Instant-runoff voting

Instant-runoff voting (IRV) is a voting system used for single-winner elections in which voters have one vote and rank candidates in order of preference. If no candidate receives a majority of first preference rankings, the candidate with the fewest number of votes is eliminated and that candidate's votes redistributed to the voters' next preferences among the remaining candidates. This process is repeated until one candidate has a majority of votes among candidates not eliminated. The term "instant runoff" is used because IRV is said to simulate a series of run-off elections tallied in rounds, as in an exhaustive ballot election.

IRV is also referred to as preferential voting in Australia, the preferential ballot in Canada, alternative voting (AV) in the United Kingdom, and sometimes ranked choice voting in the U.S. It is also referred to as the Hare system or Hare method, after Thomas Hare, an inventor of single transferable vote (STV) because IRV is the same as STV for a single seat election: Even though voters can mark multiple candidates in preference order, the elimination process results in only a single transferable vote cast for the office.

Robert's Rules of Order calls preferential voting "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 that under a rule that a plurality shall elect. . . . Preferential voting has many variations." The single transferable vote technique used by IRV is the example given. The manual goes on to note that if voters don't rank enough candidates, this may prevent any from receiving a majority and "require the voting to be repeated. . . . 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 in last place is automatically eliminated and may thus be prevented from becoming a compromise choice."

At a national level IRV is used to elect the Australian House of Representatives, the President of Ireland, the national parliament of Papua New Guinea and the Fijian House of Representatives. In the United States, it is used in four local jurisdictions, including San Francisco, California and has been approved by voters in other jurisdictions such as Minneapolis, Minnesota and Pierce County, Washington. In the United Kingdom, IRV is used for elections for leaders of the Labour Party and the Liberal Democrats, while the supplementary vote form of IRV is used for all direct elections of mayors in England, including for the Mayor of London. New Zealand cities using IRV include the capital, Wellington. IRV is used in a number of non-governmental elections, including elections for the Canadian Wheat Board and student government in universities.


Instant runoff voting has a number of other names. In the United States it is called instant runoff voting primarily because of its resemblance to runoff voting, which is not used in that country in presidential elections, although it is in many countries around the world. It has occasionally been referred to as Ware's method, after its U.S. proponent, William Robert Ware. Writers differ as to whether or not they treat instant runoff voting as a proper noun.

In the United States, instant runoff voting is an umbrella term associated with ranked ballot elections where lower choices can replace a voter's higher choice. North Carolina law uses "instant runoff" to describe the "batch elimination" form of IRV in one-seat elections where there is a single second round of counting with the top two candidates advance to the runoff. Election officials in Hendersonville (NC) 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 and Arkansas 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 then are counted in a runoff election. When the single transferable vote (STV) system is applied to a single-winner election it becomes the same as IRV. For this reason IRV is sometimes considered to be merely a special form of STV. However, because STV was designed for multi-seat constituencies, many scholars consider it to be a separate system from IRV, and that is the convention followed in this article. IRV is usually known simply as "STV" in New Zealand and Ireland, although the term Alternative Vote is also used in those countries.

Multiseat variations of the IRV elimination process have sometimes been labeled as instant runoff voting although they should be more accurately called preferential bloc voting, since like bloc voting, multiple votes are counted per ballot at the same time.

Marking a ranked ballot

In IRV (as well as other ranked election methods) the voter ranks the list of candidates in order of preference. Under a common ballot layout (as shown in the image to the right), ascending numbers are used, whereby the voter places a '1' beside the most preferred candidate, a '2' beside the second-most preferred, and so forth.

In some implementations of IRV, the voter is allowed to rank as many or as few choices as the voter wishes, while in other implementations the voter is required to rank all of the candidates, and in still other cases the voter is allowed to rank only a set number of choices.

Counting the votes

In an IRV election, every ballot expresses a rank order preference of candidates which may be used in later rounds if the voter's first (and if applicable, subsequent) choice candidates are eliminated.

  1. All ballots are counted as one vote for the top choice given.
  2. If a candidate holds a majority (more than half) of the active ballots, a winner is found. (No further elimination can change the top candidate.)
  3. Otherwise a candidate in last place is eliminated. If there is an exact tie for last place in numbers of votes, special tie-breaking rules are needed to continue the process.
  4. After elimination, the votes are recounted as one vote for the highest-ranked choice on the ballot which has not been eliminated. (If a ballot has all its ranked candidates eliminated, it is called exhausted and it can no longer be counted towards any candidate. Note that this cannot occur where all candidates are numbered.)
  5. The runoff process above is repeated (back to 2) until a winner is found.

