1. a Center for AIDS Prevention Studies , University of California , 74 New Montgomery, Suite 600, San Francisco, CA, 94105 Phone: Fax: E-mail:
2. b Department of Sociology , University of Chicago ,
3. c Center for AIDS Prevention Studies, Department of Medicine , University of California , San Francisco
4. d Center for AIDS Prevention Studies, Department of Medicine , University of California , San Francisco
5. e Department of Sociology , State University of New York , Stony Brook
6. f Center for AIDS Prevention Studies, Department of Medicine , University of California , San Francisco