1. Global Health: Introduction to Population Studies
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

2. Global Health: Introduction to Population Studies
1. Population Studies Terminology: Definitions
Definition: The United Nations Multilingual Demographic Dictionary (1958) defines Population Studies as “a broader scientific study of human populations primarily to their size, distribution and structure involving the measurement of demographic processes and their relationships to economic, social (health &education), cultural, ecological and biological processes of influencing population change”

3. Global Health: Introduction to Population Studies
In reference to its definition, population studies combines study of “formal demography” which is the statistical study of human populations involving the collection and interpretation of demographic processes or event data relating to fertility, mortality and migration and “social demography” involving the population dynamics- i.e, the changes in the structure of a population affected by the economic, social, cultural, ecological and biological processes.
These distinct features of population studies have ultimate effects of change on health, environment and population.

4. Global Health: Introduction to Population Studies
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.
The term population studies is therefore used inter-changeable with demography meaning the same concept, even though, population studies is a broader context of demography studying the relations between demographic events or processes (Fertility, Mortality, Migration) and the social and economic or other phenomena.
The main feature of formal demography are fundamentally descriptive or analytic, rather than explanatory in nature and it is concerned with demographic events in isolation.

5. Global Health: Introduction to Population Studies
To sum up the two linked concepts- Population studies –is ‘the scientific study of demographic processes and dynamics of the human population’
In other countries, it is called Population Health, or Medical Demography.
It is the discipline enshrined within the subject of Public Health

6. Global Health: Introduction to Population Studies
2. Major Comprehensive Components of Population Studies are:
Demographic processes and events: five major components: a) Fertility, b) Mortality, c) Migration, d) Marriage/ nuptiality e) Population structure (age and sex structure or composition)
Population dynamics
Demographic measurements and methods
Population Projections
Reproductive health, Nutrition &Gender
Environmental epidemiology and Geographic Information System
Social Epidemiology
Population genetics & Ageing Population
Population Policies, & Globalization
Population Information & surveillance system

7. Global Health: Introduction to Population Studies
3. 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- which makes it interesting and a productive subject in understanding causes and effects of demographic phenomena on human populations.
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

8. Introduction to Population Studies: 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) increase population growth rate leading to population explosion (overcrowding) that may not be balanced with the socio-economic growth of a country and that can affect environment, increase disease outbreak and ultimately increase in mortality.
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.

9. Introduction to Population Studies: Theories
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.

10. Introduction to Population Studies: Theories
Demographic Questions that relates to population explosion, for example are concerned with: how many people live on earth ? Are their numbers a problem? How many will be in future? How will they support themselves to survive?- seeking explanations on the effects of population growth on economic growth
These questions trigger into the minds of demographers.
Earliest scholars, such as Thomas Malthus, (1798) an English clergyman- first warned of the results of the excessive population in his essay- the ‘Principle of Population’.

11. Introduction to Population Studies: Overview
Malthus warned that- “human populations increase at a geometric rate, crowding their environment and creating a legacy of problems for generations in future leading to population explosion”
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).

12. Introduction to Population Studies: overview
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.

13. Introduction to Population Studies
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.

14. Introduction to Population Studies: Overview
Voluntary movements were seen as being in the right direction, but only few were affected.
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.

15. Introduction to Population Studies
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.

16. Introduction to Population Studies
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.

17. Introduction to Population Studies: overview
4.Demographic Transition Theory:-
It is a strong interrelationship change between population structure, fertility, mortality and migration which lie at the heart of formal demography and social demography on the other hand.
Theory of transition was first described in the 1940s based on natural increases of rural populations in Eastern Europe.
Classical description of the theory based on natural increases involves series of stages during which a population moves from a situation where both mortality and fertility are high, to a position where both mortality and fertility are low.

