Checklist for Working with the 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 number of studies using the NEDS has increased in recent years. HCUP databases, including the NEDS, are consolidated sources of information that can be used for many types of research. Researchers, peer manuscript reviewers, and journal editors need to understand the NEDS database design, its strengths and limitations, and how it has changed over time to ensure its appropriate use and to interpret study results. This document provides a checklist of key elements to consider and connects you to NEDS informational resources, organized into four sections:
  1. HCUP Data Use Agreement for Nationwide Databases and Acknowledgements
  2. Research Design
  3. Data Analysis
  4. Transition from International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) to the Tenth Revision, Clinical Modification/Procedure Coding System (ICD-10-CM/PCS).
The NEDS Database Documentation page is the main resource for all information regarding the NEDS, including the Introduction to the HCUP Nationwide Emergency Department Sample (NEDS), which is recommended as a starting resource for new users.

NEDS Data Use and Acknowledgments
  Checklist Item Description Checklist Resource
Obtain and adhere to the HCUP Nationwide Database Data Use Agreement (DUA).1 The HCUP DUA governs the disclosure and use of the data, including affirmations to protect individuals, establishments, and the database itself. For general information, review the Responsibilities of the Data Purchaser and the HCUP Nationwide Database Data Use Agreement (DUA).

To access the NEDS, you must complete the HCUP Data Use Agreement Training.
Verify privacy protections for individuals and hospitals. Individuals cannot be identified directly or indirectly.

Reporting cell sizes <10 increases the risk of re-identification and is discouraged, as specified in the Data Use Agreement.
For general information, review the Requirements for Publishing with HCUP Data page on the HCUP User Support (HCUP-US) website.
Cite HCUP, the NEDS, and other HCUP tools. HCUP, the NEDS, and other supporting tools must be correctly cited in the abstract and manuscript. For more information, review the Suggested Citations for HCUP Databases and Tools page on HCUP-US.
Acknowledge HCUP Partners. Participating HCUP Partners should be listed in the manuscript by name or acknowledged by a hyperlink to the HCUP-US website. For more information, review the List of HCUP Data Partners for Reference in Publications page on HCUP-US.
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Research Design
Learn how to account for the NEDS sampling design. The NEDS is sampled from the U.S. hospital-owned emergency departments (ED) with data in the HCUP State Emergency Department Databases (SEDD) and the State Inpatient Databases (SID). Accounting for the sampling design is critical for accurate analyses. For detailed information, review the Introduction to the HCUP Nationwide Emergency Department Sample (NEDS).

To learn more about the NEDS sample design, view the HCUP Sample Design tutorial on the HCUP Online Tutorial Series page on HCUP-US.
Two types of ED visits are included in the NEDS: ED visits that result in the patient being admitted to the same hospital and those that do not. The unit of analysis in the NIS is inpatient stays, not individual patients. Only conditions, procedures, and diagnostic tests occurring during a specific inpatient hospital encounter are captured in the NIS. Records of events and diagnoses before or after the stay are not available.

NEDS records include information on services provided during the hospital encounter. Information on services prior to or after discharge are not included. For patients who were directly admitted to the same hospital through the ED, it is not possible to identify whether a procedure was performed in the ED or as part of the inpatient stay.
For more information, review the NEDS Description of Data Elements page on HCUP-US.
Revisit analyses cannot be performed. The NEDS cannot be used to conduct revisit analyses. There is no synthetic patient identifier that would allow patient-level analysis to identify individuals with more than one ED visit. In contrast, some HCUP State databases may be used for this type of analysis. For more information on conducting revisit analyses at the State level, review the HCUP Supplemental Variables for Revisit Analyses page on HCUP-US.
No State-level analyses are performed. State identifiers are not included in the NEDS. To conduct State-level analysis, you must use the SID or SEDD. To learn more about the SEDD, review the Overview of the State Emergency Department Databases page on HCUP-US.

To learn more about the SID, review the Overview of the State Inpatient Databases (SID) page on HCUP-US.
Facility-level analyses are limited. Hospital identifiers are not included in the NEDS. The NEDS hospital number (HOSP_ED) can be used to determine ED volume for the facility, but not to directly identify the hospital. In addition, this data element links the NEDS Core file to the NEDS Hospital file but does not link to other HCUP or external databases.

You should not attempt to identify individual facilities, as specified in the Data Use Agreement.
For more information, review the Sampling Design of the NEDS section of the Introduction to the NEDS on the NEDS Database Documentation page on HCUP-US.
No physician-level analyses are performed. Physician identifiers are not included in the NEDS. Some HCUP State databases may be used for this type of analysis. For more information, review the NEDS Description of Data Elements on the NEDS Database Documentation page on HCUP-US.

For more information, review the Sampling Design of the NEDS section of the Introduction to the NEDS on the NEDS Database Documentation page on HCUP-US.
Administrative (ICD and CPT) codes are appropriate for the outcomes of interest. Administrative codes for the diagnoses or procedures of interest (ICD-9-CM, ICD-10-CM/PCS, and Current Procedural Terminology [CPT®)) should be used with care, especially over time, as codes and coding rules change annually. For more information, review the ICD-9-CM and ICD-10-CM/PCS Diagnosis and Procedure Codes and CPT Procedure Codes section of the Introduction to the NEDS on the NEDS Database Documentation page on HCUP-US.

Refer to the ICD-10-CM/PCS Resources page on HCUP-US under Data Innovations for a summary of key issues for researchers using HCUP and other administrative databases that include ICD-10-CM/PCS coding.

To check for year-to-year variation in administrative codes, consult with a medical coding professional.
Administrative (ICD and CPT) codes are appropriate for the setting of care. The NEDS contains ICD-9-CM or ICD-10-PCS procedure information (depending on the data year) on its Supplemental Inpatient File and CPT procedure information on its Supplemental ED File.

