INTRODUCTION TO POPULATION STUDIES By Mwakalinga mboka Presentation Transcript
G E 2 4 7
I N T R O D U C T I O N
P O P U L A T I O N
S T U D I E S
Topic 2 : Population Data, Structure and Theories
–Nature and sources of population data
–Age and sex population composition;
–Determinants of age and sex
composition; sex ratios
–Measures of population: Fertility and
–Basic population theories
Nature And Sources of Population Data
• One of the major role of demographers is to find
information on the number of people in a given
time and place.
• Estimating population size is not an easy task.
• It is of one of the involving work, requiring a lot of
investment in terms of resources.
• In order to obtain population data, demographers
rely on a wide array of instruments and institutions
to carry out their work.
• Population data can be generally divided into two
main categories which are stock and flow data.
1. Stock Data
Stock data is the one that shows the state of
population in an area at a given point in time.
2. Flow Data
This is the one that shows how the population
changes with time.
THE NEED FOR POPULATION DATA.
• In any given country, population data is required in
order to provide information on the following.
The number of people and their distribution within
that particular country.
Population characteristics, for different populations
might have different characteristics.
The current trends, levels, and patterns of fertility
Migration patterns within and outside the country’s
SOURCES OF POPULATION DATA.
• There are several major and minor methods that
have been adopted and are therefore used by
demographers to obtain population data.
• The major ways includes
1. Census 2. Sample surveys
3.Vital Registration System
• At a simple level, a census is a straightforward count
of the number of people in a country, region or a
• UN (1967), defines a census as the total process of
collecting, compiling and publishing
demographic, economic and social data pertaining
at a specified time or times to all persons in a
• This therefore, implies that, though the exercise
may sound simple in its definition, censuses
however are not usually so simple.
• This is because, most census are also directed at
gathering other information about people such as
people’s economic and social information, such
as, marital status and income, education
levels, previous residences, etc.
• The UN has given the essential features that a
population census need to have, which are as
1. It must be carried by the government.
2. Individual enumeration, i. e. all people must be
listed with their specified characteristics.
3. Universality within a territory, i. e, it should cover
the country’s entire territory.
4. Simultaneity, i. e. popn enumeration should refer
to one, well defined point in time. e.g number of
people in a given night.
5. Defined territory, i.e A census should relate to a
defined territory so as to allow comparison with
6. Defined periodicity. e. it should be taken at regular
intervals e.g every ten years or so for easy
comparison and population projections
DE JURE AND DE FACTO CENSUS
• Enumeration of people in a census may be done
using a de facto method or de jure method.
1. DE FACTO METHOD
• In this method, a person is counted wherever that
person is found at the time of census.
• This method is recommended by the UN.
2. DE JURE METHOD
• In this method, a person is enumerated at his or
her usual place of residence, irrespective of where
they were at the time of census.
• NB: Each country have to decide on the method to
• In most African countries, census was and still is the
main source of obtaining population data.
• In most of these countries, census has passed into
different stages from colonial periods, where census
was carried out mainly for colonial administrative
purposes and for the aim of obtaining human
resource for various areas and fields of population
• Therefore, the census were at the favour of
colonialists and not to the native people.
• In 1969 the African census programme was
formed, the purpose was for marking, identify
resources and identifying demographic strengths
of the nations.
• Even after the abolition of slave trade, most
African countries realized that census is important
for statistical needs.
• Census data was needed in order to make resource
allocation, provision of public services and other
• Due to the needs, most African countries opted on
taking census for their own uses and the exercise
• Census exercise therefore was adopted by many
African countries as one of the important exercises
for any given nation.
• But with few resources and expertise, most census
exercises were confronted by some problems.
• These were like, problems of census mapping
,census tests enumeration procedures, quality
control and definition of various terms.
• The quality of census data in Africa has improved
• Despite the fact that most of African countries are
now able to carry out periodic census, still a lot
remain to be done.
• Most of African countries are still not collecting
accurate data on various issues that characterise
population. These are like fertility and mortality
data, education, employment, migration, etc.
• Therefore periodic census taking is very vital
because population is very vital in environmental
issues for environment sustainability. Generally
census is vital because of sustainable development
and environmental management.
• Advantages / Uses of Census Data.
Census are provide useful information to the
government on various issues, which are.
To know the actual number of people in a given
tome and space
This will help in resource allocation and provision
of other public services like schools, hospitals, etc
Census helps to know social characteristics in
births, mortality, marriages, divorces, migrations
To plan for administration patterns and other
political aspects within a country, and collection of
taxes and other issues.
• Information from census will help to know the
actual human resource in terms of economic
production s and dependency.
• Census data is useful for estimating future
population trends of a given society.
• To know the current trends on the use of natural
resources and the environment at large, and this
helps for planning for environmental conservation
and conservation measures to be taken.
Generally, information obtained from census is vital
for any nation to have sustainable economic, social
and political development.
Limitation of census
• Census enumeration are an extremely expensive
and labour intensive undertaking for any
governmental jurisdiction as a result they occur
rather infrequently usually no more than every 5 or
• The incompatibility of enumeration dates makes
comparison among countries difficulty. Language
barrier might be an obstacle to some of
• There is no a census which is entirely
comprehensive as all census tend to under
represent nonmainstream kinds of household as
well as homeless individuals
2. Sample Surveys
• This is the second and most important source of
• This is a method in which information is collected
only from a portion of a population.
• It is a kind of mini census which is small, well
designed and well administered. It is less expensive
and more accurate than the census. Its reliability
depend on sampling methods and the
recommended one is that which uses probability
• Sample survey are done periodically , especially
during inter census period in order to get
information on population characteristics like
population migration, fertility, mortality etc, and
they are used to check the accuracy of census data.
Types of Sample Survey.
There are two types of sample surveys
1.Single round survey 2.Multi round survey
1.Single Round Survey
• These are always done once in a periodic time.
Simple to conduct
Flexible for easily administration
Under or over reporting of information
It has non sampling error ( it is somehow biased)
2.Multi Round Survey
• This is a kind of sample survey in which, a sample is
choose and used as follow up surveys over a period
• Here repeated visits are made to the selected
respondents to ascertain what events have
occurred during the period between the visits.
• It is useful in providing information that can be
used for checking and correcting previous collected
• Expensive and difficult to administer
Uses Of Sample Survey Information
• To collect vital statistics where official registration
system is inadequate or hasn’t been existed
• To collect supplementary data where it is not
possible to collect the same information during
• To test the accuracy of the census information
• To estimate the total population and its distribution
• It provide information in-between the census
Limitations Of Sample Survey
• Possibility of making error in sampling and hence
become less reliable
• There is a possibility of being biased rising from the
design of the survey or failure to design properly
that may lead into some sub group be omitted from
• Sample survey is most used in developing countries
because they can not afford census
3.VITAL REGISTRATION SYSTEM/ VITAL RECORDS
• Vital events are those that affect population its size
and composition. Vital registration system is among
the major sources of population information.
• The UN defines vital registration system as a system
that include the legal registration, statistical
collection, recording, compilation and
analysis, presentation and reporting of the statistics
patterning to vital events which include live
births, deaths, foetal death, marriage
divorce, abortions, separation and migration.
