The present study proposed the use of the corrected actual reproduction number, R a , for statistical inference of R 0 based on incidence and known relative frequency of secondary transmissions (i.e., the generation time distribution) during the early growth phase of an epidemic. The previously available method using (5) forced us to adopt an exponential growth assumption, and moreover, an additional step towards the estimation of r (i.e., the translation of r to R 0 ) was required [9] . The proposed method does not necessarily require an exponential growth assumption and provides a "short-cut" to estimate R 0 from incidence data. The simple likelihood function employing a binomial distribution was also proposed to yield an appropriate uncertainty bound of R 0 . It should be noted that given the knowledge of g s and readily available incidence data, equation (15) permits calculation of the expected value of R 0 without likelihood. Such a calculation can be attained using any spreadsheet.