At the root of parliamentary party cohesion: the role of intraparty heterogeneity and party ideology

Party cohesion is a central issue in legislative studies. The way cohesion is reached in parliamentary parties has therefore attracted a lot of attention. A frequent assumption states that party cohesion stems from party agreement measured as the homogeneity of preferences among MPs. This paper argues that the two concepts –agreement and homogeneity– cover different realities, and shows that the relationship between them is not as straightforward as often suggested. The paper contends that party ideology works as a mediator between the heterogeneity of preferences and intra-party disagreement. The analysis is based on attitudinal data collected among 840 MPs from 15 European national assemblies and is computed at the aggregate –party– level. The results bring new perspectives on the relationship between ideology, homogeneity of preferences and agreement within parliamentary parties.0