The meaning of the first listed diagnosis (DX1 or I10_DX1) differs based on the type of ED visit. The first-listed diagnosis on an ED admission (SID record) is the condition principally responsible for the inpatient stay. The first-listed diagnosis on an ED treat-and-release visit (SEDD record) is the condition, problem, or symptom identified in the medical record to be chiefly responsible for the services provided.

Secondary diagnoses reported on an inpatient admission from the ED may be from either the ED or inpatient hospital setting.
For more information, review the ICD-9-CM and ICD-10-CM/PCS Diagnosis and Procedure Codes and CPT Procedure Codes section of the Introduction to the NEDS on the NEDS Database Documentation page on HCUP-US.

Please refer to the HCUP Methods Series Report #2011-03, Special Study on the Meaning of the First-Listed Diagnosis on Emergency Department and Ambulatory Surgery Records.
Account for year- based differences in data element availability in the NEDS. The study design should account for differences in data element availability across data years. For example, the number of diagnosis codes present can vary by year. For more information about data element availability in the NEDS, review the NEDS Description of Data Elements on the NEDS Database Documentation page on HCUP-US.
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Data Analysis
Use weights for national estimates. To generate national estimates using the NEDS, use either the hospital weight (HOSPWT) to weight sampled hospitals to all community hospitals located in the United States, or the discharge weight (DISCWT) to weight sampled discharges to the discharges from community hospitals located in the United States. To learn how to apply NEDS weights, view the Producing National HCUP Estimates On-line Tutorial on the Tutorial Series page on HCUP-US.
Account for the design of the NEDS when calculating standard errors. There are two methods for calculating standard errors for estimates produced from the NEDS. To learn how to calculate standard errors, view the HCUP Calculating Standard Errors On-line Tutorial on the Tutorial Series page on HCUP-US.

Review the HCUP Methods Series Report # 2003-02, Calculating Nationwide Inpatient Sample Variances. Prior to 2012, the NIS used stratified sample design similar to the NEDS, so techniques appropriate for the NIS prior to 2012 are also appropriate for the NEDS.
Account for clustering or nesting of observations. Discharges in the NEDS are clustered, or nested, within hospitals. Hierarchical linear modeling (HLM) is one way to account for this design aspect of the NEDS. For information on using HLM, review the HCUP Methods Series Report # 2007-01, Hierarchical Modeling Using HCUP Data. Although this report references the NIS, HLM can also be applied to the NEDS.
Account for missing values. Several techniques are available to assess and reduce the impact of missing data when using the NEDS. For general information, review the Missing Values section of the Introduction to the NEDS on the NEDS Database Documentation page on HCUP-US.

For detailed information on missing values, review the HCUP Methods Series Report # 2015-01, Missing Data Methods for the NIS and SID. Although the report uses examples from the NIS and the SID, the methods may also be applied to the NEDS.
Calculate rates of ED visits per population when you need to control for differences in the underlying populations. There are several sources of population data that can be used with the HCUP databases to calculate rates of ED visits per population to improve comparisons between subgroups (e.g., region of the country). More information is available in HCUP Methods Series Reports by Topic page on HCUP-US Population Denominator Data for Use with the HCUP Databases (multiple documents; updated annually).
Estimate incidence or prevalence. The NEDS can be used to estimate incidence or prevalence of both common and rare conditions in some, but not all, scenarios. For information on estimating incidence and prevalence, review the HCUP Methods Series Report # 2016-06, Using the HCUP Databases to Study Incidence and Prevalence.
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ICD-9-CM to ICD-10-CM/PCS Transition
Account for changes in the NEDS related to ICD-10-CM/PCS. The transition to ICD-10-CM/PCS has had a direct impact on the reporting of medical services, and these changes affect research using administrative data.

The structure of and data elements included in the NEDS are affected by the transition to ICD-10-CM/PCS.
For more information, refer to the ICD-10-CM/PCS Resources page on HCUP-US that summarizes key issues for researchers using HCUP and other administrative databases that include ICD-9-CM and ICD-10-CM/PCS coding.

For additional information about these changes, review the 2015 NEDS Revised File Structure and New Data Elements on the NEDS Database Documentation page on HCUP-US.
Follow HCUP recommendations for reporting trends with data that include both ICD-9-CM and ICD-10-CM/PCS coding. Recommendations for reporting trends based on HCUP data that span the October 1, 2015 transition date (before and after the introduction of ICD-10-CM/PCS) have been developed to help researchers design studies. For more information, review the Recommendations for Reporting Trends Using ICD-9-CM and ICD-10-CM/PCS Data.
Use current versions of HCUP Tools for ICD-10-CM/PCS-coded data. ICD-10-CM/PCS coding guidance is continuing to evolve. HCUP software tools for ICD-10-CM/PCS will be updated and should be reapplied throughout the research process. For this reason, it is important to always use the most current version of these tools. Consult the HCUP Tools & Software page on HCUP-US regularly for the most current versions of the HCUP software tools.
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1 HCUP data users acknowledge that violation of the AHRQ confidentiality statute is subject to a civil penalty of up to $14,140 under 42 U.S.C. 299c-3(d), and that deliberately making a false statement about this or any matter within the jurisdiction of any department or agency of the Federal Government violates 18 U.S.C. 1001 and is punishable by a fine, up to five years in prison, or both. Violators of this Agreement may also be subject to penalties under state confidentiality statutes that apply to these data for particular states.

Internet Citation: Checklist for Working with the NEDS. Healthcare Cost and Utilization Project (HCUP). November 2020. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/db/nation/neds/nedschecklist.jsp.
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Last modified 11/12/20