Party organization and party unity

peer-reviewed This chapter examines the crucial role that political parties play in maintaining a unified voting bloc in parliament. This party-based approach sets it apart from most existing studies in this area. The focus of this chapter is on the factors that incentivize MPs to vote in a unified manner. The chapter tests three hypotheses: (1) whether party unity is improved by greater party organizational strength; (2) whether the greater threat of disciplinary sanctions increases party unity; and (3) whether greater access to resources by MPs reduces party unity. The authors use the Political Party Database (PPDB) dataset to test these hypotheses in thirteen of Europe’s democracies, finding strong support for the third hypothesis, some support for the first hypothesis, but little support for the second hypothesis. This study adds an important new dimension to research on how institutions affect party unity by showing the distinct role party organizations can play in this regard.