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WOLLEGA UNIVERSITY, NEKEMETE, Ethiopia
CHAPTER I INTRODUCTION
1. Introduction to population statistics1.1. Some demographic Concepts1.2. Development of demographic studies1.3. Types and sources of Demographic data1.3.1. Data collection methods and instruments1.3.2. Principal sources of demographic data1.4. Uses and purposes of demographic data 1.5. Basic demographic measures1. Introduction
Demography is the statistical study of population data. By the term “Demography” (we mean demo- people, graph- description) is the study of population structure and change. In Demography it includes
1. Examination of the total size of population.2. Examination of population distribution3. Examination of the structure of population.4. Examination of changes in population over time.5. Examination of the cause and effects of its changes.
In these modern days, with increase of complexity, it becomes necessary to study the changes in size and composition of population. Globalization leads, a compulsory picture to make estimates of future size and composition of the population, projections and forecasting are the important terms in demographical study.
Population statistics (Demography or Vital statistics) is a branch that deals with people (Population) of a country or region or an area or world. It deals with the vital events such as fertility, mortality, marriage, divorce, separation, adoption, number of children in a family and their related problems. Since it deals with vital events of human life, it may also refer as “vital statistics”.
The term vital statistics refers to the numerical data or techniques used in the analysis of the data pertaining to vital events occurring in the given section of the population.
DEMOGRAPHY 2
Population studies deals with the socio-economic data, hence it may also referred as “Demography”. Thus demography is the science of population. The word “Demography” was coined by a Belgian named as Achille Guillard, in his work of elements of human statistics or comparative demography in 1855. In his work it deals with the natural and social history of the human species or the mathematical knowledge of populations, of their general changes, and of their physical, civil, intellectual, and moral conditions.
In usual terms, the discipline of the study of human population is known by (a). Population studies and (b). Demography .
Under population studies it is a study as population, where as demography is the science of population. Further demographic analysis is confined to a study of the components of population variation and change, but in population studies it deals with population variables but also relationships between population changes and other variables- social, economic ,political, biological, genetic, geographical and the like.
Here in this course, the terms “Demography” and “Population studies” are used interchangeably.
Demography is defined as “Demography is the scientific study of human population or more specifically the study of size, geographic distribution, age-sex structure, and socioeconomic composition of populations and the factors that effect change in these dimensions of population namely, fertility, mortality and migration.:
1.1. Some demographic concepts1. Observation
Demographic facts and figures are assembled on the basis of the observation of individuals and groups. Observations are events which are seeing in direct and counting by cases. Observations are in different types. Observation is quantifying the events.
2. Relative number
It is known that in demography, collecting facts and establishing relations between sets of data and find out ratio and rates. These ratios and rates are relative measures and express a relation between two or more numbers. It is common to say that
DEMOGRAPHY 3
relative numbers are more useful than absolute numbers. Sometimes it may not helpful to serve the purpose. Absolute numbers are raw data of population. In certain cases absolute numbers can be preferred rather than relative numbers.
3. Rates
Rates are used to observe demographic figures in a meaningful way. Some important demographic rates are
a. Crude birth rateb. Crude death ratec. Crude marriage rated. Crude rate of natural increasee. Crude divorce rate and so on4. Ratio
A ratio prevails at a particular point in time. Ratios are different from ratio. A rate counts the number of events in a restricted time of period. In the sense ratio is prevalence concept rather than the incidence concept underlying a rate. Some of the ratios used in demography.
a. Abortion ratiob. Age – dependency ratioc. Child – woman ratiod. Dependency ratio
There is no unanimity among demographers on the point of its definition; it is the common terms for economists, sociologist and other discipliners. The term Demography has its own scientific values and utilities should be kept in mind while defining.
Demography (may also population studies or vital statistics) is a science of people or human activities. Demography may be defined narrowly or broadly. It is necessary to known these terms and its importance in demography.
Population studies are the study of all the five determinants of population-fertility, mortality, nuptiality, migration and social mobility are studies in relation to its composition and time factor.
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The narrowest sense is that of “formal demography”. Formal demography is concerned with the size, distribution, structure and change of populations.
a. Size: the number of units (persons) in the populationb. Distribution: the arrangement of the population in space at a given time in
various residential areasc. Structure: the distribution of the population among its se and age groupings.d. Change : the growth or decline of the total population or of one of its
structural units
A broader sense includes additional characteristics of the units. These include ethnic characteristics, social characteristics and economic characteristics.
a. Ethnic characteristics: it is like race , legal nationality and mother tongue b. Social characteristics: it is marital and family status, place of birth, literacy
and educational attainment.c. Economic characteristics: it includes economic activity, employment status,
occupation, industry and income among others.
The widest sense of demography extends to applications of its data and findings in a number of fields including the study of problems related to demographic process. These include the pressure of populations upon resources, depopulation, family limitation, eugenics, and the assimilation of immigrants, urban problems, legislative apportionment, manpower and the misdistribution of income.
Demographic analysis is confined to the study of components of population variations and change. On the other hand Population studies are concerned not only with population variables but also with relationships between population changes and other variables – social, economic, political, biological, genetic, geographical and so on.
According to Hauser and Duncan the field of demography as consisting of a narrow scope – demographic analysis and a wider scope- population studies
Thus the field of population studies is at least as broad as interest in the “Determinants and consequences of population trends”. The components of change in total population are births, deaths and migrations.
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To study demographic methods, it is necessary to discuss the following terms. Most of the time we have to refer at many times, an early overview of how demographers organize and analyze their data seems necessary.
It is already noted by Hauser and Duncan in their work. They pointing out that demography share many of its methods with science in general and especially with statistics. Further they listed some techniques that are useful in carryout the demographic analysis.
“Demography is the scientific study of human population or more specifically, the study of the size, geographic distribution, age-sex structure, and socioeconomic composition of populations and the factors that effect change in these dimensions of population, namely, fertility, mortality, and migration.”
The techniques include:
1. Techniques of data collection
2. Techniques of data evaluation and adjustment and of statistical estimation
3. Techniques of analysis including demographic projections or forecasts
Demography as “Static “ : the demographer depends largely on general statistical descriptive techniques with some special rates and graphic devices which have become widely used.
Demography as “Dynamic”: demography has developed a rather comprehensive and elaborate set of rates and ratios.
Thus from the above discussions it is clear that no singular scholar has been unanimously accepted. Further we can observe that:
1. Demography is the study of human beings collectively. It does not deals with the individuals problems.
2. Mathematics and statistics are frequently used in the study of population.3. Studies about the size, composition, distribution and their interrelationship
about a population or group of population only, as study of human beings can be made by different political, social, ethical, religious or other points of view
4. Under the size of population, fertility and mortality is studied in relation to its rates and determinants, whereas sex-ratio, classification by sex and age, life-
DEMOGRAPHY 6
table, population density, rural-urban ratio, migration etc., are studied in population distribution.
Briefly, the subject includes
a. Study of various demographic theoriesb. Measurement of variables involvedc. Study of trend and changes in a region, area, country etc., and their causesd. Study of populations structure and composition
Basic demographic equation
One of the fundamental facts about population change is that populations only change occur a limited, countable , number of events.
It is given in terms of an equation which popularly known to be “Balancing equation”. It is given as
Pt+1=Pt+B t+ I t−Dt−Et
Where B, D are respectively he number of births and deaths occurring in population between times and I, E are respectively the number of immigrants to and emigrant from the country during the same period .
The quantity B-D is known as the natural increase, if D>B natural decrease or negative natural increase, the quantity I-E is known as the net migration.
The above given equation may also known to be a Basic demographic equation or accounting equation. From this equation we can get an idea of the country’s population size change with respect to birth, death and migration. These three events are known as Components of population change.
The process by which a population bears children is known as its fertility. The process by which the number of population is reduced by death is known as mortality.
DEMOGRAPHY 7
Demographic process as transitions between states
The components of demographic change expressed in the form of equation, the other way to express this by transitions between these states. The figure below shows the transitions between states.
E
I
B D
From the above diagram, B, D, E and I are transitions which are expressed in basic demographic equation. This way of viewing demographic processes may be called a multiple-state representation. It is used to help demographers to understand complex processes.
