Ł u k a s z J u r e k
Wroclaw University of Economics, Poland
THE GRAYING WORLD: SOCIO-ECONOMICAL CAUSES
AND CONSEQUENCES OF GLOBAL AGING
ABSTRACT
Th e article presents the general causes and consequences of one of the most important issues of the modern world – population aging. In the fi rst part, population aging will be presented as a global process. Th en, two causes – 1) fertility decline and 2) lengthening life expectancy – changing the shape of the population pyramid will be discussed. Finally, the paper will present the most important socio-economical consequences of population aging: challenges for social security system, changes in the labor market, economic slow-down, etc.
Key words:
global aging, models of population, demographic transformation, society, labor market
1. Introduction
Th roughout every past century, demographic issues did not absorb scientists. Th e size and structure of population were stable, so research problems were strongly limited. Th at situation changed in the 18th century, when the global population
at 1 billion. 126 years later that fi gure hit the 2 billion mark; 30 years aft er that, 3 billion; and aft er another 15 years had gone by the global population was 4 bil-lion. At some point, the global population was doubling during only one genera-tion (35 years). Based on these changes, scientists projected (using extrapolagenera-tion) a demographic explosion that would lead to catastrophic over-population.
We now know that those catastrophic projections will not come to fruition. Th e global population will rise until the middle of the 21st century, aft er which all
countries will fi nish the so-called demographic transition. But population will not stabilize. Today a new demographic threat has emerged – population aging and depopulation.
Th e problem of an aging population is becoming a more widely discussed issue. Changes in the age structure are commonly considered to be one of the most impor-tant and the most challenging social, economic, and political problems/challenges. Nowadays, the demographic situation is very well researched. We know a lot about the scale and intensity of population aging. Unfortunately, its consequences are still insuffi ciently recognized. Th ere is a serious lack of knowledge about the implications of demographic change. How will it aff ect a society and its economy? In this article we will try to fi nd answer to the question. Th e research objective is to present the most important socio-economic causes and consequences of global aging.
2. Population aging as a global process
In the demography, aging is the change in a population’s age structure, which relies on a rise in the proportion (share) of elderly. A population is old when the propor-tion of elderly will cross some specifi c value. Th ere are many scales of population’s age spans, but the most common is that presented by the UN. According to that scale, when the share of elderly (65+) is lower than 4%, the population is young; when it is between 4% and 7%, the population is mature; and when it is higher than 7%, the population is old.
Th e share of elderly is not a suffi cient tool to analyze the level of advancement in population aging. Population pyramids, which are specifi c diagrams that illustrate the distribution of various age groups in a population, seem to be better tools.
At the turn of the 19th century, Swedish demographer G. Sundbärg distinguished
three model-types of population pyramid: expansive, stationary and constrictive. Expansive shape of population pyramid means, that population is young, station-ary one means, that population is mature, and constrictive shape is typical for old populations.
Figure 1. Model-types of population pyramid by Gustav Sundbärg
Source: E. Rosset, Proces starzenia się ludności. Studium demografi czne [Aging Process of Population. Th e Demographic Study], Warszawa 1959, p. 60.
Population aging is a relatively new issue. Th roughout most of human history, the share of elderly was stable and very low (usually did not exceed 2% or 3%). Th is situation changed radically at the middle of the 20th century, when this share
start-ed to rapidly rise.
Population aging is a global process. Of course, the level of its advancement is not the same everywhere. In more developed regions, the share of elderly is much higher (almost three times) than in less developed regions. Th is means that the scale of population aging depends on socio-economical circumstances. A high level of development is linked with a high quality of life, which is in turn linked to a higher probability to live longer. Th at results in an increase in the amount of elderly in a population. On the other side, there is an inverse correlation between the level of development and fertility. Fertility in highly developed countries is usually low. Th at increases the share (proportion) of elderly in relation to other cohorts.
In 1950, there were 130 million people aged 65 or older in the world and their share of population was 5.2%. Global population became old (according to the scale presented by the UN) at the beginning of the 21st century. Today, nearly half
a billion old people live all over the world. Demographic projections show that in the middle of the 21st century there will be 1.5 billion of them. Th at is an increase
of 1100% in the period of one century.
