1

Linda McCaig and David Woodwell

Ambulatory Care Statistics Branch

Division of Health Care Statistics

Overview of the NAMCSOverview of the NAMCSand NHAMCSand NHAMCS

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICESCenters for Disease Control and PreventionNational Center for Health Statistics

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICESCenters for Disease Control and PreventionNational Center for Health Statistics

2

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

3

4

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

5

Original NAMCS survey Original NAMCS survey goalsgoals

• National statistics• Professional education• Health policy formulation• Medical practice management• Quality assurance

6

NAMCS historyNAMCS history

Survey began in 1973 Annual data collection through

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

(Census)

7

NHAMCS historyNHAMCS history

Survey began in 1992 Annual data collection (Census)

8

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

9

Data usesData uses

Understand health care practiceExamine the quality of careTrack certain conditionsFind health disparitiesMeasure Healthy People 2010

objectivesServe as benchmark for states

10

Data usersData users

Over 100 journal publications in last 2 years

Medical associationsGovernment agenciesHealth services researchersUniversity and medical schoolsBroadcast and print media

11

12

13

Total Ambulatory Care Visits

SOURCE: CDC/NCHS, NAMCS and NHAMCS, 2001.

14

Annual rate of injury-related Annual rate of injury-related ED visits for seniors by patient ED visits for seniors by patient

residenceresidence

Age in years

Institution Community

Number of visits per 100 persons

65-79 41 8

80+ 37 14

15

Percent of physician office Percent of physician office visits by type of cardiac visits by type of cardiac rhythm modifying agentrhythm modifying agent

01020304050607080

Ventricular ratecontrol

Sinus rhythmmaintenance

Neither

Per

cen

t o

f vi

sits

1991-92 1999-00

Fang et al. Arch Intern Med 2004;164(1):55-60.Fang et al. Arch Intern Med 2004;164(1):55-60.

16

Percent of selected ED visit Percent of selected ED visit characteristics among released characteristics among released

patients who had a blood culturepatients who had a blood culture

Visit

characteristic

Antibiotics prescribed

Antibiotics not prescribed

Total

Fever 19% 17% 36%

No fever 28% 36% 64%

Total 47% 53% 100%

17

Potentially inappropriate drug Potentially inappropriate drug prescribing at elderly physician prescribing at elderly physician

office visitsoffice visits

0

1

2

3

4

5

6

7

1 2 3 4 5 6

Number of prescription drugs

Ad

just

ed o

dd

s ra

tio

Goulding. Arch Intern Med 2004;164(3):305-312.Goulding. Arch Intern Med 2004;164(3):305-312.

18

Number and rate of physician Number and rate of physician office visits for diabetesoffice visits for diabetes

0

5

10

15

20

25

30

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

Year

Number of visits in millions

Rate per 100 persons

Grant et al. Arch Intern Med 2004;164(10):1134-1139.Grant et al. Arch Intern Med 2004;164(10):1134-1139.

19

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

20

Variations in drug mention rates for Variations in drug mention rates for selected therapeutic classes by source selected therapeutic classes by source

of paymentof payment

0 5 10 15 20 25

Drug mentions per 100 visits

Uninsured Private

21

Variations in drug mention rates for Variations in drug mention rates for selected therapeutic classes by MSA selected therapeutic classes by MSA

statusstatus

0 5 10 15 20 25

Pain relief

Otologics

Antimicrobials

Drug mentions per 100 visits

Non-MSA MSA

22

HP2010 Objectives on HP2010 Objectives on antibiotic prescribingantibiotic prescribing

Ear infections

(Antibiotics per 1000 persons)

Common cold

(Antibiotics per 1000 persons)

Baseline 693 25

1998/99 545 18

2000/01 595 18

Target 561 13

23

NAMCS and NHAMCS NAMCS and NHAMCS MethodologyMethodology

24

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 certain specialties

25

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

centersNon-federal government clinicFamily planning clinicHMOFaculty practice planPrivate solo or group practice

26

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

Hospital EDs and OPDsAmbulatory surgicenterInstitutional setting (schools, prisons)Industrial outpatient facilityFederal Government operated clinicLaser vision surgery