1.2. Development of demographic studies
Despite the long history as independent nation, census undertakings that attempted to cover the entire country began only recently. The first ever Population and Housing Census was conducted in 1984 covering about 81 % of the country. The lowland areas which were predominately inhabited by the pastoral population & some of the rural and urban parts of the country were not covered. The 1984 total population of the country was 42.6 million (this figure includes Eritrea which was part of the country). The 2nd Population and Housing Census were conducted in 1994. It has covered relatively larger proportions of the country as compared to the first census. The total population count in 1994 was 53.5 million including estimated population number for those areas not covered by the census ( i.e. 345,008 persons were estimated). The 3rd Population and Housing Census was planned to be conducted in 2005 but postponed to 2007. The Census Commission had fixed two census dates for the sedentary and pastoral area of the country for various reasons. May 28, 2007 for the sedentary population. November 28, 2007 for the Pastoral Regions of Affar and Somalie.
DEMOGRAPHY 8
Alive(Same population)
Alive(another Population)
Unborn Dead
For the first time in its history the third population census canvassed the entire country
1.3. Types and sources of demographic data
There are certain properties that demographers would like their data to possess. We are concerned with all types of demographic data- from censuses, sample surveys, vital records, continuous population registers and immigration and emigration controls. In general, data should completely cover the units of the specified universe or a representative sample of them. The data should be comparable over time and space. They should be published promptly and in adequate detail.
Most of the time in collection of data compromises are made with the goals of the study because of the practical restrictions, the nature of these deviations should be imparted to the public in the resulting statistical publications. Furthermore, when unintended errors of coverage, classification, rounding the facts and so on., occur in the data gathering and processing, some sources should be devoted to evaluating them, on a quantitative basis if possible.
Type of sources
As in statistical point of view, the sources are primary and secondary sources
The primary sources of demographic statistics may be regarded as the published reports, unpublished worksheets, and tally tapes etc., which are produced by official or private agencies. The reports may contain texts that tell how the report is organized, how the statistics were obtained and how accurate the statistics are deemed to be. The texts may also contain descriptive or analytical material based on the statistics.
As the secondary sources of demographic statistics may be regarded as, the reports on primary sources statistics selectively reproduced or rearranged in terms of abstracts or compendia and yearbooks. Additional derived figures may be introduced at this stage. Other secondary sources that present some of these statistics are journals, textbooks, and research reports.
Many important kinds of demographic statistics are produced by combining census and vital statistics.
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In order to calculate the rate, data are required on both the number of events occurring within the given time interval, and the population exposed to the risk of experiencing those events. There are three sources of population data: 1. Censuses 2. Vital Registration systems 3. Sample Surveys
1. Population Censuses Censuses taking started nearly 6000 years ago. Babylonians are said to be the pioneers in the field, followed later on by Persians and other civilizations, including the Greeks, Romans and the various Chinese dynasties. The practice also underlies a fundamental belief in Christianity regarding Jesus Christ’s place of birth. “It was the five-yearly census ordered by Caesar Augustus which required every man in the Roman Empire to return to his place of origin, thus ensuring that Joseph and Mary travelled to Bethlehem for the birth of Jesus”. The 1841 census of England and Wales is widely regarded as the first truly modern census.
The following paragraphs are based on United Nations recommendations on census taking
Census: Definition Population “ A population census is the total process of collecting, compiling, evaluating, analyzing and publishing or otherwise disseminating demographic, economic and social data pertaining, at a specified time, to all persons in a country or in a well delimited part of a country”
Housing “A housing census is the total process of collecting, compiling, evaluating, analyzing and publishing or otherwise disseminating statistical data pertaining, at a specified time, to all living quarters1 and occupants thereof in a country or in a well-delimited part of a country” A census must have the following essential features Individual enumeration – each individual and living quarter has to be enumerated separately.Universality – A census must cover every individual or housing unit present within the defined census area. Simultaneity – Each person and housing unit must be canvassed within a defined point in time. Defined periodicity - There should be a defined time gap between censuses. The most commonly used interval is 10 years.
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Uses of censuses To provide facts to policy makers and planners Policy development and management/evaluation of programs Gerrymandering or redistricting – delimitation of election boundaries to insure adequate representation Scientific research Industry – to determine consumer demand and availability of labor
Other Censuses Agriculture Livestock Industry and commerce Two Types of enumeration: Canvasser (enumerator) method – information on each individual or housing unit is entered by a census official. Household method: responsibility for entering information given to an individual in the housing unit.
List of Census Topics
1. Geographical and internal migration characteristics (a) Place of usual residence (b) Place where present at time of census, Locality (c) Place of birth (d) Duration of residence (e) Place of previous residence (f) Place of residence at a specified date in the past
2. Household and family characteristics
(a) Relationship to head or other reference member of (b) Household and family composition household (c) Household and family status 3. Demographic and social characteristics(a) Sex (b) Age (c) Marital status (d) Citizenship
DEMOGRAPHY 11
(e) Religion (f) Language (g) National and/or ethnic group
4. Fertility and mortality (a) Children ever born (b) Children living (c) Date of birth of last child born alive (d) Deaths in the past 12 months (e) Maternal or paternal orphanhood
Principles and recommendations for population and housing censuses
Topics collected directly Derived topics
(f) Age, date or duration of first marriage (g) Age of mother at birth of first child born alive 5. Educational characteristics (a) Literacy (b) School attendance (c) Educational attainment (d) Field of education and educational qualifications 6. Economic characteristics (a) Activity status (b) Time worked (c) Occupation (d) Industry (e) Status in employment (f) Income (g) Institutional sector of employment (h) Place of work 7. International migration characteristics (a) Country of birth (b) Citizenship (c) Year or period of arrival
8. Disability characteristics
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(a) Disability (b) Impairment and handicap (c) Causes of disability Vital Registration Systems “Although local or parish registers were kept by some churches in Europe from the 14 Century onwards, civil or state registration systems did not develop until the 19 centuries…….Unlike censuses that describe the state of the population at a fixed point in time, vital statistics are collected on a continuous basis” Life events registered under a complete registration system include
Live Births Deaths Foetal deaths Marriages Annulments/ Legal separations AdoptionsIn developed countries it is usual requirement to register the birth of every child, all marriages, and each death. At the time of registration, other details may be collected. The registration system is a continuous registration in which all changes of events to be registered then and there.Important principles of a Vital Registration system: Universal coverage: A vital statistics system should include all vital events occurring in every geographic area and in every population group comprising the national area.
Continuity: Continuity is important to insure that short-term fluctuations including seasonal movements, as well as long-term movements will be accounted for.
Confidentiality: It is important to safeguard confidentiality of personal information and vital records to insure that use of information and data for specific administrative and statistical purposes is consistent with the intended uses of the records. Regular dissemination: The minimum requirements for using vital statistics should include a)the provision of monthly or quarterly summary, and b) “the
DEMOGRAPHY 13
production of detailed annual tabulations of each type of vital event across classified by its demographic and socioeconomic characteristics.”
Definition of Vital Events “LIVE BIRTH is the complete expulsion or extraction from its mother of a product of conception, irrespective of the duration of pregnancy, which after such separation, breathes or shows any other evidence of life” “DEATH is the permanent disappearance of all evidence of life at any time after live birth has taken place (this definition excludes foetal deaths, which are defined separately below).” “MARRIAGE is the act, ceremony or process by which the legal relationship of husband and wife is constituted”.
“DIVORCE is a final legal dissolution of a marriage”.
“ANNULMENT is the invalidation or voiding of a marriage by a competent authority”, “ADOPTION is the legal and voluntary taking and treating of the child of other parents as one's own, in so far as provided by the laws of each country.”
“LEGITIMATION is the formal investing of a person with the status and rights of a person born in wedlock, according to the laws of each country.”
Summary Definition of Civil Registration Systems “Civil registration is defined as the continuous, permanent, compulsory and universal recording of the occurrence and characteristics of vital events”. These events pertain to the population as decreed in accordance with the legal necessities of a country. It is carried out first and foremost for the purpose of putting in place the legal documents provided by the law. Vital registration records are also a main source of vital statistical data. Data quality requirements for vital statistics include completeness of coverage, timeliness, and accuracy, of civil registrations.
Vital registration in Ethiopia: a Brief History Tentative and largely symbolic efforts to establish a registration system in Ethiopia include the following: The 1900 proclamation by Emperor Menelik to institute a registration system. This was well-intentioned but failed to materialize.
