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Understanding and Comparing Population Projections in Sub-Saharan Africa

The release of a new set of population projections by the Institute for Health Metrics and Evaluation (IHME) in July 2020 was greeted with extensive coverage in the media and stimulated fresh debate among demographers about calculation and communication of projections. Sound population projections serve a critical purpose. They enable policymakers, researchers, and planners to accurately estimate future service demands (for example, health care and schools) and develop policies and programs informed by predicted trends. But population projections are generated using assumptions about the future, so they always include an element of uncertainty and variability that should inform their interpretation.

IHME’s projections join an established field, with other leading demographic projections produced regularly by the United Nations Population Division (UN), one of the most longstanding and widely used sources; and the International Institute for Applied Systems Analysis (IIASA). The three sets of projections apply different assumptions about future trends in fertility. The UN assumptions are largely based on historical observations from other countries, as well as countries’ own trends. In contrast, the models of fertility developed by IHME and IIASA incorporate women’s educational attainment, and in the case of IHME, also consider met need for family planning—the percentage of women of reproductive age who wish to stop or delay childbearing and are using a modern contraceptive method. The assumptions and methods used to generate each set of projections are summarized in the webinar, “What to Expect When You’re Projecting? Interrogating Population Projections and Their Fertility Assumptions,” organized by the Health Policy Plus Project. 1

PRB reviewed these three organizations’ population and fertility projections and their underlying assumptions in sub-Saharan Africa (SSA) to see how they differ. SSA is home to countries with some of the world’s highest fertility rates, and trends in fertility and population across the region will have large implications for the future global population. Figure 1 shows wide variations in these three organizations’ projections. Even though they all have the same 2020 population of 1.1 billion, the differences in their assumptions create increasingly greater gaps in projections over time. Projections by the UN and IHME are similar until around 2060, when the organizations’ different underlying assumptions gradually begin to produce significantly different projections: The gap between the two reaches 0.4 billion people by 2085 and 0.7 billion by 2100. Projections by the UN and IIASA are also similar until around 2040, but the gap grows to 0.9 billion people by 2085, and as many as 1.2 billion by 2100. These differences have implications for policy decisionmaking and risk management related to key aspects of the global economy, environmental protection, and resource distribution.

By 2100, the UN projects the population in SSA will reach 3.8 billion, IHME projects 3.1 billion, and IIASA is the lowest at 2.6 billion. 2 These very different projections beg the question: What is the source of these differences and how can we, as consumers, assess which projection may be most realistic?

 FIGURE 1. Population Projections for Sub-Saharan Africa in 2100 Vary Greatly

Source: IHME, Population Forecasting | VizHub; UN DESA, World Population Prospects: The 2019 Revision; and Wittgenstein Centre for Demography and Global Human Capital, Wittgenstein Centre Human Capital Data Explorer.

Fertility Is Projected to Decline, but How Much and How Fast?

The ingredients of any population projection are the starting, or baseline, population combined with assumptions about future trends in fertility, mortality, and migration. Demographers generally agree that in countries where fertility is high, the total fertility rate (TFR) will gradually decrease to around what is known as replacement level (2.1 children per woman) or below. The TFR is the average number of children a woman would have assuming current age-specific birth rates remain constant throughout her childbearing years (usually considered to be ages 15 to 49).

But demographers disagree on when, by exactly how much, and how fast fertility will decrease. Assumptions for these variables make a big difference in resulting population projections. To develop their projections, demographers apply statistical methods, expert insight, the latest data and evidence or, typically, a combination of the above. Of the future trends that influence population projections, fertility is the most relevant for countries in SSA, where women have an average of 4.8 children over their lifetimes.3

The projections from UN, IIASA, and IHME each use a similar estimate of approximately 1.1 billion in 2020 for the starting population size. Across the region, the 2018 TFR estimates that each organization uses for countries in SSA vary, but with no evidence of a specific bias (figure not presented here but is available upon request). The 2018 TFRs used by one organization are not consistently higher or lower than those used by the other organizations. This lack of consistency means that neither the starting populations nor TFR estimates are likely driving the large variations in the resulting population projections for SSA.

Figure 2 shows the 2100 TFRs projected by each organization for all SSA countries, sorted by the UN’s estimates (in orange). All three organizations project that TFRs across SSA will largely be below the replacement level of 2.1 children per woman by 2100. However, the organizations differ on the degree to which they project the TFRs to decline across countries. The UN projects that nearly one-third of countries in SSA will not reach replacement-level fertility by 2100. This projection includes sizable, high-fertility countries like Tanzania, Niger, and Nigeria. In contrast, IIASA’s TFR projections for all countries in SSA are below replacement level in 2100, and are typically in between the levels projected by the UN and IHME. In IHME’s projections, TFRs in all but four countries are expected to fall below replacement level, and generally to levels substantially lower than the other two projections.

