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

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 Hospital Ambulatory Medical Care Survey (NHAMCS) collects data on the utilization and provision of ambulatory care services in the emergency and outpatient departments of noninstitutional general and short-stay hospitals in the United States. Hospital staff complete a one-page questionnaire for each patient visit sampled during a 4-week reporting period. Collected data include hospital characteristics, 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). Excluded from the sample are federal, military, and Veterans Administration hospitals. Sample data must be weighted to produce national estimates.
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: Hospital staff are asked to report one or more races (up to 5) for each sampled visit. The public use data files include 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 Emergency Department data set: 36,589
Total number of records in 2004 Outpatient Department data set: 31,783
AI/AN: 209 in 2004 Emergency Department data set; 149 in 2004 Outpatient Department data set
NH/PI: 213 in 2004 Emergency Department data set; 305 in 2004 Outpatient Department data set
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 1992.
Aggregation: Each year of data has, on average, 120-170 outpatient department visits and 160-240 emergency department visits by persons reported as AI/AN only. In addition, each year has, on average, 140-300 outpatient department visits and 200-240 emergency department 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 NHAMCS. Hospital staff are 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 hospitals was 91 percent.
Sampling Methodology: NHAMCS utilizes a multistage probability sample design where geographic primary sampling units (PSUs) are selected in the first stage; a fixed panel of 600 hospitals, developed from the SMG Hospital Market Database in 1991 and updated using data products from Verispan, LLC, comprises the second stage; the selection of outpatient department clinics and emergency service areas (ESAs) from the outpatient and emergency departments of the sampled hospitals constitutes the third stage; and the selection of patient visits within sampled clinics and ESAs during a randomly selected 4-week reporting period is the fourth stage.
Analysis: The weighting procedure produces essentially unbiased national estimates and has three components: 1) inflation by reciprocals of the probabilities of selection, 2) adjustment for nonresponse, and 3) a population weighting ratio adjustment. Two data sets are produced one for outpatient department visits and one for emergency department visits. Patient visit weights are provided on each file 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 overall item nonresponse rate is low; however it is 20.9 percent for ethnicity and 19.2 percent for race. On the outpatient department file, race and ethnicity were missing on 11.9 percent and 11.8 percent of records respectively. On the emergency department file, race and ethnicity were missing for 10.6 percent and 15.1 percent of records respectively. Race and ethnicity are imputed in both files by randomly assigning a value from another sampled visit with similar characteristics. There are also relatively few visits by patients categorized as AI/AN or NH/PI.
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 NHAMCS: http://www.cdc.gov/nchs/nhamcs.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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