While age has traditionally been measured as the time since birth, researchers from IIASA and VID have recently proposed alternative measures that are based instead on the expected time to death. The basic idea behind this is that due to increasing life expectancy, a 60 year old man, for instance, today cannot be considered to be at a comparable stage of his life cycle as a man of 60 years of age several decades ago: he is on average of better health status and can count on many more years of life to come, which will also influence his behaviour in term of investments. Hence, one may argue that both the biological and social dimensions of age are not only a function of time since birth but also of the expected time to death. Consequently, the traditional definition of age should be complemented by one that reflects the changing life expectancy at the level of individuals as well as populations.
The alternative indicators of age and ageing listed here are both based on conventional life tables. The “proportion of the population that has a remaining life expectancy of 15 years or less” is calculated in the following way: from a period life table we select all single-year age groups that have a remaining life expectancy of 15.0 or less years and calculate what proportion of the total population has ages that fall into this category. This new measure can be viewed as the complement of indicators such as the proportion of the population above age 65 measured in the conventional way. The “population average remaining years of life” is the complement of the conventional mean age of the population in reflecting the average years to death of persons alive today. It is calculated by weighting the remaining life expectancy of all ages in a period life table with the proportions of people at those ages in the population under consideration.
The map shown for the regional distribution of the proportion of the population that has a remaining life expectancy of 15 years or less reflects two demographic dimensions: the age structure of the population and the current period life expectancy. Countries with a rather old population and a low life expectancy have the highest proportions and countries with young populations and high life expectancy the lowest ones. These two dimensions partly make up for each other so that in the middle range there are combinations of both younger age structures with lower life expectancy as well as older age structures with a higher one. The appearing geographic pattern shows an East/West divide with the countries of the former Soviet Union showing by far the highest proportions of population with life expectancies of 15 or less years.
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Sanderson, W. and S. Scherbov. 2005. Average remaining lifetimes can increase as human populations age. Nature, Vol. 435: 811-813