FIGURE 2. IHME and IIASA Project Lower Fertility in Sub-Saharan Africa in 2100 Than the UN

Source: IHME, Population Forecasting | Viz Hub; UN DESA, World Population Prospects: The 2019 Revision; and Wittgenstein Centre for Demography and Global Human Capital, Wittgenstein Centre Human Capital Data Explorer.

Similar differences exist when we look at the pace at which each organization (UN, IHME, and IIASA) projects TFR to decline between 2020 and 2100. Figure 3 displays three line graphs, one for each set of projections. Each line on each graph shows the trend in TFR for all countries in SSA for which data are available. The thick colored line in each graph shows the average trend of fertility decline for the region. The horizontal black line at TFR of 2.1 indicates replacement-level fertility. In comparing when the average rate of decline dips below replacement-level fertility in each set of projections, we see a much earlier transition to below replacement-level fertility in the IHME and IIASA projections (in the 2050s) compared to the UN projections (2080s).

Figure 3. IHME and IIASA Project Much Faster Declines in Fertility than the UN

Source: IHME, Population Forecasting | Viz Hub; UN DESA, World Population Prospects: The 2019 Revision; and Wittgenstein Centre for Demography and Global Human Capital, Wittgenstein Centre Human Capital Data Explorer.

Each organizations’ fertility projections differ even more significantly for very high fertility countries. Niger currently has the world’s highest TFR at approximately 6.5 to 7.1 children per woman, depending on which estimate is used.  IHME and IIASA project that Niger’s TFR will decline to below 2.1 in the 2080s and eventually to 1.8 and 1.9, respectively, by 2100, while the UN projects Niger’s TFR will not reach replacement level before 2100.  
Another relevant example is the Democratic Republic of the Congo (DRC). IHME and IIASA project that the DRC’s TFR will decrease to 2.1 in the 2060s and further to 1.8 by 2100, while the UN projects that it will be 2100 before the DRC’s TFR reaches replacement level.

Are IHME’s Fertility Projections Too Low?

These differences become even more striking when evaluating changes in country TFR rankings between 2018 and 2100. If all the countries in the world were sorted by TFR in 2018 and again by projected TFR in 2100, we might expect some general consistency between a country’s relative standing at the two points in time.4
Ranking IHME’s projected TFRs shows that, of the 39 countries in SSA on the list of the world’s 50 highest TFRs in 2018, only nine remain on the list in 2100.  Even more surprising, IHME projections show that eight countries on the list of 50 highest TFRs in 2018 appear on the list of the world’s 50 lowest TFRs in 2100.

This shift is significant and could suggest that IHME, in particular, may be overestimating the extent of fertility decline for these and possibly other countries in the region. Making the same comparison for the UN’s projected TFRs shows that 33 of the 39 countries on the list of the world’s 50 highest TFRs in 2018 remain in 2100. Additionally, none ended up on the list of countries with the lowest TFRs in 2100. IIASA’s results are between the two, with less transition compared to IHME, but more than the UN.

How Well Do Fertility Assumptions Fare Against the Evidence?

As discussed above, IHME and IIASA incorporate women’s educational attainment in their models of fertility, and in the case of IHME, also consider met need for family planning.5
The relationships between education and fertility and between family planning use and fertility are considered universal in the IHME and IIASA models, meaning the same relationship between fertility and both girls’ education and family planning is assumed for countries around the world. Is this assumption reasonable given the latest evidence about the drivers of fertility change, particularly drivers unique to countries in SSA?

Data demonstrate that fertility transitions in SSA started later and progressed more slowly compared to what has been observed historically elsewhere, including in Asia and Latin America.6
Research also suggests that at a given level of socioeconomic development, countries in SSA tend to have higher levels of fertility and desired family size compared to other regions around the world.7
These findings indicate that SSA may have a distinct pattern of fertility transition.

