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Questionnaires, Datasets, and Related Documentation

Survey Methodology

An overview of the 2009 survey methodology is presented here. Please note that complete survey documentation for all survey years can be easily downloaded using the link under Public-Use Data Files, below.

Survey Instruments

Scope and Sample Design

Data Collection and Processing

Estimation Procedures

Reliability of Survey Estimates

Classification Systems Used with the NAMCS and NHAMCS

  • International Classification of Diseases
  • National Drug Code Directory (used in NAMCS and NHAMCS prior to 2006)
  • Multum (used in NAMCS and NHAMCS starting in 2006)
  • Reason for Visit Classification, Drug Entry List, Generic Ingredient List:
    These classifications are updated on an annual basis and printed in the documentation for each survey year. In addition, text formats for reason for visit, drug entry, and generic ingredient codes are all available in downloadable SAS formats for data years 1993-2010 and SPSS syntax files for 2002-2010. The SAS and SPSS formats also include text labels for the following codes: diagnosis, cause of injury, procedures, and therapeutic class of drug.

List of Survey Items, 1973-2012

Public-use Data Files (1973-2015)

Downloadable Data Files

Notice: Currently, NAMCS public-use files for 1993-2015 and NHAMCS public-use files for 1992-2014 contain sample design variables in masked form. The initial release of the 2000-2015 public-use files includes masked sample design variables. We re-released the 1993-99 NAMCS and 1992-99 NHAMCS files to include these variables. For re-released files, file names and layouts are essentially the same, but the design variables were appended to each file according to a generic file layout that is available for downloading. NAMCS public-use files for survey years prior to 1993 are planned to be re-released with masked sample design variables on an ongoing basis.

However, data users should note that, beginning with the 2002 public use files, two new masked design variables were added to the file, for use with statistical software that assumes a single stage of sampling. For the 2003 public use files and beyond, the decision was made to include only these two masked design variables for variance estimation. Therefore, data users who wish to combine years of data from 2003 and beyond with years prior to 2002 will need to create these two variables for each file prior to 2002. A technical paper, Using Ultimate Cluster Models with NAMCS and NHAMCS Public Use Files [PDF – 34 KB], gives instructions.

NOTICE: Some data users have experienced a problem when trying to open self-extracting compressed data files and documentation in .EXE format in survey years prior to 2003. They receive a message that the version of the file is not compatible with the version of Windows they are running. This is because the files were created when NCHS used a 32-bit version of Windows, but newer versions use a 64-bit version. One work-around for this problem involves the use of WinZip software. Save the file in your local directory as usual, but instead of double-clicking on the file name to access the data, right-click the file name, select WinZip and choose one of the options for file extraction. This will cause an uncompressed version of file to appear in the directory window. For the longer term, NCHS is working on producing a new version of the problem files. Please contact the Ambulatory and Hospital Care Statistics Branch if you have questions. (9/2014)

Downloadable Documentation

Notice: For 1993-99 NAMCS and 1992-99 NHAMCS, be sure to download not only the original file documentation for each year, but also the supplemental files that explain the new sample design variables that have been added to each file. The supplemental files also include descriptions of any revisions that may have been made to the original data files.

NAMCS and NHAMCS data can also be downloaded from the Inter-University Consortium for Political and Social Research (ICPSR).

SAS Documentation and Datasets

Notice: We now have SAS input statements, variable labels, value labels, and format assignments available for NAMCS data years 1993-2015 and NHAMCS data years 1992-2014.


  • SAS Input Statements
  • SAS Variable Labels and Format Assignments
  • SAS Value Labels
  • Pre-made SAS Dataset for 2015 NAMCS


  • SAS Input Statements
  • SAS Variable Labels and Format Assignments
  • SAS Value Labels
  • SAS Value Labels

SAS Code to Produce Aggregated Visit Statistics at the Physician or Facility Level [PDF – 34 KB]

SPSS Documentation and Datasets

Stata Documentation and Datasets

Data on CD-ROM

Additional NAMCS and NHAMCS data available at the Research Data Center

The NAMCS and NHAMCS datasets that are available to approved users of the NCHS Research Data Center contain additional variables not included on the public use datasets.