Replication Data for: Love, convenience or respectability? Understanding the alliances of the Five Star Movement in the European Parliament

The Five Star Movement (M5S) formed the Eurosceptic EFDD Group when it first elected its members in the European Parliament (EP) in 2014. Two and a half years later, the M5S sought, without success, to leave the Eurosceptics and join the Liberal group. This attempted change of transnational affiliation is puzzling: why has the M5S tried to leave the Eurosceptic group to ally with the most Europhile group in the EP? How could this U-turn be explained? Relying on several different data – the EUANDI party dataset, official EP data, and original interviews with members of the EP – this article provides a systematic answer to these questions. We test three general hypotheses on group membership in the EP, using the M5S as a case-study. We show that neither policy congruence nor the pursuit of office fully explain the M5S’s observed or attempted alliances. We suggest, instead, that ‘domestic politics’ is the key driver of the M5S’s behaviour in the EP. Political group membership is functional to the Movement’s strategic objectives at home. This article shows that national-level explanations of transnational affiliation need to be given more consideration, and highlights the ‘second order’ importance of the EU arena with respect to ‘first order’ national strategic objectives.五星运动党（Five Star Movement, 简称M5S）于2014年首次当选欧洲议会议员后，组建了疑欧主义的欧洲自由与直接民主集团（Eurosceptic EFDD Group）。两年半后，M5S试图脱离疑欧阵营并加入自由派党团，但未能成功。这一跨国党籍变更尝试令人费解：为何M5S要脱离疑欧团体，转而与欧洲议会（European Parliament, EP）中最亲欧的党团结盟？该立场反转应如何解释？本文依托欧盟政党数据集（EUANDI party dataset）、欧洲议会官方数据以及针对欧洲议会议员的原创访谈，对上述问题给出了系统性解答。我们以M5S为案例，检验了三项关于欧洲议会党团成员身份的一般性假设。研究显示，政策契合度与谋求职务的动机均无法充分解释M5S已形成及试图形成的联盟关系。与之相反，我们提出“国内政治”是M5S在欧洲议会中行为的核心驱动力：党团成员身份服务于该运动在国内的战略目标。本文指出，针对跨国党籍归属的解释应更多纳入国家层面因素，并凸显了欧盟层面事务相对于“第一层级”国内战略目标的“第二层级”重要性。