Socio-Spatial Spillovers of All-Mail Voting : Evidence from North Carolina

All-mail voting has been introduced in several jurisdictions in the United States since the SARS-CoV-2 pandemic, with the resulting need for processing larger volumes of mail ballots posing challenges to election administration. Leveraging data on more than 4.5 million eligible voters in the state of North Carolina and on online social ties between zip code tabulation areas (ZCTA) across the country, I show that local rollouts of all-mail voting also have spillover effects on choice of voting method in distant areas. Using a difference-in-differences research design, I find that an increase in the ZCTA-level share of social ties in counties that switched to all-mail voting between the 2016 and 2020 presidential elections by one standard deviation (1.77 percentage points) corresponds to an increase in the probability of casting a mail ballot by roughly 3.8 percentage points. These socio-spatial spillovers are stronger for older voters, non-Republicans, and those residing in metropolitan counties. The findings suggest that considering the aggregate social ties of a local jurisdiction in other areas may aid election officials in planning for changes in the demand for mail ballots