1. Department of Public and Occupational Health; EMGO Institute for Health and Care Research, VU University Medical Centre; Amsterdam; 1081 BT; The Netherlands
2. Department of Primary and Community Care, Centre for Family Medicine, Geriatric Care and Public Health; Radboud University Nijmegen Medical Centre; Nijmegen; 6500 HB; The Netherlands
3. Department of Public and Occupational Health; Groningen University Medical Centre; Groningen; 9700 RB; The Netherlands
4. Department of Dermatology; University Medical Centre Groningen, University of Groningen; Groningen; 9700 RB; The Netherlands