Universal mail voting increases turnout, and especially for one political party

Does mail-in voting significantly affect voter turnout? Do rates of voter turnout change based on whether the voter is Democrat, Republican, or not affiliated? In “Universal Mail Ballot Delivery Boosts Turnout: The Causal Effects of Sending Mail Ballots to All Registered Voters,” published in The Journal of Politics, authors R. Michael Alvarez and Yimeng Li examine a unique voting case in 2020 in order to present the first study of how universal voting by mail affects voter turnout within a jurisdiction.

In March 2020, the COVID-19 pandemic led Los Angeles County officials to send primary election ballots to all registered voters within their district, when previously, ballots had only been sent without request to permanent absentee voters. This policy essentially removed the barrier of requesting a mail-in ballot, an isolated shift that facilitated the study conducted by Alvarez and Li. Of additional benefit to their case study are the size and diversity of Los Angeles County; over seven million registered voters make the county the largest voting jurisdiction in the United States.

Whereas previous researchers have often concluded that voting by mail does not alter electoral outcomes to a significant degree, Alvarez and Li find that between the 2016 and 2020 primary elections in LA County, universal vote-by-mail district turnout increased by 37.6%, and nonuniversal vote-by-mail district turnout by 11.5%. This statistical difference, they write, indicates that sending ballots to every registered voter significantly increases voter turnout compared to districts where mail ballots must be requested.

Additionally, the authors evaluate the relationship between mail voting and party affiliation, finding that while non-permanent absentee Democrat voters in both universal and non-universal voting by mail districts saw decreased turnout in 2020 compared to 2016, the decrease was smaller in universal vote-by-mail districts than nonuniversal vote-by-mail districts. In contrast, non-permanent absentee Republican voters in both types of districts saw an increase in turnout in 2020 compared to 2016, and the increase was larger in universal vote-by-mail districts than nonuniversal vote-by-mail districts. Overall, these figures suggest, universal mail voting seems to encourage voter turnout for both Democrat and Republican voters but may have a stronger effect on Republicans.

Ultimately, Alvarez and Li write, universal voting by mail would likely produce an increase in voter turnout across the US. And with respect to party affiliation, they conclude: “Our results also show that turnout rises for both Democratic and Republican voters, and perhaps that it increases slightly more for registered Republicans—a result that should be of interest to legislators and policymakers on both sides of the aisle.”