About the Ambulatory Health Care Surveys

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 of anesthesiology, pathology, and radiology are excluded from the survey. The survey was conducted annually from 1973 to 1981, in 1985, and annually since 1989. In 2006 a separate sample of community health centers (CHCs) was added to the survey; the CHC component samples visits to physicians and non-physician clinicians.

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 an automated laptop-assisted data collection method in 2012. Each physician is randomly assigned to a 1-week reporting period. During this period, data for a systematic random sample of visits are recorded by Census interviewers using an automated Patient Record form developed for that purpose. Data are obtained on patient characteristics such as age, sex, race, and ethnicity, and visit characteristics such as patient’s reason for visit, physician’s diagnosis, services ordered or provided, and treatments, including medication therapy. In addition, data about the physician and his or her practice characteristics are collected as part of a survey induction interview.

For survey years 1973-91, 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. Starting in 2012, in addition to the traditional NAMCS file, a separate file of data for CHCs including physicians and non-physician clinicians will be produced.

National Hospital Ambulatory Medical Care Survey

The National Hospital Ambulatory Medical Care Survey (NHAMCS) is designed to collect data on the utilization and provision of ambulatory care services in hospital emergency and outpatient departments, and in ambulatory surgery centers. The survey of hospital emergency and outpatient departments has been ongoing each year since 1992. Annual data on ambulatory surgery performed in hospitals has been gathered every year since 2009. From 2010-2012, NHAMCS also gathered data on ambulatory surgery procedures performed in freestanding ambulatory surgery centers. In 2013, data collection from freestanding centers was suspended so that a new sampling frame could be developed.

For the hospital component of the survey, findings are based on a national sample of visits to emergency departments (EDs), outpatient departments (OPDs), and ambulatory surgery locations (ASLs) 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 four-stage probability sampling design is used. The first stage consists of a sample of geographically defined areas, and the second stage is of hospitals within these areas. In the third stage, clinics within outpatient departments are selected. All emergency service areas and in-scope ambulatory surgery locations are included. In the final stage, patient visits to these settings are sampled.

For the freestanding ambulatory surgery component of the NHAMCS, data were collected from a national sample of visits to these ambulatory surgery centers located in the 50 States and the District of Columbia that were regulated by states, certified by the Centers for Medicare and Medicaid Services, or whose primary business was ambulatory surgery. A two-stage list sample design was used that included samples of facilities and of patient visits to these facilities.

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 an automated laptop-assisted data collection method in 2012. Each sampled emergency department, outpatient department, or ambulatory surgery location 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 an automated Patient Record form which is provided in three versions, one for each type of location (ED, OPD, or ASL). 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.