Instant-runoff voting (IRV) is a type of
ranked preferential vote counting method used in single-seat elections with more than two candidates. IRV is also sometimes referred to as the alternative vote (AV), preferential voting, single transferable voting (New Zealand), or, in the United States, ranked-choice voting (RCV), though these names are also used for other systems.
Like all ranked ballot voting systems, instead of indicating support for only one candidate, voters in IRV elections can rank the candidates in order of preference. Ballots are initially counted for each voter's top choice. If a candidate has more than half of the vote based on first-choices, that candidate wins. If not, then the candidate with the fewest votes is eliminated. The voters who selected the defeated candidate as a first choice then have their votes added to the totals of their next choice. This process continues until a candidate has more than half of the votes. When the field is reduced to two, it has become an "instant runoff" that allows a comparison of the top two candidates head-to-head.
Instant-runoff voting is
used in national elections in several countries. For example, it is used to elect members of the
Australian House of Representatives
The House of Representatives is the lower house
A lower house is one of two chambers
Chambers may refer to: Places
Canada:
*Chambers Township, Ontario
United States:
*Chambers County, Alabama
*Chambers, Arizona, an unincorporated commun ...

,
the
President of India
The president of India (International Alphabet of Sanskrit Transliteration, IAST: ), officially the president of the Republic of India, is the figurehead, ceremonial head of state of India and the commander-in-chief of the Indian Armed Forces. ...
, the
President of Ireland
The president of Ireland ( ga, Uachtarán na hÉireann) is the head of state
A head of state (or chief of state) is the public persona
A persona (plural personae or personas), depending on the context, can refer to either the public ...
,
and the
National Parliament of Papua New Guinea
National may refer to:
Common uses
* Nation
A nation is a community
A community is a social unitThe term "level of analysis" is used in the social sciences to point to the location, size, or scale of a research target.
"Level of analysis ...
. It is used by many political parties (for internal primaries/elections to elect party leaders and Presidential/Prime Ministerial candidates) and private associations, for various voting purposes such as that for choosing the
Academy Award for Best Picture
The Academy Award for Best Picture is one of the Academy Awards
The Academy Awards, popularly known as the Oscars, are awards for artistic and technical merit in the film industry
The film industry or motion picture industry comprises ...
. IRV is described in ''
Robert's Rules of Order Newly Revised
''Robert's Rules of Order Newly Revised'', commonly referred to as ''Robert's Rules of Order'', RONR, or simply ''Robert's Rules'', is a political book written by Henry Martyn Robert. It is the most widely used manual of parliamentary procedure in ...
'' as an example of preferential voting.
Terminology
Instant-runoff voting derives its name from the way the ballot count simulates a series of runoffs, similar to an
exhaustive ballot system, except that voter preferences do not change between rounds.
It is also known as the alternative vote, transferable vote, ranked-choice voting (RCV), single-seat ranked-choice voting, or preferential voting.
Britons and New Zealanders generally call IRV the "alternative vote" (AV). while in Canada it is called "ranked choice voting". Australians, who use IRV for most single winner elections, call IRV "preferential voting". American NGO
FairVote
FairVote, formerly the Center for Voting and Democracy, is a 501(c)(3) organization
A 501(c)(3) organization is a corporation, trust, unincorporated association, or other type of organization exempt from federal income tax under section 501(c)(3) ...
uses the terminology "ranked choice voting" to refer to IRV in the case of single-winner offices and to refer to
single transferable vote
Single transferable vote (STV) is a type of ranked preferential electoral system
An electoral system or voting system is a set of rules that determine how elections and referendums are conducted and how their results are determined. Poli ...
in the case of multi-winner offices. Jurisdictions using IRV such as
San Francisco
San Francisco (; Spanish
Spanish may refer to:
* Items from or related to Spain:
**Spaniards, a nation and ethnic group indigenous to Spain
**Spanish language
**Spanish cuisine
Other places
* Spanish, Ontario, Canada
* Spanish River (dis ...

, California, Maine, and Minneapolis, Minnesota have codified the term "ranked choice voting" in their laws. San Francisco has argued the word "instant" in term "instant runoff voting" could confuse voters into expecting results to be immediately available.
IRV is occasionally referred to (rather confusingly) either as Hare's method (after
Sir Thomas Hare) or as Ware's method after the American
William Robert Ware
William Robert Ware (27 May 1832 – 9 June 1915), born in Cambridge, Massachusetts
Cambridge ( ) is a city in Middlesex County, Massachusetts, Middlesex County, Massachusetts, and part of the Greater Boston, Boston metropolitan area as a ma ...
. When the
single transferable vote
Single transferable vote (STV) is a type of ranked preferential electoral system
An electoral system or voting system is a set of rules that determine how elections and referendums are conducted and how their results are determined. Poli ...
(STV) method is applied to a single-winner election, it becomes IRV; the government of Ireland has called IRV "proportional representation" based on the fact that the same ballot form is used to elect its president by IRV and parliamentary seats by STV, but IRV is a winner-take-all election method. State law in
South Carolina
South Carolina () is a state
State may refer to:
Arts, entertainment, and media Literature
* ''State Magazine'', a monthly magazine published by the U.S. Department of State
* The State (newspaper), ''The State'' (newspaper), a daily newspap ...

and
Arkansas
Arkansas () is a U.S. state, state in the South Central United States, South Central region of the United States, home to more than three million people as of 2018. Its name is from the Osage language, a Dhegihan languages, Dhegiha Siouan la ...

