Overview of the National (Nationwide) Inpatient Sample (NIS) The National (Nationwide) Inpatient Sample (NIS) is part of a family of databases and software tools developed for the Healthcare Cost and Utilization Project (HCUP). The NIS is the largest publicly available all-payer inpatient health care database in the United States, yielding national estimates of hospital inpatient stays. Unweighted, it contains data from more than 7 million hospital stays each year. Weighted, it estimates more than 35 million hospitalizations nationally.
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Beginning in 2012, the NIS was redesigned. It was formerly a sample of hospitals, and all discharges from those hospitals were retained.
The new NIS starting with 2012 data is a sample of discharges from all hospitals participating in HCUP. For details, see the 2012 NIS Redesign Report. |
Developed through a Federal-State-Industry partnership sponsored by the Agency for Healthcare Research and Quality (AHRQ), HCUP data inform decisionmaking at the national, State, and community levels.
This page provides an overview of the NIS. For more details, see NIS Database Documentation and the Introduction to the NIS, 2014 (PDF file, 1.1 MB; HTML). Contents:
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Beginning with the 2012 data year, the NIS approximates a 20-percent stratified sample of all discharges from U.S. community hospitals, excluding rehabilitation and long-term acute care hospitals. The NIS contains information on all patients, regardless of payer, including individuals covered by Medicare, Medicaid, or private insurance, uninsured. The NIS is sampled from the State Inpatient Databases (SID), which include all inpatient data that are currently contributed to HCUP. Researchers and policymakers use the NIS to make national estimates of health care utilization, access, charges, quality, and outcomes. NIS data are available from 1988 through 2014, which allows analysis of trends over time. The number of States participating in the NIS has grown from 8 in the first year to 44, plus the District of Columbia, at present. Beginning with 2012 data, the NIS was redesigned to improve national estimates. To highlight the design change, beginning with 2012 data, AHRQ renamed the NIS from the "Nationwide Inpatient Sample" to the "National Inpatient Sample." The redesign incorporates three major types of changes:
Key features of the most recent NIS (2014) include:
For a detailed description of the 2012 NIS redesign, please see the 2012 NIS Redesign Report. For more details on the 2014 NIS, see the Introduction to the NIS, 2014 (PDF file, 1.1 MB; HTML). Information on previous years of the NIS may be found in the Introduction to the NIS, 2011 (PDF file, 1.3 MB; HTML). |
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The NIS contains clinical and resource-use information that is included in a typical discharge abstract, with safeguards to protect the privacy of individual patients, physicians, and hospitals (as required by data sources). It contains clinical and nonclinical data elements for each hospital stay, including:
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As a uniform, multi-State database, the NIS promotes comparative studies of health care services and supports health care policy research on a variety of topics, including:
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Spanning more than 20 years of data, the NIS is ideal for longitudinal analyses. However, the database has undergone changes over time, including the sampling and weighting strategy used. Users of the NIS should expect a one-time decrease to historical trends for discharge counts of about 4 percent beginning with data year 2012. Users should also expect smaller one-time disruptions to historical trends for rates and means estimated from the NIS, beginning with data year 2012. For trends analysis using NIS data 2011 and earlier, revised weights should be used to make estimates comparable to the new design beginning with 2012 data. These new discharge trend weights replace the earlier NIS Trend Weights that were developed for the 1988-1997 NIS following the 1998 NIS redesign. The new trend weights are available for download as ASCII files, along with SAS®, SPSS®, and Stata® load programs, under 1993-2011 NIS Trend Weights Files from the NIS Database Documentation page on the HCUP-US Web site. The report Using the HCUP Nationwide Inpatient Sample to Estimate Trends, available on the HCUP-US Web site under Methods Series, includes recommendations for trends analysis. |
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NIS releases for data years 1988 through 2011 are available for purchase online through the Online HCUP Central Distributor. All HCUP data users, including data purchasers and collaborators, must complete the online HCUP Data Use Agreement Training Tool, and must read and sign the Data Use Agreement for Nationwide Databases (PDF file, 55 KB; HTML). Questions about purchasing databases can be directed to the HCUP Central Distributor:
Email: HCUPDistributor@AHRQ.gov
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The NIS Database is distributed as fixed-width ASCII-formatted data files delivered via secure digital download from the Online HCUP Central Distributor. The files are compressed and encrypted with SecureZIP® from PKWARE. To load and analyze the NIS data on a computer, users will need the following:
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Internet Citation: HCUP Databases. Healthcare Cost and Utilization Project (HCUP). December 2016. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/nisoverview.jsp. |
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Last modified 12/14/16 |