Instant-runoff voting
Overview
 
Instant-runoff voting (IRV), also known as preferential voting
Preferential voting
Preferential voting is a type of ballot structure used in several electoral systems in which voters rank candidates in order of relative preference. For example, the voter may select their first choice as '1', their second preference a '2', and so on...

, the alternative vote and ranked choice voting, is a voting system
Voting system
A voting system or electoral system is a method by which voters make a choice between options, often in an election or on a policy referendum....

 used to elect one winner. Voters rank candidates in order of preference, and their ballots are counted as one vote for their first choice candidate. If a candidate secures a majority of votes cast, that candidate wins. Otherwise, the candidate with the fewest votes is eliminated.
Encyclopedia
Instant-runoff voting (IRV), also known as preferential voting
Preferential voting
Preferential voting is a type of ballot structure used in several electoral systems in which voters rank candidates in order of relative preference. For example, the voter may select their first choice as '1', their second preference a '2', and so on...

, the alternative vote and ranked choice voting, is a voting system
Voting system
A voting system or electoral system is a method by which voters make a choice between options, often in an election or on a policy referendum....

 used to elect one winner. Voters rank candidates in order of preference, and their ballots are counted as one vote for their first choice candidate. If a candidate secures a majority of votes cast, that candidate wins. Otherwise, the candidate with the fewest votes is eliminated. A new round of counting takes place, with each ballot counted as one vote for the advancing candidate who is ranked highest on that ballot. This process continues until the winning candidate receives a majority of the vote against the remaining candidates.

Instant runoff voting is used to elect members of the Australian House of Representatives
Australian House of Representatives
The House of Representatives is one of the two houses of the Parliament of Australia; it is the lower house; the upper house is the Senate. Members of Parliament serve for terms of approximately three years....

, the President of India
President of India
The President of India is the head of state and first citizen of India, as well as the Supreme Commander of the Indian Armed Forces. President of India is also the formal head of all the three branches of Indian Democracy - Legislature, Executive and Judiciary...

, members of legislative councils
Vidhan Parishad
The Vidhan Parishad is the upper house in those states of India that have a bicameral legislature. , six states have a Legislative Council: Andhra Pradesh, Bihar, Jammu and Kashmir, Karnataka, Maharashtra, and Uttar Pradesh...

 in India, the President of Ireland
President of Ireland
The President of Ireland is the head of state of Ireland. The President is usually directly elected by the people for seven years, and can be elected for a maximum of two terms. The presidency is largely a ceremonial office, but the President does exercise certain limited powers with absolute...

, the national parliament of Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...

, and the House of Representatives of Fiji. It is also used in Irish by-election
By-election
A by-election is an election held to fill a political office that has become vacant between regularly scheduled elections....

s and for electing hereditary peer
Hereditary peer
Hereditary peers form part of the Peerage in the United Kingdom. There are over seven hundred peers who hold titles that may be inherited. Formerly, most of them were entitled to sit in the House of Lords, but since the House of Lords Act 1999 only ninety-two are permitted to do so...

s for the British House of Lords
House of Lords
The House of Lords is the upper house of the Parliament of the United Kingdom. Like the House of Commons, it meets in the Palace of Westminster....

.

IRV is employed by several jurisdictions in the United States, including Portland, Maine
Portland, Maine
Portland is the largest city in Maine and is the county seat of Cumberland County. The 2010 city population was 66,194, growing 3 percent since the census of 2000...

; San Francisco, California; Oakland, California
Oakland, California
Oakland is a major West Coast port city on San Francisco Bay in the U.S. state of California. It is the eighth-largest city in the state with a 2010 population of 390,724...

; Minneapolis, Minnesota
Minneapolis, Minnesota
Minneapolis , nicknamed "City of Lakes" and the "Mill City," is the county seat of Hennepin County, the largest city in the U.S. state of Minnesota, and the 48th largest in the United States...

; and Saint Paul, Minnesota
Saint Paul, Minnesota
Saint Paul is the capital and second-most populous city of the U.S. state of Minnesota. The city lies mostly on the east bank of the Mississippi River in the area surrounding its point of confluence with the Minnesota River, and adjoins Minneapolis, the state's largest city...

.

It is used to elect the leaders of the Labour Party
Labour Party (UK)
The Labour Party is a centre-left democratic socialist party in the United Kingdom. It surpassed the Liberal Party in general elections during the early 1920s, forming minority governments under Ramsay MacDonald in 1924 and 1929-1931. The party was in a wartime coalition from 1940 to 1945, after...

 and the Liberal Democrats
Liberal Democrats
The Liberal Democrats are a social liberal political party in the United Kingdom which supports constitutional and electoral reform, progressive taxation, wealth taxation, human rights laws, cultural liberalism, banking reform and civil liberties .The party was formed in 1988 by a merger of the...

 in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 and the leader of the Liberal Party of Canada
Liberal Party of Canada
The Liberal Party of Canada , colloquially known as the Grits, is the oldest federally registered party in Canada. In the conventional political spectrum, the party sits between the centre and the centre-left. Historically the Liberal Party has positioned itself to the left of the Conservative...

 in a national primary and in the elections of city mayor
Mayor
In many countries, a Mayor is the highest ranking officer in the municipal government of a town or a large urban city....

s in a number of countries. IRV is used to elect the mayor in cities such as London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

 in the United Kingdom (in the variant known as supplementary vote) and Dunedin
Dunedin
Dunedin is the second-largest city in the South Island of New Zealand, and the principal city of the Otago Region. It is considered to be one of the four main urban centres of New Zealand for historic, cultural, and geographic reasons. Dunedin was the largest city by territorial land area until...

 and Wellington
Wellington
Wellington is the capital city and third most populous urban area of New Zealand, although it is likely to have surpassed Christchurch due to the exodus following the Canterbury Earthquake. It is at the southwestern tip of the North Island, between Cook Strait and the Rimutaka Range...

 in New Zealand.

Many private associations also use IRV, including the Hugo Award
Hugo Award
The Hugo Awards are given annually for the best science fiction or fantasy works and achievements of the previous year. The award is named after Hugo Gernsback, the founder of the pioneering science fiction magazine Amazing Stories, and was officially named the Science Fiction Achievement Awards...

s for science fiction and the Academy of Motion Picture Arts and Sciences
Academy of Motion Picture Arts and Sciences
The Academy of Motion Picture Arts and Sciences is a professional honorary organization dedicated to the advancement of the arts and sciences of motion pictures...

 in selection of the Oscar for best picture.

Terminology

In the United States, instant-runoff voting is an umbrella term associated with ranked choice elections where multiple rounds of counting determine majority winners; recipients of the fewest votes are eliminated between rounds, and ballots count for the top-ranked candidate not yet eliminated. The term "instant runoff" is used because the method approximates a series of runoff elections tallied in rounds, as in an exhaustive ballot election, except voters may not change their preference between rounds.