IRV batch-style is a two-round variation of IRV where if no candidate receives a majority of the first round choices, all candidates but the top two are eliminated and all ballots are recounted for whichever of these two finalists is ranked higher on each ballot. See #Contingent vote.

Example 1

In 2006 the city of Burlington, Vermont held its first mayoral election using IRV. Progressive Bob Kiss won in two rounds with 48.6% of the ballots over Democrat Hinda Miller with 40.7%, with 10.6% of the ballots exhausted (offering no preference among the final two).

In round 1 two candidates were eliminated together because their combined vote was less than the next highest candidate.

In round 2 a winner was declared with less than a majority of the ballots due to exhausted ballots, voters who did not express a preference between the final two candidates.

Candidate Round 1 Round 2
Bob Kiss (Progressive) 3809 (38.9%) 4761 (48.6%)
Hinda Miller (Democrat) 3106 (31.7%) 3986 (40.7%)
Kevin Curley (Republican) 2609 (26.7%)
Other 254 (2.6%)
Exhausted ballots 1041 (10.5%)
Total 9778 (100%) 9778 (100%)

Example 2

The Irish Presidential election, 1990 result provides a good example of where the use of instant runoff voting produced a different result than if first past the post (FPTP) had been used. There were three candidates: Brian Lenihan of the traditionally dominant Fianna Fáil party, Austin Currie of the nation's second largest party Fine Gael and Mary Robinson of the Labour Party. Robinson finished second in first choice rankings, but no candidate received a majority of the vote. In the second round of counting, third place finisher Currie was eliminated. Robinson received over 80% of Currie supporters' second choice rankings, thereby vaulting to a majority win over Lenihan and becoming the seventh President of Ireland.

Candidate Round 1 Round 2 Mary Robinson (Labour Party) 612,265 (38.88%) 817,830 (51.63%) Brian Lenihan, Sr. (Fianna Fáil) 694,484 (44.10%) 731,273 (46.16%) Austin Currie (Fine Gael) 267,902 (17.01%) — Exhausted ballots 9,444 (0.6%) 34,992 (2.21%) Total 1,584,095 (100%) 1,584,095 (100%)

History and current use

Instant runoff voting was invented around 1870 by American architect William Robert Ware. He evidently based IRV on the single-winner outcome of the Single transferable vote, originally developed by Carl Andrae and Thomas Hare. The first known use of IRV in a governmental election was in 1893 in an election for the colonial government of Queensland, in Australia. The system used for this election was a special form known as the contingent vote. IRV in its true form was first used in 1908 in a State election in Western Australia.

United States

Since 2002, Instant Runoff Voting has been adopted in a number of U.S. cities. Most of these adoptions are pending implementation; however, as of November, 2007, 33 elections have been held in four cities or towns: San Francisco, California; Burlington, Vermont; Takoma Park, Maryland; and Cary, North Carolina.

Non-governmental organizations

The sequential elimination method used by IRV is described in Robert's Rules of Order Newly Revised, 10th edition. as an example of "preferential voting," 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 single transferable vote method, with votes from a majority of ballots required to win, 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 less widely-used 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 and Riddick's Rules of Procedure.

Forms of instant runoff voting have been adopted by various private and non-profit associations. The American Political Science Association has long had the "alternative vote" in its constitution for electing its national President-Elect by mail if the official nomination, by a committee appointed by the President, is contested by a petition candidate, and there is, in addition, more than one petition candidate. There has not been a contested election for APSA President since about 1970, when there was one petition candidate. The 160,000-member American Chemical Society has established IRV for elections with exactly three candidates , if there are more than three, a two round system is to be used. No example is on record of IRV having been used by the ACS.

As of June 2008, at least 42 American college and university student governments have either adopted and actively use IRV, or approve and provide for its use in internal elections. A list of such colleges and universities and examples of their contested elections with IRV are available at the IRV advocacy organization FairVote.

Practical implications

Instant runoff voting is more complicated, both in terms of casting votes and counting them, than first-past-the-post plurality or two round systems.

