4 Demographic techniques
Atreyo Mondal and Gautam Kshatriya
Contents
Introduction
Demographic Perspective
Demographic Measurement Tools and Techniques
3.1. Tools of Measurement
3.1.1. Ratios
3.1.2. Proportion:
3.1.3. Rates
3.2. Techniques of Demographic Measurement
3.2.1. Measure of Fertility
3.2.1.1. Crude Birth Rate (CBR)
3.2.1.2 General Fertility Rate (GFR)
3.2.1.3. Age Specific Fertility Rates (ASFR)
3.2.1.4. Total Fertility Rate (TFR)
3.2.1.5. Gross Reproduction Rate (GRR)
3.2.1.6. Child – Woman Ratio (CWR)
3.2.2. Measures of Mortality (Death)
3.2.2.1. Crude Death (Mortality) Rate (CDR)
3.2.2.2. Age Specific Death (Mortality) Rates
3.2.2.3. Infant Mortality Rate (IMR)
3.2.2.4. Child Mortality Rate (CMR)
3.2.2.5. Under Five Mortality Rate (<5MR)
3.2.2.6. Neonatal Mortality Rate (NNMR)
3.2.2.7. Neonatal Mortality Rate (NNMR)
3.2.2.8. Post-Neonatal Mortality Rate (PNNMR)
3.2.2.9. Maternal Mortality (Death) Rate (MMR)
3.2.3. Sex Specific Death Rates (SSDR)
4. Understanding the Changes and Components of Population Growth
5. Summary
Learning Objectives
- To know about the Demographic Perspective
- To know about various method about measures of Fertility
- To know about various method about measures of Mortality (Death)
- To know about Changes and Components of Population Growth
Introduction
Demography is the scientific study of human population, including its size, distribution, composition, and the factors that determine changes in its size, distribution, and composition. From this definition we can say that demography focuses on five aspects of human population: (1) size, (2) distribution, (3) composition, (4) population dynamics, and (5) socioeconomic determinants and consequences of population change. (Swanson, J., 2004)
Population size is simply the number of persons in a given area at a given time. Population distribution refers to the way the population is dispersed in geographic space at a given time. (Srivastava.,1994).
Population composition refers to the numbers of person in sex, age, and other “demographic” categories. The scope of the “demographic” categories appropriate for demographic study is subject to debate.
The age, sex, race, year of birth, and place of birth are demographic characteristics. These are all characteristics that do not essentially change in the lifetime of the individual, or change in a perfectly predictable way. They are so-called ascribed characteristics. Many other characteristics also are recognized as within the purview of the demographer. These fall into a long list of social and economic characteristics, including nativity, ethnicity, ancestry, religion, citizenship, marital status, household characteristics, living arrangements, educational level, school enrolment, labour force status, income, and wealth. Most of these characteristics can change in the lifetime of the individual. They are so-called achieved characteristics (Swanson, J., 2004).
Narrowly defined, the components of change are births, deaths, and migration. In a more inclusive definition, the addition of marriage and divorce as processes affecting births, household formation, and household dissolution; and the role of sickness, or morbidity, as a process affecting mortality. The study of the interrelation of these factors and age/sex composition defines the subfield of formal demography. Beyond these demographic factors of change, there are a host of social and economic characteristics, that represent causes and consequences of change in the basic demographic characteristics and the basic components of change. Study of these topics defines the subfields of social and economic demography.
2. Demographic perspective
While the “demographic perspective” is largely a way of dealing with data, it is present when we (1) bring into play essentially demographic phenomena, such as population size, change in population numbers, numbers of births, deaths, and migration, and age/sex/race composition; (2) apply essentially demographic methods or tools, such as sex ratios, birth rates, probabilities of dying, and interstate migration rates, and their elaboration in the form of model tables, such as life tables, multistate tables, and model tables of fertility or marriage; (3) seek to measure and analyze how these demographic phenomena relate to one another and change over time, such as by cohort analysis or by analyzing the age-period-cohort interaction; and (4) construct broad theories as to the historical linkage or sequence of demographic phenomena, such as the theory of the demographic transition or theories accounting for internal migration flows.
In these terms, the demographic perspective can be applied widely to serve a broad spectrum of applied disciplines as well as aid in interpreting broad historical movements.
