Competing Principals and Vote Defection in the European Parliament

Why some Members of the European Parliament (MEPs) vote differently from their national party? Previous research on party unity in the EP has extensively focused on the conditions that increase the probability of vote dissent from European party groups and, to a lesser extent, from national parties when MEPs face competing pressures. Most of these studies have emphasized the importance of electoral institutions and candidate selection rules on party unity. However, the question of how the struture of competition among political principals affects national party defection in the European Parliament has received less attention. This paper tests several hypotheses on whether different patters of dissent between national parties, European political groups and ministers in the Council increase the probability of defection from national party, and if so, whether electoral rules have a moderating effect. The analysis is based on an original dataset on final codecision votes during the 7th legislature (N= 298,448). The findings are expected to improve our understanding of party unity and representation in the European Parliament.