Replication Data for: Adapt or Perish. How parties respond to party system saturation in 21 Western democracies, 1945-2011

This study examines whether and how parties adapt to party system saturation. A party system is oversaturated when a higher effective number of parties contests elections than predicted. Previous research has shown that parties are more likely to exit when party systems are oversaturated. We ex-amine whether parties will adapt by increasing the nicheness of their policy platform, by forming electoral alliances, or by merging. Based on time series analyses of 522 parties, 357 elections in 21 established Western democracies between 1945 and 2011, we find that parties are more likely to enter and less likely to leave electoral alliances if party system saturation increases. Additionally, a small share of older parties will merge. Hence, there are limits regarding the adaptive capacities of parties to their environments, which has important implications for the literature on party (system) change and models of electoral competition.