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Demography is the systematic and scientific study of human populations. The word Demography comes from the greek words “demos” (population), and “graphia” (description or writing), thus the phrase, “writing about populations.” The term demography is believed to have been first used in 1855 by Belgian statistician Achille Guillard in his book Elements of Human Statistics or Comparative Demography.
Demography is the social science that studies 1) the size, composition, and distribution of the human population of a given area at a specific point in time; 2) changes in population size and composition; 3) the components of these changes (fertility, mortality, and migration); 4) the factors that affect these components; and 5) the consequences of changes in population size, composition, and distribution, or in the components themselves. Demography may be defined as the scientific study of the size, composition, and distribution of human populations and their
Demography as defined by David and Julia Gary in their book, Collins Dictionary of Sociology, is the statistical study of human populations with regard to their size and structure, their compositions by sex, age, marital status and ethnic origin, and the changes to these populations like changes in their birth rates, death rates and migration. Demography is the statistical analysis and description of population aggregates with reference to the distribution, vital statistics, age, sex and related factors.
In the beginning, demography was concerned only with the enumeration of population. Gradually, it began to study population from empirical, statistical and mathematical viewpoints. Today it studies the size, the composition and distribution of population. The size includes the population at a place in different periods. The composition of population includes measurable characteristics of population such as age, sex, marital status, education, religion, caste, health, etc. These characteristics of population organization are always changing. Distribution of population may be studied according to communities and religious groups or according to fields of population. Demography studies the patterns and causes of the changes in size, composition and distribution of population. It studies the influence of these changes upon different aspects of society. It studies the birth, mortality, marriage, migration and social mobility, quantitatively.
Demographers gather, collate, and analyze population data and make a technical presentation of theory. Peterson defines demographers as people who gather data about size, distribution, composition, and change in population in order to describe them.
Ibn Khaldun (1332 - 1406) is regarded as the “father of demography” for his economic analysis of social organization which produced the first scientific and theoretical work on population.
The Natural and Political Observations ... upon the Bills of Mortality (1662) of John Graunt contains the first life table, giving probabilities of survival to each age. John Graunt defined techniques of demographic analysis. He presented what is known as analysis-approach.
Thomas Robert Malthus’ (1766 - 1834) An Essay on the Principle of Population observed that sooner or later population will be checked by famine and disease. He wrote in opposition to the popular view in 18th-century Europe that saw society as improving and in principle as perfectible. He thought that the dangers of population growth precluded progress towards a utopian society: "The power of population is indefinitely greater than the power in the earth to produce subsistence for man". As a cleric, Malthus saw this situation as divinely imposed to teach virtuous behavior.
Objectives of Demography:
1. To ascertain the number of people in a given area.
2. To know the resources available for their support.
3. To determine what changes, growth or decline this number represents and explain the clause(s) of changes.
4. To estimate on this basis the future trends.
5. To know the different kinds of people who may make up any given population with regard to their physical, mental and cultural characteristics.
6. To categorize people on the basis of characteristics like age, sex, marital status, occupation, income, nationality, race, ethnic group, religion and other characteristics.
7. To ascertain the distribution of people among the different countries and regions, both rural and urban.
8. To achieve knowledge of the size, organization and distribution of the population in the field of study.
9. To describe the past evolution of population in an area and its distribution in different fields.
10. To enquire into trends of population and its relationships with the different aspects of social organization in an area.
11. To predict the future demographic evolution and its probable consequences.
Thus, it is clear that demography performs all the functions characteristic of a science such as enquiry into cause-effect relationships, prediction about the future etc. It uses the scientific methods of observation and analysis. It is factual. It is universal. It is veridical. It finds out what will be on the basis of what is. Its laws are verifiable generalizations. As distinguish from normative science, it is a positive science, which studies facts both qualitative as well as quantitatively.
