The NIS data dictionary can be found here.
Type of Data
Speciality/General Inpatient database
Years Available
1988-Present
Note: Data have been collected from 1988 to present year, with some files such as diagnosis and procedure groups file collected not available for 2016-2017. Data are updated quarterly.
Short Description
National (Nationwide) Inpatient Sample (NIS) is largest publicly available all-payer inpatient healthcare database in US providing national estimates of hospital inpatient stays. NIS is part of family of the databases and software tools developed for the Healthcare Cost and Utilization Project (HCUP). More details about NIS can be found at their fast-facts website.
Unweighted, it contains more than 7 million hospital stays each year. Weighted, it estimates more than 35 million hospitalizations nationally. There are three discharge-level files and one hospital-level file. It contains various clinical and nonclinical data elements for each hospital stay such as ICD-9/10 diagnosis and procedure codes, patient demographics, hospital characteristics, total charges and severity and comorbidity measures.
Strengths
- A large amount of data and variables are available and ideal for longitudinal analyses
- The data are well formatted and maintained with data dictionaries, including programs for loading ASCII files into SAS, SPSS or Stata (beginning with 2004)
Limitations
- Linkage between the Inpatient Core File and the Hospital File has been changed. Beginning with 2012 NIS, the NIS hospital number provides linkage between these two files and this hospital number values are reassigned each year so they cannot be used to link hospitals across years.
- Discharge file called “Diagnosis and Procedure Groups File” is not available for 2016-2017 (this file provides additional information on diagnoses and procedures)