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by George Masnick
Senior Research Fellow |
As the youngest of the
baby boom generation has now turned 50, there is much talk about the overall
aging of the U.S. population. But recently released Census Bureau population estimates for states and counties tell a more nuanced story about the
diversity in age structures in the U.S.
The census release notes that the oldest county (Sumter County-FL) has a
median age of 65.5, while the youngest (Madison-ID) has a median age of
23.1. Quite a difference! Other counties among the oldest include
Charlotte-FL (57.5), Alcona-MI (56.9), Llano-TX (56.9), and Jefferson-WA
(55.9). The five youngest counties also
include Radford City-VA (23.3), Chattahoochee-GA (23.9), and Harrisonburg
City-VA (24.2), and Utah County-UT (24.2).
The U.S. median age is 37.6.
We should perhaps not be
surprised that the county with the oldest population is in Florida, or that
Idaho and Utah, with their Mormon influences, should have the counties with the
youngest populations. But what is going on in Michigan, Texas, and Washington
counties to rank among the oldest, and in Georgia and Virginia to produce
places with the youngest populations?
There are three main
demographic factors that influence the age structure of a population:
- Domestic
migration patterns of both young adults and the elderly;
- Settlement patterns of
international immigrants;
- Levels of fertility of both the
immigrant and native born populations.
Differences in life expectancy could also influence age structures if
those differences are large. For states
and counties in the U.S., however, mortality differences are not sufficient to
affect differences in median age.
Places with net domestic
out-migration of young adults, and/or in-migration of elderly will be older
(younger if these migration patterns are reversed). Florida is a destination state for retirement
migration, as are North Carolina, Arizona, and other warm weather and low-tax
states in the south and west. Maine,
West Virginia and many rust belt and Great Plains states lose young adults on
net, so places in these states will also have an older age structure.
Immigrants tend to be
young and have higher fertility compared to the native-born, so places that are
immigrant destinations will be younger.
While states on the coasts and along our southern border still attract
the majority of immigrants, states in the interior have increasingly become
immigrant destinations as immigrant networks have spread beyond gateway
states.
Finally, fertility
levels are the primary determinant of a population’s age structure. When fertility is above replacement (more
children born than reproductive-age adults in a family) the population pyramid
is broader at the base, and median age is lower. The pyramid becomes more
mushroom-shaped when fertility is below replacement, and median age is higher.
When the population unit
is relatively small, as with most of the counties listed above, these
demographic factors can reinforce one another and create extreme values. For larger units of population, such as large
counties, metropolitan areas and states, differences should be less extreme,
but they can still be significant.
The population estimates
from which median ages were calculated contain detail by race/Hispanic origin
and sex, allowing us to examine the percent minority as a surrogate for the
influence of immigration and the boost to overall fertility levels that
immigrants and native-born minorities provide.
We can also look at a measure of recent total fertility by calculating
the ratio of children age 0-4 to women in the primary reproductive ages of
20-44. We cannot get a direct estimate
of net domestic migration by age group from the published population estimates,
however.
The table at the bottom of this post, constructed from the 2013 population estimates, ranks states on median age,
percent minority, and fertility. While
Florida has the county with the highest median age, the state as a whole is
only the 5th oldest, surpassed by Maine, Vermont, New Hampshire and
West Virginia. The lower the percentage
minority in a state, the higher the median age (Figure 1). The oldest states are those where young immigrants and
native-born minorities with higher fertility have not settled. Maine, Vermont, West Virginia and New Hampshire
rank the lowest on percent minority. In addition, the lower the total fertility
rate, the higher the median age (Figure
2). This second relationship is the stronger of the two that are graphed,
and the relationship holds fairly well across the entire range of fertility
(discounting DC as an outlier). The New
England states collectively are also near the bottom of the ranking on total
fertility.
Source: U.S. Census Bureau Population Estimates
Older states may be
destination states for retirement migration, but can also have lost young
adults from out-migration to states with bigger cities and more job
opportunities. For example, according to
the 2012 American Community Survey, Maine gained 27,500 residents from other states
during the previous year, but lost 38,500.
If most of the out-migration from Maine were young adults, the effect
would be to increase the median age.
The youngest states,
however, are more of a mixed bag. Utah’s
very high fertility level – the highest in the nation – is sufficient to secure
its ranking as the state with the youngest median age. Utah is not completely
lacking in diversity - its percent minority (20.3%) is just the 18th
lowest, but the total fertility rate in Utah is primarily driven by its
non-Hispanic white population’s high rate of childbearing. Alaska, the second youngest state, has a
large minority population (mostly native Alaskans), as well as levels of
fertility that are well above the U.S. average.
Its young ranking, however, is likely also determined by in-migration of
young adults to work in energy and nature oriented jobs, and out-migration of
the elderly to warmer climates. The
District of Columbia has achieved its ranking as the third youngest in all
likelihood because of in-migration of young adults to work in Washington for a
spell. These adults are largely single,
as suggested by DC’s extremely low fertility. But also contributing to DC’s
young age structure is the fact that the percent minority is the highest on the
mainland (64.2%). Texas is the 4th
youngest state, both due to its high percent minority (56%) and high
fertility. Texas has received consistent
growth from both immigrants and young domestic migrants in recent years. The final state among the top five youngest
is North Dakota, which has been the beneficiary of considerable in-migration of
young adults to work in the booming energy sector in the western part of the
state. North Dakota’s fertility rate is
also among the highest, attesting to the impact of a favorable economy on family
formation.
Geographic diversity in
age structures has direct implications for housing market dynamics. Places with younger age structures will
require new construction to house young adults, both now and in the
future. If the young age structure is
created by higher fertility, homes will need to be larger to accommodate larger
families. If the younger age is created
by in-migration of singles, a different housing mix is required, at least in
the short run.
Places with older
populations are expected to show a greater balance between supply and demand
for existing housing. An older age
structure brought about by low fertility and out-migration of young adults will
have less need for new construction.
This is especially true if the existing housing is located in places
where young adults want to and can afford to live. However, if future demand for existing
housing by young adults or older in-migrants is not there, older adults may be
less able to sell their homes, and we can expect higher rates of aging in
place. In these places there would be a greater need for modification and
upgrading of existing housing to help the elderly safely stay in their
homes. On the other hand, if the older
age structure is primarily the result of in-migration of retirees, and if that
in-migration is sustained, there will be more opportunities for new
construction and for the elderly to sell their homes in order to adjust their
housing needs.
Source: 2013 Census Bureau population estimates for states and counties.
*Fertility Rate is the number of children age 0-4 per 1000 women age 20-44.