27

NAMCS Sample designNAMCS Sample design

112 geographic PSUs3,000 physicians25,000 visits

– 1 week reporting period

28

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

29

NHAMCS Sample designNHAMCS Sample design

112 geographic PSUs500 hospitals400 EDs and 250 OPDs37,000 ED and 35,000

OPD visits– 4-week reporting period

30

Gaining cooperationGaining cooperation

Advance lettersEndorsement lettersPublic relations materialsConversion of refusal

31

Data collection proceduresData collection procedures

Induction visit by Census field representative (FR)

FR training of office/hospital staffTake every numberProspective or retrospective method

32

Items collected on Patient Items collected on Patient Record form (PRF)Record form (PRF)

Patient characteristics– age, race, sex

Visit characteristics– reason for visit, diagnosis, medication

Provider characteristics– physician specialty, hospital ownership

33

Repeating fieldsRepeating fields

Reason for visit (3) Cause of injury (3) Diagnosis (3) Ambulatory surgical

procedures (2) Medications (8)

34

Data processingData processing

Data are coded and keyed by Constella Group Inc. (CG)

Quality control proceduresEdit checks by NCHS

35

Coding systems usedCoding systems used

A Reason for Visit Classification (NCHS)ICD-9-CM

– diagnoses– external causes of injury– procedures

Drug coding system (NCHS)National Drug Code Directory

36

NAMCS and NHAMCS NAMCS and NHAMCS 2001-2004 PRFs2001-2004 PRFs

37

Patient Record formPatient Record form - common items - common items

Patient’s zip codeDate of visitDate of birthSexEthnicity

38

Patient Record formPatient Record form- common items- common items

RaceSource of paymentReason for visitDiagnosis

39

Patient Record form –Patient Record form –common itemscommon items

Diagnostic/screening servicesMedications and injectionsProviders seenVisit disposition

40

Injury/poisoning/adverse effect Injury/poisoning/adverse effect itemsitems

External cause – narrative text since 1997

ED– intentionality– work related

41

NAMCS and OPD PRFNAMCS and OPD PRF- unique items- unique items

Does patient use tobaccoCounseling/education/therapySurgical proceduresTime spent with physician (NAMCS

only)

42

2001-2004 NAMCS and OPD PRF2001-2004 NAMCS and OPD PRFcontinuity of care items continuity of care items

Patient’s primary care physician/providerWas patient referred for visitPatient seen beforeSeen how many times in past 12 monthsMajor reason for visitEpisode of careOther physicians share care

43

ED Patient Record formED Patient Record form- unique items- unique items

Arrival timeDischarge timeTime seen by physicianMode of arrivalImmediacy

44

ED Patient Record formED Patient Record form- unique items- unique items

Presenting level of painAlcohol related visitWork related visitProcedure checklist

45

ED Patient Record formED Patient Record form- continuity of care items- continuity of care items

Seen ED within last 72 hoursEpisode of care

– Initial or followup visit

46

Recycled items onRecycled items on 2003-04 ED PRF 2003-04 ED PRF

On– Time seen by

physician – Mode of arrival– Presenting level

of pain

Off– Visit related to an

adverse drug event

47

NAMCS and OPD PRF NAMCS and OPD PRF revisions 2005-06 – revisions 2005-06 –

emphasis on chronic emphasis on chronic conditionsconditions

48

NAMCS and OPD PRF-NAMCS and OPD PRF- new items for 2005-06 new items for 2005-06

– Arthritis– Asthma– Cancer– Cerebrovascular

disease– CHF– Chronic renal failure– COPD

– Depression– Diabetes– Hyperlipidemia– Hypertension– Ischemic heart

disease– Obesity– Osteoporosis

49

NAMCS and OPD PRF NAMCS and OPD PRF - new items for 2005-06- new items for 2005-06

Vital signs– Height– Weight– Temperature– Blood pressure

Disease management programMedication – new or continued

50

ED PRFED PRF- new items for 2005-06- new items for 2005-06

HomelessDischarged from any hospital within

last 7 daysMedication given in ED or

prescribed at dischargeReason patient was transferred

51

ED PRFED PRF- new items for 2005-06- new items for 2005-06

Admit to hospital– Critical care/Intervention/Other bed– Hospital admission time– Hospital discharge date– Principal hospital discharge diagnosis– Alive/Dead

