1. S. J. Olshansky is in the School of Public Health, University of Illinois at Chicago and Center on Aging, The University of Chicago, Chicago, IL 60637, USA.
2. B. A. Carnes is at the National Opinion Research Center, Center on Aging, The University of Chicago, Chicago, IL 60637, USA.
3. A. Désesquelles is at the Institut National D'Études Démographiques (INED), 75980 Paris cedex 20, France.