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A Century of Population Change in the Age and Sex Composition of the Nation

September 12, 2013

An important tool for analyzing the age and sex composition of the population is the age-sex pyramid. This age-sex pyramid shows the number of males (on the left) and number of females (on the right) by single years of age.

A century of population change is shown so that population shifts in the shape of the pyramid can be more easily assessed at each point in time. The shape of the pyramid can give important information about the population’s composition. For example, the shapes of the pyramids over the latter part of the 20th century are more typical of developed countries: these feature a broad base with a middle section of nearly the same dimension that then gradually taper off at the oldest ages to a point at the top. The lopsided point at the top of the pyramid indicates differences in the number of males and females at older ages. This is a result of differences in mortality for men and women, where women tend to live longer than men. The Baby Boomer population can be seen in the pyramid as a bulge lasting from 1946 to 1964. The Baby Boom includes people born from mid-1946 to 1964. The Baby Boom is distinguished by a dramatic increase in birth rates following World War II and constitutes one of the largest generations in U.S. history.

SOURCE: Annual estimates of population by single year of age and sex 1900-2000
NOTE: The “tabletops” seen at 75 and 85 reflect data aggregation at the upper end of the range in early decades. National population data for the years 1900 to 1949 exclude the population residing in Alaska and Hawaii. Data for the years 1940 to 1979 cover the resident population plus Armed Forces overseas and for all other years cover only the resident population. The absence of the Armed Forces overseas population is visible in the young male population in 1917-1919. For more information about the annual estimates see the Population Estimates Program website at www.census.gov/programs-surveys/popest/data.html. To download the historical dataset used here see:
1900-1999: www.census.gov/data/tables/time-series/demo/popest/pre-1980-national.html
1980-1989: www.census.gov/data/datasets/time-series/demo/popest/1980s-national.html
1990-2000: www.census.gov/data/datasets/time-series/demo/popest/intercensal-1990-2000-national.html