Parliamentary party group unity: Does the electoral system matter?

Will changing the Dutch electoral system to give MPs a stronger personal mandate affect parliamentary group unity in the Dutch parliament? To discuss this question, we first describe Parliamentary Party Group (PPG) unity in the Dutch Tweede Kamer. Placing the Dutch case in perspective, we find that group unity is comparatively high. Surveying next the analytical literature to establish the relative merits of sociological, institutional and electoral system variables, we find the impact of intra-parliamentary factors to be strong. Institutional incentives to stay united in political struggles weigh heavily when explaining why most West European parliaments score high on PPG unity, regardless of electoral systems in general and preferential voting arrangements in particular. We also stress the likely strategic party responses to electoral change, for example, by revising candidate selection procedures to reduce the possibilities of unwanted NIP independence in parliaments. A stronger personal mandate may, nevertheless, give a moderate rise in the numerous ways in which MPs can communicate their personal qualities and party independence to their voters.