DEMOGRAPHY 14
The 1960 Civil Code: This too remained unimplemented for lack of institutional support and enforcement. The city of Addis Ababa started birth registration in 1942. It started registering marriages and deaths in 1953 and 1970 respectively. However, this took place at the whim of individual residents with legal and other needs for a certificate. A 1980 proclamation stipulated that the Central Statistical Authority (CSA) will begin to undertake registration of vital events. All of the preliminary efforts and attempts to lay the groundwork for a national registration system proved costly and the plan was shelved in 1999. The proclamations of 1983/88 by the Derg to register births, deaths, marriages and population numbers did not come to fruition. The 1995 FDRE constitution considered the naming of a child and record of his/her birth a fundamental right, “but the law on civil registration has not come into effect.” Sample Surveys The following are obtained from a UN “Studies in Methods” series on population sampling “Household surveys provide a cheaper alternative to censuses for timely data and a more relevant and convenient alternative to administrative record systems”. Sample surveys are used for the collection of detailed data on: Socio-demographic characteristics Conditions under which people live Their well-being Activities in which they engage Demographic characteristics and cultural factors which influence behavior, Social and economic change
They provide the structure within which other variables such as education, health status, labor force, disability, nutrition status, migration, fertility, mortality and even seemingly fringe topics such as criminal victimization are studied. Survey data often complements those obtained from registration records, or from censuses. Planning and execution of surveys requires all of the following steps below and many more that have to precede the training of interviewers, such as the selection and specification of the subject matter, development of survey design, design and printing of questionnaires, pre-testing, and preparation of instructional and training materials for field use: Training interviewers
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Data collection Field administration Data processingo Systems planning o Computer programmingo Clerical coding o Key-to-disk operations Data review and publication
The Sample design should insure the following The sample must be conducted in stages to identify accurately the locations where interviews are to be conducted and to select the study households efficiently. It has to be stratified in such a it is spread over target geographic sub-areas andpopulation sub-groups It has to make use of clusters of study households in order to keep costs down to a manageable level. The size of the study sample to try and optimally balance the competing needs of costcutting And accuracy of results.
History of Sample Surveys in Ethiopia: As discussed above, census taking is a costly and time-consuming undertaking. The continuous and complete registration of viral events – births, deaths, marriages, etc. is even costlier and beyond the financial and technical reaches of a poor country like Ethiopia. The solution has been the use of sampling. Sampling is a statistical technique, and is defined as “the analysis of a group by determining the characteristics of a significant percentage of its members chosen at random.”The organization charged with the collection, analysis, and dissemination of sample and census data in Ethiopia is the Central Statistical Authority (CSA), formerly known as the Central Statistical Office (CSO) established in 1960. In the agency’s own words, its functions are anchored in “…. running a National Integrated Household and Enterprise Survey Program (NIHESP), undertaking ad-hoc surveys, conducting census, and compilation of secondary data from administrativerecords
“The Agency has carried out several socio-economic and demographic surveys that include agriculture, price, household income, consumption and expenditure, welfare monitoring, large and medium scale manufacturing and electricity industries, small scale manufacturing industries, cottage industries, construction, mining and quarrying, transport and communications, informal sector, distributive trade and
DEMOGRAPHY 16
services, manpower, demography, family and fertility, health and nutrition, child labour, etc…. These days sample surveys undergoing by CSA cover about 2,072 rural EAs and 790 urban EAs (enumeration areas)..” The first national demographic surveys were conducted between 1964 and 67 (first round) and 1968 – 1969 (second round). Others ample surveys hitherto undertaken by the agency include the: Addis Ababa manpower and housing survey 1976
Population and housing characteristics of 17 major towns 1978
The rural labour force survey 1981/2
The rural labour force survey 1987/8
National Rural Nutrition Survey of 1992 1998 Health and Nutrition Survey
National Labour force survey 1999
Disability Survey of Selected Weredas
Demographic and Health Survey 2000
Child labor survey 2001
Biannual employment 2003
Biannual employment 2004
Demographic and Health Survey 2005
Exercise on Chapter 1.1. Define the termsa. Census. b. Vital events. c. Vital Registration d. Sample Registration System
e. 2. History of census in Ethiopia.
DEMOGRAPHY 17
CHAPTER II Population distribution and composition
2. Population distribution and composition2.1. Population Distribution2.2. Sex and age composition2.2.1. Data tabulation2.2.2. Numerical presentation2.2.3. Population pyramids2.3. Classification and quality of data2.4. Measures of sex composition2.4.1. Numerical measures2.4.2. Sex ratios in terms of population subgroups2.4.3. Uses of sex ratio in data evaluation2.5. Evaluation of age data2.5.1. Sources of errors in age data2.5.2. Measures of age reporting errors2.6. Analysis of age composition2.6.1. Age dependency ratios2.6.2. Aging of population
2.1. Population Distribution
Population data are often needed for distribution wise. In terms of distribution there are two different concepts are available. The study of the structure and characteristics of population and which is also known as the composition of population. The structure and characteristics covers the basic personal social and economic characteristics or attributes of any population; age, sex, race, nationality religion, language, marital status, household and occupation, income etc. Population distribution – Geographic areas and classification of residence.
DEMOGRAPHY 18
According to characteristics a population may be distributed into different sub-groups.
The study of population structure and characteristics may be useful in several ways 1. It helps in an elaborate study of any population and thus makes comparisons possible.
2. It is useful in the preparation of inventories of human resources which is necessary for effective developmental planning.
3. In the event of defence civil registration system, details of births and deaths data may be obtained by utilizing the data on the age-sex distribution of the population available from a census
4. Data on the distribution of population attributes provide material for the study of the social and economic structure of the population and the changes in this structure.
Population distribution – Geographic areas
Population data based on geographic subdivisions of the country is not even but is dense in some places and sparse in others. There are urban centres where millions of people live within a few square kilometres, and there are also vast stretches of mountains and deserts where the population averages only one or two persons per square kilometre. In the studying of population distribution based on geographic distribution of the population can be categorized by political areas and by other types of geographic areas.
Political areas are not ordinarily create by country’s statistical agency but instead are established by national constitutions, laws, decrees or charters. In some countries, the primary political subdivisions are empowered to create secondary and tertiary subdivisions.
The primary areas are district, province, island, department, parish, state and region. It is fairly common for the capital city to constitute a primary division in its own right and often with a distinctive name. In a few countries some of the larger cities are also primary political divisions. Countries that have been settled relatively recently or countries that contain large areas of virtually uninhabited land or land inhabited mainly by aborigines may have a different kind of primary subdivisions that has a distinctive generic name and a rudimentary political character.
DEMOGRAPHY 19
The intermediate or secondary political divisions also have a wide variety of names. These include country, district and commune. Some small countries have only primary divisions. Some large countries have three or more levels. For different administrative functions, a province, state etc., may divide into more than one set of political areas.
Method of analysis
Population density: The density of population is a simple concept much used in studies relating population size to recourses and in ecological studies. This simple concept has a number of pitfalls. Density is usually computed as population per square kilometre, or per square mile, of the land area rather than of gross area. Another measure of population density has been suggested by George, it relates to the “ratio between the requirements of a population and the resources made
available to it by production in the area it occupies. The ratio is ∆ e= NkSk ' where N
is the number of inhabitants, S are in square kilometre and k is the quantity of requirements per caput; k’ the quantity of resources produced per square kilometre.
We have a number of measures for describing the spatial distribution of a population and many graphic devices for presenting population distribution and population density. Duncan gives the following classification, which is not claimed to be exhaustive free of overlapping:
A. Spatial measures1. Number and density of inhabitants by geographic subdivisions2. Measures of concentration3. Measures of spacing4. Centro graphic measures5. Population potentialB. Categorical measures1. Rural –urban and metropolitan – non-metropolitan classification2. Community size distribution3. Concentration by proximity to centres or to designated sites.
The measures for analysis are
DEMOGRAPHY 20
Percentage distribution: Simple way of ordering the statistics that is appropriate any demographic aggregate is to compute the percentage distribution living in the geographic areas of a given class.
Rank: It is a common practice is to include a supplementary table listing the geographic areas of a given class in rank order.
Measures of average location and or concentration: It is average point for the distribution of population within a country or other area. In this, the most popular measures are the median point or location; the mean point often called the “Centre of Population” and the point of minimum aggregate travel. A somewhat different concept is that of the point of maximum “population Potential”. There has been somewhat less scientific interest in measuring the concentration or dispersion of the population. Bachi’s ”Standard distance” is another measure based on dispersion. Average positions and dispersion density surface etc., are treated systematically by Wartntz and Neft.
a. Median lines and median points: the Median lines are two orthogonal lines each of which divides the area into two parts having equal numbers of inhabitants. The median points are the intersection of these two lines. The median lines are conventionally the north-south and east-west lines, but the location of the median point depends slightly upon how these axes are rotated.
b. Centre of population: the centre of population or mean point of the population distributed over an area may be defined as the centre of population gravity for the area. In other words, the point upon which the area would balance, if it were a rigid plane without weight and the population distributed thereon, each individual being assumed to have equal weight and to exert an influence on the central point proportional to his distance from the point.
c. Point of minimum aggregate travel: it is a Centro graphic measure, sometimes called as “Median centre”. It is defined as “That point which can be reached by all items of a distribution with the least total straight line travel for all items or “ the point from which the total radial deviations of an area distribution are at a minimum”.
d. Standard Distance: measures of dispersion of population have been proposed from time to time, but the most recent exposition and the one that
DEMOGRAPHY 21
has been most thoroughly developed is Bachi’s “Standard Distance”. The standard distance bears the same kind of relationship to the centre of population that the standard deviation of any frequency distribution bears to the arithmetic mean. In other words, it is a measure of the dispersion of the distances of all inhabitants from the centre of population.
