Reference to
the published article:
Gavrilov L.A., Heuveline
P.
“Aging of
Population.”
In: Paul Demeny and Geoffrey McNicoll
(Eds.)
The Encyclopedia of Population.
Aging of
population (also known as demographic
aging, and population aging) is a summary term for shifts in the age
distribution (i.e., age structure) of a population toward older
ages. A direct consequence of the ongoing global fertility
transition (decline) and of mortality decline at older ages,
population aging is expected to be among the most prominent global demographic
trends of the 21st century. Population aging is progressing rapidly
in many industrialized countries, but those developing countries whose fertility
declines began relatively early also are experiencing rapid increases in their
proportion of elderly people. This pattern is expected to continue over the next
few decades, eventually affecting the entire world. Population aging has
many important socio-economic and health consequences, including the increase in
the old-age dependency ratio. It presents challenges for public
health (concerns over possible bankruptcy of Medicare and related programs) as
well as for economic development (shrinking and aging of labor force, possible
bankruptcy of social security systems).
Defining and measuring population aging
As the study of population aging is often driven by a concern over
its burdening of retirement systems, the aging of population is often measured
by increases in the percentage of elderly people of retirement ages. The
definition of retirement ages may vary but a typical cutoff is 65 years, and
nowadays a society is considered relatively old when the fraction of the
population aged 65 and over exceeds 8-10%. By this standard, the percentage of
elderly people in the
A related measure of population aging is the elderly dependency
ratio (EDR): the number of individuals of retirement ages compared to the
number of those of working ages. For convenience, working ages may be assumed to
start at age 15, although increasing proportions of individuals pursue their
education beyond that age and remain, meanwhile, financially dependent, either
on the state or, increasingly, on their parents or bank managers. The ratio of
the elderly dependent population to the economically active (working) population
is also known as old-age dependency ratio, age-dependency ratio or
elderly dependency burden and is used to assess intergenerational
transfers, taxation policies, and saving behavior.
These indicators of population aging are mere head-count
ratios (HCR), that is, they simply relate the number of individuals in large
age categories. These indicators fail to take into account the age distribution
within these large categories, in particular among the elderly. When the
fertility and mortality trends responsible for population aging have been fairly
regular over time, the population growth is positively correlated with age
(i.e., the oldest age groups are growing fastest). This implies that if the
proportion of the population over age 65 is increasing, within that 65-and-over
population the proportion over, say, age 80 is also increasing. As health,
financial situation, and consumption patterns may vary greatly
between 65 year-olds and 80 year-olds, simple ratios conceal important
heterogeneity in the elderly population. Increasingly, attention is paid to the
"oldest olds" (typically age 80 and over). A long-time subject of curiosity, the
number of centenarians is growing even faster. Estimated at 180,000 worldwide in
2000, it could reach 1 million by 2030 (United Nations 2001).
The second class of indicators for
population aging is the group of statistical measures of location
(median, mean and modal ages of population). The median age -- the age at
which exactly half the population is older and another half is younger -- is
perhaps the most widely used indicator. For the year 2000, the median age in the
Since population aging refers to changes in the entire age
distribution, any single indicator might appear insufficient to measure it. The
age distribution of population is often very irregular, reflecting the scars of
the past events (wars, depression etc.), and it cannot be described just by one
number without significant loss of information. Were the age distribution to
change in a very irregular fashion over the age range, for instance, much
information would be lost by a single-index summary. Therefore, perhaps the most
adequate approach to study population aging is to explore the age distribution
through a set of percentiles, or graphically by analyzing the population
pyramids. Demographers commonly use population pyramids to describe both age
and sex distributions of populations. Youthful populations are represented by
pyramids with a broad base of young children and a narrow apex of older people,
while older populations are characterized by more uniform numbers of people in
the age categories.
To understand the demographic factors that cause population aging,
demographers often refer to stable populations (Preston et al. 2001).
This population model assumes that age-specific fertility and mortality rates
remain constant over time, and this results in a
population with an age distribution that stabilizes and eventually becomes time
invariant as well. Conversely, this theoretical model suggests that any change
in age structure, and population aging in particular, can only be caused by
changes in fertility and mortality rates. The influence of changes in fertility
rates on population aging is perhaps less intuitive than that of mortality
rates. Everything else constant, however, a fertility decline reduces the size
of the most recent birth cohorts relative to the previous birth cohorts, hence
reducing the size of the youngest age groups relative to that of the older
ones.
