The challenges posed by subnational data to measure party system change: the cases of Argentina and Brazil

Understanding how political parties operate at the subnational level (besides the national level) is crucial to advancing our knowledge of how federations work. This research analyzes party system change at the subnational level in Argentina and Brazil over time. The central question is how do subnational party systems change where the territorial units are constitutionally entitled to change the electoral system, in contrast to cases where the electoral system is defined centrally, by a federal law? I propose measuring changes in subnational party systems through electoral competitiveness and patterns of alternation in executive power. I argue that in Argentine provinces, where provincial authorities’ have more autonomy to design and change local electoral laws on the basis of short-term political considerations, stability instead of change in subnational interparty interactions is more likely than in Brazil’s states.