Party system change between elections: Evidence from the 18th Italian legislature

Party systems and party system change have long been one of the most studied topics within the comparative politics literature, yet most work in this field focuses on changes that occur between elections, neglecting the possibility that parties and party systems may reconfigure during the inter-election period. Building on the studies on party system change, this paper aims to analyse how individual changes in party affiliation can aggregate into changes at the level of parliamentary party system in the 18th Italian legislature. To achieve this goal, data on individual movements in the membership of parliamentary parties in the Senate and the Chamber of Deputies are used to track the extent of party system change over time, as indicated by changes in the number of relevant parties, their relative size and strength, and the general structure of competition in the Italian parliament. Overall, our results show major changes in the main features of the Italian parliamentary party system and the structure of competition in the 18th legislature, returning the image of a fluid, unstable and constantly moving system.