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NEDS Overview
The Nationwide Emergency Department Sample (NEDS) is a set of hospital-based emergency department databases included in the HCUP family. These databases are created by AHRQ through a Federal-State-Industry partnership.
 
Overview of the Nationwide Emergency Department Sample (NEDS)

The Nationwide Emergency Department Sample (NEDS) is part of a family of databases and software tools developed for the Healthcare Cost and Utilization Project (HCUP). The NEDS is the largest all-payer emergency department (ED) database in the United States, yielding national estimates of hospital-based ED visits. Unweighted, it contains data from approximately 31 million ED visits each year. Weighted, it estimates roughly 143 million ED visits.

THE 2015 NEDS CONTAINS ICD-9-CM AND ICD-10-CM/PCS CODES
On October 1, 2015 (the beginning of fiscal year 2016), hospital administrative data began using ICD-10-CM/PCS, so the first nine months of calendar year 2015 contain ICD-9-CM codes and the last three months of calendar year 2015 contain ICD-10-CM/PCS codes.1 Data elements and data structure for the 2015 NEDS have changed. Trends based on ICD diagnoses or procedures will be affected.


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.

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 NEDS. For more details, see NEDS Database Documentation and the Introduction to the NEDS, 2015 (PDF file, 1.2 MB).

Contents:

Because of the transition to ICD-10-CM/PCS on October 1, 2015 (the beginning of fiscal year 2016), the file structure and the location of many of the data elements within the files that comprise the 2015 NEDS have changed.
  • The Core File continues to be a single file containing commonly used data elements (e.g., age, expected primary payer, total charges for ED services). The difference in 2015 is that diagnoses and procedures, and related data elements have been moved out of the Core File and into the Supplemental ED and Inpatient Files.
  • The Supplemental ED File has been split into two files.
    • Nine months of the calendar year 2015 data (ED visits discharged from January 1, 2015 - September 30, 2015) are in the Supplemental ED File labeled Q1-Q3.
      • The Q1-Q3 file includes ICD-9-CM diagnosis codes and related data elements such as the injury flags, Clinical Classification Software (CCS) categories, and other data elements derived from AHRQ software tools.
      • The Q1-Q3 file includes Healthcare Common Procedure Coding System (HCPCS) Current Procedural Terminology (CPT®) procedure codes and related data elements. The inclusion of ICD-9-CM procedure codes in the Supplemental ED file was discontinued in 2015 because that coding scheme is rarely used to report procedures on outpatient records.
    • Three months of calendar year 2015 data (ED visits discharged from October 1, 2015 - December 31, 2015) are in the Supplemental ED File labeled Q4.
      • The Q4 file includes the ICD-10-CM diagnosis codes in data elements with the prefix "I10_". Injury flags and data elements derived from the AHRQ software tools are not available in the Q4 file because the ICD-10-CM versions are still under development. Beta versions of the HCUP Tools & Software for ICD-10-CM/PCS are available on the HCUP-US Web site.
      • The Q4 file includes CPT procedure codes and related data elements.
  • The Supplemental Inpatient File has been split into two files.
    • Nine months of the calendar year 2015 data (ED admissions from January 1, 2015 - September 30, 2015) are in the Supplemental Inpatient File labeled Q1-Q3.
      • The Q1-Q3 file includes ICD-9-CM diagnosis and procedure codes, and related data elements such as the injury flags, CCS categories, and other data elements derived from AHRQ software tools.
    • Three months of calendar year 2015 data (ED admissions from October 1, 2015 - December 31, 2015) are in the Supplemental Inpatient File labeled Q4.
      • The Q4 file includes the ICD-10-CM diagnosis and ICD-10-PCS procedure codes in data elements with the prefix "I10_". The injury flags and data elements derived from the AHRQ software tools are not available in the Q4 file because the ICD-10-CM versions are still under development. Beta versions of the HCUP Tools & Software for ICD-10-CM/PCS are available on the HCUP-US Web site.
  • The Hospital Weights file continues to have hospital characteristics.
The HCUP-US Web site has a section on ICD-10-CM/PCS Resources that summarizes key issues for researchers using HCUP and other administrative databases that include ICD-9-CM and ICD-10-CM/PCS coding. The Web page provides general guidance and forewarning to users analyzing outcomes that may be affected by the transition to the ICD-10-CM/PCS coding system and lists other related Web resources.
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Sampled from the State Inpatient Databases (SID) and State Emergency Department Databases (SEDD), HCUP's NEDS can be used to create national and regional estimates of ED care. The SID contain information on patients initially seen in the ED and then admitted to the same hospital. The SEDD capture information on ED visits that do not result in an admission (i.e., treat-and-release visits and transfers to another hospital).

