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Using National Hospital Ambulatory Medical Care Survey (NHAMCS) data for injury analysis

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Center for Health Statistics. Using National Hospital Ambulatory Medical Care Survey (NHAMCS) data for injury analysis. Linda McCaig Ambulatory Care Statistics Branch

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Using National Hospital Ambulatory Medical Care Survey (NHAMCS) data for injury analysis

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  1. U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Center for Health Statistics Using National Hospital Ambulatory Medical Care Survey (NHAMCS) data for injury analysis Linda McCaig Ambulatory Care Statistics Branch Division of Health Care Statistics

  2. Overview • Background • Survey methodology • Data uses • User considerations for injury analysis

  3. NHAMCS background • National probability sample survey of visits to EDs and OPDs of non-federal, short-stay, and general hospitals • Survey began in 1992 • Annual data collection (Census)

  4. NHAMCS Methodology

  5. 112 geographic PSUs 500 hospitals 400 EDs and 250 OPDs 37,000 ED and 35,000 OPD visits 4-week reporting period NHAMCS Sample design

  6. ED Items collected • Patient characteristics • age, race, sex • Visit characteristics • Mode of arrival, immediacy, reason for visit, injury-related, diagnosis, medication • Hospital characteristics • ownership, teaching hospital

  7. Injury/poisoning/adverseeffect items • Intentionality • Unintentional • Intentional • self-inflicted • assault • Work related • External cause • Up to 3 causes • Narrative text since 1997

  8. Coding systems used • A Reason for Visit Classification (NCHS) • International Classification of Diseases-9-CM • diagnosis codes • external cause of injury codes • Barell Injury Diagnosis Matrix: Classification of Region of Body and Nature of Injury • Drug coding system (NCHS) • National Drug Code Directory

  9. Injury definition • Injury checkbox marked • Reason for visit in injury module • Diagnosis is in injury or poisoning chapter of ICD-9-CM • Cause of injury recorded

  10. Data quality • Data are coded and keyed by Constella Group Inc. (CG) • 10 percent of records are independently coded and keyed • Coding error rate for cause of injury is 0.8 percent • Item nonresponse for cause of injury 4-23%

  11. Other Ambulatory Care Surveys with Injury Data • National Ambulatory Medical Care Survey (NAMCS) • National probability sample survey of visits to office-based physicians • OPD component of the NHAMCS

  12. ED Data uses for injury • Track visits • Find health disparities • Compare illness and injury • Examine hospital level data

  13. Annual rate of injury-related ED visits for children by diagnosis Head wound Other wound Intracranial Poisoning

  14. Rate of injury-related ED visits by race and age

  15. ED visits by day of week according to illness or injury Illness Injury

  16. Average annual injury-related ED visit rates for persons 5-24 years of age by sport

  17. Most frequent annual injury visits at ambulatory care settings by body site

  18. Fall-related ED characteristics for persons 65 years of age and over

  19. Poisoning Pyramid Death 1 Hospitalizations 13 ED visits 59 Poison exposures 147

  20. Distribution of hospital EDs on the percent of visits for injuries

  21. Encounter vs. person data • NHAMCS is a record-based survey • Not population-based survey (NHIS) • Can not calculate incidence or prevalence rates from NHAMCS estimates

  22. User considerations • Sample data must be weighted to produce national estimates • Estimates must be based on at least 30 raw cases • Must use generalized variance curve or special software (e.g., SUDAAN) to calculate SEs for all estimates • Only estimates with a relative standard error < 30% are reliable

  23. Ways to improve reliability of estimates • Combine multiple years of ED data • Combine NAMCS, ED and OPD data to produce ambulatory care visit estimates

  24. Microdata files • Downloadable files • NAMCS, 1973-2002 • NHAMCS, 1992-2002 • CD-ROMs • NAMCS, 1990-2002 • NHAMCS, 1992-2001 (2002 in Aug.) • Tapes/cartridges (NTIS) • NAMCS, 1973-1997 • NHAMCS, 1992-1997

  25. Enhanced NHAMCS public-use files • SAS (1995-2002), SPSS (2002), STATA (2002) - input statements, variable and value labels, and format assignments • Masked sample design variables (1995-2002) • Allows use of SUDAAN and STATA

  26. http://www.cdc.gov/nchs/about/major/ahcd/ahcd1.htm

  27. Thank You • Linda McCaig – NHAMCS data lmccaig@cdc.gov

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