If x andyare the coordinates of the centre of population say its longitude and latitude then the distance from any item i with coordinates x i∧ y i to
the centre is given by Dic=√¿¿¿ And the standard distance D =√∑i=1
n
D ic2
n
e. Population Potential: this concept is developed by Stewart. It applies to the accessibility to the population or level of influence on the population of a point on a map or of a small unit of area. If the influence of each individual at a point considered being inversely proportional to his distance from it the total potential of population at a point Lois the sum of the reciprocals of the distance of all individuals in the population from the point .
In practice the computation is made by assuming that all the individuals within a suitably small area are equidistant fromLowhere Potential at
Lo=∑i=n
n Pi
Di
where the Pi are the population of the n areas into which a territory is
divided and the Di are the respective distances of these areas from Lo
f. Mapping devices: still another way of summarizing the population distribution of a nation, province etc is to compute the absolute or relative number of people within a specified distance from its borders. Here we are concerned with mapping just the distribution of population and of population density.
Factors affecting population distribution
Much has been described about the factors determining the geographic distribution of population – among international regions. The following list of factors is adapted from “The determinants and consequences of population Trends” with a few additions and other changes:
Climate: Temperature, Precipitation
DEMOGRAPHY 22
Landforms: Topography; Swamps, marshes, deserts
Soils: Energy resources and mineral, raw materials
Accessibility
Cultural factors
Political
Economical activities
Demographic factors
All the above factors are not all of coordinate importance. That is the cultural factors modify the effects of the natural and physical factors and all of them operate through the demographic factors.
Population distribution- Classification of residence
The importance of this distribution is on classes of geographic areas of residence that are formed primarily for statistical purposes rather than on individual areas as entities. The main classification discussed is the urban-rural: the suburban; size of locality, of metropolitan area etc., farm – nonfarm and combinations of these.
Urban-rural classification: it is easy to classify the urban and rural that is there is no problem in classifying extreme cases. It is in the case of intermediate situations that somewhat arbitrary rules have to be set up for making the urban-rural classification. For this purpose each and every country has its own recommendations to declare as Urban-rural classes with their population policies or based on the report of population census.
Because of national differences in the characteristics which distinguish urban from rural areas, the distinction between urban and rural population is not yet amenable to a single definition which would e applicable to all countries. For this reason, each country should decide for itself which areas are urban and which are rural.
To classify Urban-rural areas the underlying concept is that of
1. Administrative areas2. Population size3. Local government area
DEMOGRAPHY 23
4. Urban characteristics or5. Predominant economic activity
Concepts of URBAN-RURAL in Demographic theory
To decide an operational definition of the classification from the theoretical standpoint is necessary. Several demographers, sociologists and others discuss the concepts of urban or of urbanization population.
They suggested some views of their own ideas :
According to Eldridge “ …… a process of population concentration. It proceeds in two ways: the multiplication of points of concentration and increase in size of individual concentrations…..
Dewey takes a very similar position. He shows that there is very little consensus in the literature regarding matters that distinguish urbanism from ruralise.
Charles T. Stewart rejected size of place as the proper criterion of Urban-rural and preferred economic or social concepts.
The present authors find that the urban-rural concept advanced by Eldrige and Dewey is useful in demographic concepts.
In terms of classify urban-rural, several writers have contended that a threefold classification would describe the situation better than a dichotomy and a few countries have actually used such a classification in their official statistics. This use of a third “Semi-urban” category should be distinguished from classifications that subdivide the urban or rural total. If the intermediate category is defined purely in terms of population size, however, the resulting threefold classification may be viewed as a simple case of distribution of localities by size.
Suburbs: the idea of a suburb is a residential area that extends out from the central city following transportation arteries in a satellite shape, is dependent on the central city for many of its services, as an intermediate population density, is growing rapidly by horizontal expansion, and is peopled mainly by upper and middle class families of commuters.
Size of Locality
DEMOGRAPHY 24
If the urban-rural classification is based on size of locality then a classification by multiple size categories can be regarded as an extension of the dichotomous classification that recognizes that fact that there is an urban rural continuum; size differences and their associated demographic characteristics may be just as important within the urban, or within the rural, part of the range as are the differences between the smaller urban and the larger rural localities.
The social contrasts rest mainly on three complexes of factors:
1. Persistent currents of selective migration2. Family organization and functions and3. Economic structure and functions
Measures
Some of the measures described in the previous chapters are also applicable to classification by type of residence.
Percentage Distribution
Extent of urbanization
Lorenz curve and Gini concentration ratio
Rank size rule
2.2. Sex and age composition
Population by age and sex: The building block for virtually all demographic rates is a breakdown of the total population by age and sex. Population distributions may be reported as the total population in each age group or as the percent of total population in the age groups. If you have an age distribution but not by gender, you will have to apply a sex ratio to split the population into the appropriate genders.
The preferred groups for this breakdown are 5 year age groups, if possible, with a subdivision of the first age group into under age 1 and 1 through 4 years of age. Demographers typically describe these age groups as 5-9, 10-14, and so on using the word “through” (e.g. five through nine). Descriptions of survival rates use the alternate terminology “to” to mean “up to, but not including”. Often, however, population will be reported in more aggregate groups: 0-4, 5-14, 15-49, 50-64, 65+, or just 0-4, 5-19, 20-64, 65+. To become familiar with typical age distributions (often summarized in population pyramids) typical population pyramids are shown
DEMOGRAPHY 25
below, for four different demographic regimes: High fertility and high mortality; high fertility and dropping mortality, transitional lower fertility and lower mortality, stable low fertility and low mortality.
The personal characteristic of sex and age holds a position of prime importance in demographic studies.
As in the case of sex, separate data for males and females are important in themselves, for the analysis of other types of data, and for the evaluation of the completeness and accuracy of the census counts of population. As data on age are important in themselves, for the description and analysis of other types of demographic data, and for the evaluation of the quality of the census counts of population.
2.2.1. Data tabulation
Data on sex composition serve another important analytic purpose. Because the expected proportion of the sexes can often be independently determined within a narrow range the tabulations by sex are useful in the evaluation of census and survey data, particularly with respect to the coverage of the population by sex and age.
2.2.2. Numerical presentation
2.2.3. Population pyramidsA very effective and quite widely used method of graphically depicting the age-sex composition of a population is called a “Population Pyramids”. A population pyramid is designed to give a detailed picture of the age-sex structure of a population indicating either single age 5-year groups or other age combinations.The basic pyramid form consists of bars, representing age groups in ascending order from the lowest to the highest pyramided horizontally on one another.The basis of males is given on the left of the central vertical axis and the bars for females on the right of the axis. The number of males or females in particular age group is indicated by the length of the bars from the central axis. Age scale is usually shown straddling the central axis although it may
DEMOGRAPHY 26
be shown at the right or left of the pyramid only or both on the right and left, perhaps in terms of both age and year of birth.In general, the age groups in a given pyramid must have the same class interval and must be represented by bars of equal thickness.Most commonly pyramids show 5-year age groups. Pyramids may be constructed on the basis of either absolute numbers or percents. A special caution to be observed in constructing a “Percent” pyramid is to be sure to calculate the percents on the basis of the grand total for the population including both sexes and all ages.A “Percent” pyramid is similar in the geometric sense of the word to the corresponding “Absolute Pyramid” with an appropriate selection on scales, two pyramids are identical. The choice of one or the other type of pyramid is more important when pyramids for different date’s areas or subpopulation are to be compared. Only absolute pyramids can show the differences or change in the overall size of the total population and in the number at each age. Percent pyramids can show the differences or changes in the proportional size of each age-sex group.In general absolute or percent pyramids to be compared should be drawn with the same horizontal scale and with bars of the same thickness.Comparison between pyramids for the same area at different dates and between pyramids for the same area at different dates and between pyramids for different areas or sub population may be facilitated by superimposing one pyramid on another either entirely or partly. The pyramids may be distinguished by us of different colours or cross-hatching schemes.Any characteristics which vary by age and sex may be added to a general population pyramid, to develop a pyramid which reflects the age-sex distribution of both the general population and the population of the categories of the characteristics.Additional characteristics beyond age and sex are included in the pyramid, the principles of construction are essentially the same. The bar for each age is subdivided into parts representing each category of the characteristic for example single, married, widowed divorce: urban rural. It is important that each category shown separately occupy the same position in every bar relative to the central axis and to the other category or categories shown.
