The personal vote and party cohesion: Modeling the effects of electoral rules on intraparty politics

Conventional wisdom suggests that parties in candidate-centered electoral systems should be associated with less cohesive policy preferences among legislators. We model the incentives of party leaders to achieve voting unity accounting for the costs of discipline, showing that candidate-centered systems have the counterintuitive effect of promoting party agreement on policies and preference cohesion. These implications for cohesion derive from the degree of control over list rank held by leaders under open lists (open-list proportional representation, OLPR) and closed lists (closed-list proportional representation, CLPR). Because discipline is costlier in OLPR, owing to leaders’ lack of control over list rank, leaders seeking voting unity propose policies that promote agreement between members and leadership. Under CLPR, however, leaders can more easily achieve voting unity by relying on discipline and therefore lack incentives to promote internal agreement. We then extend the model to allow the party leader to replace members, showing that preference cohesion itself is greater under OLPR. Further, our baseline results hold when allowing legislative behavior to affect vote share and when accounting for candidates’ valence qualities. We interpret our results to suggest that candidate-centered systems result in stronger incentives for developing programmatic parties, compared with party-centered systems.