Khái niệm cốt lõi
Approval-IRV, a generalization of Instant Runoff Voting (IRV) that allows voters to express indifferences between candidates, is the unique elimination scoring rule that satisfies independence of clones and respects cohesive majorities.
Tóm tắt
The content discusses a generalization of Instant Runoff Voting (IRV), called Approval-IRV, that allows voters to express indifferences between candidates by using weak orders instead of strict rankings.
The key highlights and insights are:
Approval-IRV interprets each weak order vote as an approval vote for the top-ranked candidates that have not yet been eliminated. It then repeatedly eliminates the candidate with the lowest approval score until only one candidate remains.
Approval-IRV satisfies two key properties that are characteristic of standard IRV for linear orders: independence of clones and respect for cohesive majorities. These axioms ensure that the rule is resistant to the spoiler effect and respects the preferences of majorities.
The authors prove that Approval-IRV is the unique elimination scoring rule that satisfies these two axioms. In contrast, the alternative generalization called Split-IRV fails both axioms.
For multi-winner elections, the authors define Approval-STV and show that it preserves the strong proportional representation properties of standard STV.
Experiments suggest that a non-negligible fraction of voters (around 0.4% in the 2019 San Francisco mayoral election) would benefit from the ability to express indifferences using Approval-IRV.
Overall, the content argues that Approval-IRV is a principled and desirable generalization of IRV that allows voters more expressive power without sacrificing key properties of the original rule.