An age-sex pyramid graphically represents the distribution of a population by age and sex. In many ways, an age-sex pyramid is a summation of a population's history, reflecting long-term trends in the birth and death rates and even short-term changes resulting from baby booms and busts, wars, and epidemics. Because of differences in scale, the age-sex pyramids are not always directly comparable in terms of absolute population sizes. This tool allows you to view the pyramids over time, using the year tab under the figure.
Immigrant population: The shape of the age-sex pyramid of the immigrant population is very different from that of native-born population. There are several reasons for this. First, many migrants leave their home countries to find work abroad, so a high number of immigrants in the economically active ages of 20 to 54 is not uncommon. As can be seen in this age-sex pyramid, the majority of immigrants in 2011 were adults between the ages of 20 and 54. Second, in general, children rarely migrate by themselves and adult immigrants tend to migrate with few or no children. This helps explain the relatively small amount of people age 20 and younger. There is another reason, however: the children born in the United States to adult immigrants are considered native born and are not included in this age-sex pyramid. Third, people are less likely to migrate at older ages. In the foreign-born age-sex pyramid, there are clearly fewer people in the retirement-age groups (age 55 and over). This low number of older immigrants also has to do with many immigrants returning home for retirement and the death of older settled immigrants. All of these factors give the foreign-born age-sex pyramid its "diamond shape," making it significantly different from the native population pyramid. There were about 40.4 million immigrants residing in the United States in 2011.
Native-born population: The most striking feature of the native age-sex pyramid is the “baby boom,” the increase in the number of people born after World War II between 1946 and 1964. In 2011, the baby boomers were between age 47 and 65, as can be seen by the relatively large size of those age groups in the age-sex pyramid. The years 1965 to about 1977 are often referred to as the “baby bust” because of the smaller number of children born then. The “baby bust” generation was between the ages of 34 and 46 in 2011, as can be seen by the constriction of those age groups in the age-sex pyramid. The “echo boom” or “boomlet” occurred between 1977 and about 1988, when many of the baby boomers had children who, in 2011, were between 23 and 34. In the older age groups, there are far fewer males than females. In most populations, women live longer than men. The dearth of males age 70 and older also reflects deaths during World War II.
Migration Policy Institute tabulation of data from the U.S. Census Bureau's 2011 American Community Survey and 1970, 1980, 1990, and 2000 Census decennial data accessed from Steven Ruggles, J. Trent Alexander, Katie Genadek, Ronald Goeken, Matthew B. Schroeder, and Matthew Sobek. Integrated Public Use Microdata Series: Version 5.0 [Machine-readable database]. Minneapolis: University of Minnesota, 2010.