Total marital fertility rate
Definition
Conceptually, the total marital fertility rate (TMFR) is an attempt to measure an analogue of the total fertility rate (TFR) for married people. There are two common versions: age-based TMFR (that tends to overestimate TMFR) and duration-based TMFR (that tends to provide a more reasonable estimate).
Age-based TMFR
The idea is the same as that used for computing the (ordinary) total fertility rate. Recall that:
Total fertility rate = Sum (over all ages within the childbearing age range) of age-specific fertility rates
where the age-specific fertility rate (ASFR) for a particular age is the ratio of the number of live births to females of that age to the total female population at that age.
Similarly, we define:
Age-based total marital fertility rate = Sum (over all ages within the childbearing age range) of age-specific marital fertility rates
where the age-specific marital fertility rate (ASMFR) in a given year for a particular age is the ratio of the number of live births to married females of that age to the total population of married females of that age.
Duration-based TMFR
Instead of adding up over age, we add up over the number of years spent so far in the marriage. Specifically:
Duration-based total marital fertility = Sum (over all possible marriage durations) of duration-specific marital fertility rates
where the duration-specific marital fertility rate (DSMFR) in a given year for a particular duration is the ratio of the number of live births to females who have been married for the duration to the total number of such females. Note that durations are measured in integer number of years (we need to do this because our measurement interval for births is a year).
References
- The Total Marital Fertility Rate and Its Extensions by Jan M. Hoem and Cornelia Muresan, European Journal of Population (2011), 27:295-312, available online