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This term is used by demographers when referring to an increase over time in the proportion of older persons in the population. It does not necessarily imply an increase in life expectancy, that "people are living longer that they used to," or that they are dying on average at older ages, although these phenomena are usually observed in association with aging of the population. From the demo-graphic perspective, the principal determinant of aging in the population is a decline in the birth rate. When fewer children are born than in earlier years, the consequence is a decline in the proportion of younger persons, and it necessarily follows that there is an increase in the proportion of older persons. The proportion is further weighted toward older persons by improved survival rates from conditions that can cause death in early life, that is, in infancy and childhood and among younger adults.
In the industrialized nations, a more recent phenomenon has been an increase in life expectancy that has accompanied improved survival rates, and this, of course, contributes further to the increased proportion of older persons. However, if birth rates remain high, there is also an increase in the numbers, and therefore in the proportion, of infants and children in the population. This happened in many industrialized nations after World War II, during the "baby boom" period, roughly 1946 to 1960. There was a secondary surge in birth rates when the children born during that period reached peak reproductive ages (the echo of the baby boom) in the 1980s and 1990s. The baby boom and its echo temporarily retarded and in some nations even briefly reversed the long-term trend toward smaller families. This trend began in the Western industrial nations before the 1920s and continued through the 1930s, aggravated by the Great Depression, but persisting through good times as well as bad.
Although it is true that in the past, declining birth rates were primarily responsible and reductions in mortality rates played little part in the process of aging the population, in the future it can be expected that increases in life expectancy will contribute more to the process. Little further reduction in mortality rates in the first half of life can be expected to occur, so increased life expectancy, or mortality rate reduction, in the second half of life, from age forty-five onward, is beginning to exert more influence on the structure of the population (the shape of the population pyramid). This too is contributing to an increase in the proportion of older persons in the population, and over the coming decades, other things being equal, this will play an increasingly prominent role in the process.
JOHN M. LAST
Author Info: JOHN M. LAST, The Gale Group Inc., Macmillan Reference USA, New York, Gale Encyclopedia of Public Health, 2002
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