Exogenous Electoral Volatility. a Proposal to Create a New Index of Party System Institutionalization

Joint paper with Ignacio Lago (Pompeu Fabra University): The existing literature on the institutionalization of party systems has mainly been using the index of electoral volatility as an indicator of the patterns of stable competition in party systems.  However, high electoral stability is not always beneficial for party competition.  It is important to distinguish “healthy” volatility for party competition and electoral accountability from the volatility affecting party system institutionalization. There have already been some attempts to deal with this problem distinguishing different types of electoral volatility.  In this paper we consider these attempts unsuccessful, and we offer instead two new volatility indices: endogenous volatility (volatility in equilibrium) and exogenous volatility (volatility out of the equilibrium).  We also argue and test that the latest is the relevant one for studying party system institutionalization.