1. Clinical Effectiveness Unit, Health Services Research Unit, London School of Hygiene and Tropical Medicine, London, United Kingdom
2. Royal College of Surgeons of England, Health Services Research Unit, London School of Hygiene and Tropical Medicine, London, United Kingdom
3. National Collaborating Centre for Acute Care, Health Services Research Unit, London School of Hygiene and Tropical Medicine, London, United Kingdom
4. Institute of Urology and Nephrology, University College London, London, United Kingdom