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World Population Trends

January 26, 2012


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World Population Growth to 2005

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Top Ten Cities


Doubling Times

One way to translate the meaning of population growth rate is totranslate it into time it takes the population to double.

Let g be the rate of population growth. Then the doubling time,T solves

2 = (1 + g)T

ln 2 = T ln(1 + g)

ln(1 + g) ≈ g g small

T ≈ 0.69

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Fraction of Ever Alive

How many of people ever alive, are alive today?

Figures on population growth suggest that current populationrepresents a large proportion.

Not true. Figures misleading as more recent periods shown ongraph.

Keyfitz and others calculate roughly 8 to 10 percent of peopleevery born are alive today.


Adults Alive

However, infant mortality rates were high until the twentiethcentury. So many of the people ever born did not survive toadulthood.

If we rephrase the question in terms of adults, then the proportionincreases.

And with the expansion of education (and especially scientificeducation), likely it is truth the majority of people who becamecollege professors and engineers are alive today.


Trends

The textbook reports demographic trends by world region.

Straightforward can read on your own.

PRB reports by demographic behavior — fertility, contraceptivebehavior, mortality, urbanization and immigration.

Equally straightforward.

Will make selected comments.


Fertility

In (now) developed countries fertility declined rapidly during the19th Century, in the US from roughly 7 children 1800 to 4 childrenin 1900.

Fertility declined further and was low during the depression. In theUS fertility rose again following WWII.

Since the mid-1960s fertility to (in the US) slightly belowreplacement levels.


Fertility

Pattern for other developed countries, roughly the same. Secular(long–run) decline with current levels below replacement level.

The size and the length of the Baby Boom in the US was largerand longer than in other developed countries (boomlets).

And current fertility is higher in the US than in (nearly all) otherdeveloped countries.


Decline before Modern Contraceptives

Important to recognize the large decline in childbearing occurredbefore the introduction of modern contraceptives (e.g., pill).

Hence behavior is important. Even at 7 children, fertility is farbelow the biological maximum.

Hutterites have the highest recorded fertility, many womenreporting 16 pregnancies over their reproductive lifetimes.


Fertility Developing Countries

Here there is more variability across countries.

Countries such as (South) Korea has had very rapid decline and itsfertility rate is as low as many countries in Europe.

Countries in Africa with high fertility rates, birth rates (per 1000 inthe population) in the 40s, roughly four times the fertility ofdeveloped countries.

Highest in Africa, Southern Asia, with fertility levels in Latin andSouth America in the middle.


Cohort versus Period

Discussion above and in the readings mix two distinct notions offertility.

cohort A group of people sharing a common temporal demographicexperience observed through time.

For example, the birth cohort of 1987 is people born in that year.

A cohort measure of fertility measures completed fertility.


Period Measure

Period analysisObservation of a population at a specific period of time. Takes a“snapshot” of the population over a relatively short period of time(e.g., one year).

Most demographic rates are from period data and therefore areperiod rates.

Total Fertility Rate is a period measure of fertility. It measures theaverage number of children a woman would have given prevailingbirth rates.


Family Planning

Family Planning The conscious effort of couples to regulate thenumber and spacing of births through artificial and naturalmethods of contraception. Family planning connotes conceptioncontrol to avoid pregnancy and abortion, but it also includes effortsof couples to induce pregnancy. (PRB)

Family Planning Policy — the distribution of moderncontraceptives.


Reproductive Revolution

Use of modern contraceptive methods made it easier and safer tocontrol fertility.

Use of BC worldwide rose from under 10 percent of marriedwomen in 1960s to about 60 percent in 2003.

Debate on role family planning programs in reducing fertility indeveloping countries since 1960s. India and Indonesia primeexamples.

PBR reports family planning programs responsible for roughly halfthe decline.


Revolution or Development?

Economists frequently give less role to the programs in reducingfertility and attribute the reduction to economic development.

That economic development opens opportunities for women andlowers the demand for children.

Argument in part centers on whether reduction operates throughdemand-side or supply-side factors.


Mortality

Many different measures such as mortality rate (deaths per 1000population) and life expectancy (at birth and current)

Will define concepts when we study mortality, the PRB Handbookprovides definitions and discussion.

Life expectancy in developed countries is now about 75 to 80years. Japan has the highest and life expectancy there is 82 years.

Longer for women than men.

And varies in the US by race, lowest for African Americans.


Life Expectancy Highest and Lowest


Trend

In Europe and US death rates fell during the 19th Century andthrough the first–half of the 20th Century.

In many developing countries, mortality rates fell sharply afterWWII with the diffusion of advances in public health.

Improvements in sanitation, water

Control and near elimination of infectious diseases.


Mortality Falls Before Fertility

A common pattern is that mortality rates decline before fertilityrates decline.

Consequence: population growth


Largest Gains for the Young

Increases in life expectancy due primarily to reduction in infant andchildhood mortality.

Rare not to have a sibling die during childhood. In 1790 in the US,

life expectancy of someone 30 years old was about what it is today.

Before the 20th century in the US among women, child birth wasthe leading cause of death.


Impact of HIV/AIDS

The effect of HIV/AIDS in Africa is transparent.

98 percent of HIV/AIDS related deaths in 2003 were insub–Saharan Africa and other less developed regions.

