FpA-fpC
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, B's first preferences plus two times A's first preferences.
- The candidate with the highest score wins.
This method shares the strategy resistance of Smith-IRV hybrids, such as chicken dilemma compliance and 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.[fn 1]
It produces similar results to Condorcet,IFPP.
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Notes
- ↑ Any generalization will preserve its chicken dilemma compliance, as that criterion is only defined on three-candidate elections. However, this is not true of dominant mutual third burial resistance.
References
- ↑ Munsterhjelm, K. (2016-02-07). "Strategy-resistant monotone methods". Election-methods mailing list archives.
- ↑ Munsterhjelm, K. (2022-01-20). "A more elegant three-candidate fpA-fpC phrasing, inspired by Heaviside formulation". Election-methods mailing list archives.