[1] Univ Penn, Ctr Clin Epidemiol & Biostat, Dept Med,Perelman Sch Med, Div Rheumatol,Ctr Pharmacoepidemiol Res & Trainin, White Bldg,Room 5023,3400 Spruce St, Philadelphia, PA 19104 USA
[2] Univ Penn, Dept Dermatol, Perelman Sch Med, Philadelphia, PA 19104 USA
[3] Univ Penn, Dept Dermatol, Dept Biostat & Epidemiol, Ctr Clin Epidemiol & Biostat,Perelman Sch Med, Philadelphia, PA 19104 USA
[4] Univ Penn, Perelman Sch Med, Div Gastroenterol, Philadelphia, PA 19104 USA