using past visit information to enhance analysis of national ambulatory medical care survey (namcs)...

Using past visit information to Using past visit information to enhance analysis of National enhance analysis of National

Ambulatory Medical Care Survey Ambulatory Medical Care Survey (NAMCS) data(NAMCS) data

Session 25Session 25

July 13, 2004July 13, 200410:30-noon10:30-noon

Session overviewSession overview

Introduction and methodology for using Introduction and methodology for using past visit information – past visit information – Catharine BurtCatharine Burt

Example of analysis of quality of care for Example of analysis of quality of care for hypertension – hypertension – Esther HingEsther Hing

Using past visit information to enhance Using past visit information to enhance analysis of ambulatory care from analysis of ambulatory care from

encounter dataencounter data

Catharine W. Burt , Ed.D.

Chief, Ambulatory Care Statistics Branch

July 13, 2004 Data Users Conference

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

TopicsTopics

IntroductionIntroduction Brief survey backgroundBrief survey background Past visit itemPast visit item Re-weighting methodologyRe-weighting methodology Analysis using re-weightingAnalysis using re-weighting SummarySummary

Encounter vs. population-based Encounter vs. population-based surveys that measure ambulatory surveys that measure ambulatory

care utilizationcare utilization Population-based Population-based

National Health Interview Survey (NHIS)National Health Interview Survey (NHIS) National Health and Nutrition Examination Survey National Health and Nutrition Examination Survey

(NHANES)(NHANES) Medical Expenditure Panel Survey (MEPS)Medical Expenditure Panel Survey (MEPS)

Encounter-based Encounter-based National Ambulatory Medical Care Survey National Ambulatory Medical Care Survey

(NAMCS)(NAMCS) National Hospital Ambulatory Medical Care National Hospital Ambulatory Medical Care

Survey (NHAMCS)Survey (NHAMCS)

Pattern of ambulatory care visits accordingPattern of ambulatory care visits according to patient age: NHIS, 2001to patient age: NHIS, 2001

<06

6-17

18-24

25-44

45-64

65-74

75+

0% 20% 40% 60% 80% 100%

None 1-3 visits 4-9 visits 10 or more visits

Rate of visits per population by patient Rate of visits per population by patient age: NAMCS, NHAMCS-OPD, 2001age: NAMCS, NHAMCS-OPD, 2001

3.4

4.2

1.9

1.9

2.7

4.1

6.7

7.8

All ages

<06

6-17

18-24

25-44

45-64

65-74

75+

Patient age in years

0 2 4 6 8 10

Rate

Desired goals from adding number Desired goals from adding number of past visits to encounter dataof past visits to encounter data

Describe patterns of care by frequency of Describe patterns of care by frequency of visiting the doctorvisiting the doctor

Provide more information about patients Provide more information about patients from encounter-level datafrom encounter-level data

Better describe quality of care to patients Better describe quality of care to patients vs. describing content of encountervs. describing content of encounter

NAMCS and NHAMCS NAMCS and NHAMCS background background

NAMCS NAMCS Fielded 1973-1981, 1985, 1989-presentFielded 1973-1981, 1985, 1989-present 3-stage sample3-stage sample

• PSUs – PSUs – physicians – physicians – visits during 1 weekvisits during 1 week

NHAMCS NHAMCS Fielded annually since 1992Fielded annually since 1992 4-stage sample4-stage sample

• PSUs – PSUs – hospitals – hospitals – ED/OPD clinics – ED/OPD clinics –

visits during 4 weeksvisits during 4 weeks

SEs

rates

percents

drugsproviders

visits

sample

records

Scope of the NAMCSScope of the NAMCS

Physicians must be: Physicians must be: Primarily engaged in office-based, patient Primarily engaged in office-based, patient

carecare Non-federally employedNon-federally employed Not in anesthesiology, radiology, or Not in anesthesiology, radiology, or

pathology pathology

In-Scope Visits for NAMCSIn-Scope Visits for NAMCS

Basic unit of sampling is the physician-Basic unit of sampling is the physician-patient visit patient visit

Visit must occur in a physician’s officeVisit must occur in a physician’s office Visits must be for medical purposesVisits must be for medical purposes Out-of-scope contacts include:Out-of-scope contacts include:

Visits for administrative purposesVisits for administrative purposes House calls, phone calls, emails, visits in House calls, phone calls, emails, visits in

hospital setting unless physician has hospital setting unless physician has private office thereprivate office there

In-Scope NAMCS Locations In-Scope NAMCS Locations Freestanding private solo or group Freestanding private solo or group

practicepractice Freestanding clinic/urgicenterFreestanding clinic/urgicenter Neighborhood medical and mental Neighborhood medical and mental

health centershealth centers Privately operated clinicsPrivately operated clinics Non-Federal government clinicNon-Federal government clinic Health maintenance organizationHealth maintenance organization Federally qualified health centerFederally qualified health center Faculty practice planFaculty practice plan

Out-of-Scope NAMCS Out-of-Scope NAMCS LocationsLocations

Hospital ED’s and OPD’sHospital ED’s and OPD’s Ambulatory surgicenterAmbulatory surgicenter Institutional setting (schools, prisons)Institutional setting (schools, prisons) Industrial outpatient facilityIndustrial outpatient facility Federally operated clinicFederally operated clinic Laser vision surgeryLaser vision surgery

Scope of the NHAMCSScope of the NHAMCS

Basic unit of sampling is patient visitBasic unit of sampling is patient visit Emergency and outpatient departments of Emergency and outpatient departments of

non-federal, general and short-stay non-federal, general and short-stay hospitalshospitals

Not Federal, military, or Veterans Not Federal, military, or Veterans Administration facilitiesAdministration facilities

Located in 50 states and D.C.Located in 50 states and D.C.

Items CollectedItems Collected Patient characteristics Patient characteristics

Age, sex, race, ethnicityAge, sex, race, ethnicity Visit characteristicsVisit characteristics

Source of payment, continuity of care, reason for Source of payment, continuity of care, reason for visit, diagnosis, treatment, medications ordered visit, diagnosis, treatment, medications ordered or providedor provided

Provider characteristicsProvider characteristics Physician specialty, hospital ownershipPhysician specialty, hospital ownership

Drug characteristicsDrug characteristics Therapeutic class, composition, control status, Therapeutic class, composition, control status,

ingredients, Rx or OTCingredients, Rx or OTC

Percent distribution for number of past Percent distribution for number of past visits within l2 months: NAMCS, 2001visits within l2 months: NAMCS, 2001

New patient 0 1-2 3-5 6+ UnknownNumber of past visits

0

5

10

15

20

25

30Percent of visits

Percent distribution of past visit Percent distribution of past visit item by PCP status: NAMCS 2001item by PCP status: NAMCS 2001

New patient 0 1-2 3-5 6+ Unknown

Number of past visits

0

5

10

15

20

25

30

35Percent of visits

PCP Other

Percent of visits where the patient made 6 or Percent of visits where the patient made 6 or more visits in past year by patient age: more visits in past year by patient age:

NAMCS 2001NAMCS 2001

0

5

10

15

20

25

30

35Percent

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

Percent of visits to patient's primary care Percent of visits to patient's primary care provider (PCP) by number of past visits within provider (PCP) by number of past visits within

last l2 months: NAMCS, 2001last l2 months: NAMCS, 2001

New patients 0 1-2 3-5 6+Number of past visits

0

20

40

60

80

100Percent of visits

Drug mention rate by past visits: Drug mention rate by past visits: NAMCS, 2001NAMCS, 2001

New patient 0 1-2 3-5 6+Number of past visits

0

50

100

150

200Number of drugs per 100 visits

Drug mention rates by number of past visits Drug mention rates by number of past visits for selected therapeutic classes: NAMCS, for selected therapeutic classes: NAMCS,

20012001

New Patient 0 1-2 3-5 6+Number of past visits

0

5

10

15

20

25

30

35Number of drugs per 100 visits

Cardiovascular

CNS

Drug mention rates by number of past visits Drug mention rates by number of past visits for selected therapeutic classes: NAMCS, for selected therapeutic classes: NAMCS,

