NIS Database Documentation

The National (Nationwide) Inpatient Sample (NIS) is a large publicly available all-payer inpatient care database in the United States, containing data on more than seven million hospital stays each year.

The National (Nationwide) Inpatient Sample (NIS) is the largest publicly available all-payer inpatient care database in the United States, containing data on more than seven million hospital stays. Its large sample size is ideal for developing national and regional estimates and enables analyses of rare conditions, uncommon treatments, and special populations.

The following links provide detailed documentation for the NIS, from a high-level Overview to all the detailed specifications, restrictions, and resources necessary for researchers working and publishing with the NIS.

Description of NIS Database

NIS Overview

HCUP Partners in the NIS

Introduction to the NIS
- 2018 (PDF file, 1.1 MB; HTML)
- Prior Years
NIS Related Reports
- Prior Years
Checklist for Working With the NIS

Restrictions on Use

HCUP Data Use Agreement Training
Data Use Agreement for the National (Nationwide) Databases (PDF file, 85 KB; HTML)
Requirements for Publishing with HCUP Data

File Specifications and Load Programs

Data Elements

NIS Description of Data Elements
- Prior Years
NIS Summary Statistics
Prior to Data Year 2012
- Availability of AHA Hospital Identifiers
- Why the NIS should not be used to make State-level estimates

Additional Resources for Data Elements

NIS Severity Measures
- Overview of Severity Measures (PDF file, 60 KB; HTML)
- APR-DRGs Methodology Overview Version 31 (PDF file, 341 KB)
  - Prior Years
HCUP Quality Control Procedures (PDF file, 383 KB; HTML)
HCUP Coding Practices (PDF file, 171 KB; HTML)
HCUP Hospital Identifiers (PDF file, 174 KB; HTML)

ICD-10-CM/PCS Data Included in the NIS Starting With 2015

2016 NIS Revised File Structure and New Data Elements (PDF file, 193 KB)
Caution: 2015 NIS includes ICD-9-CM and ICD-10-CM/PCS

2015 NIS Revised File Structure and New Data Elements (PDF file, 304 KB)

Additional ICD-10-CM/PCS Resources
Tutorial for Loading HCUP Software Tools for ICD-10-CM/PCS

2012 NIS Redesign

2012 NIS Redesign Report (PDF file, 2.0 MB)
Trend Weights for the 1993-2011 NIS for Consistent Estimates with the Redesigned NIS

Known Data Issues

NIS Supplemental Files

HCUP Tools: Labels and Formats

Clinical Classifications Software (CCS)
Format Programs

DRG Formats Program (TXT file, 1.7 MB) Creates SAS formats to label the values of each DRG and MDC category
HCUP Formats Program (TXT file, 63 KB) Creates SAS formats to label the values of selected categorical data elements in HCUP files
HCUP Diagnosis and Procedure Groups Formats Program (TXT file, 39 KB) Creates SAS formats to label the values of HCUP Diagnosis and Procedure Groups data elements, including Clinical Classifications Software (CCS) data elements
ICD-9-CM Formats Program (TXT file, 910 KB) Creates SAS formats to label the values of ICD-9-CM Diagnoses and Procedures
ICD-10-CM Formats Program (TXT file, 11.8 MB) Creates SAS formats to label the values of ICD-10-CM Diagnoses and Procedures
Severity Formats Program (TXT file, 796 KB) Creates SAS formats to label the values of data elements in HCUP Severity Files

Obtaining HCUP Data

Purchase HCUP data from the HCUP Central Distributor

Internet Citation: HCUP NIS Database Documentation. Healthcare Cost and Utilization Project (HCUP). December 2020. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/db/nation/nis/nisdbdocumentation.jsp.

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Last modified 12/3/20