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Life Expectancy

Life Expectancy

Life expectancy refers to the number of years that people in a given country or population can expect to live. Conceptually, life expectancy and longevity are identical; the difference between them lies in measurement issues. Life expectancy is calculated in a very precise manner, using what social scientists call "life table analysis." Longevity is not associated with any particular statistical technique. Both life expectancy and longevity are distinct from life span, which refers to the number of years that humans could live under ideal conditions. While life expectancy is based on existing data, life span is speculative. Partly because of its speculative nature, there is considerable debate about the possible length of the human life span. Some social scientists argue that Western populations are approaching a biologically fixed maximum, or finite life span, probably in the range of 85 to 100 years. Others believe that the human life span can be extended by many more years, due to advances in molecular medicine or dietary improvements, for example. An intermediate position is taken by other researchers, who suggest that there is no rigid limit to the human life span and as-yet-unforeseen biomedical technological breakthroughs could gradually increase life span.

A considerable amount of research, based on the foundational assumption of a finite human life span, has focussed on the concept of dependency-free life expectancy (also called dependence-free life expectancy, healthy life expectancy, active life expectancy, disability-free life expectancy, and functional life expectancy). These varying terms refer to the number of years that people in a given population can expect to live in reasonably good health, with no or only minor disabling health conditions. Most of the research on dependency-free life expectancy tests, in varying ways, the validity of the compression of morbidity hypothesis, originally formulated by the researcher James F. Fries in 1983. This hypothesis states that, at least among Western populations, proportionately more people are able to postpone the age of onset of chronic disability; hence, the period of time between onset of becoming seriously ill or disabled and dying is shortening or compressing. Research findings on morbidity compression are variously supportive, negative, and mixed.

The Measurement of Life Expectancy

Life expectancy is a summary measure of mortality in a population. Statistics on life expectancy are derived from a mathematical model known as a life table. Life tables create a hypothetical cohort (or group) of 100,000 persons (usually of males and females separately) and subject it to the age-sex-specific mortality rates (the number of deaths per 1,000 or 10,000 or 100,000 persons of a given age and sex) observed in a given population. In doing this, researchers can trace how the 100,000 hypothetical persons (called a synthetic cohort) would shrink in numbers due to deaths as they age. The average age at which these persons are likely to have died is the life expectancy at birth. Life tables also provide data on life expectancy at other ages; the most commonly used statistic other than life expectancy at birth is life expectancy at age sixty-five, that is, the number of remaining years of life that persons aged sixty-five can expect to live.

Life expectancy statistics are very useful as summary measures of mortality, and they have an intuitive appeal that other measures of mortality, such as rates, lack. However, it is important to interpret data on life expectancy correctly. If it reported that life expectancy at birth in a given population is 75 years in 2000, this does not mean that all members of the population can expect to live to the age of 75. Rather, it means that babies born in that population in 2000 would have a life expectancy at birth of 75 years, if they live their lives subject to the age-specific mortality rates of the entire population in 2000. This is not likely; as they age, age-specific mortality rates will almost certainly change in some ways. Also, older people in that population will have lived their life up to the year 2000 under a different set of age-specific mortality rates. Thus, it is important to be aware of the hypothetical nature of life expectancy statistics.

Life tables require accurate data on deaths (by age and sex) and on the population (by age and sex); many countries lack that basic data and their life expectancy statistics are estimates only. However, age-specific mortality tends to be very predictable; thus, if the overall level of mortality in a population is known, it is possible to construct quite reasonable estimates of life expectancy using what are called model life tables.

Life Expectancy at Birth, Circa 2001

Life expectancy at birth for the world's population at the turn of the twenty-first century was 67 years, with females having a four-year advantage (69 years) over males (65 years); see Table 1. As expected, developed countries experience substantially higher life expectancy than less developed countries75 years and 64 years, respectively.

Life expectancy at birth by world region, 2001
Area Total Males Females
World 67 65 69
Developed countries 75 72 79
Less developed countries 64 63 66
Africa 54 52 55
Asia 67 65 68
Asia (excluding China) 64 63 66
Latin America (and Caribbean) 71 68 74
Europe 74 70 78
North America (U.S. and Canada) 77 74 80
SOURCE : Population Reference Bureau. 2001 World Population Data Sheet. Washington, DC: Population Reference Bureau, 2001.