• These data are collected , and records of them are
kept by all levels, from local to country level.
• To these authorities, vital records is a compulsory
process of recording population characteristics.
• The recording is mainly done by the government
registrar but also it can be done by other
governmental agencies like
schools, hospitals, police departments
, prisons, Immigration departments,
• For vital registration to be useful and precise it
must cover the whole country, and if it doesn’t , it
can bring incorrect information.
• The main objective of vital registration is just to
meet the national data requirements and to collect
identical information which is comparable to that of
• There are two topics/ categories covered
• The topics that describe the characteristics of the
• The other deals with topics that describe
characteristics of persons involved direct in the
events specifically parents.
• The birth registration include characteristics of the
event or child such as date of occurrence
registration name, sex, type of birth (normal or
operation ) and place of occurrence, etc.
• It also include characteristics of the parents such as
date of birth, name , date of
marriage, occupation, usual place of residence, and
names as well as ages of previous children.
• The death registration records information related
to the name, age sex, and marital status, occupation
place of birth date and cause of death.
• The marriage registration information include date
of birth, occupation, the regions place of
birth, usual places of residence, previous marital
status of both partners together with date and
place of marriage.
• The divorce registration information include date of
divorce, date of birth of partners, occupation and
usual place of residence.
• Data for international migration include
information on age, sex, marital
status, occupation, nationality of the migrant the
purpose of visit and expected time to stay
Uses Of Vital Registration
• It helps to measure rate of population change
especially in mortality and fertility it provide floor of
• It provide information which is important for social
and economic planning i.e.
education, health, voting etc
• It provide valuable record about individuals in a
• It provide legal documents that an individual may
need i.e. birth certificates, death certificates and
these help an individual to inherit or pursue his or
her own carrier , to claim allowances and
• It provides information that can be used on check
on census enumeration especially on places where
there is under enumeration.
• It help to up date information on every change that
is occurring on population for planning purposes
Limitations of Vital Registration System
• Over or underreporting of information
• It is very efficiency in urban that in rural areas
• Miss statement of the age especially the sick one or
one who has died
Therefore, vital records generally are useful in
provision of current information about the
characteristics of a given population in a given
period / time.
• Advs of vital registration over Census ans sample
• Population composition simply refers to the sub
groups that constitutes a given population.
• Population composition summaries the population
of a country or world by age and sex.
• Age and sex are two principle characteristics of a
• Sex a condition of being a male or a female, and
age, related to number of years individual males
and females have in a given population.
• Understanding population composition enables
geographers to gather important information
about population dynamics (population changes
• These two characteristics of population are
important because they bring about variations in
Foristance, knowing the number of women of
childbearing age in a population, along with other
information about opportunities and status, can
provide valuable information about the future
growth potential of a given population.
• Therefore, understanding population
composition is vital as it can tell much on future
demography of a given region as well as the present
• Many factors determine the age – sex
composition, but the most important factor is
• This is the most important factor in determining
• A population with high birth rate will have a large
proportion of young people while a population with
how birth rate will have a small number of young
• It determine the composition but in the minimal
way. Except when there is especial case like if there
is war, which wipes out certain age groups and
• This also determines population composition I a
very minimal way.
• This is because migration is also age and sex
selective, where individuals in certain age groups
and sex are liable to migration than others.eg
AGE – SEX PYRAMIDS.
• A population age - sex pyramid is a graphical
representation of all individuals in a population by
using a bar graph.
• It is a representation of the population based on its
composition according to the age and sex
• An age sex pyramid is therefore a bar graph which is
displayed horizontally, where males are portrayed
on the left hand side of the vertical axis and females
on the right hand side of the vertical axis.
• Age categories are ordered sequentially from the
youngest at the bottom of the pyramid to the oldest
at the top.
• A population pyramid is a two bar graphs, back to
back with vertical centre lines.
• The age is shown along the vertical axis and the
population is shown as percentage on the
horizontal axes on both sides.
Age sex Population Pyramid of Ethiopia, 2000.
• NB. The shape of a population pyramid can differ
slightly with places and time from the basic shape
described above. They may differ in arrangement of
the items, while the items are the same.
• The use of population age-sex pyramid is the best
way to present population data.
• A population pyramid shows the demographic
history, allow demographers to identify changes in
the age and sex composition of populations, and
provides an opportunity to demographers to access
the potential impacts of a growing and declining
• The shape of the pyramid can tell us a great deal
about the present and future of the population
• There are several types of population structures.
These are discussed below.
Types of population structure
The are five distinguished population structure
• Is a triangular shape pyramid, which is
characteristics of those countries that have high
birth rate and high death rate.
• Neither of the two (birth and death) shows
decline, it suggest more individuals who are
youth, and it has small old age group, but show a
rapid population growth.
• Pyramids of this type were more common
• During 17th and 18th centuries, and they do not
exist in today's world.
2. Type 2
• It is concave shaped population pyramid, showing a
population where death rate is declining while birth
rate is remaining high it constitute a large
population being young. eg less than 15 years.
• It shows a population where death rate is declining
whereas birth rate is still high.
• It has a narrow top and a wide base.
• It has a high potential for future population growth
due to reduced child mortality, and therefore more
young people will be able to enter child bearing
• It is a characteristic of many developing countries
today, eg Tanzania, Kenya, etc
c/ Type 3
• This is a convex shaped pyramid, which is a narrow
based pyramid with convex sides.
• It indicates low population growth and population
• It is associated with countries having low birth rate
and low death rate, eg Sweden, British.
d/ Type 4
• This is a bell shaped pyramid, which shows a
population where death rates are declining
• It is found in countries like Canada, and USA which
have experienced baby boom (abrupt increase of
• The marked narrowing in the reproductive age
period indicates a decline in the birth rate at an
• However, there is a renewed increase in birth rate
after a considerable period of low birth and low
e/ Type 5
• It is a pyramid which shows a population where
death rates are declining.
• It also shows a population that was once growing
very rapidly and then experienced a dramatic
decline and continued decline in birth rates. eg
MEASURES OF AGE SEX COMPOSITION.
1. Dependency Ratios
• Dependency ratio refers to a measure of the
economic impact of young and old people on the
more economically productive members of the
• Often is divided into three distinct groups, which
Young Cohort / Young Population, comprising of
those aged less than 15 years.
• These are considered to be too young to be fully
active in the labour force and they are therefore
Middle Cohort / Productive population comprising
of those between 15 – 64 years.
• These are considered to be economically active, as
they are actively involved in labour force.
Old Age Cohort / Aged population , comprising
those aged 65 and above.
• These are beyond their economically active and
• By dividing the population into these three groups,it
is possible to obtain a measure of the dependence
of the young and old upon the economically
active, and the impact of the dependent population
upon the undependent.
• Dependency ratio is can be easily obtained through
the following mathematical relationship.
Popn 0 -14 + popn 65+
Dependency Ratio = ………………………………… x 100
Popn 15 – 64
• Dependency ratio measures the number of
dependants that each 100 people in the middle
cohort must support.
• Depending on the population structure and
composition, each country has its own dependency
• Some countries have a high dependency
ratio, because of having many individuals in the
young and / or old cohort.
• Typical examples are found in some developing
countries, where birthrates are high and death rate
• Other countries have low dependency ratio because
of the few individuals in the young and old cohort.
