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