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.国际组织（IOs）是否会对国家偏好产生独立影响？尽管这一议题在国际关系学研究文献中具有重要地位，但受内生性问题掣肘，学界始终难以精准分离国际组织成员资格所带来的因果效应。本研究简报提出了一种新颖的实证方法，用以识别国际组织共同成员资格对成员国偏好的因果效应。研究利用了如下事实：加入欧盟（EU）的国家，可依托欧盟在相关国际组织中的成员资格，自动获得多个其他国际组织的成员身份。随后，我们采用双重差分法（difference-in-differences），估算国际组织自动成员资格对成员国与其他成员国的偏好相似度，以及与非成员国的偏好相似度所产生的影响。研究结果表明，共享国际组织成员资格能够提升国家间的偏好相似度。该方法为区分国际组织成员资格的效应与促使国家加入国际组织的选择效应提供了可行路径。