PATTERNS OF NATALITY
Births can be measured by several methods. The older way was simply to calculate the birth rate: the number of births per year per thousand people (Figure 3.3).
More revealing is the total fertility rate (TFR), which is measured as the average number of children born per woman during her reproductive lifetime, considered to be from 15 to 49 years of age (with some countries having a younger upper-age limit of 44 years of age). The TFR is a more useful measure than the birth rate because it focuses on the female segment of the population, reveals average family size, and gives an indication of future changes in the population structure. A TFR of 2.1 is needed to produce a stabilized population over time, one that does not increase or decrease. Once achieved, this condition is called zero population growth.
total fertility rate (TFR)
The number of children the average woman will bear during her reproductive lifetime (15–44 or 15–49 years of age). A TFR of less than 2.1, if maintained, will cause a natural decline of population.
zero population growth
A stabilized population created when an average of only two children per couple survive to adulthood. Eventually, the number of deaths equals the number of births.
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The TFR varies markedly from one part of the world to another, revealing a vivid geographical pattern (Figure 3.4). In southern and eastern Europe, the average TFR is only 1.3. Every country with a TFR of 2.0 or lower will eventually experience population decline. Bulgaria, for example, has a TFR of 1.2 and is expected to lose 38 percent of its population by 2050. Taiwan and Latvia are tied at 1.1 for the lowest total fertility rate in the world in 2012.
By contrast, sub-Saharan Africa has the highest TFR of any sizable part of the world, led by Niger with 7.1 as of 2014. Elsewhere in the world, only Afghanistan can rival the sub-Saharan African rates. However, according to the World Bank, during the past two decades TFRs have fallen in all sub-Saharan African nations.