Chapter One: The Shape of Things - The Meaning of Population Age Structures

In all country populations, death rates have declined—especially among infants and the very young—and life expectancy has risen. This is the initial phase of the demographic transition. In the vast majority of populations, with important exceptions that will be described in more detail in this report, some time after death rates have declined, birth rates have begun to descend as well, usually in response to higher rates of modern contraception use. In a few cases, also to be described in this report, the demographic transition has stalled or actually moved backward. In these cases, life expectancy has fallen, most often in response to a very high prevalence of HIV/AIDS in certain country populations.

The decline in the infant death rate that launches the demographic transition typically follows public health improvements such as more comprehensive access to clean water and better sanitation as well as higher rates of girls' education. The increase in the share of children surviving to adolescence tends to widen the population profile's base, which reflects the larger proportional size of age groups in infancy and early childhood within the total population.

Research provides substantial evidence that girls' education, later marriage and women's employment outside the home have played important roles in improving nutrition and decreasing mortality in childhood, and increasing the demand for contraception in adulthood.⁴ In turn, increased use of contraception leads to a decline in fertility rates, the second key characteristic of the demographic transition.⁵ This typically comes later than a decline in infant death rates, and it narrows the base of the age profile.

Figure 1.2
The Demographic Transition⁶

This pictorial representation of the demographic transition shows that as death rates decline, followed later by a decline in birth rates, populations grow rapidly but eventually plateau at a relatively stable level, presuming no further drastic changes in mortality or fertility.

Figure 1.3
Age Structure Types Along the Demographic Transition

The demographic transition is represented as a line marking the path populations make toward a more balanced age structure. Each point represents a country's population, with four colors distinguishing the four major age structure types (very young, youthful, transitional, mature) and their location along the demographic transition function in 2005.

In recent decades, the demographic transition's impact on country population profiles has been surprisingly rapid. The full transitions that took most European countries about 150 years to complete occurred in parts of East Asia and the Caribbean in less than 50 years. Yet more than one-third of all countries remain in the transition's early and middle phases.⁷ Rates of birth and death—particularly among infants, children and women in pregnancy and childbirth—remain high in most of sub-Saharan Africa and in parts of South and Central Asia. And although death rates have declined, birthrates remain high in much of the Middle East and in several Latin American countries and Pacific Islands. This places these countries in the middle of the demographic transition, mostly with youthful age structures.

Population Geometry: Age Structures Defined

This report characterizes all national populations into one of four major types of contemporary age structures: very young, youthful, transitional, and mature types. These four profiles represent progressive steps along the path of the demographic transition. Because only four major categories have been devised to contain more than 150 countries, a range of structures occurs within each type. Still, countries in each of these types experience similar challenges and successes in their economic, political and social development.

By themselves, these profiles provide an incomplete view of a country's current and future risks and opportunities. Demographic projections do not account for the historic, ethnic and cultural factors that could contribute either to government resilience or weakness in the face of challenges and threats, and they ignore the conditions in the country's geographic neighborhood. Nonetheless the associations found in comparing age structures strongly suggest that demographics should be examined in every country analysis. Governments should consider the programs and policies targeted at health, education and employment that can influence their population dynamics.

The four current age structure types are created by dividing a country's population into three age groups—youth (ages zero to 29 years), mid-adults (30 to 59 years) and older adults (60 and older)—and using those proportions to track the country's position along the demographic transition. Calculated this way using demographic data, any age structural bulges (large proportions of individuals within specific age groups) and contractions (small proportions) within the population can be identified.

Opportunities at Every Age

Among the three major age structure components, youth includes life's most formative years, and some of its riskiest. When education, health care and employment are available, young women and men hold the potential to renew and revitalize the country's economy and institutions. Without access to these social services, however, countries with a large proportion of young people tend to face escalating demands for jobs and education. These countries have historically been the most volatile and vulnerable to civil conflict.⁸  A contraction in the youthful age groups, meanwhile, generally indicates an actively declining birthrate or previous declines. This presents opportunities for governments and parents to save and to invest more in each child's education and health.

The middle age segment—composed of adults ages 30 to 59—is typically the most productive group in a country's development through the accumulation of technical expertise and financial assets. A large bulge in this age group is characteristic of populations that have experienced considerable progress along the demographic transition. With effective governance, this increases federal revenue and provides funding for state programs including education, health care for children and a social safety net for the needy and elderly. Conversely, a contraction in this age group can limit government spending unless alternative sources of revenue are available.

Most countries will eventually experience significantly larger proportions of older adults than in the past. In industrial countries, the need for health care funding for a large number of older adults and elderly was historically met by the significantly larger cohorts of younger people who could assume responsibility for their care. As populations continue to age and younger generations grow smaller, the development of a large proportion of older adults in countries with state-run pensions and health care benefits is likely to severely challenge these systems.

