Before revision:  Yet, in most models, R _0 is assumed to be a universal constant for the virus across outbreak clusters and populations -- thus neglecting the inherent variability of the transmission process due to varying population densities, demographics, temporal factors, etc.
After revision:  Yet, in most models, R is modeled as a ``universal" constant for the virus across outbreak clusters and populations -- thus neglecting the inherent variability of the transmission process due to varying population densities, demographics, temporal factors, etc.