Does Bicameralism Promote Stability? Inter-institutional Relations and Coalition Formation in the European Parliament

In the European Parliament, different coalitions form from one vote to the next. To understand the process of coalition formation it is necessary to consider the inter-institutional context in which decisions are made. This paper develops hypotheses regarding how changes in the relations between the European Parliament and the Council of Ministers affect coalition formation in the European Parliament. The hypotheses are tested using roll-call data from the fifth parliamentary term. In line with expectations, it is found that coalition patterns are more consistent in relation to final decisions under the co-decision procedure (when both institutions come to an agreement) than they are under the consultation procedure. Furthermore, the closer relations between the institutions have increased the importance of the median party group on the left-right dimension in coalition formation.