Instant runoff voting has a number of other names, often tied to countries where it is used. In the United States, many observers call it instant runoff voting because it resembles runoff voting
Two-round system
The two-round system is a voting system used to elect a single winner where the voter casts a single vote for their chosen candidate...

. The British usually refer to IRV as the "alternative vote." Although it is only one of several relying on ranking candidates, IRV is referred to as "ranked choice voting" in some American cities and the "preferential ballot" or "preferential voting" in Canada and Australia. It occasionally is referred to as Ware's method after its inventor, American William Robert Ware
William Robert Ware
William Robert Ware , born in Cambridge, Massachusetts into a family of the Unitarian clergy, was an American architect, author, and founder of two important American architectural schools....

.

North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...

 law uses "instant runoff" to describe the contingent vote or "batch elimination" form of IRV in one-seat elections. A single second round of counting produces the top two candidates for a runoff election. Election officials in Hendersonville, North Carolina
Hendersonville, North Carolina
Hendersonville is a city in Henderson County, North Carolina, USA, southeast of Asheville. In 1900, 1,917 persons lived in Hendersonville; in 1910, 2,818; and in 1940, 5,381 people lived here. As of the 2010 census, the city population was 12,223, up fivefold in one century. It is the county...

 use "instant runoff" to describe a multi-seat election system that attempts to simulate in a single round of voting their previous system of multi-seat runoffs. State law in South Carolina
South Carolina
South Carolina is a state in the Deep South of the United States that borders Georgia to the south, North Carolina to the north, and the Atlantic Ocean to the east. Originally part of the Province of Carolina, the Province of South Carolina was one of the 13 colonies that declared independence...

 and Arkansas
Arkansas
Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...

 use "instant runoff" to describe the practice of having certain categories of absentee voters cast ranked ballots before the first round of a runoff that are then counted in a runoff election.

When the single transferable vote
Single transferable vote
The single transferable vote is a voting system designed to achieve proportional representation through preferential voting. Under STV, an elector's vote is initially allocated to his or her most preferred candidate, and then, after candidates have been either elected or eliminated, any surplus or...

 (STV) system is applied to a single-winner election it becomes IRV. For this reason IRV is sometimes considered to be merely a limited form of STV. However, IRV is usually excluded from discussions of STV, because STV was designed for multi-seat constituencies, redistributes votes from both the top (winners) and bottom (dropped candidates), and produces broadly proportional results (depending on the number of seats per constituency); none of which need apply to IRV. Even so, some Irish observers mistakenly call 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.

History

Instant runoff voting was devised in 1871 by American architect
Architect
An architect is a person trained in the planning, design and oversight of the construction of buildings. To practice architecture means to offer or render services in connection with the design and construction of a building, or group of buildings and the space within the site surrounding the...

 William Robert Ware
William Robert Ware
William Robert Ware , born in Cambridge, Massachusetts into a family of the Unitarian clergy, was an American architect, author, and founder of two important American architectural schools....

, although it is, in effect, a special case of the single transferable vote
Single transferable vote
The single transferable vote is a voting system designed to achieve proportional representation through preferential voting. Under STV, an elector's vote is initially allocated to his or her most preferred candidate, and then, after candidates have been either elected or eliminated, any surplus or...

 system, which emerged independently in the 1850s. 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 system in a governmental election was in 1893 in an election for the colonial
Self-governing colony
A self-governing colony is a colony with an elected legislature, in which politicians are able to make most decisions without reference to the colonial power with formal or nominal control of the colony...

 government of Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...

, in Australia. The variant used for this election was a "contingent vote". IRV in its true form was first used in 1908 in a State election in Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

.

IRV was introduced nationally in Australia in 1918 after the Swan by-election
Swan by-election, 1918
The 1918 Swan by-election was a by-election for the Division of Swan in the Australian House of Representatives, following the death of the sitting member Sir John Forrest...

, in response to the rise of the conservative Country Party
National Party of Australia
The National Party of Australia is an Australian political party.Traditionally representing graziers, farmers and rural voters generally, it began as the The Country Party, but adopted the name The National Country Party in 1975, changed to The National Party of Australia in 1982. The party is...

, representing small farmers. The Country Party split the anti-Labor vote in conservative country areas, allowing Labor candidates to win on a minority vote. The conservative government of Billy Hughes
Billy Hughes
William Morris "Billy" Hughes, CH, KC, MHR , Australian politician, was the seventh Prime Minister of Australia from 1915 to 1923....

 introduced preferential voting as a means of allowing competition between the two conservative parties without putting seats at risk. It was first used at the Corangamite
Division of Corangamite
The Division of Corangamite is an Australian Electoral Division in Victoria. The division was one of the original 75 divisions contested at the first federal election...

 by-election on 14 December 1918. Thomas Hare and Andrew Inglis Clark
Andrew Inglis Clark
Andrew Inglis Clark was an Australian barrister, politician, electoral reformer and jurist. He initially qualified engineer, however he re-trained as a barrister in order to effectively fight for social causes which deeply concerned him...

 had previously introduced it in the Tasmanian House of Assembly
Tasmanian House of Assembly
The House of Assembly, or Lower House, is one of the two chambers of the Parliament of Tasmania in Australia. The other is the Legislative Council or Upper House...

.

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 layout, the voter marks a '1' beside the most preferred candidate, a '2' beside the second-most preferred, and so forth, in ascending order.

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.

In the initial count, the first preference of each voter is counted and used to order the candidates. Each first preference counts as one vote for the appropriate candidate. Once all the first preferences are counted, if one candidate holds a majority
Majority
A majority is a subset of a group consisting of more than half of its members. This can be compared to a plurality, which is a subset larger than any other subset; i.e. a plurality is not necessarily a majority as the largest subset may consist of less than half the group's population...

, that candidate wins. Otherwise the candidate who holds the fewest first preferences is eliminated. If there is an exact tie for last place in numbers of votes, tie-breaking rules determine which candidate to eliminate. Some jurisdictions eliminate all low-ranking candidates simultaneously whose combined number of votes is fewer than the number of votes received by the lowest remaining candidates.

Ballots assigned to eliminated candidates are recounted and assigned to one of the remaining candidates based on the next preference on each ballot. The process repeats until one candidate achieves a majority of votes cast for continuing candidates. Ballots that
'exhaust' all their preferences (all its ranked candidates are eliminated) are set aside.

Ballots

As seen above, voters in an IRV election rank candidates on a preferential ballot
Preferential voting
Preferential voting is a type of ballot structure used in several electoral systems in which voters rank candidates in order of relative preference. For example, the voter may select their first choice as '1', their second preference a '2', and so on...

. IRV systems in use in different countries vary both as to ballot design and as to whether or not voters are obliged to provide a full list of preferences. In elections such as those for the President of Ireland and the New South Wales Legislative Assembly
New South Wales Legislative Assembly
The Legislative Assembly, or lower house, is one of the two chambers of the Parliament of New South Wales, an Australian state. The other chamber is the Legislative Council. Both the Assembly and Council sit at Parliament House in the state capital, Sydney...

