1. NHS The Information Centre for Health and Social Care Hospital episode statistics online 2011 http://www.hesonline.nhs.uk/Ease/servlet/ContentServer?siteID=1937&categoryID=207
2. Department of Health and Doctor Foster Holdings LLP Doctor Foster Intelligence. Inside your hospital: Dr Foster hospital guide 2001-2011 2011 http://www.drfosterintelligence.co.uk/wp-content/uploads/2011/11/Hospital_Guide_2011.pdf
3. National Confidential Enquiry into Perioperative Deaths Classification of intervention 2004 http://www.ncepod.org.uk/pdf/NCEPODClassification.pdf