mccaig woodwell2
TRANSCRIPT
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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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15
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: [email protected]
Website: www.cdc.gov/nchs/r&d/rdc.htm
Call (301) 458-4277
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Thank YouThank You
Linda McCaig – NHAMCS data
David Woodwell – NAMCS data
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