, voters are permitted to rank as many (or as few) candidates as they wish. This is known in Australia as optional preferential voting.

Under optional preferential voting, voters may make only a first choice, known as "bullet voting
Bullet voting
Bullet voting is a tactic in which the voter only selects one candidate, despite the option to indicate a preference for other candidates. They might do this either because it is easier than evaluating all the candidates, or as a form of tactical voting.If enough voters bullet vote, almost any...

". Allowing voters to rank only as many candidates as they wish may better reflect their preferences, but may result in ballot exhaustion (where all the voters preferences are eliminated before a candidate is elected).

One IRV variant requires voters to express an order of preference for every candidate and thus they consider ballots that do not contain a complete ordering of all candidates to be spoilt
Spoilt vote
'Bold text'In voting, a ballot is considered to be spoilt, spoiled, void, null, informal or stray if it is regarded by the election authorities to be invalid and thus not included in the tally during vote counting. This may be done accidentally or deliberately...

. In Australia this variant is known as 'full preferential voting'. This can become burdensome in elections with many candidates and can lead to 'donkey voting' in which the voter simply chooses candidates at random or in top-to-bottom order. [This variant is used in some Australian federal elections
Australian electoral system
The Australian electoral system has evolved over nearly 150 years of continuous democratic government, and has a number of distinctive features including compulsory voting, preferential voting and the use of proportional voting to elect the upper house, the Australian Senate.- Compulsory voting...

 and some state elections
Electoral systems of the Australian states and territories
The legislatures of the Australian states and territories all follow the Westminster model described in the Australian electoral system. When the Australian colonies were granted responsible government in the nineteenth century, their constitutions provided for legislative assemblies elected by...

].

Candidate order on the ballot paper

The common way to list candidates on a ballot paper is alphabetically or by random lot. In some cases candidates may also be grouped by political party. Alternatively, Robson Rotation
Robson Rotation
Robson Rotation is the method of printing multiple ballots for single transferable vote elections, with each having the candidates listed in a different order....

 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. However, this relies on the assumption that supporters of a minor party will mark preferences for another party based on the advice that they have been given.

Counting logistics

Most IRV elections historically have been tallied by hand, including in elections to Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

's House of Representatives. In the modern era, voting equipment can be used to administer the count either partially or fully.

In Australia, election officials almost always conduct a first preference count (and sometimes a two candidate preference allocation) under the scrutiny of the candidates or their appointed scrutineers at individual polling booths immediately after polling closes. That count is communicated to the electorate returning officer at a central location on the night and the actual ballot papers are secured and subsequently delivered to that official. These ballots are then checked, and a final count of these ballots plus any absentee and special category ballots happens again under the scrutiny of the candidates at premises that have been set up for the purpose by the returning officer. This process may take several days but the outcome of the election is usually known well before all ballots have been counted and preferences allocated.

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, California cities such as Oakland and San Francisco administer IRV elections on voting machine, with optical scanning machines recording preferences and software tallying the IRV algorithm. Cary, North Carolina
Cary, North Carolina
Cary is a large town and suburb of Raleigh, North Carolina in Wake and Chatham counties in the U.S. state of North Carolina. Located almost entirely in Wake County, it is the second largest municipality in that county and the third largest municipality in The Triangle after Raleigh and Durham...

's pilot program in 2007 tallied first choices on optical scan equipment at the polls and then used a central hand-count for the IRV tally. Portland, Maine
Portland, Maine
Portland is the largest city in Maine and is the county seat of Cumberland County. The 2010 city population was 66,194, growing 3 percent since the census of 2000...

 in 2011 will use its usual voting machines to tally first choice at the polls, then a central scan with different equipment if an IRV tally is necessary.

2006 Burlington mayoral election

Candidate Round 1 Round 2
Bob Kiss
Bob Kiss
Bob Kiss is a Vermont politician and Mayor of Burlington, Vermont. Kiss was a member of the Vermont House of Representatives from January 2001 until he stepped down to assume office as mayor of Burlington, following his election to that office on March 7, 2006...

3,809 (38.9%) 4,761 (48.6%)
Hinda Miller
Hinda Miller
Hinda Miller is currently a Democratic member of the Vermont State Senate, representing the Chittenden senate district....

3,106 (31.7%) 3,986 (40.7%)
Kevin Curley 2,609 (26.7%)
Other 254 (2.6%)
Exhausted ballots 10 (0.1%) 1,041 (10.5%)
Total 9,778 (100%) 9,778 (100%)


In 2006 the U.S. city of Burlington, Vermont
Burlington, Vermont
Burlington is the largest city in the U.S. state of Vermont and the shire town of Chittenden County. Burlington lies south of the U.S.-Canadian border and some south of Montreal....

, held a mayoral election using instant runoff voting. Progressive Bob Kiss
Bob Kiss
Bob Kiss is a Vermont politician and Mayor of Burlington, Vermont. Kiss was a member of the Vermont House of Representatives from January 2001 until he stepped down to assume office as mayor of Burlington, following his election to that office on March 7, 2006...

 won in two rounds with 48.6% of the first round ballots, defeating Democrat Hinda Miller
Hinda Miller
Hinda Miller is currently a Democratic member of the Vermont State Senate, representing the Chittenden senate district....

 who achieved 40.7%. 10.6% (1,031) of the ballots were exhausted before the final round, because those voters (largely backers of Republican candidate Kevin Curley) offered no preference between the final two candidates, Miller and Kiss.

After the first round, all but two candidates were eliminated, as their combined vote total (2,863) was less than Miller's, so that none could pull ahead of Miller, even by receiving every vote from the other minor candidates. The votes for these candidates were recounted and redistributed between Kiss and Miller. After the second round count, Kiss was declared the winner as he had obtained a majority (54.4%) of the remaining unexhausted ballots.

1990 Irish presidential election

Irish presidential election, 1990
Candidate Round 1 Round 2
Mary Robinson
Mary Robinson
Mary Therese Winifred Robinson served as the seventh, and first female, President of Ireland from 1990 to 1997, and the United Nations High Commissioner for Human Rights, from 1997 to 2002. She first rose to prominence as an academic, barrister, campaigner and member of the Irish Senate...

612,265 (38.9%) 817,830 (51.6%)
Brian Lenihan 694,484 (43.8%) 731,273 (46.2%)
Austin Currie
Austin Currie
Austin Currie is a former politician who was elected to the parliaments of both Northern Ireland and the Republic of Ireland....

