Generation time is a quantity used in population biology and demography to reflect the relative size of intervals of offspring production. Generation time usually expresses the average age of breeding females within a population. In epidemiology, it is defined as the interval of time between receipt of infection by a host and maximal infectivity of that host. Suppose females begin breeding at age and stop breeding (or die) at age, then the average age of first reproduction of a cohort of females is
where is the hazard function and is the fecundity of females aged .
When the population is in stable age distribution, we can express the generation time as the average age of mothers of zero-year-olds:
where is the Malthusian parameter of the population.
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