlington, Vermont, mayoral election]], if Kurt Wright, the Republican candidate who lost in the end, had not run, the Democratic candidate, Andy Montroll, was expected to have defeated the winning Progressive candidate, Bob Kiss. In that sense, the Republican candidate was a spoiler—albeit for an opposing Democrat, rather than some political ally—even though he led in first-choice support.<ref name="Burlington23" /> (However, when Montroll's votes were transferred in the third round of counting, they went largely to Kiss, not to Wright.)

== Voting method criteria ==
{{main|Voting criteria}}

As shown by [[Arrow's impossibility theorem|Arrow]], [[Gibbard's theorem|Gibbard]], and others, it's usually impossible for a method to pass all of a number of seemingly reasonable properties, or criteria, at once. Instant-runoff voting is no exception: it passes some and fails others. The following criteria are satisfied and failed by instant-runoff voting:

=== Satisfied criteria ===

==== Condorcet loser criterion ====
<blockquote>The [[Condorcet loser criterion|'''Condorcet loser''']] criterion states that "if a candidate would lose a [[Condorcet method|head-to-head competition]] against every other candidate, then that candidate must not win the overall election". Instant-runoff voting (like all voting methods with a final runoff round) meets this criterion, since the Condorcet loser cannot win a runoff. </blockquote>

==== Independence of clones criterion ====
<blockquote>The '''[[independence of clones criterion]]''' states that "the election outcome remains the same even if an identical candidate who is equally preferred decides to run". Advocates have noted that instant-runoff voting meeting this criterion<ref>{{cite web |last1=Green-Armytage |first1=James |date=2004 |title=A Survey of Basic Voting Methods |url=http://www.econ.ucsb.edu/~armytage/voting/survey.htm |archive-url=https://web.archive.org/web/20130603015026/http://www.econ.ucsb.edu/~armytage/voting/survey.htm |archive-date=3 June 2013}}</ref><ref name="TC">{{cite journal |last=Tideman |first=T. N. |year=1987 |title=Independence of clones as a criterion for voting rules |journal=Social Choice and Welfare |publisher=Springer Science and Business Media LLC |volume=4 |issue=3 |pages=185–206 |doi=10.1007/bf00433944 |issn=0176-1714 |quote=Among previously proposed voting rules, the alternative vote and the GOCHA rule are independent of clones.}}</ref> greatly reduces the impact of clones compared to [[First-preference plurality|FPTP]]. </blockquote>

==== Later-no-harm criterion ====
<blockquote>The [[Later-no-harm criterion|'''later-no-harm''']] criterion states that "if a voter alters the order of candidates lower in his/her preference (e.g. swapping the second and third preferences), then that does not affect the chances of the most preferred candidate being elected". Instant runoff satisfies this criterion. </blockquote>

==== Majority criterion ====
<blockquote>The [[Majority favorite criterion|'''majority criterion''']] states that "if one candidate is preferred by an absolute majority of voters, then that candidate must win". Instant runoff also satisfies this criterion. </blockquote>

==== Mutual majority criterion ====
<blockquote>The [[Mutual majority criterion|'''mutual majority''']] criterion states that "if an absolute majority of voters prefer every member of a group of candidates to every candidate not in that group, then one of the preferred group must win". Note that this is satisfied because when all but one candidate that a mutual majority prefer is eliminated, the votes of the majority all flow to the remaining candidate, in contrast to [[FPTP]], where the majority would be treated as separate small groups. Instant runoff satisfies this criterion as well. </blockquote>

==== Resolvability criterion ====
<blockquote>The [[Resolvability criterion|'''resolvability''']] criterion states that "the probability of an exact tie must diminish as more votes are cast".{{Citation needed|date=September 2024}} </blockquote>

=== Failed criteria ===
{{Original research section|date=September 2024}}

==== Condorcet winner criterion ====
The [[Condorcet criterion|'''Condorcet winner''']] criterion states that "if a candidate would win a [[Condorcet method|head-to-head competition]] against every other candidate, then that candidate must win the overall election". It is incompatible with the later-no-harm criterion, so instant-runoff voting does not meet this criterion.

Instant-runoff voting is more likely to elect the Condorcet winner than [[plurality voting]] and [[Two-round system|traditional runoff]] elections. The California cities of Oakland, San Francisco and San Leandro in 2010 provide an example; there were a total of four elections in which the plurality-voting leader in first-choice rankings was defeated, and in each case the instant-runoff voting winner was the Condorcet winner, including a San Francisco election in which the instant-runoff voting winner was in third place in first choice rankings.

A particularly notable Condorcet failure occurred in the [[2009 Burlington mayoral election]].

==== Independence of irrelevant alternatives ====
The '''[[independence of irrelevant alternatives]]''' criterion states that "the election outcome remains the same even if a candidate who cannot win decides to run."  Instant-runoff voting violates this. In the general case, instant-runoff voting can be susceptible to [[strategic nomination]]: whether or not a candidate decides to run at all can affect the result even if the new candidate cannot themselves win. This is less likely to happen than under plurality, but much more likely than under the [[Minimax Condorcet method]].<ref name="Armytage 2014" />

==== Monotonicity criterion ====
{{Further|Monotonicity criterion#Instant-runoff voting and the two-round system are not monotonic}}

The '''[[monotonicity criterion]]''' says that a voter ranking a candidate higher on their ballot should not cause that candidate to lose and conversely, that a voter ranking a candidate lower on their ballot should not help that candidate win. The exact probability of a monotonicity failure depends on the circumstances, but with 3 major candidates, the probabilities range from 15 percent under the [[impartial culture|impartial culture model]]<ref name="Miller">{{cite conference |last=Miller |first=Nicholas R. |year=2012 |title=Monotonicity failure in IRV elections with three candidates |book-title=World meeting of the public choice societies}}</ref>{{rp|Table 6}} to 8.5 percent in the case of a strict [[Left–right political spectrum|left–right spectrum]].<ref>{{cite journal |last1=Lepelley |first1=Dominique |last2=Chantreuil |first2=Frederic |last3=Berg |first3=Sven |year=1996 |title=The likelihood of monotonicity paradoxes in run-off elections |journal=Mathematical Social Sciences |volume=31 |issue=3 |pages=133–146 |doi=10.1016/0165-4896(95)00804-7}}</ref>

==== Participation criterion ====
The '''[[participation criterion]]''' says that candidates should not lose as a result of having "too many voters"—a set of ballots that all rank A>B should not switch the election winner from B to A. Instant-runoff voting fails this criterion. In his 1984 study, mathematician Depankar Ray found that in elections where instant-runoff voting elects a different candidate from plurality, that there was an estimated 50 percent probability that some voters would have received a more preferable outcome if they had not participated.<ref name="auto4">{{cite journal |last=Ray |first=Depankar |year=1986 |title=On the practical possibility of a 'no show paradox' under the single transferable vote |journal=Mathematical Social Sciences |volume=11 |issue=2 |pages=183–189 |doi=10.1016/0165-4896(86)90024-7}}</ref>

==== Reversal symmetry criterion ====
The [[Reversal symmetry|reversal symmetry criterion]] states that the first- and last-place candidates should switch places if every ballot is reversed. In other words, it should not matter whether voters rank candidates from best-to-worst and select the best candidate, or whether they rank them worst-to-best and then select the least-bad candidate. 

