[1] Univ Calif San Francisco, Ctr AIDS Prevent Studies, San Francisco, CA 94105 USA
[2] Ctr Dis Control & Prevent, Atlanta, GA USA
[3] Univ Calif Los Angeles, Los Angeles, CA USA
[4] Dept Publ Hlth, San Francisco, CA USA
[5] Res Triangle Inst, Washington, DC USA
[6] Univ Maryland, Survey Res Ctr, College Pk, MD 20742 USA
[7] Survey Methods Grp, San Francisco, CA USA