The population pyramid is a method of visually presenting the population data of a given group. They're used to show the age and sex distribution in a population, and can be used to assess potential trends in the population in the future. These charts use a paired-bar chart, with two sets of data lined up next to each other, with the youngest members of the population listed at the bottom and the oldest at the top, forming a roughly triangular or pyramid shape. Three varieties of these charts are currently in use.
Expansive pyramids typically represent populations with high fertility rates and below-average life expectancies. They show larger numbers or percentages of younger age groups, and each successively older group is represented by a smaller bar. This pyramid type is typically applied to many Third World countries, and areas of Latin America.
Much the opposite of expansive pyramids, constrictive pyramids show lower numbers or percentages for younger people and larger numbers for adults than do expansive pyramids. These pyramids typically reflect populations with a large number of adults and a longer average life expectancy, like those found in the United States and some European countries.
Stationary pyramids are the middle ground, displaying relatively equal numbers and percentages for almost all age groups involved. These models usually reflect nations with a very even age/sex distribution. Several European countries fall under this population model.