Instant-runoff voting fails this criterion: it is possible to construct an election where reversing the order of every ballot does not alter the final winner; that is, the first- and last-place finishers, according to instant-runoff voting, are the same candidate.<ref>{{cite book |last=Felsenthal |first=Dan S. |title=Electoral Systems |date=2012 |publisher=Springer Berlin Heidelberg |isbn=978-3-642-20440-1 |editor-last=Felsenthal |editor-first=Dan S. |series=Studies in Choice and Welfare |location=Berlin, Heidelberg |pages=19–91 [§ 3.5.2.4] |chapter=Review of Paradoxes Afflicting Procedures for Electing a Single Candidate |doi=10.1007/978-3-642-20441-8_3 |access-date=2024-11-08 |editor2-last=Machover |editor2-first=Moshé |chapter-url=http://link.springer.com/10.1007/978-3-642-20441-8_3}}</ref>

=== Comparison to other voting systems ===
{{Main article|Comparison of electoral systems}}
{{Comparison of Schulze to preferential voting systems}}

== Criticism ==
The system has had a mixed reception among [[Political science|political scientists]] and [[Social choice theory|social choice theorists]].<ref name=":3">{{cite news |last1=Drutman |first1=Lee |last2=Strano |first2=Maresa |date=10 November 2021 |title=What We Know About Ranked-Choice Voting |url=https://www.newamerica.org/political-reform/reports/what-we-know-about-ranked-choice-voting/conclusion/ |access-date=28 February 2023 |publisher=New America}}</ref><ref name="auto2">{{Cite web |last=Drutman |first=Lee |date=2023-09-18 |title=How I updated my views on ranked choice voting |url=https://leedrutman.substack.com/p/how-i-updated-my-views-on-ranked |access-date=2024-09-02 |website=Undercurrent Events}}</ref>  Some have suggested that the system does not do much to decrease the impact of [[Wasted vote|wasted votes]] relative to plurality.<ref name=":23">{{Cite web |date=10 April 2017 |title=Understanding the Limited Preferential Voting system – EMTV Online |url=https://emtv.com.pg/understanding-the-limited-preferential-voting-system/ |access-date=18 February 2021}}</ref><ref name=":433">{{Cite SSRN |ssrn=4670677 |first1=Stephen |last1=Pettigrew |first2=Dylan |last2=Radley |title=Ballot Marking Errors in Ranked-Choice Voting |date=2023}}</ref><ref name=":035">{{Cite journal |last1=Endersby |first1=James W. |last2=Towle |first2=Michael J. |date=2014-03-01 |title=Making wasted votes count: Turnout, transfers, and preferential voting in practice |url=https://www.sciencedirect.com/science/article/abs/pii/S0261379413000930 |journal=Electoral Studies |volume=33 |pages=144–152 |doi=10.1016/j.electstud.2013.07.001 |issn=0261-3794|url-access=subscription }}</ref> Research has found instant-runoff voting causes lower confidence in elections<ref name="auto1">{{Cite web |title=The Effect of Ranked-Choice Voting in Maine {{!}} MIT Election Lab |url=https://electionlab.mit.edu/articles/effect-ranked-choice-voting-maine |access-date=2024-09-02 |website=electionlab.mit.edu}}</ref><ref name=":06">{{Cite journal |last1=Cerrone |first1=Joseph |last2=McClintock |first2=Cynthia |date=August 2023 |title=Come-from-behind victories under ranked-choice voting and runoff: The impact on voter satisfaction |url=https://onlinelibrary.wiley.com/doi/10.1111/polp.12544 |journal=Politics & Policy |language=en |volume=51 |issue=4 |pages=569–587 |doi=10.1111/polp.12544 |issn=1555-5623|url-access=subscription }}</ref><ref name="auto3">{{Cite journal |last=Nielson |first=Lindsay |date=August 2017 |title=Ranked Choice Voting and Attitudes toward Democracy in the United States: Results from a Survey Experiment |url=https://onlinelibrary.wiley.com/doi/10.1111/polp.12212 |journal=Politics & Policy |language=en |volume=45 |issue=4 |pages=535–570 |doi=10.1111/polp.12212 |issn=1555-5623|url-access=subscription }}</ref> and does not substantially affect minority representation,<ref name=":623">{{Cite web |title=The Short-Term Impact of Ranked-Choice Voting on Candidate Entry and Descriptive Representation |url=https://www.newamerica.org/political-reform/reports/rcv-impact-on-candidate-entry-and-representation/ |access-date=2024-09-02 |website=New America |language=en}}</ref> [[voter turnout]],<ref name=":3" /><ref name=":035" /> or long-run [[electoral competition]].<ref name=":3" /><ref name=":623" /> Opponents have also noted a high rate of repeals for the system.<ref name=":06"/>

=== Similarity to plurality ===
{{See also|Plurality-rule family}}
Often instant-runoff voting elections are won by the candidate who leads in first-count vote tallies so they choose the same winner as [[first-past-the-post voting]] would have. Such similarity between the two systems means the disproportionality of IRV is about same as results under first past the post.

Of the Australia federal elections, the [[1972 Australian federal election|1972 election]] had the largest number of winners who would not have won under first past the post, but still only 14 out of 125 seats filled were not won by the first-count leader.<ref>{{Cite web |last=Green |first=Antony |date=11 May 2010 |title=Preferential Voting in Australia |url=https://www.abc.net.au/news/2010-05-12/preferential-voting-in-australia/9389472 |access-date=1 November 2020 |website=www.abc.net.au}}</ref> In the [[2013 Australian federal election|Australian federal election in September 2013]], 135 out of the 150 [[Australian House of Representatives|House of Representatives]] seats (or 90 percent) were won by the candidate who led on first preferences. The other 15 seats (10 percent) were won by the candidate who placed second on first preferences.<ref>{{cite web |last=Green |first=Antony |date=2015-09-08 |title=Preferences, Donkey Votes and the Canning By-Election |url=https://www.abc.net.au/news/2015-09-08/preferences-donkey-votes-and-the-canning-by-election/9388654 |url-status=live |archive-url=https://web.archive.org/web/20180326041328/https://www.abc.net.au/news/2015-09-08/preferences-donkey-votes-and-the-canning-by-election/9388654 |archive-date=2018-03-26 |access-date=2015-09-08 |website=[[Antony Green]] |publisher=Australian Broadcasting Corporation |quote=...15 seats where preferences definitely determined the result by electing a second placed candidate |location=}}</ref>

=== Participation ===

The effect of instant-runoff voting on voter turnout is difficult to assess. In a 2021 report, researchers at [[New America (organization)|New America]], a [[think tank]] based in Washington, D.C., said it may increase turnout by attracting more and more diverse candidates, but the impact would be realized most significantly by eliminating the need for primaries.<ref name="auto12">{{Cite web |title=What We Know About Ranked-Choice Voting |url=http://newamerica.org/political-reform/reports/what-we-know-about-ranked-choice-voting/ |website=New America}}</ref> The overall impact on diversity of candidates is difficult to detect.<ref name=":3"/>

===Invalid, incomplete and exhausted ballots{{Anchor|Exhausted ballots}}===
All forms of ranked-choice voting reduce to plurality when all ballots rank only one candidate. By extension, ballots for which all candidates ranked are eliminated are equivalent to votes for any non-winner in plurality, and considered [[exhausted ballots]].

