1. 1Department of Non-Communicable Diseases Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom;
2. 2Department of Epidemiology, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina;
3. 3Unit of Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; and
4. 4Royal Marsden Hospital,
5. 5National Heart and Lung Institute, Imperial College London, and
6. 6Royal Brompton Hospital, London, United Kingdom.