Mccaig Woodwell2

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Linda McCaig and David Woodwell

Ambulatory Care Statistics Branch

Division of Health Care Statistics

National Center for Health Statistics/CDC

Using NAMCS andUsing NAMCS and NHAMCS Data NHAMCS Data

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OverviewOverviewBackgroundData usesSurvey methodologyCurrent and proposed survey itemsUser considerationsMethodological studiesData disseminationNCHS Research Data Center

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National probability sample National probability sample surveyssurveys

National Ambulatory Medical Care Survey (NAMCS)– Patient visits to non-federal office-

based physiciansNational Hospital Ambulatory

Medical Care Survey (NHAMCS)– Patient visits to EDs and OPDs of

non-federal short-stay hospitals

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Original NAMCS survey Original NAMCS survey goalsgoals

• National statistics• Professional education• Health policy formulation• Medical practice

management• Quality assurance

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NAMCS historyNAMCS history

Survey began in 1973 Annual data collection through

1981 (NORC)Conducted in 1985 (NORC)Annual began again in 1989

(Census)

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NHAMCS historyNHAMCS history

Survey began in 1992 Annual data collection (Census)

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How are NAMCS and How are NAMCS and NHAMCS data used?NHAMCS data used?

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Data usesData uses

To understand health care practice and find inequities

To track certain conditionsTo establish national prioritiesTo serve as comparison points for

statesTo measure Healthy People objectives

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Data usersData users

Over 100 journal publications in last 2 years

Medical associationsGovernment agenciesHealth services researchersUniversity and medical schoolsBroadcast and print media

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Setting government policySetting government policy

ED as a “safety net” for the uninsuredDevelopment of the Resource-Based

Relative Value Scale (RBRVS)

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Antibiotic prescribing rates at Antibiotic prescribing rates at physician office visits for children physician office visits for children

0

200

400

600

800

1000

89/90 91/92 93/94 95/96 97/98 99/00

Year

Rate per 1000 population

Rate per 1000 visits

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Prescribing rates at physician Prescribing rates at physician office visits by specialtyoffice visits by specialty

0

25

50

75

100

125

150

175

200

85 89/90 95/96 97/98 99

Year

Dru

g m

enti

on

s p

er 1

00 v

isit

s

Psychiatry

Ophthalmology

Otolaryngology

Orthopedic surgery

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Female ambulatory care visit rates for Female ambulatory care visit rates for selected diagnoses by raceselected diagnoses by race

0

5

10

15

20

25

30

35

Comp preg Arthritis Diabetes High BPRat

e p

er 1

00 w

om

en (

age-

adju

sted

)

White

Black

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Annual rate of illness and injury Annual rate of illness and injury ED visits for seniors by raceED visits for seniors by race

0

10

20

30

40

50

60

92 93/94 95/96 97/98 99/00

Year

Vis

its

per

100

per

son

s

Illness, black 1

Illness, white 1

Injury, black 1

NOTE: 1 p < .01.

Injury, white

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Diabetes visit rates per 10,000 Diabetes visit rates per 10,000 persons by settingpersons by setting

Year Office OPD ED

1992-93 962 84 33

1994-95 865 117 36

1996-97 1118 157 38

1998-99 1289 147 49

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NAMCS and NHAMCS NAMCS and NHAMCS MethodologyMethodology

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NAMCS ScopeNAMCS Scope

• Includes non-federal, office-based physicians

• Excludes physicians whose main activity is teaching, research, administration, hospital-based care, or who are unclassified as to activity and those in the certain specialties

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In-Scope NAMCS locations In-Scope NAMCS locations Freestanding clinic/urgicenterFederally qualified health centerNeighborhood and mental health

centersNon-federal government clinicFamily planning clinicHealth maintenance organizationFaculty practice planPrivate solo or group practice

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Out-of-Scope NAMCS locationsOut-of-Scope NAMCS locations

Hospital ED’s and OPD’sAmbulatory surgicenterInstitutional setting (schools, prisons)Industrial outpatient facilityFederal Government operated clinicLaser vision surgery

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NAMCS Sample designNAMCS Sample design

112 NHIS PSUs3,000 physicians25,000 visits

1 week reporting period

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NHAMCS Scope NHAMCS Scope

OPD was intended to be parallel to the NAMCS in the hospital setting

General medicine, surgery, pediatrics, ob/gyn, substance abuse, and “other” clinics are in-scope

Ancillary services are out of scope

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NHAMCS Sample designNHAMCS Sample design