Some political scientists have found the IRV system contributes to higher rates of [[Spoiled vote|spoiled votes]],<ref name=":433" /> partly because the ballot marking is more complex.<ref name=":433" /><ref name=":5342" /> Most jurisdictions with instant-runoff voting do not require complete rankings and may use columns to indicate preference instead of numbers. In American elections with instant-runoff voting, more than 99 percent of voters typically cast a valid ballot.<ref>{{cite web |date=1 August 2008 |title=Instant Runoff Voting and Its Impact on Racial Minorities |url=http://politicalreform.newamerica.net/files/irvracememo.pdf |archive-url=https://web.archive.org/web/20110615181347/http://politicalreform.newamerica.net/files/irvracememo.pdf |archive-date=15 June 2011 |access-date=15 August 2011 |publisher=New America Foundation}}</ref>

A 2015 study of four local US elections that used instant-runoff voting found that inactive ballots occurred often enough in each of them that the winner of each election did not receive a majority of votes cast in the first round. The rate of inactive ballots in each election ranged from a low of 9.6 percent to a high of 27.1 percent.<ref>{{cite journal |last1=Burnett |first1=Craig M. |last2=Kogan |first2=Vladimir |date=March 2015 |title=Ballot (and voter) 'exhaustion' under Instant Runoff Voting: An examination of four ranked-choice elections |journal=Electoral Studies |volume=37 |pages=41–49 |doi=10.1016/j.electstud.2014.11.006 |s2cid=11159132}}</ref>

==Terminology==
While instant run-off voting is distinguished from its multiple winner equivalent, the [[single transferable vote]], most English-speaking discussion of electoral systems does not differentiate them. In [[Republic of Ireland|Ireland]], one of the few countries to use these systems in all elections, no distinction between the two is made, either by the general population or in legal texts. The [[Constitution of Ireland]] describes the electoral system as "proportional representation by means of the single transferable vote",<ref>ref name="Articles 16.2.5°, 12.2.3°, and 18.5, Constitution of Ireland">{{cite web |date=January 2020 |title=Constitution of Ireland (English) |url=https://www.irishstatutebook.ie/eli/cons/en/html |access-date=19 December 2024 |publisher=Office of the Attourney General}}</ref> as do all other statutory authorities, when referring to either single-winner or multiple-winner elections. The acronym "PR-STV" is in general use to describe both types of elections. Examples of single-winner elections in Ireland which are described officially as "proportional representation by means of the single transferable vote" are the [[Irish presidential election|election of the President]] and the [[2024 Ceann Comhairle election|election of the Ceann Comhairle]] (chairperson of [[Dáil Éireann]]). The lack of distinction between the systems in Ireland reflects that there is no difference in the mechanics of the process from election to election, only the number of candidates to be elected by that process. This is not always the case when discussing the systems in the abstract, as there are many variations in how such elections could be run.

Instant-runoff voting derives its name from the way the ballot count simulates a series of runoffs, similar to an [[Exhaustive ballot|exhaustive ballot system]], except that voters do not need to turn out several times to vote.<ref name="publications.parliament.uk2">{{cite web |date=15 February 2001 |title=Second Report: Election of a Speaker |url=https://publications.parliament.uk/pa/cm200001/cmselect/cmproced/40/4005.htm |access-date=18 February 2008 |publisher=House of Commons Select Committee on Procedure}}<!--This ref describes similarities/differences between instant-runoff voting and exhaustive ballot.--></ref> It is also known as the alternative vote, transferable vote, ranked-choice voting (RCV), single-seat ranked-choice voting, or preferential voting (but use of some of those terms may lead to misunderstanding as they also apply to single transferable vote.)<ref>{{Cite journal |last=Cary |first=David |date=1 January 2011 |title=Estimating the Margin of Victory for Instant-runoff Voting |url=http://dl.acm.org/citation.cfm?id=2028012.2028015 |journal=Proceedings of the 2011 Conference on Electronic Voting Technology/Workshop on Trustworthy Elections |series=EVT/WOTE'11 |pages=3}}</ref>

Britons and New Zealanders generally call instant-runoff voting the "alternative vote" (AV).<ref>{{cite web |date=8 February 2012 |title=BBC News – Alternative vote |url=https://www.bbc.com/news/uk-politics-12910547 |access-date=9 October 2019 |website=bbc.com |publisher=British Broadcasting Corporation}}</ref><ref>{{cite web |date=30 September 2017 |title=Opinion: OUSA Needs the Alternative Vote |url=https://www.critic.co.nz/news/article/7194/opinion-ousa-needs-the-alternative-vote |access-date=9 October 2019 |website=Critic – Te Arohi |publisher=Otago University Students' Association |location=Otago, New Zealand}}</ref> Australians, who use instant-runoff voting for most single winner elections, call instant-runoff voting "preferential voting".<ref>{{cite news |date=11 December 2020 |title=Liberal plan to change federal voting laws may have crossbench support |url=https://www.theguardian.com/australia-news/2020/dec/12/liberal-plan-to-change-federal-voting-laws-may-have-crossbench-support |access-date=13 February 2021 |work=The Guardian}}</ref> While this term is widely used by Australians, it is somewhat of a [[misnomer]]. Depending on how "preferential" is defined, the term would include all voting systems, apply to any system that uses ranked ballots (thus both instant-runoff voting and single transferable vote), or would exclude instant-runoff voting (instant-runoff voting fails [[Monotonicity criterion|positive responsiveness]] because ballot markings are not interpreted as "preferences" in the traditional sense. Under instant-runoff voting (and single transferable vote), secondary preferences are used as back-up preferences/contingency votes).

Jurisdictions in the United States such as [[San Francisco]], [[Minneapolis]], [[Maine]], and [[Alaska]] have tended to use the term "ranked-choice voting" in their laws that apply to instant-runoff voting contests. The San Francisco Department of Elections claimed the word "instant" in the term "instant-runoff voting" could confuse voters into expecting results to be immediately available.<ref>Appendix D, Instant Runoff Voting, San Francisco Charter § 13.102 https://sfgov.org/ccsfgsa/sites/default/files/Voting%20Systems%20Task%20Force/AppendixD__.pdf.</ref><ref>{{cite web |last=Arntz |first=John |date=2 February 2005 |title=Ranked-Choice Voting: A Guide for Candidates |url=http://www.fairvote.org/media/irv/sanfrancisco/RCVCandidateGuide04.pdf |archive-url=https://web.archive.org/web/20081202040611/http://fairvote.org/media/irv/sanfrancisco/RCVCandidateGuide04.pdf |archive-date=2 December 2008 |access-date=25 August 2009 |publisher=Department of Elections: City and County of San Francisco |via=[[FairVote]] |quote=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—voters 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.}}</ref> As a result of American influence, the term ranked-choice voting is often used in Canada as well.<ref name="auto">{{cite web |title=What is Ranked Choice Voting? |url=http://www.london.ca/city-hall/elections/ranked-choice-voting/Pages/What-is-Ranked-Choice-Voting.aspx |archive-url=https://web.archive.org/web/20180226101409/http://www.london.ca/city-hall/elections/ranked-choice-voting/Pages/What-is-Ranked-Choice-Voting.aspx |archive-date=26 February 2018 |website=City of London}}</ref> When discussing his promise of electoral reform, Canadian Prime Minister Justin Trudeau used the term "preferential ballot".<ref>{{Cite news |last=Kustra |first=Tyler |last2=Raji |first2=Tobi |last3=Amenabar |first3=Teddy |last4=Dance |first4=Scott |last5=Wang |first5=Amy B. |last6=George |first6=Olivia |last7=Gathright |first7=Jenny |last8=Uber |first8=Emma |last9=Lang |first9=Marissa |date=2017-02-13 |title=Analysis {{!}} Trudeau and allies pledged 1,813 times to reform Canada’s elections. Now it won’t happen. |url=https://www.washingtonpost.com/news/monkey-cage/wp/2017/02/13/canadians-wanted-their-government-to-reflect-the-national-vote-but-these-reforms-arent-happening/ |access-date=2025-06-15 |work=The Washington Post |language=en-US |issn=0190-8286}}</ref> 