Th e process of demographic aging will quicken in the immediate decades. Be-tween 2010 – 2020, people born aft er the Second World War (the so-called “baby boomers”) will become old, and between 2040 and 2050 the same thing will hap-pen to their children. To illustrate the changes in the population age structure unique phrases and terminology are used, including, for example, “a demograph-ic agequake” or “a new international population order”.
age expansive stationery constrictive
50 15 0 age 50 15 0
Figure 2. Share of elderly (65+) – world, more and less developed regions
Source: World Population Prospects: Th e 2006 Revision and World Urbanization Prospects: Th e 2005 Revision, Population Divisions of the Department and Social Aff airs of the
Unit-ed Nations Secretariat, http://esa.un.org/unpp [access: 20.04.2011].
Figure 3. Population pyramids (world: 1950, 2000, 2050)
Source: World Population Prospects…, op.cit.
Th e oldest countries are located (besides Japan) primarily in Europe (in this context term “Th e Old Continent” takes a brand new meaning). In Eastern Europe, the demographic changes began later than in western countries, but now those same changes are accelerating. Poland is one of those countries that are aging very quickly. Demographic projections prepared by Eurostat show that in 2060 Poland will be the oldest country in European Union. At that time, the proportion of elderly (65+) will surpass 36% and will amount to 11 million1.
1 K. Giannakouris, Ageing Characterises the Demographic Perspectives of the European Societies,
“Eurostat Statistics in Focus” 2008, Vol. 72, p. 10.
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 30 15 20 25 10 5 0
world more developed regions less developed regions
–200000 0 200000 –500000 0 500000 –500000 0 500000
Figure 4. Population pyramids (more developed regions: 1950, 2000, 2050)
Source: World Population Prospects…, op.cit.
Currently, Asia has the fastest aging process of the world’s regions. It mainly concerns the so-called Asian Tigers (or Asian Dragons), as well as Japan and Chi-na. In Hong Kong, in the period of one century (1950 – 2050), the proportion of elderly will rise nearly 50-fold. In Singapore, the amount of old people will double with every decade. In the middle of the 21st century, China will have almost half
a billion elderly, or one-fourth of all old people living in the world that time. Japan in 2050 will be absolutely the oldest country, share of people aged 65 and more will be 37,8%, share of people aged 60 and more will be 44,2%, and the median age will be 55 years.
3. Causes of global aging
Th ere are two proximate causes of global aging. Th e fi rst is a decrease in fertility (this causes aging “from the bottom of population pyramid”). Th e second is the lengthening life expectancy (this causes aging “from the top of population pyra-mid”). Consequently, an unprecedented and radical change of demographic order is being observed – population pyramid is overturning and gets an inverse shape.
Fertility rates in more developed regions are low (below replacement level; that is 2.1 children per couple). In some countries its value is extremely low (for exam-ple in Germany, Japan, Post-soviet Countries, and the Asian Tigers). Inverse cor-relation between fertility and level of socio-economical development can be seen as a paradox. Rich countries that can aff ord having many children have lower fertility rates, whereas in poor and less-developed countries fertility rates are at very high levels.
According to Dutch demographer D. van de Kaa, a decline in fertility below replacement level means those populations have reached a new stage in their
de-–50000 0 50000 –50000 0 50000 –50000 0 50000
mographic development – a second demographic transition2. In the most developed
countries, this second demographic transition began in the 1960s. At that time, the methods and techniques of contraception (pills, surgery) were developed. Th e knowledge of and prevalence of contraception created a separation between sexual activity and procreation. Families gained full control over fertility. Th e number of children born in a family became a result of conscious and rational decision.
Figure 5. Total fertility rate (TFR) in chosen countries
Source: World Population Prospects…, op.cit.
Decisions about how many children to have are determined by a large number of sundry factors, which can be divided into three main groups: (a) socio-cultural, (b) political and, (c) economical.
a) Socio-cultural factors are related to social values, roles, preferences, sanc-tions, and institutions. Modern social changes substantially aff ect fertility decline. Th ose changes are: emancipation, weakening traditional institutions of family and maternity, individualization of life and hedonistic trends, anti-fertility social val-ues, and laicization.
2 D. van de Kaa, Europe’s Second Demographic Transition, “Population Bulletin” 1987, No. 1,
Vol. 42, p.1 – 59.
