Forschungsgruppe ORCOS
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Dynamics and Control of Age Structured Populations with Fixed Size

FWF, P20408, (2008 − 2011), Project leader: G. Feichtinger


Almost all parts of the world are faced with aging societies. These demographic developments are a major challenge to policy and science.The causes of the changes in the age pyramid are low birth rates and decreasing mortality at older ages. Consequently, we live in increasingly old populations and many subpopulations, as for example learned societies are no exceptions.

The first part of the project was devoted to the analysis of the demographic development of various European learned societies. Academies of Sciences thereby form interesting case studies of subpopulations, which face rapid aging problems. On the one hand, members of learned societies have a remarkable high longevity, which contributes to aging in the upper age groups. On the other hand, the aging of the Academies of Sciences is even increased through the election of old members. Our results indicate that scholars show a remarkable high longevity, especially in the 20th Century. They prove to have not only a higher life expectancy than any particular national population, but also higher than other social groups with low mortality profiles (e.g. higher social classes, tertiary educated population) in the respective countries.
A young age structure and a high number of vacant positions represent conflicting objectives.

The second part of our project was dedicated exactly to this trade-off. Using methods of dynamic optimization, we have shown that it is optimal to choose a mix of young and old recruits. This astonishing result corresponds in no way to the current election policies, such as practiced in the OEAW.

In the third part of this project, the age-specific immigration profile was determined that minimizes the dependency ratio of a population facing below-replacement fertility. It should be noted that the size and age structure of the population depend very much on the age of the immigrants. Under very general assumptions on fertility and mortality in the population, we showed that the optimal age of immigrants lies in the mid-30s. Earlier work claimed that this age is at 20. The shift to higher ages is due to the higher number of expected offspring of a 20-year-old.