Also, the gender difference in life expectancy that favors females is larger in the developed countries (seven years) than in the less developed parts of the world (three years). Regionally, North America (the United States and Canada) has the highest life expectancy overall, and for males and females separately. It might be expected that Europe would have this distinction and, indeed, there are a number of European countries with life expectancies higher than in North America; for example, the Scandinavian countries and the nations of Western Europe. However, the European average is pulled down by Russia; in 2001, this large country of 144 million people has a male life expectancy at birth of only 59 years and a female life expectancy at birth of 72 years. Male life expectancy in Russia declined over the last decades of the twentieth century, and shows no indication of improvement. A considerable amount of research has focused on the trend of increasing mortality (and concomitant decreasing life expectancy) among Russian men, pointing to a number of contributing factors: increased poverty since the fall of communism, which leads to malnutrition, especially among older people, and increases susceptibility to infectious diseases; unhealthy lifestyle behaviors, including heavy drinking and smoking, sedentary living, and high-fat diets; psychological stress, combined with heavy alcohol consumption, leading to suicide; and a deteriorating health care system.

With the exception of Russia (and Eastern Europe more generally), life expectancy at birth does not vary much within European and North American populations. However, the less developed countries have considerably more range in mortality, as measured by life expectancy at birth. This can be seen in Table 1, which shows a range in life expectancy at birth among females from 55 in Africa to 74 in Latin America. It is clear that Africa lags behind the rest of the world in achieving improvements in life expectancy. However, even within Africa, large differences in life expectancy exist. Life expectancy at birth (both sexes combined) statistics range from the low seventies (in Mauritius (71), Tunisia (72) and Libya (75)) to the low forties (in Swaziland and Zimbabwe (both 40), Niger and Botswana (both 41)) with one countryRwandahaving an estimated life expectancy at birth of only 39 years.

Life Expectancy at Birth in African Countries: The Role of HIV/AIDS

The HIV/AIDS (human immunodeficiency virus/ acquired immunodeficiency syndrome) epidemic has, thus far, hit hardest in parts of Africa, especially sub-Saharan Africa, which contains approximately 70 percent of the world's population with HIV/AIDS. Many of the African countries with the lowest life expectancies have the highest rates of HIV/AIDS infection. However, this is not always the case; for example, Niger and Rwanda, mentioned above as countries with very low life expectancies, do not have high rates of HIV/AIDS in their populations. Thus, AIDS cannot solely account for low life expectancy in Africa; social and political upheaval, poverty, and the high risk of death due to other infectious (and parasitic) diseases cannot be discounted in the African case. Nevertheless, HIV/AIDS does have a devastating impact on life expectancy in many places in Africa. The United Nations projects that by 2050 the effect of the AIDS epidemic will be to keep life expectancy at birth low in many sub-Saharan African countries, perhaps even lower than that experienced in the latter part of the twentieth century. Figure 1 shows two projected life expectancy at birth statistics for seven sub-Saharan African countries, one based on the assumption that HIV/AIDS continues to claim lives prematurely, and the other based on the optimistic assumption that HIV/AIDS was to disappear immediately. The effect of HIV/AIDS is to keep life expectancy in 2050 at levels well under 50; in the absence of the pandemic, life expectancy at birth would improve to the 65 to 70 year range. The projections based on the continuation of HIV/AIDS mark a sad departure for the demographers who make them. Until the 1990s, projections were based on a taken-for-granted assumption that life expectancy would gradually improve. And, for the most part, subsequent mortality trends backed up that assumption.

Trends in Life Expectancy at Birth in Developed Countries

In the developed countries, the fragmentary data that are available suggest that life expectancy at birth was around 35 to 40 years in the mid-1700s, that it rose to about 45 to 50 by the mid-1800s, and that rapid improvements began at the end of the nineteenth century, so that by the middle of the twentieth century it was approximately 66 to 67 years. Since 1950 gains in life expectancy have been smaller, approximately eight more years have been added (see Table 2).