American NGO [[FairVote]] has promoted the terminology "ranked-choice voting" to refer to instant-runoff voting,<ref name="auto" /><ref>{{cite web |date=17 August 2019 |title=How RCV Works |url=https://www.fairvote.org/rcv#how_rcv_works |access-date=17 August 2018 |website=FairVote}}</ref> a choice that has caused controversy and accusations that the organization is attempting to obscure the existence of other [[Ranked voting|ranked-choice]] methods that are competing or could compete with instant-runoff voting.{{Cn|date=May 2024}}

Instant-runoff voting is occasionally referred to as Hare's method<ref>{{Cite encyclopedia |title=Voting Methods |encyclopedia=The Stanford Encyclopedia of Philosophy |url=https://plato.stanford.edu/archives/fall2019/entries/voting-methods/ |last=Pacuit |first=Eric |date=24 June 2019 |orig-date=3 August 2011 |editor1-last=Zalta |editor1-first=Edward N. |edition=Fall 2019 |via=plato.stanford.edu}}</ref> (after [[Thomas Hare (political scientist)|Thomas Hare]]) to differentiate it from other ranked-choice voting methods such as [[Condorcet winner criterion|majority-choice voting]], [[Borda count|Borda]], and [[Bucklin voting|Bucklin]], which use weighted preferences or methods that allow voter's lower preference to be used against voter's most-preferred choice.

When the [[single transferable vote]] (STV) method is applied to a single-winner election, it becomes instant-runoff voting; the government of Ireland has called instant-runoff voting "proportional representation" based on the fact that the same ballot form is used to elect its president by instant-runoff voting and parliamentary seats by proportional representation (single transferable vote), but instant-runoff voting is a non-proportional single-winner election method, while single transferable vote elects multiple winners and produces minority representation, as well as majority representation, in almost all cases.<ref>{{cite web |title=Proportional Representation |url=https://www.citizensinformation.ie/en/government_in_ireland/elections_and_referenda/voting/proportional_representation.html |access-date=17 August 2019 |publisher=Citizens Information Board}}</ref>

State law in [[South Carolina]]<ref>{{cite web |title=South Carolina General Assembly : 116th Session, 2005–2006 |url=http://www.scstatehouse.gov/sess116_2005-2006/bills/3720.doc |access-date=1 March 2015 |website=Scstatehouse.gov}}</ref> and [[Arkansas]]<ref>{{cite web |title=Bill Information |url=http://www.arkleg.state.ar.us/assembly/2005/R/Pages/BillInformation.aspx?measureno=HB1770 |access-date=28 January 2015 |website=Arkleg.state.ar.us}}</ref> use "instant runoff" to describe the practice of having certain categories of absentee voters cast ranked-choice ballots before the first round of an election and counting those ballots in any subsequent runoff elections.

==History and use==
{{Main|History and use of instant-runoff voting}}

=== History ===
This method was first discussed by the [[Marquis de Condorcet]] in 1788, who quickly rejected it after showing it would often eliminate a candidate preferred by a majority of voters to any other candidate.<ref name=":032">{{Cite journal |last=Nanson |first=E. J. |date=1882 |title=Methods of election: Ware's Method |url=https://archive.org/details/transactionsproc1719roya/page/206 |journal=Transactions and Proceedings of the Royal Society of Victoria |volume=17 |pages=206 |quote=The method was, however, mentioned by Condorcet, but only to be condemned.}}</ref><ref>{{Cite book |last=Condorcet |first=Jean-Antoine-Nicolas de Caritat |chapter-url=https://books.google.com/books?id=d0cwAAAAYAAJ&q=Oeuvres%20de%20Condorcet,%20Volume%2013&pg=PA243 |chapter=On the Constitution and the Functions of Provincial Assemblies |date=1788 |title=Complete Works of Condorcet |volume=13 |publication-date=1804 |pages=243 |language=fr |quote=En effet, lorsqu'il y a plus de trois concurrents, le véritable vœu de la pluralité peut être pour un candidat qui n'ait eu aucune des voix dans le premier scrutin.}}</ref>

Instant-runoff voting was later independently reinvented by [[Thomas Hare (political reformer)|Thomas Hare]] (of England) and Carl Andrae (of Denmark) in the form of the [[single transferable vote]]. [[Henry Richmond Droop]], inventor of the [[Droop quota]], then proposed applying the system to single-winner contests.<ref name="r748">{{cite journal | last=Droop | first=H. R. | title=On Methods of Electing Representatives | journal=Journal of the Statistical Society of London | publisher=[Royal Statistical Society, Oxford University Press] | volume=44 | issue=2 | year=1881 | issn=0959-5341 | jstor=2339223 | pages=141–202 | doi=10.2307/2339223 | url=http://www.jstor.org/stable/2339223 | access-date=2025-03-01}}</ref>

After conducting a demonstration STV election in 1881, [[William Robert Ware|William R. Ware]], proposed that a single-winner versions (IRV) could be used to determine the winner in a byelection, thus helping push IRV as workable system. IRV was once known as "Ware's system" due to this advocacy.<ref>{{Cite web|url=http://archive.fairvote.org/irv/vt_lite/history.htm|title=The History of IRV|website=FairVote archives|access-date=June 19, 2019}}</ref>

==== Adoption ====
Instant-runoff voting has found some use [[History and use of instant-runoff voting|in national elections in several countries]], predominantly in the [[Anglosphere]]. It is used to elect members of the [[Australian House of Representatives]] and the [[National Parliament of Papua New Guinea]], and to elect the [[Heads of state|head of state]] in [[President of India|India]], [[President of Ireland|Ireland]], and [[President of Sri Lanka|Sri Lanka]].{{Cn|date=June 2025}}

In [[Alaska]], it is used for general elections, after a [[Top-four primary|top-four nonpartisan primary]],<ref name="boston.com2">{{cite web |date=10 November 2016 |title=Maine became the first state in the country Tuesday to pass ranked-choice voting |url=https://www.boston.com/news/politics/2016/11/10/maine-became-the-first-state-in-the-country-to-pass-ranked-choice-voting |access-date=10 November 2016}}</ref> while in [[Maine]] it is used for both general elections and for [[Primary election|primary elections]] (held separately by each party), excluding those for .<ref name="Maine20182">{{cite news |last=Russell |first=Eric |date=12 June 2018 |title=Mainers vote to keep ranked-choice voting, with supporters holding commanding lead |url=https://www.pressherald.com/2018/06/12/ranked-choice-voting-takes-lead-in-early-balloting/ |access-date=13 June 2018 |work=Portland Press Herald}}</ref><ref>{{Cite web |title=Alaska Ballot Measure 2, Top-Four Ranked-Choice Voting and Campaign Finance Laws Initiative (2020) |url=https://ballotpedia.org/Alaska_Ballot_Measure_2,_Top-Four_Ranked-Choice_Voting_and_Campaign_Finance_Laws_Initiative_(2020) |access-date=17 November 2020 |website=Ballotpedia}}</ref><ref>{{cite web |title=Ranked Choice Voting {{!}} Maine Voters Rank Candidates |url=http://mainerankedchoice.vote/ |url-status=dead |archive-url=https://web.archive.org/web/20180404201657/http://mainerankedchoice.vote/ |archive-date=4 April 2018 |access-date=8 April 2018 |website=Maine Uses Ranked Choice Voting}}</ref>

