On the age dynamics of learned societies-taking the example of the Austrian Academy of Sciences.

In a hierarchical organisation of stable size the annual intake is strictly determined by the number of deaths and a statutory retirement age (if there is one). In this paper we reconstruct the population of the Austrian Academy of Sciences from 1847 to 2005. For the Austrian Academy of Sciences we observe a shift of its age distribution towards older ages, which on the one hand is due to rising life expectancy, i.e., a rising age at death, as well as to an increased age at entry on the other hand. Therefore the number of new entrants has been fluctuating considerably-especially reflecting several statutory changes-and the length of tenure before reaching the age limit has declined during the second half of the last century.Based on alternative scenarios of the age distribution of incoming members-including a young, an old, the 'current' and a mixed-age model-we then project the population of the Austrian Academy and its ageing forward in time. Our results indicate that the 'optimum policy' would be to elect either young or old aged new members.