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Direct methods[ edit ] Direct data comes 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 Europeregistry statistics are the best method for estimating the number of births and deaths.
A census is the other common direct method of collecting demographic data. A census is usually conducted by a national government and attempts to enumerate every person in a country. In contrast to vital statistics data, which are typically collected continuously and summarized on an annual basis, censuses typically occur only every 10 years or so, and thus are not usually the best source of data on births and deaths.
Analyses are conducted after a census to estimate how much over or undercounting took place. These compare the sex ratios from the census data to those estimated from natural values and mortality data.
Censuses do more than just count people. They may also collect data on migration or place of birth or of previous residencelanguage, religion, nationality or ethnicity or raceand citizenship.
Map of countries by population Rate of human population growth showing projections for later this century Indirect methods[ edit ] 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 in contemporary demography 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 in contemporary demography include asking people about siblings, parents, and children.
Language Dynamics and Change work on such topics as the evolution of language, archaeology and linguistics (‘archaeolinguistics’), human genetic and linguistic prehistory, and the computational modeling of language dynamics. Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany John Whitman, Cornell University, USA. A Summary of Human Population Dynamics By Russell Hopfenberg In the broadest sense, the theory is very simple. The main perspective is that human population dynamics do not differ from the population dynamics of all other species. RAND's Population Matters project has undertaken this challenging task for policymakers on population issues. The Environmental Implications of Population Dynamics is Population Matters' first look at macro-level population and environment trends--and the implications these trends pose for policy at the local, national, and global levels.
Other indirect methods are necessary in historical demography. There are a variety of demographic methods for modelling population processes. The United Kingdom has a series of four national birth cohort studies, the first three spaced apart by 12 years: These have followed the lives of samples of people typically beginning with around 17, in each study for many years, and are still continuing.
As the samples have been drawn in a nationally representative way, inferences can be drawn from these studies about the differences between four distinct generations of British people in terms of their health, education, attitudes, childbearing and employment patterns.
The general fertility ratethe annual number of live births per 1, women of childbearing age often taken to be from 15 to 49 years old, but sometimes from 15 to The age-specific fertility rates, the annual number of live births per 1, women in particular age groups usually ageetc.
The crude death ratethe annual number of deaths per 1, people. The infant mortality ratethe annual number of deaths of children less than 1 year old per 1, live births. The expectation of life or life expectancythe number of years that an individual at a given age could expect to live at present mortality levels.
The total fertility ratethe number of live births per woman completing her reproductive life, if her childbearing at each age reflected current age-specific fertility rates.
The replacement level fertility, the average number of children women must have in order to replace the population for the next generation. For example, the replacement level fertility in the US is 2. The net reproduction ratio is the expected number of daughters, per newborn prospective mother, who may or may not survive to and through the ages of childbearing.
A stable population, one that has had constant crude birth and death rates for such a long period of time that the percentage of people in every age class remains constant, or equivalently, the population pyramid has an unchanging structure.
It can be expanding or shrinking. For example, the number of deaths per 1, people can be higher for developed nations than in less-developed countries, despite standards of health being better in developed countries.
This is because developed countries have proportionally more older people, who are more likely to die in a given year, so that the overall mortality rate can be higher even if the mortality rate at any given age is lower. A more complete picture of mortality is given by a life tablewhich summarizes mortality separately at each age.
A life table is necessary to give a good estimate of life expectancy. Basic equation[ edit ] Suppose that a country or other entity contains Populationt persons at time t.Population dynamics is the branch of life sciences that studies short-term and long-term changes in the size and age composition of populations, and the biological .
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Other demographic dynamics, including changes in population flows and densities, can also pose challenging environmental problems. Environmental Implications of Specific Population Factors. According to recent United Nations estimates, global population is increasing by approximately 80 million — the size of Germany — each year.
(September ) We entered the 20th century with a population of billion people. We entered the 21st century with billion people. And in , world population is billion. The increase in the size of the human population in the last half-century is unprecedented. And nearly all of the. The 7-volume Encyclopedia of Biodiversity, Overview.
Human Impacts on Ecosystems: An Overview. Hunter-Gatherer Societies, Ecological Impact of. Overview. Population Dynamics.
Population Genetics. Population Stabilization, Human. Population Viability Analysis. Poverty and Biodiversity. Population dynamics is the branch of life sciences that studies the size and age composition of populations as dynamical systems, and the biological and environmental processes driving them (such as birth and death rates, and by immigration and emigration).