Data Source
This cohort study was conducted using the NIS database, which is the largest all-payer inpatient database in the US. The NIS database contains discharge data set from a 20% stratified sample of US hospitals with patient encounter-level information. The data set includes primary and secondary diagnosis codes as well as procedure codes in form of International Classification of Diseases, Ninth Revision (ICD-9). Sample weight is used to generate national estimates for hospitalization nationwide. The approval from institutional review board was exempted as the information was obtained from a de-identified public database.