Studying the electoral success of new political parties - A methodologicalnote

Studies of new political parties often attempt to explain their electoral s uccess. Methodological problems linked to the notion of selection bias, how ever, considerably hamper the results of such studies. This note offers a d iscussion of these biases, which are due to the fact that new political par ties are a 'self-selected' sample. An empirical example studying the impact of rules regulating the access to ballots in national elections in 21 west ern democracies illustrates this problem. Taking into account the formation process when studying the success of new parties, however, allows for a co rrection. Similar solutions exist for other research designs employed to st udy the success of new parties.