Additionally, research has demonstrated that women’s secondary school attainment is a crucial factor influencing fertility levels in high-fertility countries, and women’s educational attainment progress has been comparatively slow in SSA relative to other regions.8
A study released in September 2020 found that the impact of women’s educational attainment on fertility decline is weaker in SSA than in other regions.9
> Other research suggests that the lower quality of education in SSA relative to other regions may also contribute to the weaker influence of women’s education on fertility decline in the region.10

Studies have likewise indicated a weaker relationship between modern contraceptive use and fertility decline in SSA, relative to that observed in other regions. This weaker association may be partly attributable to a higher proportion of women in many SSA countries using contraception to space births rather than to limit them.11
In addition, data indicate a preference for larger families in many SSA countries than in other regions. High ideal family size is a principal factor influencing the slow pace of fertility decline in SSA and may offset the accelerating effects of modern contraceptive use on fertility decline. 12

Given this evidence base, IHME and IIASA’s application of universal assumptions about the effects of education and contraception on fertility decline may be unwarranted. If the relationships between education, contraception, and fertility look different across and within SSA relative to other regions, models that assume these relationships to be universal could significantly overestimate the pace and magnitude of fertility decline in SSA.

The expanding pool of population projections is an exciting development for data consumers but reminds us that all projections—including more established forecasts such as the UN’s—must be critically assessed prior to use. The assumptions driving population projections should always be verified using evidence from high-quality research and knowledge of regional contexts to ensure that we are smart consumers and smart sharers of data. The coronavirus pandemic is a reminder of how much uncertainty exists in any of the underlying assumptions regarding future populations. While it is too early to tell what the pandemic’s full impact will be on fertility, mortality, and migration patterns, as well as its potential impact on family planning access and schooling, its long-term impacts add another layer of uncertainty and complexity to projection assumptions in the coming years.

Messages about various projections—and their potential policy implications—must be developed with caution and transparency. Projections not only allow us to plan for the future, but also often inform policy and program priorities and investments and can influence the future course of population trends and people’s well-being. It is our responsibility to be vigilant in our understanding of the projections we choose to use.

References

  1. Emil Vollset Stein et al., “Fertility, Mortality, Migration, and Population Scenarios for 195 Countries and Territories From 2017 to 2100: A Forecasting Analysis for the Global Burden of Disease Study,” The Lancet 396, no. 10258 (2020): 1285-306; and Wolfgang Lutz et al. (eds.), Demographic and Human Capital Scenarios for the 21st Century: 2018 Assessment for 201 Countries (Luxembourg: European Union, 2018), http://publications.jrc.ec.europa.eu/repository/bitstream/JRC111148/jrc_cepam_report_demographic_and_hc_scenarios_pdf.pdf
  2. Institute for Health Metrics and Evaluation (IHME), Population Forecasting | Viz Hub, https://vizhub.healthdata.org/population-forecast/; United Nations Department of Economic and Social Affairs (UN DESA), World Population Prospects: The 2019 Revision, https://population.un.org/wpp/; and Wittgenstein Centre for Demography and Global Human Capital, Wittgenstein Centre Human Capital Data Explorer, http://dataexplorer.wittgensteincentre.org/wcde-v2/.
  3. Toshiko Kaneda, Charlotte Greenbaum, and Kelley Kline, 2020 World Population Data Sheet, (Washington, DC: Population Reference Bureau, 2020).
  4. Stuart Gietel-Basten and Tomas Sobotka, “Uncertain Population Futures: Critical Reflections on the IHME Scenarios of Future Fertility, Mortality, Migration and Population Trends From 2017 to 2100” (2020), https://osf.io/preprints/socarxiv/5syef/.
  5. Emil Vollset Stein et al., “Fertility, Mortality, Migration, and Population Scenarios for 195 Countries and Territories From 2017 to 2100: A Forecasting Analysis for the Global Burden of Disease Study,” The Lancet 396, no. 10258 (2020): 1285-306; and Wolfgang Lutz et al. (eds.), Demographic and Human Capital Scenarios for the 21st Century: 2018 Assessment for 201 Countries (Luxembourg: European Union, 2018), http://publications.jrc.ec.europa.eu/repository/bitstream/JRC111148/jrc_cepam_report_demographic_and_hc_scenarios_pdf.pdf
  6. John Bongaarts, “Africa’s Unique Fertility Transition,” Population and Development Review 43, S1 (2017): 39-58; and Bongaarts and John Casterline, “Fertility Transition: Is Sub-Saharan Africa Different?” Population and Development Review 38, S1 (2013): 153-68.
  7. Bongaarts, “Africa’s Unique Fertility Transition;” and Bongaarts and Casterline, “Fertility Transition: Is Sub-Saharan Africa Different?”
  8. Daphne H. Liu and Adrian E. Raftery, “How Do Education and Family Planning Accelerate Fertility Decline?” Population and Development Review 46, no. 3 (2020): 409-41.
  9. Liu and Raftery, “How Do Education and Family Planning Accelerate Fertility Decline?”
    [10]  Monica J. Grant, “The Demographic Promise of Expanded Female Education: Trends in the Age at First Birth in Malawi,” Population and Development Review 41, no. 3 (2015): 409-38.
  10. Kristin Bietsch, The Relationship between Modern Contraceptive Use and Use to Limit: African Exceptionalism (Track20, Avenir Health, 2019), http://www.track20.org/download/pdf/mCPR_spacing_limiting_Memo_100919.pdf.
  11. Bongaarts and Casterline, “Fertility Transition: Is Sub-Saharan Africa Different?”; and Daphne H. Liu and Adrian E. Raftery, “How Do Education and Family Planning Accelerate Fertility Decline?”
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Population: An Introduction to Demography

