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Overview of the Nationwide Readmissions Database (NRD)
The HCUP Nationwide Readmissions Database (NRD) is a set of inpatient databases in the HCUP family designed for readmission analyses. These HCUP databases are created by AHRQ through a Federal-State-Industry partnership.
The Nationwide Readmissions Database

The Nationwide Readmissions Database (NRD) is part of a family of databases and software tools developed for the Healthcare Cost and Utilization Project (HCUP). The NRD is a unique and powerful database designed to support various types of analyses of national readmission rates for all payers and the uninsured. This database addresses a large gap in health care data - the lack of nationally representative information on hospital readmissions for all ages. Unweighted, the NRD contains data from approximately 14 million discharges each year. Weighted, it estimates roughly 36 million discharges.

Developed through a Federal-State-Industry partnership sponsored by the Agency for Healthcare Research and Quality, HCUP data inform decisionmaking at the national, State, and community levels.

This page provides an overview of the NRD. For more details, see NRD Database Documentation and the Introduction to the NRD, 2013 (PDF file, 1.0 MB; HTML).


The NRD is drawn from the HCUP State Inpatient Databases (SID) and can be used to create estimates of national readmission rates for all payers and the uninsured. The 2013 NRD was constructed from 21 States with reliable, verified patient linkage numbers in the SID that could be used to track the patient across hospitals within a State, while adhering to strict privacy guidelines.

Key features of the 2013 NRD include:
  • A large sample size, which provides sufficient data for analysis across hospital types and the study of readmissions for relatively uncommon disorders and procedures.
  • Discharge data from 21 geographically dispersed States, accounting for 49.3 percent of the total U.S. resident population and 49.1 percent of all U.S. hospitalizations.
  • Designed to be flexible to various types of analyses of readmissions in the United States for all types of payers and the uninsured.
  • Criteria to determine the relationship between multiple hospital admissions for an individual patient in a calendar year is left to the analyst using the NRD.
  • Outcomes of interest include national readmission rates, reasons for returning to the hospital for care, and the hospital costs for discharges with and without readmissions.
  • The NRD is designed to support national readmission analyses and cannot be used for regional, State-, or hospital-specific analyses.
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The NRD contains clinical and nonclinical variables that support readmission analyses, with safeguards to protect the privacy of individual patients, physicians, and hospitals. There is no data element identifying whether sequential inpatient stays are related or unrelated. The criteria to determine the relationship between hospital admissions is left to the analyst using the NRD.

The NRD is comprised of more than 100 clinical and nonclinical variables for each hospital stay, including:
  • Variables essential to readmission analyses
    • Verified patient linkage number that identifies discharges belonging to the same individual
    • Timing between admissions for a patient
    • Length of inpatient stay in days
    • Identification of transfers, same-day stays, and combined transfer records
    • Identification of the patient as a resident of the State in which he or she received hospital care
  • Variables essential to calculating national estimates
    • Discharge weight for generating national estimates
    • Stratum used for weighting
  • International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis and external cause of injury codes
  • ICD-9-CM procedure codes
  • Diagnosis and procedure classifications variables such as the Clinical Classification Software (CCS) category, Chronic Condition Indicator (CCI), and procedure class
  • Patient demographics (e.g., sex, age, median household income quartile, and urban/rural location of the patient's residence)
  • Expected payment source (e.g., Medicare, Medicaid, private insurance, uninsured, and other insurance types)
  • Total charges and hospital cost (calculated using the Cost-to-Charge Ratio file)
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As a uniform, multi-State weighted database, the NRD promotes comparative studies of health care services and supports health care policy and research on a variety of topics, including:
  • National readmission rates by diagnosis, procedure, patient demographics, or expected payment source
  • Costs associated with readmissions
  • Reasons for readmissions
  • Impact of health policy changes
  • Quality of care
  • Access to care
  • Utilization of health services by special populations, including the uninsured.
The NRD is used in a variety of publications: Return to Contents

NRD release for data year 2013 is available for purchase through the HCUP Central Distributor.

Prior to purchasing HCUP data, all individuals are required to take the online HCUP Data Use Agreement Training Course, and users of the NRD must read and sign the Data Use Agreement for Nationwide Databases (PDF file, 55 KB; HTML).

The NRD are available for purchase online through the HCUP Central Distributor.

Questions regarding purchasing databases can be directed to the HCUP Central Distributor:

Telephone: (866) 556-4287 (toll free)
Fax: (866) 792-5313 (toll free)

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The NRD data set is relatively large. The data are sent in comma-separated value (CSV) format compressed with WinZip®. In order to load and analyze the NRD data on a computer, you will need the following:
  • A DVD drive
  • A hard drive with at least 40 gigabytes (GB) of space available
  • A third-party zip utility such as ZIP Reader, 7-Zip, or WinZip®
  • SAS®, SPSS®, Stata® or similar analysis software
The data set includes weights for producing national estimates. NRD documentation and tools, including programs for loading the CSV files into SAS, SPSS, or Stata, are also available on the NRD Database Documentation page.

Please note the following based on the software you plan to use:
  • In total, the comma-delimited version of the NRD is 10 GB.
  • The NRD files loaded into SAS are about 12 GB. Most SAS data steps will require twice the storage of the file, so that the input and output files can coexist. The largest use of space typically occurs during a sort, which requires work space approximately three times the size of the file. Thus, the NRD files would require approximately 36 GB of available workspace to perform a sort.
  • The NRD files loaded into SPSS are under 23 GB.
  • Because Stata loads the entire file into memory, it may not be possible to load every data element in the NRD Core file into Stata. Stata users will need to maximize memory and use the "_skip" option to select a subset of variables. More details are provided in the Stata load programs.
With a file this size and without careful planning, space could easily become a problem in a multi-step program with the NRD. It is not unusual to have several versions of a file marking different steps while preparing it for analysis and more versions for the actual analyses; therefore, users should be aware that the amount of space required can escalate rapidly.

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Internet Citation: NRD Overview. Healthcare Cost and Utilization Project (HCUP). December 2015. Agency for Healthcare Research and Quality, Rockville, MD.
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Last modified 12/21/15