Sociology notes

1. INTRODUCTION TO
DEMOGRAPHY
Crecious Phiri

2. Introduction to demography
Core Course Session Contents:
 Population Studies Terminology: Definitions
Components of Population Studies
Theories of Population Studies
Demographic Transition Theory
Population: Age and Structure-Pyramid
Demographic Methods and Measurements
Elements of demography

3. DEMOGRAPY
• Demography: is the scientific study of human populations,
primarily with respect to their size, structure and distribution, or
in short it is a systematic study of human population.
• Demography draws on several components of the population such
as size, composition and territorial distribution
• Demographer study geographical variations and historical trends
in their efforts to develop population forecast.

4. • POPULATION is the number of person occupying a certain
geographic area drawing substance from their habitat and
interacting with one another.
• HABITAT is natural home (natural environment of an organism)
• DEMOGRAPHER commonly define population as a collective
group of individual occupying a particular place at a given time.
• Three key word are involved in definition of population
• Group
• Place
• Time

5. Components of Population Studies
Study of human population focus on:
(a) change in population size (growth or decline)
(b) composition of population( age, sex, etc)
(c) distribution of population
• It deals with`5’ “demographic processes”
(a) fertility or natality
(b) mortality
(c) marriage
(d) migration
(e) social mobility

6. Population Theories
Why concerned with population studies or demography in field of
medicine or public health?
• Population studies is interdisciplinary in nature- falls
within the realms of medicine, specifically, epidemiology,
anthropology, geography, sociology, economics and
statistics-
• It deals with human population to provide direction to
population change (i.e. increases or decreases in pop.
Growth) which depends on three major factors: fertility;
mortality and migration

7. Population Theories
• Demographic effects of health on population are mainly
associated with fertility, mortality and migration
• High births- resulting in high Total Fertility Rate
(TFR,i.e. Number of live births a woman may likely to
have during a reproductive life span)
Causes-increase population growth rate leading to population
explosion (overcrowding)
• Reduced fertility has a bearing on reduced population
growth and improve health status of population, which
may balance with the economic development of a country,
community, village or at a household level

8. Theories cont.’
• Increase in death rates -within the population due to
epidemiological emerging and re-emerging diseases of
communicable and non-communicable diseases has a
direct impact on population change (i.e. to reduce it
further in its size)- leading to an ultimate land without
human populations.
• Population structure will result in a ‘funnel’ like shaped
pyramid rather than being ‘bulky’ in its shape.
• Life expectancy will be low, with a reduced aged
population, rather than being high (e.g youthful country,
like Zambia).
• Such a country will have a cumulative youthful
population, rather than a growing ageing population

9. Theories On Population Growth And
Decline
Malthusian Theory(thomas Malthus 1766-1834 )
• “An essay and the principle of population” theorized
that population was uncontrollable & that it would.
• Argued that human population are inescapably
caught in conflict between their “need for food” and
“passion between sexes”.
population he maintained increases geometrically
(2,4,8,16,…) while food supplies increases only
arithmetically n (2,3,4,5…..)

10. Thomas Malthus Thesis
• He then advocated for population control to close between the rising
population and the food supply.
• On the other hand, he denounced the artificial use of birth control
because they were not sanctioned by religion
• He advocated that the appropriate way to control population growth
was to postpone marriage
• He further argued that couples must take responsibility for the
number of children they decide to have
• Without such restrain, the world would face widespread hunger,
poverty and misery.

11. Marxian Theory(carl Marx)
• Marx believed that problem was not primarily one
of population but one of the ownership of the
means of production and inequitable distribution of
societies wealth.

12. DEMOGRAPHIC TRANSITION THEORY ( WARREN THOMPSON )
• In 1929 the American demographer Warren Thompson
observed changes in birth and death rates in industrialized
societies over past 200 years or so and then formulated a model
called demographic transition, that describes population
change over time (demographic cycle).
•It means that as population increases in number ultimately
affects environment by overcrowding to create health, economic
and environmental problem effects on populations.
•The world population in 1650 grew at an increasing rate of 600
million, doubled in 1850 to 1.2 billion, to an increase rate of 4.4
billion in 1980, 6.1 billion in 2000 and 7.5 Billion as from June
2011 (UN 2011).