DEMOGRAPHY 27
If percents are used all percents are calculated on a single base the total population. Various cross-hatching schemes or colouring schemes may be used to distinguish the various categories of the characteristic represented in the pyramid. When characteristics are added to a population pyramid, the age-sex distribution is shown most clearly for the inner most categories in the pyramid and for the total population covered; the distribution of the other categories is harder to interpret.Population pyramids may also be employed to depict the age-sex different of demographic events such as deaths marriage divorces and migration during same periods.Pyramids may be analyzed and compared in terms of such characteristics as the relative magnitude of the area on each side of the central axis of the pyramid or a part of it, the length of a bar or group of bars in relation to adjacent bars and the steepness and regularity of the slop. These characteristics of pyramids reflect, respectively the proportion of the sexes, the proportion of the population in any particular age class or classes and the general age structure of the population.
2.3. Classification and quality of data
2.4. Measures of sex composition2.4.1. Numerical measure
The numerical measures of sex composition are few and simple to compute. They are
1. The percentage of males in the given population or the Masculinity proportion
DEMOGRAPHY 28
2. Sex ratio or the masculinity ratio3. The ratio of excess or deficit of males to the total population\
These three measures mentioned here are all useful for inter-area or intergroup comparisons, comparisons over time, since in one way or another they move the effect of variations in population size.
1. The masculinity proportion
It is the measure of sex composition most commonly used in non-technical measures. The formula to find the masculinity proportion is
Masculinity proportion =Pm
P t
X 100 where Pm=¿ Male population; Pt= total
population
For instance, in Morocco as the census shows 5809172 males and 11626232 as total population in 1960/ then the Masculinity proportion is 50% (By substituting the values )
It is important as, the value fifty is the point of balance of the sexes or the standard according to this measures.
A higher figure denotes an excess of males and lower figure denotes an excess of females. The masculinity proportion of national population varies over a rather narrow range. Usually falling just below 50 unless exceptional historical circumstances have prevailed ( such as war, flood etc).
2. The sex ratio
It is the principle measure of sex composition used in technical studies. The sex ratio is usually defined as the number of males per 100 females.
Sex ratio =Pm
Pf
X 100 where Pm=¿ male population∧Pf =female populaiton¿
A sex ratio above 100 denotes an excess of males ; a sex ratio below 100 denotes an excess of females.
The greater the excess of males the higher the sex ratio the greater the excess of female the lower the sex ratio. This form of the sex ratio is sometimes called the
DEMOGRAPHY 29
masculinity ratio. The sex ratio is also sometimes defined as the number of females per 100 males . this has been the official practices in many countries like Poland, Hungary, India, Pakistan , Iran ; but the UN and others follows the former definition.
If the sex ratio is around or nearly 100 then it might be described as “Typical” or a little above the typical level.
In general, national sex ratios tend to fall in the narrow range from about 95 to 102 baring special circumstances such as war or migration. National sex ratios outside the range of 90to 105 are to be viewed as extreme.
3. Excess or deficit of males as percentage of the total population.
The formula is Pm−P f
Pt X 100. If the figure be in negative indicated that the deficit
of males.
The point of balance of the sexes according to this measure is zero. A positive value denotes an excess of males and a negative values denotes an excess of females. It may be evident that the various measures of sex composition convey essentially the same information. Sometimes it is desired to convent the masculinity proportion into the sex ratio or the percent of excess or deficit of males or the revise in absence of the basic data on the number of males and females. These conversions may be effected by use of the following formulas
Masculinity proportion = Sexratio
1+sex ratioX 100
Sex ratio = Masculinity proportion
1−masculinity proprotionX 100
Percent of excess or deficit of males = Masculinity proportion – (1-Masculinity proportion) X 100
These are few measures which are designed specifically for description and analysis of sex composition.
The standard graphic devices including bar charts line graphs pie charts etc are available , however for depicting differences in sex composition from group to
DEMOGRAPHY 30
group or over time for a particular group Principle among these is so called population pyramid.
2.4.2. Sex ratios in terms of population subgroups
The sex ratio may vary widely from one population subgroup to another. It is necessary to present the facts separately the sex ratio of the important component subgroups in any detailed analysis of the sex composition of a population group.
The various subgroups are notably colour, race, nativity, residence, regional, age and marital status groups in the population. Account might be taken of these variations in the analysis of the overall level of the sex ratio at any date and of the differences in the sex ratio from area to area or from one population to another.
Usually , the urban population has lower sex ratio principally because to the greater migration of females to cities . The sex ratio also varies widely among regions.
Sex ratio for age groups varies widely around the sex ratio for the total population. The sex ratio for the total population, the sex ratio tends to be high at the very young ages and they tend to increase in age.
Changes in Sex ratio
It is interest to analyze the difference, in terms of components between the current sex ratio and a sex ratio of 100 representing a balance of the sexes.
Sex ratio of births
The sex ratios may be obtained from an examination of registered births for a wide array of countries, it is apparent that the component of births tends to bring about or to maintain an excess of males in the general population. The sex ratio of births is above 100 for nearly all countries for which relatively complete data are available and between 104 and 107 in most of other countries.
Careful analysis relating to the sex ratio of birth should take into account significant variations in the sex ratios of births according to demographic characteristics of the child and parents. Among the important demographic characteristics which appear to distinguish births with respect to their sex ratio are age of mother, order of birth of child and race.
DEMOGRAPHY 31
Socio-economic states of parents may also affect by the sex ratio of births. A predominance of male births has been observed among higher socio economic groups in western countries. It may also be explained by the predominance of lower order births, when fertility is low and the lower rage of prenatal deaths.
Similar information on the relationship between socioeconomic and the sex ratio of births are not available for less developed countries.
For areas with incomplete reporting of births, the observed sex ratio of births may be suspect direct or estimates from vital statistics, censuses and surveys.
Sex ratio of deaths
The sex ratio of deaths is much more variables from country to country than the sex ratio of births.
Data for a wide range of countries indicate sex ratios well above 100 in most cases. Since this factor operates in a negative fashion, the component of deaths has tended to depress the sex ratio of most population.
National differences in the sex ratio of deaths may be accounted for partly by differences from county to country in the age-sex structure of the population and partly be different in death rates for each age-sex group demographic characteristics important in the further analysis of the sex ratio of deaths include age, race or other ethnic grouping, residence status and marital status
Sex ratio of migrants
The sex ratio of migrants has been less uniform from area to area and has often shown more extreme values (above or below 100) than the sex ratio of either births or deaths.
One or the other sex may attract in greater numbers to certain areas within countries depending largely on the types of occupational opportunities and on various cultural factors, particularly customs regarding the separation of family members.
Patterns of sex-selectivity of migrants to cities appear to differ in the countries of the west and the less industrialized countries of the east. Men predominate in the migration streams to large cities in Southeast Asia
Changes in Excess or deficit of males
DEMOGRAPHY 32
The formula for analyzing the changes between two census in the excess or deficit of males in terms of components may be developed form the separate equations.
Pm1 =Pm
0 +Bm0 −Dm
0 + I m0 −Em
0
Pf1=P f
0+B f0−Df
0+ I f0−Ef
0
These are merely the usual inter-censual or component equation expressed separately for males and females. Solving these equation and taking the difference between them we have for the inter-censual change in the difference between the number of males and females.
2.4.3. Uses of sex ratio in data evaluation
Because of relativity limited variability of the national sex ratio and it independence of the absolutes number of males and females, it is employed in various ways in measuring the quality of census data on sex particularly on cross-classification with age.
2.5. Evaluation of age data2.5.1. Sources of errors in age data2.5.2. Measures of age reporting errors
2.6. Analysis of age composition2.6.1. Age dependency ratios
Dependency ratios- This ratio quantifies the number of persons in a population who are not economically active for every 100 economically active persons in that population. It can be calculated by dividing the population 0-14 years and 65 years and older by the population that is in the 15-64 year age group.
In other words, the variations in the proportions of children, aged person and persons of “working age “are taken account of jointly is the so-called age dependency ratio.
