1. Department of Dermatology and Department of Biostatistics and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19102.
2. Division of Pediatric General Thoracic and Fetal Surgery, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229.
3. Wistar Institute, Philadelphia, PA 19104.
4. Philip J. Cross and Associates, Wilmington, DE 19808.
5. Department of Biostatistics and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19102.