Treated by the Treaty? How the expansion of co-decision affected the volume and complexity of EU legislation
利用2009年《里斯本条约》扩大共同决策程序的自然实验，研究发现更包容的决策过程促使议程设定者提出更复杂的立法提案，但未改变提案总量。
The question of how the design of democratic decision-making processes affects legislative outputs is highly relevant, but notoriously difficult to answer. This is mainly because political institutions hardly ever change over time within political systems, which makes the identification of their effects challenging. This study takes advantage of an institutional change that occurred in the European Union (EU) in 2009, when decision-making processes were made more inclusive for some, but not all legal bases in the EU treaty. Specifically, the Treaty of Lisbon expanded the fully bicameral co-decision procedure to areas like agriculture and fisheries, while the (quasi)-unicameral consultation procedure remained in place for matters like taxation. Based on this quasi-experimental setup, the study employs a difference-in-differences approach to analyze whether the expansion of co-decision has affected the legislative productivity of the EU and the complexity of EU legislation. The results suggest that a more inclusive decision-making process primarily exerts its impact at the policy formulation stage. Specifically, the agenda setter anticipates the more uncertain bargaining environment and issues more complex legislative proposals, while leaving the overall volume of proposed legislation unchanged. These findings underscore the importance of institutional design for the quality of legislative outputs in democratic political systems.