 Invalid age data will be excluded either due to missing entries or mismatch with date of death. Multiple admissions cases with same identification number but more than 12 months between admissions and duplicate entries cases with same identification number will be removed from the dataset, after valuable co-morbidity data from the duplicate entries were stored in the original record. Duplicate entries originate from separate recordings from each hospital if the patient is referred to a specialised hospital. Furthermore, primarily non-surgically treated cases with a change of treatment modality are registered as surgical patients. The registered hospitalisation time for these patients is the combined non-surgical and surgical in-hospital treatment period. 