1. Department of Epidemiology and Public Health, Royal Free and University College London Medical School, London, U.K.
2. Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, the Netherlands
3. Postgraduate Medical School, University of Surrey, Guildford, Surrey, U.K.
4. Healthcare Commission, Finsbury Tower, London, U.K.
5. Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland