This paper asks two questions. First, how has the level of party based parliamentary conflict developed over time in European national parliaments and second, how do changes in the national party systems influence the overall level of conflict? The paper uses a unique dataset covering legislative decision making in nine West European countries over a period of 40 years, measuring the level of conflict in each parliament by developing a innovative index. This data is combined with information on party system composition and central institutional variables.
The study is novel, since there is a lack of data about decision making in parliaments over time. The level of conflict when parliaments legislate can vary from near unanimity to legislation passing with a margin of only a few votes. A modest level of conflict is potentially beneficial, among other things because it presents voters with clear options, while too much conflict risks rendering the system incapable of legislating efficiently. Furthermore, anti-establishment parties that are not interested in co-operation with other parties pose a particular challenge to decision making in parliaments. The paper addresses difficulties in comparing the level of conflict over time and between countries, not least because formal rules and informal norms vary from parliament to parliament.