Social distancing to slow the U.S. COVID-19 epidemic: an interrupted time-series analysis

Mark J Siedner; Guy Harling; Zahra Reynolds; Rebecca F Gilbert; Atheendar Venkataramani; Alexander C Tsai

We fit mixed effects linear regression models, specifying the log difference in daily cases as the outcome of interest and a random effect for state. Explanatory variables included time in days, implementation period, and a time-by-implementation period product term. To assess the robustness of our findings, we adjusted for additional covariates, specified longer incubation periods, and stratified the estimates based on the size of the state epidemic (see Supplementary Appendix). Table 1 ), corresponding to a doubling of total cases every 3.3 days. From fourteen days prior, through three days after, implementation of the first social distancing measure, the mean daily case growth rate did not change (-0.2% per day; 95% CI, -0.7% to 0.4%; P=0.52). Beginning four days All rights reserved. No reuse allowed without permission.