1 Biostatistics and Medical Informatics Research Group, Department of Public Health, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel (VUB), Brussels, Belgium.
2 Department of Dermatology, University Hospitals KU Leuven, Leuven, Belgium.
3 Research and Development, Northumbria Healthcare NHS Foundation Trust, North Shields, UK.
4 Pain and Rehabilitation Centre, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.