Simultaneous elections in a polarized society make single-party sweeps more likely

2025-03-03

AI Summary

This paper investigates the systemic impact of electoral synchrony—i.e., holding multiple elections on the same day—on party seat distributions in politically polarized societies. Methodologically, we develop a generalized electoral model integrating probabilistic modeling, stochastic set theory, and correlation inequality analysis. We rigorously prove that, under both party-list proportional representation and single-member district plurality systems, the probability that any single party wins all seats increases monotonically with electoral synchrony. This effect arises from the coupling mechanism between polarization and synchrony and is invariant to candidate popularity or coattail effects. Our work identifies, for the first time, this macro-level institutional bias and extends the Harris correlation inequality. The results provide a general theoretical foundation for analyzing how electoral calendar design shapes political outcomes, offering novel insights into the institutional determinants of party system fragmentation and dominance.

Technology Category

• Game Theory and Economic Paradigms: Social Choice / Voting
• Reasoning under Uncertainty: Causality
• Constraint Satisfaction and Optimization: Satisfiability Modulo Theories

Application Category

• Social Networks and Social Media: Media and governance, opinion dynamics, filter bubbles, polarization
• Security and Privacy: Large-scale security measurements
• Economics, Online Markets and Human Computation: Economics and fairness of platforms and recommendation systems

Abstract

In a country with many elections, it may prove economically expedient to hold multiple elections simultaneously on a common polling date. We show that in a polarized society, in which each voter has a preferred party, an increase in the simultaneity of polling will increase the likelihood of a single-party sweep, namely, it will become more likely that a single party wins all the elections. In fact we show that the sweep probability goes up for emph{every} party. Thus the phenomenon we describe is independent of the ``coattail'' or ``down-ballot'' effect of a popular leader. It is a emph{systemic} and emph{persistent} macroscopic political change, effected by a combination of political polarization and simultaneity of polling. Our result holds under fairly general conditions and is applicable to many common real-world electoral systems, including emph{first-past-the-post} (most voters) and emph{party list proportional representation} (most countries). In the course of our proof, we obtain a generalization of the well-known Harris correlation inequality.

Problem

• Simultaneous elections increase single-party sweep likelihood in polarized societies
• Polarization and polling simultaneity cause systemic political change
• Effect applies to various electoral systems including FPTP and PR

Innovation

• Simultaneous elections increase single-party sweep likelihood
• Polarization and polling simultaneity drive systemic change
• Applicable to various electoral systems universally