Introduction
Demography (Greek demos = people, graphia = writing) is the study of the characteristics of human populations. Medical demography studies the demographic processes that are closely related to the health of the population. This topic covers the branches of demography, its history and the demographic transition model.
Demography and its branches
Demography studies the characteristics of human populations, such as:
- Size
- Growth
- Density
- Distribution
- Vital statistics
The word population means different things in demography and in statistics. In demography it relates to the number of people in a given area; in statistics it means the universe of units under consideration.
Demography has 2 main branches.
A. Population statics (point in time)
- Studies the size, distribution and structure of the population (the status of the population) by age, sex, education, income, residence and other factors.
- The main instrument is the census; calculations (forecasts) and the microcensus are also used.
- Census is the total process of collecting, compiling and publishing demographic, economic and social data pertaining, at a specified time, to all persons in a country or delimited territory.
- Demography in Bulgaria is monitored by the National Statistical Institute.
B. Population dynamics (period in time)
- The study of changes in the population and of the processes influencing those changes.
- Natural and vital events: births, deaths, marriages, divorces, etc.
- Migration: external (migrants, emigrants, immigrants), forced (slavery, natural disasters) and voluntary (new job, better life); and internal.
- Internal migration occurs within a country and involves movement between rural and urban areas, both permanent and temporary:
- Permanent: urbanisation (rural to urban areas), urban depopulation (urban to rural areas), regional migration (permanent movement within a country).
- Temporary: daily (every day to school, work and on day trips and back); seasonal (related to agriculture, seaside in summer or mountains in winter, seasonal employment); semi-permanent (a limited period of time to work in another area of the country, not associated with seasons, e.g. oil rigs, university).
- Sources of data: registration of births and deaths (civil registration), residence registry, immigration registry.