Changes for the ballot

As seen above, voters in an IRV election rank candidates on a preferential ballot. 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, 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 some voters may rank only the candidates of a single party, or of their most preferred parties. Some voters may 'bullet vote', expressing only a first choice. Allowing voters to rank only as many candidates as they wish grants them greater freedom but can also lead to some voters ranking so few candidates that their vote eventually becomes 'exhausted'–that is, at a certain point during the count it can no longer be counted for a continuing candidate and therefore loses an opportunity to influence the result.

To prevent exhausted ballots, some IRV systems require or request that voters give a complete ordering of all of the candidates in an election - if a voter does not rank all candidates her ballot may be considered spoilt or an informal ballot. In Australia this variant is known as 'full preferential voting', and is used in elections for the federal House of Representatives and in most states. However, when there is a large set of candidates this requirement may prove burdensome and can lead to "donkey voting" in which, where a voter has no strong opinions about his or her lower preferences, the voter simply chooses them at random or in top-to-bottom order. Partly to overcome these problems, in elections to the Australian House of Representatives many parties distribute 'how-to-vote' cards, recommending how to allocate preferences on the ballot paper.

The common way to list candidates on a ballot paper is alphabetically or by random lot, a process whereby the order of the candidates published on the ballot paper is determined by lottery. In some cases candidates may also be grouped by party.

Any fixed ordering of candidates on the ballot paper will give some candidates an unfair advantage, because voters, consciously or otherwise, are influenced in their ordering of candidates by the order on the ballot paper. The random ordering of candidates is intended to overcome this. The most effective form is Robson Rotation, a system where the order of candidates on the paper is randomly changed for each print run of the same election's ballot papers. This means that any one ballot paper is almost certainly different from the next.

Changes for voters

Voters have the option to rank candidates in order of choice rather than mark a single candidate. By choosing not to rank all candidates, a voter's ballot may not be counted in the decisive round of counting. Only ballots ranking at least one of the finalists will be counted.

Where preferential voting is used for the election of an assembly or council, parties and candidates often advise their supporters on how to use their lower preferences. As noted above, in Australia parties even issue 'how-to-vote' cards to the electorate before polling day, and Australia's requirement that voters must rank all candidates contributes to some voters using them. These kinds of recommendations can increase the influence of party leaderships and lead to a form of pre-election bargaining, in which smaller parties bid to have key planks of their platforms included in those of the major parties by means of 'preference deals'.

Tactical voting

All voting methods are subject to tactical voting in some circumstances. In his book Collective Decisions and Voting Nicolaus Tideman uses real-world voting data to analyze all proposed election methods in terms of resistance to tactical voting, and states on page 194 that "the alternative vote [IRV] is quite resistant to strategy." Instant runoff voting reduces incentive for insincere voting by reducing the spoiler effect in cases where there are two major candidates and one or more minor candidates. Under the common plurality ("first past the post") voting system, voters may have an incentive to vote insincerely for one of the two major candidates, instead of their true favorite, because a vote for the favorite is likely to be "wasted." However, when there are three or more viable candidates, an incentive in IRV for insincere voting may return, because a compromise choice may not win if eliminated before the final round.

Changes for counting

Changing from plurality to IRV may require startup costs for new voting machinery, although several nations count ballot by hand. However, once the equipment is available, IRV can reduce costs of a second election (required in a two round system or nonpartisan primary).

Forms of IRV have been implemented in cities using optical scan voting systems, as in San Francisco, California and Burlington, Vermont.

A hand count also is possible under IRV and was the method used in the Cary, North Carolina pilot program in October 2007 (after initially counting first choices on optical scan equipment at the polls) and in most non-U.S. jurisdictions; however it is usually more time-consuming than a plurality count, and may need to occur over a number of rounds.

In Australia, a simplified count is sent to a central location on the night with the actual ballot papers transported there, securely, for the final count. In Ireland's presidential race, there are several dozen counting centers around the nation. Each center reports its totals for each candidate and receives instructions from the central office about which candidate or candidates to eliminate in the next round of counting.

