This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License. Your use of this
material constitutes acceptance of that license and the conditions of use of materials on this site.
Copyright 2009, The Johns Hopkins University and Nan Astone. All rights reserved. Use of these materials
permitted only in accordance with license rights granted. Materials provided “AS IS”; no representations or
warranties provided. User assumes all responsibility for use, and all liability related thereto, and must independently
review all materials for accuracy and efficacy. May contain materials owned by others. User is responsible for
obtaining permissions for use from third parties as needed.
Population Growth
Nan Astone, PhD
Johns Hopkins University
Objectives of the Lecture
„
At the end of this lecture and after reading the texts that
accompany it, students will be able to:
− Explain the demographic balancing equation
X Define natural increase and net migration
− Define population momentum
X Interpret a population pyramid
3
Section A
The Demographic Balancing Equation
Demographic Balancing Equation
„
Pt2 = Pt1 + (B – D) + (I – O)
− Where …
X Pt2 = population at time 2
X Pt1 = population at time 1
X B = births
X D = deaths
X I = in migrants
X O = out migrants
5
Demographic Balancing Equation
„
Pt2 = Pt1 + (B – D) + (I – O)
− (B – D) is referred to as natural increase
6
For Most of History, Natural Increase Was 0
„
„
Births = deaths until about 1000 CE
Then, gradually as the ability to store food and trade increased,
births began to exceed deaths
− Famines and epidemics were periodic setbacks
7
World Population Growth through History
Sources: Population Reference Bureau; United Nations. (1998). World population projections to 2100.
8
Number of Years to Add Each Billion
Sources: First and second billion: Population Reference Bureau; Third through ninth billion: United Nations. (2005).
World population prospects: the 2004 revision (medium scenario).
9
Rates of Birth, Death, and Natural Increase
„
Rates of birth, death, and natural increase per 1,000 population
Natural increase
Source: United Nations. (2005). World population prospects: the 2004 revision.
10
The Classic Stages of “Demographic Transition”
Stage 1
Stage 2
Stage 3
Stage 4
Birth rate
Natural
increase
Death rate
Time
Note: Natural increase is produced from the excess of births over deaths
11
Brief Digression
„
„
“The” demographic transition—nonsense
Many demographic transitions
− Fertility decline
− Mortality decline
− Hurricane Katrina
− The occupation of the Americas
− The Great Influenza
12
Demographic Balancing Equation
„
Pt2 = Pt1 + (B – D) + (I – O)
− (I – O) is referred to as net migration
13
Globally, Net Migration Is Always 0
„
„
„
Globally, net migration is always 0
At least, most of us think so
“The truth is out there!”
14
In Sum
„
„
„
„
For most of history, natural increase was 0
Gradually, between 1000 CE and 1800 (or so), natural increase
slowly increased as death rates went down and births began to
gradually exceed deaths
From 1800 onward, escalating sharply after 1950, births began to
exceed deaths by a great deal, resulting in dramatic population
growth
And then, fertility began to decline
15
Section B
Population Momentum
Objectives of the Lecture
„
At the end of this lecture and after reading the texts that
accompany it, students will be able to:
− Explain the demographic balancing equation
X Define natural increase and net migration
− Define population momentum
X Interpret a population pyramid
17
Average Number of Children per Woman
Source: United Nations. (2005). World population prospects: The 2004 revision.
18
Once Fertility Reaches Replacement
„
„
So, will population be stable once fertility falls (or rises) to
replacement?
Population momentum
− Population can continue to grow (or decline) even after natural
increase has reached 0, because the number of women of
childbearing age is very large (or small) because of past fertility
rates
19
Number of Births and Fertility Rate for the U.S. 1960 to 2001
4500000
140
4000000
120
3500000
100
3000000
80
2500000
Births Per 1000 Women 1549
Number of Births
2000000
60
1500000
40
1000000
20
500000
0
0
1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001
Year
number of births
fertility rates
20
Population of Ireland, 1986 to 2016
21
Population of Ireland, 1986
22
Population of Ireland, 1996
23
Population of Ireland, 2006
24
Population of Ireland, 2016
25
Population of Ireland, 2026
26
Population of Ireland, 2036
27
Population of Ireland, 2046
28
Why Is This Important?
„
Just because fertility rates have fallen for any given population
doesn’t necessarily mean that the distribution of the population by
age is going to remain the same
29