About the Ambulatory Health Care Surveys

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National Ambulatory Medical Care Survey

The National Ambulatory Medical Care Survey (NAMCS) is a national survey designed to meet the need for objective, reliable information about the provision and use of ambulatory medical care services in the United States. Findings are based on a sample of visits to nonfederally employed office-based physicians who are primarily engaged in direct patient care. Physicians in the specialties (including designated sub-specialties) of anesthesiology, pathology, and radiology are excluded from the survey. The survey was conducted annually from 1973 to 1981, again in 1985, and annually since 1989. More information on the NAMCS Health Center Component can be found here.

Data collection from the physician, rather than from the patient, provides an analytic base that expands information on ambulatory care collected through other NCHS surveys. Prior to 2012, NAMCS relied on paper instruments; the survey switched to computerized data collection in 2012. Each physician is randomly assigned to a 1-week reporting period. Data about the physician and their practice characteristics are collected during a survey induction interview.

For survey years 1973 to 1991, there are two data files: one for patient visit data and a second for drug mention data. The second file is limited to those visits with mention of medication therapy. For the 1991 data, it is possible to link information on the drug file with information on the patient visit file. Beginning with the 1992 survey year through 2011, one main data file was produced annually that contains both patient visit and drug information.


National Hospital Ambulatory Medical Care Survey

The National Hospital Ambulatory Medical Care Survey (NHAMCS) has been fielded annually since 1992 to collect data on the utilization and provision of ambulatory care services in hospital emergency and outpatient departments. Data collection from hospital-based ambulatory surgery centers began in 2009. And between 2010 and 2012 NHAMCS gathered data on visits to freestanding ambulatory surgery centers. In 2018, the survey began focusing on just the ambulatory visits made to emergency departments.

For the hospital component of the survey, findings are based on a national sample of visits to emergency departments (EDs) in noninstitutional general and short-stay hospitals, exclusive of Federal, military, and Veterans Administration hospitals, located in the 50 States and the District of Columbia. A three-stage probability sampling design is used. The first stage consists of a sample of geographically defined areas also known as Primary Sampling Units (PSU). In the second stage, is of hospitals within those PSU and all emergency service areas within the emergency department are selected. Emergency service areas (ESAs) are not sampled at this stage. In the third stage ESAs are sampled.

Specially trained interviewers visit the sampled facilities prior to their participation in the survey to explain survey procedures, verify eligibility, and develop a sampling plan. Prior to 2012, NHAMCS relied on paper instruments; the survey switched to a computerized questionnaire in 2012. Each emergency department is randomly assigned to a 4-week reporting period. During this period, data for a systematic random sample of visits are recorded by Census interviewers using a computerized Patient Record Form. Data are obtained on patient characteristics such as age, sex, race, and ethnicity, and visit characteristics such as patient’s reason for visit, provider’s diagnosis, services ordered or provided, and treatments, including medication therapy. In addition, data about the facility are collected as part of a survey induction interview.