To a large degree, this knowledge is captured in the demographic perspective. It provides demographers with a framework within which data, models, and theory can be used to explain how populations work.
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The most fundamental is to describe changes in population size, distribution, and composition as a guide for decision making. This is done by obtaining counts of persons from, for example, censuses, population registers, administrative records, or sample surveys. Counts of births and deaths can be obtained from vital registration systems or from continuous population registers. Similarly, immigration and emigration data can be obtained from immigration registration systems or from continuous population registers. As is true in many other scientific fields, demographers make use of these patterns in studying population trends, developing theories of population change, and analyzing the causes and consequences of population trends.
Various demographic measures such as ratios, percentages, rates, and averages may be derived from them. The resulting demographic data can then be used to describe the distribution of the population in space, its degree of concentration or dispersion, the fluctuations in its rate of growth, and its movements from one area to another. (EPHTI,2005).
3. Demographic Measurement Tools and Techniques
The major demographic processes of fertility, mortality and migration constitute the basic components to determine the size, composition and distribution of a population which require basic tools and techniques of measurement.
3.1. Tools of Measurement
The tools of measurement include:
• Ratios
• Proportions
• Rates
3.1.1. Ratios
Ratio is a quecient of any two demographic quantities. It is the result of dividing one quantity by another. Ratio quantifies the magnitude of one occurrence or condition in relation to another. It is expressed in the form of:
a , or a ; b
b
Examples:
• Sex Ratio (male – female) = Males
Females
• Doctor to Population Ratio = Number of Doctors Number of Population
• Dependency Ratio = No. of People < 15 years +65 years and above
No. of Population 15-64 years of age
Qualification:
• The numerator and denominator (a and b) are defined for a specific geographic area and period of time.
• The numerator may or may not be a sub – group of the denominator.
3.1.2. Proportion
A proportion is a ratio which indicates the relation in magnitude of a part of the whole. The numerator is always included in the denominator. A proportion is usually expressed as a percentage.
Example:
Males to total population ratio
Males x 100
Males + females
Illegitimate Birth Ratio = No. of illegitimate live births x 100
Total No. of live births
3.1.3. Rates
A rate measures the occurrence of some particular event (example death) in a population during a given time period. It is a statement of the risk of developing a condition. It indicates the change in some event that takes place in a population over a period of time. It is defined per unit of time.
Rate = Vital event X (K)
Population at risk
Example:
Death Rate = No. of deaths in one year X 1000
Mid year population
A rate comprises the following elements:
• Numerator
• Denominator
• Time specification and
• Multiplier or constant (100, 1000, 10000, 100,000 etc)
A Rate is a ratio or a proportion in which the numerator is part of the denominator. All rates are ratios, but all ratios are not rates.
3.2. Techniques of Demographic Measurement
A change in the overall size of a population is the result of three cumulative changes in the number of births, deaths and migrants. Since births and deaths occur continuously, and since people frequently change their place of residence, they are the bases of demographic analysis. Depending on their direction and magnitude these processes are important for social and economic planning, in assessing the present needs and the needs of the future expansion of socio-economic infrastructure. The techniques for measuring fertility, mortality and migration are described further.
3.2.1. Measure of Fertility
Fertility is the reproductive performance of an individual, a couple, a group or a population. It is meant the actual bearing of children. Some demographers prefer to use natality in place of fertility.
Fertility leads to increase of population. It differs from fecundity – which refers to the physiological capability of a woman to reproduce. A woman’s reproductive period is roughly 15 – 49 years of age.
The most important measures of fertility include:
3.2.1.1. Crude Birth Rate (CBR)
The crude birth rate indicates the number of live births (children born alive) per 1000 mid – year population in a given year.
CBR = Number of live births in a year X 1000
Total mid – year population
In the world CBR varies widely from population to population. It is high for population of the developing countries and low for those of the developed ones.
