Ideological Cohesion and Party Survival in Central European Parliaments, 1990–2025

Party survival is a key parameter of their institutionalisation (Randall & Svåsand 2002; Mainwaring & Torcal 2006; Harmel, Svåsand & Mjelde 2019) and a core component of parliamentary democracy, contributing to the stability of the political system and the effectiveness of policy implementation (Lijphart 1999; Powell 2000). The disappearance of a particular party from parliament can result in inadequate political representation for certain social groups and diminish the diversity of electoral choices (Zur 2019). Concurrently, electoral volatility is a prevalent phenomenon, particularly in new democracies (Mainwaring & Torcal 2006; Cyr 2016; Zur 2019). While the topic of political party survival has been extensively studied (e.g. Cyr 2016; Deegan-Krause & Haughton 2018; Mainwaring & Torcal 2006), the specific relationship between a party’s ability to survive to the next term and its ideological coherence during parliamentary debates is an understudied topic. Previous studies have mostly used roll call voting (Carey 2007; Kam 2009), party manifestos (Benoit et al. 2009) or expert surveys (Steenbergen & Marks 2007) data as a proxy for measuring ideological coherence, but those approaches have inherent severe limitations, including reduced generalizability, precision and inability to grasp the dynamic nature of the coherence (Clinton, Jackman & Rivers 2004; Steenbergen & Marks 2007; Benoit et al. 2009). To address these limitations, we conduct an in-depth analysis of data on political parties from four Central European countries: Poland (1991-2025), Slovakia (2002-2025), the Czech Republic (1993-2025), and Hungary (1998-2025). Drawing on a novel dataset of over 150,000 parliamentary speeches and using complementary methods of word embeddings (word2vec) to create numerical vectors based on the word co-occurrence, and the Bertopic algorithm, which uses transformer model embeddings to automatically split the text into different topics, we analyse ideological coherence of parliamentary parties over a span of over 30 years. We operationalise cohesion through cross-document cosine similarity and community detection (Louvain clustering), allowing us to trace internal fragmentation and factionalisation over time. Further, we explore variations in ideological coherence and party survival across countries, party families, and other factors, such as government/opposition dynamics, party size, novelty, and the level of parliamentary activity. Our findings show that lower levels of ideological cohesion significantly increase the risk of parliamentary exit, but this relationship is non-linear and context-dependent. Importantly, we demonstrate that cohesion operates differently for governing and opposition parties, reflecting distinct strategic incentives and representational logics. Moreover, periods of democratic stress and backsliding reshape these dynamics: while some parties benefit electorally from discursive polarisation, others experience rising internal fragmentation, which undermines their long-term survival.