How the Electoral System Influences Personalization and Individual Campaign Spending: Evidence from Switzerland's First‐Time Finance Disclosure Regulations

Abstract Personalization—greater candidate‐centeredness at the expense of political parties—is a defining feature of 21st‐century electoral politics. But to what extent does the electoral system shape this trend? We develop a theoretical argument rooted in the design of open‐list proportional representation (OLPR). Because OLPR combines proportional seat allocation with intra‐party competition, it creates opportunities for candidates to cultivate a personal vote. We argue that when the institutional potential for individual preference votes to shape electoral outcomes is high, candidates respond by investing more in personalized campaigning, reflected in higher individual campaign spending. We test this argument using novel data from the 2023 Swiss federal elections, the first held under mandatory campaign finance disclosure rules. Our findings show that greater voter ability to allocate individual preference votes is associated with higher in‐dividual campaign spending, demonstrating how electoral systems influence candidate behavior and the role of money in politics.