Below are age-sex pyramids for the total, native, and immigrant populations (including the five largest immigrant groups) in the United States for 2000.
One of the most important demographic characteristics of any population is how it is distributed by age and sex. An age-sex pyramid, also known as a population pyramid, graphically represents this distribution. 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.
Within these age-sex pyramids, the populations are divided by sex, and females are represented on the right of the graph and males on the left. The number of males and females are divided into five-year age categories.
Because of differences in scale, the age-sex pyramids are not always directly comparable. While these age-sex pyramids can be used to compare the characteristics of different populations, such as the proportion under age 15, the different scales used can make it difficult to compare the relative size of the populations. A population pyramid that is graphically presented to appear similar in size to others may or may not represent populations similar in numeric size.