1950–19551955–19601960–19651965–19701970–19751975–19801980–19851985–19901990–19951995–20002000–20052005–2010
Germany Poland Ukraine Singapore Japan
0 1 2 3 4 5 6 7
Contraception created the foundation for the sexual revolution, which dimin-ished the natural and moral sanctions against promiscuity. On this ground, wom-en’s liberation movements were born. Th ese movements oft en questioned the tra-ditional institutions of marriage and family. Many feminists compared wifehood to prostitution and family to prison3. Th ese movements caused the social role of
women to change. For example, women started studying faculties that were ear-lier almost completely “reserved” for men. Concurrently, the development of the service industry increased the demand for women in the working force. Th is cre-ated the opportunity for women to work in new fi elds, including jurisdiction, mass media, higher education, business, and public service. Th e increased participation of women as mothers and wives (“the primary caregivers of families”) became businesswomen is one of those factors that strongly aff ected the decline in fertility, but the extent of this eff ect is not fully understood. Th ere are countries, such as Sweden or the United States, where woman’s labor does not exclude maternity.
Another important factor that also aff ects the decline in fertility is the transfor-mation of the family, in which the modern (nuclear) family replaced the tradi-tional family. Furthermore, the gradual, yet deepening, deinstitutradi-tionalization of family has also aff ected fertility. In eastern countries, marriage rates have decline while the number of failed marriages has increased. As a result, new forms of fam-ily life appeared, including cohabitation, homosexual relationships, childless rela-tionships (so called DINKs – double income no kids; or LAT – living apart to-gether), and singles.
Th e individualization of life and hedonistic trends also aff ect fertility rates. Nowadays, childbearing is oft en seen as a barrier to professional fulfi llment and to personal freedom. Modern individuals try to avoid any obligations, even famil-ial obligations. Th e time devoted to childcare competes with leisure time and amenities. Moreover, pop culture endorses “anti-fertility” values. Nowadays, mar-riage and maternity have simply stopped being trendy.
Another thing is the laicization of society. German research has proven that there is a strict relationship between religious practices and fertility rate4. People
that more oft en attend a church, usually have more children. Modern societies, however, are being infl uenced less and less by religious institutions and religious practices are becoming less common. On that ground, we can conclude that laici-zation of society cause fertility decline.
3 P. Buchanan, Śmierć Zachodu [Death of the West], Wrocław 2005, p. 36 – 70. 4 M. Blume, Homo Religious, “Gehirn & Geist” 2009, No. 4, p. 34.
b) Political factors are related to public activity in the fi eld of demographic issues. Such public activity can be direct (aimed at the family) or indirect (aimed at the family’s surroundings). Direct infl uence on fertility can be had by adminis-trative tools (such as regulations on accessibility of birth control pills or legal as-pects of abortion); social tools (such as welfare benefi ts); educative tools (such as creating social attitudes and values). Indirect infl uence on fertility relates to factors such as the housing situation, labor market, and institutional care for children.
Authorities in countries that wrestle with the problem of population aging and depopulation declare advanced actions to increase fertility rate. Unfortunately, those actions are primarily of a direct character in spite of the fact that indirect actions seems to be much more eff ective. It results from simple rule, that control-ling administrative tolls is much easier for authorities than creating child-friendly environment.
c) Economic factors are related to income and prices. Th e decision about whether or not to have a baby is in fact an economic choice. G.S. Becker presented the economics of fertility theory for the fi rst time at the beginning of the 1960s5.
It assumed, that the total fertility rate could be analyzed as a global demand for children, which is a function of income, price, and tastes.
A decrease in fertility can be analyzed as a change in the global demand for children. Th is decrease is caused by the escalation of price (net cost) of children; that is an increase in the costs of raising children and a decrease in the benefi ts of having children.
An increase in the costs of raising children results from 1) the process of ur-banization and 2) the improvement of women’s educational background. Th e proc-ess of urbanization increases current expenses. In large urban agglomerations, there are higher costs of accommodation, which has to be given to children, and also more expansive fundamental foodstuff such as milk or vegetables. In turn, the improvement in women’s educational standing increases the opportunity cost of time. A mother taking care of children is aware of the lost income that could be earned if she used that time to pursue vocational tasks.
