Reallocating Wasted Votes in Proportional Parliamentary Elections with Thresholds

2025-03-21

AI Summary

In proportional representation systems, electoral thresholds (3–5%) enhance governmental stability but render a substantial share of votes ineffective, undermining representativeness. This paper proposes reallocating votes cast for parties failing to meet the threshold via pre-specified substitute parties or ranked preferences. We formally model party-list voting with thresholds for the first time, integrating social choice theory and axiomatic analysis to design and evaluate three novel vote-counting rules—Delegate Override (DO), Sequential Transferable Vote (STV), and Generalized Preference (GP). Using empirical data from the 2024 French European Parliament election, we assess their performance. Results show that all three rules significantly increase vote efficacy and small-party representation compared to the status quo single-threshold system. Among them, the GP rule achieves the optimal trade-off across computational efficiency, outcome rationality, and implementability.

Technology Category

• Game Theory and Economic Paradigms: Social Choice / Voting
• Knowledge Representation and Reasoning: Preferences
• Humans and AI: Voting

Application Category

• Web Mining and Content Analysis: Robustness and generalizability of Web mining methods
• Security and Privacy: Large-scale security measurements
• Search and Retrieval-Augmented AI: Web evaluation methodologies and metrics

Abstract

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).

Problem

• Address wasted votes in proportional parliamentary elections
• Compare party selection rules for vote reallocation
• Evaluate methods to enhance electoral representativeness

Innovation

• Formal model for party voting with thresholds
• Compare party selection rules axiomatically and experimentally
• Identify three attractive rules: DO, STV, GP