Understanding population trends is essential in tackling many of the world’s greatest challenges, among them hunger and malnutrition, poverty, climate change, and disease, including the coronavirus pandemic. Population data are a vital tool for policymakers, business leaders, scientists, and others seeking to make informed decisions on important issues.

This Population Bulletin, “Population: An Introduction to Demography,” provides a basic understanding of demography and demographic processes, including fertility, mortality, and migration, and their effects on the world. First published in 1991 as “Population: A Lively Introduction,” this newly revised edition gives readers a greater understanding of why today’s population trends matter—not just to researchers and academics but to all of us.


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Glossary of Demographic Terms

– A –

Abortion Rate The number of abortions per 1,000 women ages 15-44 or 15-49 in a given year.

Abortion Ratio The number of abortions per 1,000 live births in a given year.

Acquired Immunodeficiency Syndrome (AIDS) Applies to the most advanced stages of HIV infection. It is defined by the occurrence of any of more than 20 opportunistic infections or HIV-related cancers.

Age-Dependency Ratio The ratio of persons in the ages defined as dependent (under 15 years and over 64 years) to persons in the ages defined as economically productive (15-64 years) in a population.

Age Structure The proportion of the total population in each age group.

Age-Sex Structure The composition of a population as determined by the number or proportion of males and females in each age category. The age-sex structure of a population is the cumulative result of past trends in fertility, mortality, and migration. Information on age-sex composition is essential for the description and analysis of many other types of demographic data. See also population pyramid.

Age-Specific Rate Rate obtained for specific age groups (for example, age-specific fertility rate, death rate, marriage rate, illiteracy rate, or school enrollment rate).

Aging of Population A process in which the proportions of adults and elderly increase in a population, while the proportions of children and adolescents decrease. This process results in a rise in the median age of the population. Aging occurs when fertility rates decline while life expectancy remains constant or improves at the older ages.

Antinatalist Policy The policy of a government, society, or social group to slow population growth by attempting to limit the number of births.

Antiretroviral therapy (ART) Treatment of people infected with human immunodeficiency virus (HIV) using anti-HIV drugs. The standard treatment consists of a combination of at least three drugs (often called “highly active antiretroviral therapy” or HAART) that suppress HIV replication. Three drugs are used in order to reduce the likelihood of the virus developing resistance. ART has the potential both to reduce mortality and morbidity rates among HIV-infected people, and to improve their quality of life.

– B –

Baby Boom A dramatic increase in fertility rates and in the absolute number of births in the United States, Canada, Australia, and New Zealand during the period following World War II (1947-1961).

Baby Bust A rapid decline in U.S. fertility rates to record-low levels during the period immediately after the baby boom.

Balancing Equation A basic demographic formula used to estimate total population change between two points in time — or to estimate any unknown component of population change, provided that the other components are known. The balancing equation includes all components of population change: births, deaths, immigration, emigration, in-migration, and out-migration.

Birth Control Practices employed by couples that permit sexual intercourse with reduced likelihood of conception and birth. The term birth control is often used synonymously with such terms as contraception, fertility control, and family planning. But birth control includes abortion to prevent a birth, whereas family planning methods explicitly do not include abortion.

Birth Rate (or crude birth rate) The number of live births per 1,000 population in a given year. Not to be confused with the growth rate.

Birth Rate for Unmarried Women The number of live births per 1,000 unmarried women (never married, widowed, or divorced) ages 15-49 in a given year.

Brain Drain The emigration of a significant proportion of a country’s highly skilled, highly educated professional population, usually to other countries offering better economic and social opportunity (for example, physicians leaving a developing country to practice medicine in a developed country).

– C –

Carrying Capacity The maximum sustainable size of a resident population in a given ecosystem.

Case Fatality Rate The proportion of persons contracting a disease who die from it during a specified time period.