Handling ties

Exact ties can happen in any election; although the odds remain very low when many votes are cast, the multiple rounds of counting used in IRV create more opportunities for a tie than there are in some other voting systems. If there is a tie for last place in the elimination process, various rules can be used to break it:

  1. If the total of all the combined votes of any grouping of the candidates with the fewest votes is fewer than the votes cast for the next weakest candidate, then all those bottom tier candidates can be eliminated simultaneously.
  2. One candidate, from among those tied, is eliminated at random (e.g. by a coin toss).
  3. In Australia the candidate, from among those tied, with the fewest votes in the previous round is eliminated. If there is still a tie those counting votes then look back to the next most recent round and then, if necessary, to further progressively earlier rounds until one candidate can be eliminated.
  4. In Irish presidential elections, the candidate, from among those tied, with fewest first choices is eliminated. If this cannot break the tie, ballot-counters look forwards, first to find the tied candidate with fewest votes in the second round and then, if necessary, to the third, fourth and subsequent rounds.
  5. In some private elections the method is to 'conditionally eliminate' candidates from the tie and recount to see if either (or any) can survive. Usually the full set will become eliminated in any order.

Winner-take-all elections vs minority representation

The intention of IRV is to find one candidate acceptable to a majority of voters. It is intended as an improvement on the 'First Past the Post' (plurality) voting system. Under 'First Past the Post' the candidate with most votes (a plurality) wins, even if they do not have a majority (more than half) of votes (unless election rules require a runoff under that condition).

IRV is most suited to elections in which there can be only one winner, such as a mayor or governor. Legislative bodies, city councils or boards also often elect winners by dividing voters into geographic districts.

Australia is the only nation with a long record of using IRV for the election of legislative bodies. IRV produces representation very similar to those produced by the plurality system, with a two party system in parliament similar to those found in many countries that use plurality and two round systems. A significant difference is that a smaller third party, the National Party of Australia, can co-exist with its coalition partner the Liberal Party of Australia, and can compete against it without fear of losing seats to other parties due to vote splitting. In the November 2007 elections, at least four candidates ran in every constituency, with an average of seven, but every constituency was won with an absolute majority of votes.

If IRV is used to elect a council or legislature it will not produce proportional representation (PR). This means that it is likely to lead to the representation of a small number of larger parties in an assembly, rather than a proliferation of small parties. Under a parliamentary system it is more likely to produce single party governments than are PR systems, which tend to produce coalition governments. While IRV is designed to ensure that each individual candidate elected is supported by a majority of those in his or her constituency, if used to elect an assembly it does not ensure this result on a national level. As in other non-PR systems the party or coalition that wins a majority of seats will often not have the support of an overall majority of voters across the nation.

Many election reformers do not advocate IRV for legislative bodies or city councils that are intended to represent both majorities and minorities (in appropriate proportions). As with any winner-take-all election method, IRV can result in a shut-out of minority representation. Gerrymandering of single seat districts can also result in minorities gaining majority control of a legislative body, with IRV or any other winner-take-all election method.

According to a 2007 Brookings Institute paper, IRV can empower moderate voters in the U.S.. Presumably, this effect would result from combining the primary and general election into a single election that would have higher participation rates by moderates than typical primaries. However, empirical evidence suggests that IRV does not always favor moderates. A 2006 study found that "Fiji's objective of ameliorating ethnic divisions by the adoption of [IRV] was not successful"; the moderate parties would have fared better under PR.

Is IRV better than other winner-take-all systems?

In the United States, there are campaigns for IRV in a number of states and local jurisdictions, which have been largely promoted and supported, in recent years, by a non-profit educational and advocacy organization, FairVote.

Opposition to this campaign can be classified into two broad categories:

  1. Those who prefer to maintain the status quo, which is generally Plurality voting, or two-round runoff elections.
  2. Those who prefer reforms other than Instant Runoff Voting, e.g. Approval voting or the Schulze method.

The arguments of these two groups are different, and sometimes the same argument is used on both sides; for example, some IRV advocates claim that IRV will help third parties to gain a toehold and, if they can eventually muster majority support, to win elections. This argument has been summarized as "IRV will allow third parties to grow without being spoilers." In seeming agreement with this, some opponents of IRV argue that IRV will indeed damage the two-party system, which these critics consider important to American democracy.

On the other hand, critics of IRV who prefer other reformed methods have claimed that IRV will help preserve the two-party system, pointing to the countries that use single-winner STV, which have long maintained strong two-party systems with little exception. Further, some support for IRV comes from major-party supporters who want to eliminate the spoiler effect caused by vote-splitting, as with the Ralph Nader vote in Florida in the 2000 U.S. Presidential election, which presumably came largely from voters who would prefer Al Gore over George W. Bush, and which vote was more than enough to turn that election. These supporters of IRV expect that it will help maintain the two-party system by preventing spoiled elections.

