A poor-man’s approach to the effective reproduction number: the COVID-19 case

It is shown that estimates of the effective reproduction number R _t for COVID-19 using standard packages such as E <sc>pi</sc> E <sc>stim</sc> can be reproduced very accurately using the expression R _t = c ( t )/ c ( t − τ ), where c ( t ) is the incidence at time t and τ the mean value of the series interval.