Consort diagram showing the derivation of the study cohort. Of the 39,051 CABG/valve operations in the database over a 6-year period, 22% were excluded because STS risk scores were unavailable for the given procedure. From these 30,410 patients, 17,316 were excluded, with the majority of these due to elective admission status. Of the 13,094 patients admitted preoperatively for a qualified operation, over half were transferred from another institution. (CABG: Coronary Artery Bypass Grafting; STS: Society of Thoracic Surgeons; MD: Medical Doctor)