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The Laakso-Taagepera Index in A Mean and Variance Framework

Author

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  • Scott L. Feld

    (Department of Sociology & Anthropology, Purdue University, 700 West State Street, West Lafayette, IN 47907, USA)

  • Bernard Grofman

    (Department of Political Science, University of California, Irvine, 3151 Social Science Plaza, Irvine, CA 92697-5100, USA; bgrofman@uci.edu)

Abstract

The Laakso-Taagepera index (Laakso and Taagepera, 1979) has become the most commonly used measure to specify the ‘effective’number of political parties in a party system where parties vary substantially in their vote and/or seat shares. It is well known that the Laakso-Taagepera index is the inverse of the even more widely used Herfindahl-Hirschman index of concentration (Hirschman, 1945; Herfindahl, 1950; cf. Taagepera and Grofman, 1981). Drawing on little known work by Feld and Grofman (1977, 1980) on the so called ‘class-size paradox’, it can also be shown that both indices may be re-expressed as simple functions of a distribution's mean and variance. As far as we can judge, these latter relationships appear to be unknown in the party and electoral systems literatures. By expressing the Herfindahl-Hirschman index and the Laakso-Taagepera index in terms of means and variances we can see that each index has a ‘natural’ interpretation in terms of well known statistical parameters which allows their fundamental mathematical properties to be more clearly revealed.

Suggested Citation

  • Scott L. Feld & Bernard Grofman, 2007. "The Laakso-Taagepera Index in A Mean and Variance Framework," Journal of Theoretical Politics, , vol. 19(1), pages 101-106, January.
    • Handle: RePEc:sae:jothpo:v:19:y:2007:i:1:p:101-106
    DOI: 10.1177/0951629807071021
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    References listed on IDEAS

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    1. Caulier, Jean-François & Dumont, Patrick, 2005. "The effective number of relevant parties : how voting power improves Laakso-Taagepera’s index," MPRA Paper 17846, University Library of Munich, Germany.
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    Cited by:

    1. Leech, Dennis, 2010. "Power Indices in Large Voting Bodies," Economic Research Papers 270996, University of Warwick - Department of Economics.
    2. Steven J Brams & D Marc Kilgour, 2012. "Narrowing the field in elections: The Next-Two rule," Journal of Theoretical Politics, , vol. 24(4), pages 507-525, October.

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