Simulations show that IRV often does not result in electing a Condorcet winner but behaves erratically.

Controversies over Instant Runoff Voting can be broken down into a series of specific issues. These may be defined by arguments being presented that are in favor of IRV or opposed to it. Each argument will be examined in turn.

Arguments made in favor of IRV: it is claimed that

IRV allows one ballot to determine a majority winner

Rank ballots allow a simulated runoff process to eliminate candidates without asking voters again for their top remaining choice. The process logically must end in a majority winner (or a tie) when two final candidates remain, the winner having a majority of votes in the final round. Because IRV collects additional preferences beyond first, given the same number of candidates, IRV is more likely to find a majority than would be the case with a Plurality election.

However, if there are exhausted ballots, not showing a preference between the two remaining candidates, that last round majority may still only be a plurality with respect to valid ballots cast in the election.

There are two sources of this failure of incomplete ranking:

  1. Some IRV implementations don't allow complete ranking, either due to voting machine limitations or other reasons; for example, in San Francisco, only three ranks are available on the ballot, whereas there may be over twenty candidates.
  2. Some voters don't rank enough of the candidates to express a preference between the final two candidates, even if the ballot allows it.

In both cases such ballots, with all choices eliminated, are considered exhausted and don't count for or against any remaining candidate, in most implementations of IRV.

In order to avoid this issue, in Australia it is generally required that voters rank all candidates, which, by definition, creates a majority winner, because ballots not ranking all candidates are considered spoiled and invalid, but this has not been proposed for the United States. In New South Wales and Queensland, however, Optional Preferential Voting has been introduced as a reform, thus finding no absolute majority becomes, once again, possible. Antony Green notes that "The exhaustion rate has approached 80% in some seats.... In summary, optional preferential voting almost always assists the party with the highest primary vote.

IRV will eliminate some of the spoiler effect

In plurality elections, a third party candidate may draw sufficient votes away from a candidate who would otherwise be a majority winner, causing a different candidate to win with only minority support. In this case, the election has been "spoiled."

Using ranked preference ballots, more candidates can run without talk of spoilers. 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. Every seat was won with a majority of the vote, including several where results would have been different under plurality voting.

In the United States, IRV addressed the spoiler effect in Ann Arbor, Michigan, where IRV was implemented in 1975 after passing in a 1974 referendum. It resulted in election of the city's first African-American mayor, a Democrat, who won after trailing the Republican incumbent 49% to 40% in the first count of ballots, with remaining votes cast for the Human Rights Party. A new referendum to rescind the reform was then placed on the ballot for a special election, with low turnout, which reversed the reform.

Other election reformers point out that there are other Single-winner voting systems which could also reduce the spoiler effect.

The only election reforms actually implemented in the United States, in recent times, that deal with the Spoiler effect, are IRV, single transferable vote and Runoff voting. Previously, Bucklin voting was tried.

IRV gives voters a wider range of choices

Like the two round system, IRV tends to give voters a wider range of choice among candidates than plurality. More independent and third party candidates are likely to run because the spoiler problems are less severe. The sequential method of IRV accommodates choices differently than runoff voting by not immediately reducing the field to two in the second round, as typically done in runoff elections like the French presidential election, 2002.

IRV will reduce negative campaigning

John Russo, Oakland City Attorney, argued in the Oakland Tribune that "Instant runoff voting is an antidote to the disease of negative campaigning, and the New York Times in a 2004 news article highlighted how some San Francisco candidates were conducting their campaigns more cooperatively. Under the system, their candidates were less likely to engage in malicious campaigning because such tactics would risk alienating the voters who support 'attacked' candidates.

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

No formal studies are known to have been conducted in the United States. Internationally, scholarship by Benjamin Reilly suggests instant runoff voting eases ethnic conflict in divided societies., and this feature was a leading argument for why Papua New Guinea adopted instant runoff voting.

Arguments in opposition to IRV: it is claimed that

Instant runoff voting fails the monotonicity criterion

Like all runoff processes with forced elimination, Instant runoff voting fails the monotonicity criterion. In certain scenarios, raising the rank of a winning candidate on some ballots, which originally had ranked that candidate last, could counter-intuitively result in the winning candidate becoming a loser.

