In: E. Kikilias, C. Bagavos, P. Tinios, M. Chletsos (eds); Demographic Ageing: Proceedings of a European Union-sponsored Symposium on "The Challenge of Demographic Ageing and the Knowledge-Based Society"; 2-3 November 2000, Ethniko Institouto Ergasias, Athens, Greece pp.37-50 (2000)