Voting with Bidirectional Elimination

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Abstract/Contents

Abstract: Two important criteria for judging the quality of a voting algorithm are strategy-proofness and Condorcet efficiency. While, according to the Gibbard-Satterthwaite theorem, we can expect no voting mechanism to be fully strategy proof, many Condorcet methods are quite susceptible to compromising, burying, and bullet voting. In this paper I propose a new algorithm which I call “Bidirectional Elimination,” a composite of Instant Runoff Voting and the Coombs Method, which offers the benefit of greater resistance to tactical voting while nearly always electing the Condorcet winner when one exists. A program was used to test IRV, the Coombs Method, and Bidirectional Elimination on tens of billions of social preferences profiles in combinations of up to ten voters and ten candidates. I offer mathematical proofs that this new algorithm meets the Condorcet criterion for up to 4 voters and N candidates, or M voters and up to 3 candidates; beyond this, results from the program show that Bidirectional Elimination offers a significant advantage over both IRV and Coombs in approaching Condorcet efficiency.

Type of resource	text
Date created	March 2011

Author	Cook, Matthew S.
Primary advisor	Levin, Jonathan
Degree granting institution	Stanford University, Department of Economics

Subject	Stanford Department of Economics
Subject	Voting
Subject	tactical voting
Subject	Condorcet criterion
Subject	instant runoff voting
Subject	Coombs Method
Genre	Thesis

Related item	Title 2011 Anna Laura Myers Prize for an Outstanding Thesis
Location	https://purl.stanford.edu/kd252ks1117

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Preferred Citation: Cook, Matthew S. (2011). Voting with Bidirectional Elimination . Stanford Digital Repository. Available at: https://purl.stanford.edu/kd252ks1117

Stanford University, Department of Economics, Honors Theses

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