1992 to present
Mode of Collection
Multi-stage probability sample survey: computer assisted personal interviews (CAPI) and abstraction of data.
The National Hospital Ambulatory Medical Care Survey (NHAMCS) collects data on the utilization and provision of medical care services provided in hospital emergency and outpatient departments. Data are collected from medical records.
Data are collected on types of providers seen, reason for visit, diagnoses, drugs ordered, provided, or continued, and selected procedures and tests performed during the visit. Other data collected include patient demographics, method of payment, and selected characteristics of the hospital.
The survey is a representative sample of visits to emergency departments and outpatient departments of nonfederal, short-stay, or general hospitals. Telephone contacts are excluded.
A four-stage probability sample design is used in NHAMCS, involving (a) samples of geographically defined primary sampling units (PSUs), (b) hospitals within PSUs, (c) emergency departments (EDs) within hospitals, and (d) ED patient visits. All ED service areas are included. EDs included in the survey must offer 24-hour physician services. Trained interviewers visit the sampled facilities prior to their participation in the survey to collect information about the facility, explain survey procedures, verify eligibility, and develop a sampling plan. Each ED is randomly assigned to a 4-week reporting period. During this period, data for a systematic random sample of visits are recorded by the interviewers using a computerized Patient Record Form. Sample data are weighted to produce national estimates.
Response Rates and Sample Size
In any given year, the hospital sample consists of approximately 450 hospitals, of which 80% have EDs. In 2016, 19,467 ED patient record forms were completed, for an overall ED response rate of 56%.
The NHAMCS patient record form is modified approximately every 2 to 4 years to reflect changes in physician practice characteristics, patterns of care, and technological innovations.