*Department of Surgery and Cancer, Queen Elizabeth the Queen Mother Wing, St Mary's Hospital, Imperial College London, London, UK
†Statistical Laboratory, Centre for Mathematical Sciences, Cambridge University, Cambridge, UK
‡Dr Foster Unit at Imperial College, Department of Primary Care and Public Health, Imperial College London, London, UK
§Surgical Epidemiology, Trials and Outcome Centre (SETOC), St Mark's Hospital and Academic Institute, Harrow, Middlesex, UK.
Reprints: George B. Hanna, 10th Floor QEQM Wing, St Mary's Hospital, London W2 1NY, UK. E-mail: [email protected].
Sources of support: This article represents independent research supported by the National Institute for Health Research Diagnostic Evidence Cooperatives (NIHR-DEC). The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, or the Department of Health.
We have permission from the Confidentiality Advisory Group under Section 251 of the NHS Act 2006 (formerly Section 60 approval from the Patient Information Advisory Group) to hold confidential data and analyze them for research purposes [PIAG 2-05(d)/2007]. We have approval to use them for research and measuring quality of delivery of healthcare, from the South East Ethics Research Committee (10/H1102/25).