Advocates of IRV point out that it is not the additional vote in favor of a candidate that can cause the candidate to lose, but rather the change in relative support among the other candidates resulting from a vote switch. It is the switch away from another candidate, whether that switch be to the current winner, or some other candidate, that changes which candidates are in the runoff and can cause a winner to turn loser. Simply adding new first-preferences for a candidate can never cause the candidate to lose -- IRV is monotonic as far as additional votes are concerned. IRV advocates argue that it is unlikely that the monotonicity "winner turn loser" dynamic will ever occur in any real-world elections. Austan-Smith and Banks argued, in 1991, that "monotonicity/nonmonotonicity in electoral systems is a nonissue.

It can be best understood by trying to exploit a tactical voting strategy called push-over, used in a runoff process with 3 or more strong candidates. If your candidate is in the lead, with two nearly equally supported competitors and you believe one of your competitors will be weaker in the final round, you might try insincerely supporting this weaker competitor to help eliminate the stronger competitor.

In runoffs with sequential voting, this is a relatively safe strategy because you can move your vote back to your favorite in the final round. It is much more difficult in an instant runoff with a single ballot where insincere votes will stay with the competitor if the strategy succeeds.

"if it ain't broke don't fix it" or "plurality voting is good enough"

Plurality supporters point to the fact that most elections in the U.S. use plurality voting, and voters seem to accept plurality winners as legitimate. The fact that some revered leaders, such as Abraham Lincoln, did not receive a majority of the vote is sometimes mentioned.

It can be claimed that the spoiler effect is not a weakness but a strength because it encourages and rewards like-minded candidates and voters to work together before the election. This encourages the formation of strong coalitions or parties, who attempt to best represent a collective position to the largest set of voters they can. Thus once an election is held, all compromising work has been completed and it's up to the voters to decide a first choice and accept the results as best.

Writing in the Canadian Journal of Political Science, Harold J. Jansen studied the Alternative Vote in Canada, concluding that "On balance, it differed little from the single member plurality system.

IRV violates the one person one vote mandate

Ann Arbor, Michigan, through a petition drive, implemented "preference voting" in 1974. The arguments given in letters to newspapers included "Gives minority candidate voters two votes." In the other direction, it was argued, "The same 'two vote privilege' is extended to supporters of losing candidates in primaries or where there are run-off elections. This procedure went before the Michigan courts, and a ruling was issued in Stephenson vs. the Ann Arbor Board of City Canvassers in 1975. Majority Preferential Voting (or M.P.V., as it was called) was upheld as in compliance with the constitution. In his decision, Judge James Fleming wrote that

On the other hand, in Minnesota, there is the precedent of Brown v. Smallwood, a case which addressed the constitutionality under Minnesota law of Bucklin Voting. Bucklin also involves, like IRV, alternative votes from a ranked ballot, but adds them in, if no majority has been found, as additional votes, instead of through substitution. Focusing on an alleged one-person, one-vote violation in this, advocates of IRV have claimed that Brown v. Smallwood will not apply, in any challenge, to IRV. However, the majority argued in Brown v. Smallwood, repetitively, against the principle of any kind of alternative vote, so some legal opinion has been given that Brown v. Smallwood does indeed apply to other alternative voting systems. There was a dissent in Brown v. Smallwood which specifically attempted to refute the one-person, one-vote argument, and there is reference that the predominant legal opinion of the time, as well as other precedent in U.S. law, was reversed by the court, and the judgment in Brown v. Smallwood was not replicated elsewhere.

Similar systems

Bucklin voting

Bucklin Voting is an alternative electoral reform that was used in several states in the United States in the early part of the twentieth century. Like instant runoff voting, it used a preferential ballot, so that alternate choices could come in to play if no candidate was the first choice of a majority of voters. However, unlike a runoff election or IRV, Bucklin rules add the next preferences to the existing totals.

Contingent vote

The contingent vote, also known as Top-two IRV, or batch-style, is the same as IRV except that all but the two candidates with most votes are eliminated after the first round; the count therefore only ever has two rounds. This differs from the 'two round' runoff voting system described above in that only one round of voting is conducted. The two rounds are only for counting and both take place after voting has finished. Two particular variants of the contingent vote differ from IRV in a further way. Under the forms of the contingent vote used in Sri Lanka, and the elections for Mayor of London in the United Kingdom, voters are not permitted to rank all of the candidates, but only a certain maximum number. Under the variant used in London, called the supplementary vote, voters are only permitted to express a first and a second preference. Under the Sri Lankan form of the contingent vote voters are only permitted to rank three candidates. The supplementary vote is used for mayoral elections while the Sri Lankan contingent vote is used to elect the President of Sri Lanka.

