National Ambulatory Medical Care Survey
The National Ambulatory Medical Care Survey (NAMCS) is a national survey designed to provide information about the provision of medical care services in office-based physician practices in the U.S. All 50 states and the District of Columbia have been included in the survey since 1989.
A multistage probability design is employed. The first-stage sample consists of 112 primary sampling units (PSUs) selected from the 1,900 such units into which the U.S. has been divided. In each sample PSU, a sample of practicing nonfederal office-based physicians is selected from master files maintained by the American Medical Association and the American Osteopathic Association. The final stage involves systematic random samples of office visits during randomly assigned 7-day reporting periods. Screening interviews are conducted by survey field staff to obtain information about physicians' office-based practices and ensure that the practice is within the survey scope. Field staff visit eligible physicians prior to participation to provide materials and instruction. Participants are asked to complete patient record forms for a systematic random sample of approximately 30 office visits occurring during a randomly assigned 1-week period. Sample data are weighted to produce national estimates.
In 2007, a sample of 3,540 physicians was selected; 2,399 were in scope and 1,568 participated for a response rate of 65.4% Data were provided for 32,778 visits.
The NAMCS patient record form is modified approximately every 2-4 years to reflect changes in physician practice characteristics, patterns of care, and technological innovations. Sample sizes vary by survey year. For some years, it may be appropriate to combine two or more years of data when examining relatively rare populations or events.
National Center for Health Statistics. Health United States 2009: With Special Feature on Medical Technology. Hyattsville, Maryland. 2010; pp 458-459.