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.
In technical literature, this symbol means the average number of ''complete'' years of life remaining, excluding fractions of a year. The corresponding statistic including fractions of a year, the normal meaning of life expectancy, has a symbol with a small circle over the ''e''.
The life expectancy of a group of individuals is heavily dependent on the care.
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; it is calculated by the analysis of life tables (also known as actuarial tables).
The term life expectancy may also be used in the context of manufactured objects and 49.0 years in Japan (2008 est.), although Japan's recorded life expectancy may have been very slightly increased by counting many infant deaths as stillborn.
The oldest confirmed recorded age for any human is 122 years (Jeanne Calment). This is referred to as the "maximum life span", which is the upper boundary of life, the maximum number of years any human is known to have lived.
Life expectancy variation over time
The following information is derived from ''Encyclopaedia Britannica'', 1961 and other sources, and unless otherwise stated represents estimates of the life expectancies of the population as a whole. In many instances life expectancy varied considerably according to class and gender.
The life expectancies at birth listed below take account of infant mortality but not pre-natal mortality (miscarriage or abortion).
|Humans by Era
||Average Lifespan at Birth
||At age 15: 39 (to age 54)
|Bronze Age and Iron Age
||At age 15: 37 (to age 52)
|Pre-Columbian North America
|Medieval Islamic Caliphate
||At age 21: 38 (to age 59) as an average for British aristocrats
|Early Modern Britain
|Current world average
Sometimes, mainly in the past, life expectancy increased during the years of childhood, as the individual survived the high mortality rates then associated with childhood. Surviving childhood would dramatically affect life expectancy. For instance, the table above listed life expectancy at birth in Medieval Britain at 30. A male member of the English aristocracy at the same period could expect to live, having survived until the age of 21:
- 43 years → 64 years total between 1200 and 1300
- 24 years → 45 years total between 1300 and 1400 (due to the impact of the Black Death)
- 48 years → 69 years total between 1400 and 1500
- 50 years → 71 years total between 1500 and 1550.
While different sample attributes and sizes, methodologies, and theoretical assumptions produce sometimes notable variations, in general, interpretations of the available data indicate that the occurrence of older age became more common late in human evolution.
This increased longevity is attributed by some writers to cultural adaptations rather than phylogenetic change, although some research indicates that during the Neolithic Revolution there was a selection effect of extrinsic mortality risk upon genotypic expressions favouring increased longevity in subsequent populations. and in New England about 40% of children failed to reach adulthood.
During the Industrial Revolution, the life expectancy of children increased dramatically.
The percentage of children born in London who died before the age of five decreased from 74.5% in 1730-1749 to 31.8% in 1810-1829.
Public health measures are credited with much of the recent increase in life expectancy. During the 20th century, the average lifespan in the United States increased by more than 30 years, of which 25 years can be attributed to advances in public health.
In order to assess the quality of these additional years of life, 'healthy life expectancies' have been calculated for the last 30 years.
Since 2001, the World Health Organization publishes statistics called Healthy life expectancy (HALE), defined as the average number of years that a person can expect to live in "full health", excluding the years lived in less than full health due to disease and/or injury.
Since 2004, Eurostat publishes annual statistics called Healthy Life Years (HLY) based on reported activity limitations.
The United States of America uses similar indicators in the framework of their nationwide health promotion and disease prevention plan "Healthy People 2010". An increasing number of countries are using health expectancy indicators to monitor the health of their population.
There are great variations in life expectancy between different parts of the world, mostly caused by differences in public health, medical care and diet. Much of the excess mortality (higher death rates) in poorer nations is due to war, starvation, and diseases (AIDS, Malaria, etc.).
The impact of AIDS is particularly notable on life expectancy in many African countries. According to the UN, the life expectancy at birth for 2010-2015, would have been of:
- 70.7 years instead of 31.6 in Botswana, the country with the highest prevalence of HIV
- 69.9 years instead of 41.5 in South Africa
- 70.5 years instead of 31.8 in Zimbabwe.
Over the past 200 years, countries with Black or African populations have generally not had the same improvements in mortality rates that have been enjoyed by populations of European origin.
Even in countries with a majority of White people, such as USA, Britain, Ireland and France, Black people tend to have shorter life expectancies than their White counterparts.
For example, in the U.S. White Americans are expected to live until age 78.2, but black people only until age 73.6.
Climate may also have an effect, and the way data is collected may also influence the figures. According to the CIA World Factbook, Monaco has the world's longest life expectancy of 89.8 years (and Macau Special Administrative Region of the People's Republic of China has the world's second longest life expectancy of 84.4 years).
There are also significant differences in life expectancy between men and women in most countries, with women typically outliving men by around five years.
Economic circumstances also affect life expectancy. For example, in the United Kingdom, life expectancy in the wealthiest areas is several years longer than in the poorest areas.
This may reflect factors such as diet and lifestyle as well as access to medical care. It may also reflect a selective effect: people with chronic life-threatening illnesses are less likely to become wealthy or to reside in affluent areas.
In Glasgow the disparity is among the highest in the world with life expectancy for males in the heavily deprived Calton standing at 54 – 28 years less than in the affluent area of Lenzie, which is only eight kilometres away.
Life expectancy is also likely to be affected by exposure to high levels of highway air pollution or industrial air pollution. This is one way that occupation can have a major effect on life expectancy. Coal miners (and in prior generations, asbestos cutters) often have shorter than average life expancies.
Other factors affecting an individual's life expectancy are genetic disorders, obesity, access to health care, diet, exercise, tobacco smoking, drug use and excessive alcohol use.
Women tend to have a lower mortality rate at every age. In the womb, male fetuses have a higher mortality rate (babies are conceived in a ratio of about 124 males to 100 females, but the ratio of those surviving to birth is only 105 males to 100 females). Among the smallest premature babies (those under 2 pounds or 900 g) females again have a higher survival rate. At the other extreme, about 90% of individuals aged 110 are female.
The difference in life expectancy between men and women in the United States dropped from 7.8 years in 1979 to 5.3 years in 2005, with women expected to live to age 80.1 in 2005.
In the past, mortality rates for females in child-bearing age groups were higher than for males at the same age. This is no longer the case, and female human life expectancy is considerably higher than those of men.
The reasons for this are not entirely certain. Traditional arguments tend to favor socio-environmental factors: historically, men have generally consumed more tobacco, alcohol and drugs than females in most societies, and are more likely to die from many associated diseases such as lung cancer, tuberculosis and cirrhosis of the liver.
Men are also more likely to die from most of the leading causes of death (some already stated above) than women. Some of these in the United States include: cancer of the respiratory system, motor vehicle accidents, suicide, cirrhosis of the liver, emphysema, and coronary heart disease. This biological difference occurs because women have more resistance to infections and degenerative diseases. Japan is the country with the highest ratio of centenarians (347 for every 1 million inhabitants in September 2010). Shimane prefecture had an estimated 743 centenarians per million inhabitants.
In the United States, the number of centenarians grew from 32,194 in 1980 to 71,944 in November 2010 (232 centenarians per million inhabitants).
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