To the Editor: I believe that the study by Dr Markel and colleagues1 of the 1918-1919 influenza pandemic and the effectiveness of nonpharmaceutical interventions has a serious problem in its data that calls its conclusions into question. The authors assert that, of 43 cities in the study, New York City intervened the earliest, on September 18, 1918, at “−11” (11 days before excess deaths doubled the baseline), 6 days earlier than the second earliest city. Because New York City had a relatively benign experience, this assertion contributes to the conclusion that nonpharmaceutical interventions were effective.