Cross-National Measurement of Polarization in Political Discourse: Analyzing floor debate in the U.S. and the Japanese legislatures

TL;DR

This study introduces a new cross-national polarization measure based on topic modeling, revealing that Japanese legislators are more polarized than Americans, with distinct temporal dynamics influenced by institutional factors.

Contribution

The paper presents a novel, comparable polarization measure applicable across countries, and applies it to legislative debates in the U.S. and Japan, uncovering unique polarization patterns.

Findings

Japanese legislators are more polarized than U.S. counterparts.

Polarization dynamics differ: structural factors in Japan, ideological issues in the U.S.

Institutional differences significantly influence legislative debate patterns.

Abstract

Political polarization in public space can seriously hamper the function and the integrity of contemporary democratic societies. In this paper, we propose a novel measure of such polarization, which, by way of simple topic modelling, quantifies differences in collective articulation of public agendas among relevant political actors. Unlike most other polarization measures, our measure allows cross-national comparison. Analyzing a large amount of speech records of legislative debate in the United States Congress and the Japanese Diet over a long period of time, we have reached two intriguing findings. First, on average, Japanese political actors are far more polarized in their issue articulation than their counterparts in the U.S., which is somewhat surprising given the recent notion of U.S. politics as highly polarized. Second, the polarization in each country shows its own temporal dynamics in response to a different set of factors. In Japan, structural factors such as the roles of the ruling party and the opposition often dominate such dynamics, whereas the U.S. legislature suffers from persistent ideological differences over particular issues between major political parties. The analysis confirms a strong influence of institutional differences on legislative debate in parliamentary democracies.