[1] Univ Calif San Francisco, Dept Dermatol, San Francisco, CA 94143 USA
[2] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA
[3] Univ Penn, Dept Biostat Epidemiol & Informat, Philadelphia, PA 19104 USA
[4] Univ Penn, Dept Dermatol, Philadelphia, PA 19104 USA
[5] NYU, Div Biostat, New York, NY USA