Demography
By Dr. Asmaa Abel Aziz
Dr. Alaa Hassan
Demography
It is the science that studies human population
(Demos = population, Graphy = picture).
Importance of Demographic data
Health status of a community depends upon the
dynamic relationship between number of people, their
composition& distribution
Planning of health services can be guided by
demographic variables, for example: How many health
units do we need? How to distribute them in the
community in order to be accessible to the target
population? What type of manpower is needed?
The elements of demography:
Size,
Composition and,
Distribution.
These elements are affected by three main processes namely,
fertility, mortality and migration.
The current level of health services for the population
KSA (2003)
Elements of Demography
I - Size of the population
To describe the size of population it is not enough to deal with
the actual number of the population.
The size of the population is important, as
• it is the base for many vital statistics.
• It has to be related to a place and a specific time.
• It takes an additional meaning when density ( number of the
population per square kilometer) is taken into consideration
Knowing the size of the population is done by enumeration
of all persons in the community, which is called “census”.
A census is the enumeration at specific time of individuals
comprising the population within an area .It is carried every
10 years.
There are two methods of making a census:
1- De fact
2- De jure
(a): de facto census :counting individuals wherever they
actually are on the day the census is conducted. The de facto
census is much easy, less expensive and more economic to
apply than de-jure type.
The disadvantages include
1- Persons in transit may not be included
2- Provision of incorrect picture of the population
3- Vital rates may be distorted
(b):The de jure census, counting individuals at their legal
permanent residence regardless to whether or not they are
physically present at the time of the census. It gives a true
figure.
The disadvantages include
1- Expensive in time and money
2- Some individuals may be counted twice
3- Information may be incomplete
(KSA)
GDP= Gross Domestic Product
II- The Composition of the population:
This is important for the following purposes:
1-It gives a true picture of human resources and needs.
2-It provides essential data for vital statistics.
3-It forecasts changes in size and their direction.
4-It allows comparisons between populations.
Studying the composition includes : age, sex,, marital state,
education, occupation economic status etc..
Age and sex composition are the most important population
characteristics. They can be graphically presented as a population
pyramid.
Population Pyramid
This is bar graphs, one showing the number of males, the other showing the
number of females. The bars represent age bands of 5 year-intervals.
Importance of studying population pyramids
1-Different shaped population pyramids indicate the stage of development that
a certain country has reached.
2-Population pyramids can indicate birth, mortality rates as well as migration
and wars.
For instance, a country whose pyramid has a wide base has a high birth rate. If
the numbers rapidly decrease, to from a triangular shaped pyramid, then there
must also be fairly high death rates. Developed country with good health care,
and high life expectancy for example UK will have a relatively narrow base, and
there will be similar number of people in all the bands up until the age of 70,
when the numbers will start to fall.
Mortality and migration can be represented by the slope of the sides. The
decrease in the width of strata of different ages is brought about by
deaths or migration. The sharper the slope, as it goes upwards, the higher
are these reducing forces. Another type of event that can be traced easily
on the sides of population pyramids, is the effect of war. Often this leads
to large imbalances in the population, with far more women than men of
fighting age remaining as the men have been killed in battle
The life span is represented by the height of the pyramid,
while the shape of apex (narrow or wide) indicates the
percentage of individuals, who survive till advanced ages
during their life journey.
The median age is the point on the vertical axis of age
through which passes the horizontal line that divides the
surface area of the pyramid into two equal parts, i.e. 50% of
the population is younger and 50% is older than the median
age. The position of this defined point is inversely related to
the width of the base. The median age is low when the base is
wide. The reverse is true.
3- Population pyramids can also show the percentage of the
population, which is described as being “dependent”. These
are the groups of people who rely on the economically active
members of society. Dependants are classified as those
under working age (0 - 15 years old) and those who retired
(over 60). They rely on the working age group of people
between 15 and 60.
