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 healthcare database designed to produce U.S. regional and national estimates of inpatient utilization, access, charges, quality, and outcomes. Unweighted, it contains data from more than 7 million hospital stays each year. Weighted, it estimates more than 35 million hospitalizations nationally. Developed through a Federal-State-Industry partnership sponsored by the Agency for Healthcare Research and Quality (AHRQ), HCUP data inform decision making at the national, State, and community levels.
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BEGINNING WITH DATA YEAR 2016, THE NIS CONTAINS A FULL YEAR OF ICD-10-CM/PCS CODES.
Beginning with data year 2016, the NIS includes a full calendar year of data with diagnosis and procedure codes reported using the ICD-10-CM/PCS1 coding system. The file structure is similar to the file structure of the NIS in data years 2014 and prior years. THE 2015 NIS CONTAINS ICD-9-CM AND ICD-10-CM/PCS CODES. On October 1, 2015, hospital administrative data began using ICD-10-CM/PCS, so the first nine months of 2015 contain ICD-9-CM codes and the last three months contain ICD-10-CM/PCS codes. The data elements and file structure for the 2015 NIS are different. Trends based on diagnoses or procedures will be affected. Data elements derived from AHRQ software tools are not available for ICD-10-CM/PCS data on the NIS, with one exception beginning data year 2018, data elements derived from the Clinical Classifications Software Refined (CCSR) for ICD-10-CM diagnoses are included on the NIS. THE NIS WAS REDESIGNED BEGINNING WITH 2012 Starting in data year 2012, the NIS is a sample of discharges from all hospitals participating in HCUP. For prior years, the NIS was a sample of hospitals. For details, see the 2012 NIS Redesign Report. |
1 ICD-9-CM: International Classification of Diseases, Ninth Revision, Clinical Modification; ICD-10-CM/PCS: International Classification of Diseases, Tenth Revision, Clinical Modification/Procedure Coding System This page provides an overview of the NIS. For more details, see NIS Database Documentation and the Introduction to the NIS, 2018 (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 hospital stays, regardless of expected payer, for the hospital stay. 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 healthcare utilization, access, charges, quality, and outcomes. NIS data are available from 1988 through 2018, which allows analysis of trends over time. The number of States participating in the NIS has grown from 8 in the first year to 47, 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 (2018) include:
For a detailed description of the 2012 NIS redesign, please see the 2012 NIS Redesign Report. For more details on the 2017 NIS, see the Introduction to the NIS, 2018 (PDF file, 1.1 MB; HTML). Information on previous years of the NIS may be found in prior years of the Introduction to the NIS at https://www.hcup-us.ahrq.gov/db/nation/nis/nisarchive.jsp. |
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Beginning with data year 2016, the NIS is a calendar year file that includes diagnoses and procedures coded using only ICD-10-CM/PCS. The file structure is similar to the file structure of the NIS in data years 2014 and prior years. For the 2015 data, because of the transition to ICD-10-CM/PCS on October 1, 2015, data elements related to diagnoses and procedures are included in files that are split into two files. Nine months of the 2015 data with ICD-9-CM codes (discharges from January 1, 2015 - September 30, 2015) are in one set of files labeled Q1-Q3. Three months of 2015 data with ICD-10-CM/PCS codes (discharges from October 1, 2015 - December 31, 2015) are in a separate set of files labeled Q4. More information about the changes to the HCUP databases for ICD-10-CM/PCS and use of data across the two coding systems may be found on the HCUP-US website under ICD-10-CM/PCS Resources. |
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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 healthcare services and supports healthcare 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 website. The report Using the HCUP National Inpatient Sample to Estimate Trends, available on the HCUP-US website under Methods Series, includes recommendations for trends analysis. For recommendations on reporting trends across the implementation of the new coding system, please see the report HCUP Recommendations for Reporting Trends Using ICD-9-CM and ICD_10-CM/PCS Data. |
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NIS releases for data years 1988 through 2017 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, 85 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 2020. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/nisoverview.jsp. |
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Last modified 12/2/20 |