1. Department of Gastroenterology, St George’s Healthcare NHS Trust, St George’s University, London, UK
2. School of Public Health, Imperial College London, London, UK
3. Department of Primary Care and Population Health, University College London, London, UK
4. Department of Clinical Epidemiology, Aarhus University, Denmark
5. Institute of Psychiatry, Kings College London, London, UK
6. South London and Maudsley NHS Foundation Trust, London, UK