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The prevalence and consequences of ballot truncation in ranked-choice elections

  • D. Marc Kilgour
  • Jean-Charles Grégoire
  • Angèle M. FoleyEmail author
Article
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Abstract

In ranked-choice elections, voters vote by indicating their preference orderings over the candidates. A ballot is truncated when the ordering is incomplete (called partial voting). Sometimes truncation is forced—voters are allowed to rank only a limited number of candidates—but sometimes it is voluntary. During the vote tabulating process, a truncated ballot is exhausted when all of the candidates it ranks have been eliminated. Ballot exhaustion and, therefore ballot truncation, is a concern in single-winner elections when the margin of victory in the final stage is less than the number of exhausted ballots. That concern motivates our study. We review evidence from actual single-winner ranked-choice elections and conclude that voluntary ballot truncation is very common. Moreover, it is difficult to explain strategically. To assess the significance of ballot truncation, we simulate ranked-choice elections with four, five and six candidates, using both spatial and random models of voter preferences. Does truncation change the probability that a Condorcet winner wins the election? Does the winner change as the extent of truncation increases? We find that even small amounts of truncation can alter election outcomes.

Keywords

Ranked-choice selection Single-winner Ballot truncation Ballot exhaustion 

JEL Classification

D72 K16 

Notes

Acknowledgements

Work supported by the Canadian Tri-Council Research Support Fund. The authors were supported by their own individual Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants (Grant Nos. 5023, 155957-2012, 2015-06126).

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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of MathematicsWilfrid Laurier UniversityWaterlooCanada
  2. 2.Energie, Matériaux, et TélécommunicationsInstitut National de la Recherche ScientifiqueMontréalCanada

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