Party Systems and Legislative Institutions: Comparing Westminster Parliaments

How do party systems shape legislative institutions? Existing work suggests that parliamentary rules are influenced by the characteristics of party systems, and by the kinds of government and opposition this produces. However, testing these claims is difficult without reliable longitudinal data on procedural change. In this paper, we offer a new test of these arguments, using a large original dataset of all standing orders in the UK House of Commons and the Irish Dáil since 1922. The two parliaments began this period with very similar parliamentary rules, but subsequently experienced different party systems and government and opposition types. Employing a novel text analysis approach to measure the similarity of procedural rules over time, we are able to examine whether, and how, this divergence in the partisan environment affected their legislative institutions. Our analysis sheds new light on the way party politics drives the evolution of legislative institutions.