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HCUP Nationwide Inpatient Sample (NIS)

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Availability and description of data elements, sampling frame, methods

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Dataset Summary

The Nationwide Inpatient Sample is the largest U.S. database of inpatient hospital stays that incorporates data from all payers, containing data from approximately 20% of U.S. community hospitals.  Started in 1988 and continuing through the present, NIS collects information on a variety of data elements including diagnoses and procedures, severity adjustment elements (such as APR-DRGs and comorbidity indicators), admission and discharge status, payment source, hospital organizational characteristics, and more.  In addition, NIS contains hospital and county identifiers that allow linkage to the American Hospital Association Annual Survey and Area Resource File (both described elsewhere in this dataset compendium).  Extensive documentation and resources are available to facilitate data analysis.  Data is available for download after completing a data use agreement, online training, and for $200 to $350 per year ($20 to $50 for students). 

Expert comments   
The NIS is the largest all-payer database of inpatient discharge data, and hence can be a useful dataset for outcomes research.  Among hospitals participating in the survey, every discharge for the calendar year is included.  The database contains discharge-level rather than patient-level data, and there is no unique patient identifier that can serve to identify readmissions.  Several severity measures are also included in the NIS.  Researchers can use these measures for risk-adjustment or develop their own risk-adjustment models using the diagnosis and procedure codes included in the data.  The NIS does not currently identify conditions present on admission.

Hospitals in the NIS are identified by a HCUP identifier and by an AHA identifier, allowing linkage to hospital-level data in other datasets.  (HCUP comprises a series of studies, several of which are featured on the SGIM dataset compendium website; see  The AHA Annual Survey, an annual survey of hospitals, is also featured in the SGIM compendium).  Of note, at least 13 States prohibit the release of hospital-identifying information; this can reduce the number of hospitals available for merging with other datasets using the AHA identifier.  NIS online documentation includes resources to assist with loading of data into SAS, SPSS, and Stata.  As the patient-level NIS files are quite large, attention needs to be paid to data management and computer memory issues.

Dataset Details

Dataset owner / manager

Agency for Healthcare Research and Quality (AHRQ), under the Healthcare Cost and Utilization Project (HCUP)

Study and sample characteristics 

NIS contains data on a stratified sample of over 1000 U.S. hospitals with approximately 8 million hospital stays per year; weights are available to convert NIS data into national estimates.  Specialty hospitals (e.g., orthopedics or obstetrics-gynecology hospitals) are included, as are long-term acute care hospitals (since 2005).   Data has been collected on an annual basis since 1988, and resources are available to facilitate evaluation of time trends.  Please note, not all States provide identifying information for individual hospitals.

Data on sampling strategy and hospital inclusion criteria:

Resources for evaluation of time trends:

Major foci

Major topics of data collection include:

•    Primary and secondary diagnoses
•    Primary and secondary procedures
•    Severity adjustment markers (e.g., APR-DRGs, comorbidity indices, etc.)
•    Admission and discharge status
•    Patient demographics (e.g., gender, age, race, median income for ZIP Code)
•    Expected payment source
•    Total charges
•    Length of stay
•    Hospital characteristics (e.g., ownership, size, teaching status).

Specific foci     
See section on availability and description of data elements at:  

Links to other datasets

County and hospital identifiers allow for linkage with the Area Resource File and the American Hospital Association Annual Survey (described elsewhere in the SGIM Research Dataset Compendium).


Papers published

Click here for a PubMed search for articles using this dataset.

For a complete list of publications from the HCUP databases, see Publications may be searched by database at

Examples of papers published using NIS include:

Orthostatic hypotension-related hospitalizations in the United States. 
Shibao C, Grijalva CG, Raj SR, Biaggioni I, Griffin MR. 
Am J Med. 2007 Nov;120(11):975-80.

Factors associated with patients who leave acute-care hospitals against medical advice. 
Ibrahim SA, Kwoh CK, Krishnan E. 
Am J Public Health. 2007 Dec;97(12):2204-8. 

Trends in the use of the pulmonary artery catheter in the United States, 1993-2004. 
Wiener RS, Welch HG. 
JAMA. 2007 Jul 25;298(4):423-9. 

Decline in pneumonia admissions after routine childhood immunisation with pneumococcal conjugate vaccine in the USA: a time-series analysis. 
Grijalva CG, Nuorti JP, Arbogast PG, Martin SW, Edwards KM, Griffin MR. 
Lancet. 2007 Apr 7;369(9568):1179-86. 

Impact of hospital volume on racial disparities in cardiovascular procedure mortality. 
J Trivedi AN, Sequist TD, Ayanian JZ. 
Am Coll Cardiol. 2006 Jan 17;47(2):417-24.

Dataset accessibility and cost

Data is available after completion of a Data Use Agreement, HCUP online training, and NIS application kit at an approximate cost of $200 to $350 per year of data ($20 to $50 for students)

SAS, Stata, and SPSS data load programs are available, as are files to assist with dataset labeling, formatting, and coding.

Help Desk

See Frequently Asked Questions

Additional support can obtained via
•    email: 
•    Phone (toll free): 1-866-290-HCUP 
See: for details.

Request a consultation (SGIM members only)

Members of SGIM may request a one-time consultation with an expert in this dataset, for example to explore research ideas or to troubleshoot a problem or vexing question.  Please click here for guidelines and the request process.