Age Structure and Age Pyramids

The age structure of a population is the distribution of people of various ages. It is a useful tool for social scientists, public health and health care experts, policy analysts, and policy-makers because it illustrates population trends like rates of births and deaths.

They have a host of social and economic implications in society, like understanding the resources that must be allocated for child care, schooling, and health care, and the familial and greater social implications of whether there are more children or elderly in society.

In graphic form, age structure is portrayed as an age pyramid that shows the youngest age cohort at the bottom, with each additional layer showing the next oldest cohort. Typically males are indicated on the left and females on the right.​

Concepts and Implications

Both age structure and age pyramids can take a variety of forms, depending on the birth and death trends within the population, as well as a host of other social factors.

They can be:

• stable: patterns of birth and death are unchanging over time
• stationary: both low birth and death rates (they slope gently inward and have a rounded top)
• expansive: slope dramatically inward and upward from the base, indicating that a population has both high birth and death rates
• constrictive: signaling low birth and death rates, and expanding outward from the base before sloping inward to achieve a rounded peak at the top

The current U.S. age structure and pyramid, shown, is a constrictive model, which is typical of developed countries where family planning practices are common and access to birth control is (ideally) easy, and where advanced medicine and treatments are commonly available through accessible and affordable health care (again, ideally.)

This pyramid shows us that the birth rate has slowed in recent years because we can see that there are more teens and young adults in the United States today than there are young children. (The birth rate is lower today than it was in the past.)

That the pyramid moves stably upward through age 59, then only gradually shrinks inward through age 69, and only gets really narrow after age 79 shows us that people are living long lives, which means that the death rate is low. Advances in medicine and elder care over the years have produced this effect in developed countries.

The U.S. age pyramid also shows us how birth rates have shifted over the years. The millennial generation is now the largest in the United States, but it is not so much larger than Generation X and the baby boomer generation, who are now in their 50s through 70s.

This means that while birth rates have increased a bit over time, more recently they have declined. However, the death rate has declined considerably, which is why the pyramid looks the way it does.

Many social scientists and health care experts are concerned about current population trends because this large population of teens, adults, and older adults are likely to have long lives, which will put a strain on an already underfunded Social Security system.

It is implications like this that make the age structure an important tool for social scientists and policymakers.

Updated by Nicki Lisa Cole, Ph.D.