While superficially similar to "sequential elimination" forms of IRV, these contingent vote forms of IRV can produce different results. If, as occurs under all forms of the contingent vote, more than one candidate is excluded after the first count, a candidate might be eliminated who would have gone on to win the election under sequential elimination IRV. If voters are restricted to a maximum number of preferences then it is easier for their vote to become exhausted. This encourages voters to vote tactically, by giving at least one of their limited preferences to a candidate who is likely to win.

Conversely, a practical benefit of the 'contingent vote' counting process is expediency and confidence in the result with only two rounds. Most apparent in smaller elections, like with under 100 ballots among a dozen choices, confidence can be lost in a bottom-up elimination due to cumbersome ties on the bottom (or near ties affected by counting errors). Frequent and even multiple use of tie-breaking rules in one election will leave uncomfortable doubts over whether the winner might have changed if a recount was performed.

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. The simplest form of runoff voting is the two round system. Under the two round system voters vote for only one candidate but, if no candidate receives an overall majority of votes, another round of voting is held from which all but the two candidates with most votes are excluded.

Two round systems

Runoff voting differs from IRV in a number of ways. The two round system can produce different results due to the fact that it uses a different rule for eliminations, excluding typically all but two candidates after just one round, rather than gradually eliminating candidates over a series of rounds. However all forms of "delayed" runoff voting differ from IRV in that voters can change their preferences as they go along, using the results of each round to influence their decision. This is not possible in IRV, as participants vote only once, and this prohibits certain forms of tactical voting which can be prevalent in 'standard' runoff voting.

Exhaustive ballot

A closer system to IRV is the exhaustive ballot. In this system -- one familiar to American fans of the television show American Idol -- only 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. Instant runoff voting is so named because it achieves a similar effect to runoff voting but it is necessary for voters to vote only once. The result can be found 'instantly' rather than after several separate votes.

IRV in a larger runoff process

IRV may also be used within a part of a larger runoff process:

  • In some jurisdictions where top two runoff is required if no candidate gets a majority, a provision has been implemented that allows absentee voters to cast a ranked ballot. In the short window between the first election and the runoff, there often is not enough time to deal with absentee voters. With a ranked ballot, the votes of overseas citizens can count even if their first choice does not make the runoff. Arkansas, Louisiana, South Carolina and Springfield (IL) all have implemented this form of instant runoff voting on ballots for military and overseas voters.
  • It can be used to automate a faster runoff elimination of weak candidates in early rounds of an exhaustive ballot runoff, with specific rules defined that can stop with process with two or more candidates remaining for further balloting.
  • It can support a higher winner threshold not guaranteed by a single balloting, (like 60%). In such cases a second balloting may be used to confirm the winner.
  • Elections requiring a majority winner defined by the total number of ballots may not be achieved with a single IRV balloting due to exhausted ballots. In such cases a post-balloting process may be needed to determine a final winner.
  • Roberts Rules of Order, Newly Revised recommends preferential voting for elections by mail, giving the STV technique used by IRV as their example; however, the RRONR version still requires a majority of votes cast to elect a winner. For in-person elections, they recommend repeated balloting until a candidate wins with an absolute majority of all voters. Repeated ballot allows voters in a new election to turn to a candidate as a compromise who may not have polled well in the initial election.

The term "Instant-runoff voting" is often applied to all these variations, with the common feature being one-vote counted per ballot at a time, with rules defined to eliminate one or more candidates each round with the fewest votes and transfer uncovered votes for remaining candidates; however, the term implies replacement of runoff elections, and most IRV implementations do accordingly drop the majority election requirement.

Theoretical evaluation: Voting system criteria

Scholars of electoral systems often compare them using mathematically-defined voting system criteria, the value of some of which is controversial. Some of the criteria are considered by Arrow's Theorem and the Gibbard-Satterthwaite theorem, which assume that voters rank all candidates in a strict preference order, among other assumptions that do not hold for all methods. For methods such as IRV which use such ranked preferences, satisfying all of the criteria is impossible, because they are mutually exclusive.


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