Informed majority coalition criterion: Difference between revisions
Informed majority coalition criterion (view source)
Revision as of 23:13, 26 June 2023
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{{definition|A group comprising a majority of voters is always able to cast their votes so as to elect any candidate they wish, provided that the votes of the remaining minority are known to them and don't change.}}
It was independently defined by James Green-Armytage<ref name="Green-Armytage Tideman Cosman 2015 pp. 183–212">{{cite journal | last=Green-Armytage | first=James | last2=Tideman | first2=T. Nicolaus | last3=Cosman | first3=Rafael | title=Statistical evaluation of voting rules | journal=Social Choice and Welfare | publisher=Springer Science and Business Media LLC | volume=46 | issue=1 | date=2015-08-11 | issn=0176-1714 | doi=10.1007/s00355-015-0909-0 | pages=183–212 | url=https://jamesgreenarmytage.com/strategy-utility.pdf}}</ref> and Durand ''et al.''<ref name="Durand Mathieu Noirie 2016 j401">{{cite web | last=Durand | first=François | last2=Mathieu | first2=Fabien | last3=Noirie | first3=Ludovic | title=Can a Condorcet Rule Have a Low Coalitional Manipulability? | website=Archive ouverte HAL | volume=285 | date=2016-08-29 | url=https://hal.science/hal-01369877 | access-date=2023-06-26}}</ref> Any voting method passing the [[majority criterion]] automatically passes the informed majority coalition criterion, since the majority can all their preferred candidate first to make that candidate win.
[[Range voting]] and the [[Borda count]] also pass the informed majority coalition criterion, even though they fail the [[majority criterion]]. [[Anti-plurality voting]] and [[Coombs' method]] fail.
The informed majority coalition criterion is of importance when considering the implications of modifying a method to always elect an absolute majority-strength Condorcet winner if one exists. Such a modification can never make a method susceptible to strategic manipulation in more elections than it was before being modified. However, such a modification can change what strategy it's vulnerable to in those elections where it's manipulable.
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