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.