Cleavage size and stability in turbulent times: introducing the bloc volatility and fragmentation dataset

Twenty-first century West European politics is more volatile than in any period since the end of World War II. A new transnational cleavage increasingly structures party competition and voter behaviour. To what extent does this new cleavage provide electoral stability and fragment traditional camps? This article answers these questions by introducing the Bloc Volatility and Fragmentation Dataset (BVFD) including metrics of volatility and fragmentation for party blocs, cleavage types and left-right party camps in 15 West European countries from 1951 to 2023. In general, these data show that the transnational cleavage has become larger and more stable in the last 30 years while the traditional cleavages have declined. The left and right party camps have also both become more fragmented. The findings of this article and the BVFD contribute to recent advances in the study of party system and cleavage change in Western Europe.