=== ''Robert's Rules of Order'' ===
In the United States, the sequential elimination method used by instant-runoff voting is described in ''[[Robert's Rules of Order|Robert's Rules of Order Newly Revised]]'' as an example of [[Ranked voting systems|ranked-choice voting]] that can be used to elect officers.<ref name="autogenerated12">{{cite book |last=Robert |first=Henry |title=Robert's Rules of Order Newly Revised |publisher=Da Capo Press |year=2011 |isbn=978-0-306-82020-5 |edition=11th |pages=425–428}}</ref> ''Robert's Rules'' note that ranked-choice systems (including instant-runoff voting) are an improvement on [[Plurality voting|simple plurality]] but recommend against runoff-based rules because they often prevent the emergence of a consensus candidate with broad support. The book instead recommends repeated balloting until some candidate manages to win a majority of votes. Two other books on American parliamentary procedure, ''[[The Standard Code of Parliamentary Procedure]]''<ref>{{cite parl|title=TSC|page=148|edition=4th}}</ref> and ''[[Riddick's Rules of Procedure]]'',<ref>{{cite parl|title=RID|page=145|edition=1985|year=1985}}</ref> take a similar stance.

== Examples ==
The first example is a fictional one for the purpose of demonstrating the principle of instant runoff. The other examples are drawn from the results of real-life elections.

=== Tennessee capital example ===
{{Tenn_voting example}}

It takes three rounds to determine a winner in this election.
[[File:TN-round1.svg|right|frameless|175x175px]]
'''Round 1''' – In the first round no city receives a majority:
{| class="wikitable"
!Votes in round/
City Choice
!1st
|-
|Memphis
| style="background:#dfb;" |42%
|-
|Nashville
| style="background:#dfb;" |26%
|-
|Knoxville
| style="background:#dfb;" |17%
|-
|Chattanooga
| style="background:#fbb;" |''15%''
|}
If one of the cities had achieved a majority vote (more than half), the election would end there. If this were a first-past-the-post election, Memphis would win because it received the most votes. But instant-runoff voting does not allow a candidate to win on the first round without having an absolute majority of the active votes. Since no city has won yet, the city with the least first-place support (Chattanooga) is eliminated from consideration. The ballots that listed Chattanooga as first choice are added to the totals of the second-choice selection on each ballot. 
[[File:TN-round2.svg|right|frameless|161x161px]]
'''Round 2''' – In the second round of tabulation, Chattanooga's 15% of the total votes have been added to the second choices selected by the voters for whom that city was first-choice (in this example Knoxville):
{| class="wikitable"
!Votes in round/
City Choice
!1st
!2nd
|-
|Memphis
| style="background:#dfb;" |42%
| style="background:#dfb;" |42%
|-
|Nashville
| style="background:#dfb;" |26%
| style="background:#fbb;" |''26%''
|-
|Knoxville
| style="background:#dfb;" |17%
| style="background:#dfb;" |32%
|-
|Chattanooga
| style="background:#fbb;" |''15%''
|
|}
In the first round, Memphis was first, Nashville was second and Knoxville was third. With Chattanooga eliminated and its votes redistributed, the second round finds Memphis still in first place, followed by Knoxville in second and Nashville has moved down to third place. No city yet has secured a majority of votes, so the now last placed Nashville is eliminated and the ballots currently counting for Nashville are added to the totals of Memphis or Knoxville based on which city is ranked next on that ballot.

'''Round 3'''
[[File:TN-round3.svg|right|frameless|141x141px]]
As Memphis and Knoxville are the only two cities remaining in the contest, this round will be the final round. In this example the second-choice of the Nashville voters is Chattanooga, which is already eliminated. Therefore, the votes are added to their third-choice: Knoxville. The third round of tabulation yields the following result:
{| class="wikitable"
!Votes in round/
City Choice
!1st
!2nd
!3rd
|-
|Memphis
| style="background:#dfb;" |42%
| style="background:#dfb;" |42%
| style="background:#fbb;" |''42%''
|-
|Nashville
| style="background:#dfb;" |26%
| style="background:#fbb;" |''26%''
|-
|Knoxville
| style="background:#dfb;" |17%
| style="background:#dfb;" |32%
| style="background:#bfb;" |'''58%'''
|-
|Chattanooga
| style="background:#fbb;" |''15%''
|}
'''Result:''' Knoxville, which was running third in the first tabulation, has moved up from behind to take first place in the third and final round. The winner of the election is '''Knoxville'''. However, if 6% of voters in Memphis were to put Nashville first, the winner would be Nashville, a preferable outcome for voters in Memphis. This is an example of potential tactical voting, though one that would be difficult for voters to carry out in practice. Also, if 17% of voters in Memphis were to stay away from voting, the winner would be Nashville. This is an example of instant-runoff voting failing the participation criterion.

For comparison, note that traditional [[first-past-the-post voting]] would elect Memphis, even though most citizens consider it the worst choice, because 42% is larger than any other single city. As Nashville is a Condorcet winner, [[Condorcet method#Example: Voting on the location of Tennessee's capital|Condorcet methods]] would elect Nashville. A [[Two-round system#Example II|two-round method]] would have a runoff between Memphis and Nashville where Nashville would win, too.

===1990 Irish presidential election===
{{See also|Irish presidential election, 1990}}
The [[1990 Irish presidential election]] provides a simple example of how instant-runoff voting can produce a different result from [[first-past-the-post voting]] and prevent some spoiler effects associated with [[plurality voting]]. The three major candidates were [[Brian Lenihan Snr|Brian Lenihan]] of [[Fianna Fáil]], [[Austin Currie]] of [[Fine Gael]], and [[Mary Robinson]] of the [[Labour Party (Ireland)|Labour Party]]. In the first round, Lenihan had the largest share of first-choice rankings but not a majority. Currie had the fewest votes and was eliminated. After this, Robinson received 82 percent of Currie's votes. This was enough for her vote tally to pass that of Lenihan, and thus form a majority of votes.
{| class="wikitable" style="text-align:right;"
|+Irish presidential election, 1990<ref>{{cite web |title=Presidential Election November 1990 |url=http://www.electionsireland.org/result.cfm?election=1990P&cons=194 |access-date=23 November 2009 |work=ElectionsIreland.org}}</ref>
!Candidate
! colspan="2" |Round 1
! colspan="2" |Round 2
|-
![[Mary Robinson]]
|612,265
|38.7%
|'''817,830'''
|'''51.6%'''
|-
![[Brian Lenihan Snr|Brian Lenihan]]
|694,484
|43.8%
|731,273
|46.2%
|-
![[Austin Currie]]
|267,902
|16.9%{{Xmark}}
| colspan="2" align="center" |''Eliminated''
|-
!Exhausted ballots
|9,444
|0.6%
|34,992
|2.2%
|-
!Total
|1,584,095
|100%
|1,584,095
|100%
|}
<!--no cite: since only 3 candidates just simple ratio of extra votes in 2nd count.-->{{clear}}

