Keywords: Legislative party switching; Intra-party politics; Roll-call voting; Italian party system
Legislative party switching has been studied mostly from two perspectives. First, scholars have attempted to explain why MPs switch their party affiliation and under what circumstances. Second, party switching has been analyzed in order to make inferences about party discipline. Not surprisingly, Italy is one of the most examined cases within the literature on party switching, as almost a quarter of MPs switched their party affiliation during Legislature XIII (1996-2001). In the current Italian legislature (Legislature XVI, 2008- ), almost one sixth of the MPs have switched parties on at least one occasion. Among the party switchers about half have switched party on two or more times. This relatively high level of party switching is important because it has been associated with the formation of two new parliamentary parties during the inter-electoral period and with increased political instability. This article contributes to the existing literature by exploring party switching in Legislature XVI in terms of the characteristics of individual MPs and the duration of parliamentary party membership. Our research re-evaluates hypotheses proposed in the literature and tests a new event-based model of legislative party switching. This article shows that policy tensions constitute one of the main motivations for party switching; and the determinants of switching have different effects during the life of a legislature.