Iterated Bucklin: Difference between revisions
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Specified method's link to ranked Approval
(A single- or multi-winner Bucklin count variant whereby the number of top preferences an individual ballot reveals at any point is a function of the winner of the count up to that point.) |
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Iterated Bucklin (alternatively Bucklin-IRV, or BIRV) is a ranked [[Approval voting|Approval]] count, a variant of [[Bucklin voting]] whereby the number of top preferences an individual ballot reveals at any point is a function of the rank in which the ballot places the winner of the count so far
Iterated Bucklin was [http://lists.electorama.com/pipermail/election-methods-electorama.com//2020-December/002649.html proposed] by Etjon Basha in December 2020 as an attempt to produce a count that exhibits few practical violations of voting criteria (elicits the greatest degree of sincerity for voters) and the least degree of count complexity, at the cost of not formally meeting many criteria. Iterated Bucklin [http://lists.electorama.com/pipermail/election-methods-electorama.com//2020-December/002649.html violates] [[Condorcet criterion|Condorcet]], [[Later no-harm criterion|Later-No-Harm]], [http://lists.electorama.com/pipermail/election-methods-electorama.com//2020-December/002650.html Later-No-Help] and is not precinct summable. A preliminary simulation of the count’s propensity to violate various criteria was conducted by Kevin Venzke.<ref>[http://lists.electorama.com/pipermail/election-methods-electorama.com//2020-December/002650.html
A [https://www.votingmethods.net/misc/ calculator] of a somewhat simplified version of the method has been created by Kevin Venzke, which calculator also includes other methods satisfying neither the Condorcet nor the Later-No-Harm criteria. The simplification impacts the method’s behavior in case of ties.
== Purpose ==
Iterated Bucklin attempts to mimic the behavior of a rational Bucklin voter under conditions of an [[Repeated balloting|iterated count]] (hence the name), and specifically an iterated [[Approval voting|Approval Count]], where after every round a chance is given to amend one’s vote once the winner until that point is presented, and with the count only ending once no voter wishes to further amend their vote. Whilst a true iterated approval count would be impractical under conditions of all but the smallest elections, Iterated Bucklin attempts to formalize a simulation of this process. It is hoped that a count that already produces a reasonable strategy on the voter’s behalf would hopefully lead to voters presenting relatively sincere rankings as in input.
== Single-winner procedure ==
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== Multi-winner generalization ==
The same procedure can be generalized to the election of a number of winning candidates. At the first stage, all candidates with at least a quota of support (first preferences) are declared elected, and a[[Quota#Hare_quota | Hare]] or [[Droop quota|Droop]] quota of
In keeping with the method’s mimicking of a sound strategy, support from an elected candidate would first be removed from those votes that have no more candidates left to elect (have already elected all those they approve of), and only afterward (if a quota of support has not been filled yet) from other voters who still approve of as yet unelected candidates.
It is noteworthy to highlight that once the iterative procedure begins, it is not possible for a candidate to be elected whilst some of their votes have not being counted yet, an eventuality which can happen in most other ranked counts such as [[Bucklin voting|Bucklin]] or the [[Single Transferable Vote]]. The avoidance of the issues raised by such possibility has led in the latter system to the development of the complex Meek and Warren counts. Nevertheless, when applied to a multi-winner scenario, Iterated Bucklin can still elect a candidate before all of their votes are counted before the iterative procedure starts (i.e. whenever a candidate is elected based on receiving a quota of support of first preferences only.).
=== Surplus Handling ===
If viewed as a [[Cardinal_voting_systems#Sequential_Proportional_Methods | Sequential Cardinal Method]] then [[Surplus_Handling#Fractional_Surplus_Handling | Fractional Surplus Handling]] can be used. Other mechanisms like those used in [[Single transferable vote]] are also possible.
== Ties and Cycles ==
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== Example ==
The example below presents a single-winner election contested by four candidates and attended by
{| class="wikitable"
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