Example: According to world population data sheet of the Population Reference Bureau the Crude Birth Rate for 2003 was:
| • World | = 22/1000 population |
| • More developed counties | = 11/1000 population |
| • Less developed countries | = 24/1000 Population |
Fertility may be grossly determined as high, medium or low based on CBR values. High fertility Rate = > 30/1000
Medium fertility rate = 20-30/1000
Low fertility rate = < 20/1000
3.2.1.2 General Fertility Rate (GFR)
The General Fertility Rate is the number of live births per 1000 females aged 15-49 years (fertile age group) in a given year. The GFR in more sensitive measure of fertility than the CBR, since it refers to the age and sex group capable of giving birth (females 15-49 years of age). It eliminates distortions that might arise due to different age and sex distributions among the total population. The major limitation of GFR is that not all women in the denominator are exposed to the risk of child birth.
GFR = Number of live births in a year X 1000
Number of females 15-49 years of age
The GFR is approximately four times the CBR.
3.2.2.3. Age specific fertility rates (ASFR)
The Age specific fertility rate is defined as the number of children born alive to females in a specific age group per 1000 females in that specific age group, example (15-19), (20-24),….. (45-49) years of age.
ASFR = No. of live births to females in a specific age group in a year X 1000
Mid-year population of females of the same age group
For example, ASFR for women 20 – 24 years of age is expressed as:
ASFR (20-24) = Live births to women 20- 24 years of age X 1000
Total No. of females 20 – 24 years of age
For instance if there were 4,000,000 women (females) in the age group 20-24 years and if the there were 200,000 live births to women in the same age group, the Age specific fertility rate for these women (20-24 years of age) will be;
ASFR (20-24) years of age = 200,000 X 1000 = 50
4,000,000
That is, there are 50 live births for every 1000 women 20-24 years of age.
3.2.1.4. Total Fertility Rate (TFR)
The total Fertility Rate is the average number of children that would be born to a woman throughout her life time or her child bearing age (15-49 years), if she were to pass through all her child bearing years at the same rates as the women now in each age group.
The TFR sums up in a single number the Age Specific Fertility Rates of all women at a given point in time. If 5 – year age groups are used, the sum of the rates is multiplied by 5. This measure gives the approximate magnitude of “completed family size”.
The TFR is one of most useful indicators of fertility, because it gives the best picture of how many children women are having currently.
TFR = Sum of all Age specific fertility rates multiplied by age interval (Usually 5).
Total fertility rate also varies widely between populations in the world. It is higher for developing countries than developed ones. According to World Population Data Sheet of the population Bureau the TFR for 2003 was:
• World = 2.8 children per woman
• More Developed Countries = 1.5 children per woman
• Less developed countries = 3.1 Children per woman
3.2.1.5. Gross Reproduction Rate (GRR)
The Gross Reproduction Rate is the average number of daughters that would be born to a woman throughout her lifetime or child bearing age (15-49 years), if she were to pass through all her child bearing age.
This rate is like the TFR except that it counts only daughters and literally measures “reproduction”; a woman reproducing herself by having a daughter.
The GRR is calculated by multiplying the TFR by the proportion of female births (Sex Ratio at birth).
GRR = TFR X Male births
Male + Female births
Example: – The sex ratio at birth of Ethiopia (2001) = 100.6
(i.e 100.6 males for every 100 females)
– and the TFR (2001) = 5.9 (5.9 children per women)
GRR = TFR X proportion of female births
GRR = 5.9 X 100 = 2.94
200.6
= 2.9 daughters /woman
3.2.1.6. Child – Woman Ratio (CWR)
Child woman ratio is defined as the number of children 0 – 4 years of age per 1000 women of child bearing age, (15 -49 years). This ratio is used where birth registration statistics do not exist or are inadequate. It is estimated through data derived from censuses.
CWR= No of children 0 – 4 years of age X 100
Total No of women 15 – 49 years age
Example:
If the number of children under 5 years of age in an area is 2,000,000 and the number of women 15 – 49 years of age is 8,000,000.
CWR = 2,000,000 X 1000 = 250
8,000,000 1000
That is 250 children 0 – 4 years of age (under five) per 1000 women of the reproductive age.
3.2.2. Measures of Mortality (Death)
Mortality refers to deaths that occur within a population (reduction of population). The incidence of death can reveal much about the living standard, the health status of a population and the availability of health services.
• A population group exposed to the risk of death (denominator)
• The number of deaths occurring in that population group (numerator)
• A time period.
