FpA-fpC

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Revision as of 12:30, 25 January 2022 by Kristomun (talk | contribs) (Add references and 2 fpA + fpB variant)

fpA-fpC (for first preference A minus first preference C) is a three-candidate Condorcet method based on first preference Copeland.[1] Its election cases are:

  • If there's a Condorcet winner, then that candidate wins.
  • If the Smith set is size two, then the winner is according to majority rule.
  • If the Smith set is size three, then for each candidate, assume without loss of generality that the candidate is A in an A>B>C>A cycle. A's score is A's first preferences minus C's first preferences. The candidate with the highest score wins.

A more concise variant that breaks size-two Smith sets differently is:[2]

  • Let A be the candidate whose score is to be evaluated. Then A's score is the sum, over all candidates B who A pairwise beats, two times A's first preferences plus B's first preferences.
  • The candidate with the highest score wins.

This method shares the strategy resistance of Smith-IRV hybrids, such as dominant mutual third burial resistance; yet, unlike them, is monotone. It is open (not obvious) how to extend the method to more than three candidates in a way that retains both monotonicity and strategy resistance.

It produces similar results to Condorcet,IFPP.

This page is a stub - please add to it.

References

  1. Munsterhjelm, K. (2016-02-07). "Strategy-resistant monotone methods". Election-methods mailing list archives.
  2. Munsterhjelm, K. (2022-01-20). "A more elegant three-candidate fpA-fpC phrasing, inspired by Heaviside formulation". Election-methods mailing list archives.