Case Rate The number of reported cases of a specific disease per 100,000 population in a given year.

Cause-Specific Death Rate The number of deaths attributable to a specific cause per 100,000 population in a given year.

Census A canvass of a given area, resulting in an enumeration of the entire population and often the compilation of other demographic, social, and economic information pertaining to that population at a specific time. See also survey.

Childbearing Years The reproductive age span of women, assumed for statistical purposes to be 15-44 or 15-49 years of age.

Child-Woman Ratio The number of children under age 5 per 1,000 women ages 15-44 or 15-49 in a population in a given year. This crude fertility measure, based on basic census data, is sometimes used when more specific fertility information is not available.

Closed Population A population with no migratory flow either in or out, so that changes in population size occur only through births and deaths.

Cohort A group of people sharing a common temporal demographic experience who are observed through time. For example, the birth cohort of 1900 is the people born in that year. There are also marriage cohorts, school class cohorts, and so forth.

Cohort Analysis Observation of a cohort’s demographic behavior through life or through many periods; for example, examining the fertility behavior of the cohort of people born between 1940 and 1945 through their entire childbearing years. Rates derived from such cohort analyses are cohort measures. Compare with period analysis.

Completed Fertility Rate The number of children born per woman to a cohort of women by the end of their childbearing years.

Consensual Union Cohabitation by an unmarried couple for an extended period of time. Although such unions may be quite stable, they are not regarded as legal marriages in official statistics.

Contraceptive Prevalence Percentage of couples currently using a contraceptive method.

Contraceptive Use The percentage of currently married or “in union” women (unless otherwise indicated) of reproductive age who are currently using any form of contraception. Modern methods comprise clinic and supply methods, including the pill, injectable, implant, IUD, condom, and sterilization.

Crude Rate Rate of any demographic event computed for an entire population.

– D –

Death Rate (or crude death rate) The number of deaths per 1,000 population in a given year.

Demographic Transition The historical shift of birth and death rates from high to low levels in a population. The mortality decline usually precedes the fertility decline, resulting in rapid population growth during the transition period.

Demography The scientific study of human populations, including their sizes, compositions, distributions, densities, growth, and other characteristics, as well as the causes and consequences of changes in these factors.

Dependency Ratio A dependency ratio is the ratio of people in a dependent age group (those under age 15 or ages 65 and older) to those in the economically productive age group (ages 15 to 64) of a population. For instance, a child dependency ratio of 0.45 means there are 45 children for every 100 working-age adults.

Depopulation The state of population decline.

Divorce Rate (or crude divorce rate) The number of divorces per 1,000 population in a given year.

Double Dependency Moderate child dependency and relatively high old-age dependency reflect above or near replacement fertility and declining mortality.

Doubling Time The number of years required for the population of an area to double its present size, given the current rate of population growth.

– E –

Economic Infrastructure Economic infrastructure includes the internal facilities of a country that make business and financial activity possible, such as communication, transportation, and distribution networks; financial institutions and markets; and energy supply systems.

Economic Security The condition of having stable income or other resources to support a standard of living now and in the foreseeable future.

Emigration The process of leaving one country to take up permanent or semipermanent residence in another.

Emigration Rate The number of emigrants departing an area of origin per 1,000 population in that area of origin in a given year.

Ethnicity The cultural practices, language, cuisine, and traditions — not biological or physical differences — used to distinguish groups of people.

– F –

Family Usually two or more persons living together and related by birth, marriage, or adoption. Families may consist of siblings or other relatives as well as married couples and any children they have.

Family Planning The conscious effort of couples to regulate the number and spacing of births through artificial and natural methods of contraception. Family planning connotes conception control to avoid pregnancy and abortion, but it also includes efforts of couples to induce pregnancy.

Fecundity The physiological capacity of a woman to produce a child.

Fertility The actual reproductive performance of an individual, a couple, a group, or a population. See general fertility rate.

– G –

Gender refers to the economic, social, political, and cultural attributes, constraints and opportunities associated with being a woman or a man. The social definitions of what it means to be a woman or a man vary among cultures and change over time. Gender is a sociocultural expression of particular characteristics and roles that are associated with certain groups of people with reference to their sex and sexuality.

Gender Equity is the process of being fair to women and men. To ensure fairness, measures must be taken to compensate for historical and social disadvantages that prevent women and men from operating on a level playing field.

Gender Equality is the state or condition that affords women and men equal enjoyment of human rights, socially valued goods, opportunities, and resources.

General Fertility Rate The number of live births per 1,000 women ages 15-44 or 15-49 years in a given year.

