1. The University of Edinburgh; Centre for Population Health Sciences; Medical School Doorway 3, Teviot Place Edinburgh UK EH8 9AG
2. King's College London; Department of English Strand London UK WC2R 2LS
3. Centre for Population Health Sciences: GP Section, The University of Edinburgh; Allergy & Respiratory Research Group; 20 West Richmond Street Edinburgh UK EH8 9DX
4. Care and Public Health Research Institute (CAPHRI); Department of General Practice; Maastricht University Medical Center P Debyeplein 1, PO Box 616 Maastricht Netherlands 6200 MD