Purveyor: Agency for Healthcare Research and Quality

Years in the DataCore: 1988-2016

Years of data owned: 1988-2016

Unit of data: Hospital discharge

Dataset website:

Public-facing data dictionary:

General description: 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. 

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:

  • Utilization of health services by special populations
  • Hospital stays for rare conditions
  • Variations in medical practice
  • Health care cost inflation
  • Regional and national analyses
  • Quality of care and patient safety
  • Impact of health policy changes
  • Access to care

Common Key Linking Variables

Hospital Linking:

  • NIS Hospital Number (2012-2016)
  • HCUP Hospital ID (1998-2011)
  • American Hospital Association ID (1988-2011)

Patient Linking:

  • HCUP Processing ID (1988-1997)
  • NIS Key (1988-2016)

Geographic Linking:

  • Region (1988-2016)
  • Address (1988-2011)

Licensing and Access

All users of HCUP data must complete the HCUP Data Use Agreement (DUA) Training Course and sign an HCUP DUA before receipt of the data. See this website for further information:

NIS Structure

Core [1998-2016], A B C [1993-1997], Q1 Q2 Q3 Q4 [1988-1992]

Every row of the Core dataset is a hospital discharge.

The primary key of the Core table is:

  • Sequence Number (SEQ) 1988-1997
  • Unique Record Identifier (KEY) 1998-2011
  • NIS Record Number (KEY_NIS) 2012-2016

Hospital [1988-2016]

Every row of NIS Hospital is a hospital.

The primary key of the Hospital table is:

  • Data source hospital number (DSHOSPID) 1988-2011
  • NIS Hospital Number (HOSP_NIS) 2012-2016

Severity [2002-2016]

Every row of severity is All Patient Refined DRG codes from 2015Q4-2016; however, Severity also contains comorbidity data before that. The severity table can be directly mapped to the Core or Hospital tables.

The primary key of the Severity table is KEY_NIS.

DX_PR_GRPS [2005-2015], Dx Pr [1993-1997]

Diagnosis and Procedure information contains data about diagnosis and procedures performed during an admission. It can also be mapped to the Core of Hospital tables.

The primary key of the DX_PR_GRPS table is KEY_NIS.

DataCore Staff Errata

5/28/2019: No data errata, data exceptions or data corrections have been issued.

DataCore Purveyor Errata

5/28/2019: No data errata, data exceptions or data corrections have been implemented.


The data from HCUP was sent in ascii files (.asc) with associated file specification files. It was found that these file specifications offered an accurate depiction of the data.

  1. For the code used for these processes, email
  2. Stata .do files provided by HCUP were used to load the .asc files into Stata. These files were then exported in tab separated value files (.tsv). For 1988-2003 data, stata load files were created following the same structure as the provided .do files in order to load the data into Stata to explore it as .tsv.
  3. The provided file specification files were used in order to create SQL tables to fit the data.
  4. A bulk copy program (BCP) was used in order to upload the .tsv into SQL.
  5. The website was used to generate metadata about the dataset fields and was used to generate the data dictionary.