The Interpretation of the Laakso-Taagepera Effective Number of Parties

Abstract

In this paper, we present a general statistical framework within which we can draw a new interpretation of the Laakso-Taagepera effective number of parties fragmentation index. With the particular method of sampling with probability proportional to the party sizes, we show that the Laakso-Taagepera effective number of parties is the inverse of the size biased version of the traditional expected party size in shares. Further, we provide an axiomatic definition of the Laakso-Taagepera effective number of parties.Fragmentation, effective number of parties, concentration index, size biased sampling, length biased sampling.