Demography is the scientific study of human population,
including its size, distribution, composition, and the factors
that determine changes in its size, distribution, and composition.
From this definition we can say that demography
focuses on five aspects of human population: (1) size, (2)
distribution, (3) composition, (4) population dynamics, and
(5) socioeconomic determinants and consequences of population
change. Population size is simply the number of
persons in a given area at a given time. Population distribution
refers to the way the population is dispersed in
geographic space at a given time. Population composition
refers to the numbers of person in sex, age, and other
“demographic” categories. The scope of the “demographic”
categories appropriate for demographic study is subject to
debate. All demographers would agree that age, sex, race,
year of birth, and place of birth are demographic characteristics.
These are all characteristics that do not essentially
change in the lifetime of the individual, or change in a perfectly
predictable way. They are so-called ascribed characteristics.
Many other characteristics also are recognized as
within the purview of the demographer. These fall into a
long list of social and economic characteristics, including
nativity, ethnicity, ancestry, religion, citizenship, marital
status, household characteristics, living arrangements, educational
level, school enrollment, labor force status,
income, and wealth. Most of these characteristics can
change in the lifetime of the individual. They are so-called
achieved characteristics. Of course, some of these characteristics
are the specialty of other disciplines as well, albeit
the focus of interest is different. Some would include as
demography all the areas about which questions are asked
in the decennial population census. Our view of this question
has a bearing on the subjects about which we write in
this volume.