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.
Comparison to other voting methods
Instant-runoff voting avoids the problem of
wasted vote In electoral system
An electoral system or voting system is a set of rules that determine how elections and Referendum, referendums are conducted and how their results are determined. Political electoral systems are organized by governments, whi ...
s
[J. R. Chamberlin and M. D. Cohen, ‘Toward Applicable Social Choice Theory...’, (1978).] but (unlike other ranked voting methods) does not ensure the election of a consensus candidate. In other words, votes are not wasted, but consensus candidates are not elected. These issues are illustrated in the following election:

* A wins plurality vote: Second place preferences are ignored, so candidate A wins with 36% of the vote as against 34% for C and 30% (10+20) for B.
* C wins IRV vote: Candidate B gets the fewest first place votes so they are eliminated in the first round. Candidate C gets more of B's second choice preferences than candidate A, winning the second round by 54% (20+34) to 46% (36+10). This result is the same as would occur if there was a primary with 3 candidates and a general election with the two remaining candidates.
* B wins IRV / Bottom Two Runoff: In the first round candidates B and C are in last place, so they go head to head. Candidate A's second place votes go to candidate B, so candidate B wins 66% (36+10+20) to 34% over candidate C. In the second runoff round candidate C has been eliminated so candidates A and B go head to head. Candidate C's second place votes go to candidate B, so candidate B wins 64% (10+20+34) to 36% over candidate A. Head to head elimination methods like Bottom Two Runoff and
Condorcet voting
A Condorcet method (; ) is an election method that elects the candidate who wins a majority rule, majority of the vote in every head-to-head election against each of the other candidates, that is, a candidate preferred by more voters than any othe ...
favor compromise candidates.
Equal rankings
Unlike many single-winner methods, instant-runoff cannot accept equal rankings, and must discard ballots with multiple first-preferred remaining alternatives: such ballots would be equivalent to casting multiple ballots in a plurality election. The inability to cast equal votes—including the inability to truncate ballots in some jurisdictional rules—creates difficulties for the
epistemic properties of democracy. Under theories of
public reason, a democratic decision uses the knowledge of the whole voting body. When a voter has no preference, or decides themselves that their ability to form a correct preference is insufficient, the correct vote is no vote. This is expressed by equal rankings, and when all rankings are equal it is expressed by no vote.
Comparison to first-past-the-post
At
the Australian federal election in September 2013, 135 out of the 150
House of Representatives
House of Representatives is the name of legislative bodies
A legislature is a deliberative assembly
A deliberative assembly is a gathering of members (of any kind of collective) who use parliamentary procedure
Parliamentary procedure is ...

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.
Variations

A number of IRV methods, varying as to ballot design and as to whether or not voters are obliged to provide a full list of preferences, are in use in different countries and local governments.
In an
optional preferential voting
One of the ways in which ranked voting systems vary is whether an individual vote must express a minimum number of preferences to avoid being considered spoilt vote, invalid ("spoiled" or "informal"). Possibilities are:
* Full 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 votingBullet voting, also known as single-shot voting and plump voting, is a voting tactic, usually in multiple-winner elections, where a voter is entitled to vote for more than one candidate, but instead votes for only one candidate.
A voter might do th ...
", and some jurisdictions accept a single box marked with an "X" (as opposed to a numeral "1") as valid for the first preference. This 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 only constitute a minority fraction of all ballots cast. Optional preferential voting is used for elections for the
President of Ireland
The president of Ireland ( ga, Uachtarán na hÉireann) is the head of state
A head of state (or chief of state) is the public persona
A persona (plural personae or personas), depending on the context, can refer to either the public ...
and the
New South Wales Legislative Assembly
The New South Wales Legislative Assembly is the lower of the two houses of the Parliament of New South Wales, an Australian state. The upper house is the New South Wales Legislative Council. Both the Assembly and Council sit at Parliament House ...
. Optional preferential voting is used for some elections in
Queensland
Queensland ( ) is a state situated in northeastern Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the ...

.
In a full preferential voting method, voters are required to mark a preference for every candidate standing. Ballots that do not contain a complete ordering of all candidates are in some jurisdictions considered
or invalid, even if there are only two candidates standing. This 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 federal parliament
The Parliament of Australia (officially the Federal Parliament, also called the Commonwealth Parliament) is the legislative branch of the government of Australia
The Australian Government, also known as the Commonwealth Government, i ...
and for most
State parliaments.
Other methods only allow marking preferences for a maximum of the voter's top three favorites, a form of partial preferential voting.
History
This method was considered by Condorcet as early as 1788, though only to condemn it, for its ability to eliminate a candidate preferred by a majority of voters.
IRV can be seen as a special case of the
single transferable vote
Single transferable vote (STV) is a type of ranked preferential electoral system
An electoral system or voting system is a set of rules that determine how elections and referendums are conducted and how their results are determined. Poli ...
method, which
began use in the 1850s. It is historically known as Ware's method, due to the implementation of STV in 1871 at
Harvard College
Harvard College is the undergraduate
Undergraduate education is education conducted after secondary education and prior to postgraduate education. It typically includes all postsecondary programs up to the level of a bachelor's degree
A b ...
by American
architect
An architect is a person who plans, designs and oversees the construction of buildings. To practice architecture means to provide services in connection with the design of buildings and the space within the site surrounding the buildings that h ...

