Data on Health and Well-being of American Indians, Alaska Natives, and Other Native Americans. National Ambulatory Medical Care Survey (NAMCS)

12/01/2006

Sponsor: U.S. Department of Health and Human Services (DHHS)/Centers for Disease Control and Prevention (CDC)/National Center for Health Statistics (NCHS)
Description: The National Ambulatory Medical Care Survey (NAMCS) collects information about the provision and use of ambulatory medical care services in the United States. Non-federally employed office-based physicians complete a one-page questionnaire for each patient visit sampled during a one-week reporting period. Collected data include physician characteristics (obtained during a survey induction interview), patient demographic characteristics (age, sex, race, ethnicity), and visit characteristics (patients symptoms, complaints or other reasons for the visit, physicians diagnoses, diagnostic and therapeutic services ordered or provided at the visit including medications, expected sources of payment, visit disposition, time spent with physician, etc.). Participating physicians must be primarily involved in office-based direct patient care, with anesthesiologists, pathologists and radiologists excluded.
Relevant Policy Issues: Measurement of Health Status, Key Health Disparities, and Factors Contributing to Measured Health Disparities.
Data Type(s): Survey
Unit of Analysis: Patient visit
Identification of AI/AN/NA: Physicians are asked to report one or more races (up to 5) for each sampled visit. The public use data file includes five single race categories and an aggregated category for visits with more than one race checked.
  • White
  • Black/African American
  • Asian
  • Native Hawaiian/Other Pacific Islander (NH/PI)
  • American Indian/Alaska Native (AI/AN)
  • More than one race reported
AI/AN/NA Population in Data Set: Total number of records in 2004 data set: 25,286
AI/AN: 93
NH/PI: 70
Geographic Scope: The geographic scope of the study is national. Analysis is possible for the following regions: Northeast, Midwest, South, West.
Date or Frequency: Data are available annually from 1973 to 1981, in 1985, and annually since 1989.
Aggregation: Each year of data, on average, has 50-90 visits by persons reported as AI/AN only and 60-100 visits by persons reported as NH/PI only. According to the NCHS, researchers frequently combine years of data for analysis in order to achieve reliable estimates. Researchers considering aggregation should take special note of changes in sample design variables across the years, as these will affect variance estimation. They should also be particularly aware of any possible clustering by race that may affect sample estimates. The format and content of the survey questionnaires has also changed across the years. Data must be weighted to produce national estimates, and researchers may wish to seek guidance about the use of weights with aggregated files.
Data Collection Methodology: The U.S. Census Bureau acts as the data collection agent for the NAMCS. The physician, or his/her staff, is trained by Census field representatives to sample patients and to complete the 1-page reporting form for each sampled visit.
Participation: Optional, without incentives
Response Rate: In the 2004 survey, the response rate for participating physicians was 64.7 percent.
Sampling Methodology: NAMCS utilizes a multistage probability sample design where geographic primary sampling units (PSUs) are selected in the first stage, physician practices within PSUs in the second stage (using the American Medical Association and American Osteopathic Association directories as the sampling frame), and a random sample of patient visits to selected physicians in the third stage.
Analysis: The weighting procedure produces essentially unbiased national estimates and has basically four components: 1) inflation by reciprocals of the probabilities of selection, 2) adjustment for nonresponse, 3) a ratio adjustment to fixed totals, and 4) weight smoothing. Patient visit weights are provided in the data set to produce accurate national estimates.
Strengths: Data are collected on key policy issues pertaining to health. There are multiple years of data available.
Limitations: In the 2004 survey, the item nonresponse rate is low overall; however this rate for the variables measuring ethnicity and race is 20.9 percent and 19.2 percent, respectively. Race and ethnicity are imputed from records with similar characteristics based on physician specialty, geographic region (in the case of ethnicity, state is used rather than region), and primary diagnosis. There are also few visits by patients categorized as AI/AN or NH/PI. Finally, NAMCS does not include physicians from Indian Health Service (IHS) in the sample frame.
Access Requirements and Use Restrictions: Data are available to the public at no cost. Restricted files which contain additional variables and non-masked data can be accessed by applying to the NCHS Research Data Center and paying a fee.
Contact Information: Main website for NAMCS http://www.cdc.gov/nchs/namcs.htm

Data Download: http://www.cdc.gov/nchs/about/major/ahcd/ahcd1.htm#Micro-data

Contact Information:
National Center for Health Statistics
Ambulatory Care Statistics Branch
3311 Toledo Road, Rm. 3409
Hyattsville, MD 20782
(301) 458-4600

 

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