Measures of mortality include:
Mortality (Death) rates have three essential elements:
3.2.2.1. Crude Death (Mortality) Rate (CDR)
The crude death rate is the number of deaths per 1000 population in a given year.
CDR = Total number of deaths in a year X 1000
Mid-year population
As its name implies the CDR is not a sensitive measure (indicator) of health status of a population. It is affected by particularly the age structure of the population.
Crude Death Rate also varies between populations of the world. According to the “World Population Data Sheet of the population Reference Bureau the crude Death Rate during 2003 was.
| • World | = 9 deaths per 1000 population |
| • More developed countries | =10 deaths per 1000 population |
| • Less Developed countries | = 8 deaths per 1000 population |
3.2.2.2. Age specific Death (Mortality) Rates
Death Rates can be calculated for specific age groups, in order to compare mortality at different ages. E.g. for infants (< one year of age), children 1-4 yeas of age, children under five years, etc.
ASMR = Number of deaths in a specific age group X 1000
Mid-year population of the same age group
3.2.2.3. Infant Mortality Rate (IMR)
Infant Mortality Rate is the number of deaths of infants under one year of age (0-11 months of age) per 1000 live births in a given year.
Infant (children under one year of age) are at highest risk of death than any other age group.
IMR = Number of death of children < 1 year of age in a year X 1000
Total live births during that year
The infant mortality rate is considered to be a sensitive indicator of the health status of a community, because it reflects the socio-economic condition of the population; i.e. the level of education, environmental sanitation, adequate and safe water supply, communicable diseases, provision of health services etc. These factors mostly affect infants and children under five years of age. Hence, IMR widely varies between countries in the world.
According to the “world population Data sheet of the population reference Bureau for 2003”, the infant mortality rate of:
• World = 55 infant deaths per 1000 live births
• More developed countries = 7 infant deaths per 1000 live births
• Less developed countries = 61 infant deaths per 1000 live births
3.2.2.4. Child Mortality Rate (CMR)
It is the number of deaths of children 1-4 years of age per 1000 children 1-4 years of age. It is a sensitive indicators of the health status of a community.
CMR = Number of deaths of children 1-4 year of age in a year X 000
Total number of children 1-4 years of age
3.2.2.5. Under Five Mortality Rate (<5MR)
It is the number of deaths of children under five years of age in a year (0-4 years of age) per 1000 children under five years of age (0-4 year). It is also a very good indicator of the health states of a community
It can also be calculated as the number of deaths of children under five years of age in a year per 1000
live births.
<5MR = Number of deaths of children <5 yrs in a year X 1000
Total number of children < 5 years of age
OR
< 5MR = Number of deaths of children <5years in a year X 1000
Total live births in the same year
• According to Health and Health Related Indicators (MOH), the under five mortality Rate of Ethiopia is estimated to be: – 140/1000 live births, currently – 161/1000 live births, (Srivastava., 1994).
3.2.2.7. Neonatal Mortality Rate (NNMR)
Neonatal period is the first month of age of an infant. Neonatal mortality (death) is the death of infants under one month (<4 weeks). Per 1000 live births.
Neonatal Mortality Rate (NNMR)
= Number of deaths of infants < 1 mouth in a year X 1000
Total number of live births in the same year
Neonatal mortality rate reflects mortality due to
- Maternal factors during pregnancy
- Birth injuries
- Neonatal infection, etc.
It is an indicator of the level of prenatal and obstetric components of maternal and child health care (MCH).
3.2.2.8. Post-Neonatal Mortality Rate (PNNMR)
The post neonatal age is the period of time between one month up to one year. Post – Neonatal mortality (death) is deaths of infants one month (four weeks) of age up to one year (1 – 11 months age of) per 1000 live births.
PNNMR = Number of deaths of infants 1 month to 1 year of age in a year X 1000
Total Number of live births during the same year
The post-neonatal mortality rate reflects deaths due to factors related to;
• Environmental sanitation
• Infections (communicable diseases)
• Nutritional problems
• Child care etc.
It can be used as an indicator to evaluate Maternal and Child Health Care services and socio-economic development of a community or country.