William Robert Ware
William Robert Ware (27 May 1832 – 9 June 1915), born in Cambridge, Massachusetts
Cambridge ( ) is a city in Middlesex County, Massachusetts, Middlesex County, Massachusetts, and part of the Greater Boston, Boston metropolitan area as a ma ...
, who suggested it could also be used for single-winner elections. Unlike the single transferable vote in multi-seat elections, however, the only ballot transfers are from backers of candidates who have been eliminated.
The first known use of an IRV-like method in a governmental election was in the
1893 general election in the
Colony of Queensland
The Colony of Queensland was a colony of the British Empire
The British Empire was composed of the dominions, Crown colony, colonies, protectorates, League of Nations mandate, mandates, and other Dependent territory, territories ruled or ...
(in present-day Australia). The variant used for this election was a "
contingent vote
250px, A flowchart for the ''contingent vote''.
The contingent vote is an electoral system used to elect a single representative in which a candidate requires a majority of votes to win. It is a variation of instant-runoff voting
Instant- ...
", where all candidates but two are eliminated in the first round. IRV in its true form was first used in
Western Australia
Western Australia (abbreviated as WA) is a state
State may refer to:
Arts, entertainment, and media Literature
* ''State Magazine'', a monthly magazine published by the U.S. Department of State
* The State (newspaper), ''The State'' (newspape ...

, in the
1908 state election. The
Hare-Clark system was introduced for the
Tasmanian House of Assembly
The House of Assembly, or Lower House, is one of the two chambers of the Parliament of Tasmania
In modern politics and history, a parliament is a legislature, legislative body of government. Generally, a modern parliament has three fu ...

at the
1909 state election.
IRV was introduced for federal (nationwide) elections in Australia after the
Swan by-election in October 1918, in response to the rise of the conservative
Country Party, representing small farmers. The Country Party split the non-
Labor
Labour or labor may refer to:
* , the delivery of a baby
* , or work
** , physical work
** , a socioeconomic relationship between a worker and an employer
Literature
* , an American quarterly on the history of the labor movement
* ', an academic ...
vote in conservative country areas, allowing Labor candidates to win without a majority of the vote. The conservative government of
Billy Hughes
William Morris Hughes, (25 September 1862 – 28 October 1952), was an Australian politician who served as the List of prime ministers of Australia by time in office, 7th Prime Minister of Australia, in office from 1915 to 1923. He is best kn ...

introduced IRV (in Australia called "preferential voting") as a means of allowing competition between the
Coalition
The term "coalition" is the denotation for a group formed when two or more people, factions, states, political parties, militaries etc. agree to work together temporarily in a partnership to achieve a common goal. The word coalition connotes a co ...
parties without putting seats at risk. It was first used at the
Corangamite by-election on 14 December 1918, and at a national level at the
1919 election. IRV continued to benefit the Coalition until the
1990 election, when for the first time Labor obtained a net benefit from IRV.
Election procedure
Process

In instant-runoff voting, as with other ranked election methods, each voter ranks the list of candidates in order of preference. Under a common
ballot
A ballot is a device used to cast votes in an election and may be found as a piece of paper or a small ball used in secret voting
Voting is a method for a group, such as a meeting or an electorate
Electorate may refer to:
* The people who ...
layout, the voter marks a '1' beside the most preferred candidate, a '2' beside the second-most preferred, and so forth, in
ascending order. This is shown in the example Australian ballot above.
The mechanics of the process are the same regardless of how many candidates the voter ranks, and how many are left unranked. In some implementations, the voter ranks as many or as few choices as they wish, while in other implementations the voter is ''required'' to rank either all candidates, or a prescribed number of them.
The instant-runoff vote counting procedure is as follows:
# Eliminate the candidate appearing as the first preference on the fewest ballots.
# If only one candidate remains, elect this candidate and stop.
# Otherwise go to 1.
If there is an exact tie for last place in numbers of votes, various tie-breaking rules determine which candidate to eliminate. The set of all candidates with the fewest first-order votes whose votes together total less than any other candidate's can be eliminated without changing the outcome. This bulk elimination can bypass irrelevant ties, for example if one candidate receives 15 first-order votes and four others receive 5, 5, 3, and 1, and no other candidate receives fewer than 15, all four of the latter candidates will be eliminated during the next four rounds, and so can be eliminated immediately without considering the tie.
Ballots assigned to eliminated candidates are added to the totals of one of the remaining candidates based on the next preference ranked on each ballot. The process repeats until one candidate achieves a majority of votes cast for continuing candidates. Ballots on which all of a voter's ranked candidates are eliminated become inactive.
Candidate order on the ballot paper

The common ways to list candidates on a ballot paper are alphabetically or by random lot. In some cases, candidates may also be grouped by political party. Alternatively,
Robson Rotation involves randomly changing candidate order for each print run.
Party strategies
Where preferential voting is used for the election of an assembly or council, parties and candidates often advise their supporters on their lower preferences, especially in Australia where a voter must rank all candidates to cast a valid ballot. This can lead to "preference deals", a form of pre-election bargaining, in which smaller parties agree to direct their voters in return for support from the winning party on issues critical to the small party. It can also sometimes lead to joint campaigning between candidates with similar platforms. However, these strategies rely on the assumption that supporters of a party or candidate are receptive to advice on the other preferences on their ballot.
Counting logistics
Most IRV elections historically have been tallied by hand, including in elections to Australia's House of Representatives and most state governments. In the modern era, voting equipment can be used to administer the count either partially or fully.
In Australia, the
returning officer now usually declares the two candidates that are most likely to win each seat. The votes are always counted by hand at the polling booth monitored by scrutineers from each candidate. The first part of the count is to record the first choice for all candidates. Votes for candidates other than the two likely winners are then allocated to them in a second pass. The whole process of counting the votes by hand and allocating preferences is typically completed within two hours on election night at a cost of $7.68 per elector in 2010 to run the entire election.
Ireland in its presidential elections has several dozen counting centers around the nation. Each center reports its totals and receives instructions from the central office about which candidate or candidates to eliminate in the next round of counting based on which candidate is in last place. The count typically is completed the day after the election, as in 1997.
In the United States, nearly all jurisdictions that use this format—like
Maine
Maine () is a U.S. state, state in the New England region of the United States, bordered by New Hampshire to the west; the Gulf of Maine to the southeast; and the Provinces and territories of Canada, Canadian provinces of New Brunswick and Qu ...