The major factors accounting for increasing life expectancy, especially in the period of rapid improvement, were better nutrition and hygiene practices (both private and public), as well as enhanced knowledge of public health measures. These advances were particularly important in lowering infant mortality; when mortality is not controlled, the risk of death is high among infants and young children (and their mothers), and the major cause of death is infectious diseases (which are better fought off by well-fed infants and children). Being that a large proportion of deaths occurs to infants and young children, their improved longevity plays a key role in increasing life expectancy at birth. The period from the late 1800s to 1950 in the West, then, saw significant improvement in the mortality of infants and children (and their mothers); it was reductions in their mortality that led to the largest increases in life expectancy ever experienced in developed countries. It is noteworthy that medical advances, save for smallpox vaccination, played a relatively small role in reducing infant and childhood mortality and increasing life expectancy.

Since the middle of the twentieth century, gains in life expectancy have been due more to medical factors that have reduced mortality among older persons. These reductions are harder to achieve than decreases in infant mortality; hence, improvements in life expectancy at birth have slowed down. However, reductions in deaths due to cardiovascular disease, cancer (at least for some kinds), and cerebrovascular disease (strokes)the three major takers-of-life in developed countries as well as in other types of chronic and degenerative disease have gradually taken place, and life expectancy continues to improve. Nevertheless, looking at the twentieth century as a whole, reductions in mortality among younger persons played the major role in increasing life expectancy at birth; for example, 58 percent of the gain in American life expectancy over the century was due to mortality reductions among persons aged under 20 and a further 17 percent can be accounted for by reductions among the age group 20 to 39.

Trends in Life Expectancy in Less Developed Countries

Very little improvement in life expectancy at birth had occurred in the third world by the middle of the twentieth century. Unlike the developed countries, which had a life expectancy at birth of 67

Life expectancy at birth by world region, 19502000
Area Years
  1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
1995
2000
World 46 52 58 61 64 66
Developed Countries 67 70 71 73 74 74
Less Developed Countries 41 48 55 59 62 64
Africa 38 42 46 49 53 54
Asia 41 48 56 60 65 66
Latin America (and Caribbean) 51 57 61 65 69 70
Europe 66 70 71 72 73 73
North America (U.S. and Canada) 69 70 72 75 76 77
SOURCE : Yaukey, David, and Douglas L. Anderton. Demography: The Study of Human Population. Prospect Heights, IL: Waveland, 2001.

years at that time, the third world's life expectancy approximated 41 yearsa difference of 26 years. However, after the end of World War II, life expectancy in the developing countries began to increase very rapidly. For example, between 1950 and 1970, life expectancy at birth improved by 14 years (see Table 2). Mortality decline was faster than in the West during its period of most rapid decline, and it was much faster than in the West over the second half of the twentieth century. By the end of the century, the 26-year difference had been reduced to 10 years (although Africa lags behind the rest of the developing world).

The rapid improvement in life expectancy at birth in the third world occurred for different reasons than in the West. In the West, mortality declined paralleled socioeconomic development. In contrast, in the developing countries, mortality reductions were, in large part, due to the borrowing of Western death-control technology and public health measures. This in part was the result of the post-cold-war that saw the United States and other Western countries assist nonaligned countries with public health and mortality control in order to win their political allegiance. Whatever the political motives, the result was very successful. As in the West, life expectancy at birth was initially improved by controlling the infectious diseases to which infants and children are particularly susceptible and was accomplished by improvements in diet, sanitation, and public health. In addition, the third world was able to benefit from Western technology, such as pesticides, which played a major role in killing the mosquitoes that cause malaria, a leading cause of death in many countries. This exogenously caused reduction in mortality led to very rapid rates of population growth in most third world countries, creating what became known as the "population bomb." It also left these poor countries without a basic health (and public health) infrastructure, making them vulnerable to the effects of cutbacks in aid from foreign (Western) governments and foundations. It is in such a context that many third world countries (especially in sub-Saharan Africa but also in Southeast Asia and the Caribbean) are attempting to deal with the HIV/AIDS crisis, as well as a number of infectious diseases that were believed to have been conquered but have resurfaced through mutations.

It is difficult to predict if life expectancy differences at birth between the more and less developed countries will continue to converge. On the one hand, further increases in life expectancy in the West will be slow, resulting from improvements in the treatment and management of chronic diseases among older people. Theoretically, it would be expected that the third world could, thus, continue to catch up with West. However, new infectious diseases such as HIVS/AIDS and the re-emergence of "old" infectious diseases, sometimes in more virulent or antibiotic resistant forms, are attacking many third world countries that lack the resources to cope.

