About the population pyramid and data
Population pyramids are commonly used by
demographers to illustrate age and sex structure of a country's population.
Countries that are expected to grow rapidly typically have a large
number of individuals in their reproductive years and the population
pyramid is wider of "heavier" at the bottom. In contrast, populations
that are expected to have slow, zero, or negative growth typically
have more individuals beyond reproductive age, and their pyramids
tend to be "top heavy". Population distributions for the United
States (moderate growth) and Mexico (rapid growth) can be found in
QELP data sets #031
and #032
, respectively.
Making predictions about a country's future population is aided by studying age cohorts (groups)
such as those defined in the accompanying data set. Instead of considering a single growth or birth rate
for the entire population, demographers estimate each cohort's birth and death rate to increase the predictive
power of their models. Also taken into consideration is immigration and emigration from each cohort to other
countries. Using dynamic cohort models, population pyramids can be computed predicting population structural
changes over time. For an example of these pyramids visit the extraordinary website http://www.census.gov/ipc/www/idbpyr.html
. This site is part of the much larger US Census International Data Base (IDB) website where additional country
by country demographics can be found.
Germany's population structure is somewhat like that of the United States in that there is
a "bulge" in the middle, reflecting the fact that the most numerous cohorts are in the age range of 30-55.
In addition, the net number of migrants for each country is nearly the same, both numbering between 3 and 4 (per
1000 people) . Also, both countries have advanced systems of education and health care, and both are highly
industrialized with high employment of women. With these similarities, one might think that future population
growth for these two countries would be similar. This is not the case. Models predict that the US population
will continue to grow over the next 30 years at a rate of about 0.8% per year. In contrast, Germany's population
growth rate, currently at 0.3% yearly, is predicted to drop. In about 20 years, despite sustained positive
migration, the overall growth rate will become negative and the population of Germany will begin to decrease. (Note:
If not for positive migration today, the growth rate would be negative as deaths exceed births by about 1.15 per
1000 people.)
Source of the Data: US Census http://www.census.gov/
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