===2014 Prahran election (Victoria)===
Another real-life example of instant-runoff voting producing results different from first-past-the-post can be seen in the [[2014 Victorian state election|2014 Victorian general election]] in [[Electoral district of Prahran|Prahran]]. In this rare instance, the candidate who initially placed third, ([[Australian Greens|Greens]] candidate [[Sam Hibbins]]), won the seat.<ref name="PrahranResults2">{{cite web |title=State Election 2014: Prahran District (Distribution of preference votes) |url=https://www.vec.vic.gov.au/Results/State2014/distributionPrahranDistrict.html |work=Victorian Electoral Commission |access-date=25 July 2018 |archive-date=25 July 2018 |archive-url=https://web.archive.org/web/20180725092627/https://www.vec.vic.gov.au/Results/State2014/distributionPrahranDistrict.html |url-status=dead }}</ref> In the 7th and final round, Hibbins narrowly defeated [[Liberal Party of Australia|Liberal]] candidate Clem Newton-Brown by a margin of 277 votes, having eliminated Neil Pharaoh by the even narrower margin of 31 votes in the previous round.
{{table alignment}}
{| class="wikitable sortable col1left" style="text-align:right;"
!Candidate
! colspan="2" |1st
!2nd
!3rd
!4th
!5th
!6th
! colspan="2" |7th
|-
|[[Clem Newton-Brown]] ([[Liberal Party of Australia|LIB]])
|44.8%
|'''16,582'''
|'''16,592'''
|'''16,644'''
|'''16,726'''
|'''16,843'''
|'''17,076'''
|18,363
|49.6%
|-
|Neil Pharaoh ([[Australian Labor Party|ALP]])
|25.9%
|'''9,586'''
|'''9,593'''
|'''9,639'''
|'''9,690'''
|'''9,758'''
| style="background:#FFDDDD;" |9,948
| colspan="2" align="left" |{{Xmark}}''Eliminated''
|-
|[[Sam Hibbins]] ([[Australian Greens|GRN]])
|24.8%
|9,160
|9,171
|9,218
|9,310
|9,403
|'''9,979'''
|'''18,640'''
|'''50.4%'''
|-
|Eleonora Gullone ([[Animal Justice Party|AJP]])
|2.3%
|837
|860
|891
|928
| style="background:#FFDDDD;" |999
| colspan="3" align="left" |{{Xmark}}''Eliminated''
|-
|Alan Walker ([[Family First Party|FFP]])
|0.8%
|282
|283
| style="background:#FFDDDD;" |295
| colspan="5" align="left" |{{Xmark}}''Eliminated''
|-
|Jason Goldsmith ([[Independent (politician)|IND]])
|0.7%
|247
|263
|316
| style="background:#FFDDDD;" |349
| colspan="4" align="left" |{{Xmark}}''Eliminated''
|-
|Steve Stefanopoulos ([[Independent (politician)|IND]])
|0.6%
|227
| style="background:#FFDDDD;" |241
| colspan="6" align="left" |{{Xmark}}''Eliminated''
|-
|Alan Menadue ([[Independent (politician)|IND]])
|0.2%
| style="background:#FFDDDD;" |82
| colspan="7" align="left" |{{Xmark}}''Eliminated''
|-
!Total
|'''100%'''
|'''37,003'''
|}

===2009 Burlington mayoral election===
{{See also|2009 Burlington mayoral election}}
{| class="wikitable" style="text-align:right;"
|+ Burlington mayoral election, 2009 (round-by-round analysis of votes)
|-
! colspan="2" |Candidates
! colspan="2" |1st round
! colspan="2" |2nd round
! colspan="2" |3rd round
|-
!Candidate
!Party
!Votes
!±
!Votes
!±
!Votes
!±
|- {{Party shading/Vermont Progressive}}
| style="text-align:left;" | '''[[Bob Kiss]]'''
| style="text-align:left;" | [[Vermont Progressive Party|Progressive]]
| 2585
| +2585
| 2981
| +396
| '''4313'''
| +1332
|- {{Party shading/Republican}}
| style="text-align:left;" | Kurt Wright
| style="text-align:left;" | [[Vermont Republican Party|Republican]]
| '''2951'''
| +2951
| '''3294'''
| +343
| 4061
| +767
|- {{Party shading/Democratic}}
| style="text-align:left;" | Andy Montroll
| style="text-align:left;" | [[Vermont Democratic Party|Democrat]]
| 2063
| +2063
| 2554
| +491
| colspan="2" |Eliminated
|- {{Party shading/Independent}}
| style="text-align:left;" | Dan Smith
| style="text-align:left;" | [[Independent (politician)|Independent]]
| 1306
| +1306
| colspan="2" |Eliminated
|- 
! style="text-align:left;" | Others
|
| 71
| +71
| colspan="2" |Eliminated
|- 
! style="text-align:left;" | [[Exhausted ballot|Exhausted]]
|
| 4
| +4
| 151
| +147 
| 606
| +455
|}
Under Burlington, Vermont's second-ever instant-runoff voting mayoral election in 2009, the winner, Bob Kiss, was elected over the more-popular Andy Montroll as a result of a first-round spoiler effect.{{dubious|date=June 2025}}

[[FairVote]] touted the 2009 election as one of its major success stories,<ref name=":4">{{Cite news |last=Etnier |first=Carl |date=6 March 2009 |title=Instant runoff was success |url=https://www.rutlandherald.com/articles/instant-runoff-was-success/ |access-date=17 March 2018 |work=Rutland Herald }}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> claiming it helped the city save on costs of a traditional runoff<ref name=":4" /><ref name=":5">{{Cite news |last=Totten |first=Shay |title=Burlington Residents Seek Repeal of Instant Runoff Voting |url=https://www.sevendaysvt.com/vermont/burlington-residents-seek-repeal-of-instant-runoff-voting/Content?oid=2177125 |access-date=17 March 2018 |work=Seven Days |language=en |quote=We waited to bring in the signatures because we didn't want this to be about Kurt Wright losing after being ahead, or Andy Montroll who had more first and second place votes and didn't win. We wanted this to be about IRV.}}</ref> and prevented a [[spoiler effect]],<ref name=":02">{{Cite web |last=Bouricius |first=Terry |date=17 March 2009 |title=Response to Faulty Analysis of Burlington IRV Election |url=http://www.fairvote.org/response-to-faulty-analysis-of-burlington-irv-election |access-date=1 October 2017 |website=FairVote.org |quote=successfully prevented the election of the candidate who would likely have won under plurality rules, but would have lost to either of the other top finishers in a runoff}}</ref> although later analysis showed that without Wright in the election, Montroll would have defeated Kiss in a one-on-one race.<ref name=":10">{{Cite journal |last=Lewyn |first=Michael |date=2012 |title=Two Cheers for Instant Runoff Voting |journal=Phoenix L. Rev. |language=en |volume=6 |page=117 |ssrn=2276015 |quote=election where Democratic candidate for mayor was Condorcet winner but finished third behind Republican and 'Progressive{{'-}}}}</ref>