and cities like
Oakland
Oakland is the largest city and the county seat
A county seat is an administrative centerAn administrative centre is a seat of regional administration or local government, or a county town, or the place where the central administration of a ...

and
San Francisco
San Francisco (; Spanish
Spanish may refer to:
* Items from or related to Spain:
**Spaniards, a nation and ethnic group indigenous to Spain
**Spanish language
**Spanish cuisine
Other places
* Spanish, Ontario, Canada
* Spanish River (dis ...

, administer IRV elections on voting machines, with optical scanning machines recording preferences and software tallying the IRV algorithm as soon as ballots are tallied. In its first use of IRV in 2009,
Minneapolis, Minnesota
Minneapolis () is a city in the U.S. state of Minnesota. With a population of 429,954 as of 2020 United States census, 2020, it is the most populous city in the state and the 46th most populous in the nation. The county seat of Hennepin County, ...

, tallied first choices on optical scan equipment at the polls and then used a central hand-count for the IRV tally, but has since administered elections without hand tallies
Portland, Maine
Portland is the List of cities in Maine, largest city in the U.S. state of Maine and the County seat, seat of Cumberland County, Maine, Cumberland County. Portland's population was 68,408 in April 2020. The Portland metropolitan area, Maine, Gre ...
in 2011 used its usual voting machines to tally first choice at the polls, then a central scan with different equipment if an IRV tally was necessary.
The election results from IRV cannot be counted additively: all ballots must be present prior to the first elimination. Methods like plurality voting and pairwise voting can divide the work of counting and sum the results as more votes are reported. To produce pairwise results, each candidate ranked on a ballot receives one vote against each alternative ranked lower and each not ranked on that ballot; equal rankings, including non-ranked candidates, are ties and no vote is tallied. These tallies can be summed to produce a complete matrix of pairwise elections, which can then be used to compute the
Smith set
In voting systems, the Smith set, named after John H. Smith (mathematician), John H. Smith, but also known as the top cycle, or as Generalized Top-Choice Assumption (GETCHA), is the smallest non-empty set of candidates in a particular election such ...
or to calculate the outcomes of Schulze, Minimax, Ranked Pairs, and other methods.
IRV is very unlikely to give rise to a tie when the number of voters is large. For this reason it is sometimes advocated as part of a tie break for methods (such as the Smith set) which do not have this property: see
Smith/IRV and
Tideman's Alternative.
Invalid ballots and incomplete 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.
Because the ballot marking is more complex, there can be an increase in spoiled ballots. In Australia, voters are required to write a number beside every candidate, and the rate of spoiled ballots can be five times higher than plurality voting elections. Since Australia has compulsory voting, however, it is difficult to tell how many ballots are deliberately spoiled. Where complete rankings are not required, a ballot may become inactive if none of the ranked choices on that ballot advance to the next round.
Most jurisdictions with IRV do not require complete rankings and may use columns to indicate preference instead of numbers. In American elections with IRV, more than 99% of voters typically cast a valid ballot.
A 2015 study of four local U.S. elections that used IRV 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% to a high of 27.1%. As one point of comparison, the number of votes cast in the 190 regularly scheduled primary runoff elections for the U.S House and U.S. Senate from 1994 to 2016 decreased from the initial primary on average by 39%,
according to a 2016 study by FairVote.
Resistance to strategy
Instant Runoff Voting has notably high resistance to tactical voting, but less to strategic nomination.
Tactical voting
The
Gibbard–Satterthwaite theorem
In social choice theory, the Gibbard–Satterthwaite theorem is a result published independently by philosopher Allan Gibbard in 1973 and economist Mark Satterthwaite in 1975. It deals with deterministic Ranked voting, ordinal electoral systems that ...
demonstrates that no (deterministic, non-dictatorial) voting method using only the preference rankings of the voters can be entirely immune from tactical voting. This implies that IRV is susceptible to tactical voting in some circumstances.
Research concludes that IRV is one of the voting methods least vulnerable to tactical voting, with theorist
Nicolaus Tideman
Thorwald Nicolaus Tideman (, not ; born August 11, 1943 in Chicago, Illinois) is a Georgist economist and professor at Virginia Polytechnic Institute and State University, Virginia Tech. He received his Bachelor of Arts in economics and mathematics ...
noting that, "alternative vote is quite resistant to strategy"
and Australian political analyst
Antony Green
Antony John Green (born 2 March 1960) is an Australian psephologist and commentator. He is the Australian Broadcasting Corporation's election analyst.
Early years and background
Born in Warrington, Lancashire, in northern England, Green emigr ...
dismissing suggestions of tactical voting. James Green-Armytage tested four ranked-choice methods, and found the alternative vote to be the second-most-resistant to tactical voting, though it was beaten by a class of AV-Condorcet hybrids, and did not resist strategic withdrawal by candidates well.
These analyses only apply to tactical voting, but not to other forms of manipulation; for example, Tideman and Robinette demonstrate a method by which a candidate modifies their campaign to appeal to a slightly broader range of voters, including those of a popular opponent, so as to "bracket" that opponent out (cause them to be eliminated earlier).
By not meeting the monotonicity, Condorcet winner, and participation criteria, IRV permits forms of tactical voting when voters have sufficient information about other voters' preferences, such as from accurate pre-election polling.
FairVote
FairVote, formerly the Center for Voting and Democracy, is a 501(c)(3) organization
A 501(c)(3) organization is a corporation, trust, unincorporated association, or other type of organization exempt from federal income tax under section 501(c)(3) ...
mentions that monotonicity failure can lead to situations where "Having more voters rank
candidate first, can cause
hem
A hem in sewing
Sewing is the craft of fastening or attaching objects using stitches made with a sewing needle
A sewing needle, used for hand- sewing, is a long slender tool with a pointed tip at one end and a hole (or ''eye'') at the oth ...

