Life Expectancy

Life expectancy is an estimate of the average number of additional years a person of a given age can expect to live. The most common measure of life expectancy is life expectancy at birth. Life expectancy is a hypothetical measure. It assumes that the age-specific death rates for the year in question will apply throughout the lifetime of those born in that year. The process, in effect, projects the age-specific mortality rates for a given period over the entire lifetime of the population born (or alive) during that time. The measure differs considerably by sex, age, race, and geographic location. Therefore, life expectancy is commonly given for specific categories, rather than for the population in general. For example, the life expectancy for white females in the United States who were born in 2003 is 80.5 years; that is, white female infants born in the United States in the year 2003 would be expected to live, on average, 80.5 years.

[Page 594]Life expectancy reflects local conditions. In less developed countries, life expectancy at birth is relatively low compared with more developed countries. In poor countries, life expectancy at birth is often lower than life expectancy at 1 year of age, because of a high infant mortality rate (commonly due to infectious disease or lack of access to a clean water supply).

Life expectancy is calculated by constructing a life table. The data required to construct a life table are the age-specific death rates for the population in question, which requires enumeration data for the number of people, and the number of deaths at each age for that population. By applying the age-specific death rates that were observed during the period, the average life expectancy for each of the age groups within this population is calculated. Life expectancy at any given age is the average number of additional years a person of that age would live if the agespecific mortality rates for that year continued to apply. For example, U.S. males who were 50 years old in 2003 had an average additional life expectancy of 28.5 years.

The potential accuracy of the estimated life expectancy depends on the completeness of the [Page 595]census and mortality data available for the population in question. The completeness of this data varies from country to country. In the United States, official complete life tables based on registered deaths have been prepared since 1900, in connection with the decennial census. Beginning in 1945, annual abridged U.S. life tables have been published based on the annual death registration and estimates of the population. Complete life tables show life expectancy for every year of age, and abridged tables show life expectancy for 5or 10-year age groups, rather than for single years. The U.S. National Center for Health Statistics is the agency that currently publishes national life tables, as well as state and regional life tables. The United Nations publishes national life tables for many countries in its Demographic Yearbook.

The ‘healthy life expectancy’ or ‘disability-free life expectancy’ is the average number of years a person is expected to live in good health, or without disability, given current age-specific mortality rates and disease and disability prevalence rates. Calculation of these figures requires reliable health statistics, as well as mortality and census data.

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