13. • It has 5 stages through which each country passes during
course of time.
• STAGE 1:HIGH STATIONARY :At this stage the
population is not growing and the number of people is
small. This is because the birth rate and death rates are
both high.
• STAGE 2:EARLY EXPANDING :Here the number of
people are starting to grow as the death rates start to fall
but the birth rates remain quite high
• STAGE 3:LATE EXPANDING :At this stage the
population is growing very rapidly but the gap between the
birth and the death rates is starting to become narrower. At
this stage the NATURAL INCREASE is HIGH
• INDIA, Malaysia and Bangladesh

14. • STAGE 4:LOW STATIONARY: the total population is
high but it is no longer growing very quickly. This is
because the birth rate and death rate are balanced as both
are now low. Developed countries . NZ, China
• STAGE 5:DECLINING:This stage would occur in
countries where the number of babies born (birth rate) is
less than the number of people dying (death rate) We call
this being below REPLACEMENT level, as in, there are
not enough babies born to replace the old people dying
• Countries reaching this stage are likely to be Japan and

15. Stages Of Demography Cycle And Countries
STAGE BIRTH RATE DEATH RATE COUNTRIES
HIGH STATIONARY HIGH HIGH INDIA (1920)
EARLY EXPANDING UNCHANGED DECLINE SOUTH ASIA,
AFRICA
LATE EXPANDING FALL FURTHER DECLINE CHINA,
SINGAPORE, INDIA
LOW STATIONARY LOW LOW AUSTRIA (1980-
1985)
DECLINING FURTHER LOWERS UNCHANGED GERMANY,
HUNGARY

16. •These patterns resulted from centuries of acceleration in the average
annual growth rate -i.e. percentage by which a population is increasing
because of the relationship between births and immigration on the other
hand, and deaths and emigration on the other hand
• Some European countries are getting to zero pop. growth (ZPG), i.e.
‘population is no longer growing’
•Rate of population or demographic change result from the relationship
between fertility- the actual reproduction of the population, and mortality-
the deaths in the population- which is a natural increase or natural
reduction in population.
• The analysis of demographic change relies on the availability of accurate
data about the relevant population characteristics & processes.

17. • Population theory brought about conflicting statements of
attempting to maintain population to improve the welfare of the
individuals and that of the state (i.e.country).
In 6th Century B.C. Chinese writers stated that, when the
population was too small the land remained idle and no taxes were
paid. The need to increase population was highly demanded.
But when the population was too large hardships existed due to
famines, floods, and epidemics, which compelled people shifting
from overpopulated to under populated regions.

18. • Rapid population growth took place twice in Chinese history:
• First, 1000 A.D. and second in the 18th Century with the
introduction of fast growing crops from South East Asia, and
other crops, such as maize, potatoes and peanuts from America.
• Expanded food supplies brought about increase of population

19. Population Theories (Cont)
• Greek thought of population developed in city-states with
constitutional rule by the minority who were citizens.
• According to Plato (1982), a population must be sufficient to
defend itself against its neighbours.
• Population was required to increase for self defence.
• Christian thought: developed in declining Roman Empire
encouraged population growth to meet the needs of the Empire,
but with minimum impact

20. • To the Church fathers of the Roman Catholics-, virginity
was the ideal- only for those too weak to abstain from the
‘temptations of the flesh’ where marriage was
recommended.
• The early Christian theologians of the Roman Empire did
not refer to the theory of Genesis: “to increase and
multiply,” nor spreading Christianity by having children,
but later in years introduced the concept of ‘nature’ for
creating children.
• Thomas Aquinas emphasized on the concept of nature that
just as ‘it is the nature of the eyes to see, so it is the nature
of the genitalia to procreate’
• It means that it is right and pleasant to do what is according
to nature to create children.

