This document discusses factors that contribute to population growth even after fertility declines below replacement levels. It proposes quantifying the contributions of four factors - fertility, mortality, age structure, and migration - through "multiplier" estimates. Projections show momentum from a young age structure is the largest growth component worldwide except Europe. Fertility remains above replacement in most developing regions but below in Europe, North America, and East Asia. The standard assumptions of fertility reaching replacement and zero migration may not reflect reality.

1. Completing The
Demographic Transition
JOHN BONGAART
RODOLFO A. BULATAO
Presented By
Md Azizul Haque
Department of Population Sciences
Second Semester
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2. Introduction
Despite 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 exceed
10 billion by the end of Demographic transition. Three
Causes of this growth are identified and quantified:
1)Fertility above replacement
2)Continuing decline in mortality
3)Population momentum resulting from a young age
structure.
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3. 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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4. Why population growth continues?
Four factors are responsible for this:
1.Fertility above replacement
2.Declining mortality
3.Young age structure
4.Net immigration
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5. Components of future population
growth
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
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6. 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 Projected population size
growth
1.Standard Young age structure, rising life Ps
expectency,fertility above
replecement,net immigration
2.Natural Young age structure, rising life Pn
expectency,fertility above
replacement
Replacement Young age structure, rising life Pr
expectancy
Momentum Young age structure Pm
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7. 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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8. Continue
In 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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9. Population Projection variants 2000-2100,by region
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10. Continue
Population projections for 2000 and 2100 and factor multipliers for
migration,fertility,mortality and momentum to 2100.
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11. 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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12. 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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13. Mortality
Md =Am/Ar
Where Ar is the proportion of females under 30 at the
end of the replacement projection
Migration
Mf=(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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14. Replacement Growth
The 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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15. 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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16. 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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17. Thank You
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