The Nationwide Emergency Department Sample (NEDS) is one in a family of databases and software tools developed as part of the Healthcare Cost and Utilization Project (HCUP), a Federal-State-Industry partnership sponsored by the Agency for Healthcare Research and Quality. HCUP data inform decision-making at the national, State, and community levels. This page provides an overview of the NEDS.

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Contents:

• What Is the NEDS?
• What Data Elements Are in the NEDS?
• How Does the NEDS Differ From the NIS?
• What NEDS Databases Are Available?
• How Is the NEDS Used?
• Who Uses the NEDS?
• Hardware and Software Requirements
• How Can Users Obtain NEDS Data?
• Need Help?

The Nationwide Emergency Department Sample (NEDS) is a unique and powerful database that yields national estimates of emergency department (ED) visits. The NEDS was created to enable analyses of emergency department (ED) utilization patterns and support public health professionals, administrators, policymakers, and clinicians in their decision-making regarding this critical source of care. The ED serves a dual role in the U.S. healthcare system infrastructure as a point of entry for approximately 50% of inpatient hospital admissions and as a setting for treat-and-release outpatient visits.¹

• The NEDS is the largest all-payer ED database in the United States.
• The NEDS was constructed using records from both the HCUP State Emergency Department Databases (SEDD) and the State Inpatient Databases (SID). 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). The SID contain information on patients initially seen in the emergency room and then admitted to the same hospital.
• The NEDS contains between 25 and 30 million (unweighted) records for ED visits for over 950 hospitals and approximates a 20-percent stratified sample of U.S. hospital-based EDs.
• The NEDS has many research applications, as it contains information about geographic characteristics, hospital characteristics, patient characteristics, and the nature of visits (e.g., common reasons for ED visits, including injuries).
• The NEDS includes ED charge information for over 75% of patients, regardless of payer, including patients covered by Medicaid, private insurance, and the uninsured.

The NEDS contains clinical and resource use information 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 can be weighted to produce national estimates.

The NEDS excludes data elements that could directly or indirectly identify individuals, hospitals, or states. Purchase of the NEDS beginning in 2006 is open to all users who sign a Data Use Agreement (PDF, 41 KB; HTML). Users must agree to use the database for research and statistical purposes only and to make no attempts to identify individuals.

¹Owens, P. and Elixhauser, A. Hospital Admissions That Began in the Emergency Department, 2003. Statistical Brief #1. February 2006. Agency for Healthcare Research and Quality, Rockville, Md. http://www.hcup-us.ahrq.gov/reports/statbriefs/sb1.pdf

The NEDS is composed of more than 100 clinical and nonclinical variables for each hospital stay. These include:

• ICD-9-CM diagnoses and external cause of injury codes
• Identification of injury-related ED visits including mechanism and intent of injury and severity of injury
• ICD-9-CM and CPT-4 procedures
• Discharge status from the ED
• Patient demographics (e.g., gender, age, urban-rural designation of residence, national quartile of median household income for patient's ZIP Code)
• Expected payment source (e.g., Medicare, Medicaid, private insurance, self-pay)
• Total ED charges (for ED visits) and total hospital charges (for inpatient stays for those visits that result in admission)
• Hospital characteristics (e.g., region, trauma center indicator, urban-rural location, teaching status).

More information on data elements is available in the Introduction to the NEDS.

This NIS is constructed from the State Inpatient Databases (SID) and the NEDS is constructed from the State Emergency Department Databases (SEDD) and the State Inpatient Databases (SID). Both the NEDS and NIS include records for ED visits that resulted in an admission. The NEDS also includes ED visits that did not result in admission (e.g., treated and released, transferred to another hospital, transferred to another type of health facility, left against medical advice, or died in ED).

Similar to the design of the NIS, the NEDS is built using a 20% stratified sample of institutions (for the NEDS, the institutions are hospital-based EDs). For the NEDS, all visits within the sample of selected EDs are included. So, if a hospital-based ED is selected for the NEDS sample, then all of the ED admissions from the SID and all of the ED visits from the SEDD are included in the NEDS. Both the NEDS and NIS include records for ED visits that resulted in an admission. However, the NEDS also includes ED visits that did not result in admission.