Gross National Income (GNI) GNI (formerly GNP) is the sum of value added by all resident producers plus any product taxes (less subsidies) not included in the valuation of output plus net receipts of primary income (compensation of employees and property income) from abroad. Data are in current U.S. dollars. GNI, calculated in national currency, is usually converted to U.S. dollars at official exchange rates for comparisons across economies, although an alternative rate is used when the official exchange rate is judged to diverge by an exceptionally large margin from the rate actually applied in international transactions.

Gross Reproduction Rate (GRR) The average number of daughters that would be born alive to a woman (or group of women) during her lifetime if she passed through her childbearing years conforming to the age-specific fertility rates of a given year. See also net reproduction rate and total fertility rate.

Growth Rate The number of people added to (or subtracted from) a population in a year due to natural increase and net migration expressed as a percentage of the population at the beginning of the time period.

– H –

High Child Dependency High fertility and relatively high mortality contribute to a large young population and a small old-age population.

High-risk pregnancies Pregnancies occurring under the following conditions: too closely spaces, too frequent, mother too young or too old, or accompanied by such high-risk factors as high blood pressure or diabetes.

High-Old-Age Dependency Moderate child dependency and relatively high old-age dependency reflect above or near replacement fertility and declining mortality.

Household One or more persons occupying a housing unit.

Human Immunodeficiency Virus (HIV) Retrovirus that infects cells of the immune system, destroying or impairing their function. As the infection progresses, the immune system becomes weaker, and the person becomes more susceptible to infections.
HIV is transmitted through unprotected sexual intercourse, transfusion of contaminated blood, sharing of contaminated needles, and between a mother and her infant during pregnancy, childbirth and breastfeeding.

– I –

Immigration The process of entering one country from another to take up permanent or semipermanent residence.

Immigration Rate The number of immigrants arriving at a destination per 1,000 population at that destination in a given year.

Incidence Rate The number of persons contracting a disease per 1,000 population at risk, for a given period of time.

Infant Mortality Rate The number of deaths of infants under age 1 per 1,000 live births in a given year.

In-migration The process of entering one administrative subdivision of a country (such as a province or state) from another subdivision to take up residence.

– L –

Least Developed Countries Following United Nations’ definitions, the term “least developed countries” includes as of March 2018: Afghanistan, Angola, Bangladesh, Benin, Bhutan, Burkina Faso, Burundi, Cambodia, Central African Republic, Chad, Comoros, Democratic Republic of the Congo, Djibouti, Eritria, Ethiopia, Gambia, Guinea, Guinea-Bissau, Haiti, Kiribati, Lao People’s Democratic Republic, Lesotho, Liberia, Madagascar, Malawi, Mali, Mauritania, Mozambique, Myanmar, Nepal, Niger, Rwanda, São Tomé and Príncipe, Senegal, Sierra Leone, Solomon Islands, Somalia, Sudan,  Timor-Leste, Togo, Tuvalu, Uganda, Vanuatu, Yemen, and Zambia. These countries are also “less developed” in United Nations’ terminology.

Less Developed Countries Following United Nations’ definitions, the term “less developed countries” (or regions) refers to countries in Africa, Asia (except Japan), Latin America and the Caribbean, and Oceania (except Australia and New Zealand).

Life Expectancy The average number of additional years a person could expect to live if current mortality trends were to continue for the rest of that person’s life. Most commonly cited as life expectancy at birth.

Life Span The maximum age that human beings could reach under optimum conditions.

Life Table A tabular display of life expectancy and the probability of dying at each age (or age group) for a given population, according to the age-specific death rates prevailing at that time. The life table gives an organized, complete picture of a population’s mortality.

Low Overall Dependency Sustained immigration of working-age adults, with a small share of the population ages 65+, results in low overall dependency.

– M –

Male Involvement means engaging men in actively promoting gender equity with regard to reproductive health, increases men’s support for women’s reproductive health and children’s well-being, and advances the reproductive health of both men and women.

Malthus, Thomas R. (1766-1834) English clergyman and economist famous for his theory (expounded in the ‘Essay on the Principle of Population’) that the world’s population tends to increase faster than the food supply and that unless fertility is controlled (by late marriage or celibacy), famine, disease, and war must serve as natural population restrictions. See neo-Malthusian.

Marital Fertility Rate Number of live births to married women per 1,000 married women ages 15-44 or 15-49 in a given year.

Marriage Rate (or crude marriage rate) The number of marriages per 1,000 population in a given year.

Maternal Mortality Ratio The number of women who die as a result of pregnancy and childbirth complications per 100,000 live births in a given year.