The age dependency ratio of the combined child population and age population to the population of intermediate age. The formula to find age dependency ratio is
P0−14+P65+¿
P15−64
X 100¿
DEMOGRAPHY 33
This measure is useful for international comparison relates the different age groups.
Separate calculation of the child dependency ratio and old-age dependency ratio are available. Variations in the age dependency ratio reflect in a general way the contribution of variations in age composition to variations in economic dependency. The age dependency ratio is a measure of age composition, not of economic dependency however the economic dependency ratio may be defined as the ratio of economically inactive population to the active population over all ages or of non-workers to workers.
Example: A community has 41,650 children under age 14 and 6,800 persons age 65 and over. The total population is 85,000.
The dependency ratio is: (48450/ (85000- 48450)) * 100 = 133.
You can also use the percentages from age distributions.
Example: (57%/43%) * 100 = 133.
You can calculate separate dependency ratios: child dependency ratio (Pop 0-14 / Pop 15-64) and old age dependency ratio (Pop 65+/Pop 15-64).
Ranges for child dependency ratios:
Least Developed: 80.8 Developing: 53.1 More Developed: 29.4
Child-woman ratio- This ratio, the CWR, the ratio of children under 5 per 1000 women of reproductive age. It is usually calculated by dividing the number of children in the age group 0-4 (of both sexes) by the number of women of reproductive age (15-49 years), and then multiplying by 1000.
Example: A district in Viet Nam has the 4896 children under age 5 and 10,200 women aged 15-49. The CWR is:
(4896/10200) * 1000 = 480.
In the absence of a direct measure of births, this ratio can be used as a rough indicator of fertility levels. In countries with high levels of infant and child
DEMOGRAPHY 34
mortality, this ratio can be quite biased- as it only accounts for children who survive to 4 years of age.
Ranges for the CWR:
Least Developed: 710 Developing: 400 More Developed: 255
2.6.2. Aging of population
The median age is often used as a basis for describing of population as “Young” or old or a ”Aging” or “Younging”
Population with medians under 20 may be described as “Young” those with medians 30 and over as old and those with medians 20 to 29 as intermediate age when the median age raises the population may be said to be “Aging” and when it falls the population may be said to be “Younging”
The proportion of aged persons has also been regarded as an indicator of a young or old population of a population that is ageing or younging. Proportion of children under 15 is an indication of the degree to which a population is old or young and is aging or younging.
The aged-child ratio is also known to be the ratio of the number of elderly persons to the number of children. This measure takes into account the number and changes at both ends of the age distribution simultaneously. The formula to calculate this
ratio is P65+¿
P0−14
X 100¿
Many less developed countries have so small a proportion of persons 65 and over and so large a proportion of children under 1 that it seems desirable to broaden the range of the numerator and narrow that of the denominator. When the aging of a population has progressed rather far as in the more developed countries.
The indicators of aging we have mentioned are most useful measures in the “Aging” tasks. From all the measures-increase in median age, increase in proportion of aged persons, decrease in proportion of children and increase in ratio of aged persons to children- the last measure is one or another variant, is most sensitive to
DEMOGRAPHY 35
differences or changes in age composition affecting the number or proportion of children and aged persons and it may be considered the best index of “aging”.
The four criteria of ageing described may not give a consistent indication as to whether the population is ageing or not.
Since changes in the median age over some period depend merely on the relative magnitude of the growth rates of the total age segments above and below the initial median age during the period, the median age may hardly change while the proportions of aged persons and of children may both increase or both decrease.
Accordingly, a population may in some cases appear to be aging and younging at the same time a combination of a rise in the proportion 65 and over and a rise in the proportion under 15 would be accompanied by a decline in the proportion in the intermediate age.
Aging of a population should be distinguished from the aging of individuals, an increase in the longevity of individuals, or an increase in the average length of life pertaining to a population. The latter two types of changes result from important in the quality of the environment and from medical advances among other factors. The aging of a population is a characteristic of an age distribution importantly affected by the trend of the birth rate.
CHAPTER III MORTALITY
DEMOGRAPHY 36
3. Mortality3.1. Concepts and data requirements of death statistics3.2. Percentage distribution of death3.3. Basic Mortality measures
3.3.1. Crude death rate3.3.2. Specific death rates3.3.3. Age specific death rates (ASDR)3.3.4. Graphical presentation of ASDR
3.4. Standardization methods3.5. Conventional infant mortality rates3.6. Maternal death rate3.7. Life tables
3.7.1. Types of life tables3.7.2. Life tables functions3.7.3. Construction of a simple life table3.7.4. Interpretation of a simple life table
3.0. Mortality
In demography, mortality is related to Death. It is a principal “Vital event” for which vital statistics are collected and complied by the vital statistics registration system (VRS). The purposes of death statistics in demography are
1. Analysis of the present demographic status of the population as well as its potential growth2. Filling the administrative and research needs of public health agencies in connection with the
development, operation and evaluation of public health programs3. Determination of administrative policy and action in connection with the programs of
government agencies other than those concerned with public health4. Filling the need for information on population changes in relation to numerous professional and
commercial activities;
Death analysis are very much important in making analysis of past population changes which are required for making projections of population and other demographic characteristics
3.1.Concepts and data requirements of death statistics
Concepts:
It is necessary to gain knowledge about mortality. Mortality is one of the vital events.
The UN and WHO have proposed the following definition of “”Death”
“Death is the permanent disappearance of all evidence of life at any time after birth has taken place”.
A death can occur only after a live birth has occurred. This definition of death can be easily understandable. The definition of a “death” excludes deaths prior to birth that is so-called fetal death. A
DEMOGRAPHY 37
fetal death is formally defined as ”Death” prior to the complete expulsion or extraction from its mother of a product of conception irrespective of duration of pregnancy. The death is indicated by the fact that after such separation the fetus does not breathe or show any other evidence of life such as beating of the heart, pulsation of the umbilical cord or definite movement of voluntary muscles. The term fetal dath is employed in present demographic practice to difference the other deaths such as stillbirth, miscarriages, and abortions in popular, medical and legal usages.
The term stillbirth is defined as a death that occurs in the duration of 20 or 28 weeks of gestation or more. This term is employed in the place of late fetal deaths.
The term Miscarriage is defined as spontaneous or accidental terminations of fetal life occurring early in pregnancy.
The term abortion is popularly used to refer to induced early fetal deaths, including both those which are legal or illegal. In medical usage, an abortion is the expulsion of the fetus prematurely, particularly at any time be for it is visible or capable of sustaining life. From a technical point of view the terms abortion and miscarriage can be hard to distinguish.
The recommendation of UN and WHO is to group all of these events : miscarriage and abortion as well as still births under the heading of “Fetal Death” and to classify them as early, intermediate and late according to the months of gestation.
Data requirements of death statistics
The basic data on deaths for mortality studies, for the statistically developed areas , come from vital statistics registration systems and less commonly, from national population register systems. The analysis of death statistics from the vital statistics registration depends on the availability of appropriate population data from a census or survey or population estimates to be used as bases for computing rages of various kinds. This dependence on a second data collection is avoided where an adequate national population register system is in effect.
The VRS is likely to be inadequate in the underdeveloped countries: for these areas, other sources of data for measuring morality have to be considered. The principle alternative sources are
1. National census and 2. National sample surveys.
Census data and sample surveys may provide
a. Data on age composition on recent mortality and b. Direct data on mortality3.2.Percentage distribution of death
A distribution of deaths by age is percentage distribution of death. It has a pattern based on the death data. It is described as in x-axis with age and in y- axis percentage of deaths in the given region or area or country.
DEMOGRAPHY 38
A combination of high rates and large proportion of children in the population as occurs in many under developed countries, results in a tremendous proportion of deaths among children under age 5. On the other hand, in certain developed countries the proportion of deaths of young children is very small.
3.3.Basic Mortality measures3.3.1. Crude death rate (C.D.R)
It is the simplest of all the indices of mortality. It is defined as “the number of deaths per K persons in the population of any given region or community during a given period”. Thus in particular the annual Crude death rate denoted by m for any given region or community is given by
m= AnnualdeathsAnnualmean population
X k where k = 1000 usually
The CRD for any period gives the rate at which the population is depleted through deaths over the course of the period.
The midyear population is employed as an approximation to the average population “exposed to risk” of death during the year. The midyear population may approximated by combining data on births, deaths and immigration for the period between the census date and the estimated date with the count from the last census, as an arithmetic or geometric mean of the population estimated directly on the basis of these components for two successive dates usually it will be January 1 and in other ways.
Crude death rates may be computed for any period, but typically they are computed for the calendar year or the “Fiscal year”. That is the 12 month period from July1 to June 30.
