1. Dr Foster Unit, Department of Primary Care and Public Health, School of Public Health, Imperial College, London, United Kingdom
2. Leicester Cardiovascular Biomedical Research Unit & Department of Cardiovascular Sciences, Glenfield Hospital, University of Leicester, United Kingdom
3. Information Department, Liverpool Heart and Chest Hospital, Liverpool, United Kingdom
4. School of Clinical Sciences, Bristol Heart Institute, University of Bristol, United Kingdom
5. Department of Health Economics, University of Liverpool, United Kingdom
6. Department of Cardiothoracic Surgery, Papworth Hospital, Cambridge, United Kingdom
7. Department of Cardiothoracic Surgery, Liverpool Heart and Chest Hospital, Liverpool, United Kingdom