NEDS data are available from 2006 through 2015, which allows researchers to analyze trends over time. Key features of the most recent NEDS database year (2015) include:
  • A large sample size, which provides sufficient data for analysis across hospital types and the study of relatively uncommon disorders and procedures
  • Discharge data for ED visits from 953 hospitals located in 34 States and the District of Columbia, approximating a 20-percent stratified sample of U.S. hospital-based EDs
  • Demographic data such as hospital and patient characteristics, geographic area, and the nature of ED visits (e.g., common reasons for ED visits, including injuries)
  • ED charge information for 85 percent of patients, including individuals covered by Medicare, Medicaid, or private insurance, as well as those who are uninsured
  • Children's hospitals with trauma centers, which are classified with adult and pediatric trauma centers in the current versions of the NEDS.

Information on previous years of the NEDS may be found in the Introduction to the NEDS, 2015 (PDF file, 956 KB).
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The NEDS are calendar year files based on discharge date for all data years except 2015. Because of the transition to ICD-10-CM/PCS on October 1, 2015 (the beginning of fiscal year 2016), data elements related to diagnoses and procedures are included in the supplemental ED and inpatient files and each supplemental file is split into two files. Nine months of the calendar year 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 the calendar year 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 Web site under ICD-10-CM/PCS Resources.
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The NEDS 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). The NEDS is composed of more than 100 clinical and nonclinical variables for each hospital stay. These include:
  • ICD-9-CM diagnosis, procedures, and external cause of injury codes (prior to October 1, 2015)
  • ICD-10-CM/PCS diagnosis, procedure, and external cause of morbidity codes (starting on October 1, 2015)
  • Current Procedural Terminology, Fourth Edition (CPT®-4) procedure codes on ED visits that do not results in an admission to the same hospital
  • Identification of injury-related ED visits including mechanism, intent, and severity of injury, based on ICD-9-CM coded data only
  • Admission and discharge status
  • Patient demographics characteristics (e.g., sex, age, urban-rural designation of residence, national quartile of median household income for patient's ZIP Code)
  • Expected payment source
  • Total ED charges (for ED visits) and total hospital charges (for inpatient stays for ED visits that result in admission)
  • Hospital characteristics (e.g., region, trauma center indicator, urban-rural location, teaching status)
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As a uniform, multi-State database, the NEDS promotes comparative studies of health care services and supports health care policy and research on a variety of topics, including:
  • Use of and charges for ED services
  • Medical treatment effectiveness
  • Quality of ED care
  • Impact of health policy changes
  • Access to care
  • Utilization of health services by special populations
The NEDS is used in a variety of publications: Return to Contents
 

NEDS releases for data years 2006 through 2015 are available for purchase through the 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, 54 KB; HTML).

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

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

E-mail: HCUPDistributor@AHRQ.gov
Telephone: (866) 556-4287 (toll free)
Fax: (866) 792-5313 (toll free)

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The NEDS data set is extremely large. The data are distributed as comma-separated value (CSV) 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 NEDS data on a computer, users will need the following:
  • The password provided by the HCUP Central Distributor
  • A hard drive with 60 to 100 gigabytes of space available
  • A third-party zip utility such as ZIP Reader, Secure ZIP®, WinZip®, or Stuffit Expander®
  • SAS®, SPSS®, Stata® or similar analysis software
The data set includes weights for producing national and regional estimates. NEDS documentation and tools, including programs for loading the CSV file into SAS, SPSS, or Stata, are also available on the NEDS Database Documentation page.

Please note the following based on the software you plan to use:
  • In total, the CSV version of the NEDS is almost 15 gigabytes (GB).
  • The NEDS files loaded into SAS are about 18 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 NEDS files would require approximately 55 GB of available workspace to perform a sort.
  • The NEDS files loaded into SPSS are about 35 GB.
  • Because Stata loads the entire file into memory, it may not be possible to load every data element in the NEDS 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 NEDS. 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: NEDS Overview. Healthcare Cost and Utilization Project (HCUP). December 2017. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/nedsoverview.jsp.
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Last modified 12/14/17