Demography in Sociology
Briefly defined, demography is the study of human population change. Many of our oldest documents make reference to counting or detailing populations. Populations are dynamic, constantly changing. This constant change in populations and their characteristics is the focus of demography, yet also presents challenges to demographers. The study of human society, or sociology, developed in tandem with demographic studies. A vast and formidable field of study in and of itself, demography is considered an essential sub-field of sociology as well as a number of other human and biological sciences. Dynamic models of population change processes not only answer questions about current populations but also give us a glimpse of possible future scenarios for population growth and change. This article explains some basic demographic concepts and gives examples of their use in demographic studies.
ACADEMIC TOPIC OVERVIEWS
Briefly defined, demography is the study of human population change. The term derives from the Greek words demos, or "people," and graph, which means "cipher" or "write." Population change has been a human fascination since the beginning of recorded history. Many of our oldest documents make reference to counting or detailing populations through a census, which is an enumeration and description of people in a given area at a given point in time. Even these early counts detailed the characteristics of a population, such as a person's origin, dwelling place, and property owned. These accounts were often used for purposes of assessing taxes.
One of the oldest surviving census rolls is known as the Domesday Book, a work commissioned in 1085 by William the Conqueror after he invaded British lands in 1066. The Domesday Book contains records of 13,418 settlements in the southern part of England. William needed an accounting of the new people and property under his dominion so that he could command tax payments to support his rule and conscript men for service (Maitland, 1987). Now housed at the National Archives in Kew, London, this document can be viewed online at the Open Domesday website.
However, references to census taking predate the Domesday Book and are found even in the oldest scriptures of the world's most enduring religions, including Judaism, Christianity, and Islam. A Muslim scholar, Ibn Khaldûn, is often credited with first using demographic methods in his study of social and economic systems in the mid-fourteenth century (Boulakia, 1971). Populations are dynamic and constantly changing. Certainly the world's population is much changed from the time of William the Conquerer, or even Ibn Khaldûn. This constant change in populations and their characteristics is the focus of demography. The evolution of contemporary demography coincided with the development of the new techniques of statistics, arithmetical and mathematical methods extended to assemble, classify, and tabulate numerically based data. The study of human society, or sociology, grew alongside demographic studies. Indeed, demographic techniques allowed sociologists to assert the empirical--that is, observable--nature of their formal discipline, giving rise to early studies of society such as those of Auguste Comte, who first coined the term "sociology." A vast and formidable field of study in and of itself, demography is considered an essential subfield of sociology and a number of other human and biological sciences as well.
Demographic Concepts: The Basics
Vital statistics, such as births and deaths, are direct building blocks used in demographic analysis. They are primary data, assembled through direct observations of life events, typically collected continuously and summarized on an annual basis by governmental units. Another source of primary data is censuses, which are usually conducted by a national government or intergovernmental organization that attempts to enumerate every person in a given location. A census often does more than just count people; it also gathers information about families or households, as well as individual characteristics such as age, sex, marital status, literacy, education, employment status, occupation, and geographical location. Censuses are usually conducted only every few years, often once per decade or less. The study of population change would not exist without the human ability to assemble and tabulate these fundamental data points.
While a census provides a snapshot of a population at one point in time, the most important task of demographers is to document population dynamics, or the processes by which populations change. The three most basic processes of population dynamics are those that affect population size:
* Mortality, and
* Migration (Weinstein & Pillai, 2000).
These three essential population processes underlie all other changes in population and are used in the most basic model of population dynamics. Models of population processes are developed through theories, or sets of hypotheses, pertaining to how population processes operate together to dynamically produce change. These hypotheses are ultimately expressed as sets of equations called models, which must then be tested against actual observed data points.
A logical starting point in the study of population dynamics is the assembly and tabulation of fertility data. Fertility is the variable frequency of childbearing in a given population. The crude birth rate, or the annual number of live births per 1,000 people in a population, is used to represent fertility.
Even as children are born, people die. Mortality, the variable frequency of death in a given population, is represented by the crude death rate, or the annual number of deaths per 1,000 people in a population.
The size of a given population is also affected by migration, the variable movement of people into and out of the population. Demographers must consider both immigration, in which people move into a specified population, and emigration or out-migration, in which people leave a specified population. The combination of the two is the net migration rate, which is the difference between persons gained through immigration and those lost through emigration, expressed as a ratio per 1,000 people in the population.
Population Dynamics: The Most Basic Demographic Formula
The most basic formula in demography uses these basic changes in the size of a population to provide an overall rate of population growth or decline. In its simplest form, this formula can be expressed as:
Pt2 = Pt1 + (CBR - CDR) + NMR where:
Pt2 = total number of persons in a population at time t2
Pt1 = total number of persons in a population at time t1
CBR = crude birth rate
CDR = crude death rate
NMR = net migration rate
With this formula and the data needed to calculate a basic population growth rate (or rate of decline), we now have the foundation from which to begin investigating other population characteristics and the parts these characteristics play in population dynamics. Also called demographic variables, these include any characteristics, attributes, or properties of people or collectives of people that can vary between persons or collectives. Many of these characteristics affect or are otherwise related to the three basic population processes.
Widely Used Demographic Variables
There are so many variations between people and collectives of people that we cannot begin to detail them all in this context. Age, sex, pregnancies, births, siblings, sexual orientation, gender orientation, ethnicity, race, national citizenship, religious preference, occupation, income, and wealth are just a few of the variables most frequently used in the study of human societies. Models are assembled to represent the interrelation of these variables. We can look at an example of how such characteristics are related to basic population processes, beginning with fertility. Obviously, sex and sexual orientation affect sexual reproduction and fertility. Age is also closely related to sexual reproduction, as it affects a woman's ability to bear children. The widest range of the childbearing age for women is from onset of menarche, around 12 years of age, to onset of menopause, usually in the late forties to mid-fifties. All of these factors affect fecundity, the maximum possible number of births per woman in the population.
While it is possible, indeed documented, that women can give birth to 30 or more children--usually including multiple births, such as twins or triplets (Pearl, 1939)--these are rare cases. Typically, fecundity is estimated at around 12 to...
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