What is Population Growth?
• The overall rate of population increase depends on the number of births and deaths, but also on the length of generations -- the age at which women have their first baby.
- For example, if all women had three children with a 15-year average generation time, the rate of population growth would be 2.7%. If the average spacing were 30 years, the growth would drop in half -- to 1.35%.
Population Age Structure:
Birth and death rates do not tell the whole story of population growth. A country's TFR can be below replacement level while the population continues to grow, if there are a disproportionately large number of couples in these younger age groups. That is the situation in Kenya and, to a lesser degree, the United States. The age structure of the population, then, is also an important factor in population change. When a substantial proportion of a country's population is young, high population growth rates in a country are to be expected, even if the average TFR is modest. The reason is that so many females are of childbearing age, that even a modest average TFR results in a large number of births.
• Replacement-level fertility = the number of children a couple must bear to replace themselves
- slightly more than 2 children because some children die before reaching their reproductive years
- reproducing at this level does NOT mean that population growth stops; there are so many "future parents" already alive that, even at replacement-level, population will continue to grow for many years
• Total fertility rate (TFR) - estimate of the average number of children a woman will have during childbearing years
- In 1998, the TFR was 2.9 children per woman (1.6 in MDCs & 3.2 in LDCs); still far above replacement level