Bicameralism, nationality and party cohesion in the European Parliament

Costello, Rory and Thomson, Robert (2016) Bicameralism, nationality and party cohesion in the European Parliament. Party Politics, 22 (6). pp. 773-783. ISSN 1354-0688 (

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Party cohesion in legislatures is a topic of longstanding concern to political scientists because cohesion facilitates democratic representation. We examine the cohesion of transnational party groups in the European Parliament, which is part of the EU’s bicameral system, and study the oftentimes competing pressures to which MEPs are subject from their EP party groups and national governments. Our explanation focuses on the conditions under which MEPs take policy positions that differ from those of their party groups. We propose that national governments lobby their national MEPs more intensely on issues of high national salience and on which they are in a weak bargaining position in the Council. The analyses offer a unique approach to the study of party cohesion that is based on the policy positions taken by each national delegation of MEPs in each of the three main party groups and national governments on specific controversial issues.