Ranked Choice Including Pairwise Elimination: Difference between revisions
Ranked Choice Including Pairwise Elimination (view source)
Revision as of 21:47, 18 April 2022
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== RCIPE STV ==
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 other candidates, even when the number of ranking levels is fewer than the number of candidates.
*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 candidate while other ballots determine which of the more-popular candidates win seats and which of the less-popular candidates get eliminated.
*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:
* Vote transfer counts are re-calculated after each candidate is elected.
* If a counting round does not elect a candidate, the pairwise losing candidate is eliminated. If there is no pairwise losing candidate, the candidate with the lowest vote transfer count is eliminated.
* Ties are resolved using pairwise elimination.▼
* 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.
* The choice of which ballot transfers to which candidate
Some jurisdictions may have laws that allow a ballot to have decimal influence amounts that range between zero and one. If this is allowed, the above rules can be modified to use decimal influence values. This approach eliminates the possibility that changing the ballot sequence can change the election results.
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