When institutions matter: electoral systems and intraparty fractionalization in Western Europe

The comparative study of intraparty divisions and their determinants has been a long-debated matter, but some issues remain unresolved. First, the problem of the empirical identification of intraparty groups. Second, the lack of comparative perspective and large-N cross-country and cross-time analyses, given intraparty divisions have been studied mostly through theoretical or, at best, small-N analyses. Third, the underestimation of the potential role exerted by contextual factors because of the emphasis put almost exclusively on intraparty dynamics. To fill these gaps, the article employs a measure of visible intraparty fractionalization allowing for large-N cross-time and cross-country comparison. Moreover, by focusing on about 700 party cases in 11 Western European countries since 1965, the article shows that institutional factors, particularly electoral systems’ characteristics, impact intraparty fractionalization. Specifically, intraparty fractionalization is higher in more disproportional systems and where there are stronger incentives for personal vote.