267,902 (16.9%)
Exhausted ballots 9,444 (0.6%) 34,992 (2.2%)
Total 1,584,095 (100%) 1,584,095 (100%)


The result of the 1990 Irish presidential election
Irish presidential election, 1990
-Aftermath:While the role of the presidency in day to day politics is a very limited one the Robinson presidency is regarded by many observers as a watershed in Irish society symbolising the shift away from the conservative ultracatholic male-dominated Ireland which existed up until the end of the...

 provides an example of how instant runoff voting can produce a different result than first-past-the-post voting. The three candidates were Brian Lenihan of the traditionally dominant Fianna Fáil
Fianna Fáil
Fianna Fáil – The Republican Party , more commonly known as Fianna Fáil is a centrist political party in the Republic of Ireland, founded on 23 March 1926. Fianna Fáil's name is traditionally translated into English as Soldiers of Destiny, although a more accurate rendition would be Warriors of Fál...

 party, Austin Currie
Austin Currie
Austin Currie is a former politician who was elected to the parliaments of both Northern Ireland and the Republic of Ireland....

 of Fine Gael
Fine Gael
Fine Gael is a centre-right to centrist political party in the Republic of Ireland. It is the single largest party in Ireland in the Oireachtas, in local government, and in terms of Members of the European Parliament. The party has a membership of over 35,000...

, and Mary Robinson
Mary Robinson
Mary Therese Winifred Robinson served as the seventh, and first female, President of Ireland from 1990 to 1997, and the United Nations High Commissioner for Human Rights, from 1997 to 2002. She first rose to prominence as an academic, barrister, campaigner and member of the Irish Senate...

, nominated by the Labour Party
Labour Party (Ireland)
The Labour Party is a social-democratic political party in the Republic of Ireland. The Labour Party was founded in 1912 in Clonmel, County Tipperary, by James Connolly, James Larkin and William X. O'Brien as the political wing of the Irish Trade Union Congress. Unlike the other main Irish...

 and the Worker's Party
Workers' Party of Ireland
The Workers' Party is a left-wing republican political party in Ireland. Originating in the Sinn Féin organisation founded in 1905 by Arthur Griffith, it took its current form in 1970 after a split within the party, adopting its current name in 1982....

. After the first round, Lenihan had the largest share of the first choice rankings (and hence would have won a first-past-the-post vote), but no candidate attained the necessary majority. Currie was eliminated and his votes reassigned to the next choice ranked on each ballot; in this process, Robinson received 82% of Currie's votes, thereby overtaking Lenihan.

Voting system criteria

Scholars rate voting systems using mathematically derived voting system criteria, which describe desirable features of a system. 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
Arrow's impossibility theorem
In social choice theory, Arrow’s impossibility theorem, the General Possibility Theorem, or Arrow’s paradox, states that, when voters have three or more distinct alternatives , no voting system can convert the ranked preferences of individuals into a community-wide ranking while also meeting a...

 and the Gibbard-Satterthwaite theorem
Gibbard-Satterthwaite theorem
The Gibbard–Satterthwaite theorem, named after Allan Gibbard and Mark Satterthwaite, is a result about the deterministic voting systems that choose a single winner using only the preferences of the voters, where each voter ranks all candidates in order of preference...

.

Many of the mathematical criteria by which voting systems are compared were formulated for voters with ordinal preferences. If voters vote according to a the same ordinal preferences in both rounds, criteria can be applied to two-round system
Two-round system
The two-round system is a voting system used to elect a single winner where the voter casts a single vote for their chosen candidate...

s of runoffs, and in that case, each of the criteria failed by IRV is also failed by the two-round system
Two-round system
The two-round system is a voting system used to elect a single winner where the voter casts a single vote for their chosen candidate...

 as they relate to automatic elimination of trailing candidates. Partial results exist for other models of voter behavior in the two-round system: see the two-round system article's criterion compliance section for more information.

The criteria that IRV meets, and those that it does not, are listed below.

Majority criterion

The majority
Majority criterion
The majority criterion is a single-winner voting system criterion, used to compare such systems. The criterion states that "if one candidate is preferred by a majority of voters, then that candidate must win"....

criterion states that "if one candidate is preferred by an absolute majority of voters, then that candidate must win". IRV meets this criterion.

Mutual majority criterion

The mutual majority
Mutual majority criterion
The mutual majority criterion is a criterion used to compare voting systems. It is also known as the majority criterion for solid coalitions and the generalized majority criterion...

criterion states that "if every voter prefers every member of a group of candidates to every candidate not in that group, then one of the preferred group must win". IRV meets this criterion.

Later-no-harm criterion

The later-no-harm
Later-no-harm criterion
The later-no-harm criterion is a voting system criterion formulated by Douglas Woodall. The criterion is satisfied if, in any election, a voter giving an additional ranking or positive rating to a less preferred candidate cannot cause a more preferred candidate to lose.- Complying methods :Single...

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". IRV meets this criterion.

Resolvability criterion

The resolvability
Resolvability criterion
Resolvability criterion can refer to any voting system criterion that ensures a low possibility of tie votes.#Nicolaus Tideman's version of the criterion demands that if and only if for every winner in a result, a vote exists, such that when added, makes that winner unique.#Douglas R...

criterion states that "the probability of an exact tie must diminish as more votes are cast". IRV meets this criterion.

Condorcet winner criterion

The Condorcet winner
Condorcet criterion
The Condorcet candidate or Condorcet winner of an election is the candidate who, when compared with every other candidate, is preferred by more voters. Informally, the Condorcet winner is the person who would win a two-candidate election against each of the other candidates...

criterion states that "if a candidate would win a head-to-head competition
Condorcet method
A Condorcet method is any single-winner election method that meets the Condorcet criterion, which means the method always selects the Condorcet winner if such a candidate exists. The Condorcet winner is the candidate who would beat each of the other candidates in a run-off election.In modern...

 against every other candidate, then that candidate must win the overall election". IRV does not meet this criterion.

IRV is more likely to elect the Condorcet winner than plurality voting and 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 IRV winner was the Condorcet winner, including a San Francisco election in which the IRV winner was in third place in first choice rankings.

Condorcet loser criterion

The Condorcet loser
Condorcet loser criterion
In single-winner voting system theory, the Condorcet loser criterion is a measure for differentiating voting systems. It implies the majority loser criterion....

criterion states that "if a candidate would lose a head-to-head competition
Condorcet method
A Condorcet method is any single-winner election method that meets the Condorcet criterion, which means the method always selects the Condorcet winner if such a candidate exists. The Condorcet winner is the candidate who would beat each of the other candidates in a run-off election.In modern...

 against every other candidate, then that candidate must not win the overall election". IRV meets this criterion.

Consistency criterion

The consistency
Consistency criterion
A voting system is consistent if, when the electorate is divided arbitrarily into two parts and separate elections in each part result in the same choice being selected, an election of the entire electorate also selects that alternative...

criterion states that if dividing the electorate into two groups and running the same election separately with each group returns the same result for both groups, then the election over the whole electorate should return this result. IRV, like all preferential voting systems which are not positional
Positional voting system
A positional voting system is a ranked voting method in which the options receive points based on their position on each ballot, and the option with the most points wins....

