Disentangling Electoral Volatility: Party System Innovation and Deinstitutionalisation in Western Europe (1945 – 2014)

Since Pedersen’s seminal contribution, the index of electoral volatility has become the most widely used indicator of party system instability. During the last years, scholars studying party system instability in Central and Eastern Europe as well as in Latin America have attempted to disentangle the synthetic index of volatility in order to distinguish between the so-called “within system volatility” and “extra-system volatility”. The former consists of electoral shifts between existing parties, while the latter is the volatility caused by the entry and exit of parties from the party system. So far, these kind of studies have not flourished in Western Europe, where the presence of stable and predictable patterns of interactions among political actors has been generally taken for granted. Nevertheless, recent political events seem to show that even the long-term consolidated Western Europe is experiencing a process of growing political instability that can lead in certain contexts toward a process of de-institutionalization. An ongoing party system de-institutionalization is an empirical outcome that can be reached if three conditions occur: first, the presence of an unstable electoral environment (high levels of electoral volatility); second, a significant part of this electoral instability is triggered by party innovation (old parties disappear and new parties successfully emerge); third, unstable elections with significant innovation are not a one-off, but tend to be sequential or at least to cluster in a certain period of time. The paper tries to verify the presence of these conditions in 19 Western European countries since 1945 and to detect if certain party system have experienced or are actually experiencing a phase of growing de-institutionalization.