Figure 1.4
Age Structure Type Summary

This table shows the number of countries in each of the four major age structure types across the past 35 years. The range of possibilities for the number of countries in each type (and one speculative type) within two different future population projections is also shown.

Figure 1.5
World Age Structure Types, 2005

Countries are indicated by color in each of the four major types and three subtypes of age structures, based on their 2005 population.

Click on map to view larger in popup window.

<< 1 | 2 | 3 | >>

Notes

1. Rice, X. 2006. "Population Explosion Threatens to Trap Africa in Cycle of Poverty" The Guardian, 25 August.
2. "Cradle snatching; German demography" 2006. The Economist, 18 March.
3. United Nations Population Division. 2005. World Population Prospects: The 2004 Revision. New York: United Nations Population Division.
4. Smith L., and L. Haddad. 2000. "Overcoming Child Malnutrition in Developing Countries: Past Achievements & Future Choices," Report 30. Washington, DC: International Food Policy Research Institute; Lutz, W., and A. Goujon. 2001. "The World's Changing Human Capital Stock: Multi-state Population Forecasts by Educational Attainment" Population and Development Review 27(2):323-339; Bongaarts, J., Mauldin, W.P., and J.F. Phillips. 1990. "The Demographic Impact of Family Planning Programs" Studies in Family Planning 21(6): 299-310.
5. Robey, B., S.O. Rutstein, and L. Morris. 1993. "Fertility Decline in Developing Countries" Scientific American 269(6 (December)):60-67.
6. Cincotta, R., R. Engelman and D. Anastasion. 2003. The Security Demographic: Population and Civil Conflict After the Cold War. Washington, DC: Population Action International.
7. For this estimate, early-transition countries were assumed to have total fertility rates of 4.5 children per woman or more (for 2000 to 2005, a total of 47 countries, each with a population over 150,000), and middle-transition countries 3.5 to 4.5 children per woman (22 countries). These 69 countries comprised nearly one billion people.
8. Moller, H. 1967-68. "Youth as a Force in the Modern World" Comparative Studies in Society and History 10:237-260; Goldstone, J.A. 1991. Revolution and Rebellion in the Early Modern World. Berkeley: University of California Press.
9. For example, the United Nations Development Programme's annual Human Development Report assigns countries a comprehensive development score based on poverty, economic performance and income equality; many aspects of health, disease and mortality; technology; the environment; aid and public spending; gender; politics and human rights. See here for more information.
10. Cincotta, R., R. Engelman and D. Anastasion. 2003. The Security Demographic: Population and Civil Conflict After the Cold War. Washington, DC: Population Action International; Goldstone, J.A. 1991. Revolution and Rebellion in the Early Modern World. Berkeley: University of California Press; Mesquida, C.G., and N. Wiener. 1999. "Male Age Composition and Severity of Conflicts" Politics and the Life Sciences 18(2): 181-189; Urdal, H. 2004. The Devil in the Demographics: The Effect of Youth Bulges on Domestic Armed Conflict, 1950-2000. Social Development Paper 14. Washington, DC: World Bank.
11. 2006. Where is the Wealth of Nations? Measuring Capital for the 21st Century. Washington, DC: World Bank.
12. May, J.F. 2005. "Population Policy" in Poston, D., and M. Micklin (eds). The Handbook of Population. New York: Kluwer Academic/Plenum Publishers, pp. 827-852.
13. For the various approaches to birth subsidies, see: Boling, P. 2002. "Family Support Policies in Japan" Available here, Internet, last accessed 13 September 2006; Grant, J, et al. 2004. "Low Fertility and Population Ageing: Causes, Consequences, and Policy Options" Leiden: RAND Europe; Kakuchi, S. 2006. "Easing Japan's Tread Mill" Asian Times Online, July 13. Available here, Internet, last accessed 13 September 2006; Fullbrook, D. 2000. "Singapore Offers $300 Bonus for Second Child" Christian Science Monitor. 27 September.
14. Rosenthal, E. 2006. "Europe, East and West, Wrestles with Falling Birthrates" International Herald Tribune, 3 September. Available here; last accessed 27 September 2006; Kim, T. 2006. "Childbirth Incentives Get Creative" Korea Times, 19 May. Available here; last accessed 22 September 2006; Chung-a, P. 2006. "Government to Expand Childbirth Incentives" Korea Times, 14 July. Available here; last accessed 22 September 2006; May, J.F. 2005. "Population Policy" in Poston, D., and M. Micklin (eds). The Handbook of Population. New York: Kluwer Academic/Plenum Publishers, pp. 827-852.
15. European Parliament and European Council. 2003. Regulation on Aid for Policies and Actions on Reproductive and Sexual Health and Rights in Developing Countries. Available here; last accessed 20 December 2006.