When Does the Personal Vote Matter for Party Loyalty? The Conditional Effects of Candidate-Centred Electoral Systems

When do candidate-centred electoral systems produce undisciplined parties? In this article, we examine party discipline under open-list proportional representation, a system associated with MPs cultivating personal constituencies. We present a model explaining how legislators’ preferences and support among voters mediate political leaders’ ability to enforce discipline. We show that disloyalty in candidate-centred systems depends on parties’ costs for enforcing discipline, but only conditional on MP preferences. MPs who share the policy preferences of their leaders will be loyal even when the leaders cannot discipline them. To test the model’s implications, we use data on legislative voting in Poland’s parliament. Our empirical findings confirm that disloyalty is conditioned on party leaders’ enforcement capacity and MP preferences. We find that legislators who contribute more to the party electorally in terms of votes are more disloyal, but only if their preferences diverge from the leadership. Our results suggest that the relationship between open lists and party disloyalty is conditional on the context of the party system.