introduction: Demography is the statistical study of living populations. It can be a very general science that can be applied to any kind of dynamic living population, i.e., one that changes over time or space (see population dynamics). It encompasses the study of the size, structure, and distribution of these populations, and spatial and/or temporal changes in them in response to birth, migration, aging and death. For etymology(origins) of demography
Demographic analysis can be applied to whole societies or to groups defined by criteria such as education, nationality, religion and ethnicity. Institutionally, demography is usually considered a field of sociology, though there are a number of independent demography departments.Formal demography limits its object of study to the measurement of populations processes, while the broader field of social demography population studies also analyze the relationships between economic, social, cultural and biological processes influencing a population.
counted in three stages.
Stability or instability, increase or decrease of a population is dependent upon
Its age ratio.
(b) Sex-ratio.It is the ratio between male and female individuals in a given population. If the number of males is more, the population is said to be polyandrous, and if the number of females is more, it is called polygynous. Sex ratio can change with the age group of a population.
(c) Birth rate: The number of individuals born per thousand of population.
(d) Death rate: The number of individuals dying per thousand of population.
Following are the limiting factors which prevent the earth from supporting:
Human population of limiting size:
1. Adequate food supply.
2. The habitable area on the land is limited. If man tries to create more habitable areas by cutting down trees in forests, it would lead to imbalances in the nature.
3. Limited natural resources.
4. Adaptability of an organism for growth to the conditions.
5. Famine, floods and epidemic diseases.
Crude birth rate and crude death rate: rude birth and crude death rates are the number of live birth and deaths respectively per thousand people, on July 7 i.e. middle of a year.
Dependency ratio = person in Dependent ages/ person in economically providing ages
Demographic transition: Demographic transition. If birth and death rates are equal, it results into zero population growth rates, it is termed demographic transition. It may occur in all countries as they become developed but it may take many decades in underdeveloped countries.
Data and methods: There are two types of data collection — direct and indirect — with several different methods of each type.
Direct data come from vital statistics registries that track all births and deaths as well as certain changes in legal status such as marriage, divorce, and migration (registration of place of residence). In developed countries with good registration systems (such as the United States and much of Europe), registry statistics are the best method for estimating the number of births and deaths.
Indirect methods of collecting data are required in countries and periods where full data are not available, such as is the case in much of the developing world, and most of historical demography. One of these techniques is the sister method, where survey researchers ask women how many of their sisters have died or had children and at what age. With these surveys, researchers can then indirectly estimate birth or death rates for the entire population. Other indirect methods include asking people about siblings, parents, and children.
There are a variety of demographic methods for modeling population processes. They include models of mortality (including the life table, Gompertz models, hazards models, Cox proportional hazards models, multiple decrement life tables, Brass relational logits), fertility (Hernes model, Coale-Trussell models, parity progression ratios), marriage (Singulate Mean at Marriage, Page model), disability (Sullivan's method, multistate life tables), population projections (Lee Carter, the Leslie Matrix), and population momentum.