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 non-federal 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.

Specially trained interviewers visit the physicians prior to their participation in the survey in order to provide them with survey materials and instruct them on how to complete the forms. 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. 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 the physician or office staff on an encounter form provided for that purpose. Data are obtained on patients' symptoms, physicians' diagnoses, and medications ordered or provided. The survey also provides statistics on the demographic characteristics of patients and services provided, including information on diagnostic procedures, patient management, and planned future treatment.

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, only one data file is produced annually that contains both patient visit and drug information.

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. Hospital-based ambulatory surgery centers were first added to this study in 2009, and freestanding ambulatory surgery centers were added in 2010. 

For the hospital component of the survey, findings are based on a national sample of visits to emergency and outpatient departments and to ambulatory surgery facilities 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, findings are based a national sample of visits to these ambulatory surgery centers located in the 50 States and the District of Columbia that are regulated by states, certified by the Centers for Medicare and Medicaid Services, or whose primary business is ambulatory surgery. A two-stage list sample design is used that includes samples of facilities and of patient visits to these facilities.

Specially trained interviewers visit facilities prior to their participation in the survey to explain survey procedures, verify eligibility, develop a sampling plan, and train staff in data collection procedures. The survey instrument is the Patient Record form, which is provided in three versions -- one for the emergency department, one for the outpatient department, and one for the ambulatory surgery facilities. Staff are instructed to complete Patient Record forms for a systematic random sample of patient visits during a randomly assigned 4-week reporting period. Data are obtained on demographic characteristics of patients, expected source(s) of payment, patients' complaints, diagnoses, diagnostic/screening services, procedures, medication therapy, disposition, types of providers seen, causes of injury (emergency department and ambulatory surgery center only), and certain characteristics of the facility, such as, geographic region and metropolitan status