Emergency Department Injury Data from NHAMCS: A Guide

The data source

The National Hospital Ambulatory Medical Care Survey (NHAMCS), run by CDC's National Center for Health Statistics (NCHS), collects data on emergency department (ED) visits, including visits for injury.

What each visit record holds

Recorded on a one-page Patient Record Form:

• up to three reasons for the visit, in the patient's words;
• up to three diagnoses by the physician;
• up to three external causes of injury, for injury visits;
• checklists of tests, screening and procedures;
• up to six medications ordered, given or continued.

Diagnoses are coded in ICD-9-CM (International Classification of Diseases, 9th Revision, Clinical Modification).

What counts as an injury visit

NCHS defines injury visits in two ways:

Under the narrow definition, an injury visit is an initial visit with either a first-listed injury diagnosis or a valid external-cause code. Visits whose first diagnosis is a complication or adverse effect of medical care are excluded, whatever the cause code. The codes are listed in the report's tables 2 and 3 and in the tools and frameworks section.

Public-use data

• Microdata for every survey year from 1992 on, in ASCII, for use with SAS, SPSS or Stata (files and documentation).
• Files from 1993 on include masked design variables for variance estimation, with SAS input, label and format statements; Stata and SPSS statements from 2002 on.
• Rates: base them on the U.S. civilian population. NCHS provides population estimates by single year of age and sex, based on Census 2000, from 1992 on.

Tools

• Barell Matrix: a two-way grid of ICD-9-CM injury codes by body region and nature of injury, from the International Collaborative Effort on Injury Statistics.
• ICD-9-CM external-cause framework for morbidity data — including codes not in the ICD-9 mortality codes, and those added since 1994.

Analysis programs:

• SAS statements assigning external-cause codes to mechanism and intent;
• SAS and Stata programs selecting the first-listed injury diagnosis and E-code to define an injury record;
• SAS and SUDAAN code for variance estimation;
• sample SAS/SUDAAN programs producing weighted counts of injury visits by age and sex, exported to Excel.

More

• NHAMCS ED publications and presentations.
• Other ED data: the National Trauma Data Bank, AHRQ's Healthcare Cost and Utilization Project and CDC's WISQARS Nonfatal, with national estimates of nonfatal ED injuries from the National Electronic Injury Surveillance System–All Injury Program.

Sources

Based on "Emergency Department Visit Data," National Center for Health Statistics, Centers for Disease Control and Prevention; a work of the United States government in the public domain.