Causal Impacts of Teaching Modality on U.S. COVID-19 Spread in Fall 2020 Semester

We study the impact of college openings and teaching modality on county-level COVID-19 cases and deaths using information of 745 U.S. colleges. We group the colleges by their teaching modes in fall 2020 semester: in-person, online, and hybrid; and employ a logistic model and a gradient boosting algorithm to estimate the propensity scores for the three groups to adjust the pre-treatment imbalances of college and county level covariates. We find that greater enrollments, individual mask policies, and fewer republican votes in the county are major predictors of adopting online or hybrid modes. Treatment effects provide evidence that college reopenings, especially with in-person teaching elements, increase daily new cases and deaths.