1 Centre of Evidence Based Dermatology, University of Nottingham, Nottingham NG7 2NR, UK. Electronic address: hywel.williams@nottingham.ac.uk.
2 Centre of Evidence Based Dermatology, University of Nottingham, Nottingham NG7 2NR, UK.
3 Medical Research Council Clinical Trials Unit at University College London, London, UK.
4 Institute of General Medicine and Interprofessional Care, University of Tübingen, Tübingen, Germany; Centre of Evidence Based Dermatology, University of Nottingham, Nottingham NG7 2NR, UK.
5 Department of Dermatology, University of Lübeck, Lübeck, Germany.