Differentials in Life Expectancy at Birth

Within populations, differences in life expectancy exist; that is, with regard to gender. Females tend to outlive males in all populations, and have lower mortality rates at all ages, starting from infancy. However, the degree to which females outlive males varies; as seen in Table 1, the difference is around three years in the less developed countries and approximately seven years in developed countries.

Another difference in life expectancy lies in social class, as assessed through occupation, income, or education. This research tends to deal with life expectancy among adults, rather than at birth. The earliest work on occupational differences was done in England using 1951 data; in 1969 the researcher Bernard Benjamin, grouping occupations into five classes, found that mortality was 18 percent higher than average in the lowest class, and 2 percent lower than average in the highest class. In the United States in 1973, Evelyn Kitagawa and Philip Hauser, using 1960 data, found that both higher education and higher income were independently associated with longer life expectancy, that is, having both high income and high education was more advantageous than just having one or the other. This was later replicated by researchers in 1993, with the additional finding that the socioeconomic difference was widening over time.

Data on social class differences in life expectancy are difficult to obtain, even in highly developed countries. A 1999 study by Tapani Valkonen contains exceptionally good data on occupational differences in life expectancy in Finland. Figure 2 shows life expectancy at age 35 for four classes of workers, by gender, for the period of 1971 to 1996. While this figure indicates that life expectancy differences by occupation show a female advantage for all occupations and that male longevity differentials are much bigger than female ones, the most important information conveyed for the purposes here is that the occupational gap in life expectancy increased over the period. This finding concurs with that for the United States.

It is not clear why socioeconomic differences in adult life expectancy are growing in Western populations. The major cause of death responsible for the widening differential is cardiovascular disease; persons of higher social classes have experienced much larger declines in death due to cardiovascular disease than persons of lower classes. It is possible that the widening is only temporary, the result of earlier declines in cardiovascular mortality among higher socioeconomic groups. Or, it may be that the widening reflects increasing polarization in health status and living conditions within Western populations. It does not appear that differences in access to health care are responsible, seeing as the trend appears in countries that both have and do not have national medical/health insurance.

Another difference in life expectancy relates to race/ethnicity. For example, in the United States, the expectation of life at birth for whites is six years higher than for African Americans. However, the difference in life expectancy at age sixty-five is less than two years. The narrowing gap with age suggests that mortality associated with younger age groups is an important factor; this inference is reinforced by high rates of homicide among African Americans, especially young males. Ethnic differences in mortality are not unique to the United States. Among countries with reliable data, it is known that the Parsis in India and the Jews in Israel have lower mortality than other ethnic groups; they share, along with whites in the United States, a place of privilege in the socioeconomic order.

See also: Aids; Causes of Death; Public Health

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ELLEN M. GEE

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Life Expectancy

LIFE EXPECTANCY

LIFE EXPECTANCY at birth is defined as the average number of years that a newborn would live under mortality conditions prevailing at that time. For example, life expectancy for females born in the United States in 1900 was forty-nine years. This means that if mortality conditions existing in 1900 did not change, baby girls born at that time would have lived, on average, until they were forty-nine. In addition to life expectancy at birth, one can also examine life expectancy at other ages. For example, life expectancy at age sixty (which was fifteen years for women in 1900) is the average number of years of life remaining for someone who survives to age sixty, under mortality conditions prevailing at that time. A life table provides information on life expectancy at various ages. When correctly understood, life expectancy provides a useful summary measure of mortality conditions at a particular time in history.

Although life expectancy is a good starting point for discussing mortality patterns, it is important to note two significant limitations of this measure. First, mortality conditions often change over time, so this measure may not reflect the actual experience of a birth cohort. (A birth cohort consists of all individuals born in a particular time period.) To illustrate this point, females born in the United States in 1900 actually lived for an average of fifty-eight years. The discrepancy between life expectancy in 1900 and the average years lived by those born in 1900 occurred because mortality conditions improved as this cohort aged over the twentieth century. The second limitation of life expectancy as a mortality index is its failure to reveal anything about the distribution of deaths across ages. Relatively few of the girls born in 1900 actually died around age forty-nine; 20 percent died before reaching age ten, and over fifty percent were still alive at age seventy. In other words, the average age at death does not mean that this was the typical experience of individuals. Given the limited information contained in the life expectancy statistic, a satisfying discussion of changing mortality experiences in American history must use additional information on the timing and patterning of deaths.

