|
Population Stistics
Modern national governments and international organizations place a high
priority on the accurate determination of national and worldwide
populations. Describing the present population and predicting those of the
future with reasonable accuracy requires reliable data.
Methods of Research
National censuses, civil registration, and, since the 1960s, national
sample surveys are the major sources of demographic data. They provide the
raw materials for investigating the causes and consequences of population
changes. The most common source is the population census, a count of all
persons by age and with specified social and economic characteristics
within a given area at a particular time. A register is a continuous record
of births, deaths, migrations, marriages, and divorces, often maintained by
a local government; reliability varies with the scrupulousness of citizens
in reporting these data. In the sample survey, a statistically selected
portion is used to represent the total population.
In the U.S., decennial censuses have been taken since 1790. Since the 1950s
the U.S. Bureau of the Census has conducted an annual Current Population
Survey, a highly detailed sample survey of many aspects of demographic
behavior and related socioeconomic factors. International population data
are compiled in systematic form by the United Nations Statistical Office,
which prepares an annual Demographic Yearbook; by the United Nations
Demographic Division, which issues biennial assessments and projections of
world population; and by the International Bank for Reconstruction and
Development.
[pic]
Measures of Population
The numbers of births, deaths, immigrants, and emigrants over a specified
time interval determine the change in population size. For comparative
purposes, these components of change are expressed as proportions of the
total population, to yield the birth rate, death rate, migration rates, and
the population growth rate. (Birth and death rates typically are stated as
numbers per 1000 population per year.) These rates are affected by the age-
composition of the population; for example, a very healthy population,
which, as a result, has a relatively large proportion of old people, might
have a death rate similar to that of a poor population made up of
predominantly younger members. Demographers, therefore, often use measures
that are free of this age-distribution influence. Two such widely used
measures are the total fertility rate (TFR) and the life expectancy at
birth.
The total fertility rate is the number of children a woman would have
during her reproductive life if she experienced the prevailing rates of
fertility at each age. High-fertility countries may have birth rates of 40
or even 50 per 1000 populatio |