Praag, B.M.S. van, Dalen, H. van, & Lutz, W. <https://pure.iiasa.ac.at/view/iiasa/190.html> ORCID: https://orcid.org/0000-0001-7975-8145 <https://orcid.org/0000-0001-7975-8145>  (1994).  Aging Populations and Social Challenges. Paper presented on IIASA's 20th Anniversary.   IIASA Collaborative Paper. IIASA, Laxenburg, Austria: CP-94-007