• Developed countries shows a low dependency
• A high dependency ratio means less servings and
therefore little or no money will be available for
investments, while with a low dependency
ratio, there will be serving and investment will be
2. Sex Ratios
• This refers to the ratio of males to females in a
• It is the number of males per 100 females in a
• Sex ratio can be easily obtained for a given
population by using the following formula.
Number of males
Sex ratio = ………………………………………… x 100
Number of females
• The sex ratios are important to demographers because
they can affect the population dynamics in in a given
• Sex ratios indicates the following
The sex ratios of 100 indicates that there are equal
numbers of males and females in a population.
• In this kind of population, there is a great probability of
population increase, as these people reach
reproductive age, it will be easy to find mates.
A ratio of over hundred indicates that there are
more males than females, a condition which
predicts a slow population growth.
A ratio of below hundred indicates that there are
more females than males.
• The naturally occuring sex ratio in human
population at birth features a slight predominance
of males than females, i. e. for every 100 female
infant born, 105 to 106 males are born.
• Sex ratio is normally affected by
mortality, migration and fertility.
• At every age, males have a higher death rate than
• Foristance, long distance migration is preferred
most by males than females, who prefer short
• Other catastrophes like wars tend to wipe more
males than females.
• Selective abortions on the other hand have got
significant impacts in the population. This is
because some couples will selectively abort a given
fetus of a given sex due some cultural dictations.
• There are several measures of population, which
Count – The absolute number of a population or
demographic event (eg a birth) for a specific time
Rate – The frequency of a demographic event in a
population for a given time period.
Ration – The relation of one population sub group
to the total population or to another sub group
MEASURES OF POPULATION
• In order to arrive at different understanding of
population growth and change, experts look at two
significant factors which are fertility /natality and
• This is because the two are important measure of
population change in a given society.
• Birth and death rates, along with other factors like
migration help to determine whether a human
population grows, shrinks or remain fairly stable.
The Concept of Fertility.
• Births are the primary means by which numbers are
being added to the existing population, and
therefore it is an important demographic variable in
overall population growth.
• Fertility/ Natality refers to actual bearing of
children. It refers to the number of individuals
added to the population through reproduction.
• Fertility rates refers to the relative frequency with
which births occur within a given population.
• Therefore, fertility is the actual number of live
births born by a female.
• Live births reset to any child born alive. Fertility
occurs over time and therefore it can be measured.
• Fertility differs from fecundity in a sense that
fecundity is the biological capacity to bear children.
i. e. the potential to give birth.
• Fertility can be looked at with regard to the
• Marital fertility which refers to fertility that occur
within marriage and it counts for greatest
percentage of all fertility.
• Teenage fertility, which refers to fertility that occurs
• Non - Marital Fertility which is any fertility that
occurs outside marriage boundary.
• Overall fertility refers to total fertility, whether
within or outside marriage boundaries.
• Fertility is an important factor in demography
simply because it can happen more than once to
the same individual, while death happens only
• However, fertility is less predictable than mortality
mainly because it is linked to a wide range of
cultural and social variables and to the level of
MEASUREMENTS OF FERTILITY.
• Fertility can be measured.
• For convenience, fertility is measured by accessing
the rates that shows the frequency with which it
• There are several measures of fertility, and these
are as follows.
1. Crude Birth Rate,(CBR).
• This is the ratio of the number of live births in a
single year for every thousand people in a
• It is called crude because it measures the birthrate
in term of the total population and not with respect
to a particular age specific group/cohort.
• To calculate the CRB, take the total number of births
in a year for a region and divide by the mid – year
population then multiply by 1000.
CBR = Number of live Births
...................................... X 1000
• The CRB of any given society/country is affected by
many factors, which includes the level of economic
development, women’s educational
achievements, religion, social
customs, diet, health, political and civic unrest, etc.
Foristance, if the total population of country X in a
given year X is 40 000,000 people and the number
of live births in the same year is 4000 births, then
CRB = ..................... X 1000 = 10
The CRB will be equal to 40. (i. e 40 children per 1000
people in a population.
• The major weakness of this measure is that it
assumes the involvement of the whole population.
• It includes even children who do not have the
biological capacity to bear children ,males and
elderly people who are in their post reproductive
• Therefore it is not an inadequate measure of actual
fertility because its denominator includes many
persons who do not contribute to births.
• If a population consists of a higher proportion of
children, males and older people, then the CRB will
be lower than its actually supposed to be.
2. General Fertility Rate, (GFR)
• This refers to the number of live births per 1,000
women aged 15 – 49 which is the typical cohort of
child bearing years in a particular year.
• To calculate the GRF, the total number of births in a
year for region is divided by the total number of
women age 15 – 49 in the same year (i.e those “at
risk of giving birth), then multiply by 1000.
Number of live births
GFR = ....................................................... X 1000
Number of women aged 15- 49
For example, if a given population has about 215 live
births per year and the total number of women of
child bearing ages are about 22500, the GRF will be
Number of live births per yr
• GFR = ………………………………………………... x 1000
Number of women of 15-49 yrs
= 215/22500 x 1000 = 9.5/1000
i. e, there are 9. 5 live births for every 1000 women in
child bearing age.
3. Age – Specific Birth Rate, (ASBR)
• This refers to the number of live births to women in
a give age class, like 15- 19, 20 – 24, 40 – 44, etc.
• It is obtained by taking the total number of birth to
women in a particular age group and divided by the
total number of women in that age group.
Number of live births by x age group
ASBR = .......................................................... X 1000
Number of Women of x age group
• Foristance, live birth to women 15 – 19 were
200, while the total number of women aged 15 – 19
ASBR = (200/665) x 1000 = 12/1000
• This means that for every 1000 women in that age
group, there were 12 live births.
• ASBRs are useful because child bearing varies
considerably with age, i. e it is not evenly
distributed over the whole period from 15 to 49
• Therefore, the ASBR brings out the differences in
fertility that is due to age.
• Child bearing begins gradually and reaches its peak
in late twenties and early thirties, from there, it
declines slowly among some populations and more
rapid among others.
• ASBR is more referred measure of fertility because
the dominants include the women only those on
their child bearing ages, who are at the risk of
having live births.
3. The Total Fertility Rate (TFR).
• This is a measure of the average of number of
children a woman will have throughout the years of
her childbearing ages, which are 15 to 49.
• It is a more predictive measure of fertility than
CRB, that tries to portray what birth rates will be
among a particular cohort of women over time/
during her life time.
• Replacement fertility , on the other hand is the TFR
that keeps the population stable.
• For humans, the RF is equal to the TFR of 2.1.
• A TFR higher than 2 implies the replacement and a
stable population, but below 2, and in absence of
migration, the population will shrink.
• This is an artificial measure, as it does not apply to
any individual woman. It is a way to asses the child
bearing habits of a typical woman using the
dominant child bearing habits of all women in a
society at a given time.
• Here the age specific birth rate is not multiplied by
100 or 1000 but by five. Multiplying each of the rate
by five provides the number of children she would
have for each five years period. Summing up the
rates for all age categories results in the number of
children she would have by age 49 , which is the
total fertility rate.
READ & WRITE ON
The Concept of Death/Mortality.
• Mortality refers to deaths occuring in a population.
• Death is defined a the permanent disappearance of
all evidences of life at any time after birth has taken
• Death is one of the life certainties, as every
individual in a population will eventually die at one
• Though death is certain, the length of time a person
lives depends on many factors.
• Some people die sooner than others, and
generally, death comes earlier to males than
Causes of Mortality.
• In any given population, mortality varies from time to
time and from place to place.
• The UN has grouped its causes into five major groups.
Group 1 – Includes all deaths which results from
infectious, parasitic and respiratory
Group 2 - Deaths occuring due to cancer.
Group 3 - Deaths occuring from diseases of circulatory
system e.g. BP, Hypertension, e.t.c
Group 4 – Deaths occuring from violence including
Group 5 – Deaths occuring due to other causes, e.g birth
injuries, diabetes, etc.
• The prevalence of each cause of death is strongly
related to overall level of mortality.
• As the average life expectancy of a population
increases, the proportion of deaths due to group 1
• The proportion of deaths due to group 2 and 3
increases slowly until life expectancy is sixty and
then increases sharply.
• The proportion of deaths due to group 5 diseases
increases slightly until life expectancy reaches 70
years and then declines sharply.
• Deaths attributed to violence or accidents do not
seem to be related to overall mortality.
• The pattern shows that, as a society
modernizes, the infectious and parasitic diseases
are brought under control and deaths declines.
• This is due to modern medical services and the
improved standards of living of people.
• At the same time, the proportional of deaths due to
degenerative diseases increases significantly, as
observed from most developed countries.
• Causes of deaths can also be explained as follows.
1. Congenital malformation and genetic errors of
reproduction and diseases.
2. Famine or malnutrition and accidents.
3. Wear ant tear of vital organs due to old age.
1. Group one diseases are responsible of the early
mortality during infancy and childhood
2. Deaths in the second group occurs during the later part
of infancy and early part of childhood. Most of them
are attributed to infectious or parasitic diseases.
Scarcity of food, increases mortality rated to
infants, children, pregnant mothers and old people.
3. The third group affects more later stages of lifespan.
Though they are automatic, but human behaviors can
accelerate them e.g. food, leisure, alcohol and drug
use, smoking, environmental pollution e.t.c
NB. Causes are also explained by the epidemiological
transition model which will be studied later.
• The timing of death varies among categories of
people ,where the risk of dying differs with age, sex
, race and economic status.
• Mortality is closely related to age, where death
rates are more to infants under age 1, and is low
for children, adolescents and young adults and the
increases in old ages.
• Death risk appears to be more to males than
females at all ages and in all
populations, therefore, males have a higher death
rates than females.
• It is argued that, this is brought by the biological
differences between males and females where females
are biologically superior to males
• The other reason is that males are deployed more in
hazardous occupations than females.
• Females lives about 4 years longer than males and in
developed countries, this difference is as high a 7 years.
3. Economic Status
• The higher the social economic status, the lower the
level of mortality.
• Coupled with occupation and levels of education, the
social economic status of the population is an
important aspect in mortality because, it reflects the
differences in income/earnings, which in turn affects a
number of life related facilities.
• Differences in income and earnings leads to
differences in access for health facilities, diets and
general nutrition, clean and safe
environments, amount of stress and strain that
exists within social and economic strata e.t.c.
• Occupational differences also brings about
differences in mortality rates in a given
population, lifestyle differences associated with
membership to various social economic strata are
also factors for differences in mortality rates.
• Education on the other hand is an important aspect
of differences in mortality rates in a population.
Measures Of Mortality.
• Several methods have been devised by
demographers in order to have mortality statistics.
• These includes the following.
1. Crude Death Rate (CDR)
• This refers to the number of deaths in a year per
thousand people in the population
• To calculate, take the total number of deaths in a
year for a region and divide by the total population
Number of deaths in a year
CDR = .................................................... X 1000
Total population in a year
• It is a crude measure because the total population
is taken as the denominator, whereas the
probability of dying in a particular period is not
equally foe everyone in the population.
• It is therefore affected by a number of factors
including the age sex composition of the population
and other population characteristics.
• Age structure affects CDR, where older population
may have high CDRs, but these reflect the age
structure not the health conditions or other factors.
• However, CDR is useful as it gives a general
indication of the levels of mortality in a given
2. Age Specific Death/ Mortality Rate (ASDR)
• This refers to the number of deaths that occur
within a specific age in a given year, e.g. 0 – 4, 5 –
9, 30 – 34, e.t.c.
• It is amore refined measure of death, because
death is more likely to dominate more in some
No. of deaths in a specific age
ASDR = …………………………………………………… X 1000
Total Population in the same age
• This rate is computed separately for each sex.
• ASDR is more accurate measure of death because it
takes consideration of specific age groups.
• Generally, death rates are lowest for adolescents
and young adults and the rates are highest in
infancy and in early childhood as well as in old ages.
3. Infant Mortality Rate (IMR)
• This refers to the number of death of infants under
age I per 1,000 live births in a given year.
No of deaths of infants under age 1
IMR = ...................................................... x 1000
Total live births
4. Cause Specific Death Rate, (CSDR).
• This measures the importance of certain cause of
deaths in a given year.
• It gives the percentage of deaths due to a certain
cause as opposed to total deaths in a year.
Deaths due to a certain cause
CSDR = …………………………………………… x 1000
Total Deaths in a year
• This measure helps to show which cause is
important in causing deaths and therefore it gives
an opportunity of eradicating it.
• Life expectancy refers to the average number of
years one could expect to live if the current age –
specific death rates remained the same for the rest
of his or her life.
• Life expectancy varies by sex, age and other factors.
It is usually cited separately for males and females.
• Life expectantly at birth – Average number of years
a baby born this year can expect to live if current
specific death rates remain the same.
• Life expectancy is a good indicator of health
condition and a general estimate of population of
individuals in a given population.
FACTORS THAT CAN DETERMINE IF WORLD
POPULATION GROWTH RATE IS RAPID
Population growth rate between years
e.g. Between 1880s to 1890
1990 – 2005
• This can show if it is increasing or decreasing
Population size from various census is also an
important factor for determining whether a
population is changing or not. Also other forms of
census data will give the same information.
Example, from various census we are able to
conclude that the population of Tanzania is
growing, as it is shown by the figure below.
Doubling time is another indicator which refers to a
period over which a population will double itself.
• The standard time to calculate the DT is to assume
that the population grows exponentially(i. e. Has a
constant growth rate).
• DT is estimated by dividing 70 by the annual growth
rate which is stated as percentage.
• However it is important to note that, DT is very
sensitive to growth rate, and it changes quickly as
growth rates changes
• For example if the population is growing at 1% it
will double after 70 years, and if it grows at 2 %, the
DT will be 35 years.
• If the growth rate increases the doubling time
decrease for example in Tanzania, growth rate is 3%
Therefore, the DT = 70/3 = 23 Years.
BASIC POPULATION THEORIES.
• A term population theory refers to the body of
generalizations and population principles found
various disciplines within social science.
• These generalizations consists of coherent set of
hypothetical and conceptual principles forming the
general frame of reference for population studies.