Mean Age The mathematical average age of all the members of a population.

Median Age The age that divides a population into two numerically equal groups; that is, half the people are younger than this age and half are older.

Megalopolis A term denoting an interconnected group of cities and connecting urbanized bands.

MENA Countries The Middle East and North Africa (MENA) is an economically diverse region that includes both the oil-rich economies in the Gulf and countries that are resource-scarce in relation to population. The region’s economic fortunes over much of the past quarter century have been heavily influenced by two factors: the price of oil and the legacy of economic policies and structures that had emphasized a leading role for the state. The MENA region includes: Algeria, Bahrain, Djibouti, Egypt, Iran, Iraq, Israel, Jordan, Kuwait, Lebanon, Libya, Malta, Morocco. Oman, Qatar, Saudi Arabia, Syria, Tunisia, United Arab Emirates, West Bank and Gaza, and Yemen.

Metropolitan Area A large concentration of population, usually an area with 100,000 or more people. The area typically includes an important city with 50,000 or more inhabitants and the administrative areas bordering the city that are socially and economically integrated with it.

Migration The movement of people across a specified boundary for the purpose of establishing a new or semipermanent residence. Divided into international migration (migration between countries) and internal migration (migration within a country).

Millennium Development Goals (MDGs) The United Nations Millennium Development Goals are eight goals that all 191 UN member states have agreed to try to achieve by the year 2015. The United Nations Millennium Declaration, signed in September 2000, commits world leaders to combat poverty, hunger, disease, illiteracy, environmental degradation, and discrimination against women. The MDGs are derived from this declaration, and all have specific targets and indicators.

Mobility The geographic movement of people.

Moderate Child Dependency Declining fertility lowers child dependency to a moderate level; relatively high mortality keeps old-age dependency low.

More Developed Countries Following United Nations’ definitions, “more developed countries,” or industrialized countries (or regions), include Europe (including all of Russia), the United States, Canada, Australia, New Zealand, and Japan.

Mortality Deaths as a component of population change.

– N –

Natality Births as a component of population change.

Natural Increase (or Decrease) The surplus (or deficit) of births over deaths in a population in a given time period.

Neo-Malthusian An advocate of restricting population growth through the use of birth control. (Thomas Malthus himself did not advocate birth control as a remedy for rapid population growth.)

Neonatal Mortality Rate The number of deaths to infants under 28 days of age in a given year per 1,000 live births in that year.

Net Migration The estimated rate of net migration (immigration minus emigration) per 1,000 population. For some countries, data are derived as a residual from estimated birth, death, and population growth rates.

Net Migration Rate The net effect of immigration and emigration on an area’s population, expressed as an increase or decrease per 1,000 population of the area in a given year.

Net Reproduction Rate (NRR) The average number of daughters that would be born to a woman (or a group of women) if she passed through her lifetime conforming to the age-specific fertility and mortality rates of a given year. This rate is similar to the gross reproduction rate but takes into account that some women will die before completing their childbearing years. An NRR of one means that each generation of mothers is having exactly enough daughters to replace itself in the population. See also total fertility rate and replacement-level fertility.

Nuptiality The frequency, characteristics, and dissolution of marriages in a population.

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“Old” Population A population with a relatively high proportion of middle-age and elderly persons, a high median age, and thus a lower growth potential.

Out-migration The process of leaving one subdivision of a country to take up residence in another.

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Parity The number of children previously born alive to a woman; for example, ‘two-parity women’ are women who have had two children and ‘zero-parity women’ have had no live births.

Percent Urban Percentage of the total population living in areas termed “urban” by that country or by the UN.

Perinatal Mortality Rate The number of fetal deaths after 28 weeks of pregnancy (late fetal deaths) plus the number of deaths to infants under 7 days of age per 1,000 live births.

Period Analysis Observation of a population at a specific period of time. Such an analysis in effect takes a ‘snapshot’ of a population in a relatively short time period — for example, one year. Most rates are derived from period data and therefore are period rates. Compare to cohort analysis.

Population A group of objects or organisms of the same kind.

Population Control A broad concept that addresses the relationship between fertility, mortality, and migration, but is most commonly used to refer to efforts to slow population growth through action to lower fertility. It should not be confused with family planning. See also family planning.

Population Density Population per unit of land area; for example, people per square mile or people per square kilometer of arable land.

Population Distribution The patterns of settlement and dispersal of a population.

“Population Explosion” (or “Population Bomb”) Expressions used to describe the 20th century worldwide trend of rapid population growth, resulting from a world birth rate much higher than the world death rate.

