When the total number of children bom during the life time of the women belonging to a stated birth cohort is divided by the number of those women who reach the age of 30 years while resident in the community, an Actual Fertility Rate (cohort AFR30) is obtained, whose informativeness is absolute, and whose precision is determined only by the specificity of the original data. When related to cohort survivorship rates (which include the effects of migration) a variety of replacement ratios can be obtained which have the advantage over the NRR (and other traditional replacement rates) in that they assume the purpose of reproduction to be the replacement of the adults in the population, and not the neonates. The corresponding period AFR30 is calculated by dividing the total number of live births in the stated year, by the number of women who reached the mid-point of the reproductive period (taken to be age 30 years) during that year. It can be thought of as the average number of births per woman if all (instead of most of) the babies bom each year were bom to mothers at the fertility mode, or, the degree to which the reproductive effort of the year contributed towards the replacement of the women at the fertility mode. It is shown that the period AFR30 generally is a good predictor of the corresponding cohort AFR30, indicating that it too is a informative demographic parameter, which includes amongst its recommendable features a trivially easy calculation.
Koeslag, J H.
"On the Calculation of Actual Fertility Rates,"
4, Article 13.
Available at: https://digitalcommons.wayne.edu/humbiol/vol58/iss4/13