Independence vs affiliation: Understanding entry into parliamentary party groups

Political parties are often considered essential for structuring parliamentary decision-making in democracies. However, many MPs experience spells of being non-affiliated with any parliamentary party group (PPG), either because they were elected as independent candidates or left their PPGs earlier in the legislative term. Whether such non-affiliation periods end with an entry to a PPG, which PPG the legislator enters and how long they remain independent before the entry, as well as explanations for these patterns, remain under-researched questions despite their substantive, theoretical and empirical relevance. Substantively, the presence of independent MPs makes the legislative decision-making process and ruling majorities less stable and predictable. Theoretically, the study of PPG entry is propitious for understanding why MPs join PPGs and what motivates PPGs to accept switchers. This is because internal politics in the “home” PPG, crucial for explaining other forms of legislative party switching, are not relevant in the case of independent MPs. Empirically, PPG entry is one of the most common forms of legislative party switching, as demonstrated by the dataset built by the INSTAPARTY project team. In this paper, we examine PPG entry in three Central and Eastern European countries (Lithuania, Poland, and Romania) since the early 2000s. Building on the literature on legislative party switching, we test an argument that electoral and office concerns of both the MPs considering the entry and the potential receiving parties play an important role in driving entry. In the first step of our analysis, we examine why and when non-affiliated MPs join PPGs. We expect that better chances of re-election and access to office positions should provide strong incentives for independent MPs to become affiliated. However, affiliation is less attractive for MPs who are leaders or members of minor parties that cannot form their own PPGs. For these MPs, being affiliated with a larger PPG may dilute the electoral brand of the MP’s party. On the side of PPGs, potential switchers are more attractive if, in the previous election, they had a strong personal following or held high positions on the lists of the parties they ran for. However, the recent involvement of MPs in corruption or other scandals reduces their attractiveness to other PPGs. Moreover, switchers are more attractive to both government and opposition parties when the parliamentary support of government parties is close to the majority threshold, and switching can therefore change parliamentary decision-making or even government composition. In the second stage of our analysis, we examine which PPGs independent legislators enter. We expect that PPGs with stronger performance in polls and presence in government are more attractive destinations. We test these arguments using a new dataset that distinguishes between different forms of legislative party switching and provides comprehensive information about its potential determinants. The inclusion of multiple parliamentary terms in several countries also allows us to provide insights into the effect of election proximity and institutional factors. Overall, our findings contribute to the research on legislative party switching and the rise of the importance of independent politicians in contemporary democracies.