In the latter case, the population figure should relate to January 1 of the fiscal year. Crude death rates are calculated for 12 month periods such as calendar years or fiscal years so as to eliminate the effect of seasonal or monthly variations on the comparability of the rates.
Merits and demerits
Merits
1. It is simple and easy to calculate2. CRD is perhaps the most widely used of any vital statistics rates3. By CDR is a probability that a person belonging to the given population will die in the given period
Demerits
1. It ignores the age and sex distribution of the population2. CDR is not suitable for comparing the mortality in two places.
Remark
DEMOGRAPHY 39
We can compute the CDR for males and females separately.
For male the formula: mD
mP
X 1000 where mD is number of male deaths and mP is male population in the
given region during the given period. Similarly for female the formula is f D
f P
X 1000
CDR usually lies between 8 and 30 per thousand and female CDR is generally less than male CDR.
3.3.2. Specific death rates
The CDR gives only a very general indication of the level of mortality and its changes In other words while computing CDR, there was a drawback that it ignores the age and sex of the population. There is also need for measures that describe the specific components of the overall number of deaths and the crude rate. Various types of specific death rates are interest in the analysis. To overcome this drawback we must need a more useful figure than CDR, we must take into the fact that the mortality pattern is different in different segments of the population. Various segments may be age, sex, occupation, etc.,
Death rate computed for a particular specified section of the population is termed as specific death rate (SDR). SDR for given geographical region during a given period is
SDR = [Total number of deaths∈the specified section of the population∈the given periodTotal populationof thespecifiedsection∈the same period ]X k
Usually SDR is computed specific to age and sex.
3.3.3. Age specific death rates (ASDR)
As we know age is the most important variable in the analysis of mortality. Most tabulation of deaths requires cross- classification with age if they are to be useful. The tabulations of deaths by age are subject to a number of deficiencies. The principal ones are substantial and variable under-registration of deaths by age, extensive misreporting of the age of the decedent, and an excessive proportion of “age not stated”. Reporting of age decedents among the extreme aged is believed to be quite inaccurate.
The principle way of measuring the variation in mortality by age is in terms of age-specific death rates.
An ASDR is defined conventionally as the number of deaths of persons of a given age during a year per1000 of the midyear population at the age.
ASDR = Da
Pa
X 1000
To formulate the ideas mathematically,
Let
Dxn =¿ Number of deaths in the age group (x, x+n)
DEMOGRAPHY 40
Pxn =¿total opulation of the age group (x, x+n)
The age-specific death rate for theage group(x,x+n) denoted by mxn
Then mxn =
Dxn
Pxn X 1000
Merits and Demerits
Merits
1. SDR provide more appropriate measures of the relative mortality situation in the regions2. It is the one of the most important and widely applicable types of death rates3. It useful in construction of life table4. It supplies one of the essential component required for the computation of Net reproduction rate
Demerits
1. It is not much useful for overall comparison of mortality conditions2. SDR completely ignore differential mortality 3.3.4. Graphical presentation of ASDR
3.4.Standardization methods
3.5.Conventional infant mortality rates
Analysis of infant mortality has commonly been carried out in terms of the “Infant mortality rate” rather than the infant death rate, in order to approximate the probability of death among infants in a given year. The accuracy of the approximation varies from one situation to another but depends in general on the annual fluctuations in the number of births. This is termed to be “Conventional Infant Mortality Rates” (CIMR).
The term CIMR is defined as “ the number of infant deaths per year per 1000 live birth during the year.
CIMR = D0
BX 1000 D0−¿deaths of infants during a year and B-live birth during the same year.
DEMOGRAPHY 41
The CIMR gives a sufficiently close approximation to the chance of dying between birth and attainment of the first birthday for the year to which the basic data on deaths relate. It has been widely used as an indicator of the health conditions of a community and hence of its level of living although it may not be particularly appropriate for this purpose in “developed” areas.
3.6.Maternal death rate
3.7.Life tables3.7.1. Types of life tables3.7.2. Life tables functions3.7.3. Construction of a simple life table3.7.4. Interpretation of a simple life table
CHAPTER IV FERTILITY
DEMOGRAPHY 42
4.1. Concepts of fertility and fecundity 4.2. Sources of data for fertility studies4.3. Basic Mortality measures4.3.1. Crude birth rate4.3.2. Child women ratio4.3.3. General fertility rate4.3.4. Age specific death rates (ASDR)4.3.5. Total fertility rate4.4. Reproduction rates4.4.1. Gross reproduction rate4.4.2. Net reproduction rate4.0.Introduction to Fertility
We employ the term “Fertility” as a term to represents the role of births in population change and human reproduction. The other terms for representing birth are Natality. The three terms “ Birth”, “Fertility” and “Natality” have alternative and overlapping meanings and convention has often established a particular choice of term to be used in particular context.
The term fertility in one sense is synonymous with natality in referring to the birth factor in population change in the broadest sense.
4.1. Concepts of fertility and fecundity
Fertility refers to actual birth performance and fecundity refers to the physiological capacity to reproduce. one’s fertility is limited by one’s fecundity and is far below it. Infecund persons are also described as sterile. The term fecundibility refers to a special aspect of fecundity namely the probability of conceiving measured on a monthly basis.
4.2.Sources of data for fertility studies
The basic data for fertility studies come from
1. The vital registration system2. National census3. National sample surveys
In several countries in which the vital registration system has been incorporated into a national population register system, the source of fertility data.
The first source, the registration system, provides birth statistics principally. The second source, national censuses provides
a. Data on the age composition of the population from which the level of recent fertility can be inferredb. Direct data on births and fertilityc. Statistics on children by family status of their parentsd. Population data on fertility related variables
DEMOGRAPHY 43
e. Population bases for calculation various types of fertility rates.
The national sample survey may provide
a. The same types of data as a census b. Additional detailed data permitting a more complete analysis of fertility.
4.3.Basic Mortality measures
There are a great number of measures based on birth statistics. These vary with the aspect of fertility that they are describing their degree of refinement or elaboration, whether they are summary measures or specific measures and whether they are measures of fertility.
As in the case of measures of mortality, our outline of measures of fertility distinguishes, first, observed rates from adjusted rates. The distinction is only approximate. The observed rates are the simpler rates, and are computed directly from actual data in a single brief calculation, whereas the adjusted rates are more complex both with respect to method of calculation and to interpretation.
4.3.1. Crude birth rate
The simplest and commonly used measure of birth rate is crude birth rate (CBR). The CBR is defined as “ the number of births in a year per 1000 midyear population”.
CBR = BP
X 1000
The midyear population is employed as an approximation to the average population “exposed to risk” of birth during the year. The midyear population may approximated by combining data on births, deaths and immigration for the period between the census date and the estimated date with the count from the last census, as an arithmetic or geometric mean of the population estimated directly on the basis of these components for two successive dates usually it will be January 1 and in other ways.
4.3.2. Child women ratio
The measure commonly used is the ratio of children under 5 years old to women of child bearing age, referred .to as the “General fertility ratio” or “ratio of children to women “ or “child-women ratio”. This measure is computed by dividing the number of children under 5 years old in the population by number of women 15 to 49 years old. The childbearing ages in the denominator are sometimes approximated by the ages 20 to 49 or 15 to 44. It must e noted that the children under 5 may have been borne up to 5 years prior to the census date when the women were up to 5 years younger. Although some mother are left out, they have contributed so few of the children under 5 that the inclusion of younger or older ages would include mostly women who are not “exposed to risk”. The computation formula is
CW Ratio=p0−4
p f 15−49
X 1000
Where p0−4 is the number of children under 5 years old∧¿ p f 15−49 is the number ofwomen between exact ages 15∧50
DEMOGRAPHY 44
The numerator and denominator for the fertility ratio are drawn from the same universe, the population by age and sex as given by the census.
The general fertility ratio may be viewed as either a substitute for the general fertility rate or as a measure of effective fertility, which takes into account child mortality. Although the ratio of children 1 year old to the total population in the census could be used as an approximation to the CBR, the measure is seldom used.
Children under 5 years old have been traditionally used instead of children under 1 year of age, because:
a. Age distributions are frequently limited to 5-years groupb. There is proportionately less under numeration of children under 5 years old than of children
under 1 year old.c. The ratio is more stable when a larger numerator is used.4.3.3. General fertility rate
Although the CBR is a valuable measure of natality, particularly in indicating directly the contribution of natality to the growth rate, its analytic utility is extremely limited. This is because it is affected by many factors, particularly the specific composition of a population with respect to age, sex and other characteristics. Since the age and sex composition of a population has such a strong influence on the level of its CBR, measures of fertility that are less affected by differences in age-sex composition from one population group to another are more useful analytically for inter-area and intergroup comparisons .
