How many political parties are there, really? A new measure of the ideologically cognizable number of parties/party groupings

We offer a new measure of the ideologically cognizable number of political parties/party groupings that is intended to be complementary to the standard approach to counting the effective number of political parties – the Laakso–Taagepera index (1979). This approach allows the possibility of precise measurement of concepts such as polarized pluralism or fragmented bipolarism and is applicable to both unidimensional and multidimensional representations of party locations. Using recent CSES (Comparative Study of Electoral Systems) data on one-dimensional representations of party locations in four real-world examples (two of which are available in an online appendix), we find that Slovenia, treated initially as a five-party system, has its optimal reduction as a two-bloc/party system, as does Spain, which is treated initially as a four-party system. However, Canada, treated initially as a four-party system, has its optimal reduction as a three-bloc/party system if we look at a unidimensional representation of the party space, while it remains a four-bloc system if we draw on Johnston’s two-dimensional characterization of Canadian political competition. Finally, the Czech Republic, initially a five-party system, is optimally reduced to a system with four party groupings. Corresponding author: Bernard Grofman, School of Social Sciences Plaza, Irvine, CA 92697-5100, USA Email: [email protected] Party Politics 18(4) 523–544 a The Author(s) 2011 Reprints and permission: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1354068810386838 ppq.sagepub.com