to switch from being a winner to being a loser." This occurs when a mutual majority exists which would elect a different candidate than the Condorcet candidate and a minority coalition running off to a single candidate exceeds one-half the size of this majority: the minority candidate cannot be eliminated until the mutual majority runs off to a majority winner. Moving the winner to the top of the minority ballots can shrink the minority sufficiently for their candidate to be eliminated, and their votes then cause the election of a different candidate. This situation occurred in the
2009 Burlington mayoral election: had several Kurt Wright voters moved Bob Kiss to the top of their ballots, the winner would have changed from Bob Kiss to Andy Montroll. The change in lower candidates is important: whether votes are shifted to the leading candidate, shifted to a fringe candidate, or discarded altogether is of no importance.
Tactical voting in IRV 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 and right prefer the centrist candidate to stop the "enemy" candidate winning, those voters who care more about defeating the "enemy" than electing their own candidate may cast a tactical first preference vote for the centrist candidate.
The 2009
mayoral election in
Burlington, Vermont
Burlington is the List of cities in Vermont, most-populous city in Vermont and the county seat, seat of Chittenden County, Vermont, Chittenden County. It is south of the Canada–United States border and south of Montreal. The population was 42 ...

provides an example in which strategy theoretically could have worked but would have been unlikely in practice. In that election, most supporters of the candidate who lost in the final round (a Republican who led in first choices) preferred the
Condorcet
Marie Jean Antoine Nicolas de Caritat, Marquis of Condorcet (; 17 September 1743 – 29 March 1794), known as Nicolas de Condorcet, was a French philosopher
A philosopher is someone who practices philosophy. The term ''philosopher'' comes from ...
winner, a Democrat, to the IRV winner, the Progressive Party nominee. If 371 (24.7%) out of the 1510 backers of the Republican candidate (who also preferred the Democrat over the Progressive candidate for mayor) had insincerely raised the Democrat from their second choice to their first (not changing their rankings relative to their least favorite candidate, the Progressive), the Democrat would then have advanced to the final round (instead of their favorite), defeated any opponent, and proceeded to win the IRV election.
[Warren Smith (2009]
"Burlington Vermont 2009 IRV mayor election; Thwarted-majority, non-monotonicity & other failures (oops)"
/ref> This is an example of potential voter regret in that these voters who sincerely ranked their favorite candidate as first, find out after the fact that they caused the election of their least favorite candidate, which can lead to the voting tactic of compromising. Yet because the Republican led in first choices and only narrowly lost the final instant runoff, his backers would have been highly unlikely to pursue such a strategy. This strategy still would not elect the Republican, due to a lack of preferences towards them.
Spoiler Effect
The spoiler effect is when a difference is made to the anticipated outcome of an election due to the presence on the ballot paper of a candidate who (predictably) will lose. Most often this is when two or more politically similar candidates divide the vote for the more popular end of the political spectrum. That is, each receives fewer votes than a single opponent on the unpopular end of the spectrum who is disliked by the majority of voters but who wins from the advantage that, on that unpopular side, they are unopposed. Strategic nomination relies on triggering this situation, and requires understanding of both the electoral process and the demographics of the district.
Proponents of IRV claim that IRV eliminates the spoiler effect, since IRV 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. An IRV method 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 IRV, 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 favorite second rather than first (favorite betrayal.) 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.
For example, in the 2009 Burlington, Vermont mayoral election, if the Republican candidate who lost in the final instant runoff had not run, the Democratic candidate would have defeated the winning Progressive candidate. In that sense, the Republican candidate was a spoiler—(albeit for an opposing Democrat, rather than some political ally) even though leading in first choice support.
By contrast, in the seat of Prahran during the 2014 Victorian State Election, despite the Greens candidate outlasting the more centrist Labor candidate during counting, most of the Labor preferences ultimately helped elect the Greens rather than the further right Liberal candidate. In this case, the Greens candidate, despite only having the third most primary votes, ultimately was not a spoiler and was able to be elected.
In practice, IRV does not seem to discourage candidacies. In Australia's House of Representatives elections in 2007, for example, the average number of candidates in a district was seven, and at least four candidates ran in every district; notwithstanding the fact that Australia only has two major political parties. Every seat was won with a majority of the vote, including several where results would have been different under plurality voting. A study of ballot image data found that all of the 138 RCV elections held in four Bay Area cities in California elected the Condorcet winner, including many with large fields of candidates and 46 where multiple rounds of counting were required to determine a winner.
Proportionality
IRV is not a proportional voting method. Like all winner-take-all voting methods, IRV tends to exaggerate the number of seats won by the largest parties; small parties without majority support in any given constituency are unlikely to earn seats in a legislature, although their supporters will be more likely to be part of the final choice between the two strongest candidates. A simulation of IRV in the 2010 UK general election by the Electoral Reform Society
The Electoral Reform Society (ERS) is an Advocacy group, independent campaigning organisation based in the United Kingdom which promotes electoral reform. It seeks to replace the first-past-the-post voting system with one of proportional repres ...
concluded that the election would have altered the balance of seats among the three main parties, but the number of seats won by minor parties would have remained unchanged.
Australia