52

Examples of Examples of Collaboration with Other Collaboration with Other Government AgenciesGovernment Agencies

53

Emergency Pediatric Services Emergency Pediatric Services and Equipment Supplement and Equipment Supplement

(EPSES)(EPSES)

Funded by the Health Resources and Services Administration

Added as a supplement to the 2002-03 NHAMCS– Services related to treating children– Availability of pediatric supplies

54

Medical Specialty Number of EDs

Percent of EDs

Board Certified Emergency Medicine Attending Physician

3,550 73

Board Certified Pediatric Emergency Medicine Attending Physician

1,270 26

Board Certified Pediatric Attending Physician 3,249 67

Attending Physician Specialty Attending Physician Specialty (available 24/7 in-house or on-call) (available 24/7 in-house or on-call)

55

Bioterrorism and mass Bioterrorism and mass casualty preparednesscasualty preparedness

Funded by the DHHS Assistant Secretary for Planning and Evaluation

2003-4 NAMCS Physician induction interview– Diagnosis of terror-related conditions– Assistance in making a diagnosis– Reporting a suspect case

2003-04 NHAMCS supplement– Hospital response plan, training, and resources

56

57

2003-04 NHAMCS Supplements2003-04 NHAMCS Supplements

Hospital inpatient occupancy rateED capacity and staffing

– Number of treatment spaces– Percent of vacant nursing positions– Physicians employed by hospital or

contractorAmbulance diversion

– Percent of days on diversion– Mean number of hours on diversion

58

59

Percent distribution of hospital Percent distribution of hospital emergency departments by safety-net emergency departments by safety-net

criteriacriteria

0 10 20 30 40 50 60 70

Low safety net

High combined

High Medicaid/low uninsured

High uninsured/low Medicaid

High Medicaid/low unisured

Percent of hospital emergency departments

60

Percent distribution of emergency Percent distribution of emergency department visits by selected department visits by selected

characteristics according to size characteristics according to size of annual visit volumeof annual visit volume

0

20

40

60

80

100

Electronicmedicalrecords

Automateddrug

dispensing

Board-certifiedEM physicians

Per

cen

t d

istr

ibu

tio

n

Small

Medium

Large

61

Percent of physicians accepting Percent of physicians accepting new patients by pay sourcenew patients by pay source

0

20

40

60

80

100

Medicare Medcaid

Per

cen

t o

f p

hys

icia

ns

Primary care Surgical Medical

62

OverviewOverview

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

Methodological studiesHIPAAData disseminationNCHS Research Data Center

63

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

personsCannot calculate incidence or

prevalence rates from our estimates

64

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

65

Sampling errorSampling error

NAMCS and NHAMCS are not simple random samples

Clustering effects: – Providers within PSUs– Visits within physician practice or hospital

Must use generalized variance curve or special software (e.g., SUDAAN) to calculate SEs for all estimates, percents, and rates.

66

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

67

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

68

Nonsampling errorNonsampling error

Frame coverageReporting and processing errorsBiases due to survey and item

nonresponseIncomplete responses

69

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

70

NAMCS Response rate NAMCS Response rate

55

60

65

70

75

89 90 91 92 93 94 95 96 97 98 99 '00 '01 '02

Year

Per

cen

t

71

NHAMCS Response ratesNHAMCS Response rates

50

60

70

80

90

100

92 93 94 95 96 97 98 99 '00 '01 '02

Year

Per

cen

t

ED

OPD

72

Attempts to improve response Attempts to improve response rate rate

Publicity Eliminating questions that have a high

item non-responseMethodological studies

73

Methodological studiesMethodological studies

• Complement study 1997-1999• 500 physicians in each year• 17% of classified as nonoffice-based saw

patients• Represented 11% of total• Difference not accounted for in weighting

74

Methodological studiesMethodological studies

• NAMCS Motivational insert• Conducted last half of 2000• Insert (n=513); no insert (n=499)• RR - 68% vs. 64%• No difference in RR