To calculate the life expectancy for a population, one would ideally have a complete registration of deaths by age and a complete enumeration of the population by age. With these data, it is a straightforward exercise to calculate age-specific death rates and to construct the life table. In the United States, mortality and population data of good quality are available for most of the twentieth century, so we can report with confidence life expectancy patterns over this period. Because of data limitations, there is less certainty about mortality conditions in earlier American history. However, a number of careful and creative studies of the existing death records for some communities (or other populations) provide enough information to justify a discussion of changing mortality conditions from the colonial era to the present.

Colonial America

The first life table for an American population was published by Edward Wigglesworth in 1793, and was based on mortality data from Massachusetts, Maine, and New Hampshire in 1789. Until the 1960s, this life table, which reported an expectation of life of about thirty-five years for New England, was the primary source of information on the level of mortality in America prior to the nineteenth century. Since the 1960s, however, quantitative historians have analyzed a variety of mortality records from various sources, providing a more comprehensive and varied picture of mortality conditions in the colonial era.

These historical studies have presented conflicting evidence regarding the trend in life expectancy between the founding of the colonies and the Revolutionary War (1775–1783)—some reported a significant decline over time, while others argued that life expectancy was increasing. One explanation for the different findings is that there were large fluctuations in death rates from year to year (as epidemics broke out and then rescinded) and significant variations across communities. Based on the most reliable data, it seems likely that overall conditions were not much different around 1800 than they were around 1700. After considerable work to analyze data from various sources, the Wigglesworth estimate of life expectancy around thirty-five years in New England during the colonial period appears reasonable. Although this is an extraordinarily low life expectancy by contemporary standards, it reflects a higher survival rate than the population of England enjoyed at that time. Life expectancy in the Southern and Mid-Atlantic colonies, where severe and frequent epidemics of smallpox, malaria, and yellow fever occurred throughout the eighteenth century, was significantly lower than in New England.

There are two primary reasons life expectancy was so low in colonial America. First, the average years lived reflects the impact of many babies dying in infancy or childhood. Studies from various communities found that between 10 and 30 percent of newborns died in the first year of life (now only seven out of 1,000 die before age one). Those who survived the perilous early years of life and reached age twenty could expect, on average, to live another forty years. The second factor was that, lacking public health and medical knowledge of how to prevent or treat infectious diseases, the population was extremely vulnerable to both endemic diseases (malaria, dysentery and diarrhea, tuberculosis) and epidemics (smallpox, diphtheria, yellow fever). An indication of the deadly potential of epidemics is seen in Boston in 1721, when 10 percent of the population died in one year from a smallpox out-break, and in New Hampton Falls, New Hampshire, in 1735, when one-sixth of the population died from a diphtheria epidemic. Despite the dramatic effects of epidemics, it was the infectious endemic diseases that killed most people in colonial America.

Nineteenth Century

Life expectancy increased significantly over the nineteenth century, from about thirty-five years in 1800 to forty-seven years in 1900. However, this increase was not uniform throughout the century. In fact, death rates may have increased during the first several decades, and by midcentury, life expectancy was not much higher than it had been at the beginning of the century. After the Civil War (1861–1865) there was a sustained increase in life expectancy, and this upward trend would continue throughout the twentieth century.

Two conflicting forces were influencing mortality patterns prior to the Civil War. On one hand, per capita income was increasing, a trend that is generally associated with increasing life expectancy. On the other hand, the proportion of the population living in urban areas was also increasing, and death rates were higher in urban than in rural environments. An examination of data from 1890, for example, found death rates 27 percent higher in urban areas than in rural areas. This excess mortality in urban areas was common in almost all societies before the twentieth century, and is explained by the greater exposure to germs as population density increased. Studies of nineteenth century death rates in such cities as New York, Philadelphia, Baltimore, Boston, and New Orleans document the high risks that urban residents had of contracting such infectious diseases as tuberculosis, pneumonia, cholera, typhoid, and scarlet fever. It was not until after the 1870s that the health picture in American cities improved and life expectancy for the entire population began its steady ascent.