• Population theories attempt to explain major
factors determining population growth and /or
demographic characteristics of a given population.
• A population theory should satisfy certain
conditions which includes the following.
a) It should consist of a set of hypothesis or principles
b) It should explain historically the observes changes
in fertility, mortality and migration patterns
c) It should be able to provide the basis for predicting
with some accuracy future levels and trends of
population growth as determined b stages of socio
- economic development.
d) It should be able to help us understand the
relationships between changes in
mortality, fertility and migration.
History of Population Theories.
• Historical evidence suggests that man has been
concerned with population problems since ancient
• Thus the history of population theory may be
divided into three phases which are
a) Pre Malthusian Period.
b) Malthusian Period.
c) Post Malthusian Period.
Post Malthusian Period.
• These are theories that were developed after
Malthus and Karl Max.
They include the following.
Biological Theories of population
Sociological Theories of Population
The Demographic Transition Theory
READ ON THE FOLLOWING
THE DEMOGRAPHIC TRANSITION MODEL
• The demographic transition model describes a
sequence of change over a period of time in
relation to birth and death rates and overall
population change, ( i.e. natural increase).
• The theories describe and predict the future
population of any area (place).
• It is based on the population changes in several
industrialised countries in Western Europe and
• The model assumed that, all countries pass through
similar demographic transition or population cycles.
• The model tell us that, the population of any region
changes from high births and high deaths to low
births and low deaths as a society progresses from
rural agricultural and illiterate to urban industrial
and literate society.
• The theory have its roots from 19th century, where
through various studies it was noted that fertility
levels were falling in many western countries.
• These demographics studies gave birth to what is
called demographic transition theory.
• The main contributors to the theory are Landry W.
Thompson, C. P. Blaker, Kingsley Davis and F. Noteisteint
.Their contribution to the models is as follows.
• Landry published a paper in 1909,where he identified
three main stages of population growth which are
a) The primitive stage, in which fertility is not restricted
at any cost.
b) Intermediate stage in which fertility is in the process
of being restricted through postponement of
c) Modern stage in which mortality rates are declining
due to conscious efforts being made to limit family
• However, he did not develop his description into a
theory with universal application.
• W. Thompson (1929) and C. P. Blacker (1947) made
attempts to generalize the demographic experience of
Europe into a theoretical framework which they
believed could work for other areas as well.
• W. Thompson divided the nations of the world into
three categories according to their levels of mortality
a) The first category comprised all countries with high
birth and death rates.
b) The second category includes all countries
characterized by declining rates in fertility and
c) The third category includes countries experiencing
decrease in population growth rates due to rapid
decline in fertility and mortality rates.
• On the other hand, Blacker identified five stages of
demographic transition which are as follows.
a) The first stationary stage characterized by high
birth rates and death rates.
b) The second, early expanding stage with high
birthrates but with decline in mortality rates.
c) The third, late expanding stage with falling
birthrates but more decreasing death rates .
d) The fourth, low stationary stage with low birth
rates are balanced with low mortality rates.
e) The fifth, declining stage where mortality rates
exceeds fertility rates.
• Contributions of these scholars is highly
appreciated, as their work formed the basis of the
modern demographic transition theory we know
today, which was developed in its mature form by
another scholar, who is Frank Notesteint in
1945, and expanded it in 1953.
• Due to his work, he is regarded as a father of
demographic transition theory.
• Through his observations on the population of
Europe in 19th century, Notestein relates mortality
and fertility levels to fundamental economic and
social forces of modernization experienced in
Europe in that time.
• Many demographers believe that fertility and
mortality rates are directly linked to the level of
economic development of a country, region or
• Therefore, demographic transition theory was
developed in respect to the history of demographic
change in core countries, where they contended
that many economic, political, social, and
technological transformations associated with
industrialization and urbanization lead to a
• The model also gives reasons for transition/change
at each transition stage and more specifically it
gives example of countries that appear to fit each
• According to the model, there are four stages
through which a population of a given country must
pass through, and they are named as stage 1, stage
2, stage 3 and stage 4, where each stage has got its
• This means that, population changes occur in stages
which are collectively known as the demographic
• These are explained as follows.
• This is a first stage characterised with primitive
demographic growth, where birth rates and death
rates are high and fluctuate giving a small
• Many children die in infant and hence parents tend
to produce more hoping that few will survive.
• In this stage, children are seen as symbols for
economic and cultural wealth.
• Economically, children are needed to work on land
as most people are engaging in agriculture so large
families are economic assets.
• Socially, children’s are regarded as a sign of virility
• There are believes that discourage the use of family
planning methods and a result, many are added to
the existing population.
• In the past years, most countries belonged to this
• Reasons to why there is high death rate includes
lack of both birth and death controls.
• Conditions like infectious disease like
cholera, famine ,Poor diet and hygiene, lack of
health facilities, low education levels etc are typical
characteristics of the stage.
• This is a second stage where birth rates remain
high but death rate fall rapidly about 20 per
thousand people and hence giving rapid population
Why there is decline on death rate?
Improved medical services ie availability of
hospitals, vaccination, scientific research
Improved water supply and sanitation.
Improvement in food production both in term of
quality and quantity.
Improvement in transport and communication
• All these results into the dramatic decrease in death
rates and this ensures the survival of most of the
individuals who are added to the population
• Therefore, this decrease in death rates leads to an
increased population and ensures maximum
• This is a third stage where birth rate fall rapidly
while death rate decline slightly giving a slowly
decreasing population. The fall in birth rate is
• The decreased death rates are due to many
These are like availability and acceptance of the
modern family planning methods, industrialization
and mechanization higher levels of
education, changes in the social patterns including
women empowerment, human rights, e.t.c.
• Here, there is great desire for material possession
and therefore children’s are less desired.
• Both death rate and birth rate remain low
fluctuating slightly to give a steady population.
• The population here remains fairly steady because
deaths and deaths have amore or less similar
Possibly Stage Five?
• Though the model has not stated, in reality there is
a new tendency where the number of deaths
outweighs the number of individuals replaced
through births, giving an overall negative
• Scandinavian countries, specifically Sweden is
currently entering into negative growth
rate, meaning that there are fever births than
deaths so that the country’s population is declining
Limitations of The Model.
The model is Eurocentric in nature because it
assumes that all countries will pass through the
Birth rates for instance in German and Sweden
declined before even the model was put. This
suggests the new stage to be added in that model.
There are cultural and political values that influence
changes. But the model is based on social economic
factors only. Foristance, it does not take migration
into account as a component of population
The time scale is not well organized i.e. What is the
estimated / specific time from are stage to the next.
It does not take into account if the pandemic
diseases like AIDS, which may wipe signifanct
numbers of people in a given population.
Applicability of the Model
• Together with the weaknesses shown by the
model, this model is highly applicable because of
The model show the population of a country
changes over time.
It compares rates of growth between countries.
The model has shown the factors for change in a
population i.e. diseases, industrialization, e.t.c.
The model has tried to give some examples of
countries that seem to appear from one stage to
2. EPIDEMOLOGICAL TRANSITION MODEL.
• This model explains the causes of death.
• Death is the disappearance of all evidence of life at
any time after birth has taken place.
