1. Carolina Population Center and Department of Biostatistics, University of North Carolina, Chapel Hill, North Carolina 27514-3997
2. International Statistical Programs Center, U.S. Bureau of the Census, Suitland, Maryland
3. Population Studies Center, University of Michigan, Ann Arbor, Michigan 48109
4. Carolina Population Center and Department of Sociology, University of North Carolina, Chapel Hili, North Carolina 27514-3997