Completing The Demographic Transition

JOHN BONGAART

RODOLFO A. BULATAO

Presented By

Md Azizul Haque

Department of Population Sciences

Second Semester

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IntroductionDespite ongoing decline in fertility in many countries,the population of the world is experiencing a period of rapid expansion, and its size is expected to exceed10 billion by the end of Demographic transition. Three Causes of this growth are identified and quantified:

1)Fertility above replacement2)Continuing decline in mortality3)Population momentum resulting from a young age

structure.

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Objectives of the Article

1.To propose a procedure for quantifying four components of future population growth.

2.To improve understanding of the demographic factors that determine long range population growth.

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Four factors are responsible for this:

1.Fertility above replacement

2.Declining mortality

3.Young age structure

4.Net immigration

Why population growth continues?

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Projection made by UN,WB, and other agencies that at the end of transection each of these four factors will have moved to level at which they no longer contribute to population growth.

That is

Fertility moves to replacement level

Life expectancy to its presumed maximum

Migration to zero

Age structure to its post-transitional equilibrium

Components of future population growth

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Continue

This set of assumptions conveniently ensures zero population growth. But there is no assurance that this is in fact will happen.

Now we made a hypothetical projection on the contribution of each of the four factors to future population growth.

Projection Variant Factors affecting future growth

Projected population size

1.Standard Young age structure, rising life expectency,fertility above replecement,net immigration

Ps

2.Natural Young age structure, rising life expectency,fertility above replacement

Pn

Replacement Young age structure, rising life expectancy

Pr

Momentum Young age structure Pm

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For this study we have made a series of projections, resulting in

estimates of Ps,Pn,Pr and Pm from 2000 to 2100 for all countries.

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ContinueIn order to directly compare the contributions of the different factors to future population growth, a set of factor “multiplier” is calculated.

Immigration multiplier Mi=Ps/Pn

Fertility multiplier Mf=Pn/Pr

Mortality Multiplier Md=Pr/Pm

Momentum Multiplier Mm=Pm/P

Where P represents the population size in 2000.

The combined effect of all factors is responsible for the population growth in the standard projection:

Ps=Mi.Mf.Md.Mm.P

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Population Projection variants 2000-2100,by region

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Population projections for 2000 and 2100 and factor multipliers for migration,fertility,mortality and momentum to 2100.

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Continue

The results in previous two figure show wide variation among regions in the contributions of the different factors to growth over next century.

-Momentum is the largest component of future growth in the world except in Europe.

-Migration, as currently projected, is a minor factor even in Northern America, Where Mi is just 1.03.

-The multipliers for fertility, mortality and momentum are larger in Sub-Sharan Africa than in any other region.

-The fertility multiplier exceeds one in the world and in most developing regions, but it is less than one in Europe, Northern America and East Asia, areas where fertility is currently below replacement.

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Alternative estimates of the population growth components

Momentum

Mm=A/Am

Where A represents the proportion of females under age 30 at the beginning of the projection periods i.e.2000.

Am is the same proportion at the end of the transection in a momentum projection.

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Mortality

Md =Am/Ar

Where Ar is the proportion of females under 30 at the end of the replacement projection

MigrationMf=(1+d)Y/30

This equation predicts that if fertility averages 50 percent above the replecement level over 330-year period(i.e.d=0.5,and y=30) then Mf=1.5

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Replacement GrowthThe ratio of population sizes at the beginnings and end of the replacement projection will be called the replacement growth multipliers. It is the product of mortality and momentum multipliers:PMr=Md.Mm

Natural Growth

The ratio of population sizes at the beginnings and end of the natural projection will be called the natural growth multipliers. It is the product of fertility, mortality and momentum multipliers:PMr=Mf.Md.Mm

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The end of transition

• Existing projections of UN and WB assume that at the end of the transition all countries will have fixed levels of fertility and mortality and zero migration.

• In reality,however,there are likely to be variations in levels of fertility, mortality,and migration among countries for the indefinite future.

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Conclusion

Population momentum is shown to be the main cause of future growth in most countries

and regions.ie, Africa,South,West Asia, Latin America.

In north, that means the developed countries will grow little or decline, as in that countries ferity is low, mortality is low and the age structure are no longer young.

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Thank You

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