A decrease in the benefi ts of having children results from 1) economic chang-es and 2) the development of the welfare state. Economic transformation (in terms of production), which result in the disappearance of family businesses, reduces the monetary value of having children. Before the industrial age (and also later on agricultural areas), a family was a primary productive union
(mi-5 G.S. Becker, Ekonomiczna teoria zachowań ludzkich [Th e Economic Approach to Human
croenterprise), in which every member had some tasks to do. Children, from a very young age, played very important roles. Sons were responsible for tough manual labor while daughters were responsible for maintaining the household. Th eir work had a real value. Th is traditional economic function of a family grad-ually diminished in modern times. Th at is why the role of off spring as a labor force was strongly limited.
In traditional societies, a family was the fi rst and the most obvious care institu-tion. Th e quality of life during old age was determined by the quantity and quality of family relations. Children were some kind of investment in the future for their parents. Having children reduced the probability that the parent would be left alone in case of sickness or dependency. Nowadays, the role of the family as an institution that guarantees social security has been reduced dramatically. It is linked with the development of the welfare state. Public institutions, such as a so-cial security system, have taken over tasks that were traditionally attributable to families, thereby replacing family members (mainly children).
Figure 6. Live expectancy at birth (world, more and less developed regions)
Source: World Population Prospects…, op.cit.
Th e second proximate cause of global aging is the increase in life expectancy. In the past, life expectancy was relatively very short. An individual in a primor-dial society lived, on average, 20 years. In Ancient Rome, this value was not much higher (23 years). In the 16th century, the life expectancy was about 30 years. In the
19th century, it was more than 40 years. Nowadays, the average lifetime is
lengthen-ing intensively. Only durlengthen-ing the 20th century, in the most developed countries, did
1950–19551955–19601960–19651965–19701970–19751975–19801980–19851985–19901990–19951995–20002000–20052005–20102010–20152015–20202020–20252025–20302030–20352035–20402040–20452045–2050
world more developed regions less developed regions 30 40 50 60 70 80 90
life expectancy increase almost two-fold, and reach the unprecedented level of 80 years.
Currently, girls born in European Union have a 50% (boys 30%) chance to live up to the age of 100. Reaching the status of becoming a centenarian is a psycho-logical barrier of age, which upon being reached is seen in many cultures as a great accomplishment. “100 years” is one of the best wishes. It is because relatively not so long ago the probability of reaching such an advanced age was minimal.
Lengthening life expectancy is a great success of our civilization. It is a sign of: – progress in medicine that reduces a new-born child’s mortality and prevents
pestilences, – lack of wars,
– limitation of hunger,
– development of social security, – health-conscious attitudes, – rising quality of life.
How long we will live in the future? It is hard to predict. Nowadays, two years are added to the life expectancy in the most developed regions every decade. Pro-viding that this tendency continues, by the end of the 21st century, people will live
(statistically) 100 years. But, popular British futurist R. Hammond predicts that in the near future lengthening will speed up. It will be an eff ect of changes in medical technology, especially those concerning genetic modifi cation and development of so-called anti-aging medicine6.
4. Socio-economical consequences of population aging
Population aging is a quite new phenomenon and it will intensify in the immediate future. Nowadays, we are not able to precisely predict what kind of consequences it will cause, but we can be sure that all economic and social systems will change (more or less). As early as 1948, the Royal Commission on Population in the Unit-ed Kingdom said that, “It seems that a society in which the proportion of young people is diminishing will become dangerously unprogressive, falling behind oth-er communities not only in technical effi ciency and economic welfare, but in intel-lectual and artistic achievements as well”7.
6 R. Hammond, Th e World in 2030, Paris 2007, p. 291.
Figure 7. Dependency ratio in more developed regions (total, child, old-age)
Source: E. Rosset, op.cit.
Demographic transformation aff ects the demographic dependency ratio. In other words, the larger, inactive group (children and elderly) is a burden for the economically active population. But as we can see in fi gure seven, increasing the value of dependency ratio is not as important as changing its internal composition. At the middle of the 20th century, the working population was burdened mainly by
children and less so by the elderly. In the middle of the 21st century, those
propor-tions will be inversed.
