Electoral Reform and Legislative Behaviour: Evidence from Denmark’s Transition to Proportional Representation

Abstract

This article examines the effect of electoral system reform on legislative speech-making by Members of Parliament (MPs), focusing on the case of Denmark's 1918 shift from single-member districts (SMD) to proportional representation (PR) in elections to the lower chamber. While the relationship between electoral systems and MP behavior is well established, few studies have been able to isolate causal effects using a natural control group. Leveraging the unique institutional configuration of Denmark's bicameral parliament—where the upper chamber remained unaffected by the reform—this study applies a difference-in-differences design to assess how reform shaped parliamentary behavior. Using a novel dataset covering all MPs between 1901 and 1939, the analysis compares both the absolute number of speeches delivered and the relative speech frequency of MPs across 1 electoral periods. The results demonstrate that MPs in the reformed lower chamber spoke significantly less following the introduction of PR, aligning their behavior more closely with that of MPs in the unreformed upper chamber. These findings hold across both outcome measures and after accounting for relevant controls, including seniority, party affiliation, and chamber-specific institutional differences. The analysis provides strong support for the argument that PR enhances party control over individual legislators and reduces incentives for personal vote-seeking via speech-making. The article contributes to the broader literature on electoral systems and legislative behavior, and offers new historical insight into the institutional development of representative democracy in early twentieth-century Europe.