“…Of these, 26 7 , 13 - 18 , 20 - 22 , 24 , 25 , 27 , 28 , 33 - 40 , 42 - 45 were retrospective cohort studies, 1 23 was a prospective cohort study and 9 8 , 9 , 19 , 26 , 29 - 32 , 41 were case-control studies. Among them, 20 7 , 9 , 15 - 17 , 23 , 25 , 26 , 29 , 32 - 36 , 38 - 40 , 42 , 44 , 45 included patients from the NSQIP database, 2 from State Inpatient Databases (SID) 13 , 28 , 3 from Nationwide Readmissions Database (NRD) 8 , 18 , 41 , 4 from the Medicare database 20 , 24 , 37 , 43 , 2 from the Quality Outcomes Database (QOD) 21 , 22 , and 3 from institutional database ...…”