Minimax Condorcet method: Difference between revisions

Rewrote the defeat-dropper note to clarify how they fail DMTBR.
m (RobLa moved page Minmax Condorcet method to Minimax Condorcet method: Oops, I left out one of "i"s from "Minimax")
(Rewrote the defeat-dropper note to clarify how they fail DMTBR.)
 
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{{Wikipedia|Minimax Condorcet method}}
 
In [[voting system]]s, the '''MinmaxMinimax Condorcet method''' or(often referred to as "'''the Minimax method,'''" alsoand sometimes as "'''minmax'''" or "'''min-max'''") is one of several [[Condorcet method]]s used for tabulating votes and determining a winner when using [[Ranked voting systems|ranked voting]] in a [[single-member district|single-winner]] election. It is sometimes referred to as the '''Simpson-KramerSimpson–Kramer method''',<ref name="Caplin Nalebuff 1988 pp. 787–814">{{cite journal | last=Caplin | first=Andrew | last2=Nalebuff | first2=Barry | title=On 64%-Majority Rule | journal=Econometrica | publisher=[Wiley, Econometric Society] | volume=56 | issue=4 | year=1988 | issn=00129682 | jstor=1912699 | pages=787–814 | url=https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=c10e05dc6ea7cfa1ba1b28aa6c54e7abbf96eccc | access-date=2023-05-27}}</ref> is the name of a class of election methods based on electing the candidate with the most consistently high performance in pairwise contests with other candidates. It is sometimes also calledand the '''leastsuccessive reversal''' or method'''successive reversal''' method,.<ref name="Green-Armytage">{{cite web|url=http://lists.electorama.com/pipermail/election-methods-electorama.com/2003-August/075781.html|title=the name of the rose|website=Election-methods mailing list archives|date=2003-08-04|last=Green-Armytage|first=J. }}</ref> although this term is ambiguous.
 
Minimax selects as the winner the candidate whose greatest pairwise defeat is smaller than the greatest pairwise defeat of any other candidate: or, put another way, "the only candidate whose support never drops below [N] percent" in any pairwise contest.<ref>The introduction to this article was initially copied from https://en.wikipedia.org/w/index.php?title=Minimax_Condorcet_method&oldid=1156877070</ref>
 
== Variants ==
 
'''Minmax''' or Minimax method, also referred to as the '''Simpson-Kramer method''',<ref name="Caplin" /> is the name of a class of election methods based on electing the candidate with the most consistently high performance in pairwise contests with other candidates. It is sometimes also called the '''least reversal''' or '''successive reversal''' method,<ref name="Green-Armytage" /> although this term is ambiguous.
 
'''Minmax(winning votes)''' elects the candidate whose greatest pairwise loss to another candidate is the least, when the strength of a pairwise loss is measured as the number of voters who voted for the winning side.
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MMPO has been criticized for its counter-intuitive behavior on some elections.<ref>{{cite web|url=http://lists.electorama.com/pipermail/election-methods-electorama.com/2016-September/000523.html|title=Re: MMPO objections (hopefully better posted)|website=Election-methods mailing list archives|date=2016-09-21|last=Benham|first=C.}}</ref> Given this election (called the "bad-example" on EM):
 
* x: '''A'''>B=C
* 1: '''A=C'''>B
* 1: '''B=C'''>A
* x: '''B'''>A=C
 
MMPO elects C even if x is made arbitrarily large (say, 3.95 billion voters). This is a [[Plurality criterion|Plurality]] failure.
 
== Notes ==
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This contrasts with [[Schulze]], which alternates between eliminating all candidates not in the [[Schwartz set]] and dropping defeats.
 
All [[:Category:Defeat-dropping Condorcet methods|defeat-dropping Condorcet methods]] become equivalent to Minimax whenwith there are 3three or fewer candidates with no pairwise ties between them. Because of this, defeat-droppersdropping methods that pass [[ISDA]] are equivalent to [[Smith//Minimax]] when the abovecycle conditionsinvolves holdonly for3 the Smith setcandidates. Example:
 
{{ballots|
25: A>B>C
40: B>C>A
35: C>A>B
}}
 
The pairwise victories are 60 A>B, 65 B>C, 75 C>A. The A>B defeat is weakest by winning votes, so dropping it results in B being undefeated (alternatively, B's win can be explained as them being on the losing end of this defeat, and this defeat being their strongest defeat, since it's their only defeat).
 
Since the defeat-droppers are equivalent to either Minmax or Smith//MinmaxMinimax when three or fewer candidates run, they all fail [[dominant mutual third burial resistance]]. This follows from the equivalence and the three-candidate Minimax DMTBR failure example given above.
 
== References ==
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[[Category:Single-winner voting methods]]
[[Category:Ranked voting methods]]
[[Category:Condorcet methods]]
[[Category:Monotonic electoral systems]]
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