1. St George's, University of London; Population Health Sciences and Education; Cranmer Terrace London UK SW17 0RE
2. BMJ; BMJ-TAG; Tavistock Square London UK WC1H 9JR
3. Karolinska University Hospital Solna; Department of Respiratory Medicine and Allergy; Stockholm Sweden SE-171 76
4. Karolinska Institutet; Respiratory Medicine Unit, Department of Medicine; Stockholm Sweden
5. University of Perugia; Section of Respiratory Diseases, Department of Internal Medicine; Perugia Italy