112 NHIS PSUs500 hospitals400 EDs and 250 OPDs24,000 ED visits and

30,000 OPD visits

4-week reporting period

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Gaining cooperationGaining cooperation

Advance lettersEndorsement lettersPublic relations materialsConversion of refusal

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Data collection proceduresData collection procedures

Induction visit by Census field representative (FR)

FR training of office/hospital staffRandom start numberTake every numberProspective or retrospective method

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Items collectedItems collected

Patient characteristics– age, race, sex

Visit characteristics– Reason for visit, diagnosis, medication

Provider characteristics– physician specialty, hospital ownership

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Repeating fieldsRepeating fields

Reason for visit (3)Cause of injury (3)Diagnosis (3)Ambulatory surgical procedures (2)Medications (6)

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Data processingData processing

Data are coded and keyed by Analytical Sciences Inc. (ASI)

Quality control proceduresEdit checks by NCHS

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Coding systems usedCoding systems used

A Reason for Visit Classification (NCHS)ICD-9-CMDrug coding classification system (NCHS)National Drug Code Directory

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NAMCS and NHAMCS NAMCS and NHAMCS 1999-2000 PRFs1999-2000 PRFs

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Patient record formPatient record form - common items - common items

Patient’s zip codeDate of visitDate of birthSexEthnicity

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Patient record formPatient record form- common items- common items

RaceSource of paymentHMO statusReason for visit

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Patient record form –Patient record form –common itemscommon items

DiagnosisDiagnostic/screening servicesMedicationsProviders seenVisit disposition

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Injury itemsInjury items

External cause – narrative text since 1997

Place of injuryWork related injuryIntent

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Office and OPD PRFOffice and OPD PRF- unique items- unique items

Was patient referred for visitPatient’s primary care physicianPatient seen beforeMajor reason for visit

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Office and OPD PRFOffice and OPD PRF- unique items- unique items

Ambulatory surgical proceduresTherapeutic and preventive servicesTime spent with physician (NAMCS

only)

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ED Patient record formED Patient record form- unique items- unique items

Arrival timeDischarge timeImmediacyPresenting level of painProcedures

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NAMCS and NHAMCS PRF NAMCS and NHAMCS PRF revisions 2001-02 – revisions 2001-02 –

emphasis on the continuity emphasis on the continuity of careof care

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Office and OPD PRF Office and OPD PRF - new items for 2001-02- new items for 2001-02

How many visits in last 12 monthsInitial or follow-up visitDo other physicians share careTotal number of medications

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ED PRFED PRF- new items for 2001-02- new items for 2001-02

Discharge timeVisit related to alcohol usePatient seen in last 72 hoursInitial or follow-up visitVisit related to adverse drug eventInitial vital signsTotal number of medications

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NAMCS and NHAMCS PRF NAMCS and NHAMCS PRF revisions 2003-04revisions 2003-04

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ED PRF- revisions for 2003-04ED PRF- revisions for 2003-04

New– oriented X 3 – is visit work

related – list up to 8

medications

Recycled– mode of arrival– presenting level

of pain– time seen by

physician

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2001-02 Induction Interview 2001-02 Induction Interview revisionsrevisions

NAMCS – e.g., electronic medical records, number of managed care contracts

NHAMCS – e.g., Pediatric Emergency Services and Equipment Supplement (HRSA)

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2003-04 Induction Interview 2003-04 Induction Interview revisionsrevisions

NAMCS – e.g., Physician was a member of a practice-based research network (PBRN)

NHAMCS – e.g., Daily census of occupied and available beds

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ED OvercrowdingED Overcrowding

Physician coverage hoursLog of ambulance diversion

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Analysis of Facility Level Analysis of Facility Level DataData

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Percent of physicians who do not Percent of physicians who do not accept new patients by payment typeaccept new patients by payment type

0 5 10 15 20 25 30 35

Self-pay

Private

Medicare

Medicaid

Worker's comp

No charge

Percent of physicians

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Distribution of hospital EDs Distribution of hospital EDs on average waiting timeon average waiting time

0 10 20 30

>= 105

90-104

75-89

60-74

45-59

30-44

15-29

< 15

Tim

e in

min

ute

s

Percent of hospital EDs

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OverviewOverview

User considerations– Encounter vs. person data– Sampling error– Nonsampling error

Methodological studiesData disseminationNCHS Research Data Center

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Encounter vs. person dataEncounter vs. person data

NAMCS and NHAMCS are record-based surveys

Not population-based surveys (NHIS)Estimates are in terms of visits and not

personsCan not calculate incidence or

prevalence rates from our estimates

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Sample weightSample weight

Sample data MUST be weighted to produce national estimates

Estimation process– Adjusts for survey and item nonresponse– Makes several ratio adjustments within and

across physician specialties and hospitals

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Sampling errorSampling errorNAMCS and NHAMCS are not simple

random samplesClustering effects of visits within the

physician’s practice and also physician practices within PSUs

Must use generalized variance curve or SUDAAN to calculate SEs for all estimates, percents, and rates.