3.2.2.9. Maternal Mortality (Death) Rate (MMR)
Maternal mortality rate is the number of maternal deaths related to pregnancy, child birth and post natal (peurperium) complications per 1000 live births (usually per 100,000 L.B).
MMR
= Number of deaths of women related to pregnancy child birth and peurperium in a year X 100,000
Total number of live births in the same year
It is a sensitive indicator of health status of a population. It reflects the socio- economic status of a community.
The Maternal Mortality Rate of Ethiopia is estimated to be more than 850 deaths per 100,000 live births annually. This is among the highest in the world.
3.2.2.9. Sex Specific Death Rates (SSDR)
Sex Specific Death Rate is the number of deaths among a specific sex group (males or females) per 1000 population of the same sex group.
Sex specific Death (Mortality) Rate for males
= Number of deaths among males X 100
Total number of males
Sex specific mortality rate is used to determine which sex group is at higher risk of death than the other.
4. Understanding the changes and components of population growth
If we assume that the number of individuals entering a population (immigration), equals the number of leaving (emigration), population growth is the result of the increase of births over deaths. This relationship is summarized by a formula known as the balancing equation. It is expressed as:
P 2 = P1 + ( B – D) + ( I + E)
Where:-
P2 = Size of population for the year under consideration
P 1 = Size of population in the preceding year
B = Number of births between the two dates
D = Number of deaths between the two date.
I = Number of immigrants in the time under consideration (between P2 and P1) E = Number of emigrants in the time under consideration (between P2 and P1)
The differences between births and deaths in a population produces the Natural Increase (or Decrease) of a population.
The rate of Natural Population increase is the rate at which a population is increasing (or decreasing) in a given year due to excess (or deficit) of births over deaths expressed as a percentage of the base population.
RNI = Births – Deaths X 100
Total Population
OR
Birth Rate – Death Rate
10
Net Migration: is the difference between the numbers of persons entering a geographic area (Immigrants) and those leaving the area (emigrants).
5. Summary
Demography is the scientific study of human population, including its size, distribution, composition, and the factors that determine changes in its size, distribution, and composition. Population size is simply the number of persons in a given area at a given time. Population distribution refers to the way the population is dispersed in geographic space at a given time. Population composition refers to the numbers of person in sex, age, and other “demographic” categories. Demographers describe changes in population size, distribution, and composition makes use of these patterns in studying population trends, developing theories of population change, and analyzing the causes and consequences of population trends.
Various demographic measures such as ratios, percentages, rates, and averages may be derived from them. The resulting demographic data can then be used to describe the distribution of the population in space, its degree of concentration or dispersion, the fluctuations in its rate of growth, and its movements from one area to another.
A change in the overall size of a population is the result of three cumulative changes in the number of births, deaths and migrants. Since births and deaths occur continuously, and since people frequently change their place of residence, they are the bases of demographic analysis. Depending on their direction and magnitude these processes are important for social and economic planning, in assessing the present needs and the needs of the future expansion of socio-economic infrastructure. There are techniques for measuring fertility, mortality and migration in a population which are used to depict the picture of the population.
The major demographic processes of fertility, mortality and migration constitute the basic components to determine the size, composition and distribution of a population which require basic tools and techniques of measurement. The tools of measurement are ratios, proportions and rates.
To a large degree, this knowledge is captured in the demographic perspective. It provides demographers with a framework within which data, models, and theory can be used to explain how populations work.
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References
- Bhende, A., & T. Kanitkar, T., (2000). Principles of Population Studies. Himalayan Publishing House.
- EPHTI.,(2005)., Lecture Notes For Health Science Students on Population and Development Ethiopia Public Health Training Initiative, The Carter Center, the Ethiopia Ministry of Health, and the Ethiopia Ministry of Education.
- SIEGEL, S. J., & SWANSON, A. D., (2004). The Methods and Materials of Demography. Elsevier Academic Press ISBN: 0-12-641955-8
- Srivastava, S. O., (1994). Demography and Population Studies. Vikas Publishing House.
Suggested Readings
- Survey of Research in Demography by P.B. Desai.
- An Introduction to Population by O.W Kenneth and Kammeyer.
- Dynamics of Population and Family Welfare in India by Srinivasan and Mukerjee.
- Principals of Population Genetics by , A., Bhende and T. Kanitkar.