Editing Life expectancy (section)

{{short description|Measure of average lifespan in a given population}}
{{About|normal lifespan|the novel|Life Expectancy (novel){{!}}''Life Expectancy'' (novel)}}
{{Redirect|Human lifespan|the lifespan of a person in stages|Developmental psychology{{!}}Maturation}}
{{Cleanup|reason=Clarification needed at times|date=November 2022}}
{{Use dmy dates|date=December 2024}}
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[[File:Healthy life expectancy bar chart -world.png|thumb|300px|Life expectancy and healthy life expectancy in various countries of the world in 2019, according to [[World Health Organization|WHO]]<ref name="who_2019">{{cite web|title=Life expectancy and Healthy life expectancy, data by country|language=en|publisher=World Health Organization|url=https://apps.who.int/gho/data/node.main.688|date=4 December 2020}}</ref>]]
[[File:Life expectancy UN map gradient 2023.png|thumb|300px|Map of the life expectancy at birth in the world in 2023 (UN estimate, smooth palette)<ref name="un_prospects">{{cite web|url=https://population.un.org/wpp/Download/Standard/MostUsed/|title=World Population Prospects 2024|publisher=[[United Nations Department of Economic and Social Affairs]]|format=XLSX|language=en}} – see file "Compact (most used: estimates and medium projections)"</ref>
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[[File:Life expectancy UN map gradient 2023 at age 15.png|thumb|300px|Life expectancy at age 15 years<ref name="un_prospects" />
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[[File:Life expectancy UN map gradient 2023 at age 65.png|thumb|300px|Life expectancy at age 65 years<ref name="un_prospects" />
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[[File:Life expectancy UN map gradient 2023 at age 80.png|thumb|300px|Life expectancy at age 80 years<ref name="un_prospects" />
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[[File:Life expectancy in some big countries.png|thumb|300px|Life expectancy development in some big countries of the world since 1960]]
[[File: Life Expectancy At Birth By Region.png|thumb|300px|Life expectancy at birth, measured by region, between 1950 and 2050]]
[[File: Life expectancy by world region since 1770, OWID.svg|thumb|300px|Life expectancy by world region, from 1770 to 2018]]

'''Human life expectancy''' is a statistical measure of the estimate of the average remaining years of life at a given age. The most commonly used measure is ''life expectancy at birth'' (LEB, or in demographic notation ''e''<sub>0</sub>, where ''e''<sub>x</sub> denotes the average life remaining at age ''x''). This can be defined in two ways. ''Cohort'' LEB is the mean length of life of a birth [[Cohort (statistics)|cohort]] (in this case, all individuals born in a given year) and can be computed only for cohorts born so long ago that all their members have died. ''Period'' LEB is the mean length of life of a [[hypothetical]] cohort<ref>{{cite web|title="Life Expectancy" – What does this actually mean?|url=https://ourworldindata.org/life-expectancy-how-is-it-calculated-and-how-should-it-be-interpreted|access-date=2020-08-31|website=Our World in Data|date=28 August 2017 | vauthors = Ortiz-Ospina E }}</ref><ref>{{cite web|title=Period and cohort life expectancy explained: December 2019|work=Office for National Statistics|publisher=UK Government|url=https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/lifeexpectancies/methodologies/periodandcohortlifeexpectancyexplained|access-date=2020-08-31}}</ref> assumed to be exposed, from birth through death, to the [[mortality rate]]s observed at a given year.<ref>{{cite book|vauthors=Shryock HS, Siegel JS|title=The Methods and Materials of Demography|edition=rev.|location=Washington, DC|publisher=Bureau of the Census, Government Printing Office|date=1973}}</ref> National LEB figures reported by national agencies and international organizations for human populations are estimates of ''period'' LEB.

