Reply to Zhang et al.: Linear regression does not encapsulate the effect of non-pharmaceutical interventions on the number of COVID-19 cases

Zhang et al. (2020) used linear regression to quantify the effect of lockdowns on the number of cases of COVID-19. We show using differential equations from the susceptible-exposed-infected-recovered (SEIR) model and with an example from another location not previously considered that the Zhang et al. analysis should not be considered sound evidence that mask mandates are sufficient to control or the primary factor controlling the spread of COVID-19.
Comment: Submitted as a letter to Proceedings of the National Academy of Sciences of the United States of America