, does not meet this criterion: dividing the electorate into two groups and running the same election separately with each group is not guaranteed to return the same results as the election over the whole electorate. In a general sense, this reflects the fact that the system does not produce as evenly spread a set of winners as a proportional
Proportional representation
Proportional representation is a concept in voting systems used to elect an assembly or council. PR means that the number of seats won by a party or group of candidates is proportionate to the number of votes received. For example, under a PR voting system if 30% of voters support a particular...

 process.

Monotonicity criterion

The monotonicity
Monotonicity criterion
The monotonicity criterion is a voting system criterion used to analyze both single and multiple winner voting systems. A voting system is monotonic if it satisfies one of the definitions of the monotonicity criterion, given below.Douglas R...

criterion states that "a voter can't harm a candidate's chances of winning by voting that candidate higher, or help a candidate by voting that candidate lower, while keeping the relative order of all the other candidates equal." IRV does not meet this criterion. Allard claims failure is unlikely, at a less than 0.03% chance per election. Some critics argue in turn that Allard's calculations are wrong and the probability of monotonicity failure is much greater, at 14.5% under the impartial culture election model in the three-candidate case, or 7-10% in the case of a left-right spectrum. Lepelly et al. find a 2%-5% probability of monotonicity failure under the same election model as Allard.

Participation criterion

The participation
Participation criterion
The participation criterion is a voting system criterion. It is also known as the "no show paradox". It has been defined as follows:* In a deterministic framework, the participation criterion says that the addition of a ballot, where candidate A is strictly preferred to candidate B, to an existing...

criterion states that "the best way to help a candidate win must not be to abstain". IRV does not meet this criterion: in some cases, the voter's preferred candidate can be best helped if the voter does not vote at all. Depankar Ray finds a 50% probability that, when IRV elects a different candidate than Plurality, some voters would have been better off not showing up.
In a large scale election, the issue is academic since the behaviors required of the electors to achieve it do not scale.

Reversal symmetry criterion

The reversal symmetry
Reversal symmetry
Reversal symmetry is a voting system criterion which requires that if candidate A is the unique winner, and each voter's individual preferences are inverted, then A must not be elected. Methods that satisfy reversal symmetry include Borda count, the Kemeny-Young method, and the Schulze method...

criterion states that "if candidate A is the unique winner, and each voter's individual preferences are inverted, then A must not be elected". IRV does not meet this criterion: it is possible to construct an election where reversing the order of every ballot paper does not alter the final winner. However, this is essentially an academic exercise.

Independence of irrelevant alternatives criterion

The independence of irrelevant alternatives
Independence of irrelevant alternatives
Independence of irrelevant alternatives is an axiom of decision theory and various social sciences.The word is used in different meanings in different contexts....

criterion states that "the election outcome remains the same even if a candidate who cannot win decides to run." IRV does not meet this criterion; in the general case, instant-runoff voting can be susceptible to strategic nomination
Strategic nomination
Strategic nomination is the manipulation of an election through its candidate set...

: whether or not a candidate decides to run at all can affect the result even if the new candidate cannot themselves win.

Independence of clones criterion

The independence of clones criterion
Independence of clones criterion
In voting systems theory, the independence of clones criterion measures an election method's robustness to strategic nomination. Nicolaus Tideman first formulated the criterion, which states that the addition of a candidate identical to one already present in an election will not cause the winner...

states that "the election outcome remains the same even if an identical candidate who is equally preferred decides to run." IRV meets this criterion.

Comparison to other voting systems

Is tactical voting possible?

The Gibbard–Satterthwaite theorem demonstrates that no voting system can be entirely immune from tactical voting unless it is dictatorial (there is only one person who is able to choose the winner) or incorporates an element of chance. IRV is considered one of the less-manipulable voting systems, with theorist Nicolaus Tideman
Nicolaus Tideman
T. Nicolaus Tideman is a Professor of Economics at Virginia Polytechnic Institute and State University. He received his Bachelor of Arts in economics and mathematics from Reed College in 1965 and his PhD in economics from the University of Chicago in 1969...

 noting that "alternative vote is quite resistant to strategy" and Australian political analyst Antony Green dismissing suggestions of tactical voting. James Green-Armytage finds the alternative vote to be second most resistant to tactical voting among the methods tested, only beaten by a class of AV-Condorcet hybrids, although the alternative vote resists strategic withdrawal by candidates less well.

By not meeting the monotonicity, Condorcet winner, and participation criteria, IRV theoretically could permit forms of tactical voting if voters had complete and reliable information about voters' full preferences. However, FairVote
FairVote
FairVote is a U.S. non-profit organization based in Takoma Park, Maryland, whose mission is to achieve universal access to participation, a full spectrum of meaningful ballot choices and majority rule with fair representation for all...

 claims that monotonicity failure can be misconstrued to suggest that "Having more voters rank [a] candidate first, can cause [them] to switch from being a winner to being a loser." In fact, it is the change in lower candidates that is important: whether votes are shifted to the leading candidate, shifted to a fringe candidate, or discarded altogether is of no importance. What tactical voting would seek to achieve is 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. 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 on the left and right 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
Burlington, Vermont mayoral election, 2009
The Burlington mayoral election of 2009 occurred on Tuesday, March 3, 2009. Burlington's mayoral race is partisan election that occurs every three years, and there are no term limits. The current mayor, Bob Kiss, has served since 2006. This marks the second mayoral election in Burlington using...

 in Burlington, Vermont
Burlington, Vermont
Burlington is the largest city in the U.S. state of Vermont and the shire town of Chittenden County. Burlington lies south of the U.S.-Canadian border and some south of Montreal....

 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 came in second (a Republican who led in first choices) preferred the Condorcet
Condorcet method
A Condorcet method is any single-winner election method that meets the Condorcet criterion, which means the method always selects the Condorcet winner if such a candidate exists. The Condorcet winner is the candidate who would beat each of the other candidates in a run-off election.In modern...

 winner, a Democrat, to the IRV winner, the Progressive Party nominee. If about 20% of the backers of the Republican candidate had insincerely raised the Democrat from their second choice to their first, the Republican would have dropped from first to third in first choices, and the Democrat would then have won the instant runoff. But given that the Republican was a strong candidate who nearly won in the instant runoff, few of his backers would have risked giving up on his candidacy based on a chance, unknown before the fact, to elect the compromise Condorcet winner.

Is tactical voting necessary?

The spoiler effect is where two or more equally popular candidates divide the vote, meaning that each receives fewer votes than a single opponent who is disliked by the majority of voters but has little competition. Proponents of IRV note that by reducing the spoiler effect, IRV makes it safe to vote honestly for marginal parties, and so discourages tactical voting
Tactical voting
In voting systems, tactical voting occurs, in elections with more than two viable candidates, when a voter supports a candidate other than his or her sincere preference in order to prevent an undesirable outcome.It has been shown by the Gibbard-Satterthwaite theorem that any voting method which is...

