Heterogeneity, electoral rules and the number of candidates: an empirical investigation using a quasi-natural experiment

There is an open debate in social sciences concerning the impact of different electoral rules and societal heterogeneity on the number of candidates vying for a seat during election times. Using data from Brazil’s municipal mayoral elections, this paper assesses the empirical validity of the so-called nuanced view, which claims the interaction between societal heterogeneity and institutional permissiveness of electoral rules (presence of a runoff, in our case) is key to explain the number of candidates. Our study differs from others in the literature in two major aspects: (i) we have a truly exogenous source of variation in electoral rules due to a change in legislation introduced by the constitutional reform of 1988 and, (ii) we use panel-data techniques that allow for a more reliable identification of the parameters. Our results provide support for the nuanced-view: the coefficient of the interaction between heterogeneity and the presence of a runoff is always positive and statistically significant.