1. University Department of Surgery, Gartnavel General Hospital, Glasgow, UK
2. Department of Surgery, Royal Infirmary, Edinburgh, UK
3. Robertson Centre for Biostatistics, Glasgow University, Gartnavel General Hospital, Glasgow, UK
4. Department of Anaesthesia, Western Infirmary, Gartnavel General Hospital, Glasgow, UK
5. Department of Surgery, Gartnavel General Hospital, Glasgow, UK