It is clear that increasing life expectancy in the last third of the nineteenth century was due to decreasing death rates from infectious diseases. But why did death rates decline? Medical historians have given considerable attention to three possible explanations: improving medical practices, advances in public health, and improved diet, housing, and personal hygiene. Most agree that medicine had little to do with the decline in infectious diseases in the nineteenth century (although it later played an important role when penicillin and other antibiotic drugs became widely used after 1940). Physicians in the nineteenth century had few specific remedies for disease, and some of their practices (bleeding and purging their patients) were actually harmful. Some evidence suggests that diet and personal hygiene improved in the late nineteenth century, and these changes may account for some decline in diseases. The greatest credit for improving life expectancy, however, must go to intentional public health efforts. With growing acceptance of the germ theory, organized efforts were made to improve sanitary conditions in the large cities. The construction of municipal water and sewer systems provided protection against common sources of infection. Other important developments included cleaning streets, more attention to removal of garbage, draining stagnant pools of water, quarantining sick people, and regulating foodstuffs (especially the milk supply).

Twentieth Century

The gain in life expectancy at birth over the twentieth century, from forty-seven to seventy-seven years, far exceeded the increase that occurred from the beginning of human civilization up to 1900. This extraordinary change reflects profound changes both in the timing of deaths and the causes of deaths. In 1900, 20 percent of newborns died before reaching age five—in 1999, fewer than 20 percent died before age sixty-five. In 1900, the annual crude death rate from infectious diseases was 800 per 100,000—in 1980 it was thirty-six per 100,000 (but it crept back up to sixty-three per 100,000 by 1995, because of the impact of AIDS). At the beginning of the twentieth century the time of death was unpredictable and most deaths occurred quickly. By the end of the century, deaths were heavily concentrated in old age (past age seventy), and the dying process was often drawn out over months.

In 1999, the Centers for Disease Control ran a series in its publication Morbidity and Mortality Weekly Report to highlight some of the great public health accomplishments of the twentieth century. Among the most important accomplishments featured in this series that contributed to the dramatic increase in life expectancy were the following:

Vaccinations. Vaccination campaigns in the United States have virtually eliminated diseases that were once common, including diphtheria, tetanus, poliomyelitis, smallpox, measles, mumps, and rubella.

Control of infectious diseases. Public health efforts led to the establishment of state and local health departments that contributed to improving the environment (clean drinking water, sewage disposal, food safety, garbage disposal, mosquito-control programs). These efforts, as well as educational programs, decreased exposure to micro-organisms that cause many serious diseases (for example, cholera, typhoid, and tuberculosis).

Healthier mothers and babies. Deaths to mothers and infants were reduced by better hygiene and nutrition, access to prenatal care, availability of antibiotics, and increases in family planning programs. Over the century, infant death rates decreased by 90 percent and maternal mortality rates decreased by 99 percent.

Safer workplaces. Fatal occupational injuries decreased 40 percent after 1980, as new regulations greatly improved safety in the mining, manufacturing, construction, and transportation industries.

Motor vehicle safety. Important changes affecting vehicle fatalities include both engineering efforts to make highways and vehicles safer and public campaigns to change such personal behaviors as use of seat belts, use of child safety seats, and driving while drunk. The number of deaths per million vehicle miles traveled was 90 percent lower in 1997 than in 1925.

Recognition of tobacco use as a health hazard. Anti-smoking campaigns since the 1964 Surgeon General's report have reduced the proportion of smokers in the population and consequently prevented millions of smoking-related deaths.

Decline in deaths from coronary heart disease and stroke.

Educational programs have informed the public of how to reduce risk of heart disease through smoking cessation, diet, exercise, and blood pressure control. In addition, access to early detection, emergency services, and better treatment has contributed to the 51 percent decrease since 1972 in the death rate from coronary heart disease.

Despite the advances in life expectancy between 1900 and the present, several striking differences in longevity within the population have persisted. Researchers have given a lot of attention to three differentials in life expectancy—sex, race, and social class. The female advantage over males in life expectancy increased from 2.0 years in 1900 to 7.8 years in 1975. Most of this increasing gap is explained by the shift in cause of death from infectious diseases (for which females have no survival advantage over males) to degenerative diseases (where the female advantage is large). Also, the decline in deaths associated with pregnancy and childbearing contributed to the more rapid increase in life expectancy of females. After 1975, the gender gap in life expectancy decreased, and by 2000 it was down to 5.4 years. The primary explanation for the narrowing gap in the last decades of the twentieth century is that female cigarette smoking increased rapidly after mid-century and became increasingly similar to the male pattern. In other words, females lost some of the health advantage over males that they had when they smoked less.