21. Global Health: Introduction to Population Studies
Critics of Evaluation of Transition Theory Model:
• Migration variable: Demographic transition focuses on natural increase
and leaves out the role of immigration into population and emigration
from it.
• Western Bias: The theory is modeled after what happened in part of the
highly industrialized western countries, especially after the Cold War II.
• Time Differences: Birth rates are unpredictable- time to lower birth rates
is differentiated from one place to another.
• Birth rate increases: The birth rate could still be expected to rise
significantly within regions affected by varied factors.

22. Population Pyramid
Age and Sex Structure:
• A population pyramid- is a principal tool used to study the age
and sex composition of a population (population structure).
• It is a device that allows us or a scientist to classify and organize
the multitudes of data sets.
• A pyramid comprises two histograms placed on their sides, back
to back.

23. • Male side
• It’s usually in blue
and at the left side
• Female side
• It’s usually in pink and
at the right side

24. Global Health: Introduction to Population Studies
Construction of a Population Pyramid:
• Construction of an age-sex pyramid is relatively simple.
• First, age groupings are placed in order on the vertical scale,
with the youngest age-group located at the bottom and the oldest
at the top.
• Second, males are represented on one side of the pyramid
(usually on the left), and females on the other (usually on the
right).

25. Global Health: Introduction to Population
Studies
• Third, because most censuses report the data by five- year age
cohorts, male children aged 0-4 make up the lowest bar on the
pyramid, female children aged 0-4 on the other side.
• Fourth, the horizontal scale (as a bottom scale) contains the
percentages that each cohort constitutes of whole population.
• The bottom scale can be graduated as either absolute numbers or
percentages.
• The shape of the pyramid cannot be affected by all the graduation.

26. Global Health: Introduction to Population Studies
• It is important to know that percentages are calculated using the
total population of both sexes combined, as a base.
• In the pyramid, all the age bars for both sexes together represent
the total population.
• For example, males 0-4 are 7.3 per cent of that total, females 0-4
are 7.0 per cent; males 20-24 are 4.8 per cent, females 20-24 in
that cohort are 5.0 per cent; and so on.

27. Global Health: Introduction to Population Studies
• The result is a pyramidal structure that changes as long as
fertility, mortality and migration change, and that reflects many
important events occurring during the periods prior to the census
that produces the data, including wars, epidemics, depressions
and booms, and all other events that affect the three processes
• These population processes- are the only demographic dynamics
that can directly affect the size, distribution and composition of
any population, including its age and sex structure.

28. Global Health: Introduction to Population Studies
• Age-sex patterns have an impact on the three population
processes and are cause and effect of other population changes.
• For example, very low birth rates help to create a relatively old
population, provided death rates are comparatively low for
people throughout the scale.
• The high proportion of elderly people serves to depress births
even more.

29. Global Health: Introduction to Population Studies
• Differential death rates by sex are likely to enlarge the proportion
of elderly women far beyond that of elderly men, if it involves
the personal and social results that go with widowhood.
• In summary, the pyramid is a sensitive reflection of changes in
the three population processes, and they in turn show a whole
range of socio-cultural fluctuations in a society or country.
• Age and sex are two of the basic ‘characteristics or features of
the population’ that distinguish one person from another.
• They are used to classify populations into fundamental
categories, and collectively, the characteristics make up the
‘composition of the population.’

30. POOREST DEVELOPING
COUNTRIES.
(SUDAN)
• The top is narrow
because the life
expectancy is low
• The base is large
because the birth rate is
very high

31. Economically Developing Countries
(Mexico)
• The top is less narrow
because the life
expectancy is higher
• The base is smaller
because the birth rate is
falling slowly
• There are also a lack of
population in some ages
(20- 25) because of the
migration

32. DEVELOPED COUNTRIES
(USA)
• The top is bigger because
the life expectancy is higher
• The base is narrow because
the birth rate is low
• There are sectors which are
bigger because the in migrants
who come to their countries

33. • Comprises young populations
(high percentage under age 15)
need to invest more in schools
• The age structure can also be
used to help predict potential
political issues. For example,
the rapid growth of a young
adult population unable to find
employment can lead to unrest.
The age structure of a population
affects a nation's key
socioeconomic issues.