Aspects of Social Demography
1. Size of population
2. Organization of population
3. Population Distribution
4. Fertility
5. Mortality
6. Migration
7. Labor force
8. Institutional demography
9. Population policy
Importance of Demography
The importance of the study of demography is clear from the increasing scope of thise important field of study. Since the scope is constantly increasing, therefore, there is growing recognition of its importance. Demography helps in the understanding of population problems particularly of the less developed regions of the world. It also helps in planning the population of developed and undeveloped countries. International agencies are publishing data in this connection form time to time. The importance of demographical studies is clarified by the seriousness of the implications of rapid population growth. The chief problem concerning population in a country is to control population growth in relation with the growth of health amenities, food supplies, employment, education and housing. Demographical studies point out the conditions and requirements in these areas so that future development and growth may be planned accordingly. In brief, the following points many be noted about the importance of Demography:
1. Health planning
2. Planning of food supply
3. Employment planning
4. Educational planning
5. Housing planning
6. Planning concerning migration
The Demographic Equation
It should be clear that the size of a population can change only through the process of fertility, mortality, and migration. There are only two ways of entering a population – being born or moving to. There are only also two, and only two, ways of leaving a population – dying or moving out of it. One of the fundamental facts about population change, thus, is that populations only change because of a limited, countable number of events. For example, consider the population size of the country. Suppose that this country at time t contains persons, and that one year later it contains persons. We may write this as the following equation: (1.1) where and are, respectively, the number of births and deaths occurring in the population between times t and t+1; and and are respectively, the number of immigrants (or in-migrants) to and emigrants (or out-migrants) from the population between time t and t+1.
Equation (1.1) is known as the basic demographic equation, or sometimes as the demographic balancing or accounting equation. It states that an area’s population size can change because of only three types of events: births, deaths, and migration. These three events are known as the components of demographic change and also as the three demographic processes.
The quantity () refers to the difference between the number of births and the number of deaths occurring during the time increases in the degree of gender equity in societies, the migration of females tends to approximate that of males. In fact, almost half of the international migrants worldwide are now women, and more than half of the legal immigrants to the United States are women (Population Reference Bureau, 2007b: 9). Migration is also age selective, with the largest numbers of immigrants found among young adults (Tobler, 1995)
Age and sex are not the only important compositional variables in demography. Other variable are also related to the three demographic processes. Knowing something about marital status, for example, is important when studying fertility. Race is strongly associated with socioeconomic status. Black, whites, Asians, and Hispanics all have somewhat different lifestyles, and these are related to the basic demographic processes. Education is an especially important variable to consider. In general, the higher the education attained, the lower the fertility and the lower the mortality.
These are just hints of the many compositional variable that demographer consider. The umber if large, giving demographers a wide field to study. They are interests in anything that is related to demographic behavior.
Finally, compositional variables are both the cause and effect of population changes. In turn, demographic changes can affect the compositional variables.
The Nature of Demographic data
How data are collected
Information about population is collected in two main ways: by enumeration at a point of time, and by recording events as they occur over a period. Censuses and social surveys are examples of the first method, and provide ‘stock’ data, while birth registrations and migration records (‘flow; data) are examples of the second. The information may purport to be complete or it may take the form of a sample. In this connexion it is important to consider the relationship the data bear to the biological events in human existence which is the basic objects of study. Although these events are essentially the ‘fact of life’ with which people generally are familiar, what the student of population need is a precise knowledge of how they are defined for practical purposes and their consequent place in demographic analysis.
Reliance on ‘common sense’ may not be enough to prevent serious misinterpretation of the results of statistical studies. While it is obvious what a ‘birth’ is, the demographer requires knowing whether recorded birth include or exclude still-birth and how still-births are defined. Are the births those which occurred in a given period, or those which were registered during that period? If the latter, what are the rules concerning registration and what delays can occur before registration is effected? Such matters can be important when analyzing changes in experience, or in measuring differences between populations – more particularly in international comparisons.
