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Predicting the Number of Parties: A Quantitative Model of Duverger's Mechanical Effect

Published online by Cambridge University Press:  02 September 2013

Rein Taagepera
Affiliation:
University of California, Irvine and Tartu University
Matthew Soberg Shugart
Affiliation:
University of California, San Diego

Abstract

The mechanical effect of electoral systems, identified by Maurice Duverger, can be estimated by means of a quantitative model. The model predicts the range within which the effective number of parties in a district should fall for a given magnitude (number of seats) of the district. At the national level, a related model predicts the effective number of parties based on the effective magnitude and the number of seats in the national assembly. The institutional variables considered—magnitude and assembly size—define a great portion of the structural constraints within which a given country's politics must take place. The model developed provides a good fit to data in spite of its having been developed from outrageously simple starting assumptions.

Information

Type
Research Notes
Copyright
Copyright © American Political Science Association 1993

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