Ideology and Party Switching: A Comparison of 12 West European Countries

Party switching can pose a severe threat to party unity and deepen internal party division. To date, research on party switching has either focused on the individual motivations for changing party or on the effects of macro-level settings. The role of party-level variables, however, has received surprisingly little attention in the literature. In particular the impact of ideology has rarely been assessed. This article tests whether specific aspects related to parties' ideology (i.e. extremism, isolation, authoritarianism, programmatic clarity and stability) are linked to different levels of defection. For this purpose I rely on an original database on party switching in 12 Western European countries from 1999 to 2015, supplemented with variables from the Chapel Hill Expert Survey. The results of multilevel negative binomial analyses show that indeed ideology and its various components have a substantial impact on the scope of switching. For instance, parties promoting authoritarian values suffer from a higher number of defectors. Moreover, parties with more unstable labels seem to be more subject to switching. This article improves our understanding of how party ideology is related to party unity and, more generally, to legislative dynamics.