The Interpretation of the Laakso-Taagepera Effective Number of Parties

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Working paper
Jean-François Caulier
Centre d’Economie de la Sorbonne
In this paper, we present a general statistical framework within which we can draw a new interpretation of the Laakso-Taagepera ef-fective number of parties fragmentation index. With the particular method of sampling with probability proportional to the party sizes, we show that the Laakso-Taagepera e ective number of parties is the inverse of the size biased version of the traditional expected party size in shares. Further, we provide an axiomatic de nition of the Laakso-Taagepera e ective number of parties.
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