We study the impact of compulsory voting in Brazil, where voting is mandatory from age 18 to 70 and voluntary for those aged 16, 17 and 70+. Using a survey sample of 8008 respondents, we document voter confusion about how the age criterion applies. Some people falsely believe that what matters is one's age in an election year rather than on Election Day. Next, we perform a regression discontinuity (RD) analysis of compulsory voting among young voters with register-based data from six Brazilian elections (2008–2018). We find that the effect of compulsory voting is seriously underestimated if we focus solely on the discontinuities prescribed by the law. Our findings carry important implications for studies adopting the RD design where knowledge of the cutoff is expected of the units of interest (like those about compulsory voting) and confirm that compulsory voting is a strong institutional arrangement that promotes greater electoral participation.
