Introduction: Legislative party switching, parties, and party systems

That political parties are fundamental to the functioning of modern democracies is well known. Politicians build their careers within parties, parties convey information to voters about candidate preferences, and parties provide labels that identify candidates to voters. When voters choose candidates for office, they delegate decision making on public policy to parties and to party-identified representatives. Repeated elections give voters the opportunity to hold parties responsible and accountable for policy decisions and outcomes. Parties thus are indispensable elements of democratic delegation and representation (Cox 1997; Filippov, Ordeshook, and Shvetsova 2004; Powell 2000; Schattschneider 1942; Stokes 1999).