UNDERSTANDING POPULATION PROJECTIONS
FERTILITY MORTALITY MIGRATION

 

Projections are exercises showing the possible future size of a population and its age and sex distribution. In making projections, demographers make assumptions about future trends in FERTILITY, MORTALITY, and MIGRATION. Because projections can vary significantly depending on their assumptions, users of projections need to understand these assumptions before using them. Projections alert policymakers and program planners to major demographic trends that will affect key social and economic programs. The three main projections produced by the UN Population Division (UNPD) illustrate how assumptions can produce significantly different results over time.

 

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UNPD WORLD POPULATION PROJECTIONS

THREE

FERTILITY VARIANTS

The Medium Fertility Variant, most often cited, assumes an increase in the use of family planning resulting in fertility reductions in patterns similar to what occurred in other countries. The Low Fertility Variant simply assumes that in each country the average number of children a woman would bear at most periods in time is one-half child less than the Medium Fertility Variant, while the High Variant assumes that figure is one-half child more than the Medium Variant. Under these three scenarios, world population total would range from 8.3 billion to 10.9 billion in 2050 and from 6.8 billion to 16.6 billion in 2100.

 

 

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FERTILITY
BRAZIL

FERTILITY ASSUMPTIONS AND POPULATION PROJECTIONS

KENYA KENYA

FERTILITY ASSUMPTIONS AND POPULATION PROJECTIONS

FERTILITY ASSUMPTIONS AND POPULATION PROJECTIONS

Fertility often has the largest effect on future population size. Fertility is expressed as the total fertility rate (TFR), a measure of how many children women would bear in their lives if the rate of childbearing of a given year remained unchanged. Where fertility is high, it is usually assumed that fertility will decline as it did in countries with low fertility and eventually stabilize near two children per woman. That is referred to as “replacement level” fertility as couples merely “replace” themselves. Because of great variability in the future course of fertility, multiple projections are often created using different fertility scenarios, such as the UNPD’s High, Medium, and Low variants.

 

MORTALITY
JAPAN

LIFE EXPECTANCY AT BIRTH AND AT AGE 60

MALAWI

TOTAL POPULATION WITH AND WITHOUT THE EFFECT OF HIV

Mortality is incorporated into projections by estimating death rates by age groups and sex. Where mortality is relatively high and the resulting life expectancy at birth relatively low, changes in mortality also play an important role in future population size. Where mortality is already low and life expectancy has risen to high levels, mortality has much less effect. Demographers generally assume a continued decline in death rates and increased life expectancy. For the countries affected by the HIV epidemic, the impact of HIV on mortality is also assumed to continue for many decades, though now at a declining rate.

MIGRATION
MIGRATION FLOWS

BETWEEN MORE AND LESS DEVELOPED REGIONS

International migration can be particularly unpredictable and difficult to incorporate into projection assumptions. Migration flows often result from short-term and unanticipated changes in economic, social, environmental, or political factors. For many countries, reliable information on the number of immigrants and emigrants is not available. Given those factors, it may often be assumed that current migration levels will persist for a time and then slowly decline. Migration assumptions often take into account countries with historically high immigration, such as the United States. Still, the UNPD projects that net flows of immigrants from developing to developed regions will decline from today’s 2.6 million annually to 2.1 million in 2050, finally reaching zero by 2100.

 

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SOURCES:

United Nations Population Division, World Population Prospects: The 2012 Revision.

United Nations Population Division, World Population Prospects: The 2010 Revision.

AUTHOR:

TOSHIKO KANEDA, PRB

DESIGNED BY:

TESSA TRIPODI GRAPHIC DESIGNER, PRB

ERICHA GUDMASTAD MULTIMEDIA PRODUCER, PRB

FOR MORE INFORMATION ON HOW POPULATION PROJECTIONS ARE MADE, CHECK OUT THE UNDERSTANDING POPULATION PROJECTIONS POLICY BRIEF

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