Why Do Vote-by-Mail Elections Boost Voter Turnout?

Abstract

Vote-by-Mail (VBM) is a unique mode of voting that allows voters to receive an unsolicited ballot and choose to return their ballot either by mail or in person. Despite growing evidence that adopting VBM boosts voter turnout, previous research lacks a unified explanation for why. We introduce a novel theory that explains that adopting VBM increases turnout because it reduces the physical costs of voting for all voters and mitigates the information costs of voting conditional on the types of voters and salience of elections. Using over 9.5 million individual voting records from the 2012, 2014, and 2016 general elections in Colorado and New Mexico, we find consistent evidence for multiple hypotheses based on our theory. Our results show the benefits of taking treatment effect heterogeneity seriously in election studies, shed new light on campaigning and political participation, and imply potential advantages of nudge intervention in elections.