[[Mathematicians]] and [[Voting theory|voting theorists]] criticized the election results as revealing several [[Pathological (mathematics)|pathologies]] associated with instant-runoff voting, noting that Kiss was elected as a result of 750 votes [[Participation criterion|cast against him]] (ranking Kiss in last place).<ref>{{Cite journal |last1=Felsenthal |first1=Dan S. |last2=Tideman |first2=Nicolaus |date=2014 |title=Interacting double monotonicity failure with direction of impact under five voting methods |journal=Mathematical Social Sciences |volume=67 |pages=57–66 |doi=10.1016/j.mathsocsci.2013.08.001 |issn=0165-4896 |quote=A display of non-monotonicity under the Alternative Vote method was reported recently, for the March 2009 mayoral election in Burlington, Vermont.}}</ref><ref name=":8">{{Cite journal |last1=Ornstein |first1=Joseph T. |last2=Norman |first2=Robert Z. |date=1 October 2014 |title=Frequency of monotonicity failure under Instant Runoff Voting: estimates based on a spatial model of elections |journal=Public Choice |language=en |volume=161 |issue=1–2 |pages=1–9 |doi=10.1007/s11127-013-0118-2 |issn=0048-5829 |s2cid=30833409 |quote=Although the Democrat was the Condorcet winner (a majority of voters preferred him in all two way contests), he received the fewest first-place votes and so was eliminated ... 2009 mayoral election in Burlington, VT, which illustrates the key features of an upward monotonicity failure}}</ref>

Several [[electoral reform]] advocates branded the election a failure after Kiss was elected, despite 54 percent of voters voting for Montroll over Kiss,<ref>{{Cite journal |last1=Bristow-Johnson |first1=Robert |date=2023 |title=The failure of Instant Runoff to accomplish the purpose for which it was adopted: a case study from Burlington Vermont |journal=Constitutional Political Economy |volume=34 |issue=3 |pages=378–389 |doi=10.1007/s10602-023-09393-1}}</ref> violating the principle of [[Condorcet winner|majority rule]].<ref name=":10" /><ref>{{Cite book |last=Ellenberg |first=Jordan |url=https://archive.org/details/hownottobewrongp0000elle |title=How Not to Be Wrong: The Power of Mathematical Thinking |date=29 May 2014 |publisher=Penguin |isbn=9780698163843 |page=[https://archive.org/details/hownottobewrongp0000elle/page/385 385] |language=en |quote=a majority of voters liked the centrist candidate Montroll better than Kiss, and a majority of voters liked Montroll better than Wright ... yet Montroll was tossed in the first round. |url-access=registration}}</ref><ref>{{Cite SSRN |last=Stensholt |first=Eivind |date=7 October 2015 |title=What Happened in Burlington? |ssrn=2670462 |quote=K was elected even though M was a clear Condorcet winner and W was a clear Plurality winner.}}</ref><ref name=":6">{{Cite news |last=Dopp |first=Kathy |date=10 June 2009 |title=IRV much worse than old runoffs |url=https://www.aspentimes.com/news/irv-much-worse-than-old-runoffs/ |access-date=17 March 2018 |work=The Aspen Times |language=en}}</ref>

<!-- Lint
{{Election box ranked choice candidate with party link|party=Vermont Progressive Party|candidate=[[Bob Kiss]]|maxround=3|maxvotes=4313|maxvotespercent=48.0|r1votes=2585|fullwidthvotes=4500}}
{{Election box ranked choice candidate with party link|party=Vermont Republican Party|candidate=Kurt Wright|maxround=3|maxvotes=4061|maxvotespercent=45.2|r1votes=2951|fullwidthvotes=4500}}
{{Election box ranked choice candidate with party link|party=Vermont Democratic Party|candidate=Andy Montroll|maxround=2|maxvotes=2554|maxvotespercent=28.4|r1votes=2063|fullwidthvotes=4500}}
{{Election box ranked choice candidate with party link|party=Independent politician|candidate=Dan Smith|maxround=1|maxvotes=1306|maxvotespercent=14.5|r1votes=1306|fullwidthvotes=4500}}
{{Election box ranked choice candidate with party link|party=Green Party (United States)|candidate=James Simpson|maxround=1|maxvotes=35|maxvotespercent=0.4|r1votes=35|fullwidthvotes=4500}}
{{Election box ranked choice candidate with party not linked|party=Write-in|candidate=|maxround=1|maxvotes=36|maxvotespercent=0.4|r1votes=36|fullwidthvotes=4500}}
{{Election box ranked choice exhausted no party no change with bar|maxvotes=606|maxvotespercent=6.7|r1votes=4|fullwidthvotes=4500|votes=606|percentage=6.7}}
{{Election box ranked choice end}}-->==Similar methods==
===Runoff voting===
{{Original research section|date=August 2024}}

The term ''instant-runoff voting'' is derived from the name of a class of voting methods called runoff voting. In runoff voting voters do not rank candidates on the ballot - each voter marks only one preference. When no candidate receives a majority of voters in the first round, voters cast votes in two or more subsequent rounds of voting as the field of candidates is reduced. Multi-round runoff voting methods allow voters to change their preferences in each round, incorporating the results of the prior round to influence their decision, which is not possible in instant-runoff voting.

The runoff method closest to instant-runoff voting is the [[exhaustive ballot]]. In this method—familiar to fans of the television show ''[[American Idol]]''—one candidate is eliminated in each round, and many rounds of voting may be necessary. Because holding many rounds of voting on separate days is generally expensive, the exhaustive ballot is not used for large-scale, public elections.

A more practical form of runoff voting is the [[two-round system]]. If no candidate receives a majority of votes in the first round, all but the top-two candidates are excluded after the first round, and just one more round of voting determines the winner. Eliminations can occur with or without allowing and applying preference votes to choose the final two candidates. This method is used in Mali and France, and in Finnish and Slovenian presidential elections.

===Contingent vote===
{{Original research section|date=August 2024}}
[[File:IRV-toptwo_flowchart.png|thumb|Top-two instant-runoff voting]]
The [[contingent vote]], also known as "top-two instant-runoff voting" ("top-two IRV"), is the same as instant-runoff voting, except that if no candidate achieves a majority in the first round of counting, all but the two candidates with the most votes are eliminated, and the second preferences for those ballots are counted. As in instant-runoff voting, there is only one round of voting. Unlike instant-runoff voting, the vote count process entails only two rounds of counting, while instant-runoff voting can entail many rounds.

Under a variant of contingent voting used in [[Sri Lanka]], and formerly for the elections for [[Mayor of London]] in the United Kingdom, voters rank a specified maximum number of candidates. In London, the [[Contingent vote|supplementary vote]] allowed{{efn|Following the [[Elections Act 2022]], voting in mayoral elections now takes place under the [[First-past-the-post voting|first-past-the-post]] system.}} voters to express first and second preferences only. Sri Lankan voters [[Contingent vote#contingent vote in Sri Lanka|rank up to three candidates to elect the president of Sri Lanka]].

While similar to "sequential-elimination" instant-runoff voting, top-two can produce different results. Excluding more than one candidate after the first count might eliminate a candidate who would have won under sequential elimination instant-runoff voting. Restricting voters to a maximum number of preferences is more likely to exhaust ballots if voters do not anticipate which candidates will finish in the top two. This can encourage voters to vote more [[Tactical voting|tactically]], by ranking at least one candidate they think is likely to win.