Australia, a nation with a long record of using IRV for the election of legislative bodies, has had representation in its parliament broadly similar to that expected by plurality methods; for its House of Representatives
House of Representatives is the name of legislative bodies
A legislature is a deliberative assembly
A deliberative assembly is a gathering of members (of any kind of collective) who use parliamentary procedure
Parliamentary procedure is ...
, Australia is a two-party system
A two-party system is a Politics, political party system in which two major party, major political parties consistently dominate the political landscape. At any point in time, one of the two parties typically holds a majority in the legislature ...
.
Medium-sized parties, such as the National Party of Australia
The National Party of Australia (NPA), also known as The Nationals or The Nats, is an Australian political party. Traditionally representing graziers, farmers, and regional voters generally, it began as the Australian Country Party (ACP) in 1 ...
, can co-exist with coalition
The term "coalition" is the denotation for a group formed when two or more people, factions, states, political parties, militaries etc. agree to work together temporarily in a partnership to achieve a common goal. The word coalition connotes a co ...
partners such as the Liberal Party of Australia
The Liberal Party of Australia is a major Centre-right politics, centre-right list of political parties in Australia, political party in Australia, one of the two Major party, major parties in politics of Australia, Australian politics, along w ...
, and can compete against it without fear of losing seats to other parties due to vote splitting, although generally in practice these two parties only compete against each other when a sitting member of the coalition leaves Parliament. IRV is more likely to result in legislatures where no single party has an absolute majority of seats (a hung parliament
A hung parliament is a term used in legislatures under the Westminster system to describe a situation in which no particular political party or pre-existing coalition (also known as an alliance or bloc) has an absolute majority of legislators (c ...
), but does not generally produce as fragmented a legislature as a fully proportional method, such as is used for the House of Representatives of the Netherlands
The House of Representatives (, pronounced ; commonly referred to as the ', literally Second Chamber ''of the States General'') is the lower house of the Bicameralism, bicameral parliament of the Netherlands, the States General of the Netherlan ...
, where coalitions of numerous small parties are needed for a majority.
Costs
The costs of printing and counting ballot papers for an IRV election are no different from those of any other method using the same technology. However, the more-complicated counting system may encourage officials to introduce more advanced technology, such as software counters or electronic voting machines. Pierce County, Washington, election officials outlined one-time costs of $857,000 to implement IRV for its elections in 2008, covering software and equipment, voter education and testing.
Because it does not require two separate votes, IRV is assumed to cost less than two-round primary/general or general/runoff election methods. However, in 2009, the auditor of Pierce County reported that the ongoing costs of the system were not necessarily balanced by the costs of eliminating runoffs for most county offices, because those elections may be needed for other offices not elected by IRV. Other jurisdictions have reported immediate cost savings.
Australian elections are counted by hand. The 2010 federal election cost a total of $7.68 per elector of which only a small proportion is the actual counting of votes. Counting is now normally performed in a single pass at the polling center as described above.
The perceived costs or cost savings of adopting an IRV method are commonly used by both supporters and critics. In the 2011 referendum on the Alternative Vote in the UK, the NOtoAV
NOtoAV was a political campaign
A political campaign is an organized effort which seeks to influence the decision making progress within a specific group. In democracies, political campaigns often refer to electoral campaigns, by which repr ...
campaign was launched with a claim that adopting the method would cost £250 million; commentators argued that this headline figure had been inflated by including £82 million for the cost of the referendum itself, and a further £130 million on the assumption that the UK would need to introduce electronic voting systems, when ministers had confirmed that there was no intention of implementing such technology, whatever the outcome of the election. Automated vote counting is seen by some to have a greater potential for election fraud; IRV supporters counter these claims with recommended audit procedures, or note that automated counting is not required for the method at all.
Negative campaigning
John Russo, Oakland City Attorney, argued in the ''Oakland Tribune
The ''Oakland Tribune'' is a weekly newspaper
A newspaper is a periodical
Periodical literature (also called a periodical publication or simply a periodical) is a category of Serial (publishing), serial published, publications that appea ...
'' on 24 July 2006 that "Instant runoff voting is an antidote to the disease of negative campaigning. IRV led to San Francisco candidates campaigning more cooperatively. Under the method, their candidates were less likely to engage in negative campaigning because such tactics would risk alienating the voters who support 'attacked' candidates", reducing the chance that they would support the attacker as a second or third choice.
In 2013–2014, the Rutgers-Eagleton Poll surveyed more than 4,800 likely voters in 21 cities after their local city elections—half in cities with IRV elections and 14 in control cities selected by project leaders Caroline Tolbert of the University of Iowa and Todd Donovan of Western Washington University. Among findings, respondents in IRV cities reported candidates spent less time criticizing opponents than in cities that did not use IRV. In the 2013 survey, for example, 5% of respondents said that candidates criticized each other "a great deal of the time" as opposed to 25% in non-IRV cities. An accompanying survey of candidates reported similar findings.
Internationally, Benjamin Reilly suggests instant-runoff voting eases ethnic conflict in divided societies. This feature was a leading argument for why Papua New Guinea
Papua New Guinea (PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country in Oceania th ...