Why data are collected
The keeping of records of births, marriages and deaths originates long before the beginning of the scientific study of population. Its primary purpose was – and still is – the noting down permanently for reference purposes of the most important events in people’s lives. The proof of age provided by birth certificate is useful on many occasions – for instance in order to be able to sit for a certain examinations, to receive a bequest which is conditional on the attainment of (say) 21 years, or to claim a pension. The recording of marriages is a feature, inter alia, in the enforcement of the law against bigamy. Proof of death is likely to be of importance in the establishment of title to the proceeds of life assurance policies. These are just a few examples of the practical utility of registration.
Although enumeration data normally have no direct administrative uses, censuses help greatly in dealing with the complex problems of social administration in industrialized communities, for instance in the solution of transport difficulties and the determination of manpower available for industry and the defense services.
In neither instance is the process of collecting statistics devised solely or even primarily for the benefit of the demographer. He may, for his own considerations of cost normally restrict these to a small-sample basis. Moreover, such surveys usually have to rely upon the voluntary co-operation of the public to a much greater extent than in the regular official enumerations, backed as they are with the force of law; the value of private surveys may therefore be vitiated in some degree by refusals to respond on the part of some people.
Methods and Sources of Demographic Data
Contents of Demographic Data
1. Birth rate. Birth rate includes live birth. Live birth is 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, such as beating of the hear, pulsation of the umbilical cord, or definite movement of voluntary muscles, whether or not the umbilical cord has been cut or the placenta is attached; each product of such a birth is considered live born.
2. Death rate. This includes both foetal death and still birth. Foetal death is death prior to the complete expulsion or extraction from its mother of a product of conception irrespective of the duration of pregnancy; the death is indicated by the fact that after such extraction the fetus does not breathe or show any other evidence of life. A still-birth is a foetal death occurring late in the gestation period, ‘late’ is usually defined as after 28 completes weeks of gestation.
3. Data concerning population structure. These include sex structure, age structure, marital status, literacy and educational attainments. Sex structure depicts factors affecting overall sex ratio. Age structure shows the proportion of persons of various ages in the total population. Marital status shows the number of married, unmarried, males and females, widowers and widows, etc. In demography the rate of marriage is known as nuptiality. Most of the marriages are registered to be legal, in most of the countries. Marriage has been defined by UNO as the legal union of persons of opposite sex. This has been further explained as: “The legality of the union may be established by civil, religious or other means as recognizes by the laws of each country, and irrespective of the type of marriage, each should be reported for vital statistics purposes.” Besides literacy and educational attainments, population structure data also shows the population according to religion, rural and urban population and also the number of foreigners.
4. Fertility data. Fertility data includes both fecundity and fertility. Fecundity is determined by rhythm method. Fecundity does not work in the conditions known as Parturition, Postpartum, Amenorrhea and Anovulatory-Side. Fecundity depends upon lactation. It is also influenced by social taboos. Some persons are sterile and sub-fecund. Their number, however, is generally not more than 10% of the total pairs in the population. Fecundity and fertility is judged by electronic computer through a flowchart or diagram. The fertility data tell about sterility, family size, parity, conception, contraception and different types of factors affecting fertility.
5. Mortality data. These include crude death rate, average expectation of life and birth, infant mortality rate, sex and age patterns of mortality, causes of death, levels and trends on mortality and mortality differentials.
6. Migration data. These include immigration as well as emigration, their rate, trends and casual factors.
7. Size of population data. These include vital statistics. The growth and trend of population and the present size are known through census surveys.
8. Population distribution. This data is particularly gathered on the basis of geographic areas. It also shows population distribution by classification of residence such as rural, urban, etc. Besides, it also shows trends in realization and urbanization.
9. Labor force. Data concerning labor force shows economically active and inactive population. The former includes employed as well as unemployed, and the latter population includes home makers, students and income recipients. Besides, the data shows levels of male and female labor force, age specific labor force, rural and urban labor force, educated and uneducated labor force, etc.
