Encyclopedia of Sociology

BIRTH AND DEATH RATES

condensed in an age–sex adjusted birth rate
(Shryock and Siegel 1976, pp. 284–288). The most
frequently used age–sex adjusted rate is calculated:

( 4 )

Sum (age-specific fertility rates per 1,000 X 5)

1,000

Total fertility rate=

if the age-specific fertility rates are for five-year age
groups. Single-year age-specific rates are summed
without the five-year adjustment. When expressed
per single woman, as in equation (4), the total
fertility rate can be interpreted as the average
number of births that a hypothetical group would
have at the end of their reproduction if they
experienced the age-specific fertility observed in a
particular year over the course of their childbear-
ing years.

Age-specific rates in real populations that con-
sciously control fertility can be volatile. For exam-
ple, the fertility rate of American women ages
thirty to thirty-four fell to 71 per 1,000 in the
middle of the Great Depression and climbed back
to 119 during the postwar Baby Boom, only to fall
again to 53 in 1975 and rebound to 84 in 1996
(U.S. Bureau of the Census 1975, p. 50; Ventura et
al. 1998, p. 32). Consequently, a total fertility rate
calculated from one year’s observed age-specific
rates is not a good estimate of the eventual com-
pleted fertility of childbearing-age women. It is,
however, an excellent index of the level of fertility
observed in a year that is unaffected by age
composition.

The total fertility rate also can be interpreted
as an estimate of the reproductivity of a popula-
tion. Reproductivity is the extent to which a gen-
eration exactly replaces its eventual deaths. While
the total fertility measures the replacement of
both sexes, other measures of reproductivity focus
only on the replacement of females in the popula-
tion (Shryock and Siegel 1976, pp. 314–316). The
gross reproduction rate is similar to the total
fertility rate except that only female births are
included in the calculation of the age-specific rates.
It is often approximated by multiplying the total
fertility rate by the ratio of female births to all births.

Theoretically, women need to average two
births, one female and one male, and female new-
borns need to live long enough to have their own

female births at the same ages that their mothers

gave birth to them to maintain a constant popula-

tion size. In real populations some female new-

borns die before their mothers’ ages at their births

and the tempo of fertility fluctuates. As a result,

both the total fertility rate and the gross reproduc-

tion rate overestimate reproductivity. The net re-

production rate adjusts for mortality, although it

remains sensitive to shifts in the tempo of child-

bearing. This measure of reproductivity is calculat-

ed by multiplying the age-specific fertility rates for

female births by the corresponding life-table sur-

vival rates that measure the probability of female

children surviving from birth to the age of their

mothers, and summing across childbearing ages.

If the tempo of fertility is constant, a net reproduc-

tion rate of greater than one indicates population

growth; less than one indicates decline; and one

indicates a stationary population.

Because of the impact of female mortality, the

total fertility rate must exceed two for a generation

to replace all of its deaths. In industrialized coun-

tries with a low risk of dying before age fifty, the

total fertility rate needs to be about 2.1 for replace-

ment. Developing countries with higher mortality

need a higher total fertility rate for replacement.

Malawi, for example, with an infant mortality rate

of 140 per 1,000 live births and a life expectancy of

only thirty-six needs a rate of about three births

per woman for replacement.

The fertility of most industrialized countries

has fallen below replacement (Population Refer-

ence Bureau 1998). Some, including the United

States (Figure 2), Ireland, Iceland, and New Zea-

land, are barely below replacement. Others have

declined to unprecedented low rates. Spain (Fig-

ure 2), Portugal, Italy, Greece, Germany, most

Eastern European countries, and Japan have total

fertility rates of 1.1 to 1.4 births per woman. Some

of these populations are already declining. With-

out constant, substantial net in-migration, all will

decline unless their fertility rates rebound to re-

placement levels or above.

In contrast, the total fertility rates of most

developing countries whose economies are still

dependent primarily on agriculture exceed re-

placement (Population Reference Bureau 1998).

The highest rates are found in Africa where most

countries have rates greater than five births per