Coombs' method: Difference between revisions
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{{Wikipedia}} |
{{Wikipedia}} |
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'''Coombs' method''' (or the '''Coombs rule''')<ref>Grofman, Bernard, and Scott L. Feld (2004) [https://dx.doi.org/10.1016/j.electstud.2003.08.001 "If you like the alternative vote (a.k.a. the instant runoff), then you ought to know about the Coombs rule,"] ''Electoral Studies'' '''23''':641-59.</ref> is a [[ranked voting systems|ranked voting system]] created by [[wikipedia:Clyde Coombs|Clyde Coombs]] used for single-winner [[election]]s. Similarly to [[instant-runoff voting]], it uses candidate elimination and redistribution of votes cast for that candidate until one candidate has a majority of votes. |
'''Coombs' method''' (or the '''Coombs rule''')<ref>Grofman, Bernard, and Scott L. Feld (2004) [https://dx.doi.org/10.1016/j.electstud.2003.08.001 "If you like the alternative vote (a.k.a. the instant runoff), then you ought to know about the Coombs rule,"] ''Electoral Studies'' '''23''':641-59.</ref> is a [[ranked voting systems|ranked voting system]] created by [[wikipedia:Clyde Coombs|Clyde Coombs]] used for single-winner [[election]]s. Similarly to [[instant-runoff voting]], it uses candidate elimination and redistribution of votes cast for that candidate until one candidate has a majority of votes. |
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==Example == |
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Coombs' method frequently selects the [[Condorcet winner criterion|Condorcet winner]]. However, this does not always happen. For example: |
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7:a>c>d>b |
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6:a>d>b>c |
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3:b>a>c>d |
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7:b>c>a>d |
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9:b>c>d>a |
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4:c>a>d>b |
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6:d>a>b>c |
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3:a>c>b>d |
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This example, placed in [https://cs.angelo.edu/~rlegrand/rbvote/calc.html Rob LeGrand's voting calculator], shows that Coombs arrives at a different result than Condorcet. The example is pulled from a Felsenthal and Tideman paper.<ref>{{Cite journal |last=Felsenthal |first=Dan |last2=Tideman |first2=Nicolaus |date=2013 |title=Varieties of failure of monotonicity and participation under five voting methods |url=https://www.researchgate.net/profile/Dan-Felsenthal/publication/257667897_Varieties_of_failure_of_monotonicity_and_participation_under_five_voting_methods/links/54aec0fb0cf21670b35870a6/Varieties-of-failure-of-monotonicity-and-participation-under-five-voting-methods.pdf?origin=publication_detail|journal=Theory and Decision |language=en |volume=75 |issue=1 |pages=59–77}}</ref> |
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==Links== |
==Links== |
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*1996 |
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**http://lists.electorama.com/pipermail/election-methods-electorama.com/1996-March/thread.html#65497 - "'Spokane' method" |
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*2005 |
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**https://web.archive.org/web/20050909092356/http://condorcet.org/emr/methods.shtml#Coombs - 2005 archive of Condorcet.org glossary of terminology |
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*2019 |
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**https://imgur.com/gallery/SLTHgCO - Diagram of Coombs' and [[center squeeze]] |
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*2020 |
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**https://www.reddit.com/r/EndFPTP/comments/js1qlt/wouldnt_a_rcv_method_where_you_eliminated_the/ |
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==Footnotes== |
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<references /> |
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{{fromwikipedia}} |
{{fromwikipedia}} |
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Revision as of 06:15, 20 October 2022
Coombs' method (or the Coombs rule)[1] is a ranked voting system created by Clyde Coombs used for single-winner elections. Similarly to instant-runoff voting, it uses candidate elimination and redistribution of votes cast for that candidate until one candidate has a majority of votes.
Example
Coombs' method frequently selects the Condorcet winner. However, this does not always happen. For example:
7:a>c>d>b 6:a>d>b>c 3:b>a>c>d 7:b>c>a>d 9:b>c>d>a 4:c>a>d>b 6:d>a>b>c 3:a>c>b>d
This example, placed in Rob LeGrand's voting calculator, shows that Coombs arrives at a different result than Condorcet. The example is pulled from a Felsenthal and Tideman paper.[2]
Links
- 1996
- 2005
- https://web.archive.org/web/20050909092356/http://condorcet.org/emr/methods.shtml#Coombs - 2005 archive of Condorcet.org glossary of terminology
- 2019
- https://imgur.com/gallery/SLTHgCO - Diagram of Coombs' and center squeeze
- 2020
Footnotes
- ↑ Grofman, Bernard, and Scott L. Feld (2004) "If you like the alternative vote (a.k.a. the instant runoff), then you ought to know about the Coombs rule," Electoral Studies 23:641-59.
- ↑ Felsenthal, Dan; Tideman, Nicolaus (2013). "Varieties of failure of monotonicity and participation under five voting methods" (PDF). Theory and Decision. 75 (1): 59–77.