The above discussion of the various constituents of population data shows that it requires large scale and detailed surveys from time to time throughout the country. It is the necessary basis of all planning and development in a country.
Sources of Demographic Data
There are varied sources of the population’s composition and distribution. The main sources of demographic data are:
Population Census like population count.
Vital registration statistics system like birth, death, marriage, and divorce.
Sample or Special Surveys like surveys of households; and
Demographic data gathered and processed by government agencies
Components of Population change
Population change occurs as growth or decline. Sociologists enumerate three variables or components: fertility (births), mortality (deaths), and migration (immigration and emigration). The combination of these variables has resulted in changes in the demographic structure, influencing the social, economic, and political structure of the society.
Demographers often employ the analogy of the bathtub in explaining how these three variables affect population size. Water enters the tub through two faucets analogous to births and immigration (movement to an area). The water leaves through two drains, analogous to deaths and emigration (movement out of an area).
Fertility
Fertility refers to the actual production of children, which is the strictest sense is a biological process. A zygote is produced when the sperm of a male and the egg of the female are united, and around nine mounts later a baby is born. Most often in this process, though not always, a man and a woman have sexual intercourse, the woman conceives, and the conception results in a live birth. Even though the production of a child is a biological process, the various activities and events that lead to the act of sexual intercourse and, later, giving birth are affected by social, economic, cultural, and psychological characteristics of the woman and the man, as well as by the environment in which they live. The key to this seeming paradox is that engaging in intercourse, conceiving, and giving birth are themselves behaviors that are influenced by other factors, most of them social and cultural. So while we have no influence at all with regard to the family and parents we receive when we are born, we do have a significant influence on our own fertility, that is, whether or not we produce children, and if so, the number and timing of the children produced. That is, whether we decide to engage in sexual intercourse, whether this intercourse results in a conception, and whether a live birth is the outcome are all driven largely by social and cultural considerations.
Fertility is classically identified as the number of live births a woman has, but this is not always clear or unambiguous. There are many still births (where fetus is delivered to term but is born without life) and there are many miscarriages, mostly spontaneous but often also managed in abortion, both medically supervised (generally ‘safe’) and tradition (often ‘unsafe’). Both stillbirths are miscarriages are much more common in developing countries than in developed countries, and their incidence may affect the perception and calculation of the number of live births a woman may record at a census or survey. In the absence of national and complete registration of births, as is typical of developing countries, data on fertility are collected from census question answered by women on the number of births they had over some given period, usually one year before the census or survey. Alternatively, as is the normal practice on Demographic and Health Surveys, the reproductive history of each sample woman is recorded, specifying not only the number of births, but also their dates, and thus allowing the speculation of birth intervals.
The simple way to measure fertility is to get the crude birth rate: the number of registered births per 1,000 of the population in a given area at a specified time. In equation form,

Crude birth rate (CBR) is the number of births in a year per 1,000 population. Despite its simplicity and relative ease of calculation (number of births per total population) and availability of data for such a calculation, it is seriously inadequate as a comparative measure of fertility in developing countries where age structures are highly variable and the numbers of very young or very old do not necessarily bear any relationship to that group in the population ‘at risk’ of bearing a child, that is, women after menarche (generally about 13-15 years) and before the menopause (generally at between 50 and 55 years). Thus analysts have moved to direct age-specific measures of fertility as the basis for international and local comparisons between populations.
The most important and the most widely used measure of fertility is the total fertility rate (TFR). The TFR is a synthetic index, the aggregate of age-specific fertility rates (ASFR) over any given period. The ASFRs are normally derived from 5-year age groups, from 15 to 50 years, and is the ration of births to women ‘at risk’ in that age group: for example, ASFR (15-19) = the number of live births to 15-19-year old/number of women aged 15-19.
