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Overview of the Nationwide Inpatient Sample (NIS)
The HCUP Nationwide Inpatient Sample (NIS) is a set of longitudinal hospital inpatient databases included in the HCUP family. These databases are created by AHRQ through a Federal-State-Industry partnership.
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Nationwide Inpatient Sample

The Nationwide Inpatient Sample (NIS) is one in a family of databases and software tools developed as part of the Healthcare Cost and Utilization Project (HCUP). A Federal-State-Industry partnership sponsored by the Agency for Healthcare Research and Quality, HCUP data inform decision making at the national, State, and community levels. This page provides an overview of the NIS. For more details, see Introduction to the NIS, 2006 (PDF file, 242 KB; HTML).

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The Nationwide Inpatient Sample (NIS) is a unique and powerful database of hospital inpatient stays. Researchers and policymakers use the NIS to identify, track, and analyze national trends in health care utilization, access, charges, quality, and outcomes. Key features of this database include the following:
  • The NIS is the largest all-payer inpatient care database in the United States. It contains data from approximately 8 million hospital stays each year.
  • The 2006 NIS contains all discharge data from 1,045 hospitals located in 38 States, approximating a 20-percent stratified sample of U.S. community hospitals.
  • The sampling frame for the 2006 NIS is a sample of hospitals that comprises approximately 90 percent of all hospital discharges in the United States.
  • NIS data are available from 1988 to 2006, allowing analysis of trends over time. The number of States in the NIS has grown from 8 in the first year to 38 at present.
  • The NIS is the only national hospital database containing charge information on all patients, regardless of payer, including persons covered by Medicare, Medicaid, private insurance, and the uninsured.
  • The NIS's large sample size enables analyses of rare conditions, such as congenital anomalies; uncommon treatments, such as organ transplantation; and special patient populations, such as the uninsured.
  • For most States, the NIS includes hospital identifiers that permit linkages to the American Hospital Association (AHA) Annual Survey Database (Health Forum, LLC © 2007) and county identifiers that permit linkages to the Area Resource File.
The NIS contains clinical and resource use information included in a typical discharge abstract, with safeguards to protect the privacy of individual patients, physicians, and hospitals (as required by data sources). The NIS can be weighted to produce national estimates. Beginning with the 2002 NIS, severity adjustment data elements including APR-DRGs, APS-DRGs, Disease Staging, and AHRQ Comorbidity Indicators, are available. A new feature, beginning with the 2005 NIS, is the addition of Diagnosis and Procedure Groups Files. These discharge-level files contain data elements from AHRQ software tools designed to facilitate the use of the ICD-9-CM diagnostic and procedure information in the HCUP databases.

The NIS excludes data elements that could directly or indirectly identify individuals. Purchase of the files is open to all users who sign a Data Use Agreement (PDF file, 55 KB; HTML). Users must agree to use the database for research and statistical purposes only and to make no attempts to identify individuals.

Identities of institutions are available only in States where data sources already make that information public or agree to its release. For these institutions and for research purposes only, linkage is possible to data from the Annual Survey of the American Hospital Association's Annual Survey Database.

Select for the Introduction to the NIS, 2006 (PDF file, 242 KB; HTML).

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The NIS includes more than 100 clinical and nonclinical data elements for each hospital stay. These include:
  • Primary and secondary diagnoses
  • Primary and secondary procedures
  • 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).
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The Nationwide Inpatient Sample (NIS) for 2006 includes 1,045 hospitals from 38 States. Earlier releases of the NIS are also available, as displayed below:
  • NIS Release 1 includes data from 8-11 States and spans the years 1988 to 1992.
  • NIS Releases 2 and 3 contain data from 17 States for 1993 and 1994, respectively.
  • NIS Releases 4 and 5 contain data from 19 States for 1995 and 1996.
  • NIS Release 6 contains data from 22 States for 1997.
  • NIS 1998 contains data from 22 States.
  • NIS 1999 contains data from 24 States.
  • NIS 2000 contains data from 28 States.
  • NIS 2001 contains data from 33 States.
  • NIS 2002 contains data from 35 States.
  • NIS 2003 contains data from 37 States.
  • NIS 2004 contains data from 37 States.
  • NIS 2005 contains data from 37 States.
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The NIS is a uniform, multi-State database that promotes comparative studies of health care services and will support health care policy research on a variety of topics including:
  • Use and cost of hospital services
  • Medical practice variation
  • Health care cost inflation
  • Hospital financial distress
  • Analyses of States and communities
  • Medical treatment effectiveness
  • Quality of care
  • Impact of health policy changes
  • Access to care
  • Diffusion of medical technology
  • Utilization of health services by special populations.
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The NIS has undergone some changes over time in 1) the sampling and weighting strategy, 2) the data elements that are available 3) the definitions of the data elements. For analyses that span multiple years, NIS Trends Supplemental files (NIS-Trends) are available to ease the burden of using multiple years of the NIS. These files contain revised trend weights and data elements that are consistently defined across data years. For more information, refer to the NIS Trends Supplemental Files
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NIS data can help answer a wide array of questions, such as:
  • What is the association between patient outcomes and the volume of specific high-tech hospital procedures?
  • What is the total cost of hospital care provided for the uninsured? How is this care distributed across various types of hospitals?
  • How do alternative cardiac procedures, such as coronary artery bypass graft surgery and coronary angioplasty, compare in terms of patient outcomes and costs?
  • To what extent is electroconvulsive therapy being used to treat recurrent major depression?
  • What is the cost of treating community-acquired pneumonia, childhood asthma, and similar conditions that might not have required hospitalization if they had been treated earlier by a primary care provider?
  • Has the use of pacemakers by older patients changed from 1988 to 2006?
  • What impact do hospital nurse-to-patient ratios have on post-surgical complications?
  • Are there racial differences in the utilization of high-cost procedures, such as organ transplantation?
  • How does the utilization, outcome, or cost experience of a given hospital or health plan compare with national trends?
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NIS data are used by a variety of non-profit and for-profit organizations, including:
  • Actuarial firms
  • Accrediting bodies
  • State and Federal Government agencies
  • Health care consultants
  • Health professions societies
  • Health services researchers and policy analysts
  • Hospital information system firms
  • Hospitals and health care systems
  • Health and life insurance companies
  • Investment firms
  • Managed care organizations
  • Pharmaceutical and medical product manufacturers and marketing firms
  • Schools of business
  • Schools of public health
  • Utilization review organizations.
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The NIS data set can be run on desktop computers with a CD-ROM reader, and comes in ASCII format. The data on the CD set require a statistical software package such as SAS or SPSS to use for analytic purposes. The data set includes weights for producing national and regional estimates. The documentation and tools, including programs to load the ASCII data into SAS, SPSS, or Stata, are available for downloading from this Website.

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NIS releases for data years 1988-2006 are available from the HCUP Central Distributor. The 2006 NIS may be purchased for $200 in a set of two CD-ROMs with accompanying documentation. Contact the HCUP Central Distributor to complete your Data Use Agreement, answer questions about any year of the NIS, and to purchase your own copy.

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For answers to commonly asked questions regarding HCUP databases and tools, please review the HCUP Index Page. If you cannot find an answer to your question, please contact HCUP User Support Staff.

To reach HCUP User Support, please contact us by e-mail or phone: We review messages daily and will respond to all inquiries within 3 business days.

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Additional information is available on the AHRQ Website.
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Internet Citation: HCUP Databases. Healthcare Cost and Utilization Project (HCUP). July 2008
Agency for Healthcare Research and Quality, Rockville, MD.
Last modified 7/11/08