Instant-runoff voting

When the Single Transferable Vote voting system is applied to a single-winner election it is sometimes called instant-runoff voting (IRV), as it is much like holding a series of runoff elections in which the lowest polling candidate is eliminated in each round until someone receives majority vote. IRV is often considered independently of multi-winner Single transferable vote (STV) because it is simpler and is a widely advocated electoral reform in the USA.

Assessing IRV

Comparison of IRV to normal runoff voting

Advantages of instant runoff ballot: (IRV)

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• FEWER GAMES: Voters and parties have less opportunity for playing games in early round(s) to influence the elimination order in favor of easier competition. (Runoffs allow more flexibility in tactical votes, influencing elimination, and still having a chance to move back to a favorite in the final round)
• MORE POSITIVE: Candidates are discouraged from negative campaigning. (A winning candidate will usually need first, second and lower ranked preferences to win, and can't safely afford to make enemies with no second chance vote)
• AVOIDS SOME PERVERSE RACES: In a runoff, a major political interest may fracture into a variety of parties, and its vote so splits in the first ballot that all those parties candidates are eliminated in the first ballot. (Compare the 2002 French Presidential election, when the minority Front National candidate won through to the final ballot when the more numerous Socialist vote split.)

Advantages of sequential balloting: (runoff voting)

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• EASIER TO VOTE: A runoff allows voters and factions to refocus their attention on remaining candidates in each round. (In IRV, voters must make careful choices among a large set of candidates in one ballot and may not have enough information to make informed rankings among the competitive candidates.)
• CHANCE FOR APPEAL: Candidates that were eliminated are given another chance to endorse and remaining candidates have another chance to court voters supporting the eliminated candidates.
• PRESENTATION OF MINOR PARTIES: In a runoff, minor parties stand on their own merits in the first round of voting. Under the single event IRV, interest in the minor parties only focuses on how they recommend their supporters cast their preferences between the major parties: the electoral system configures minor parties as preference 'cows'. In a runoff minor parties have the power to recommend second preferences in the final round.

Effect on parties and candidates

Unlike runoff voting, however, there are no chances to deal in between rounds, change voters' minds, or gain support of the other candidates.

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Giving them only one chance to do so, instant runoff preference voting encourages candidates to balance earning core support through winning first choice support and earning broad support through winning the second and third preferences of other candidates' core supporters. As with first-past-the-post, however, any bloc of more than half the voters can elect a candidate regardless of the opinion of the rest of the voters.

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This is considered a weakness by the advocates of a more deliberative democracy, who point to the French system of presidential election where such between-round dealings are heavily exploited and useful (they say) to draw together a very factionalized electorate. However, critics of the French runoff system point to the dreaded "votez escroc, pas facho" (vote for the crook, not the fascist) phenomenon, which they believe awarded Chirac an undeserved landslide victory in 2002.

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The Australian system also allows minority parties to have key planks of their platforms included in those of the major parties by means of so-called "preference deals". This is seen as legitimate political activity. If enough people care about (for instance) Green Party issues that that party's second preference can swing the vote, then it is fair enough that it have some limited say in policy.

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Another advantage of runoff voting is that it usually allows a "protest vote" to be made without penalty. A person voting for a minority party does not "throw his vote away", as with first-past-the-post systems, so allowing the electorate to send clear signals to the major parties.

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Criteria passed

There are several voting system criteria that have been defined by political scientists for assessment of voting systems.

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IRV meets the majority criterion, the mutual majority criterion, the Condorcet loser criterion, the Non-compulsory support criterion (truncatable only), and the independence of clones criterion.

Related Topics:
Majority criterion - Mutual majority criterion - Condorcet loser criterion - Non-compulsory support criterion - Independence of clones

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IRV is invulnerable to the burying strategy.

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Criteria failed

IRV does not pass the monotonicity criterion, the consistency criterion, the Condorcet criterion, the summability criterion, the participation criterion, reversal symmetry, or the Independence of irrelevant alternatives criterion.

Related Topics:
Monotonicity criterion - Consistency criterion - Condorcet criterion - Summability criterion - Participation criterion - Reversal symmetry - Independence of irrelevant alternatives

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These theoretical objections may correspond with practical failures of IRV, discussed below. The first two, compromise and push-over, are types of tactical voting, where voters vote insincerely to increase the likelihood of a favored outcome. Some argue that Condorcet methods and approval voting are better at selecting compromise candidates and at reducing the spoiler effect.

Related Topics:
Tactical voting - Condorcet methods - Approval voting - Spoiler effect

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Compromise

Assume the earlier Tennessee example. The voters from Memphis can get a better result by "compromising": They can rank Nashville over Memphis, and thus ensure that Nashville, their second choice, will win, rather than Knoxville, their last choice.

