The nationalization of party systems: Conceptual issues and alternative district-focused measures

The degree of party system nationalization, defined as the extent to which parties compete with similar strength across sub-national geographic units, is an important but understudied issue. We attempt to make two contributions to this topic. First, we provide a two-dimensional conceptual map of party system nationalization, consisting of the dimensions of 'inflation' and 'dispersion,' while previous studies only considered the inflation dimension. Second, we introduce alternative measures to gauge these two dimensions. We also combine these two to measure overall party system nationalization. The paper demonstrates the relevance of this two-dimensional conception and the usefulness of our measures by applying them to some real-world examples, including the US party system development from 1870 to 2002.