HIV/AIDS reversing many of the gains in health and lifeexpectancy obtained in the last 50 years.


Migration and Urbanization

Migration within and between countries affects population growth,and the distribution of the population by age, sex and otherdimensions.

20th Century movement from rural to urban areas

Yet only 18 percent of population in developing countries lived inurban areas in 1950. Increased to 40 percent by 2000. Rapidchange.


Migration and Immigration

Approximately 175 million people are international migrants.(about half the size of the US population)

5 to 10 million people become international migrants each year

Most international migrants move from one developing country toanother.

Most move to take advantage of economic opportunities, but 14million are refugees


South to North

Flows from developing to developed countries, labeled as “Southto North”

From South and Central America and Asia to North America, andfrom North Africa and the Middle East to Europe.

Flows among developed countries relatively small.


Population Momentum

Ferility, mortality and migration trends reflected in the age and sexprofiles of the world’s countries.

Fertility has the greatest influence and decades of high fertility inthe less developed countries have meant ever–increasing numbersof young people.


Age Pyramids


Comments on Age Pyramids

Provide a simple graphical device to describe the age and gendercomposition of a population.

Men on the left and women on the right. Percent share of anabsolute count is the base while (5–yr) birth cohorts comprise thevertical axis.

Several striking features.


West Africa Pyramid

West Africa — a region with high fertility and mortality. Ravagedby HIV/AIDS.

High fertility rate evident in the large base of the pyramid.

High mortality rate evident by the sharply declining steps.

Also possible to see the effect of differential mortality by sex.


Western Europe Pyramid

Western Europe — a region with low mortality and very lowfertility.

Low fertility rates evident by the relative small share ofchildren/youth in the population.

Low mortality evident from the large elderly population. As manyelderly as there are young!

Effect of WWI and WWII evident as well.


Population Momentum: Example

Consequence of the large base of the West African population is apowerful force for future population growth as the ever–largercohorts move into childbearing ages.

The number of women in childbearing ages in West Africa willroughly triple between 2000 and 2050 (i.e., from 52 million to 151million).

Even if they have fewer children than their mothers did, WestAfrican women will produce 11 million births annually during the50–year period.


Population Momentum: Definition

Population Momentum is the tendency for population growth tocontinue beyond the time that replacement–level fertility as beenachieved because of the relatively high concentration of people inchildbearing ages.


Western Europe Negative Momentum

The narrow base of the population pyramid in Western Eurpe is apowerful force for “negative momentum.”

The number of potential mothers is shrinking from 44 million in2000 to 36 million in 2050.

Even if women in Western Europe have slightly more children thantheir mothers, the annual number of births is projected to decline,staying below 2 million per year.

And with large share of the population that is old, the annualnumber of deaths will increase, from 1.8 million in 2000 to 2.5million by 2050.


Consequence of Momentum

Population growth is virtually certain in West Africa

Population will decline in Western Europe unless there issubstantial immigration


Explaining Population Change

Here I (economists) separate company with the demographers.

Demographers appeal to proximate determinants.

So will ascribe fertility reduction to increased use of contraceptivesand abortion.

An example is in PRB (2004, p.15)


TFR Mali vs. Brazil

The vast difference in contraceptive use in Mali andBrazil is the primary reason why Mali’s TFR was 6.8 andBrazil’s TFR was 2.5 in 2003. In Mail, less than 9percent of women of reproductive age used acontraceptive in 2003, compared to about 76 percent ofBrazilian women. (page 15)


Proximate Determinants

Useful to tell us about the prevalence of contraceptive usage.

But what kind of behavioral explanation is it?

Contraceptive use is a choice, and a means to an end. Why is thedemand for children less in Brazil than in Mali?


Other factors

PRB also considers the effects

I Education

I Household income

on fertility.

Same concern about interpretation.


Gender Roles

PRB discusses the effect of Gender Roles.

Accept their presence. Question of interpretation.

Part of individual preferences. Economists take preferences asgiven.

Yet, where does “culture” come from? Why do some societiesgenerate preferences for sons?


Policy Responses — Fertility

Fertility of central importance for population change.

Is it possible for governments to intervene and increase fertilityrates?

Family policies — subsidize child care, housing, parental benefits.Equal opportunity for women to balance family and workplacedemands.

Extreme is China’s “One Child” Policy. Largely criticized asregressive and harshly administered.


Policy Responses — Immigration

Policy can also influence immigration flows.

Social planner would move population from West Africa toWestern Europe.

Solve overcrowding, rapid population growth in Western Africa

and the consequences of an aging and declining population inWestern Europe.


Germany shows not so easy

Germany needs 3.4 million immigrants per year to retain aconstant ratio of working–age to retired people.

From 2003 to 2050 the total number of immigrants needs will bealmost 175 million, or twice Germany’s current population.

Germany not so keen to see this as a solution.


Questions for Future

From the PRB (2004)

I Will people in Africa, Asia, and Latin America come to prefermuch smaller families now preferred in Europe?

I Will developing countries be able to provide family planningservices to impoverished populations?

I Will the HIV/AIDS epidemic in Asia and other developingregions reach the catastrophic levels seen in Southern Africa

I Will increased mortality from HIV/AIDS spur families to havelarger families?

I Will climate change or environmental degradation threatenhuman health?

I Will couples in Europe and other low–fertility societies havemore children?


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