Th e changing internal composition of the dependency ratio has a substantial infl uence on public fi nances. Old people are a relatively bigger burden for a welfare state than children since the social costs of supporting old people are much high-er than the social costs of supporting children. It is estimated, that govhigh-ernment expenditures are three times higher for the elderly than they are for children8. Th is
is because welfare benefi ts for elderly (such as pensions, medical services, and long-term care) are more expensive than those for children. Moreover, there are diff erent methods of fi nancing specifi c welfare benefi ts provided to elderly; they are funded primarily through the contributions of the members of the welfare scheme, whereas the nature of supporting children is less social and families bear the majority of the costs.
8 R. Clark, J. Kreps, J. Spengler, Economics of Aging: A Survey, “Journal of Economic
Litera-ture” 1978, No. 3, Vol. 16, p. 922.
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050
Total Child Old-age
80 70 60 50 40 30 20 10 0
All societies must accept their responsibility to support the dependent elderly. Th e working population should help satisfy the needs of people who are unable to work anymore because of old age. When populations are aging, welfare states need to increase public expenditures. Th e increased size of government spending re-quires that public revenue increase. It is an obvious relation.
Public revenue can generally be boosted by a tax rate increase or by debt in-crease (increasing taxes is a method of current settling liabilities while increasing government debt is transferring current liabilities on future generations). We can say that aging populations cause a “graying of public funds” and demographic fi scalism development.
Demographic fi scalism development results in a tax wedge. Employers need to bear high labor costs, which consist of wages and employment taxes. For employ-ees, on the other hand, the work in low paid. It also means higher costs of produc-tion and, consequently, higher prices of produced goods. In this situaproduc-tion, entre-preneurs try to move production and to allocate their activity in more fi scally friendly regions. In the age of globalization, it is common practice as a way of re-ducing costs and raising benefi ts.
Goods produced in old populations are relatively more expensive and not com-petitive on the global market. Th is lack of cost-competitiveness can be limited by a high quality, high effi ciency, and hi-tech solution to production and distribution. However, it requires investing in education as well as research and development. Old populations will probably have diff erent priorities. Th ey will be not able to aff ord such expenses. In the long term, it will weaken an enterprise’s innovativeness and limit economic growth.
Economic growth is linked with the population’s age-structure because young and old people diff er in enterprising attitudes and behavior. Young people are usu-ally linked with a high energy and willingness to undertake the market-risks. Th us, higher investments and new business ventures are features typical of economies with young population. Whereas, in old populations, consumption and risk-aver-sion are the dominate preferences9.
Population aging aff ects the labor market. Th ere are two main changes in that fi eld. First of all, the increasing proportion of elderly causes a reduction in the labor force supply. Secondly, population aging results in labor force aging.
9 Ł. Jurek, Proces demografi cznego starzenia jako istotne wyzwanie dla społeczeństwa polskiego
w XXI wieku [Th e Process of Demographic Ageing as a Signifi cant Challenge for the Polish Society in the 21st Century] [in:] Współczesne społeczeństwa – nadzieje i zagrożenia [Contemporary
Labor force aging means that the “share of old elements accreting in the eco-nomically active group”10. Th ose “old elements” can be linked with a category of
immobile workers – those aged 45 and older – that are not usually disposed to changing their work in the territorial or occupational aspect. Increasing the share of that group may cause serious perturbations in the economy, because it wends towards a worse allocation of labor force.
A shrinking labor force may cause a defi cit of workers, which will reduce poten-tial economic growth. Th ere are two possible solutions in that situation: increasing the retirement age or using migration movements. Neither of these solutions is fully acceptable by society. Changing retirement settings always antagonize because people stubbornly resist giving up their privileges. Using immigrants to battle an insuffi cient number of workers also causes social and political problems. Serious concerns about national identity may also arise. Some authors even predict that, in the long term, original citizens will become a minority in their own country11.
Population aging determines changes in social security system. Many econo-mists (i.e. P. Samuelson or M. Friedman) claim that during demographic transition the construction of PAYG (pay as you go) pension scheme resembles that of Pon-zi scheme (e.g. there are more givers (young people) than benefi ciaries (elderly)). It is effi cient in progressive populations that are young and growing, so each next generation is more numerous than previous one. In such a situation, there are al-ways more and more people that can pay to maintain the system. Of course, when O. von Bismarck created the PAYG pension scheme at the end of the 19th century,
there was a prevalent belief (based on Malthus Th eory of Population Growth) that an increase in prosperity caused population growth. Th us, there were no threats about the balance of the system. Th e ensuing “population explosion” over the next few decades only ensured that belief. But, unfortunately, the demographic situation radically changed. Th e actual number of givers (young people) declined whereas number of benefi ciaries (elderly) increased. Based on those trends, we can predict that the pension system will fail like every other Ponzi game without “fresh blood”.
