Ranked Choice Including Pairwise Elimination: Difference between revisions
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'''Ranked Choice Including Pairwise Elimination''' (abbreviated as '''RCIPE''' which is pronounced "recipe") is an election vote-counting method that uses ranked ballots and eliminates '''pairwise losing candidates''' (elimination-round-specific [[Condorcet loser criterion|Condorcet losers]]) when they occur, and otherwise eliminates the candidate who currently has the smallest top-choice count.
This method modifies [[Instant-Runoff Voting|instant runoff voting]] (IRV) by adding the elimination of pairwise losing candidates. This addition reduces the failure rate for the [[Independence of irrelevant alternatives|Independence of Irrelevant Alternatives]] (IIA), which is the kind of failure that occurred in the [
This method further modifies simple IRV by specifying how to handle ballots on which the voter has marked more than one candidate at the same ranking level.
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* [[Condorcet loser criterion|Condorcet loser]]: pass
* Mutual majority: [[Sequential loser-elimination method#Criteria|pass]]
* Resolvable: pass
* Polytime: pass
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* [[Condorcet criterion|Condorcet]]: fail
▲* [[Majority criterion|Majority]]: fail
▲* [[Majority loser criterion|Majority loser]]: fail
* [[Smith criterion|Smith]]/[[ISDA]]: fail
* Cloneproof: fail▼
* LIIA: fail
* IIA: fail
▲* Cloneproof: fail
* Monotone: fail
* Consistency: fail
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* Participation: fail
* No favorite betrayal: fail
▲It is [[Summability criterion|summable]] with O(N<sup>2</sup>).
== RCIPE STV ==
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RCIPE STV is the multi-winner version of the RCIPE method, which means it functions like the [[Single transferable vote|Single Transferable Vote]] (STV) for electing multiple legislators within the same district, and electing non-partisan members of a city council. RCIPE STV offers these advantages over plain STV:
* A voter can mark two or more candidates at the same ranking level. This flexibility allows voters to fully rank all the candidates, including the ability to rank the voter's most-disliked candidate lower than all
*The counting process considers all the marks on all the ballots. This deeper counting is done when identifying pairwise losing candidates. It prevents a voter's ballot transfer from getting stuck on an unpopular pairwise-losing candidate while other ballots determine which
*Changing the ballot-counting sequence does not change who wins. In contrast, plain STV can elect different winners if the ballots are supplied in a different sequence.
These advantages occur because:
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* During pairwise counting all the ballots are counted, but the ballots that have zero influence do not contribute any votes to either side of the one-on-one matches.
* If a full-influence ballot ranks two or more remaining (not-yet-elected and not-yet-eliminated) candidates at the same preference level, and if there are not any remaining candidates ranked higher on this ballot, then this ballot is grouped with other similar (although not necessarily identical) ballots and their influence counts are equally split among the remaining candidates who are ranked at that shared preference level. For example, if candidates A and B have been elected or eliminated, and a ballot ranks candidate A highest and ranks candidates B, C, and D at the next-highest level, and another ballot ranks candidate B highest and ranks candidates A, C, and D at the next-highest level, then one of these two ballots transfers to candidate C and the other ballot transfers to candidate D.
*
*Ties are resolved using pairwise elimination.
If a jurisdiction has laws that allow a ballot to have decimal influence amounts that range between zero and one, the above rules can be simplified to use decimal influence values.
== External links ==
* [https://github.com/cpsolver/VoteFair-ranking-cpp/blob/master/rcipe_stv.cpp RCIPE_STV software that calculates RCIPE and RCIPE STV methods]
[[Category:Sequential loser-elimination methods]]
[[Category:Ranked voting methods]]
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