Birds of a Feather Flock Together? Empirically Testing the Cartel Party Thesis

The cartel party thesis formulated by Katz and Mair almost three decades ago represents one of the most accomplished theoretical effort in party studies. Based on the convergence hypothesis, the cartel party thesis rests on parties’ observable transition from agents of the civil society to appendages of the state, and on the parallel reconfiguration of democracy as a service provided by the state for civil society. In line with the prevailing environment-induced approach to party change, the authors emphasize the relevance of contextual factors, at domestic and international level, in shaping both party organizational strategies and competition over policy issues. Party convergence, which is primarily expected among office-seeking parties, is assumed to be a correlate of political development, whose patterns are largely determined by environmental factors. Against this background, this study aims to empirically assess the propositions presented by Katz and Mair. By resorting to the data available from the Political Party Database and Katz and Mair’s Data Handbook, our focus is on scrutinizing a number of key aspects of the cartel party thesis, such as the mainstream parties' convergence towards a specific organizational model, increased dependence on State resources, and the impact of contextual factors in driving these changes. We thus test a Party Organizational Variance index on 228 cases across 11 Western European countries, from the 1970s to the 2010s, and we then correlate the results with data pertaining to those environmental trends believed to influence the emergence of the cartel party. Our findings reveal a lack of discernible patterns indicating cross-country party organizational convergence. Furthermore, the assumed relevance of cultural, legislative, and socioeconomic factors on party change is challenged in real-world data. This brings us to reconsider some of the foundational principles on which the cartel party thesis was built, by emphasizing the intricate and nuanced nature of the evolving landscape of party organizations.