• The model explains about studying death rate in a
population. The effect of parasitic and contagious
diseases have been drastically reduced in many
parts of the world .
• As a result the large proportion of the population
lives long enough to diseases to be afflicted by and
in due cause die from degenerative diseases.
• It has been recognized that societies pass through
various patterns of mobility (illness and diseases)
and mortality as the causes of death.
• Mortality (causes of death) during the development
process, it can be even if not at all stages and
sequences are identical in every case.
• Health improves mortality and mobility fall down.
• The model states that societies during their
development they have to pass in epidemological
• The model explains the complex changes in pattern
of diseases that a population passes through and
the social and biological determinants. It shows dis-
placed or replaced by degenerative diseases as
causes of mortality.
• The transition model is associated with various
degree of development from social economic point
of view to medical aspect. And therefore the result
is a shift in life expectancy.
• Many people were dying at young ages but
currently the majority thrives to old ages.
• The theory has five proposition or stages, which are
1. Proposition One
• Mortality is fundamental factor of population
dynamism or change .It occurs at every body at
various time scales.
2. Proposition Two.
There is a shift in mortality and disease
patterns, where the pandemic of infection diseases
are progressively delivering and now being replaced
by degenerative diseases or man made diseases.
• The replacement is assumed in three stages
(a)Age Pestilence and Famine. It is a stage of pre
industry where people lived in problems from
environment, there was no control of calamities.
(b)Age of Receding Pandemics of infectious
diseases, where the main problem were infectious
(c) Age of degenerative and man made diseases, with
the improved livelihoods and medical sector, people
are suffering from diseases mostly resulting from
their lifestyles, feeding habits and all other forms of
3. Proposition Three
• During the epidemiologic transition the most
profound changes in health and disease patterns
obtain among children and young women.
• The genuine improvements in survivorship that
occur with the recession of pandemics are
peculiarly beneficial to children of both sexes and to
females in the adolescent and reproductive age
periods, probably because the susceptibility of
these groups to infectious and deficiency diseases is
4. Proposition Four
• The shifts in health and disease patterns that
characterize the epidemiologic transition are closely
associated with the demographic and
socioeconomic transitions that constitute the
• This proposition in some ways bridges the other
propositions in that, consistent with third, it is
characterized by lower fertility and longer birth
intervals, and in keeping with the second and the
fifth, it is posited that, improved socioeconomic
status leads to better nutrition and
sanitation, which in turn improve health and reduce
morbidity and mortality.
5. Proposition Five
• Peculiar variations in the pattern, the pace, the
determinants and the consequences of population
change differentiate three basic models of the
epidemiologic transition: 1. the classical or western
model, 2. the accelerated model and 3. the
contemporary or delayed model.
• They roughly correspond to (1) the experience of
developed countries that evidence slow declines in
death rates followed by lower fertility rates that
accompany modernization, (2) the experiences of
some countries like Japan, where the course of
transition was much more rapid and the amount of
time required to reach the milestone mortality rate of
10 deaths per 1000 is much shorter, and (3) the
experience of developing countries where there have
been more recent declines in mortality but not in
fertility rates because infant and maternal mortality
rates are still high.
• Through the description, analysis and comparison of
mortality patterns in many societies and at different
points in time, distinctive core patterns of the
epidemiologic transition emerge.
• The fundamental purpose of delineating these models
is to visualize the different matrices of determinants
and consequences associated with mortality (and
fertility) patterns and to elucidate some of the
fundamental issues confronting population policy-
• The theory of Epidemiological transition usually
favours some groups.
e.g. It favour young over old, Females over
males, Rich people over poor people, etc.
• This is because, foristance, children are more
vulnerable to diseases than old people, rich people
are less affected by mortality because they have
recourses to control diseases.
• Therefore, the model argues that there people
(groups) that are advantaged while other people
(groups) are disadvantaged in terms of diseases.
• Though many contributed to the theory, A.M.
Omran is a typically credited with formulating the
theory of epidemiological transition.
• In 1971, he wrote his publication on which the
following were cited most, ‘Conceptually, the theory
of epidemiological transition focuses on the
complex change in patterns of health and
diseases, and on the interactions btn these patterns
and their demographic, economic and sociological
determinants and consequences.’
• Therefore, the propositions are also known as the
Omran’s Five Propositions.
THEORIES OF FERTILITY
• Malthus Theory
• Marxist theory
• Neo Malthus theory
• Micro economic theory
1. MALTHUS THEORY
The theory was developed by Thomas Malthus.
Malthus argued that there was a positive
relationship between family size and income.
There was a strong and stable passion among sex
and this could be fulfilled by marriage.
The passion between the sexes is constant.
Marriage is a pre – condition for child bearing.
Discouragement of early marriage through
economic and other functions affect the level of
• He assumed that agricultural resources were limited
and could only increase arithmetically, i. e.,1, 2, 3,4
• On the other hand, population were increasing at a
geometric progression, i. e. 1, 2, 4, 16,32,64, etc.
• With this trend therefore, people will experience
• He argued that, if population increase will not be
controlled through various undertakings, natural
factors will take their role.
• Malthus argued that the only way the people could
escape poverty was by delaying marriage.
• Despite the good explanations made by Malthus, he
failed to foresee technological change that can
• He argued that since the resources are scarce high
fertility always lead to poverty. And therefore this
theory is called MACRO ECONOMIC THEORY.
• Because it try to explain group behaviour of fertility
rather than individual behaviour of fertility. And
therefore it can not predict fertility at family level.
THE THEORY OF FERTILITY BY KARL MARX
• He argued that fertility is not much affected by
natural laws as argued by Malthus but it is affected
by social law found in a given society at a given
• Marxists argue that the level of fertility is a function
of existing class structure and the laws /roles
assigned to different classes within a society.
• He argued that in capitalistic system, a lot of cheap
labour was needed and the system encourage high
fertility while in socialist system fertility will be low
because there is no need of creating labourers.
• According to him, fertility was a reflection of social
and political condition.
• Despite a good job done, the theory focuses more
on social classes as an explanatory variable.
• Also, the theory sees fertility as a part of large
economic and social system
• It sees both, biological and cultural factors playing a
little role in affecting fertility.
• Neither Malthus nor Karl Marx was concerned with the
effect of infant mortality on fertility.
• They both looked at fertility at the macro level (at the
MICRO – ECONOMIC THEORY OF FERTILITY
• It is based on individual differences that can affect
fertility. i.e household income, education, age, etc. i. e.
individual matters that affect fertility.
• There is an assumption that fertility is related to a
single family, couple, etc.
• The emphasis on these theories are on environmental
constraints. They argue that biological factors are not a
determinant that governs the fertility rate but it bases
THE NEW HOME ECONOMIC APPROACH
• This falls under the micro economic theory, and it is
an expansion of the micro economic theory, where
the main argument was that, fertility discussions
are economic because they involve the search for
an optimum number of children in the place of
• Here, parents have three things to deal with and
The number of children they have/need to have.
The quality of children
The quality and quantity of other goods wich they
• According to this theory, the quantity and quality of
children and goods they consume are interrelated.
Weaknesses of The Theory.
• The theory is static because it assumes that the
couple knows very early in marriage its
future, income and occupation and the number of
children they will have.
• The theory doesn’t consider contraceptic failure
and mortality of children or parents.