: under a plurality system, 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 fringe candidate is largely wasted. In an IRV system this is no longer an issue 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. In Australia's national 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.

Proportionality

IRV is not a proportional voting system. Like all winner-take-all voting systems, 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
Electoral Reform Society
The Electoral Reform Society is a political pressure group based in the United Kingdom which promotes electoral reform. It is believed to be the oldest organisation concerned with electoral systems in the world.-Aims:...

 concluded that the election would have altered the balance of seats between the three main parties, but the number of seats won by minor parties would have remained unchanged.

Australia, a nation with a long record of using IRV for election of legislative bodies, has had representation in its parliament broadly similar to that expected by plurality systems
Plurality voting system
The plurality voting system is a single-winner voting system often used to elect executive officers or to elect members of a legislative assembly which is based on single-member constituencies...

. Medium-sized parties, such as the National Party of Australia
National Party of Australia
The National Party of Australia is an Australian political party.Traditionally representing graziers, farmers and rural voters generally, it began as the The Country Party, but adopted the name The National Country Party in 1975, changed to The National Party of Australia in 1982. The party is...

, can co-exist with coalition
Coalition (Australia)
The Coalition in Australian politics refers to a group of centre-right parties that has existed in the form of a coalition agreement since 1922...

 partners such as the Liberal Party of Australia
Liberal Party of Australia
The Liberal Party of Australia is an Australian political party.Founded a year after the 1943 federal election to replace the United Australia Party, the centre-right Liberal Party typically competes with the centre-left Australian Labor Party for political office...

, and can compete against it without fear of losing seats to other parties due to vote splitting. IRV is more likely to result in legislatures where no single party has an absolute majority of seats (a hung parliament
Hung parliament
In a two-party parliamentary system of government, a hung parliament occurs when neither major political party has an absolute majority of seats in the parliament . It is also less commonly known as a balanced parliament or a legislature under no overall control...

), but does not generally produce as fragmented a legislature as a fully proportional system, such as is used for the House of Representatives of the Netherlands or the New Zealand House of Representatives
New Zealand House of Representatives
The New Zealand House of Representatives is the sole chamber of the legislature of New Zealand. The House and the Queen of New Zealand form the New Zealand Parliament....

, 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 system 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
Pierce County, Washington
right|thumb|[[Tacoma, Washington|Tacoma]] - Seat of Pierce CountyPierce County is the second most populous county in the U.S. state of Washington. Formed out of Thurston County on December 22, 1852, by the legislature of Oregon Territory...

 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. In 2009 the auditor of Washington counties 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.

It is possible to count IRV ballots by hand, and this is done for the Australian federal elections. Because multiple rounds of counting are required, the ballots must either be collected in one central location, or the interim results of each count must be collated and instructions sent out to each counting centre as to what action to take next. In Australia counting takes place in each polling centre individually, and the results of the first-preference votes are aggregated by telephone; for subsequent rounds the papers are brought to one central counting centre.

The perceived costs or cost savings of adopting an IRV system are commonly used by both supporters and critics. In the 2011 referendum on the Alternative Vote in the UK, the NOtoAV
NOtoAV
NOtoAV was a political campaign in the United Kingdom whose purpose was to persuade the public to vote against the Alternative Vote in the referendum on Thursday, 5 May 2011. NOtoAV was successful in maintaining the current voting system having received 67.9% of votes cast.-Parties in the House of...

 campaign launched with a claim that adopting the system 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 system at all.

Because it does not require two separate votes, IRV is accepted to cost less than two-round primary/general or general/runoff election systems.

Negative campaigning

John Russo, Oakland City Attorney, argued in the Oakland Tribune on July 24, 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 system, 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.

No formal studies have been conducted in the United States. 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
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...

 adopted instant runoff voting.

Critics allege there is a lack of evidence that such an effect occurs as often as suggested. Indeed, 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

In Ann Arbor, Michigan
Ann Arbor, Michigan
Ann Arbor is a city in the U.S. state of Michigan and the county seat of Washtenaw County. The 2010 census places the population at 113,934, making it the sixth largest city in Michigan. The Ann Arbor Metropolitan Statistical Area had a population of 344,791 as of 2010...

 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 voting
Plural voting
Plural 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...

 is sometimes used in arguments over the 'fairness' of the system, and has led to several legal challenges in the United States. 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:

Invalid ballots and exhausted ballots

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 error rates 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. 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.

Robert's Rules of Order

The sequential elimination method used by IRV is described in Robert's Rules of Order
Robert's Rules of Order
Robert's Rules of Order is the short title of a book containing rules of order intended to be adopted as a parliamentary authority for use by a deliberative assembly written by Brig. Gen...

 Newly Revised, 10th edition.
as an example of "preferential voting
Preferential voting
Preferential voting is a type of ballot structure used in several electoral systems in which voters rank candidates in order of relative preference. For example, the voter may select their first choice as '1', their second preference a '2', and so on...

", a term covering "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 ... by way of illustration." And then the instant runoff voting method is 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 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
The Standard Code of Parliamentary Procedure is a book of rules of order. It is the second most popular parliamentary authority in the United States after Robert's Rules of Order. It was first published in 1950...

 and Riddick's Rules of Procedure
Riddick's Rules of Procedure
Riddick's Rules of Procedure is a parliamentary authority - a book explaining the parliamentary procedure, including the rules, ethics, and customs governing meetings and other operations of the United States Senate. It was written by Floyd M. Riddick and co-authored by Miriam Butcher...

.

Global use

Australia

Instant-runoff voting is used for national elections in Australia to elect members of the Australian House of Representatives
Australian House of Representatives
The House of Representatives is one of the two houses of the Parliament of Australia; it is the lower house; the upper house is the Senate. Members of Parliament serve for terms of approximately three years....

. The Australian Senate
Australian Senate
The Senate is the upper house of the bicameral Parliament of Australia, the lower house being the House of Representatives. Senators are popularly elected under a system of proportional representation. Senators are elected for a term that is usually six years; after a double dissolution, however,...

 uses a modified form, combining it with a proportional representation
Proportional representation
Proportional representation is a concept in voting systems used to elect an assembly or council. PR means that the number of seats won by a party or group of candidates is proportionate to the number of votes received. For example, under a PR voting system if 30% of voters support a particular...

 system (the Single transferable vote
Single transferable vote
The single transferable vote is a voting system designed to achieve proportional representation through preferential voting. Under STV, an elector's vote is initially allocated to his or her most preferred candidate, and then, after candidates have been either elected or eliminated, any surplus or...

); candidates are eliminated until the remaining parties can be said to have a sufficient proportion of the vote to earn a seat.

