On the stability of the Brazilian presidential regime: A statistical analysis

Brazil’s presidential system is characterized by the existence of many political parties that are elected for the Chamber of Deputies and unite in legislative coalitions to form a majority. Since the re-democratization in 1985, Brazil has had 8 direct presidential elections, among which there were two impeachments of the elected presidents. In this work we identify clear differences between stable presidential periods and Legislative terms with an impeachment by analyzing the votes that took place in the Chamber of Deputies from 1991 to 2019. Our statistical analysis are blind to the content of the bills. We start by measuring the cohesion of the parties and the congress for each bill. We then quantify the agreement between the votes of congressmen and observe that there is a stronger polarization among congressmen during legislative periods where there was no impeachment, referred here as stable legislative periods. Using clustering algorithms, we are able to associate these polarized groups observed during the stable periods with the opposition to the government and government base. For periods with an impeachment, the data shows that the congress split up in more than two groups. To characterize the impeachment of Collor and Dilma Rousseff (in 1992 and 2016, respectively) we analyze how the agreement between congressmen and the government evolved over time and we also propose a division of the congressmen in three groups. We identified that, in periods with an impeachment, the third group aligns itself against the president.