One of the tools that demographers use to understand populations is the age structure diagram. This diagram shows the distribution by ages of females and males within a certain population in graphic form. Figure $$\PageIndex{1}$$ shows a diagram for the United States population. In this diagram, the ages are arranged so that age ranges are grouped together, for example: 0 – 4 years, 5 – 9 years, and so on. The population of each group is represented as a bar extending from a central vertical line, with the length of each bar dependent upon the total population for that particular group. The centerline separates the females from the males. The female and male populations for each group are represented by the distance from the centerline, with females on the right and males on the left.
The following age structure diagrams (Figure $$\PageIndex{2}$$) show the United States in 2005 and 2010. Please note the slightly different x-axes scale on these diagrams compared to the 2000 diagram above (Figure $$\PageIndex{1}$$). You can see the ageing group of baby boomers move upward when you compare these 3 age structure diagrams. There are also more elderly (80+) individuals, especially women, in 2005 and 2010.