Age-specific fertility rate

Definition

Conceptual definition

The age-specific fertility rate (ASFR) refers to the number of live births that females of a given age have on average in a year.

Operationalization

The age-specific fertility rate for an age $x$ may be defined in two related ways that yield slightly different numbers (mathematically) but not by too much.

• Non-preferred operationalization:It could be defined as the ratio of the number of recorded live births in a given year to females who, at the time of giving birth, had age $x$, to the size of the population of all females who had their age $x$ birthday at some time in the year.
• Preferred operationalization: We could fix a birth cohort of females whose birthdate for age $x$ falls somewhere within the year. We could then consider the ratio of the number of recorded live births in the given year to that birth cohort, to the total population of that birth cohort.

Note that the definitions differ subtly in that the numerator for the former is interested in the age of the female at the time of giving birth, whereas the numerator for the latter is interested in membership in a pre-specified birth cohort. Thus, for instance, somebody whose birthday is in February but who had the baby in January might count in one numerator and not in the other.

ASFRs might be reported in either of two ways:

• As plain numbers, with an implied denominator of 1. This approach is more useful in the context of computing the total fertility rate.
• As numbers scaled out of 1000, i.e., the number of live births per 1000 women of a given age. This approach is more useful in the context of computing the general fertility rate.