Table 1.

Required research practices for studies using the National Inpatient Sample^a

Research practice criteria	Required research practices for conducting studies using the NIS
1	Identifying observations as hospitalization events rather than unique patients
2	Not performing state-level analyses
3	Limiting hospital-level analyses to data from years 1988-2011
4	Not performing physician-level analyses
5	Avoiding use of nonspecific secondary diagnosis codes to infer in-hospital events
6	Using survey-specific analysis methods that account for clustering, stratification, and weighting
7	Accounting for data changes in trend analyses spanning major transition periods in the data set (1997-1998 and 2011-2012)

^aAdapted from Khera et al. [11].