A population pyramid illustrates the age and sex structure of a country’s population and may provide insights about political and social stability, as well as economic development. The population is distributed along the horizontal axis, with males shown on the left and females on the right. The male and female populations are broken down into 5-year age groups represented as horizontal bars along the vertical axis, with the youngest age groups at the bottom and the oldest at the top. The shape of the population pyramid gradually evolves over time based on fertility, mortality, and international migration trends.
Some distinctive types of population pyramids are:
- A youthful distribution has a broad base and narrow peak and is characterized by a high proportion of children and low proportion of the elderly. This population distribution results from high fertility, high mortality, low life expectancy, and high population growth. It is typical of developing countries where female education and contraceptive use are low and health care and sanitation are poor.
- A transitional distribution is caused by declining fertility and mortality rates, increasing life expectancy, and slowing population growth. The population has a larger proportion of working-age people relative to children and the elderly and produces a barrel-shaped pyramid, where the mid-section bulges and the base and top are narrower. The large proportion of working-age people can create a “demographic bonus” if it is educated and productively employed.
- A mature distribution has fairly balanced proportions of the population in the child, working-age, and elderly age groups and will gradually form an inverted triangle population pyramid as population growth continues to fall or ceases and the proportion of older people increases. Low fertility, low mortality, and high life expectancy - made possible by the availability of advanced healthcare, family planning, sanitation, and education - lead to aging populations in industrialized countries.