Counting organized interests in the European Union: a comparison of data sources

In contrast to large-n research on US interest organizations using lobby registration data, European Union (EU) scholars have used a variety of data sources, including registries maintained by the European Commission, directories of interest organizations active in Brussels, and data on access to the European Parliament (EP). This diversity of sources raises important questions about their comparability. To what extent do these different EU sources actually measure the same population of interest organizations? We find that the several data sources vary markedly over EU institution and publisher. The paper discusses the methodological and substantive causes of these differences and their implications for further development of large-n research on interest organization politics in the EU.