National Hospital Ambulatory Medical Care Survey, 2004 (ICPSR 4530)

Principal Investigator(s): United States Department of Health and Human Services. National Center for Health Statistics


The National Hospital Ambulatory Medical Care Survey (NHAMCS) provides data from samples of patient records selected from emergency departments (EDs) and outpatient departments (OPDs) of a national sample of hospitals. The resulting national estimates describe the use of hospital ambulatory medical care services in the United States. For the 2004 survey, data were collected from 204 OPDs and 458 EDs. Among the variables included are age, race, and sex of the patient, reason for the visit, physician's diagnoses, cause of injury, surgical procedures (OPDs only), medication therapy, and expected source of payment. For 2004, additional updates and revisions have been made to the drug characteristics data. The variables CSTRATM and CPSUM have been added to assist in the computation of variances.

Series: National Hospital Ambulatory Medical Care Survey Series

Access Notes

  • The public-use data files in this collection are available for access by the general public. Access does not require affiliation with an ICPSR member institution.

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    This study is provided by ICPSR. ICPSR provides leadership and training in data access, curation, and methods of analysis for a diverse and expanding social science research community.


DS0:  Study-Level Files
DS1:  Emergency Department Data - Download All Files (189.374 MB) large file
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ASCII + SAS Setup    SPSS Setup    Stata Setup   
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DS2:  Outpatient Department Data - Download All Files (189.147 MB) large file
SAS    SPSS    Stata    ASCII   
ASCII + SAS Setup    SPSS Setup    Stata Setup   
Analyze Online:

Study Description


U.S. Dept. of Health and Human Services. National Center for Health Statistics. NATIONAL HOSPITAL AMBULATORY MEDICAL CARE SURVEY, 2004. ICPSR04530-v1. Hyattsville, MD: U.S. Dept. of Health and Human Services, National Center for Health Statistics [producer], 2006. Ann Arbor, MI: Inter-university Consortium for Political and Social Research [distributor], 2006-09-06.

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Scope of Study

Subject Terms:    ambulatory care, emergency services, health care services, hospitalization, hospitals, injuries, medical care, medical evaluation, medical procedures, medical records, patient care, patients, payment methods, surgery, treatment

Geographic Coverage:    United States

Time Period:   

  • 2004

Date of Collection:   

  • 2003-12-29--2004-12-26

Universe:    Visits to the emergency and outpatient departments of noninstitutional general and short-stay hospitals within the 50 states and the District of Columbia, which had an average length of stay of less than 30 days, or to hospitals whose specialty was general (medical or surgical) or children's general. Excluded were federal hospitals, hospital units within institutions, and hospitals with less than six beds staffed for patient use.

Data Type(s):    administrative records data

Data Collection Notes:

(1) Users should be aware that Stata will not allow value labels for character (string) format variables. The NHAMCS 2004 data contain a number of character variables (e.g., DIAG1, DIAG2, DIAG3 -- physician's listed diagnosis codes). (2) A numeric recode version of the diagnosis variables (DIAG1R, DIAG2R, DIAG3R) has been included in the data. Value labels have been added to the SAS and SPSS setup files. Users may verify the labeling of the numeric recode variables by referring to the character (string) format variables DIAG1, DIAG2, DIAG3. Please consult the User Guide for detailed information regarding numeric recodes for cause of injury, diagnosis, and procedure codes. (3) Per agreement with the National Center for Health Statistics (NCHS), ICPSR distributes the data files and text of the technical documentation for this collection as prepared by NCHS. (4) Detailed information regarding the use of weight variables and variance estimation is located in the User Guide.


Sample:    The National Hospital Ambulatory Medical Care Survey (NHAMCS) used a four-stage probability design with samples of primary sampling units (PSUs), hospitals within PSUs, clinics within hospitals, and patient visits within clinics.

Weight:    Users should use the variable PATWT when performing analyses.

Data Source:

Patient visit records from hospital emergency departments and outpatient departments.

Restrictions: In preparing the data files for this collection, the National Center for Health Statistics (NCHS) has removed direct identifiers and characteristics that might lead to identification of data subjects. As an additional precaution NCHS requires, under Section 308(d) of the Public Health Service Act (42 U.S.C. 242m), that data collected by NCHS not be used for any purpose other than statistical analysis and reporting. NCHS further requires that analysts not use the data to learn the identity of any persons or establishments and that the director of NCHS be notified if any identities are inadvertently discovered. ICPSR member institutions and other users ordering data from ICPSR are expected to adhere to these restrictions.


Original ICPSR Release:   2006-09-06

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