Chapter Six: Subtypes and a Speculative Structure

In addition to the four major profiles, this report identifies three contemporary subtypes of age structures and one future, speculative type. The first two subtypes are age structures in which the typical effects of the demographic transition on a country's population are altered by the influx of international immigrants (immigration-youthful structures, immigration-mature structures).

A third subtype, HIV/AIDS structures, reflects the impact of extremely high HIV prevalence rates (18 percent or above among adults) on the age structures of countries with very young and youthful populations. The speculative type, a fifth potential category of age structures, would demonstrate the impact of population aging in a few countries with the very lowest fertility rates.

Youth (ages 0-29) approximately 45-55 percent of the population
Mid-Adults (ages 30-59) approximately 45-50 percent of the population
Seniors (ages 60+) approximately 1-5 percent of the population
Country count 4
Demographic character Highly aberrant compared to all other types; largest proportion of population comprised of mid-age adults with an even proportion among children and adolescents and almost no seniors. Also likely to skew unevenly towards males due to higher numbers of men migrating in for work opportunities
Population doubling time about 30 years
Regional prevalence Persian Gulf
Civil conflict risk No immigration-youthful countries experienced conflict between 1970-99
Economic performance 4.8 percent average annual GDP growth rate, 1970-99 (no data for Qatar)
Governance No immigration-youthful countries were measured as having fully democratic governance, 1970-99

Figure 6.1
Immigration-Youthful Subtype Profiles

How Immigration and AIDS Change the Demographic Transition

At sustained high levels, international migration can have a major impact on population age structures. In countries where inward migration has averaged 0.35 percent or more over the past 25 years, age structures have been altered. In immigration-youthful countries, such as the small states of the Persian Gulf, immigrants–primarily men–fill both managerial and service positions in expanding economies. Labor migration to the Arab Gulf states makes their age structures, which are in the middle of the demographic transition, more mature than expected. Although mortality rates have declined in these countries, fertility rates among the native-born population remain above replacement level. Since most immigrants in this region are of working age and policies discourage or prohibit their remaining in the country after retirement, the countries' age structures contain a bulge in the middle of the population, with an extremely small proportion of older adults.

Figure 6.2
Immigration-Mature Subtype Profiles

Youth (ages 0-29) approximately 35-43 percent of the population
Mid-Adults (ages 30-59) approximately 40-50 percent of the population
Seniors (ages 60+) approximately 13-23 percent of the population
Demographic character Largest proportion of population comprised of adults age 30-55, with a slightly smaller proportion of youth and a pyramid shape for seniors.
Population doubling time 60-500 years
Country count 7
Regional prevalence North America, Australia, southern Europe
Civil conflict risk 5 percent probability of experiencing civil conflict, 1970-99
Economic performance 4.7 percent average annual GDP growth rate, 1970-99
Governance 76 percent probability of fully democratic governance, 1970-99

In immigration-mature countries, such as the United States and Australia, age structures are generally younger than they would be otherwise, because immigrants tend to have higher fertility rates than the native-born population.¹ Though these countries are far along the demographic transition and their mortality and fertility rates have already declined, the impact of immigration keeps most of them in the earlier stages of the mature category. Most documented immigrants to industrialized countries are between 15 and 44 years of age (Figure 6.3).² These immigrants have helped keep labor sectors fully employed and economies growing even as fertility rates among native-born residents decline and population growth slows.

Figure 6.3
Age Profile of Immigrants to U.S.³

This population profile of recent documented immigrants to the United States shows that more than half of all immigrants entering the country are 25-39 years old, the prime working ages.

Figure 6.4
HIV/AIDS Subtype Profiles

(HIV prevalence among adults 18 percent or greater in 2005)
Youth (ages 0-29) approximately 60 to 75 percent of the population
Mid-Adults (ages 30-59) approximately 20 to 32 percent of the population
Seniors (ages 60+) approximately 5 to 8 percent of the population
Demographic character Very low proportions and classic pyramid shape among those 30 and older; rapidly increasing cohort size among consecutively younger age groups.
Population doubling time Ranges between declining populations to those with a doubling time of 75 years
Country count 6
Regional prevalence Southern Africa
Civil conflict risk 17 percent probability of experiencing civil conflict, 1970-99
Economic performance 5.5 percent average annual GDP growth rate, 1970-99
Governance 5 percent probability of fully democratic governance, 1970-99

The age structure changes caused by AIDS, which has reversed the decline of death rates in more than 30 countries, were wholly unforeseen by those who first recognized the demographic transition and projected its spread. The age structure-altering capacity of this disease is unprecedented: Some 90 percent of fatalities associated with HIV infection occur among people of working age, with the largest concentration of deaths from the age of 25 to 39 years. The impact of AIDS mortality on countries' economies has been pervasive, as skilled workers and professionals are often the hardest hit. In the countries most heavily affected by the disease, two to three percent of working-age adults die each year–more than 10 times the normal rate–leaving behind a large number of "AIDS orphans" with little adult support. Still, high fertility rates mean that AIDS mortality is not having significant impact on population growth, while straining educational opportunities for children left behind.

From the projections of future populations devised by the United Nations, a fifth major age structure type beyond completion of the demographic transition (aged structures) could develop by 2025. The profiles in this type, with the bulges in the share of their population older than 50, reflect the impact of continued low fertility and population aging. In the UN's medium-fertility variant for 2025, Italy and Japan would reach the aged category, and in the low-fertility variant, six other countries would join them. However, no country has yet developed this structure and demographic shifts could alter it, so it should be regarded as speculative.

Figure 6.5
Aged Structure Profiles*

Youth (ages 0-29) approximately 20-27 percent of the population
Mid-Adults (ages 30-59) approximately 40-45 percent of the population
Seniors (ages 60+) greater than 30 percent of the population
Demographic character Bulges among mid- and senior adults above age 50, steadily decreasing proportion sizes among age cohorts younger than 50.
Country count No countries in 2005; 2 countries in UN's medium-fertility population projection for 2025; 8 countries in low-fertility projection for 2025

*Profiles shown are speculative, based on UN's low-fertility projection for 2025.