|
| ||||||
MEDIA CENTER How Long Do We Live? NEW YORK (27 May 2002) — Human longevity—one of the oldest and most important indicators in demography—may be overestimated by up to a few years in contemporary countries with high life expectancy, say two demographers who have analyzed past and future trends. Calling conventional calculations of current life expectancy at birth potentially "misleading," John Bongaarts and Griffith Feeney present their findings in the latest issue of Population and Development Review, a peer-reviewed journal published by the Population Council. "We are not living as long as we thought we were," Bongaarts and Feeney conclude, based on a detailed analysis of changing age patterns of adult mortality. Estimates of current life expectancy at birth are now routinely provided by national and international statistical agencies. For example, the United Nations Population Division publishes such estimates for all countries in the world, ranging from a low of 37 years in Sierra Leone to a high of 80 years in Japan for the period 1995–2000. Life expectancy at birth worldwide is estimated at 63 years for males and 67 years for females. Life expectancy can be calculated as the average age at death if a group of individuals is observed from birth until the last person dies. According to Bongaarts and Feeney, this calculation is unsatisfactory for many purposes because it provides a summary of mortality over nearly a century, an interval during which mortality conditions are likely to have changed. Life expectancy at birth calculated in this way is not useful for studying mortality change over periods of less than a century. Demographers therefore rely on so-called mortality life tables to obtain current estimates of life expectancy. But, according to Bongaarts and Feeney, these life table calculations are flawed: when the mean age at death is rising, current life expectancy at birth as conventionally calculated overestimates life expectancy. A similar bias in the opposite direction occurs when the mean age at death is falling. They refer to these effects as mortality tempo biases and provide a formula for determining their magnitude. Estimates of this upward bias range from 1.6 years for the United States and Sweden to 3.3 years for Japan for the period of 1980–95. John Bongaarts is vice president, Population Council, and director of the Policy Research Division. Griffith Feeney is a consultant to the Population Division of the United Nations. Population and Development Review, Vol. 28, No. 1, March 2002, also includes Notes and Commentary, Data and Perspectives, Archives, Book Reviews, and Documents.
|
