Relation between crude birth rate and total fertility rate

From Demography

This page describes the empirical and conceptual relationship between crude birth rate and total fertility rate.

Conceptual relationship

Intermediate notion: general fertility rate

The relation between the crude birth rate and total fertility rate can be understood best by looking at a demographic variable that is intermediate, albeit not midway, between them: the general fertility rate (GFR). This is not separately reported in most datasets, but is still conceptually useful.

  • Relationship between CBR and GFR: Crude birth rate measures the number of live births per 1000 members of the total population. General fertility rate, on the other hand, measures the number of live births per 1000 women of childbearing age. The relation between CBR and GFR depends on the age-sex structure of the population, or explicitly, on an estimate of the proportion of the population that comprises women of childbearing age.
  • Relationship between GFR and TFR: See total fertility rate versus general fertility rate. Essentially, the general fertility rate is a population-weighted average (scaled to a denominator of 1000) of the age-specific fertility rates, whereas the total fertility rate is simply the sum of the fertility rates. TFR and GFR can also be related linearly if we know both the distribution of women in childbearing years between different ages, and the relative fertility rates in different years (i.e., their ratios with one another). Note that there are two extreme cases where the relation between TFR and GFR is easy to obtain: population sizes are same at all ages, or age-specific fertility rates are the same at all ages. In either case, TFR = GFR times the number of childbearing ages. However, both assumptions are unrealistic.
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