Replication Data for: A Friend Like Me: The Effect of IO Membership on State Preferences

Do international organizations (IOs) have an independent effect on state preferences? Despite the importance of this question in the International Relations literature, isolating the causal effect of IO membership has proven difficult due to endogeneity concerns. This research note offers a novel empirical approach to identifying the causal effect of shared membership in IOs on member state preferences. We exploit the fact that states joining the European Union (EU) obtain automatic membership in several other IOs through the EU's membership in these organizations. We then use a difference-in-differences strategy to estimate the effect of automatic membership in IOs on preference similarity with other members versus preference similarity with non-members. We demonstrate that shared IO membership leads to an increase in preference similarity. This approach offers a useful way to disentangle the effect of IO membership from selection effects that lead states to join IOs.