Communication Dans Un Congrès Année : 2025

Reallocating Wasted Votes in Proportional Parliamentary Elections with Thresholds

Résumé

In many proportional parliamentary elections, electoral thresholds (typically 3-5%) are used to promote stability and governability by preventing the election of parties with very small representation. However, these thresholds often result in a significant number of "wasted votes" cast for parties that fail to meet the threshold, which reduces representativeness. One proposal is to allow voters to specify replacement votes, by either indicating a second choice party or by ranking a subset of the parties, but there are several ways of deciding on the scores of the parties (and thus the composition of the parliament) given those votes. We introduce a formal model of party voting with thresholds, and compare a variety of party selection rules axiomatically, and experimentally using a dataset we collected during the 2024 European election in France. We identify three particularly attractive rules, called Direct Winners Only (DO), Single Transferable Vote (STV) and Greedy Plurality (GP).

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hal-05183352 , version 1 (23-07-2025)

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Théo Delemazure, Rupert Freeman, Jérôme Lang, Jean-François Laslier, Dominik Peters. Reallocating Wasted Votes in Proportional Parliamentary Elections with Thresholds. EC '25: 26th ACM Conference on Economics and Computation, Jul 2025, Stanford University Stanford CA USA, France. pp.446-446, ⟨10.1145/3736252.3742568⟩. ⟨hal-05183352⟩
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