Human remains from the early [[Bronze Age]] indicate an LEB of 24.<ref name="MacLennan_1999">{{cite journal|vauthors=MacLennan WJ, Sellers WI|title=Ageing through the ages|journal=Proceedings of the Royal College of Physicians of Edinburgh|volume=29|issue=1|pages=71–5|date=January 1999|pmid=11623672|doi=10.1177/147827159902900114}}</ref> In 2019, world LEB was 73.3.<ref>{{cite web|publisher=World Health Organization|date=2023|title=Life expectancy at birth (years) [Indicator]|url=https://data.who.int/indicators/i/90E2E48|access-date=18 December 2023}}</ref> A combination of high [[infant mortality]] and deaths in young adulthood from accidents, [[epidemic]]s, plagues, wars, and childbirth, before modern medicine was widely available, significantly lowers LEB. For example, a society with a LEB of 40 would have relatively few people dying at exactly 40: most will die before 30 or after 55. In populations with high infant mortality rates, LEB is highly sensitive to the rate of death in the first few years of life. Because of this sensitivity, LEB can be grossly misinterpreted, leading to the belief that a population with a low LEB would have a small proportion of older people.<ref name="Laden2011">{{cite news|vauthors=Laden G|url=http://scienceblogs.com/gregladen/2011/05/01/falsehood-if-this-was-the-ston/|archive-url=https://web.archive.org/web/20121111192623/http://scienceblogs.com/gregladen/2011/05/01/falsehood-if-this-was-the-ston/|url-status=dead|archive-date=11 November 2012|title=Falsehood: "If this was the Stone Age, I'd be dead by now"|work=ScienceBlogs|date=2011-05-01|access-date=2014-08-31}}</ref> A different measure, such as life expectancy at age 5 (e<sub>5</sub>), can be used to exclude the effect of infant mortality to provide a simple measure of overall mortality rates other than in early childhood. For instance, in a society with a life expectancy of 30, it may nevertheless be common to have a 40-year remaining timespan at age 5 (but not a 60-year one{{dubious|date=September 2024}}).

Aggregate population measures—such as the proportion of the population in various age groups—are also used alongside individual-based measures—such as formal life expectancy—when analyzing population structure and dynamics. Pre-modern societies had universally higher mortality rates and lower life expectancies at every age for both males and females.

Life expectancy, [[longevity]], and [[maximum lifespan]] are not synonymous. Longevity refers to the relatively long lifespan of some members of a population. Maximum lifespan is the age at death for the longest-lived individual of a species. Mathematically, life expectancy is denoted <math>e_x</math>{{Efn|name=exsymbol}} and is the mean number of years of life remaining at a given age <math>x</math>, with a particular [[wikt:mortality|mortality]].<ref name="O'Sullivan_2003">{{cite book|vauthors=O'Sullivan A, Sheffrin SM|title=Economics: Principles in Action|publisher=Pearson Prentice Hall|year=2003|isbn=978-0-13-063085-8|page=473|author-link=Arthur O'Sullivan (economist)}}</ref> Because life expectancy is an average, a particular person may die many years before or after the expected survival.

Life expectancy is also used in plant or animal [[ecology]],<ref>{{cite journal|vauthors=Contreras SC, Jurema AL, Claudino ES, Bresciani E, Caneppele TM|title=Monowave and polywave light-curing of bulk-fill resin composites: degree of conversion and marginal adaptation following thermomechanical aging|journal=Biomaterial Investigations in Dentistry|volume=8|issue=1|pages=72–78|year=1983|pmid=34368776|doi=10.2307/1937181|publisher=Ecological Society of America|bibcode=1983Ecol...64..631M|jstor=1937181|pmc=8317947}}</ref> and in [[life table]]s (also known as [[actuary|actuarial]] tables). The concept of life expectancy may also be used in the context of manufactured objects,<ref name="machine">{{cite book|vauthors=Zahavi E, Torbilo V|title=Fatigue Design: Life Expectancy of Machine Parts.|date=1996|publisher=CRC Press|location=Boca Raton|isbn=978-0-8493-8970-2}}</ref> though the related term{{dubious|reason=Is that very well related? Perhaps for perishable food, but for manufactured items that start wearing down during use, it is not an indication of the useful life (starting when put into service) and thus value of the item (as MTBF would be).|date=September 2022}} [[shelf life]] is commonly used for consumer products, and the terms "mean time to breakdown" and "[[mean time between failures]]" are used in engineering.