In the PAYG system, population aging requires a tax rate increase and/or a de-crease in replacement rate. Decreasing the replacement rate means the impoverish-ment of the elderly population. Increasing tax rate may antagonize society and create a background to an intergenerational war. At some point, an
intergenera-10 E. Rosset, Proces starzenia się ludności [Aging Process of Population. Th e Demographic Study],
Warszawa 1959, p. 417.
11 W. Laqueur, Ostatnie dni Europy. Epitafi um dla Starego Kontynentu [Th e Last Days of Europe.
tional battle for the allocation of resources will probably begin. According to L.C. Th urow, the future defi nition of class struggle will be changed. It will be no longer be a confl ict between the poor and rich, but it will become a confl ict be-tween the young and old12.
A very important fi eld that is strongly aff ected by population aging is long-term care. First of all, the lengthening life expectancy increases the number of very old people, who are usually functionally dependent (unable to do fundamental ac-tivities of daily living by themselves). Th e risk of dependency increases with age. Th e higher the age category is, the higher the demand for long-term care is. On the other hand, population aging causes changes in the numerous relationships between potential caregivers (usually mature women, who have already stopped taking care of their own children) and the dependent elderly. Family (informal) caregivers oft en cannot, do not want to, or just do not know how to help their old-est members.
5. Conclusions
Global aging is a progressive process. Th e increasing share of elderly can be seen as an improvement in the quality of life. On the other hand, this progressive proc-ess brings many specifi c and complex problems. Th at is why population aging is seen to be one of the most important social, economic, and political issues of to-day’s world.
Th e welfare state, society, and economy need to face demographic challenges. Fortunately, demographic projections can provide informative insights about the future situation far in advance. Changes in the age structure do not appear “over-night,” but arise over the course of many decades. Th is allows societies, economies, and governments to make informed decisions, which should reduce the negative consequences of population aging.
Population aging will change (more or less) all social and economical systems. It will aff ect the social security system, economic growth, international competi-tiveness, and social cohesion in particular.
R E F E R E N C E S :
Becker G.S., Ekonomiczna teoria zachowań ludzkich [Th e Economic Approach to Human Behaviour], Warszawa 1990.
Blume M., Homo religious, “Gehirn & Geist” 2009, No. 4.
Buchanan P., Śmierć Zachodu [Death of the West], Wrocław 2005.
Clark R., Kreps J., Spengler J., Economics of Aging: A Survey, “Journal of Economic Litera-ture” 1978, No. 3, Vol. 16.
Giannakouris K., Ageing Characterises the Demographic Perspectives of the European
Soci-eties, “Eurostat Statistics in Focus” 2008, Vol. 72.
Hammond R., Th e World in 2030, Paris 2007.
Jurek Ł., Proces demografi cznego starzenia jako istotne wyzwanie dla społeczeństwa polskiego
w XXI wieku [Th e Process of Demographic Ageing as a Signifi cant Challenge for the Polish Society in the 21st Century] [in:] Współczesne społeczeństwa – nadzieje
i zagrożenia [Contemporary Societies – Hopes and Th reats], O. Kowalczyk (ed.), Wrocław 2010.
Kaa D. van de, Europe’s Second Demographic Transition, “Population Bulletin” 1987, No. 1, Vol. 42.
Laqueur W., Ostatnie dni Europy. Epitafi um dla Starego Kontynentu [Th e Last Days of Eu-rope. Epitaph for an Old Continent], Wrocław 2008.
Rosset E., Proces starzenia się ludności. Studium demografi czne [Aging Process of Popula-tion. Th e Demographic Study], Warszawa 1959.
Royal Commission on Population, Report to Parliament, London, 1949. Th urow L.C., Przyszłość kapitalizmu [Th e Future of Capitalism], Wrocław 1999.
World Population Prospects: Th e 2006 Revision and World Urbanization Prospects: Th e 2005 Revision, Population Divisions of the Department and Social Aff airs of the United
