Research Tools

Ambulatory Care Drug Database System

This query system allows you to search for drugs mentioned in the NAMCS and NHAMCS by entry name, by generic name, and by ingredients. It can provide information on drug characteristics including therapeutic class, composition status, prescription status, and control status.

Diagnosis Master Category List

The Diagnosis Master Category List (DMCL) is a classification scheme that can be used across inpatient and ambulatory settings when analyzing data. The DMCL is based on the International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) and can be used to classify diagnosis codes into clinically meaningful categories. The DMCL classification was used in Summary Web Tables starting from 2016.


Expected Sources of Payment Data in NAMCS and NHAMCS [ PDF – 44 KB]


Methodology Used to Create “Initial Visit” for 2005 and 2006 NHAMCS [PDF – 37 KB]


Physician-Level Estimates

  • NAMCS data can be used to make physician estimates as well as visit estimates. As part of the survey induction process, physicians are interviewed about themselves and their practices, using the Physician Induction Interview Form. NAMCS public use files from 2005 forward contain a physician-level weight that can be used to make estimates of office-based physicians who saw patients during their reporting week, representing the majority of NAMCS participants. The public use files contain a variety of physician-level variables, and additional items [PDF – 50 KB] are available through the NCHS Research Data Center. The RDC files also contain records for NAMCS physicians who are not included on the public use files for various reasons (did not see patients during reporting week, did not submit visit forms). Including these physicians in one’s analysis along with those who saw patients can provide national estimates of all office-based physicians.
  • A NAMCS Public Use Physician Trend File is also available.  This file includes all previously released physician data from the 2005 through 2010 NAMCS Public Use Files; no visit data are included.  A single record is included for each physician in every survey year; each record contains information collected during the Physician Induction Interview along with a weighting variable which enables researchers to make national estimates. File documentation is also available for downloading, along with SAS files for reading and formatting the data.

Public Use Data Documentation Updates


Public Use Data File Updates


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


Staff Presentations

Includes PowerPoint and PDF documents from various presentations in past Data User Conferences (2004-2015).

Tips for Using NHAMCS Data

  • A new template for producing Methods sections of journal articles using NHAMCS data is available [PDF – 31 KB], covering data years 1992-2016.
  • Two former NHAMCS statisticians were interviewed by an editor of the Annals of Emergency Medicine about how to access NHAMCS public use files, analyze the data, and report the results. Read their recommendations [PDF – 85 KB]. Note that, while this information is still applicable for the most part, the interview dates from 2012 and some updates have occurred since then.  The updated template above provides the most up-to-date information.  Please contact the Ambulatory and Hospital Care Statistics Branch at 301-458-4600 or by email if you have questions.

Trend Analysis Using NAMCS and NHAMCS Drug Data

Details changes that were made in the processing of NAMCS and NHAMCS drug data starting with the 2006 surveys.