34. USEFULNESS OF POPULATION PYRAMID
This information is very useful to governments for policy
planning
• Population structures can predict the changes of a
population in the future.
• Show the level of development of a population

35. DEMOGRAPHIC INDICATORS
• Mortality.
• Morbidity.
• disability.
• natality.
• Measurement of the presence, absence or
distribution of the characteristics or attributes of the
disease.

36. DEMOGRAPHIC INDICATORS
• Measurement of medical needs, health care facilities,
utilization of health services and other health related
events.
• Measurement of the presence, absence or distribution
of the environmental and other factors suspected of
causing the disease.

37. Source of demographic data
• Main source of demographic data are:
Population census
National sample surveys
Registration of vital events

38. Demographic Data Methods and Measurements
Demographic Data Methods:
• Demographic data is collected through-
-Census- Head count of all population in a country. Population census for a 10
year interval- to keep population stock, its size and structure
-Surveys- carried out as inter-census survey to monitor events of population.
-Registration system of events- recorded during a particular time interval
usually a year- i.e births, deaths and moves, or whatever occurring during a
period affected by the numbers ‘at risk’ of having a birth, dying, and moving.

39. Demographic Measures
 Demographic data take the form of frequencies of either qualitative
or discrete (i.e. counted) quantitative variables.
•Statistics used to manipulate such data are: rates, ratios, and
proportions
•These constitute the most basic tools of formal demography

40. Basic Demographic Equation for Population Change
Estimation:
• One of the fundamental facts about population change is that populations
only change because of a limited, countable number of events.
• For example, consider the population of a country.
• Suppose that this country at some time ‘t’ contains ‘Pt’ persons, and that 1
year later, it contains P t +1 persons.
• It is then written as the following equation:
P t + 1 = P1 + B1-D1+I1-E1

41. -The population of an area at time ‘t +1’ is just the population at time
‘ t’ plus number of births between t and t +1, less the number of
deaths, plus the number of migrants entering the area, less the
number leaving.
-The difference between the numbers of births and deaths gives the
Natural increase’, while the difference between the numbers of
migrants in and out gives ‘ net migration’

42. • Then the rate of population change is just:
Pt + 1 – Pt B D IN out
--------------- = -------- - -------- + ------ - ------
MYP MYP MYP MYP MYP
•Difference between the Birth rate and Death rate is the Rate of Natural
Increase, the difference between the In- and Out- Migration Rates is the Net
Migration Rate
• So the equation can also be written as:
Growth Rate = Rate of Natural Increase + Net Migration Rate.

43. •Thus the equation can be written as:
Population Change = Natural Increase + Net migration
•Population change is dominated by the rate of ‘natural increase’, in
others net migration is more important (such as western countries),
and in some both the rate of natural increase and rate of net migration.
•Basic Demographic Equation is sometimes called ‘Balancing
Equation’.
• The Equation can also be expressed in terms of rates, by dividing
each element by the mid-year population (MYP) and multiplying by
100 per cent.

44. Demographic Processes as Transitions between Countries or
States for Understanding BDE:
• One way of representing the components (i.e. fertility/ births,
mortality and migration) of population change is to view them
as a set of transitions made by individuals between various
countries or states.
• The basic demographic equation may in this way be represented
by four states: ‘alive, and in the population; ‘alive, but in another
country; ‘not yet born’; and ‘dead’

45. ELEMENTS OFDEMOGRAPHY
These are special elements that demographers use o interpret
populations
• Birth rate
• Death rate
• Crude birth rate
• Crude death rate
• Total Fertility rate (TFR)
• Infant mortality rate
• Child mortality rate
• Maternal mortality rate
• Life expectancy
• Growth rate

46. Elements of demography
• Birth rate: the number live births in per 1000 population in
a given year
• Death rate: is the number of death per 1000 population in a
given year
• Total Fertility rate (TFR): this is the average amount of
children born alive to any woman

