“Effective” Number of Parties: A Measure with Application to West Europe

Abstract

The qEffectiveq Number of Parties: qA Measure with Application to West Europeq Laakso, Markku;Taagepera, Rein Comparative Political Studies; Apr 1, 1979; 12, 1; Proouest pg. 3 “EFFECTIVE” NUMBER OF PARTIES A Measure with Application to West Europe MARKKU LAAKSO University of Helsinki REIN TAAGEPERA University of California, Irvine I s a large number of parties bound to destabilize a political system (Duverger, 1954) or is it not (e.g., Lijphart, 1968; Nilson, 1974)? Before this question can be answered, the number of parties must be operationally defined in a way that takes into account their relative size. Such a number is also needed if one wants to detect trends toward fewer or more numerous parties over time, or the effects of a proposed change in electoral rules. This article presents ways to calculate this important political variable, calculates it for I42 post-1944 elections in 15 West European countries, and analyzes its possible effect on stability. We often talk of two-party and multiparty systems. We further dis- tinguish three~ or four—party systems in some countries, and even talk (e. g., Blondel, 1969: 535) of a two-and-a-half-party system whenthere is a third party of marginal size. Mexico could be viewed as a one-and-a- half-party system because the PR1 is so much larger than all other parties. Rather than take the number of all existing parties, including even the very smallest, one visibly has a need for a number that takes into account their relative size. We will call this number the “effective number of parties,” using the word “effectiveq somewhat in the sense pressure group literature uses it when talking about “effective access” (Truman, 195]: 506), but even more in the operational sense physicists give it when they talk about effective current (Richards et al., 1960: 594), COMPARATIVE POLITICAL STUDIES. Vol. I2 No. I. April 1979 3-27 © I979 Sage Publications. Inc. Copyright (c) 2000 Bell & Howell Information and Learning Company Copyright (c) Sage Inc.