Canada

IRV is used to elect the leaders of two political parties in Canada, the Liberal Party of Canada
Liberal Party of Canada
The Liberal Party of Canada , colloquially known as the Grits, is the oldest federally registered party in Canada. In the conventional political spectrum, the party sits between the centre and the centre-left. Historically the Liberal Party has positioned itself to the left of the Conservative...

 and the Conservative Party of Canada
Conservative Party of Canada
The Conservative Party of Canada , is a political party in Canada which was formed by the merger of the Canadian Alliance and the Progressive Conservative Party of Canada in 2003. It is positioned on the right of the Canadian political spectrum...

. Canadian Prime Minister Stephen Harper
Stephen Harper
Stephen Joseph Harper is the 22nd and current Prime Minister of Canada and leader of the Conservative Party. Harper became prime minister when his party formed a minority government after the 2006 federal election...

 won an IRV election to become party leader in the 2004 leadership election
Conservative Party of Canada leadership election, 2004
The 2004 Conservative Party of Canada leadership election took place on March 20, 2004 in Toronto, Ontario, and resulted in the election of Stephen Harper as the first leader of the new Canadian Conservative Party...

.

Fiji

Instant-runoff voting is used for national elections to elect members of the House of Representatives of Fiji. In Fiji, each voter casts ballots in two elections: one for the minority of seats that are elected by universal suffrage and the remaining in one of the communal constituencies reserved to different ethnic groups.

India

IRV is used in numerous electoral college
Electoral college
An electoral college is a set of electors who are selected to elect a candidate to a particular office. Often these represent different organizations or entities, with each organization or entity represented by a particular number of electors or with votes weighted in a particular way...

 environments, including the election of the President of India
President of India
The President of India is the head of state and first citizen of India, as well as the Supreme Commander of the Indian Armed Forces. President of India is also the formal head of all the three branches of Indian Democracy - Legislature, Executive and Judiciary...

 by the members of the Parliament of India
Parliament of India
The Parliament of India is the supreme legislative body in India. Founded in 1919, the Parliament alone possesses legislative supremacy and thereby ultimate power over all political bodies in India. The Parliament of India comprises the President and the two Houses, Lok Sabha and Rajya Sabha...

 and of the Vidhan Sabha
Vidhan Sabha
The Vidhan Sabha or the Legislative Assembly is the lower house or the sole house of the provincial legislature in the different states of India. The same name is also used for the lower house of the legislatures for two of the union territories, Delhi and Pondicherry...

s – the state
States and territories of India
India is a federal union of states comprising twenty-eight states and seven union territories. The states and territories are further subdivided into districts and so on.-List of states and territories:...

 legislatures.

Ireland

While most elections in the Republic of Ireland uses the single transferable vote
Single transferable vote
The single transferable vote is a voting system designed to achieve proportional representation through preferential voting. Under STV, an elector's vote is initially allocated to his or her most preferred candidate, and then, after candidates have been either elected or eliminated, any surplus or...

 (STV), in single-winner contests this reduces to IRV. This is the case in all Presidential elections
Irish presidential election
The Irish presidential election determines who serves as the President of Ireland; the head of state of Ireland. The most recent election took place on 27 October 2011.-Overview:...

 and Seanad panel by-elections, and most Dáil by-elections In the rare event of multiple simultaneous vacancies in a single Dáil constituency, a single STV by-election may be held; for Seanad panels, multiple IRV by-elections are held.

New Zealand

IRV is used in the elections of mayor
Mayor
In many countries, a Mayor is the highest ranking officer in the municipal government of a town or a large urban city....

s and councillors in single-member wards in some New Zealand cities such as Dunedin and Wellington. Multi-member wards in these cities use STV.

IRV, under the name Alternative Vote, was one of the four alternative systems available (alongside MMP
Mixed member proportional representation
Mixed-member proportional representation, also termed mixed-member proportional voting and commonly abbreviated to MMP, is a voting system originally used to elect representatives to the German Bundestag, and nowadays adopted by numerous legislatures around the world...

, STV
Single transferable vote
The single transferable vote is a voting system designed to achieve proportional representation through preferential voting. Under STV, an elector's vote is initially allocated to his or her most preferred candidate, and then, after candidates have been either elected or eliminated, any surplus or...

 and SM) in the 1992 referendum on the voting method
Electoral reform in New Zealand
Electoral reform in New Zealand has, in recent years, become a political issue as major changes have been made to both Parliamentary and local government electoral systems.- Parliamentary Electoral Reform :...

 to elect MP's to the New Zealand House of Representatives
New Zealand House of Representatives
The New Zealand House of Representatives is the sole chamber of the legislature of New Zealand. The House and the Queen of New Zealand form the New Zealand Parliament....

. It came third of the alternative systems (ahead of SM) with 6.6% of the vote. IRV, under the name Preferential Vote, will again be one of the four alternative systems available in the upcoming 2011 voting method referendum
New Zealand voting method referendum, 2011
The New Zealand voting system referendum, 2011, was a referendum on whether to keep the existing mixed member proportional voting system, or to change to another voting system, for electing Members of Parliament to New Zealand's House of Representatives...

.

Papua New Guinea

Since 2003 the national parliament of Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...

 has been elected using an IRV variant called Limited Preferential Voting, where voters are limited to ranking three candidates.

United Kingdom

In the United Kingdom the system is commonly known as the alternative vote. It is used to elect the leaders of the Labour Party
Labour Party (UK)
The Labour Party is a centre-left democratic socialist party in the United Kingdom. It surpassed the Liberal Party in general elections during the early 1920s, forming minority governments under Ramsay MacDonald in 1924 and 1929-1931. The party was in a wartime coalition from 1940 to 1945, after...

 and the Liberal Democrats
Liberal Democrats
The Liberal Democrats are a social liberal political party in the United Kingdom which supports constitutional and electoral reform, progressive taxation, wealth taxation, human rights laws, cultural liberalism, banking reform and civil liberties .The party was formed in 1988 by a merger of the...

. (The leader of the Conservative Party
Conservative Party (UK)
The Conservative Party, formally the Conservative and Unionist Party, is a centre-right political party in the United Kingdom that adheres to the philosophies of conservatism and British unionism. It is the largest political party in the UK, and is currently the largest single party in the House...

 is elected under a similar system, a variant of the exhaustive ballot
Exhaustive ballot
The exhaustive ballot is a voting system used to elect a single winner. Under the exhaustive ballot the elector simply casts a single vote for his or her favorite candidate. However if no candidate is supported by an overall majority of votes then the candidate with the fewest votes is eliminated...

.) It is also used for by-elections to the British House of Lords
By elections to the House of Lords
Following passing of the House of Lords Act 1999 the number of hereditary peers entitled to sit in the House of Lords was reduced to ninety-two. The first ninety-two were elected by all hereditary peers before the passing of the reform...

