1. Center for Biostatistics in AIDS Research, Harvard School of Public Health, Boston, Massachusetts.
2. Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland.
3. Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts.
4. University of Alabama at Birmingham School of Medicine, Birmingham, Alabama.
5. Children's Memorial Hospital, Chicago, Illinois.
6. University of Illinois at Chicago College of Medicine, Chicago, Illinois.