Do quick shutdowns work to fight the spread of Covid-19? Joe Malchow, Yinon Weiss and I wanted to find out. We set out to quantify how many deaths were caused by delayed shutdown orders on a state-by-state basis.

To normalize for an unambiguous comparison of deaths between states at the midpoint of an epidemic, we counted deaths per million population for a fixed 21-day period, measured from when the death rate first hit 1 per million—e.g.,‒three deaths in Iowa or 19 in New York state. A state’s “days to shutdown” was the...