Median age is one way to represent an area’s age distribution. Another way is using population pyramids providing the age and sex structure.
Population pyramids in the data visualization below are commonly used in demographic research because they provide a condensed but powerful illustration of a population’s age distribution by sex.
A population pyramid is essentially two bar charts, one for the male population on the left and the other for the female population on the right. The base of the pyramid, or bottom of the chart, has the youngest population (ages 0-4) and the top has the oldest (ages 85 and older).
The pyramid can reveal differences in age structure between two counties that have the same median age. For example, the median age in both Leon County, Florida, and Davis County, Utah, was 32.1 years in 2021. Their population pyramids, however, show differences in their age structures.
The relatively low median age in Leon County, Florida, was primarily due to a large population between the ages of 20 and 24, while in Davis County, Utah, the largest age group was the population ages 10 to 14.
Similarly in California, Orange County and Santa Cruz County both had a median age of 39.1 in 2021, but the underlying age structure in each county was different.
Orange County had comparably sized age groups that become smaller at older ages with the largest segment of the county’s population in ages 30 to 34. In contrast, Santa Cruz County had the largest share of its population in the younger age group of 20 to 24.
The visualization provides estimates for July 1, 2020, and July 1, 2021. The panel on the bottom-right shows the selected county’s population by race and Hispanic origin. The race groups shown are for race alone or in combination.
Because some people identify as multiracial and indicate more than one race on their census form, the race numbers add up to more than the total population for the county. The visualization also shows estimates for the Hispanic population that can be of any race.
When considering data by race, it is important to note that the race categories used for the Population Estimates Program differ from the decennial census.
The 2020 Census included the category “Some Other Race,” but the input data used to produce the population estimates do not have that category.
Responses of “Some Other Race” from the decennial census are reclassified into the five racial categories included in the 1997 Office of Management and Budget’s standards, either alone or in combination with another race category. This process produces a “Modified Race” file that allows data users to connect the two.
In addition, the race and Hispanic origin distributions in the “blended base” used for the Vintage 2021 estimates were developed using data from the Vintage 2020 estimates. Vintage 2020 used the 2010 Census as the estimates base.
Improvements in how the Census Bureau collected and processed race information for the 2020 Census led to notable differences in the racial and ethnic composition of the population compared to what was measured in the 2010 Census.
The 2020 Census results revealed our country is much more multiracial and much more diverse than in previous decades. This also contributes to differences between the population estimates for specific race categories shown and those published from the 2020 Census.
For these reasons, comparisons between the estimates by race released today and the results of the 2020 Census by race will not be valid. For insight into the complex racial and ethnic diversity and composition of the U.S. population we advise using the 2020 Census race and ethnicity statistics.
Work is underway to develop a “modified race” variable for the 2020 Census data. This will allow us to use race and Hispanic origin information from the 2020 Census to produce the population estimates and will also enable us to make meaningful comparisons between the two sources. In the meantime, for more information see Using Demographic Benchmarks to Help Evaluate 2020 Census Results.