1 using national hospital ambulatory medical care survey (nhamcs) data for injury analysis linda...
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Using National Hospital Using National Hospital Ambulatory Medical Care Survey Ambulatory Medical Care Survey
(NHAMCS) data for injury analysis(NHAMCS) data for injury analysis Linda McCaig
Ambulatory Care Statistics Branch
Division of Health Care Statistics
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICESCenters for Disease Control and PreventionNational Center for Health Statistics
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OverviewOverview
BackgroundSurvey methodologyData usesUser considerations for injury analysis
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NHAMCS backgroundNHAMCS background
National probability sample survey of visits to EDs and OPDs of non-federal, short-stay, and general hospitals
Survey began in 1992Annual data collection (Census)
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NHAMCS MethodologyNHAMCS Methodology
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NHAMCS Sample designNHAMCS Sample design
112 geographic PSUs500 hospitals400 EDs and 250 OPDs37,000 ED and 35,000
OPD visits– 4-week reporting period
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ED Items collectedED Items collected
Patient characteristics– age, race, sex
Visit characteristics– Mode of arrival, immediacy, reason for
visit, injury-related, diagnosis, medicationHospital characteristics
– ownership, teaching hospital
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Injury/poisoning/adverseInjury/poisoning/adverseeffect itemseffect items
Intentionality– Unintentional– Intentional
self-inflictedassault
Work relatedExternal cause
– Up to 3 causes– Narrative text since 1997
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Coding systems usedCoding systems usedA 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
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Injury definitionInjury definition
Injury checkbox markedReason for visit in injury moduleDiagnosis is in injury or poisoning
chapter of ICD-9-CMCause of injury recorded
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Data qualityData 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%
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Other Ambulatory Care Other Ambulatory Care Surveys with Injury DataSurveys with Injury Data
National Ambulatory Medical Care Survey (NAMCS) – National probability sample survey of
visits to office-based physiciansOPD component of the NHAMCS
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ED Data uses for injuryED Data uses for injury
Track visitsFind health disparitiesCompare illness and injuryExamine hospital level data
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Annual rate of injury-related ED Annual rate of injury-related ED visits for children by diagnosisvisits for children by diagnosis
0
5
10
15
20
25
30
1993/94 1995/96 1997/98 1999/00 2001/02
Year
Vis
its
per
100
per
son
s
Head wound
Other wound
IntracranialPoisoning
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Rate of injury-related ED visits Rate of injury-related ED visits by race and ageby race and age
0
5
10
15
20
25
30
Under15
15-24 25-44 45-64 65-74 75 andover
Age in years
Rat
e p
er 1
00 p
erso
ns
Black
White
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ED visits by day of week ED visits by day of week according to illness or injuryaccording to illness or injury
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14
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Per
cent
of v
isits
Illness
Injury
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Average annual injury-related ED Average annual injury-related ED visit rates for persons 5-24 years of visit rates for persons 5-24 years of
age by sportage by sport
0 1 2 3 4 5 6
Gymnastics
Skating
Baseball
Football
Pedal cycling
Basketball
No. of visits per 1,000 persons
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Most frequent annual injury visits at Most frequent annual injury visits at ambulatory care settings by body siteambulatory care settings by body site
0 1 2 3 4 5
Open wound - face
Sprain/strains - lumbar VCI
Fractures - hand, wrist &fingers
Sprains/strains - lower leg &ankles
Sprains/strains - cervical VCI
Open wound - hand, wrist &fingers
Number of visits in millions
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Fall-related ED characteristics for Fall-related ED characteristics for persons 65 years of age and overpersons 65 years of age and over
Characteristic Number in 1,000s
Percent Adjusted odds ratio
Age in years
65-79 949 9.5 Referent
80 and over 1,002 16.1 2.0
Residence
Community 1,369 11.1 Referent
Institution 379 19.2 2.0
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Poisoning PyramidPoisoning Pyramid
Poison exposures 147
ED visits 59
Hospitalizations 13
Death 1
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Distribution of hospital EDs on Distribution of hospital EDs on the percent of visits for injuriesthe percent of visits for injuries
0 10 20 30 40
60-69
50-59
40-49
30-39
20-29
'10-19
Under 10
Per
cen
t o
f vi
sits
Percent of hospital emergency departments
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Encounter vs. person dataEncounter vs. person data
NHAMCS is a record-based surveyNot population-based survey (NHIS)Can not calculate incidence or
prevalence rates from NHAMCS estimates
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User considerationsUser considerationsSample data must be weighted to produce
national estimatesEstimates must be based on at least 30
raw casesMust 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
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Ways to improve reliability Ways to improve reliability of estimatesof estimates
Combine multiple years of ED dataCombine NAMCS, ED and OPD data to
produce ambulatory care visit estimates
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Microdata filesMicrodata filesDownloadable files
NAMCS, 1973-2002NHAMCS, 1992-2002
CD-ROMsNAMCS, 1990-2002NHAMCS, 1992-2001 (2002 in Aug.)
Tapes/cartridges (NTIS)NAMCS, 1973-1997NHAMCS, 1992-1997
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Enhanced NHAMCS public-use filesEnhanced 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
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http://www.cdc.gov/nchs/about/major/ahcd/ahcd1.htmhttp://www.cdc.gov/nchs/about/major/ahcd/ahcd1.htm
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