[1] Univ Penn, Dept Dermatol, Philadelphia, PA 16104 USA
[2] Univ Penn, Dept Biostat & Epidemiol, Philadelphia, PA 16104 USA
[3] Univ Penn, Ctr Clin Epidemiol & Biostat, Philadelphia, PA 16104 USA
[4] NYU, Dept Internal Med, Langone Med Ctr, New York, NY USA