Instant-runoff voting: Difference between revisions
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=== Variants ===
See the [[Equal-ranking methods in IRV]] article. IRV can be done with equal ranking allowed. The two main ways of doing this are either fractional (split the voter's ballot equally between all of their highest-ranked candidates that are ranked equally (3 candidates ranked 1st each get 1/3rd of a vote)), or whole votes (give each highest-equally-ranked candidate one vote (3 candidates get 1 vote each and 3 votes total)).
With whole votes equal-ranking, there are two ways to find a winner (which give the same result in standard IRV but differ for whole votes): either eliminate candidates until only two remain, and declare the one with more votes the winner, or eliminate candidates until one or more candidates are supported by a majority of active ballots, and then elect the candidate with the largest majority. Some have argued<ref>[https://www.reddit.com/r/EndFPTP/comments/e6bt6s/proportionality_failure_in_stv_with_equalranks/f9s5yno/?context=3]</ref> that in order to limit opportunities for pushover strategy with whole votes, a ballot that equally ranks candidates should be allowed to help those candidates win, but not prevent those candidates from getting eliminated.
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== Notes ==
IRV can rather simply be thought of as a modification to [[Choose-one FPTP voting|choose-one FPTP voting]] to pass the [[Mutual majority criterion|mutual majority criterion]] (and further, always elect from the [[Dominant mutual third set|dominant mutual third set]]). This is because when all but one of the candidates in the mutual majority-preferred set of candidates is eliminated, the remaining candidate will guaranteeably be the majority's 1st choice among the remaining candidates and thus win.
The simplest way to modify IRV to address many of the issues IRV opponents have without changing IRV fundamentally is to allow voters to approve candidates (using an [[Approval threshold|approval threshold]]). If there are any majority-approved candidates, elect the most-approved of them, otherwise run IRV. Even if voters [[Favorite Betrayal|Favorite Betray]], they can still approve their honest favorite, giving that candidate a chance to still win. In addition, this allows voters to better avert the [[Center squeeze effect|center squeeze effect]]. The standard argument made by IRV advocates against [[Approval voting]], that it fails [[later-no-harm]], has little to no relevance to this modification, since voters seeking to avoid hurting their favorite candidates' chances of winning in the approval round can simply refrain from approving anyone, forcing the election to run under IRV rules. ▼
▲The simplest way to modify IRV to address many of the issues IRV opponents have without changing IRV fundamentally is to allow voters to approve candidates (using an [[
Though IRV is often praised for passing [[later-no-harm]], which is claimed to encourage voters to rank all of their preferences, it doesn't tend to use as much of the information provided by the voters as other ranked methods, such as [[Condorcet methods]]. This is a less extreme analog to how [[First Past the Post electoral system|first past the post]] technically passes [[later-no-harm]] by ignoring later preferences altogether. So IRV's [[later-no-harm]] compliance has to be evaluated in context of the other criteria it fails due to using less information than other methods - that is, there may be ambiguity to how much IRV is truly protecting a voter's interests by not using their later-preference information at all.
IRV always elects a Condorcet winner who receives over [[Dominant mutual third|1/3rd]] of 1st choice votes. More generally, a candidate who at any point when they are uneliminated receives over 1/3rd of all active votes and [[Pairwise counting|pairwise beats]] (is preferred by more voters than) all other uneliminated candidates is guaranteed to win. This is because when all but two candidates are eliminated, the one preferred by more voters is guaranteed to win in IRV, and a candidate with over 1/3rd of active votes is guaranteed to be one of the final two remaining candidates, because at most only one other candidate can get more active votes than the over-1/3rd pairwise victor.
The number of votes a candidate has in any round of an IRV election is guaranteed to be
40 B
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Votes in the 1st round are 45 A 35 B 65 C.
If you elect a candidate the moment they have a majority, C would win, making the strategy backfire. But if you keep eliminating until you have only two candidates, then B is eliminated first, and then A wins with 80 votes.<ref>https://www.reddit.com/r/EndFPTP/comments/f7daa0/key_details_emerge_for_how_rankedchoice_in_nyc/fib0pgd?utm_source=share&utm_medium=web2x</ref></blockquote>Several variations of IRV have been proposed to meet the [[Condorcet]] and [[Smith criterion|Smith]] criteria. The simplest of these are to
==See also==
*[[Australian electoral system]]
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