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Crowded Space, Fertile Ground: Party Entry and the Effective Number of Parties*


This paper develops a novel argument as to the conditions under which new political parties will form in democratic states. Our approach hinges on the manner in which politicians evaluate the policy implications of new party entry alongside considerations of incumbency for its own sake. We demonstrate that if candidates care sufficiently about policy outcomes, then the likelihood of party entry should increase with the effective number of status quo parties in the party system. This relationship weakens, and eventually disappears, as politicians’ emphasis on “office-seeking” motivations increases relative to their interest in public policy. We test these predictions with both aggregate electoral data in contemporary Europe and a data set on legislative volatility in Turkey, uncovering support for the argument that party system fragmentation should positively affect the likelihood of entry when policy-seeking motivations are relevant, but not otherwise.

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Daniel M. Kselman, IE School of International Relations ( Eleanor Neff Powell, University of Wisconsin, Madison ( Joshua A. Tucker, New York University ( The authors thank Jon Eguia, Herbert Kitschelt, Alex Kuo, Kevin Morrison, and participants in the International Conference on Political Economy and Institutions (ECOPEAI), University of Virgo 2012, for valuable feedback on previous versions. To view supplementary material for this article, please visit

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Political Science Research and Methods
  • ISSN: 2049-8470
  • EISSN: 2049-8489
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