18. Introduction to Population Studies
Both Before and after the transition population growth is very low.
In between during the transition, population growth is very rapid, essentially because decline in mortality tends to occur before the decline in fertility.
Major Seven (7) Transition Phases:
Stage 1: Potential growth- 1st stage combines high births rates with death rates remaining high- just as Malthus predicted- increasing population growth to create population explosion.
Stage 2: Incipient growth- combines persisted high birth rates with death rates that started declining- most likely by improvements in medicine, nutrition and sanitation- increase life expectancy.

19. Introduction to Population Studies
-Stage 3: Transitional growth: critical stage- combines stubbornly high birth rates with death rates that have dropped very substantially, and represents the population explosion in force.
-Stage 4: Incipient Decline: birth rate begins to move down- wards toward a fairly low and relatively stable death rate that no longer has the potential to drop greatly.
-Stage 5: Controlled growth- Birth rates drop low- couples are planning their families and avoiding unwanted pregnancies- growth still goes on ‘cos’ number of children average to 2.1 or 2.2.

20. Introduction to Population Studies
-Stage 6: Equilibrium at ZPG ( Zero Population Growth):- Demographic transition has death rates near some irreducible minimum and fertility rates that vary slightly on either side of the mortality levels over short periods- Not many people are born and life expectancy is prolonged- Population growth neither growth nor declines.
- Stage 7: Absolute Decline: demographic transition occurs when the birth rate in consistently below the death rate- thus absolute decline or a negative growth rate- (observed in Germany and Switzerland in decline-0.1%

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. Global Health: Introduction to Population Studies
5. 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. 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).

24. 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.

25. 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 are 4.8 per cent, females in that cohort are 5.0 per cent; and so on.

26. 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.

27. 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.

28. 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.

29. Global Health: Introduction to Population Studies
They are used to classify populations into fundamental categories, and collectively, the characteristics make up the ‘composition of the population.’

30. Global Health: Introduction to Population Studies
6. 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.

31. Global Health: Introduction to Population Studies
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

32. Global Health: Introduction to Population Studies
A). 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

33. Introduction to Population Studies
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’

34. Introduction to Population Studies
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.

35. Introduction to Population Studies
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.

36. Introduction to Population Studies
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’

37. Introduction to Population Studies
The components of demographic change are then represented by transitions between conditions within the population are demonstrated in figure below:
Figure : Et It Dt Bt
The illustration shows the multiple-state representation of the basic demographic equation: Bt, Dt, Et, and It to represent transitions (i.e. population changes).
Alive and in Population
Alive and in another population
Dead
Unborn

38. Introduction to Population Studies
Age and Sex Structure Measures:
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

39. 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 =
It means that 105 boys were born for every 100 females

40. Introduction to Population Studies
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.

41. Introduction to Population Studies
For example, an estimated 10,251,300 children,30,571,500 productive adults, and 9,098,700 elderly people, the ratio is:
10,251, ,098,700
Dependency ratio = x 100
30,571,500
= per 100 productive people, or
= per cent

42. Introduction to Population Studies
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.

43. Introduction to Population Studies
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.

44. Introduction to Population studies
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.

45. Introduction to Population studies
C) Fertility Measures:
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

46. Introduction to Population studies
ii) General Fertility Rate (GFR):
General Fertility Rate expressed as:
Births during year
GFR = x 1000
women or 49 at mid-year
For example, if births during the year were 3, 689,000 and women 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
= per 1,000

47. Introduction to Population studies
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.

48. Introduction to Population Studies
iii). Age-Specific Fertility Rate (ASFR):
Age- Specific Fertility Rates expressed as:
Births in year to women aged x
ASFR = x 1000
women aged 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

49. Introduction to Population Studies
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
,777, ,
,101, ,046,
,636, ,
,161, ,
,793, ,
,484, ,
,222, ,

50. Introduction to Population Studies
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 or 1,000

51. Introduction to Population Studies
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:
( ) x5
TFR =
= 7.08 live children per woman

52. Introduction to Population Studies
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.

53. 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)

54. 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.

55. 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

56. 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

57. 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 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