1. Department of Dermatology
2. Department of Biostatistics, Epidemiology and Informatics, Perelman School of Medicine at the University of Pennsylvania , Philadelphia, PA , USA
3. Temple School of Medicine , Philadelphia, PA , USA
4. Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine , London , UK
5. Department of Primary Care & Population Health, University College London , London , UK
6. Department of Clinical Epidemiology, Aarhus University , Denmark