47. Introduction to Population Studies
B) Age and Sex Structure Measures:
i. Ratio:
• A ratio - is simply any number divided by any other number, e.g. the sex
ratio- number of males per 100 females:
Males
---------- x 100
Females
or
Sex ratio at birth= Male births
-------------- x 100
Female births
• Sex ratio is simply the ratio of males to females in the
population- expressed as the number of males per 100 females

48. Introduction to Population Studies
• Sex ratio at birth is just the number of male births per 100
female births.
• For example, if Zambia in 2011, there were 336,835 male and
319,582 female births, the sex ratio was:
336,835
--------------- x 100
319,582
= 105.4
It means that 105 boys were born for every 100 females

49. Dependency Ratio:
• It is an index summarizing an age distribution in a population.
• It is the ratio of economically active to economically inactive persons in a
population.
• The ratio is computed as:
Children + Elderly
Dependency Ratio = ---------------------- x 100
Working Ages
• Ages being used depends entirely on classification of population by each
country, e.g who is a child and retirement ages of elderly persons.

50. For example, an estimated 10,251,300 children,30,571,500 productive adults, and
9,098,700 elderly people, the ratio is:
10,251,300 + 9,098,700
Dependency ratio = ----------------------------------- x 100
30,571,500
= 63.3 per 100 productive people, or
= 63.3 per cent

51. ii). Proportion:
• A proportion- is a special type of ratio in which the numerator is
included in the denominator:
x
Proportion = -------
x + y
e.g, the proportion of the population that is female is the number of
females divided by the total number of males and females, and multiplying
by 100 percent to get proportion expressed as percent.

52. iii) Rate:
•A rate- is used very loosely in demography, and this can create
confusion.
•The numerator is a rate is a number of events, such as, births or
deaths occurring during the period of time.
•The denominator- is the number of ‘person-years of exposure to
risk’ experienced by the population at mid-year during period
under consideration- crucial point is specification of time period.
•In demography rates are most frequently calculated for period of
one year.

53. • Rates in demography are strictly ratios or proportions.
• For example, ‘Literacy rate’ is just the proportion of the population that is
literate, while ‘ Crude Birth Rate’ is really a ratio since it includes in its
denominator- the old, children and males, none of whom are at risk of
giving birth.

54. C) Fertility Measures:
i. Crude Birth Rate:
• Crude Birth rate is a measure of fertility-defined as
Births in year
CBR= ----------------- x 1000
Population at mid-year
• For example, an estimated 3,689,000 in a total population of
76,398,000 for a particular country, the CBR will be:
3,689,000
-------------- x 1,000
76,398,000
= 48.3 per 1,000

55. ii) General Fertility Rate (GFR):
•General Fertility Rate expressed as:
Births during year
GFR = ---------------------------- x 1000
women 15-44 or 49 at mid-year
• For example, if births during the year were 3, 689,000 and
women 15-49 were 14,952,000 for a country in a particular year,
gives a GFR as:
3,689,000
GFR = -------------- x 1,000
14,952,000
= 246.7 per 1,000

56. • The general fertility rate is a fertility rate rather than a birth rate,
because it expresses the births relative to a number of women in
reproductive age.
• The main advantage of GFR over the CBR is that it controls for
age and sex structure by relating the births to women at risk of
having them.

57. iii). Age-Specific Fertility Rate (ASFR):
•Age- Specific Fertility Rates expressed as:
Births in year to women aged x
ASFR = --------------------------------------- x 1000
women aged 15-44 or 49 as ‘x’ at mid-year
• ASFRs are expressed per 1,000 population
• Births for each five year age-group, for example, 15-19,20-24,
and so on are usually used to calculate the ASFRs

58. • For example, calculating ASFRs for a country for a particular
year, you need to construct a table as follows:
Age-group Women Births ASFR per 1,000
-------------------------------------------------------------------------------------------------
15-19 3,777,000 756,900 200.4
20-24 3,101,000 1,046,000 337.3
25-29 2,636,000 819,500 310.9
30-34 2,161,000 565,100 261.5
35-39 1,793,000 353,200 187.0
40-44 1,484,000 141,600 95.4
45-49 1,222,000 16,500 13.5
-------------------------------------------------------------------------------------------------------

