[1] Georgetown Univ, Ctr Populat & Hlth, Washington, DC 20057 USA
[2] Univ Michigan, Ctr Populat Studies, Inst Social Res, Ann Arbor, MI USA
[3] RAND Corp, Arlington, VA USA
[4] NICHHD, DBSB, Bethesda, MD USA
[5] Univ Penn, Ctr Populat Studies, Philadelphia, PA 19104 USA
[6] Populat Reference Bur, Domest Program, Washington, DC USA
[7] Univ N Carolina, Dept Epidemiol, Chapel Hill, NC USA
[8] Natl Ctr Hlth Stat, Hyattsville, MD 20782 USA