Sanderson Warren C, Scherbov Sergei
Department of Economics, State University of New York at Stony Brook, Stony Brook, New York 11794-4384, USA.
Nature. 2005 Jun 9;435(7043):811-3. doi: 10.1038/nature03593.
Increases in median ages, the most commonly used measure of population ageing, are rapid in today's wealthier countries, and population ageing is widely considered to be a significant challenge to the well-being of citizens there. Conventional measures of age count years since birth; however, as lives lengthen, we need to think of age also in terms of years left until death or in proportion to the expanding lifespan. Here we propose a new measure of ageing: the median age of the population standardized for expected remaining years of life. We show, using historical data and forecasts for Germany, Japan and the United States, that although these populations will be growing older, as measured by their median ages, they will probably experience periods in which they grow younger, as measured by their standardized median ages. Furthermore, we provide forecasts for these countries of the old-age dependency ratio rescaled for increases in life expectancy at birth. These ratios are forecasted to change much less than their unscaled counterparts, and also exhibit periods when the population is effectively growing younger.
中位数年龄的增加是当今较富裕国家人口老龄化最常用的衡量标准，且增速很快，人口老龄化被广泛认为是这些国家公民福祉面临的重大挑战。传统的年龄衡量方法是计算自出生以来的年份；然而，随着寿命延长，我们还需要从离死亡还剩的年份或相对于不断延长的寿命的比例来考虑年龄。在此，我们提出一种新的老龄化衡量标准：根据预期剩余寿命进行标准化的人口中位数年龄。我们利用德国、日本和美国的历史数据及预测表明，尽管按照中位数年龄衡量，这些人口将老龄化，但按照标准化中位数年龄衡量，他们可能会经历年龄变小的时期。此外，我们还对这些国家的老年抚养比进行了预测，该抚养比根据出生时预期寿命的增加进行了重新调整。预计这些比率的变化远小于未调整的对应比率，并且也会出现人口实际上在变年轻的时期。