Stratification for the NEDS and NIS include four of the same hospital characteristics: region, teaching status, control, and urban-rural location, but the NEDS includes a more detailed designation for metropolitan areas. While the NIS uses hospital bed size as the fifth stratifier, the NEDS uses trauma center designation. Information on ED bed size was not available.

Unlike the NIS, the NEDS does not contain any state identifiers. The NEDS also does not contain the same hospitals as the NIS. Although many of the data elements found on the NIS are also available on the NEDS, data elements that are more relevant to the inpatient setting (such as the neonatal/maternal indicator) are not included in the NEDS.

The Nationwide Emergency Department Sample (NEDS) is available for purchase through the HCUP Central Distributor.

• The 2010 NEDS includes almost 29 million ED visits from 961 hospital-based EDs in 28 states.
• The 2009 NEDS includes almost 29 million ED visits from 964 hospital-based EDs in 29 states.
• The 2008 NEDS includes over 28 million ED visits from 980 hospital-based EDs in 28 states.
• The 2007 NEDS includes about 27 million ED visits from almost 966 hospital-based EDs in 27 states.
• The 2006 NEDS includes almost 26 million ED visits from over 955 hospital-based EDs in 24 states.

Children’s hospitals with trauma centers are classified with adult/pediatric trauma centers in the 2009 NEDS, 2008 NEDS, Version 2 of the 2007 NEDS (released April 2010), and Version 3 of the 2006 NEDS (released April 2010).

The NEDS generates estimates on almost 130 million ED visits (weighted), thereby making it an exceptional resource for conducting research on high-profile emergent health delivery issues. One of the most distinctive features of the NEDS is its large sample size, which allows for analysis across hospital types and the study of relatively uncommon disorders and procedures.

The NEDS is a uniform, nationwide sample that promotes comparative studies of health care services and will support health care policy research on a variety of topics including:

• Use and charges of ED services
• Medical treatment effectiveness
• Quality of ED care
• Impact of health policy changes
• Access to care
• Utilization of health services by special populations.

NEDS data may be used by a variety of nonprofit and for-profit organizations, including:

• Actuarial firms
• State and Federal Government agencies
• Health care consultants
• Health professions societies
• Health services researchers and policy analysts
• Hospital information system firms
• Hospitals and health care systems
• Health and life insurance companies
• Managed care organizations
• Pharmaceutical and medical product manufacturers and marketing firms
• Schools of business
• Schools of public health
• Utilization review organizations
• Health care planning organizations
• Public health and emergency preparedness agencies.

The NEDS data set comes in comma-delimited (CSV) format compressed with WinZip®. In order to load and analyze the NEDS data on a computer, you will need the following:

• A DVD drive
• A hard drive with 60 to 100 gigabytes (GB) of space available
• SAS®, SPSS®, Stata® or similar analysis software
• A third-party zip utility such as ZIP Reader, WinZip® or 7-Zip.

The NEDS is an extremely large database that requires sophisticated, statistical software for analysis. SAS, SPSS, and Stata users are provided programs for converting CSV files.

• In total, the comma-delimited version of the NEDS is almost 14 gigabytes (GB).
• The NEDS files loaded into SAS are about 11 GB. In SAS, the largest use of space typically occurs during a sort, which requires work space about three times the size of the file. Thus, the NEDS files would require about 33 GB of available workspace to perform a sort. Even most SAS data steps will require twice the storage of the file, so that both the input and output files can coexist.
• The NEDS files loaded into SPSS are under 30 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. Because 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, the amount of space required could escalate rapidly.

The 2006-2010 NEDS are available for purchase through the HCUP Central Distributor.

For answers to commonly asked questions regarding HCUP databases and tools, please review the HCUP Index Page. If you cannot find an answer to your question, please contact HCUP User Support Staff.

To reach HCUP User Support, please contact us by e-mail or phone:

• e-mail: hcup@ahrq.gov
• Phone (toll free): 1-866-290-HCUP

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