Total fertility rate is a cross-sectional index (that is, it measures fertility at any point of time), and approximates to the expected completed fertility of all women in the childbearing age groups. However, since age group differentiates is, it takes on a cohort dimension to seek to take account of the tempo of fertility change, as a women progress through the 35 years or so of their reproductive period, from about age 15 to 50. The TFR may remain unchanged, but there may be changes in the ages at which women have their babies. In many developing countries, late marriages and greater use of contraception by younger women – for spacing rather than for stopping reason – also means that the age profile of births is also moving to older women. Other more complex indicates of fertility measure the completed fertility of particular cohorts of women, or to measure and cohere birth intervals (for example, parity progression ratio) to identify fertility trends.
Children ever born (CEB) is the number of children each woman in a population has had at the time of enumeration in a census or survey. This is also sometimes used as a measure of fertility, but it is misleading as an aggregate at any given point in time for whole populations where younger women who have not completes their childbearing are included. CEB is the most appropriately used to compare completed fertility of older women, to examine and compare changes for complete cohort, for example, of women born in the 1940s who had reached 50 by 2000 and therefore completed their childbearing, compared with women born in the 1950s their childbearing, who will have completed their childbearing only by 2010.
Mortality
Mortality refers to the number of deaths per 1,000 of the total mid-year population in a particular place at a specified time, and is measured by the crude date rate. In equation form,

This is defined as the ration of the total midyear population for that year. The CDR is affected by age composition. In other words, the population in the denominator differs in its death risk. For instance, infants and those over 50 or more prone to death than other age groups. To account for these variations, Age-Specific Death Rates are calculates by taking the ration of deaths that would occur in a particular age group in a particular year of a given population to the midyear population of that age group for that year. One can also calculate sex-specific and cause-of-death-specific mortality rates. Finally, there are various techniques for calculating standardized rates which control for differences in population age composition.
Migration
Migration is an intrinsically spatial phenomenon involving movement of individuals and groups across space into and out of an area. The process of movement is therefore about flows, how they are measured and described. However, in any population there will be stocks of migrants, the accumulated number of people who have moved into that population. Usually, movement is conceptualized in terms of flows, but migrant populations are seen as stocks. Differentiating between stocks and flows is central to understanding the migration/development nexus.
People migrate for a variety of reasons: economic, political, social, psychological, religious, educational, or medical. Overpopulation and resource pressure, differential technology, and great opportunities offered by a more developed society may impel one to move to anew area whether within a territory or from one country to another.
The Push and pull factors are set of force involved in any migration. Push refers to the unfavorable or unattractive conditions which impel a person or group of persons to move out of an area. These include natural disasters, such as famines, floods, or volcanic eruptions; political repressions; religious or racial discrimination or persecution; or internal disorders, such as war and other forms of conflict. Pull refers to the favorable conditions to attractions of a locality which lure a person or group of persons to move into that area. Among these are favorable climate, employment and opportunities, peace and order, political and religious freedoms, respect for human rights, better recreational and cultural facilities.
Migration may be internal or international. Internal migration is the spatial movement of a person or groups of persons within a country or specified territory, more or less for permanent residency. International migration is the spatial movement of a person or groups of person from one country to another, more or less for permanent settlement.
When one enters the country of destination, this is called immigration. When one leaves one’s country in order to move into another, this is called migration.

Bibliography
Rejandra K. Sharma, Demography and Population Problems
Peter R. Cox, Demography (fifth edition)
Dudley L. Poston, Jr., Leon F. Bouvier, Population and Society An introduction to Demography
W.T.S Gould, Population and Development
Shiva S. Halli, K. Vaninadha Rao, Advanced Techniques of Population Analysis
Wilfredo R. San Juan, Ma. Luz J. Centeno, Sociology, Culture and Family Planning (A conceptual, experiential and interactive approach)

Martisano, Glydel B.
Polytechnic University of the Philippines
Sta. Mesa, Manila
College of Communication
Department of Journalism
BAJ 1 – 1D