Party System Congruence and Bicameralism

We compare the nature of party systems across bicameral legislatures using newly available data on upper chamber elections. We examine the similarity in the composition of political parties between the lower and upper chambers (partisan congruence) and introduce a novel measure that captures differences in the nationalization of parties between the two chambers (nationalization congruence). We explore variations in these measures across countries and over time and demonstrate that the power of the upper chamber (symmetry) is linked to both forms of congruence. Moreover, we apply these measures to understand how the interaction between congruence and symmetry—two key dimensions of bicameralism—influences policymaking, focusing on government spending patterns. Our findings reveal that partisan and nationalization congruence can have contrasting implications for government spending in symmetric bicameral systems but have negligible implications in asymmetric bicameral systems.