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

Kilgour, D. Marc; Grégoire, Jean-Charles; Foley, Angèle M.

doi:10.1007/s11127-019-00723-2

Cited by 23 publications

(16 citation statements)

References 18 publications

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“…The techniques we present did not deal with partial or truncated ballots [ 43 , 44 ]. We investigated sensitivity analyses when models consistently ‘bias’ a single first preference but did not investigate when models may consistently ‘bias’ a single worst preference.…”

Section: Discussionmentioning

confidence: 99%

Vote-processing rules for combining control recommendations from multiple models

Probert

Nicol

Ferrari

et al. 2022

Phil. Trans. R. Soc. A.

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Mathematical modelling is used during disease outbreaks to compare control interventions. Using multiple models, the best method to combine model recommendations is unclear. Existing methods weight model projections, then rank control interventions using the combined projections, presuming model outputs are directly comparable. However, the way each model represents the epidemiological system will vary. We apply electoral vote-processing rules to combine model-generated rankings of interventions. Combining rankings of interventions, instead of combining model projections, avoids assuming that projections are comparable as all comparisons of projections are made within each model. We investigate four rules: First-past-the-post, Alternative Vote (AV), Coombs Method and Borda Count. We investigate rule sensitivity by including models that favour only one action or including those that rank interventions randomly. We investigate two case studies: the 2014 Ebola outbreak in West Africa (37 compartmental models) and a hypothetical foot-and-mouth disease outbreak in UK (four individual-based models). The Coombs Method was least susceptible to adding models that favoured a single action, Borda Count and AV were most susceptible to adding models that ranked interventions randomly. Each rule chose the same intervention as when ranking interventions by mean projections, suggesting that combining rankings provides similar recommendations with fewer assumptions about model comparability. This article is part of the theme issue ‘Technical challenges of modelling real-life epidemics and examples of overcoming these’.

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Section: Discussionmentioning

confidence: 99%

Vote-processing rules for combining control recommendations from multiple models

Probert

Nicol

Ferrari

et al. 2022

Phil. Trans. R. Soc. A.

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“…There has been considerable work on what happens when individual voters choose not to rank all the candidates-a practice sometimes called voluntary truncation-in contrast with forced truncation (i.e., ballot length restrictions) [22]. In many voting systems including IRV, election outcomes can change dramatically as voters independently choose to rank more or fewer candidates [33].…”

Section: Related Workmentioning

confidence: 99%

“…As noted above, plurality voting can be viewed as IRV with ballot length one, and so the fact that plurality and IRV can produce different outcomes already gives us a first indication that ballot length can have important consequences. But aside from work using simulation and a few real-world elections [6,22] we do not have much insight into these consequences more generally. Perhaps, for example, there are underlying structural properties to be discovered that constrain how many winners are possible as we vary the length of the ballot.…”

Section: Introductionmentioning

confidence: 99%

Ballot Length in Instant Runoff Voting

Tomlinson¹,

Ugander²,

Kleinberg³

2022

Preprint

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Instant runoff voting (IRV) is an increasingly-popular alternative to traditional plurality voting in which voters submit rankings over the candidates rather than individual votes. In practice, municipalities often restrict the ballot length, the number of candidates a voter is allowed to rank on their ballot. We theoretically and empirically analyze how ballot length can influence the outcome of an election, given fixed voter preferences. We show that there exist preference profiles over k candidates such that up to k − 1 different candidates win at different ballot lengths. We derive exact lower bounds on the number of voters required for such profiles and provide constructions matching these bounds. Additionally, we fully characterize which sequences of winners are possible over ballot lengths and provide explicit profile constructions achieving any feasible winner sequence. Finally, we analyze a collection of 168 real-world elections, where we truncate rankings to simulate shorter ballots. We find that shorter ballots could have changed the outcome in one quarter of these elections and that longer ballots can favor particular candidates. Our results highlight ballot length as a consequential degree of freedom in the design of IRV elections.

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“…However, when it leads to winners without full quotas of total ballots cast, it is common to refer to the rate of 'ballot exhaustion.' Analysts of ballot exhaustion have tended to study AV, pointing out winners without overall vote majorities (Burnett & Kogan, 2015;Kilgour, Grégoire, & Foley, 2020). But in multi-seat elections, we may care about legislative majorities.…”

Section: Strategic Implications For Two-party Politicsmentioning

confidence: 99%

Variants of Ranked-Choice Voting from a Strategic Perspective

Santucci

2021

PaG

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Ranked-choice voting has come to mean a range of electoral systems. Broadly, they can facilitate (a) majority winners in single-seat districts, (b) majority rule with minority representation in multi-seat districts, or (c) majority sweeps in multi-seat districts. Further, such systems can combine with rules to encourage/discourage slate voting. This article describes five major versions used, abandoned, and/or proposed for US public elections: alternative vote, single transferable vote, block-preferential voting, the bottoms-up system, and alternative vote with numbered posts. It then considers each from the perspective of a ‘political strategist.’ Simple models of voting (one with two parties, another with three) draw attention to real-world strategic issues: effects on minority representation, importance of party cues, and reasons for the political strategist to care about how voters rank choices. Unsurprisingly, different rules produce different outcomes with the same sets of ballots. Specific problems from the strategist’s perspective are: ‘majority reversal,’ serving ‘two masters,’ and undisciplined third-party voters (or ‘pure’ independents). Some of these stem from well-known phenomena, e.g., ranking truncation and ‘vote leakage.’ The article also alludes to ‘vote-management’ tactics, i.e., rationing nominations and ensuring even distributions of first-choice votes. Illustrative examples come from American history and comparative politics. A running theme is the two-pronged failure of the Progressive Era reform wave: with respect to minority representation, then ranked voting's durability.

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

Cited by 23 publications

References 18 publications

Vote-processing rules for combining control recommendations from multiple models

Vote-processing rules for combining control recommendations from multiple models

Ballot Length in Instant Runoff Voting

Variants of Ranked-Choice Voting from a Strategic Perspective

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