Life expectancy

Life expectancy is a concept in demography that measures the mean number of years of life for babies born in a specified year. It is heavily influenced by the rate of infant mortality. But when infant mortality drops below 100 deaths per 1000 births, life expectancy switches and depends on the lifetimes of older people. It is a common fallacy to read that "life expectancy was 40 years" and deduce that few people lived beyond age 40; the correct reading is that many infants died.

Historical trends

Riley (2005) uses estimates from some 700 national studies of survival since the 18th century to create a broad picture of regional and global life expectancy gains across space and time and to examine the implications of that picture. At the initiation of their health transitions, most countries had a life expectancy between 25 and 35 years. Countries that began later made gains at a faster pace. Those faster gains are usually associated with the dissemination of Western medicine, but rapid gains occurred in the period 1920-50, largely before the availability of antibiotics or modern vaccines. Especially rapid gains came in the years immediately after World War II in countries where the leading causes of death were communicable diseases that could be managed with antibiotics, but also in countries where the leading causes of death were degenerative organ diseases. Both periods of rapid gain in the 20th century await satisfactory explanation.

Convergence in late 20th century

Becker e al (2005) use estimates of gains in life expectancy along with per capita income statistics for a more valid analysis of cross-country welfare equality. Between 1960 and 2000, the mortality rate fell in many countries due to technological improvements in health care. Poorer countries utilized the technology and knowledge previously available in more wealthy nations to reduce the mortality rate of young people by providing more effective medical intervention to those afflicted with infectious, respiratory, or digestive diseases. Econometric analysis of income per capita from Penn World Tables and life expectancy data from the World Bank indicates that inequality of welfare between countries has been reduced.

To explain these changes, demographers have used longitudinal studies. They support the proposition that the extent and severity of chronic conditions in middle and late life are to a large extent the outcome of environmental insults at early ages, including in utero. Data from the Early Indicators Project, undertaken at the Center for Population Economics at the University of Chicago, suggest that the range of differences in exposure to disease narrowed greatly over the course of the 20th century, that age-specific prevalence rates of chronic diseases were much lower at the end of the 20th century than they were at the beginning of the 20th century or during the last half of the 19th century, and that there was a significant delay in the onset of chronic diseases over the course of the 20th century. These trends appear to be related to changes in levels of environmental hazards and in body size. These findings have led investigators to posit a synergism between technological and physiological improvements. This synergism contributed to reductions in inequality in real income, body size, and life expectancy during the 20th century.

Upper limits?

There has been much speculation about an upper limit of average life expectancy--90? 100? higher? Is expectancy now approaching this hypothetical limit? For 160 years, best-performance life expectancy has steadily increased by a quarter of a year per year, an extraordinary constancy of human achievement. Mortality experts in the past often asserted life expectancy is close to its ceiling; these experts have repeatedly been proven wrong. The apparent leveling off of life expectancy in various countries is an artifact of laggards catching up and leaders falling behind.

Regional studies

Decline in Russia

In the 1990s life expectancy in Russia fell an astonishing six years. Statistical analysis indicates that one-quarter of the increase in mortality was due to an increase in alcohol consumption and one-quarter was a consequence of stress due to economic uncertainty.

Latin America

New and consistent series for Latin American real incomes, life expectancy, and adult literacy over the 20th century reveal that living standards rose most rapidly between the 1930's and 1970's, a period characterized by increased state intervention and reduced trade openness. Within the region, Brazil and Mexico advanced most over the century as a whole despite the early start made by Argentina and Chile, although convergence between larger countries was accompanied by divergence from smaller ones. There was no sustained narrowing of the income gap with the United States at all between 1900 and 2000 but some convergence in living standards due to improved life expectancy. The authors' estimates of regional per capita income also permit a clearer comparison with both Europe and Asia. The major advances in living standards achieved in the middle decades of the century were closely related to early industrialization, rapid urbanization, and the extension of primary health and education. Subsequent economic volatility and fiscal fragility limited further increases in living standards, undermining social consensus on development strategy.

Bibliography

• Becker, Gary S.; Philipson, Tomas J.; and Soares, Rodrigo R. "The Quantity and Quality of Life and the Evolution of World Inequality." American Economic Review 2005 95(1): 277-291. Issn: 0002-8282 Fulltext: in Ebsco
• Edwards, Ryan D. and Tuljapurkar, Shripad. "Inequality In Life Spans And A New Perspective On Mortality Convergence Across Industrialized Countries." Population And Development Review 2005 31(4): 645-674. Issn: 0098-7921

History

• Fogel, Robert W. The Escape from Hunger and Premature Death, 1700-2100: Europe, America, and the Third World (2004)
• Fogel, Robert W. "Changes In The Disparities In Chronic Diseases During The Course Of The 20th Century." Perspectives In Biology And Medicine 2005 48(1 Supplement): S150-S165. Issn: 0031-5982 Fulltext: in Project Muse
• Oeppen, Jim, and James W. Vaupel, "Enhanced: Broken Limits to Life Expectancy," Science (May 10 2002): Vol. 296. no. 5570, pp. 1029 - 1031
• Riley, James C. Rising Life Expectancy: A Global History (2001)
• Riley, James C. "The Timing And Pace Of Health Transitions Around The World." Population and Development Review 2005 31(4): 741-764. ISSN: 0098-7921

Statistics

• Helmut Wendel, and Christopher S Wendel. Vital Statistics of the United States Births, Life Expectancy, Deaths and Selected Health Data (2006)

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External links

• Bibliography of 700+ sources by Riley