Thus, the estimator of corrected R a in (11) is identical to that of R 0 . In other words, R 0 can be estimated from the incidence data and the generation time without assuming exponential growth of cases during the early phase of an epidemic. It should be noted that the ratio of prevalence to mean generation time p(t)/D in the denominator of the right-hand side of (10) has been replaced by "the total number of effective contacts that have equal potential to generate secondary cases".