This function calculates one version of the effective number of parties introduced by Laakso and Taagepera (1979). It can be used to estimate the effective number of groups in a population.
This is one of two functions to calculate the number of effective parties. It gives 1 divided by the sum of Z squared. This function can be used to enumerate the effective number of parties, but also the effective number of groups in a population or representative body.
Effective number of parties
Laakso, M., and R. Taagepera (1979) The Effective Number of Parties: A Measure with Application to West Europe. Comparative Political Studies 12(1): 3-27.
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