Branching process results in terms of moments of the generation-time distribution.

A number of simple formulae concerning the growth rate, doubling time, and age distribution of cell populations are in common usage. Many of these are invalid unless the generation times have no variation, a situation which occurs rarely. The correct formulae, which are available from the theory of age-dependent branching processes, are often ignored in the biological literature, perhaps due to their complexity. In this paper the major formulae from the theory of age-dependent branching processes are reorganised in terms of the mean, coefficient of variation, and skewness of the generation times. This leads to a greater insight into the theory and some simple formulae which account for the variability.