The effects of changes in mortality rates on population aging
appear more intuitive, but are in fact more ambiguous. If increases in the human
life span are correctly linked to population aging, reductions in
mortality rates do not necessarily contribute to population aging. More
specifically, mortality declines among infants, children and persons younger
than the population mean age tend to lower the population mean age. A
moment of thought suggests that indeed a reduction of neonatal mortality (i.e.,
death in the first month of life) adds individual at age 0 and should lead to
the same partial alleviation of population aging as an increase in
childbearing.
Population aging is thus related to the demographic transition,
that is the processes that lead a society from a demographic
regime characterized by high rates of fertility and mortality to another one
with lower fertility and mortality rates. In the course of this transition, the
age structure is subjected to different influences. In the typical sequence, the
transition begins with successes in preventing infectious and parasitic diseases
that benefit infants and young children most. The resulting improvement in life
expectancy at birth occurs while fertility tends to remain unchanged, thereby
producing large birth cohorts and an expanding proportion of children relative
to adults. Other things being equal, this initial decline in mortality generates
a younger population age structure.
After initial and sometimes very rapid gains in infant and child
mortality have been achieved, further mortality declines increasingly benefit
older ages and are eventually accompanied by fertility declines. Both changes
contribute to reverse the early effect of mortality decline on the age
structure, and this synergy is known as the double aging process. This
corresponds to the experience of most developed countries today, but further
decomposition suggest that their history of declining mortality is the dominant
factor in current aging (Preston, Himes and Eggers 1989). Mortality declines
continue in these countries and the decrease in mortality rates among the
oldest-old (85+ years) has actually accelerated since the 1950s (Gavrilov, Gavrilova, 1991). This
latest phase of mortality decline, which is concentrated in the older age
groups, is becoming an important determinant of population aging, particularly
among women.
The rate of population aging may also be modulated by
migration. Immigration usually slows down population aging (in
The current level and pace of population
aging vary widely by geographic region, and usually within regions as well, but
virtually all nations are now experiencing growth in their numbers of elderly
residents (for selected regions and countries, see Table 1). The
percentage of world population aged 65 and over only increased from 5.2% in 1950
to 6.9% in 2000. In
Table 1 About
Here
Population aging has the following notable features:
(1) The most rapid growth occurs in the oldest age groups – the
oldest-old (80+ or 85+ years) and centenarians (100+ years) in particular.
In other words, population aging is becoming “deeper” with preferential
accumulation of particularly old and frail people.
(2) Population aging is particularly rapid among women, resulting in
“feminization” of population aging (because of lower mortality rates among
women). For example, in the
(3) Another consequence of lower female mortality is the fact that
almost half of older women (45%) in 2000 were widows, thus living without
spousal support.
(4) Population aging also causes changes in living arrangements
resulting in increasing number of older people living alone (about 30% of all
non-institutionalized older persons in 2000 lived alone in the United
States).
(5) Since older persons have usually lower income and a higher
proportion of them are living below the poverty line, population aging is
associated with poverty, particularly in developing countries.
Projections of
population aging in the 21st century
Future
population aging will depend on future demographic trends, but most demographers
agree that the fertility and mortality changes that would be required to reverse
population aging in the coming decades are very unlikely. According to current
population forecasts, population aging in the first half of this century should
exceed that of the second half of the 20th century. For the world as
a whole, the elderly will grow from 6.9% of the population in 2000 to a
projected 19.3% in 2050 (Table 1). In other words, the world average should then
be higher than the current world record. All regions are expected to see an
increase, although it should be milder in some regions, such as
If population
aging is thus far from limited to the most developed regions, the countries of
these regions will likely continue to experience the highest proportions ever
known. The forecasts suggest 29.2% of elderly in the European population as a
whole, but more than 30% in a number of specific European countries, and perhaps
as much as 36.4% in
There is of
course some uncertainty with any forecast, but it is important to note that
previous population forecasts underestimated rather than overstated the current
pace of population aging. Before the 1980s the process of population aging
was considered as an exclusive consequence of fertility decline and it was
predicted that the pace of population aging would decrease after stabilization
of fertility rates at some low levels. Rapid decline in old-age mortality
observed in developed countries in the last decades of the 20th
century significantly accelerated population aging. Now the old-age
mortality trends are becoming the key demographic component in projecting the
size and composition of the world's future elderly population. Current and
future uncertainties about changing mortality may produce widely divergent
projections of the size of tomorrow's elderly population. For example, the
U.S. Census Bureau's middle-mortality series projection suggests that there will
be 14.3 million people aged 85 and over in the year 2040, while the
low-mortality (i.e., high life expectancy) series implies 16.8 million.