THE SOCIAL DETERMINANT SCHOOL OF THOUGHTS
• The main contributors to this theory are Leibenstein
• Their major argument is that, families differ
fundamentary in the value they place on children.
• They add that biological constraint on fertility is
important contributor to fertility differences. They
suggested that variables like religion and education
should be used as control variables.
• They argue that the combination of biological and
cultural factors determines the natural fertility of
the population and it is that which determine the
limit of the family size.
OTHER FACTORS THAT CAN AFFECT FERTILTY
• There are other factors that have been associated
with fertility and they do with.
The percentage of women that remain single
The level of education of the family.
The occupation of the female
Religion or religious status of the couples
Transitions In Epidemiology And Public Health.
• It is instructive to consider historical transitions in
epidemiology and public health that in some ways
mirror the transitions described above.
• The modern public health movement had its origins in
the Sanitary Movement of the 18th and early 19th
centuries, with its focus on community
characteristics, economic conditions, and
• Improvement of living conditions was seen as a means
of improving health.
• This formative period in the history of public health
continues to be relevant, reflecting a rudimentary
version of the current understanding of the
• By the end of the 19th century, the germ theory of
diseases had matured and largely displaced the
miasma theory on the basis of scientific advances in
bacteriology, chemistry, and medicine as well as
• The recognition of infectious diseases as major
contributors to morbidity and mortality, the rapid
development of new knowledge and tools, and the
effectiveness of public health efforts in reducing the
incidence of and mortality from some infectious
diseases led to increasing dominance of this
theory, which dramatically shaped public health
programs and practices, and contributed to steep
declines in mortality from infectious diseases in the U.S.
and other developed countries.
• The other side of this development was that public
health came to be viewed largely through the lens
of disease prevention and control.
• Consistent with the transition theory, by mid-20th
century, public health attention shifted to chronic
disease prevention and control, with emphasis on
risk factor epidemiology and interventions directed
toward individual behaviour and lifestyles.
• The earlier dominance of germ theory and
microbiology may have narrowed the view of the
mission of public health, putting the population
focus and developing quantitative approaches in
competition with the microscope, but new
developments in understanding genetic and
cellular processes,(a potential new “germ theory”)
have been accompanied by renewed interest in
both psychosocial characteristics and broader
contextual and environmental influences.
• This broader perspective on the determinants of
health and disease encompasses but goes beyond
traditional risk factor epidemiology.
• It includes explicit attention to the complexity of
systems and the challenges of integrating multiple
levels from the genetic to the personal to
social, political, and economic contexts across the
• This methodological transition has been particularly
evident in the remarkable evolution of epidemiology as
a discipline since World War II.
• These changes have resulted from developments on
several interrelated fronts, both within and outside the
field. Theories of health and disease have received
greater attention, with broader concepts of health as
encompassing more than the absence of disease.
• A renewed focus on population health, as well as
development of more complex causal models reflecting
new discoveries focused greater attention on more
thoughtful considerations of causal inference and
explanation of causal associations, not just
identification of risk factors.
• The continuing threat from infectious diseases and
increasing attention to health disparities have
challenged traditional risk factor approaches.
• Some of the more recent discoveries in infectious
disease have arisen from an approach and
conceptual framework and methodology rather
distinct from that of the golden age of late 19th and
early 20th century microbiology.
• Awareness of the importance of a life span
perspective has also been accompanied by
increased attention to etiologic
investigations(scientific studies of diseases causes)
of degenerative diseases of aging formerly thought
to be unavoidable.
• Alongside, explorations of genetic causes has been
renewed interest in research on environmental
factors, both as external causal agents and as
potential modifiers of genetic causes, with the goal of
understanding processes in order to develop more
effective preventive interventions.
• While retaining intervention and prevention as
goals, epidemiologists now seek to incorporate systems
perspectives within an ecological model with its multi-
leveled approach and life span considerations.
• In sum, the eco-epidemiologic approach is
characterized by a life course perspective, recognition
of multiple, interrelated levels of causation, and an
emphasis on models that are more integrated rather
• The implications for research methods parallels
those three components.
• First, the life course perspective requires us to think
in terms of changes in causal pathways across the
life span when considering shifts in the age
distribution of a population as described by the
epidemiologic transition theory.
• Second, the causal models on which we rely must
allow for multiple levels of determinants acting in
complex and interrelated ways, often synergistically
or with feed-back loops or reciprocal lines of
• Third,we have to consider that higher level or
“upstream” determinants may have emergent
properties that are more than the aggregate of their
constituent parts, so that we must consider them
along with the lower level elements in our models
• Finally, when considering the multiple levels of the
ecological model, we rely on the understanding that
disease occurs in individuals, but interventions can
occur at any level, including communities.
• The 2002 Institute of Medicine follow-up report
emphasized the “public” aspect of public
health, that is, “healthy people in healthy
• This in some ways is a recapitulation of the Sanitary
Movement’s emphasis on living conditions, but
goes beyond that earlier perspective. There has
been a rich discussion in the public health literature
on the definition and nature of healthy
• The critical development is that, public health
professionals increasingly recognize an organic
notion of community, emphasizing that individual
health is achieved or threatened by larger scale
contextual factors, including social
networks, environment, education, economic
opportunity, and other characteristics of
• This emerging perspective sees the whole range of
determinants as integral to personal and
community health and well-being.
• The modern ecological model of public health
practice stresses the multiple dimensions that
constitute our lives, relationships and
environments, and, therefore, contribute to health
and wellness or disease and disability.
• Further, the threat of emerging infectious diseases
continues to have global significance in an era of
resurgent multidrug resistant
tuberculosis, pandemic such as AIDS, and
widespread distribution of vector borne diseases.
• These demonstrate that the transitions cannot be
neatly categorized into either historical periods or
Critiques of the theory
• The epidemiologic transition theory appears to
have some confirmation in recent trends that were
characterized by increased life expectancy and a
shift in the population age distribution to older ages
as well as the concomitant increase in the numbers
of people living with chronic degenerative disease.
• These changes have profound impact on public
health planning, health care resources and
workforce development, and a range of
social, political, and financial policies.
• While such changes consistent with the theory have
been evident, the theory has not been without its
critics and a number of issues remain controversial.
1. The theory fails to grasp the global nature and
historical sequence of the mortality transition as it
• Criticisms of the original theory reflect continuing
development in theories of health and
disease, disagreement about the role of advances in
medicine relative to public health
interventions, and debate about the relative
importance of various contributors to the
unquestioned changes in mortality and disease
patterns, especially with regard to
nutrition, poverty, and income inequalities.
2. Another argument is that, the emergence of cities
and organized societies that triggered the first
transition came with social stratification ,that is a
precursor of the disparities in social position and
wealth observed in later stages.
• The argument is that, wealth and poverty and their
relative distribution play central roles in health and
well being in each stage.