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Reliability criteriaReliability criteria

Estimates based on at least 30 raw cases are reliable

Estimates with a relative standard error (RSE) less than 30 percent are reliable

Both conditions must be met

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Ways to improve reliability Ways to improve reliability of estimatesof estimates

Combine NAMCS, ED and OPD data to produce ambulatory care visit estimates

Combine multiple years of data

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Nonsampling errorNonsampling error

Frame coverageReporting and processing errorsBiases due to survey and item

nonresponseIncomplete responses

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Minimizing nonsampling errorMinimizing nonsampling error

Improve sample frame for better coverage

Encourage uniform reporting and eliminate ambiguities

Pretest survey items and proceduresPerform quality control procedures –

consistency and edit checksTrain Census field representatives

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NAMCS Response rates NAMCS Response rates

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60

65

70

75

89 90 91 92 93 94 95 96 97 98 99 '00

Year

Per

cen

t

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NHAMCS Response ratesNHAMCS Response rates

50

60

70

80

90

100

92 93 94 95 96 97 98 99 '00

Year

Per

cen

t

ED

OPD

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Attempts to improve response Attempts to improve response rate rate

Publicity Eliminating questions that have a high item

non-responseIncentives test

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Methodological studiesMethodological studies

• Nonresponse study• Complement study• Motivational insert• Form length• Incentive test

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Initial results of incentives testInitial results of incentives test

Still very early Participation in some “on the fence” casesNo effect on “extreme” cases

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Data disseminationData dissemination

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NAMCS and NHAMCS NAMCS and NHAMCS MethodologyMethodology

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Outside researchOutside research

Journal articles– List on Ambulatory Care web site

Text books

Department level publications– Health US

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Microdata filesMicrodata filesDownloadable files

NAMCS, 1973-2000NHAMCS, 1992-2000

CD-ROMsNAMCS, 1990-2000NHAMCS, 1992-2000

Tapes/cartridges (NTIS)NAMCS, 1973-1997NHAMCS, 1992-1997

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Enhanced public-use filesEnhanced public-use files

SAS variable labels, value labels, and format assignments (1997-2000)

Sample design variables– Allow use of SUDAAN and STATA– 1997-2000 NAMCS and NHAMCS– Files prior to 2000 have been updated on

web site

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Comparison of RSEsComparison of RSEs

Physician assistant

Seen by Cardiac monitor IV fluids Admitted to hosp0

5

10

15

20RSE

In-house Masked GVC

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Comparison of RSEs for ED visits Comparison of RSEs for ED visits by ageby age

Patient age in years

<15 15-24 25-44 45-64 65-74 75+0

5

10

15RSE

In-house Public-use 1-stage gvc

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Future releaseFuture release

NAMCS Trend file – 1980-81, 1985, 1990-91, 1995-96, and

1999-20002001 NAMCS and NHAMCS data

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Where to get more Where to get more informationinformation

Ambulatory Care information boothAmbulatory Care websiteCall Ambulatory Care Statistics Branch

at (301) 458-4600Academy for Health Services Research

and Health Policy seminar Fall, 2002

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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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NCHS Research NCHS Research Data CenterData Center

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Why the Research Data Center?Why the Research Data Center?

Have access to information not available on public use files

– Patient: zip code linked income, education, or urbanicity status

– Provider: physician sex and age, board certification, teaching hospital

– Geographic: state and county codes

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Data Center-Data Center-cont.cont.

Can merge with contextual variables (e.g., ARF, NHIS, Census, NHDS)

– Health status level– HMO penetration– Physician and specialist supply– Medicaid reimbursement– Air quality– Percent in poverty

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Data Center rulesData Center rules

Submit a proposalCannot use data to identify patients or

providers or geographic location of providers

Cannot remove data filesFee – onsite / remote / file construction

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I need more information !I need more information !

Visit the Research Data Center booth

E-mail: rdca@cdc.gov

Website: www.cdc.gov/nchs/r&d/rdc.htm

Call (301) 458-4277

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Thank YouThank You

Linda McCaig – NHAMCS data

lmccaig@cdc.gov

David Woodwell – NAMCS data

dwoodwell@cdc.gov

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