1. Young dependency : Presented by the surface area below the
horizontal line passing through 15 years of age.
Young dependency ratio
Population aged 0-15 years in a year & locality X 100
Population aged15-60 years ( same year & locality)
2-Old dependency: Presented by the surface area above the
horizontal line passing through 60 years of age
Old dependency ratio =
Population aged 60 Years and more in a year& locality X 100
Population aged15-60 years ( same year & locality)
3-Total dependency: Presented by the surface area below the
horizontal line passing through 15 years of age and that
above the horizontal line passing through 60 years of age
Total dependency ratio:
Pop. aged 60 years in a year&localityX 100
Population aged15-60 years ( same year & locality)
Population pyramids can be used to help planning for the
future, as they can be used to project the percentages of
certain age groups in the population over the next 50
years.
Comparison between the Pyramids of developing & developed Countries
Developed countries Developing countries
Base Narrow ( Low BR) Wide (high BR)
Side Not sloping (Straight ). Sloping.
(low mortality ) (high mortality)
Height Tall Short
(high life expectancy). (Low life expectancy)
Apex Wide Narrow
(large numbers of people > (few people survive to old
60. age)
Median Age High (low birth) Low ( High births)
Old dependency High Low
ratio
Young dependency Low High
ratio
This shape is typical of a developed country. It is narrow at the base,
wider in the middle, and stays quite wide until the top, as there is a
sizable percentage of older people. Note that there are more old women
than men. Italy and Japan have population structures that are of this
shape.
Japan Population Pyramid
Significantly, the average number of children that married women are having
has remained at around 2.2 over the last three decades the decrease in
fertility is almost totally due to an increase in women of reproductive age not
getting married and not having children. This is due to a choice to stay in
employment and not have children:
Female Male
This population pyramid of the Canadian population in 1961.
You can see that the pyramid narrows toward the top. This is because the death
rate is higher among older people than among younger people.
There are also a few bulges and narrower parts in the middle part of the pyramid.
For example, there are not as many people in their 20s as in their 30s in Canada
in 1961. The people in their 20s in 1961 were born during the Depression, a time
of economic hardship in Canada when people were having fewer children.
III- Distribution of the population
The following questions need to be answered:
What is the percentage of inhabited land in relation to available land within the
national borders of a given country?
What is the population density/km2 for the inhabited area?
What is the population density/km2 for the available land?
What are the occurring population movements between different areas of the
country (e.g.: Urban - rural migration-).?
The answers to these questions are significant politically, economically and
socially
Changes in distribution are caused by the cumulative effects of fertility, mortality
external and internal migration.
Saudi Arabia is a vast country, covering an area of 2.15 million sq km, known for
its desert arid nature and its various highlands.
Major demographic processes: Population
Dynamics
• Fertility
• Mortality
• Migration
I - Fertility (Natality)
Fertility is the actual reproductive performance of a woman or
a group of women. A woman's reproductive period is roughly
from 15 to 49 years of age.
• Fertility indicators
• Crude birth rate
• General fertility rate
• Age specific mortality rate
• Total fertility rate
Crude Birth Rate (CBR)
Is the simplest indicator of fertility.
The Crude Birth rate=
The total number of live births in a year & locality X 1000
The estimated midyear population in the same year &
locality
=… Live Births/ 1000 population in a year.
CBR in Egypt (year 2000) = 26 LB/1000
population.
CBR is a crude index of fertility as it relates births to total
population (including males and females outside the
reproductive age period, as well as unmarried females).
However, it is useful in
(i) making annual comparisons
(ii) to detect trends in fertility in a given country and
(iii) in comparing different populations.