• This was argued by Pearson, that, the roles of
income and education in the most recent stage are
paradoxical in that, compared to those who are
poor and less educated, wealthier and more
educated persons tended to be earlier adopters of
lifestyles that contributed to the increased risk of
those diseases that now constitute the major
causes of death, but they were also earlier
adopters of treatments and lifestyle changes that
subsequently reduce the risk of morbidity and
• The result, according to Pearson is that poor and
poorly educated populations may experience later
peaks in the incidence of the diseases that define
the third transition phase, but also continue to
suffer from elevated rates of those chronic diseases
after rates have begun to decline among those
• Pearson argues that this requires simultaneously
working for economic development and improved
education to reduce prenatal, infectious, and
nutrition-related diseases while implementing
proven strategies to discourage adoption of those
detrimental behaviours and exposures associated
with chronic diseases in more prosperous segments
of the population.
• Note that these differences are most evident in
comparisons of developed and underdeveloped
countries, but also hold for different segments of
the population within the same society or country.
• It can be argued that, the publication of Omran’s
paper came at a time of naïve optimism concerning
mortality patterns, causes of morbidity and
mortality, and global progress in life expectancy.
• In 1969 testimony before congress, the US Surgeon
General said that it was “time to close the book on
infectious disease as a major health threat. ”
• Though it might have been impossible at that point
to foresee the global emergence of HIV/AIDS and
other so-called emerging infectious diseases and
the serious challenges of antibiotic
resistance, ecological disruption with its
consequences for health and environment
(including contributing to emerging diseases) was
taking place, and the
devastating impact of infectious disease on the
poor and those living in developing or under-
developed countries was evident.
• More recently, recognition of the continuing impact
of infectious diseases and inadequate
nutrition, coupled with ecological disruption, has
come with an emphasis on the role of poverty in
poorer outcomes and wider disparities.
• Armelagos et al., wrote: “While disease and death
are inevitable, a major cause of
unnecessary, premature, preventable disease and
death is simple; it is extreme poverty.”
3. Another criticism of the traditional theory is that, it
fails to distinguish adequately the risk of dying
from any given cause or set of causes from the
relative contributions of the various causes of death
to overall mortality.
• To take an example , accidents (unintentional
injuries) are among the leading cause of death
among persons, especially those of around 15 to 24
years old in the US, accounting for 46% of all deaths
in that age group in 2004, while among those ages
65 to 74 they accounted for just over 2% of all
• As patterns of disease and mortality change, there
are changes in the relative contributions of
different causes to overall mortality that may not
reflect changes in actual risk.
• Therefore, these and related others are the major
contributors of deaths and impairs public health in
many modern societies and they are acknowledged
as one of the major causes of deaths in our
• Both, the relative contributions and the actual risk
of death from the major cause of death categories
vary widely across countries, even between
countries in the same region, as well as across
population groups within a country.
• The point is that, the epidemiologic transition
theory oversimplifies the patterns and relations
among risk of mortality, mortality causes, and life
• The patterns are clearly more complex than simply
declining mortality rates from infectious diseases
and increasing rates of death from the so-called
chronic diseases and do not fit neatly into either
historical periods or geographic locations.
4. Also, a further complexity now being recognized is
that, the distinction between infectious and chronic
disease is not clearly demarcated.
• Not only is it the case that some infectious diseases
have chronic disease characteristics, but we have
come to recognize the importance of infectious
agents and related inflammatory processes in the
etiology of a number of chronic diseases and
adverse outcomes, such as cervical cancer, gastro
duodenal ulcer (H. Pylori), and cardiovascular
disease (inflammation), and there is more research
now on links to outcomes as divergent as
diabetes, preterm delivery, and some mental
OF THE THEORY.
• Demographic factors are important components of
both, the causes of and responses to future
economic, environmental, and social change.
• Interdisciplinary studies of future global change can
draw on projected trends in population size and
growth rate, structure, urbanization, and
migration, among other variables.
• Often, however, integration does not proceed far
beyond uncritical acceptance of a single projection
of future population size. For example, studies of
environmental change may use projections simply
to scale per capita trends in other factors.
• Part of the difficulty in making full use of projections in
such work stems from uncertainties is how
demographics, acting in concert with
social, economic, and cultural forces, may affect the
• However, the historical nature of the projection process
has presented obstacles as well. How projections are
made, the basis for key assumptions, and how
projections differ among institutions that produce
them has not always been clear to users, making the
interpretation of results somewhat difficult.
• We present a guide to long-term, global projections
aimed at researchers and educators who might benefit
from putting them to greater use.
• There has been a resurgence of research and new
practices in projecting population that are likely to
make results more useful and methodology more
• New thinking is being employed on how best to
express uncertainty, on new methodological
approaches to projections, and on the likely future
courses of fertility and life expectancy.
• In addition, projections have demonstrated the
importance of recent revisions to current estimates
of demographic variables.
2. Projections and their uses
• Population projections differ widely in their
geographic coverage, time horizon, types of
output, and use. Spatial dimensions can range from
local areas (like counties or cities) to the entire
• Local-area projections tend to use shorter time
horizons, typically less than 10 years, whereas
national and global projections can use decades
into the future, and in some cases more than a
• These longer-term projections typically produce a
more limited number of output variables, primarily
population broken down by age and sex.
• In contrast, projections for smaller regions often
include other characteristics as well, which might
include educational and labour force
composition, urban residence, or household type, etc.
• The diversity of types of projections is driven by the
diversity of users' needs (Lutz et al 1996a). Commercial
organizations often use projections for marketing
research and generally want a single most likely
• They typically want population classified by
socioeconomic categories such as income and
consumption habits (in addition to age and sex), and by
place of residence. Government planners may be
concerned with population aging and its potential
social and economic impact.
• They may therefore desire longer-term
projections, and want to know more about the
health status and living arrangements of the
• The policy community, including advocacy
groups, often would like alternatives to a single
most likely scenario, including projections that
reflect the influence of policy.
• For example, those concerned with the
environmental impacts of population growth may
be interested in the potential for reductions in such
growth through population related policies.
• In addition, they may want to know what the
potential effect of environmental feedbacks on
growth might be, a topic recently highlighted as
underdeveloped by the National Research Council
• Global change researchers often use projections as
exogenous inputs to studies on topics such as
energy consumption, food supply, and global
• These studies usually require projections with long
time horizons (a century or more) and a range of
scenarios rather than a single most likely projection.
• We focus here on a relatively small subset of
projections: long-term, global population
projections - that is, sets of projections that may be
made at the national or regional level but that cover
the entire world.
• The time horizon of these projections typically
ranges from 50 to 150 years.
• Demographers often feel uncomfortable making
projections farther than a few decades into the
future; uncertainty grows with the time
horizon, and increases substantially beyond 30-40
years, when most of the population will be made up
of people not yet born.
• Nonetheless, long-term global projections are
increasingly in demand by global change
researchers and educators. Only a few institutions
produce such projections, but research and practice
has been evolving rapidly.
3. Who produces projections?
• The earliest systematic global population projection
dates to Notestein (1945), although many national
level projection efforts began over half a century
• At our national level, Nations Bureau of Statistics
(NBS) has taken a leadership role in the production
of projections and dissemination of their results.
• Later efforts, most of which continue to date, have
been undertaken by three other institutions :), the
IMF and the World Bank (WB), and the
International Institute for Applied Systems Analysis
• Global long-run population projections tend not to
be undertaken by individual researchers. Individual
researchers have tended to create projections at
the national-level (or below) and at this level have
made significant contributions to varying
READ ON :