Coalition Tactics: Bribery and Control in Parliamentary Elections

Fuente: arXiv
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Autori principali: Barr, Hodaya, Hartman, Eden, Aumann, Yonatan, Kraus, Sarit
Natura: Preprint
Pubblicazione: 2026
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author Barr, Hodaya
Hartman, Eden
Aumann, Yonatan
Kraus, Sarit
author_facet Barr, Hodaya
Hartman, Eden
Aumann, Yonatan
Kraus, Sarit
contents Strategic manipulation of elections is typically studied in the context of promoting individual candidates. In parliamentary elections, however, the focus shifts: voters may care more about the overall governing coalition than the individual parties' seat counts. This paper studies this new problem: manipulating parliamentary elections with the goal of promoting the collective seat count of a coalition of parties. We focus on proportional representation elections, and consider two variants of the problem; one in which the sole goal is to maximize the total number of seats held by the desired coalition, and the other with a dual objective of both promoting the coalition and promoting the relative power of some favorite party within the coalition. We examine two types of strategic manipulations: \emph{bribery}, which allows modifying voters' preferences, and \emph{control}, which allows changing the sets of voters and parties. We consider multiple bribery types, presenting polynomial-time algorithms for some, while proving NP-hardness for others. For control, we provide polynomial-time algorithms for control by adding and deleting voters. In contrast, control by adding and deleting parties, we show, is either impossible (i.e., the problem is immune to control) or computationally hard, in particular, W[1]-hard when parameterized by the number of parties that can be added or deleted.
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publishDate 2026
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spellingShingle Coalition Tactics: Bribery and Control in Parliamentary Elections
Barr, Hodaya
Hartman, Eden
Aumann, Yonatan
Kraus, Sarit
Computer Science and Game Theory
Theoretical Economics
Strategic manipulation of elections is typically studied in the context of promoting individual candidates. In parliamentary elections, however, the focus shifts: voters may care more about the overall governing coalition than the individual parties' seat counts. This paper studies this new problem: manipulating parliamentary elections with the goal of promoting the collective seat count of a coalition of parties. We focus on proportional representation elections, and consider two variants of the problem; one in which the sole goal is to maximize the total number of seats held by the desired coalition, and the other with a dual objective of both promoting the coalition and promoting the relative power of some favorite party within the coalition. We examine two types of strategic manipulations: \emph{bribery}, which allows modifying voters' preferences, and \emph{control}, which allows changing the sets of voters and parties. We consider multiple bribery types, presenting polynomial-time algorithms for some, while proving NP-hardness for others. For control, we provide polynomial-time algorithms for control by adding and deleting voters. In contrast, control by adding and deleting parties, we show, is either impossible (i.e., the problem is immune to control) or computationally hard, in particular, W[1]-hard when parameterized by the number of parties that can be added or deleted.
title Coalition Tactics: Bribery and Control in Parliamentary Elections
topic Computer Science and Game Theory
Theoretical Economics
url https://arxiv.org/abs/2601.07279