Abstract
Hospital admissions in England were obtained from the hospital episode statistics system (www.dh.gov.uk). This database contains personal, administrative, and medical data on all patients admitted to NHS hospitals in England. It records episodes of care following admission to hospital and assigns a primary diagnosis on discharge using the WHO International Classification of Diseases (ICD). Data are available by financial year (1 April to 31 March). From April 1995 diagnoses were classified using the 10th revision of ICD (ICD 10).