Life expectancy is the expected (in the statistical sense) number of years of life remaining at a given age.[1] It is denoted by ex, which means the average number of subsequent years of life for someone now aged x, according to a particular mortality experience. (In technical literature, this symbol means the average number of complete years of life remaining, ie excluding fractions of a year. The corresponding statistic including fractions of a year, ie the normal meaning of life expectancy, has a symbol with a small circle over the e.)[citation needed](see for example [1])
The term is most often used in the human context, but is also used in plant or animal ecology Ecology is the interdisciplinary scientific study of the interactions between organisms and their environment. Ecology is also the study of ecosystems. Ecosystems describe the web or network of relations among organisms at different scales of organization. Since ecology refers to any form of biodiversity, ecologists research everything from tiny[2]; it is calculated by the analysis of life tables In actuarial science, a life table is a table which shows, for each age, what the probability is that a person of that age will die before their next birthday. From this starting point, a number of statistics can be derived and thus also included in the table: (also known as actuarial tables An actuary is a business professional who deals with the financial impact of risk and uncertainty. Actuaries have a deep understanding of financial security systems, with a focus on their complexity, their mathematics, and their mechanisms). The term life expectancy may also be used in the context of manufactured objects[3] although the related term shelf life Shelf life is the length of time that food, drink, medicine and other perishable items are given before they are considered unsuitable for sale or consumption. In some regions, a best before, use by or freshness date is required on packaged perishable foods is used for consumer products and the term mean time to breakdown (MTTB) is used in engineering literature.
Life expectancy is heavily dependent on the criteria used to select the group. For example, in countries with high infant mortality Infant mortality is defined as the number of infant deaths per 1000 live births. The most common cause worldwide has traditionally been due to dehydration from diarrhea. However, the spreading information about Oral Rehydration Solution (a mixture of salts, sugar, and water) to mothers around the world has decreased the rate of children dying from rates, the life expectancy at birth is highly sensitive to the rate of death in the first few years of life. In these cases, another measure such as life expectancy at age 5 (e5) can be used to exclude the effects of infant mortality to provide a simple measure of overall mortality rates other than in early childhood.
Life expectancy is usually calculated separately for males and females.
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Due to this and other factors, the life expectancy of a person with colon cancer is much higher in the US than in the UK This example illustrates two ...
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