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Ignacio Lago and Ferran Martinez, "Why new parties?," Party Politics, 17 (January, 2011), 3-20 [Available at http://ppq.sagepub.com/content/vol17/issue1/ ]

First paragraph:
The question why new viable parties emerge in well-established party systems, or the slope in the equation of the number of parties, is a core topic in political science. However, as Tavits (2006: 99) has noted, 'a parsimonious empirical model explaining this phenomenon is still lacking', which is surprising, given that political science knows a fair amount about the variables explaining party system fragmentation, or the constant in the equation of the number of parties (see, e.g., Amorim Neto and Cox, 1997). The analytical literature on new parties entering a parliament, even if only implicitly, revolves around the theory of strategic entry developed by Cox (1997): parties will enter the fray only if their probability of victory is high enough to justify the cost. Given that entering the electoral fray is costly, once political actors have good information about the relative chances of potential competitors, over time the number of parties within countries tends to decrease. Candidates prefer not to invest their resources when they believe that they will surely lose; therefore, their dominant strategy is withdrawal. However, we sometimes observe that new parties appear as viable competitors, upsetting the equilibria. If electoral systems and cleavages within countries rarely change significantly, how can the new equilibria be explained? There are two types of study that have dealt with this question. On the one hand, there are what we have labelled inter-variation studies, such as those by Bollin (2007), Harmel and Robertson (1985), Hug (2000, 2001), Lucardie (2000) and Tavits (2006). These principally explain why new viable parties enter in some institutional settings but not in others. On the other hand, there are what we call intravariation studies: for example, the work of Chhibber and Kollman (1998, 2004). These latter studies show that decentralization, that is, the degree of economic and political control over local areas, plays a key role in explaining the emergence of new parties.

Figures and Tables:
Figure 1. Average effective threshold over time in regional elections in Spain, 1980-2006
Figure 2. Standard deviation of the average effective threshold within electoral systems and over time in regional elections in Spain, 1980-2006
Figure 3. Regional government expenditure over GDP in Spain
Table 2. New viable competitors
Table 3. The determinants of successful entries (logit regression estimates)a
Table 4. Simulating the entry of a viable party

Last Paragraph:
(First paragraph of conclusion) In this article we have argued that the slope in the equation of the number of parties is positive in many districts and elections. Using empirical evidence from regional elections in Spain, where the democratic transition and consolidation has taken shape around a dual process of democratization and decentralization, we have shown that party system change is frequent: in a third of the 343 districts analysed, we found changes in the viable parties.

Last updated December 2011