, in which hereditary peer
Hereditary peer
Hereditary peers form part of the Peerage in the United Kingdom. There are over seven hundred peers who hold titles that may be inherited. Formerly, most of them were entitled to sit in the House of Lords, but since the House of Lords Act 1999 only ninety-two are permitted to do so...

s are selected for that body. AV is also used by members of parliament to elect the chairmen of select committees and the Speaker of the House of Lords. The Speaker of the House of Commons is elected by the exhaustive ballot.

In 2010 the Conservative/Liberal Democrat coalition government agreed to hold a national referendum on the alternative vote, held on 5 May 2011. The proposal would have affected the way in which Members of Parliament are elected to the British House of Commons at Westminster. The result of the referendum
Results of the United Kingdom Alternative Vote referendum, 2011
-Results by regions:-Local results:Of the 440 counting areas, ten returned a majority in favour of the change...

 was a vote against adoption of the alternative vote by a margin of 67.9 percent to 32.1 percent.

United States

Main article: Instant-runoff voting in the United States.

IRV is used by several jurisdictions in the United States, including San Francisco, Oakland, California
Oakland, California
Oakland is a major West Coast port city on San Francisco Bay in the U.S. state of California. It is the eighth-largest city in the state with a 2010 population of 390,724...

, and Minneapolis and Saint Paul, Minnesota
Saint Paul, Minnesota
Saint Paul is the capital and second-most populous city of the U.S. state of Minnesota. The city lies mostly on the east bank of the Mississippi River in the area surrounding its point of confluence with the Minnesota River, and adjoins Minneapolis, the state's largest city...

. United States private associations that use IRV include the Hugo Award
Hugo Award
The Hugo Awards are given annually for the best science fiction or fantasy works and achievements of the previous year. The award is named after Hugo Gernsback, the founder of the pioneering science fiction magazine Amazing Stories, and was officially named the Science Fiction Achievement Awards...

s for science fiction, the Academy of Motion Picture Arts and Sciences
Academy of Motion Picture Arts and Sciences
The Academy of Motion Picture Arts and Sciences is a professional honorary organization dedicated to the advancement of the arts and sciences of motion pictures...

 in selection of the Oscar for Best Picture, and more than fifty colleges and universities for student elections.

Runoff voting

The term instant runoff voting is derived from the name of a class of voting systems 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 systems 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
Tactical voting
In voting systems, tactical voting occurs, in elections with more than two viable candidates, when a voter supports a candidate other than his or her sincere preference in order to prevent an undesirable outcome.It has been shown by the Gibbard-Satterthwaite theorem that any voting method which is...

 that can be prevalent in 'standard' runoff voting.

Exhaustive ballot

A system closer to IRV is the exhaustive ballot
Exhaustive ballot
The exhaustive ballot is a voting system used to elect a single winner. Under the exhaustive ballot the elector simply casts a single vote for his or her favorite candidate. However if no candidate is supported by an overall majority of votes then the candidate with the fewest votes is eliminated...

. In this system—one familiar to fans of the television show American Idol
American Idol
American Idol, titled American Idol: The Search for a Superstar for the first season, is a reality television singing competition created by Simon Fuller and produced by FremantleMedia North America and 19 Entertainment...

—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 systems

The simplest form of runoff voting is the two-round system
Two-round system
The two-round system is a voting system used to elect a single winner where the voter casts a single vote for their chosen candidate...

, 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 system is used in France and the Finnish presidential election.

Contingent vote (supplementary)

The contingent vote
Contingent vote
The contingent vote 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 the two leading candidates are eliminated and there is a...

, 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
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...

, and the elections for Mayor of London
Mayor of London
The Mayor of London is an elected politician who, along with the London Assembly of 25 members, is accountable for the strategic government of Greater London. Conservative Boris Johnson has held the position since 4 May 2008...

 in the United Kingdom, voters rank a specified maximum number of candidates. In London, the Supplementary Vote, allows voters to express first and second preferences only. Sri Lankan voters rank up to three candidates for the President of Sri Lanka
President of Sri Lanka
The President of Democratic Socialist Republic of Sri Lanka is the elected head of state and the head of government. The President is a dominant political figure in Sri Lanka. The office was created in 1978 but has grown so powerful there have been calls to restrict or even eliminate its power...

, in a variant of the contingent vote.

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
Tactical voting
In voting systems, tactical voting occurs, in elections with more than two viable candidates, when a voter supports a candidate other than his or her sincere preference in order to prevent an undesirable outcome.It has been shown by the Gibbard-Satterthwaite theorem that any voting method which is...

, by ranking at least one a 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 was performed.

In a 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
    Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...

    , Louisiana
    Louisiana
    Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

    , South Carolina
    South Carolina
    South Carolina is a state in the Deep South of the United States that borders Georgia to the south, North Carolina to the north, and the Atlantic Ocean to the east. Originally part of the Province of Carolina, the Province of South Carolina was one of the 13 colonies that declared independence...

     and Springfield, Illinois
    Springfield, Illinois
    Springfield is the third and current capital of the US state of Illinois and the county seat of Sangamon County with a population of 117,400 , making it the sixth most populated city in the state and the second most populated Illinois city outside of the Chicago Metropolitan Area...

     adopt this approach.
  • IRV can quickly eliminate weak candidates in early rounds of an exhaustive ballot
    Exhaustive ballot
    The exhaustive ballot is a voting system used to elect a single winner. Under the exhaustive ballot the elector simply casts a single vote for his or her favorite candidate. However if no candidate is supported by an overall majority of votes then the candidate with the fewest votes is eliminated...

     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
    Preferential voting is a type of ballot structure used in several electoral systems in which voters rank candidates in order of relative preference. For example, the voter may select their first choice as '1', their second preference a '2', and so on...

     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 the one vote is counted per ballot per round, with rules that eliminate the weakest candidate(s) in successive rounds. Most IRV implementations drop the "majority
Majority
A majority is a subset of a group consisting of more than half of its members. This can be compared to a plurality, which is a subset larger than any other subset; i.e. a plurality is not necessarily a majority as the largest subset may consist of less than half the group's population...

 of cast ballots" requirement.

See also

  • Alternative Vote Plus (AV+) or Alternative Vote Top-up proposed by the Jenkins Commission (UK)
    Jenkins Commission (UK)
    The Independent Commission on the Voting System, popularly known as the Jenkins Commission after its chairman Roy Jenkins, was a commission into possible reform of the United Kingdom electoral system.-The commission:...

  • Outline of democracy
    Outline of democracy
    The following outline is provided as an overview of and topical guide to democracy:Democracy – form of government in which all people have an equal say in the decisions that affect their lives...

  • None of the above
    None of the above
    None of the Above or against all is a ballot option in some jurisdictions or organizations, designed to allow the voter to indicate disapproval of all of the candidates in a voting system...

     (NOTA) or Re-Open Nominations (RON)
  • First-past-the-post voting

External links


IRV in practice

Demos and simulations

Advocacy groups and positions

Opposition groups and positions
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