Replication Data for: Prime Ministers and Party System Stability in Post-communist Democracies

A stable party system is central to making democratic accountability work. Challenges arise from high electoral volatility, reflecting large vote shifts among established parties (“within-system”) or to new parties (“extra-system”). While intriguing patterns of volatility often defy structural and institutional explanations, political agency may be critical for stabilizing party systems especially in new democracies—or for undermining their consolidation. We explore this new theoretical perspective by investigating how Prime Ministers affect volatility in the paradigmatic case of post-communist Central and Eastern Europe. Building on a unique dataset of prime-ministerial performance in 129 cabinets from eleven countries, quantitative and qualitative analyses demonstrate how agency in chief executive office shapes the reelection of government parties and the rise of new contenders. While the former effect on within-system volatility is immediate, effects on extra-system volatility unfold over time. Hence, executive leadership is key to understanding the dynamics of party-system stability and democratic accountability.