ABSTRACT. In this paper, we analyze European Union (EU) decision-making before and after Eastern Enlargement. Theoretically, we take up the debate on whether and under which conditions a growth in group size leads to a formalization or an informalization of political decision-making. We test two hypotheses related to this question by comparing the fit of established decision-making models on a pre- and post-enlargement dataset of EU decision-making. For the pre-enlargement period we utilize the dataset from the Decision-Making in the European Union (DEU) project. Additionally, our dataset includes the ideal points of the 27 member states, the European Commission and the European Parliament on 120 issues from the post enlargement period. Against our initial expectation, we do not find an improved fit of the procedural model as compared to the compromise model after enlargement. While the paper is primarily a process-oriented contribution to the growing literature on how enlargements affect political decision-making, we also present first evidence for a growing status-quo bias pointing towards qualitative effects of enlargement. pp. 59–76

Keywords: EU decision-making, Eastern Enlargement, group size, formalization