Editing Demography (section)

==Common rates and ratios==
* The '''crude [[birth rate]]''', the annual number of live births per 1,000 people.
* The '''general [[fertility rate]]''', the annual number of live births per 1,000 women of childbearing age (often taken to be from 15 to 49 years old, but sometimes from 15 to 44).
* The '''age-specific fertility''' rates, the annual number of live births per 1,000 women in particular age groups (usually age 15–19, 20–24 etc.)
* The '''crude [[death rate]]''', the annual number of deaths per 1,000 people.
* The '''[[infant mortality rate]]''', the annual number of deaths of children less than 1 year old per 1,000 live births.
* The '''expectation of life''' (or [[life expectancy]]), the number of years that an individual at a given age could expect to live at present mortality levels.
* The '''[[total fertility rate]]''', the 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|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 2.11.<ref name="Ela 2008">Introduction to environmental engineering and science by Masters and Ela, 2008, Pearson Education, chapter 3</ref>
* The '''[[gross reproduction rate]]''', the number of daughters who would be born to a woman completing her reproductive life at current age-specific fertility rates.
* The '''[[Net reproduction rate|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.<ref name="Ela 2008"/>
* A '''stationary population''', one that is both stable and unchanging in size (the difference between crude birth rate and crude death rate is zero).<ref name="Ela 2008"/>
* Measures of centralisation are concerned with the extent to which an area's population is concentrated in its [[urban area|urban centres]].<ref>Hoyt, H., [https://www.jstor.org/stable/2769393 Forces of Urban Centralization and Decentralization], [[American Journal of Sociology]], Vol. 46, No. 6 (May, 1941), pp. 843-852, accessed 2 July 2023</ref><ref>Cooper-Douglas, E., [https://www.abc.net.au/news/2023-01-06/population-outside-hobart-means-struggle-for-services/101829418 Tasmania forecast to have 79,000 more residents by 2033, with most living outside Greater Hobart], ''[[ABC News (Australia)|ABC News]]'', published 5 January 2023, accessed 2 July 2023</ref>

A stable population does not necessarily remain fixed in size. It can be expanding or shrinking.<ref name="Ela 2008"/>

The crude death rate as defined above and applied to a whole population can give a misleading impression. For example, the number of deaths per 1,000 people can be higher in 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 table]], which summarizes mortality separately at each age. A life table is necessary to give a good estimate of life expectancy.