Socioeconomic heterogeneity and party system fragmentation

Considerable evidence suggests that social diversity increases the number of political parties. While a vast literature examines this relationship by measuring social diversity as ethnic fragmentation, the convenience of capturing the level of social heterogeneity by using alternative indicators has been traditionally overlooked. In this article, I offer new evidence that documents the impact of social diversity on party system size by proxying the former as the number of social classes. Using both objective class positions and subjective class identifications and employing two different datasets that cover democratic legislative elections around the world between 1981 and 2015, I find that the effective number of social classes has a positive effect on party system fragmentation when the average district magnitude in a democracy is high. Given the difficulty to test these effects in a cross-country environment net of unobserved heterogeneity, I examine the robustness of the findings in Spain between 2000 and 2016, an ideal case due to large differences in district magnitude and a changing party system. Overall, the results suggest that high levels of social diversity are likely to increase party system fragmentation when the electoral system is permissive enough.