adopted instant-runoff voting. However, Lord Alexander's objections to the conclusions of the British Independent Commission on the Voting System's report cites the example of Australia saying "their politicians tend to be, if anything, more blunt and outspoken than our own".
Plural voting
Some critics of IRV hold that voters supporting major candidates get their second and third place preferences ignored as those candidates are eliminated before their first choice is eliminated. Meanwhile, if you support a fringe candidate, it is more likely that your second and third place choices will be used. In Ann Arbor, Michigan
Ann Arbor is a city
A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routledge ...

, for example, arguments over IRV in letters to newspapers included the belief that IRV "gives minority candidate voters two votes", because some voters' ballots may count for their first choice in the first round and a lesser choice in a later round. The argument that IRV represents plural votingPlural voting is the practice whereby one person might be able to vote multiple times in an election. It is not to be confused with a plurality voting system which does not necessarily involve plural voting. Weighted voting is a generalisation of plu ...
is sometimes used in arguments over the "fairness" of the method, and has led to several legal challenges in the United States. In every instance, state and federal judges have rejected this argument.
The argument was addressed and rejected by a Michigan court in 1975; in '' Stephenson v. the Ann Arbor Board of City Canvassers'', the court held "majority preferential voting" (as IRV was then known) to be in compliance with the Michigan and United States constitutions, writing:
The same argument was advanced in opposition to IRV in Maine. Governor Paul LePage
Paul Richard LePage (; born October 9, 1948) is an American businessman and politician who was the 74th Governor of Maine, from 2011 to 2019. A member of the Republican Party, LePage served two terms as a city councilor in Waterville, Maine, b ...
claimed, ahead of the 2018 primary elections, that IRV would result in "one person, five votes", as opposed to "one person, one vote
One man, one vote (or one person, one vote) expresses the principle that individuals should have equal representation in voting. This slogan is used by advocates of political equality to refer to such electoral reforms as universal suffrage
Uni ...
". In litigation following the results of the 2018 election for Maine's 2nd congressional district, Representative Bruce Poliquin claimed that IRV allowed his opponents to "cast ballots for three different candidates in the same election". Federal judge Lance Walker rejected this claim, and the 1st circuit court denied Poliquin's emergency appeal, leading to Poliquin dropping his claim.
''Robert's Rules of Order''
In the United States, the sequential elimination method used by IRV is described in ''Robert's Rules of Order Newly Revised
''Robert's Rules of Order Newly Revised'', commonly referred to as ''Robert's Rules of Order'', RONR, or simply ''Robert's Rules'', is a political book written by Henry Martyn Robert. It is the most widely used manual of parliamentary procedure in ...
'' as an example of preferential voting
Preferential voting or preference voting (PV) may refer to different Electoral system, election systems or groups of election systems:
* Ranked voting methods, all election methods that involve ranking candidates in order of preference (United Sta ...
:The term preferential voting refers to any of a number of voting methods by which, on a single ballot when there are more than two possible choices, the second or less-preferred choices of voters can be taken into account if no candidate or proposition attains a majority. While it is more complicated than other methods of voting in common use, and is not a substitute for the normal procedure of repeated balloting until a majority is obtained, preferential voting is especially useful and fair in an election by mail if it is impractical to take more than one ballot. In such cases, it makes possible a more representative result than under a rule that a plurality shall elect ... Preferential voting has many variations. One method is described here by way of illustration.
The instant-runoff voting method is then detailed.
''Robert's Rules'' continues:The system of preferential voting just described should not be used in cases where it is possible to follow the normal procedure of repeated balloting until one candidate or proposition attains a majority. Although this type of preferential ballot is preferable to an election by plurality, it affords less freedom of choice than repeated balloting, because it denies voters the opportunity of basing their second or lesser choices on the results of earlier ballots, and because the candidate or proposition in last place is automatically eliminated and may thus be prevented from becoming a compromise choice.
Two other books on American parliamentary procedure take a similar stance, disapproving of plurality voting and describing preferential voting as an option, if authorized in the bylaws, when repeated balloting is impractical: ''The Standard Code of Parliamentary Procedure
''The Standard Code of Parliamentary Procedure'' (formerly the ''Sturgis Standard Code of Parliamentary Procedure'' by Alice Sturgis) is a book of rules of order. It is the second most popular parliamentary authority in the United States after ...
'' and '' Riddick's Rules of Procedure''.
Global use
Similar methods
Runoff voting
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 in order of preference on a single ballot. Instead a similar effect is achieved by using multiple rounds of voting. All 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. This is not possible in IRV, as participants vote only once, and this prohibits certain forms of tactical voting
In voting method
Voting is a method for a group, such as a meeting or an Constituency, electorate, in order to make a collective decision making, decision or express an opinion usually following discussions, debates or election campaigns. Demo ...
that can be prevalent in 'standard' runoff voting.
Exhaustive ballot
A method closer to IRV is the exhaustive ballot
The exhaustive ballot is a voting system
An electoral system or voting system is a set of rules that determine how elections and referendums
A referendum (plural: referendums or less commonly referenda) is a direct and universal vote in w ...
. In this method—one familiar to fans of the television show ''American Idol
''American Idol'' is an American singing competition television series created by Simon Fuller
Simon Fuller (born 17 May 1960) is a British entrepreneur, artist manager, film and television producer. He is the creator of the Idol series, ...

