Hello everyone. I am working with the EpiEstim package (on R) in order to estimate "Rt" with incidence data. However, in the package documentation (https://cran.r-project.org/web/packages/EpiEstim/EpiEstim.pdf) there is a point that I can't properly understand. The function "discr_si" (which computes the discrete distribution of the serial interval) assumes that the serial interval is shifted Gamma distributed, with shift 1. However, the input parameters are the following: k (positive integer, or vector of positive ingerers for which the discrete distribution is desired); mu (a positive real giving the mean of the Gamma distribution); sigma (a non-negative real giving the standard deviation of the Gamma distribution). My question is: should I consider mu as already shifted or should I consider mu without shift? I have a value for non shifted mu equal to 6.66 and I don't know whether use 6.66 or 7.66 (mu of shifted gamma with shift 1). In the source code (https://rdrr.io/cran/EpiEstim/src/R/discr_si.R) the Gamma parameters are computed as: a <- ((mu - 1) / sigma)^2 b <- sigma^2 / (mu - 1) so I think that it is possible that I have to use as input parameter "mu+1" (7.66).. but why asking for a shifted distribution when the code shift it back? Am I missing something? Thank you in advance for your help.