An
important factor that can delay changes in population growth is the average number of children expected to
be born to a woman during her lifetime, known as the total fertility rate, or TFR.
A population that maintained a TFR of 3.8 over a long time would increase
rapidly, whereas a population that had a TFR of 2.1 over a long time would
decline.
Replacement-level fertility (RLF) is the TFR required for a
population to remain constant. It is the
average number of children a couple must produce in order to “replace”
themselves. A total fertility rate of 2.1, that is, replacement-level
fertility will not necessarily immediately result in a stable population with
zero growth for several reasons. First, the death rate may fall as living
conditions improve and people live longer. If the death rate falls faster than
the birthrate, there will still be an increase in the population even though it
is reproducing at the replacement rate.
A
comparison of nations suggests that the TFR
declines as income increases. China is the country where TFR is
less than 1. Bangladesh,
which has an average income per person of a few hundred dollars per year, has a
high fertility rate—approximately 2.83
children born to each woman.
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