59. iv). Total Fertility Rate:
• Total Fertility Rate (TFR) and sometimes called Total Period
Fertility Rate (TPFR) in some countries, it is defined as a
number of live births a women is expected to have during a
reproductive life span at 44 or 49 years period.
• It is the measure of fertility that is widely used by most
demographers.
• It is calculated by simply adding ASFRs and multiplying by
five year interval and divided by women populations 15-49 or
1,000

60. • Total Fertility Rate(TFR) is calculated as:
Sum of ASFRS x 5
TFR = -------------------------------
1,000
• Five is used for age-intervals, as five years long.
• Using data from the table gives:
(200.4+ 337.3+ 310.9+ 261.5+ 197.0+95.4+ 13.5) x5
TFR =-------------------------------------------------------------------
1,000
= 7.08 live children per woman

61. D) Basic Mortality Measures:
i) The Crude Death Rates:
• The Crude Death Rate (CDR)- is simply the deaths in a population
at mid-year and multiplied by 1,000, that is:
Deaths in year
CDR = ------------------ x 1,000
Total Population at mid-year
• One important use of the CDR is to calculate the Crude Rate of
natural increase- the difference between the CBR and the CDR- a
measure of the current rate of population growth rate for the natural
increase.

62. Introduction To demography
•CDR covers all ages, yet a crucial aspect of mortality is the way it
varies by age.
• One important use of CDR is to calculate the Crude rate of
Natural Increase- the difference between the CBR and the CDR- a
measure of the current rate of population growth if net migration is
not substantial.
•A death rate- defined as
Number of deaths in a specific time period or year
Death rate = --------------------------------------------------------- x1000
Number of people exposed to the risk of dying during
that time period( consider mid-year population)

63. Introduction to demography
•The Infant Mortality Rate:- this is defined as
Death under age 1 in year
IMR= ------------------------------ x 1000
Live births in year
• IMR - is the probability of dying during the first year of life.
•Neonatal Mortality rates: Deaths concentrated in the first week or
one month of life.
• IMR is often broken down in three parts: Early, Late and post-
neonatal mortality rates.

64. Introduction to demography
•Formulae used are:
Deaths under 1 week
a) Early neonatal mortality rate= -------------------------- x 1000
Live Births
Deaths1-4 weeks
b) Late neonatal mortality rate=-----------------------x 1000
Live births
Deaths 4-52 weeks
c) Post-Neonatal mortality rate = ------------------------- x 1000
Live Births

65. Introduction to demography
• Late Foetal Death rate:- this also called ‘stillbirth rate’- defined
as
Late foetal deaths
Late foetal deaths= -------------------- x 1000
Late stillbirths + Live births
• Perinatal Mortality Rate: defined as
Stillbirths + Deaths under 1 week
PMR = ------------------------------------------- x 1000
Stillbirths + Live births

66. Introduction to Demography: Mortality Component
Maternal Mortality Ratio (MMR):
The measure is computed as:
Deaths of women in child birth
(due to maternal causes)
Maternal Mortality Ratio = ---------------------------------- x 100,000
Live births
• Note that the denominator is the total number of live births born to women
at risk of dying 15-49 years
• The enumerator is the total number of women dying during pregnancy,
child birth, or after birth for the first 48 hours following birth due to
maternal related causes or complications.
• Ratio is expressed per 100,000 live births

67. IMPORTANCE OF DEMOGRAPHIC
DATA
Demographic data provide a basis for predicting future trends &
making decisions.
It is also important for formulation, implementation & evaluation of
plan ,policies &programs.
It is a guide to policy makers to make policies that can fulfill the
needs of various sector of society such as young ,adult, & aged,
unemployed, poor & various cultural group.

68. Introduction to Demography: Discussion Points
Why is population studies important in public health?