1. Julia Mobley Professor of Economics; Hendrix College; Conway AR 72032 U.S.A.
2. Professor of Economics, Department of Economics; Deakin University; Burwood 3125 Victoria Australia
3. C.F. Rehnborg Chair in Disease Prevention, Professor of Medicine, of Health Research and Policy and of Statistics, and Co-Director, METRICS; Stanford University; Stanford CA 94305 U.S.A.