''—one candidate is eliminated after each round, and many rounds of voting are used, rather than just two. Because holding many rounds of voting on separate days is generally expensive, the exhaustive ballot is not used for large-scale, public elections.
Two-round methods
The simplest form of runoff voting is the two-round system
The two-round system, also known as the second ballot, runoff voting, or ballotage, is a voting method
Voting is a method for a group, such as a meeting or an electorate
Electorate may refer to:
* The people who are eligible to vote in an ...
, which typically excludes all but two candidates after the first round, rather than gradually eliminating candidates over a series of rounds. Eliminations can occur with or without allowing and applying preference votes to choose the final two candidates. A second round of voting or counting is only necessary if no candidate receives an overall majority of votes. This method is used in Mali, France and the Finnish and Slovenian presidential election.
Contingent vote
The contingent vote
250px, A flowchart for the ''contingent vote''.
The contingent vote is an electoral system used to elect a single representative in which a candidate requires a majority of votes to win. It is a variation of instant-runoff voting
Instant- ...
, also known as Top-two IRV, or ''batch-style'', is the same as IRV 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 IRV, there is only one round of voting.
Under a variant of contingent voting used in Sri Lanka
Sri Lanka (, ; si, ශ්රී ලංකාව, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon, and officially the Democratic Socialist Republic of Sri Lanka, is ...

, and the elections for Mayor of London
The mayor of London is the chief executive of the Greater London Authority
The Greater London Authority (GLA), colloquially known by the metonym "City Hall", is the Devolution in the United Kingdom, devolved Regions of England, regional ...
in the United Kingdom, voters rank a specified maximum number of candidates. In London, the Supplementary Vote
The supplementary vote (SV) is an electoral system used to elect a single winner, in which the voter ranks the candidates in order of preference. In an election, if no candidate receives an absolute majority of first preference votes, then all but ...
allows voters to express first and second preferences only. Sri Lankan voters rank up to three candidates for the President of Sri Lanka
The president of Sri Lanka ( si, ශ්රී ලංකා ජනාධිපති ''Śrī Laṃkā Janādhipathi''; ta, இலங்கை சனாதிபதி ''Ilankai janātipati'') is the head of state
A head of state (or c ...
.
While similar to "sequential-elimination" IRV, 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 IRV. 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 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. Particularly in elections with few (e.g., fewer than 100) voters, numerous ties can destroy confidence. Heavy use of tie-breaking rules leaves uncomfortable doubts over whether the winner might have changed if a recount had been performed.
Larger runoff process
IRV may also be part of a larger runoff process:
* Some jurisdictions that hold runoff elections allow absentee (only) voters to submit IRV ballots, because the interval between votes is too short for a second round of absentee voting. IRV ballots enable absentee votes to count in the second (general) election round if their first choice does not make the runoff. Arkansas
Arkansas () is a U.S. state, state in the South Central United States, South Central region of the United States, home to more than three million people as of 2018. Its name is from the Osage language, a Dhegihan languages, Dhegiha Siouan la ...

, South Carolina
South Carolina () is a state
State may refer to:
Arts, entertainment, and media Literature
* ''State Magazine'', a monthly magazine published by the U.S. Department of State
* The State (newspaper), ''The State'' (newspaper), a daily newspap ...

and Springfield, Illinois
Springfield is the capital of the U.S. state of Illinois
Illinois ( ) is a in the region of the . Of the fifty U.S. states, it has the , population, and the . is the state's largest city and the fifth with the capital in , located ...
adopt this approach. Louisiana uses it only for members of the United States Service or who reside overseas.
* IRV can quickly eliminate weak candidates in early rounds of an exhaustive ballot
The exhaustive ballot is a voting system
An electoral system or voting system is a set of rules that determine how elections and referendums
A referendum (plural: referendums or less commonly referenda) is a direct and universal vote in w ...
runoff, using rules to leave the desired number of candidates for further balloting.
* IRV allows an arbitrary victory threshold in a single round of voting, e.g., 60%. In such cases a second vote may be held to confirm the winner.
* IRV elections that require a majority of cast ballots but not that voters rank all candidates may require more than a single IRV ballot due to exhausted ballots.
* Robert's Rules recommends preferential voting
Preferential voting or preference voting (PV) may refer to different Electoral system, election systems or groups of election systems:
* Ranked voting methods, all election methods that involve ranking candidates in order of preference (United Sta ...
for elections by mail and requiring a majority of cast votes to elect a winner, giving IRV as their example. For in-person elections, they recommend repeated balloting until one candidate receives an absolute majority of all votes cast. Repeated voting allows voters to turn to a candidate as a compromise who polled poorly in the initial election.
The common feature of these IRV variations is that one vote is counted per ballot per round, with rules that eliminate the weakest candidate(s) in successive rounds. Most IRV implementations drop the requirement for a majority
A majority, also called a simple majority to distinguish it from similar terms (see the "Related terms" section below), is the greater part, or more than half, of the total.See dictionary definitions of "majority" aMerriam-Webster
of cast ballots.
Voting method criteria
Scholars rate voting methods using mathematically-derived voting method criteria, which describe desirable features of a method. No ranked-preference method can meet all of the criteria, because some of them are mutually exclusive, as shown by statements such as Arrow's impossibility theorem#REDIRECT Arrow's impossibility theorem#REDIRECT Arrow's impossibility theorem
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