Party system classification: A methodological inquiry

Abstract

Despite the recent spread of multi-scale approaches to party system classification, the most widely accepted criterion has always been the number of parties, often defined in terms of their relative sizes. Building on the existing body of qualitative classifications and quantitative techniques, this article proposes a method that can be used for defining party system types in operational terms, and distinguishing among them by a parsimonious criterion. The proposed method is based on representing information about seat distributions by party in graphical form, segmenting the resulting bounded diagram into regions, and identifying these regions as representations of different party system types. This makes the graphical representation, dubbed the relative-size triangle, instrumental both for building categorical classifications of the empirically observed party systems and for visualizing differences among them. For illustration, the proposed method is applied to a comprehensive set of post-World War II party systems.