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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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OverviewOverviewBackgroundSurvey methodologyData usesUser considerations for injury analysis

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NHAMCS backgroundNHAMCS backgroundNational 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 qualityData are coded and keyed by Constella

Group Inc. (CG)10 percent of records are independently

coded and keyedCoding error rate for cause of injury is

0.8 percentItem 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 injuryTrack 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

Visi

ts p

er 1

00 p

erso

ns 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

05

1015202530

Under15

15-24 25-44 45-64 65-74 75 andover

Age in years

Rat

e pe

r 100

per

sons

BlackWhite

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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

16

Perc

ent o

f vis

its

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 years65-79 949 9.5 Referent80 and over 1,002 16.1 2.0ResidenceCommunity 1,369 11.1 ReferentInstitution 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

30-3920-29

'10-19

Under 10

Perc

ent o

f vis

its

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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Thank YouThank You

Linda McCaig – NHAMCS data lmccaig@cdc.gov

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