Using National Hospital Ambulatory Medical Care Survey (NHAMCS) data for injury analysis Linda Mc. Caig Ambulatory Care Statistics Branch Division of Health Care Statistics U. S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Center for Health Statistics 1
Overview l Background l Survey methodology l Data uses l User considerations for injury analysis 2
NHAMCS background l National probability sample survey of visits to EDs and OPDs of nonfederal, short-stay, and general hospitals l Survey began in 1992 l Annual data collection (Census) 3
NHAMCS Methodology 4
NHAMCS Sample design l 112 geographic PSUs l 500 hospitals l 400 EDs and 250 OPDs l 37, 000 ED and 35, 000 OPD visits – 4 -week reporting period 5
ED Items collected l Patient characteristics – age, race, sex l Visit characteristics – Mode of arrival, immediacy, reason for visit, injury-related, diagnosis, medication l Hospital characteristics – ownership, teaching hospital 6
Injury/poisoning/adverse effect items l Intentionality – Unintentional – Intentional self-inflicted l assault l l Work related l External cause – Up to 3 causes – Narrative text since 1997 7
Coding systems used l. A Reason for Visit Classification (NCHS) l International Classification of Diseases-9 CM – diagnosis codes – external cause of injury codes l Barell Injury Diagnosis Matrix: Classification of Region of Body and Nature of Injury l Drug coding system (NCHS) l National Drug Code Directory 8
Injury definition l Injury checkbox marked l Reason for visit in injury module l Diagnosis is in injury or poisoning chapter of ICD-9 -CM l Cause of injury recorded 9
Data quality l Data are coded and keyed by Constella Group Inc. (CG) l 10 percent of records are independently coded and keyed l Coding error rate for cause of injury is 0. 8 percent l Item nonresponse for cause of injury 423% 10
Other Ambulatory Care Surveys with Injury Data l National Ambulatory Medical Care Survey (NAMCS) – National probability sample survey of visits to office-based physicians l OPD component of the NHAMCS 11
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ED Data uses for injury l Track visits l Find health disparities l Compare illness and injury l 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 Characteristic Number in Percent 1, 000 s Age in years 65 -79 949 9. 5 80 and over 1, 002 16. 1 Residence Community 1, 369 11. 1 Institution 379 19. 2 Adjusted odds ratio Referent 2. 0 19
Poisoning Pyramid Death 1 Hospitalizations 13 ED visits 59 Poison exposures 147 20
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Distribution of hospital EDs on the percent of visits for injuries 22
Encounter vs. person data l NHAMCS is a record-based survey l Not population-based survey (NHIS) l Can not calculate incidence or prevalence rates from NHAMCS estimates 23
User considerations l Sample data must be weighted to produce national estimates l Estimates must be based on at least 30 raw cases l Must use generalized variance curve or special software (e. g. , SUDAAN) to calculate SEs for all estimates l Only estimates with a relative standard error < 30% are reliable 24
Ways to improve reliability of estimates l Combine multiple years of ED data l Combine NAMCS, ED and OPD data to produce ambulatory care visit estimates 25
Microdata files l Downloadable files NAMCS, 1973 -2002 l NHAMCS, 1992 -2002 l l CD-ROMs NAMCS, 1990 -2002 l NHAMCS, 1992 -2001 (2002 in Aug. ) l l Tapes/cartridges (NTIS) NAMCS, 1973 -1997 l NHAMCS, 1992 -1997 l 26
Enhanced NHAMCS public-use files l SAS (1995 -2002), SPSS (2002), STATA (2002) - input statements, variable and value labels, and format assignments l Masked sample design variables (1995 - 2002) – Allows use of SUDAAN and STATA 27
http: //www. cdc. gov/nchs/about/major/ahcd 1. htm 28
Thank You l Linda Mc. Caig – NHAMCS data lmccaig@cdc. gov 29
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