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Alternatively, if the voters from Memphis do not vote tactically (perhaps because they think they have a chance of winning outright, perhaps because they dislike insincerity, etc.), voters from Nashville can improve their result by "compromising" and ranking Chattanooga over Nashville. This would allow Chattanooga to defeat Knoxville in the first round and go on to become eventual winner, a better result for Nashville voters than a Knoxville win.

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Nearly all voting methods produce an incentive to use the compromising strategy in some scenarios, i.e. in scenarios where there is no Condorcet winner. However, IRV clearly has more frequent compromising incentive than Condorcet methods, in that it sometimes produces a compromising incentive even when there is a Condorcet winner.

Related Topics:
Condorcet winner - Condorcet methods

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This problem is exacerbated in versions of IRV that do not allow equal rankings. If voters do choose to compromise in a version of IRV that does not allow equal rankings, they will have to so by ranking a more-preferred candidate below a less-preferred candidate, which is a more severe distortion of their sincere preferences than ranking them equally.

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Push-over

IRV is unusual in that it fails the monotonicity criterion. The implication of this is that it is vulnerable to the "push-over" strategy. Tactical voters can benefit by raising "push-overs" (candidates unlikely to win) above their real favorite, causing a stronger opponent to their favorite to be eliminated early, leaving only the push-over to contend with their favorite in the last round.

Related Topics:
Monotonicity criterion - Strategy

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This strategy typically requires a great deal of coordination, and typically entails a substantial risk of backfire. Thus, some argue that IRV's vulnerability to the strategy will rarely or never manifest in practice.

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"Return of the 3rd-party spoiler effect"

Although third parties without much support are unlikely to "spoil" the race between the major parties, a third party with a substantial share of the vote can potentially cause another type of "spoiler effect" by causing the early elimination of the more similar major party, thus causing the "opposite" major party to win instead. Thus, some argue that IRV is only reliable at stopping this "spoiler effect" as long as the 3rd party clearly does not have a chance to win.

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For example, imagine that the following votes are cast in an IRV election:

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The IRV winner is the Republican candidate. However, if the Green party candidate withdrew before the race, the Democratic candidate would win instead, a result that is preferable for most Green party voters. Thus, it is difficult to argue that IRV entirely eliminates the spoiler effect.

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Failure to pick a compromise candidate

Imagine that candidates are located along a one dimensional ideological spectrum, and that the center of the spectrum is defined by the median voter. IRV does not reliably choose the option closest to the center of the spectrum. Thus it can be argued that IRV is less apt at choosing compromise candidates, and more likely to choose an ideologically polar candidate.

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For example, this failure can occur in a 3-choice election where parties A and C are bitterly opposed, and party B is first choice for a minority but tolerable for a large majority. For a real-life example, consider the 17th-century Europe struggle over "government-enforced Catholicism" versus "government-enforced Protestantism", with "freedom of private worship" as the compromise B.

Related Topics:
Catholicism - Protestantism

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Imagine that votes are cast as follows:

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In IRV, the compromise (choice B) is eliminated immediately. Choice C is elected, arguably giving severely lower total satisfaction amongst voters than choice B, who is preferred by a large majority to A, and who is also preferred by a large majority to C.

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Logistical issues

IRV fails the Summability criterion, which means that the results for a particular precinct cannot be conveniently summarized for transfer to the central tally location. Instead, the precincts must send a total record of every ordering of the candidates made by a voter, times the frequency of that ordering. The unwieldiness of this data may prolong the counting procedure, provide more opportunities for undetected tampering than in summable methods and make recounts more costly.

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If counting takes place in several places for a single IRV election (as in Australia), these counting centers must be connected by a securely authenticated channel (historically the telegraph was used) to inform them which candidate has come last and should be dropped.

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IRV also has issues with transparancy. Without a sophisticated understanding, it can be hard for voters to see the consequences of their preferences. For example, see "return of the 3rd party spoiler effect" above. This lack of transparancy could potentially cause a loss of voter confidence.

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Logistical issues in Australia

House of Representatives

Initially, in Australia, ballots are counted at the booth level, with first preference results reported to the Divisional Returning officer and then to the National Tally Room. If it is clear who the two leading candidates will be, a notional distribution of the preferences of the minor candidates may be made. Postal and absentee ballots are of course yet to be processed - that takes another week or two.

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Over the next few weeks, ballots and matching documentation are concentrated in the offices of the Divisional Returning Officer, where a actual distribution of preferences is made. This may be done by physically moving the ballots around, or by entering ballot data into a suitable computer.

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If a candidate wins 51% of first preferences, a distribution of minor party preferences is strictly speaking not necessary, however the law now allows that such preferences be distributed to see what the "two-party preferred vote" actually is.

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Federal elections are conducted by the Australian Electoral Commission, who employ all the workers at all the booths, to a common standard of neutrality and efficiency. Candidates may appoint scrutineers to watch (but not touch) what is going on.

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