Alternative projections, using assumptions of lower death rates and higher life
expectancies, have produced estimates from 23.5 to 54 million people aged 85 and
over in 2040 in the United States (see Kinsella, Velkoff, 2001).
While population aging represents, in one sense, a success story for
mankind (massive survival to old ages has become possible), it also poses
profound challenges to public institutions that must adapt to a changing age
structure.
The first challenge is associated with dramatic increase in the older
retired population relative to the shrinking population of working ages, which
creates social and political pressures on social support systems. In most
developed countries, rapid population aging places a strong pressure on social
security programs. For example, the
Population aging is also a great challenge for the health care
systems. As nations age, the prevalence of disability, frailty, and
chronic diseases (Alzheimer’s disease, cancer, cardiovascular and cerebrovascular diseases, etc.) is expected to increase
dramatically. Some experts raise concerns that the mankind may become a
“global nursing home” (Eberstadt,
1997).
The aging of the population is indeed a global phenomenon that
requires international coordination of national and local actions. The
United Nations and other international organizations developed recommendations
intended to mitigate the adverse consequences of population aging. These
recommendations include reorganization of social security systems, changes in
labor, immigration and family policies, promotion active and healthy life
styles, and more cooperation between the governments in resolving socioeconomic
and political problems posed by population aging.
On the positive side, the health status of older people of a given
age is improving over time now, because more recent generations have a lower
disease load. Older people can live vigorous and active lives until a much
later age than in the past and if they're encouraged to be productive, they can
be economic contributors as well. Also the possibility should not be
excluded that current intensive biomedical anti-aging studies may help to extend
the healthy and productive period of human life in the future (de Grey et al.,
2002).
BIBLIOGRAPHY
Administration on Aging. 2001. A Profile of Older Americans: 2001.
De Grey, Aubrey D. N., Leonid Gavrilov, S. Jay Olshansky, L.
Stephen Coles, Richard G. Cutler, Michael Fossel, and
S. Mitchell Harman. 2002. “Antiaging technology and pseudoscience.”
Science, 296: 656-656.
Eberstadt, N.
1997. “World population
implosion?” Public Interest, 129:
3-22.
Gavrilov,
Leonid A., and Natalia S. Gavrilova. 1991. The
Biology of Life Span: A Quantitative Approach. NY, etc.: Harwood
Academic Publ..
Kinsella,
Kevin, and Victoria A. Velkoff. 2001. An Aging World: 2001. U. S. Census Bureau, Series
P95/01-1,
Lutz, Wolfgang, Warren Sanderson, and Sergei Scherbow. 2001. “The end of
world population growth.” Nature 412:
543-545.
United Nations 2001. World
population prospects: the 2000 revision.
Table 1. Dynamics of
Population Aging in the Modern World
Observed and
Forecasted Percentages of the Elderly (65+ years) in Selected Areas, Regions,
and Countries of the World: 1950, 2000 and 2050.
Major Area,
region and country |
1950 |
2000 |
2050 |
World |
5.2% |
6.9% |
19.3% |
Africa |
3.2% |
3.3% |
6.9% |
|
3.7% |
5.4% |
16.9% |
China |
4.5% |
6.9% |
22.7% |
India |
3.3% |
5.0% |
14.8% |
Japan |
4.9% |
17.2% |
36.4% |
Europe |
8.2% |
14.7% |
29.2% |
Italy |
8.3% |
18.1% |
35.9% |
Germany |
9.7% |
16.4% |
31.0% |
Sweden |
10.3% |
17.4% |
30.4% |
U.S.A. |
8.3% |
12.3% |
21.1% |
Source: United Nations
2001.
Mis en ligne le 02/04/2007 par Pierre Ratcliffe. Contact: (pratclif@free.fr)