1. New York University, New York, New York 10016.
2. Harvard School of Public Health, Boston, Massachusetts 02115.
3. Social and Scientific Systems, Inc., Silver Spring, Maryland 20910.
4. Present address: National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892.
5. National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892.
6. University of Minnesota, Minneapolis, Minnesota 55455.
7. Weill Medical College of Cornell University, New York, New York 10021.
8. University of California, San Diego, La Jolla, California 92093.
9. Present address: Wyeth Laboratories, Madison, New Jersey.
10. Frontier Science and Technology Research Foundation, Chestnut Hill, Massachusetts 02467.
11. University of Cincinnati, Cincinnati, Ohio 45221.