Conversely, a practical benefit of 'contingent voting' is expediency and confidence in the result with only two rounds.

===Larger runoff process===
Instant-runoff voting may also be part of a larger runoff process:

* Some jurisdictions that hold [[Two-round system|runoff elections]] allow absentee (only) voters to submit ranked ballots, because the interval between rounds of balloting is too short for a second round of absentee voting. Ranked ballots enable absentee votes to count in the second (general) election round if their first choice does not make the second round runoff. [[Arkansas]], [[South Carolina]] and [[Springfield, Illinois]] adopt this approach.<ref>{{cite web |title=Initiatives – Pew Center on the States |url=http://www.electionline.org/Portals/1/Publications/SC.EAP.2006primary.pdf |archive-url=https://web.archive.org/web/20080516235221/http://www.electionline.org/Portals/1/Publications/SC.EAP.2006primary.pdf |archive-date=16 May 2008 |access-date=6 May 2010 |website=Electionline.org}}</ref> Louisiana uses it only for members of the United States Service or who reside overseas.<ref>{{Citation |title=IRV for Louisiana's Overseas Voters |type=web page |url=http://archive.fairvote.org/?page=1669 |access-date=16 June 2013 |publisher=FairVote IRV America}}</ref>{{Better source needed|reason=The current source is insufficiently reliable ([[WP:NOTRS]]).|date=September 2024}}{{Update needed|date=September 2024}}
* Under some [[exhaustive ballot]] runoff systems, instant-runoff voting may be used to quickly eliminate some weak candidates in early rounds, using rules to leave a desired number of candidates for further balloting.
* Instant-runoff voting elections that require a majority of cast ballots but not that voters rank all candidates may require more than a single instant-runoff voting contest due to exhausted ballots.{{cn|date=February 2025}} (Most IRV systems require a winner to have only a majority of votes still in play, not a majority of votes cast.)
* Robert's Rules recommends [[Ranked voting systems|preferential voting]] for elections by mail and requiring a majority of votes to elect a winner. For in-person elections, they recommend repeated balloting until one candidate receives a majority of votes; if candidates drop out when it becomes clear they will not win, this procedure will always elect a [[Condorcet method|Condorcet winner]]. The use of repeated balloting allows voters to resolve [[Condorcet paradox|Condorcet cycles]] by discussion and compromise, or by electing a consensus candidate who might have polled poorly in the initial election.<ref name="autogenerated12" />

=== Variations ===
[[File:2016-ballot-paper-Higgins.png|thumb|Example of a full preferential ballot paper from the [[Australian House of Representatives]]]]
A number of instant-runoff voting methods, varying as to ballot design and as to whether or not voters are obliged to rank all the candidates, are in use in different countries and local governments.

In an [[optional preferential voting]] system, voters can give a preference to as many candidates as they wish. They may make only a single choice, known as "[[bullet voting]]", and some jurisdictions accept a single box marked with an "X" (as opposed to a numeral "1") as valid for the first preference. Bullet voting may result in exhausted ballots, where all of a voter's preferences are eliminated before a candidate is elected, such that the "majority" in the final round may constitute only a minority of all ballots cast. Optional preferential voting is used for elections for the [[President of Ireland]] as well as some elections in [[New South Wales]] and [[Queensland]].<ref>{{cite web |date=28 January 2020 |title=Voting system |url=https://www.ecq.qld.gov.au/how-to-vote/voting-systems |access-date=17 November 2020 |website=www.ecq.qld.gov.au |publisher=Electoral Commission of Queensland}}</ref><ref>{{cite web |last1=Stevens |first1=Bronwyn |date=27 January 2015 |title=Are Queenslanders in danger of 'wasting' their votes? |url=https://theconversation.com/are-queenslanders-in-danger-of-wasting-their-votes-35919 |access-date=28 November 2020 |website=The Conversation}}</ref>

In a full-preferential voting method, voters are required to mark a preference for every candidate standing.<ref>{{cite web |title=Electoral Systems |url=http://www.eca.gov.au/systems/single/by_category/preferential.htm |archive-url=https://web.archive.org/web/20080309220219/http://www.eca.gov.au/systems/single/by_category/preferential.htm |archive-date=9 March 2008 |access-date=15 February 2008 |publisher=Electoral Council of Australia}}</ref> Ballots that do not contain a ranking of all candidates are in some jurisdictions considered [[Spoilt vote|spoilt]] or invalid, even if there are only two candidates standing. The full-preferential voting method can become burdensome in elections with many candidates and can lead to "[[donkey voting]]", in which some voters simply choose candidates at random or in top-to-bottom order, or a voter may order his or her preferred candidates and then fill in the remainder on a donkey basis. Full preferential voting is used for elections to the [[Australian electoral system|Australian federal parliament]] and for most [[Electoral systems of the Australian states and territories|state parliaments]].

Other methods only allow marking preferences for a maximum of the voter's top three favourites, a form of partial preferential voting.<ref>{{cite web |title=Ranked-Choice Voting |url=http://www.acgov.org/rov/rcv/faq.htm |access-date=15 December 2016 |website=Registrar of Voters, Alameda County |quote=This format allows a voter to select a first-choice candidate in the first column, a second-choice candidate in the second column, and a third-choice candidate in the third column.}}</ref> Such a system produces exhausted votes even when the voter would have been willing to rank more candidates.

A version of instant-runoff voting applying to the ranking of parties was first proposed for elections in Germany in 2013<ref>{{cite report |title=Anhörung zum Entwurf eines Gesetzes zur Abschaffung der Fünf-Prozent-Sperrklausel bei Landtagswahlen in Schleswig-Holstein |trans-title=Hearing on the draft law to abolish the five percent threshold in state elections in Schleswig-Holstein (Discussion paper) |last1=Breyer |first1=Patrick |date=November 2013 |publisher=Piratenfraktion im Schleswig-Holsteinischen Landtag |language=de |id=(Drs. 18/385) |chapter=Alternative II: Einführung einer Ersatzstimme |chapter-url=https://www.landtag.ltsh.de/infothek/wahl18/umdrucke/1900/umdruck-18-1916.pdf}}</ref> as [[spare vote]].{{Citation needed|date=September 2024}}
== See also ==
* [[Single transferable vote]], a proportional method that reduces to instant runoff in single-winner elections.
* [[Ranked voting]]
* [[Comparison of voting rules|Comparison of electoral systems]]
* [[Alternative vote plus]] (AV+), or alternative vote top-up, proposed by the [[Jenkins Commission (UK)|Jenkins Commission]] in the UK
* [[Duverger's law]]
* [[Two-party-preferred vote]]
* [[Write-in candidate]]

== Notes ==
{{notelist}}

==References==
{{Reflist}}

==External links==
{{subject bar|auto=y|d=y}}
* [https://electionlab.mit.edu/research/instant-runoff-voting# "Explainer: Instant runoff voting"] by MIT Election Science Lab

{{voting methods}}
{{Parliament of Australia}}
{{United Kingdom Alternative Vote referendum, 2011}}

[[Category:Instant-runoff voting| ]]
[[Category:Single-winner electoral systems]]
[[Category:Preferential electoral systems]]