Factors affecting the crude birth rate:
Factors affecting the Live births
• Number of females specifically those 15-49 years
• The age of marriage
• Level of infant and preschool mortality rates
• Socioeconomic level of the country
• Economic value of children and lower expenses of rearing
children
• Cultural and religious factors
• Knowledge, attitudes and motives for adopting or rejecting
family planning
Factors affecting the mid year population
• Epidemics
• Wars
• Famine
• Migration
2-General fertility rate (GFR)
The total number of live births in a year & locality X 1000
The number of women in child bearing period (15-49) years in the same
year & locality
= …Live birth/1000 female population ages 15-49.
It is a refinement of the crude birth rate. It relates births to
women in the child bearing period (15-49 years). It eliminates
the influence of the difference in the proportion of males in
the population.
The weakness of GFR is that it does not take into account
(a) the marital status and
(b) the differences in fertility levels in various age groups of
reproductive period.
3- Age specific fertility rate (ASFR)
This is a major refinement in the measures of fertility. It
allows for the age differences of women. The maximum
fertility occurs between 25-35 years. It is obtained by dividing
the number of births to mothers of each group in that year by
the number of women of this particular age group. The whole
reproductive life of females (15-49 years) is divided into
seven age groups, each of five years duration (namely 15-19,
20-24 years, … etc). There are seven age specific fertility
rates.
Age specific fertility rate =
The total number of live births from women in the specific age group in a X1000
locality
____________________________________________________________________
The number of women in the same specific age group in the same year & locality
= …Live births/1000 female population in specified age group.
4 - Total fertility rate (TFR):
It is a hypothetical measure of fertility. It is computed by
summing the current seven age specific fertility rates of the year
of calculation. To cover the whole reproductive life. Then this
summation is multiplied by 5. Calculated as such, this rate
represents the average number of children a woman would have,
if she passed through her reproductive years bearing children at
the same rates (of a specific year) as the women in each age
group.TFR =….children born/woman.
This rate does not denote actual events, but it is used for
projection. Its definition entails two assumptions. First, the age
specific fertility rates remain constant for this cohort of females till
the completion of their reproductive life. Second, none of the
women beginning their childbearing period will die before
reaching their menopause (i.e. that deaths occur among women
aged 15-49 years).
In developed countries the TFR is under 2.0. In developing
countries the TFR is over 6.0 per women.
2-Mortality indicators
They are utilized in deciding priorities for health action, in
designing intervention programs and in the assessment of public
health problems and plans.
Crude Death Rate (CDR)
The total number of deaths in a year & locality X 1000
The estimated midyear population in the same year & locality
= … Deaths/1000 individual in the specified year and
locality.
The difference in CDR between countries may be due to
difference in the population composition between these countries
III- Migration
Along with fertility and mortality, migration is a component of population
change.
Definition
Migration is the change of residence of a person or group of persons for better
life and higher standard of living.
Types of migration
I- Internal migration
It is the movement within the boundaries of a given country.
1 - Rural - Urban migration.
2 - Movement of nomads.
3 - Movement of temporary and seasonal nature.
4 - Movement between and within urban areas.
II- External migration
a) Permanent migration: An example is the permanent movement of to the
U.S.A., Australia and Canada
b) Temporary migration: It is the migration over the borders of one society to
another for the aim of working for a number of years, with the intent of an
eventual return to the motherland. An example is the migration of Egyptian
professionals and laborers to Arab Countries..
The role of migration role is minimal when compared to fertility and mortality,
Population Growth
The population grows according to two factors: birth rate and
death rate. The difference between these two is called the rate of
natural increase.
The natural increase in size of any population is the product of
subtraction of deaths from births.
The rate of natural increase is expressed as a percent =
Rate of natural increase (RNI) =CBR – CDR
10
If the CBR is higher than the CDR ,the population will grow.
If the CBR is lower than the CDR , the population will fall.
If the CBR & CDR are there will be no natural increase.
The growth rate takes into consideration birth, death &migration.
Growth rate (GR) = RNI + Net migration rate
Net migration rate = Immigrants مهاجرون للخارج – مهاجرون للداخلemigrants
GDP= Gross Domestic Product
What is the rate of natural increase ?