The racial gap in life expectancy was huge in 1900—white Americans outlived African Americans by an average of 14.6 years. This gap declined to 6.8 years by 1960 (when the civil rights movement was beginning), but declined only slightly over the rest of the century (in 2000 the racial gap was still 5.6 years). A particularly telling indicator of racial inequality is the infant mortality rate, which continues to be more than twice as large for African Americans as for white Americans (13.9 per 1,000 versus 6.0 per 1,000 in 1998). Much of the racial disparity is explained by the persistent socioeconomic disadvantage of African Americans (lower education and lower income). Social resources are related to individual health behavior (diet, exercise, health care), and to the environment within which individuals live (neighborhood, occupation). After adjusting for family income and education, African Americans still experience some excess deaths compared to white Americans. A possible cause of this residual difference may be racial discrimination that causes stress and limits access to health care.

Active Life Expectancy

The marked declines in death rates that characterized the first half of the twentieth century appeared to end around the early 1950s, and life expectancy increased by only a few months between 1954 and 1968. A number of experts concluded that we should not expect further increases in life expectancy. They reasoned that by this time a majority of deaths were occurring in old age due to degenerative diseases, and there was no historical evidence that progress could be made in reducing cardiovascular diseases and cancer. But this prediction was wrong, and life expectancy continued its upward climb after 1970. As death rates for older people began to fall, a new concern was expressed. Were the years being added to life "quality years," or were people living longer with serious functional limitations? Would we experience an increasingly frail older population?

The concern over quality of life in old age led demographers to develop a new measure, active life expectancy. Using data on age-specific disability rates, it is possible to separate the average number of years of life remaining into two categories—active years (disability-free years) and inactive years (chronic disability years). Using data since 1970, researchers have tried to determine whether gains in life expectancy have been gains in active life, gains in inactive life, or gains in both. There is some uncertainty about the 1970s, but since 1980 most of the gains have been in active life. Age-specific disability rates have been declining, so the percentage of years lived that is in good health is increasing. Two factors have contributed to increasing active-life expectancy. First, over time the educational level of the older population has risen, and disability rates are lower among more highly educated people. Second, medical advances (for example, cataract surgery, joint replacement) have reduced the disabling effect of some diseases. Thus, the good news is that at the end of the twentieth century, individuals were living both longer and healthier lives than ever before in history.

BIBLIOGRAPHY

CDC. "Ten Great Public Health Achievements—United States, 1900–1999." Morbidity and Mortality Weekly Report 48 (1999): 241–243.

Crimmins, Eileen M., Yasuhiko Saito, and Dominique Ingegneri. "Trends in Disability-Free Life Expectancy in the United States, 1970–90." Population and Development Review 23 (1997): 555–572.

Hacker, David J. "Trends and Determinants of Adult Mortality in Early New England." Social Science History 21 (1997): 481–519.

Kunitz, Stephen J. "Mortality Change in America, 1620–1929." Human Biology 56 (1984): 559–582.

Leavitt, Judith Walzer, and Ronald L. Numbers, eds. Sickness and Health in America: Readings in the History of Medicine and Public Health. 3d ed. Madison: University of Wisconsin Press, 1997.

Vinovskis, Maris A. "The 1789 Life Table of Edward Wiggles-worth." Journal of Economic History 31 (1971): 570–590.

PeterUhlenberg

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Life Expectancy

LIFE EXPECTANCY

Life expectancy is a summary measure of the average number of additional years a group of people can expect to live at a given exact age. Life expectancy figures are derived from a life table. Life table methodology has been developed for human populations to determine average lengths of life, of healthy life, of married life, and of working life. Indeed, life tables have recently been used to determine the average career length of professional athletes. And life tables have been used to determine the average length of life of nonhumans, including automobiles and animals.