Population Increase The total population increase resulting from the interaction of births, deaths, and migration in a population in a given period of time.

Population Momentum The tendency for population growth to continue beyond the time that replacement-level fertility has been achieved because of the relatively high concentration of people in the childbearing years.

Population Policy Explicit or implicit measures instituted by a government to influence population size, growth, distribution, or composition.

Population Projection Computation of future changes in population numbers, given certain assumptions about future trends in the rates of fertility, mortality, and migration. Demographers often issue low, medium, and high projections of the same population, based on different assumptions of how these rates will change in the future.

Population Pyramid A bar chart, arranged vertically, that shows the distribution of a population by age and sex. By convention, the younger ages are at the bottom, with males on the left and females on the right.

Population Register A government data collection system in which the demographic and socioeconomic characteristics of all or part of the population are continuously recorded. Denmark, Sweden, and Israel are among the countries that maintain universal registers for demographic purposes — recording the major events (birth, marriage, moves, death) that happen to each individual so that up-to-date information on the whole population is readily available. Other countries, like the United States, keep partial registers, such as social security and voter registration, for administrative purposes.

Post-Neonatal Mortality Rate The annual number of deaths of infants ages 28 days to 1 year per 1,000 live births in a given year.

Prevalence Rate The number of people having a particular disease at a given point in time per 1,000 population at risk.

Pronatalist Policy The policy of a government, society, or social group to increase population growth by attempting to raise the number of births.

Purchasing Power The ability of consumers to acquire goods and services based on their possession of money and/or their recourse to credit.

“Push-Pull” Hypothesis A migration theory that suggests that circumstances at the place of origin (such as poverty and unemployment) repel or push people out of that place to other places that exert a positive attraction or pull (such as a high standard of living or job opportunities).

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Race Race is defined primarily by society, not by genetics, and there are no universally accepted categories.

Rate of Natural Increase (or Decrease) The rate at which a population is increasing (or decreasing) in a given year due to a surplus (or deficit) of births over deaths, expressed as a percentage of the base population.

Remarriage Rate The number of remarriages per 1,000 formerly married (that is, widowed or divorced) men or women in a given year.

Replacement–Level Fertility The level of fertility at which a couple has only enough children to replace themselves, or about two children per couple.

Reproductive Age See childbearing years.

Reproductive Health Reproductive health is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity, in all matters relating to the reproductive system and to its functions and processes.

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Sex Ratio The number of males per 100 females in a population.

Social Mobility A change in status (for example, an occupational change).

Stable Population A population with an unchanging rate of growth and an unchanging age composition as a result of age-specific birth and death rates that have remained constant over a sufficient period of time.

Survey A canvass of selected persons or households in a population usually used to infer demographic characteristics or trends for a larger segment or all of the population. See also census.

Survival Rate The proportion of persons in a specified group (age, sex, or health status) alive at the beginning of an interval (such as a five-year period) who survive to the end of the interval.

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Total Fertility Rate (TFR) The average number of children that would be born alive to a woman (or group of women) during her lifetime if she were to pass through her childbearing years conforming to the age-specific fertility rates of a given year. This rate is sometimes stated as the number of children women are having today. See also gross reproduction rate and net reproduction rate.

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Under 5 (U5) Child Mortality Probability of a child born in a specific year or period dying before reaching the age of 5.

Undocumented Immigrant A foreigner who has entered a country without inspection or without proper documents, or who has violated the terms of legal admission to the country, for example, by overstaying the duration of a tourist or student visa.

Unmet Need Women with unmet need for spacing births are those who are able to become pregnant and sexually active but are not using any method of contraception (modern or traditional), and report wanting to delay the next child or limit their number of births. The concept of unmet need points to the gap between women’s reproductive intentions and their contraceptive behavior.

Urban Countries differ in the way they classify population as ‘urban’ or ‘rural.’ Typically, a community or settlement with a population of 2,000 or more is considered urban. A listing of country definitions is published annually in the United Nations Demographic Yearbook.

Urbanization Growth in the proportion of a population living in urban areas.

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Vital statistics Demographic data on births, deaths, fetal deaths, marriages and divorces.

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Women’s Empowerment means improving the status of women to enhance their decisionmaking capacity at all levels, especially as it relates to their sexuality and reproductive health.

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“Young” Population A population with a relatively high proportion of children, adolescents, and young adults; a low median age; and thus a high growth potential.

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Zero Population Growth A population in equilibrium, with a growth rate of zero, achieved when births plus immigration equal deaths plus emigration.