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

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 volun...

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Bibliographic Details
Published in:Public choice 2020-07, Vol.184 (1/2), p.197-218
Main Authors: Kilgour, D. Marc, Grégoire, Jean-Charles, Foley, Angèle M.
Format: Article
Language:English
Subjects:
Ballots
Candidates
Economics
Economics and Finance
Elections
Fatigue
Political Science
Public Finance
Voter behavior
Voters
Voting
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Summary: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 rankedchoice 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.
ISSN:0048-5829
1573-7101
DOI:10.1007/s11127-019-00723-2