Life expectancy at birth is derived by applying a set of age-specific mortality rates to a hypothetical group of newborns. For example, with data for the year 2000, we could impose the current age-specific mortality patterns of individuals from birth through the oldest ages onto a group of newborns. These calculations are based on mortality rates prevailing today, not in the future; individuals born today may actually experience lower (or possibly higher) mortality one hundred years hence, when they reach age one hundred. Thus, life expectancies represent a current, and not future, measure of survival. Further, period-specific events influence life expectancies. For instance, mortality due to human immunodeficiency virus (HIV), a cause of death that was not evident before the 1980s, affects current life expectancy estimates.

Life expectancy is most commonly used for cohorts of newborns, but can also be reported for other ages, as Table 1 depicts. The first row reveals that individuals born in the United States in 1998 can expect to live an average of 76.7 years, the highest figure ever achieved by individuals in this country. Indeed, in 1900, the average life expectancy at birth was just 47.3 years (Anderson).

The table shows the remaining life expectancy for selected ages. The remaining life expectancy is an additional 72.4 years at age 5 and 3.5 years at age 95. With increasing age, remaining years of expected life generally decreases because individuals have already lived through previous years; but the total life expectancy (age plus remaining years) increases because individuals have already survived earlier ages. Thus, at age 75, the remaining life expectancy is 11.3 years, while the total life expectancy is 86.3 years.

Life expectancy is often confused with life span, a demographic term that refers to the maximum number of years a person can be expected to live under the most ideal circumstances (Nam). Life span for humans is about 120 years. In contrast, life expectancy at birth for individuals in the most long-lived nations around the world is approximately eighty years.

A number of factors influence life expectancies, including socioeconomic status, health behaviors, chronic conditions, sex, race, and ethnicity. Indeed, life expectancy figures are often calculated separately by sex and by race/ethnicity. Life expectancy estimates contribute to aging research by providing an excellent summary measure of the length of life of current and future populations.

Richard G. Rogers Robert A. Hummer Patrick M. Krueger

See also Life Span Extension; Longevity: Social Aspects; Population Aging.

BIBLIOGRAPHY

Anderson, R. N. "United States Life Tables, 1997." National Vital Statistics Reports 47 (1999): 140.

Murphy, S. L. "Deaths: Final Data for 1998." National Vital Statistics Reports 48 (2000): 1106.

Nam, C. B. Understanding Population Change. Itasca, Ill.: FE Peacock Publishers, 1994.

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Life Expectancy

Life Expectancy

The term life expectancy is used to describe the average life span of an individual. Life expectancy can vary considerably in different areas of the world. Compared to other advanced countries, for example, people in the United States "die earlier and spend more time disabled" (WHO, 2000). Factors that affect life expectancy in the United States include: (1) the HIV epidemic, (2) cancers relating to tobacco, (3) high rates of coronary heart disease , (4) poor health among minority groups living in rural areas, and (5) high levels of violence.

According to the World Health Organization (WHO) the Japanese have the longest healthy life expectancy (74.5) among 191 countries the organization examined in 2000. In contrast, the shortest life expectancy (26 years) exists among the people of Sierra Leone. These figures were based on a new method of calculating healthy life expectancy called Disability Adjusted Life Expectancy (DALE), which was developed by the WHO. DALE summarizes the expected number of years to be lived in adequate health, rather than just the expected number of years lived.

According to DALE the United States ranks twenty-fourth, with an average life expectancy of 70.0 years for babies born in 1999. (Examined by gender, U.S. female babies in 1999 could expect 72.6 years of life, while male babies could expect only 67.5 years.) Life expectancy based on DALE for other countries are: Australia, 73.2 years; France, 73.1; Sweden, 73.0; Spain, 72.8; Italy, 72.7; Greece, 72.5; Switzerland, 72.5; Monaco, 72.4; and Andorra, 72.3.

The world's average life expectancy at birth rose to 67 years in 1998 (from 61 years in 1980). Although individual countries vary in average life-span years, the average number of years has increased due to increases in intake of nutritious food, primary health care (including safe water, sanitation, and immunizations), and education.

see also Infant Mortality Rate; Maternal Mortality Rate.

Daphne C. Watkins

Internet Resources

World Bank. "Life Expectancy." Available from <http://www.worldbank.org/depweb/english/modules>

World Health Organization (2000). "Japan Number One in New 'Healthy Life' System." Available from <http://www.int/inf-pr-2000/en/pr2000-life.html>

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life expectancy

life ex·pec·tan·cy • n. the average period that a person may expect to live.

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