Age and Sex Structure

The shape of a society's population

Two of the most common variables demographers study are the age and sex (whether a person is male or female) of individuals within a given area. The Census Bureau has several types of age-related data that they report. For instance, they may list an area's median age, population age 18 years and over, and population age 65 and over. One reason for reporting these data are that policymakers and others are often concerned with a population's dependency ratio, which John Weeks defines as a ratio of the dependent population (typically those younger than 14 and older than 65) to people of working age (generally 15-64).

The Census Bureau also arranges age and sex data into age cohorts of several years (such as 0-4 years, 5-9 years, and so on). These cohorts can be used to construct a population pyramid, which is one of the most common visual representations of a location's age and sex structure. This figure consists of two sets of horizontal bars for each age cohort, one for males and one for females. These bars are then layered on top of each other. The resulting shape can tell a person much about what is happening in the population. One can see if there is a larger dependent population (with bulges at the top and/or bottom), an aging population (with a base narrower than the top), or a young population (with a wider base and narrower peak). An example of a population pyramid for Brookings, South Dakota is available.


The Data Center has completed the following materials concerning age and sex structure:

Data Summaries


Preliminary Populations Projections 2010-2035

For more detailed information about a population's age and sex structure, please call (605) 688-4899 or email us.