Life expectancy

Life expectancy is the expected (in the statistical sense) number of years of life remaining at a given age. It is denoted by e_x,[which means the average number of subsequent years of life for someone now aged x, according to a particular mortality experience. Because life expectancy is an average, a particular person may well die many years before or many years after their "expected" survival. The term "maximum life span" has a quite different meaning. The "median life span" is also a different concept although fairly similar to life expectancy numerically in most developed countries. The term that is known as life expectancy is most often used in the context of human populations, but is also used in plant or animal ecology; life tables (also known as actuarial tables). The term life expectancy may also be used in the context of manufactured objects, although the related term shelf life is used for consumer products and the terms "mean time to breakdown" (MTTB) and "mean time between failures" (MTBF) are used in engineering. http://en.wikipedia.org/wiki/Life_expectancy

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