75

Methodological studiesMethodological studies

• NAMCS and OPD PRF length• Conducted 2001• NAMCS: short (n=941); long (n=969)• OPD: short (n=132); long (n=129)• NAMCS RR - 68% (short) vs. 62% (long) • NAMCS short PRF had a higher RR• No effect on RR in OPD

76

Methodological studiesMethodological studies

• Incentives test• Conducted last 3 quarters of 2002• 3 groups: control (n=418), gift (n=401), and

monetary (n=456)• RR – 73%, 68%, and 73%, respectively• No difference in RR between incentive

groups

77

HIPAAHIPAA

• No directly identifiable information collected

• PHS Act 308(d) / Title 15• Data Use Agreement w/ Limited Dataset• IRB approval w/ waiver of patient

authorization• Accounting Document

78

HIPAAHIPAA

• 1-800 telephone number• Respondent website

• www.cdc.gov/namcs• www.cdc.gov/nhamcs

• Training• Written instructions• CD-ROM• Self-study

• Follow-up

79

Impact of HIPAA on 2003 Impact of HIPAA on 2003 NAMCS and NHAMCSNAMCS and NHAMCS

• Induction process in hospitals is longer due to additional levels of approval process

• Less likely to allow FR abstraction• Response rate not affected• 2004 may be more difficult…

80

81

Outside researchOutside research

Journal articles– List on Ambulatory Care web site

Text books

Department level publications– Health US

82

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

83

Enhanced public-use filesEnhanced public-use files

New survey items and facility level data

SAS input statements, variable labels, value labels, and format assignments– 1993 – 2002 for NAMCS– 1995 – 2002 for NHAMCS

SPSS & STATA input statements, variable labels, value labels, and format assignments in 2002

84

Enhanced public-use filesEnhanced public-use filesSample design variables

– Masked variables for multi-stage sampling are available:

1993-2002 NAMCS 1995-2002 NHAMCS

– In 2002, NAMCS & NHAMCS will have masked variables for use in software using 1-stage sampling. Prior years with formula

– In 2003, we will only release masked variables for use in software using 1-stage

85

2001*

3- & 4-Stage

design variables

2003

2002

1-Stage design

variables only

1-Stage design

variables

3- & 4-Stage design

variables

Design Variables—Survey YearsDesign Variables—Survey Years

*Plan to re-release years with 1-stage design variables.

86

Ratio of masked to unmasked SUDAAN standard errors using four-stage WOR

Source: Inquiry 40: 401-415 (Winter 2003/2004)

87

Average comparison ratios by alternative standard error method and

type of setting

Type of setting

Masked 4-stage WOR SUDAAN

Masked 1-stage WR SUDAAN

Masked SURVEY- MEANS

GVC

All settings 1.03 1.03 1.02 0.84

Physician’s offices

1.02 1.02 1.01 0.93

Hospital OPD 0.99 1.03 1.02 0.94

Hospital ED 1.03 1.06 1.06 0.91

Source: Inquiry 40: 401-415 (Winter 2003/2004)

88

0

5000000

10000000

15000000

20000000

25000000

30000000

35000000

40000000

45000000

0 5000000 10000000 15000000 20000000 25000000 30000000 35000000 40000000

Scatter plot of masked and unmasked 4-stage WOR SUDAAN SE for all settings

89

Future releasesFuture releases

2003 NAMCS & NHAMCS in Spring 2005

All settings Series report in Fall 2004 with NAMCS data for primary care and surgical and medical specialties

90

Where to get more Where to get more informationinformation

Ambulatory Care information boothAmbulatory Care website

– Ambulatory Care listserveCall Ambulatory Care Statistics Branch

at (301) 458-4600

91

http://www.cdc.gov/nchs/about/major/ahcd/ahcd1.htmhttp://www.cdc.gov/nchs/about/major/ahcd/ahcd1.htm

92

NCHS Research NCHS Research Data CenterData Center

93

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 gender and age, board certification, teaching hospital, medical school affiliation, ED size, provider weight

– Geographic: state and county FIPS codes

94

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

95

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

96

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

97

Thank YouThank YouLinda McCaig – NHAMCS data

lmccaig@cdc.gov

David Woodwell – NAMCS data

dwoodwell@cdc.gov

98