A number of such measures have been developed and are variously referred to as specific, general, adjusted or standardized and as birth rates, fertility rates or reproduction rates depending generally on their degree of complexity or on their particular significance.
The simplest overall age-limited measure is the general fertility rate, defined as the number of births per 1000 women of childbearing age. The formula is
GFR= B
p15−44f
X 100
The total number of births, regardless of age of mother is employed in the numerator and the female population 15-44 years of age is employed in denominator.
The GFR sometimes defined in relation to the number of women 15-49 years of age but as note a below women aged 45-49 contribute relatively few birth to the total number. It is preferable to avoid dilution of the denominator of the rate with this group when the risk is so low by excluding if from the population of childbearing age used in the rate.
4.3.4. Age specific Birth rates (ASBR)
A set or “schedule” of age-specific birth rates for a given date and population group seves as a basis for a detailed comparison, with corresponding rates for other population groups, that is unaffected by differences between the groups in age-sex composition. A set of rates may consists of the rates for 5-
DEMOGRAPHY 45
years age group from 10-14 to 45-49,15-19 to 45-49, or 15-19 to 40-44. The age classification recommended by UN has 10 categories, less than 15 years, quinquennial groups 15-19 to 45-49, a terminal group 50 and over and a group of unknown ages
An age-specific birth rate is defined as the number of births to women of a given age group per 1000 women in the age group;
f a=Ba
Paf X 1000
The formula for the birth rate at ages 20-24 is
f 20−24=B20−24
P20−24f X 1000
Age specific birth rates as here defined are a type of “central” rate, in somewhat the same sense that age-specific death rates are central rates.
4.3.5. Total fertility rate
The total fertility rate is the sum of the age-specific birth rates of women over their reproductive span, as observed in a given year. It is expressed as
TFR=∑w 1
w 2 Bx
px
X 1000
Where Bx isthe number of liveberths registered during the year ¿mothers of age x
where xrepresents an interval of one year of age∧¿ px is themidyear population of womenof the same age
The age-specific fertility rates are cumulated from x=w1 to x=w2 may me 10-54, 15-44 or whatever range is available and appropriate.
In usual practice, the TFR is calculated by a shorter method. The specific births rate are calculated for 5 year age groups and thus the subscript i represents 5 year intervals suchas 15-19,20-24 upto 45-49 years. The expression for TFR, using seven five years age groups then the formula is
TFR=5∑i=1
7 B i
pi
X 1000
Where Bi is the number of live berths registered during the year ¿mothersof agegroup i
where i representsan interval of five years of age∧¿ pi isthe midyear populationof women of the same age
DEMOGRAPHY 46
For convenience we use seven 5 year age groups in our calculations, the age limits will not encompass the full childbearing range. Births to younger, women should then be allocated to the youngest age group shown and those to older women to the oldest age group shown. The TFR states the number of births 1000 women would have if they experienced a given set of age-specific bieth rates throughout their reproductive span.
4.4.Reproduction rates
The conventional reproduction rate measure the replacement of the female population only, where as the TFR involves births of both sexes. The Net reproduction rate (NRR) was devised by the German statistician, Richard Bockh in 1884.
The another person put his effort on these rates was Lotka, he implemented a mathematical analysis of these rates as measure of reproductivity and their place in a wholes of measures relating intrinsic population change and the stable population.
4.4.1. Gross reproduction rate (GRR)
The GRR is a special case of the TFR whereas the TFR measures the total number of children a cohort of women will have, the GRR measures the number of daughters it will have. Thus a TFR can be converted to a GRR simply by multiplying it by the proportion of the total births that were female births in the calendar year of years for which it is computed. This conversion is not mathematically exact, but it is a close approximation to the GRR we should obtain if births at each age of woman were tabulated by the sex of the child. There is a slight variation of the sex ratio at beith with the age of the mother. The GRR also assumes that all females survive to the end of the childbearing period. The formula for the GRR is
GRR=B f
Bt ∑w 1
w 2 Bx
Px
X 1000 where Bx is the number of infants born to mothers of age x, P x is the
number of womenof age x∈the midyear popuation B f
Bt is the proportion of total birth that are female.
If data are available on the number of female births by age of mother, the GRR can be calucalted directly
without the B f
Bt and the adjustment as follows:
GRR=∑w 1
w 2 Bx 1
Px
X 1000 where Bx 1 is the number of female infant born to mothers of age x.
If the computation uses 5-year age groups then the formula for GRR will be
GRR=5B f
Bt ∑i=1
7 Bi
Pi
X 1000
The GRR is such an important demographic measure that we should realize that it may be viewed and defined several ways.
DEMOGRAPHY 47
1. An age standardized fertility rate with each age given a weight of one2. The average number of daughters that a group of females starting life together would bear if all
the initial group of females survived the childbearing period3. The ratio between the number of females in one generation at age 15 and the number of their
daughters at the same age if there were no mortality during the child bearing period or4. The ratio between female births in two successive generations assuming no deaths before the
end of the childbearing period.
The last three definitions are phrased as if the measure applied to a real cohort, or pair of cohorts; but any of these interpretations can be used regardless of whether the GRR was computed from synthetic cohort data or data complied over the lifetime of a real cohort.
Out initial definition of reproductivity stated that it is the natural increase of a population over a generation and hence implied that it was the resultant of mortality and fertility over this period. The gross reproduction rate thus represents a limiting case of these concepts where mortality through the end of child bearing period is zero.
4.4.2. Net reproduction rate (NRR)
The NRR is a measure of the number of daughters that a cohort of new born girl babies will bear during their lifetime assuming a fixed schedule of age-specific fertility rates and a fixed set of mortality rates.
Thus the NRR is a measure of the extent to which a cohort of newly born girls will replace themselves under given schedules of age-specific fertility and mortality. Some girls will die before attaining the age of reproduction, others will die during the reproductive span and other will live to complete their reproductive life.
Express in symbols we have
NRR=B f
Bt ∑w 1
w 2 Bx
Px
Lx
l0
WhereBx
Px
=tx the age specific fertility rate age age x andLx
l0
is a life- table survival rate, with l0 being
radix of the life table or 100000. Again when 5year age groups are used, we have
NRR=5B f
Bt∑i=1
7 Bi
Pi
5 Lx
l0
= Bf
B t∑i=1
7 Bi
Pi
5 Lx
100000
If the survivors in each age interval are assumed to bear daughters as specified by a current schedule of age-specific birth rates, then to obtain the NRR one multiplies each value nLx by the corresponding age-specific birth rate for baby girls, sums the cross-products, and divides by 100000.
A rate of1.00 means exact replacement, a rate above unity indicates that the population is more than replacing itself, and a rate below unity means that the population is not replacing itself. The parallel interpretations to those gie for the gross rate are:
DEMOGRAPHY 48
1. The average number of daughters borne by a group of females starting life together2. The ratio between the number of females in one generation age 15 and the nmber of their
daughters at the same age and3. The ratio between female births in two successive generations.
The steps to calculate NRR is :
1. Compute the ASBR per female and enter it in column (1).2. From an appropriate life table, find the number of years lived by females in the stationary
population for each interval of age.3. Divide 5 Lx by 100000 and enter the result in column (2).4. Multiply each entry of column (2) by corresponding entry in column (1) and enter the result in
column (3) 5. To obtain the GRR, multiply the sum of the entries in column (1) by the proportion of births that
are female and then by the factor 5.6. To obtain NRR, apply the factor to the sum of column (3). These rates are expressed per woman,
but they could also have been per 100 women or per 1000 women.
It is important to keep in mind that, in the Conventional reproduction rates, age-specific fertility and mortality rates all refer to the same fixed period of time, say given calendar year or the average of several years. Moreover, if a life table is not available for exactly the same year as that of the fertility schedule; approximate reproduction rates for that year may be obtained by using life table for an adjacent year or years. There is certainly no need to insist on identity of the two time references if the basic population, fertility and mortality statistics are not very accurate.
These reproduction rates are defined in terms of the female population, but analogous rates can also be computed for both sexes combined or for the male population only. Reproductively are usually studies in terms of mothers and daughters because the fecund period for females is shorter than it is for males and because characteristics are much more likely to be known for the mothers of illegitimate babies than for their fathers.
The ratio of the NRR to the GRR is called the Reproduction- survival rate. It is the proportion of potential reproductively that survives the effects of mortality.
DEMOGRAPHY 49
DEMOGRAPHY 50
