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Anomalies of Instant Runoff Voting

Author

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  • Stensholt, Eivind

    (Dept. of Business and Management Science, Norwegian School of Economics)

Abstract

Struggles over the single-seat preferential election method IRV (Instant Runoff Voting) go on in public arenas and scientific journals, with focus on two “anomalies”. “Monotonicity failures” are preference distributions that allow a startling strategic voting called Pushover or its reverse. Analysis shows how a Pushover action works, and why it is hard to predict and exploit an opportunity. While not rare, monotonicity failures should be seen as a minor nuisance. “No-Show paradoxes” are alarms. The IRV tally eliminates a very clear Condorcet winner in a realistic, but somewhat unusual preference structure, too close to Duncan Black’s Single- Peak condition: Too many YXZ-ballots let Z win instead of a very clear Condorcet-winner X who is eliminated; this harms IRV’s legitimacy. Baldwin’s elimination rule when three candidates remain is a suggested remedy. Preference distributions with the same IRV-tally are grouped together and analyzed with “pictograms” as a tool. That allows a generalization of Black’s Single-Peak condition; real cases are close to “Perfect Pie-sharing”, which explains why Condorcet cycles are rare.

Suggested Citation

  • Stensholt, Eivind, 2020. "Anomalies of Instant Runoff Voting," Discussion Papers 2020/6, Norwegian School of Economics, Department of Business and Management Science.
    • Handle: RePEc:hhs:nhhfms:2020_006
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    File URL: https://hdl.handle.net/11250/2659146
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    References listed on IDEAS

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    1. Stensholt, E., 1992. "Circle Pictograms for Vote Vectors," Papers 14-92, Norwegian School of Economics and Business Administration-.
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    More about this item

    Keywords

    Instant Runoff Voting; Condorcet methods; Duncan Black’s Single-Peak condition; Baldwin’s elimination rule;
    All these keywords.

    JEL classification:

    • D72 - Microeconomics - - Analysis of Collective Decision-Making - - - Political Processes: Rent-seeking, Lobbying, Elections, Legislatures, and Voting Behavior

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