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 30 million ED visits each year. Weighted, it estimates roughly 135 million ED visits. 

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:

• International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis and external cause of injury codes
• ICD-9-CM and Current Procedural Terminology, Fourth Edition (CPT®-4) procedure codes
• Identification of injury-related ED visits including mechanism, intent, and severity of injury
• 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)  

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 2013 through 2014, which allows researchers to analyze trends over time. Key features of the most recent NEDS database year (2014) 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 945 hospitals located in 33 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 84 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.

The NEDS is a stratified sample of hospitals from the State Emergency Department Databases, or SEDD, and the State Inpatient Databases, or SID.

The target universe for the NEDS is all US community hospital-based emergency departments. We define the target universe from the American Hospital Association (AHA) Annual Survey of Hospitals.

Both the State Emergency Department Databases, the SEDD, and the State Inpatient Databases, the SID, are used to construct the NEDS - or, in other words, they are the frame for the NEDS. The SEDD provides data on treat-and-release emergency department visits, which account for more than 80% of all emergency department visits. The SID provides data on the emergency department visits that resulted in an inpatient admission. The NEDS includes data on care that began in the emergency department regardless of whether the patient was treated and released or admitted to the hospital.

The strata used in creating the NEDS are US region, urban or rural location, teaching status, ownership, and trauma-level. These strata will be described in more detail later in this tutorial. As in the NIS sample design, "state" is not included as a stratum; therefore state-level analyses cannot be conducted. If you are interested in analyses by state, you should use the state-specific SID or SEDD.

Once the hospital-based emergency departments have been stratified, a sample that approximates a 20% stratified sample of US hospital-based emergency departments (the target universe) is constructed. 100% of all emergency department visits from the selected hospitals are included in the NEDS. This type of sampling design is referred to as a stratified, single-stage cluster sample. A stratified random sample of hospitals (clusters) is drawn and then all discharges are included from each selected hospital.