20012001

New Patient 0 1-2 3-5 6+Number of past visits

0

5

10

15

20

25

30

35Number of drugs per 100 visits

Antimicrobials

Cardiovascular

CNS

Pain relief

Re-weighting methodologyRe-weighting methodology

Assumptions and definitionsAssumptions and definitions Dividing the visit weight by number of visits Dividing the visit weight by number of visits

within year provides a measure of patientswithin year provides a measure of patients Patient is relation between person and Patient is relation between person and

sampled doctorsampled doctor One person can be different patients to One person can be different patients to

different doctorsdifferent doctors Assumes previous visits by same patient have Assumes previous visits by same patient have

similar visit characteristicssimilar visit characteristics

3 patients making a total of 7 visits

4/72/71/7

Probability of selecting a visit

4/72/71/7

1 .5 .25

Multiplicity factor

Creation of a re-weighting factorCreation of a re-weighting factorItem Item categoriescategories

Past Past visitsvisits

Annual Annual visitsvisits

Interval Interval midpointmidpoint

Viz ratioViz ratio

NewNew 00 11 11 11

00 00 11 11 11

1-21-2 1-21-2 2-32-3 2.52.5 .4.4

3-53-5 3-53-5 4-64-6 55 .2.2

6+6+ 6+6+ 7+7+ 88 .125.125

Patient weight = Visit weight * Viz ratio Patient weight = Visit weight * Viz ratio

Visit weight Visit weight → 880,487,000 visits→ 880,487,000 visits

± 33,373,000± 33,373,000

Patient weight → 322,739,000 patientsPatient weight → 322,739,000 patients

± 13,073,000± 13,073,000

Re-weighting exampleRe-weighting example

Annual Annual visitsvisits

Interval Interval midpointmidpoint

Visit Visit weightweight

Viz ratioViz ratio Patient Patient weightweight

11 11 1010 11 1010

2-32-3 2.52.5 2020 .4.4 88

4-64-6 55 4040 .2.2 88

7+7+ 88 4040 .125.125 55

Sum = 110 visits 31 patients

Analysis using re-weightingAnalysis using re-weighting

Comparison of visits and patientsComparison of visits and patients Analysis of patientsAnalysis of patients

Comparison of distributions for Comparison of distributions for visits and patients: NAMCS 2001visits and patients: NAMCS 2001

Visits Patients

1 2-3 4-6 7+ 1 2-3 4-6 7+0

10

20

30

40

50

60Percent

Percent distribution for people making any Percent distribution for people making any health care visits by number of visits made in health care visits by number of visits made in

one year: NHIS, 1999-2000one year: NHIS, 1999-2000

1-3 4-9 10+Number of visits

0

10

20

30

40

50

60Percent of persons

Rate of persons making no health care visit was 17.5.

Rate of visits per population by patient Rate of visits per population by patient age: NAMCS, NHAMCS-OPD, 2001age: NAMCS, NHAMCS-OPD, 2001

3.4

4.2

1.9

1.9

2.7

4.1

6.7

7.8

All ages

<06

6-17

18-24

25-44

45-64

65-74

75+

Patient age in years

0 2 4 6 8 10

Rate

Components of utilization ratesComponents of utilization rates

Rate of visits per population =Rate of visits per population = Rate of visits Rate of visits per patientper patient

multiplied bymultiplied by

Rate of Rate of patients patients per populationper population

Rate of visits per patient and patients per Rate of visits per patient and patients per population by patient age: NAMCS, population by patient age: NAMCS,

NHAMCS-OPD, 2001NHAMCS-OPD, 2001

All ages

<06

6-17

18-24

25-44

45-64

65-74

75+

Patient age in years

0 0.5 1 1.5 2 2.5 3 3.5

Rate

Visits per patient

Patients per pop

Comparison of population-based and encounter-based estimatesComparison of population-based and encounter-based estimates of ambulatory care utilization by patient age: NAMCS,of ambulatory care utilization by patient age: NAMCS,

NHAMCS-OPD, NHIS 2001NHAMCS-OPD, NHIS 2001

Source: NHIS, NAMCS & NHAMCS-OPD

<06 6-17 18-24 25-44 45-64 65-74 75+

Patient age

0

0.2

0.4

0.6

0.8

1Probability

0

2

4

6

8

10Rate per pop

4+ visits

Any visits

Patients

Visits

Percent of visits and patients where the patient Percent of visits and patients where the patient made 7 or more visits in the year by patient made 7 or more visits in the year by patient

age: NAMCS 2001age: NAMCS 2001

Visits Patients

0

5

10

15

20

25

30

35Percent

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

Percent of visits and patients where the patient Percent of visits and patients where the patient made only 1 visit in the year by patient age: made only 1 visit in the year by patient age:

NAMCS 2001NAMCS 2001

Visits Patients0

10

20

30

40

50

60Percent

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

Rate per 100 pop of patients to same provider Rate per 100 pop of patients to same provider by type of setting and patient age: NAMCS, by type of setting and patient age: NAMCS,

NHAMCS-OPD, 2001NHAMCS-OPD, 2001

<15

15-24

25-44

45-64

65-74

75+

Patient age in years

0 50 100 150 200 250

Number of patients per 100 pop

Primary care Surgical spec Medical spec OPD

Rate per 100 pop of patients by number of Rate per 100 pop of patients by number of visits within a year to same provider and PCP visits within a year to same provider and PCP

status: NAMCS, 2001status: NAMCS, 2001

1

2-3

4-6

7+

Number of visits

0 10 20 30 40 50 60

Number of patients per 100 pop

PCP Non-PCP

Rate per 100 pop of patients by number of Rate per 100 pop of patients by number of visits within a year to PCP: NAMCS and visits within a year to PCP: NAMCS and

NHAMCS-OPD, 2001NHAMCS-OPD, 2001

Private ins

Medicaid

Uninsured

0 10 20 30 40 50

Number of patients per 100 pop

1 2-3 4-6 7+

Incidence of tobacco use cessation Incidence of tobacco use cessation counseling at PCP visits: NAMCS & counseling at PCP visits: NAMCS &

NHAMCS-OPD, 2001NHAMCS-OPD, 2001

23.7

27.3

Visits Patients0

5

10

15

20

25

30Percent

Percent of visits by tobacco users to their PCP Percent of visits by tobacco users to their PCP with tobacco cessation counseling by number with tobacco cessation counseling by number

of past visits within l2 months: NAMCS & of past visits within l2 months: NAMCS & NHAMCS-OPD, 2001NHAMCS-OPD, 2001

New patient 0 1-2 3-5 6+Number of past visits

0

10

20

30

40Percent of visits

Public health examplePublic health example

Women at risk for bearing children with birth Women at risk for bearing children with birth defects defects Levothyroxine (evidence of hypothyroid)Levothyroxine (evidence of hypothyroid)

• 2.6 million visits2.6 million visits• 2.3 million patients2.3 million patients

AccutaneAccutane• 397 thousand visits397 thousand visits• 272 thousand patients272 thousand patients

Comparison of drug mention rates Comparison of drug mention rates for visits and patientsfor visits and patients

Drug classDrug class Visit Visit DMRDMR

Patient Patient DMRDMR

RatioRatio

CNSCNS 1313 1010 1.351.35

CardioCardio 2222 1717 1.291.29

Pain reliefPain relief 1818 1717 1.101.10

AntimicrobialAntimicrobial 1313 1212 1.081.08

DMR is number of drugs per 100 visits/patients.

Ratio of drug mention rates based on Ratio of drug mention rates based on visits and patients: NAMCS, 2001visits and patients: NAMCS, 2001

,

,

,

,

CNS Cardio Pain relief Antimicrobial .0.6

0.8

1

1.2

1.4

1.6

1.8

SummarySummary Past visits items provides depth to analysis Past visits items provides depth to analysis

of ambulatory care utilizationof ambulatory care utilization Visit records may be re-weighted to provide Visit records may be re-weighted to provide

patient-level estimatespatient-level estimates Re-weighted distribution more closely Re-weighted distribution more closely

resembles population-based estimatesresembles population-based estimates No change in sampling variance estimation No change in sampling variance estimation

procedure other than using the new weight procedure other than using the new weight CaveatsCaveats

Assumption of similar characteristics is not Assumption of similar characteristics is not applicable to all analytical variablesapplicable to all analytical variables

Still is not equivalent to person-level estimatesStill is not equivalent to person-level estimates

Information available on the Information available on the InternetInternet

NCHS website is NCHS website is www.cdc.gov/nchswww.cdc.gov/nchs

National Health Care Survey website National Health Care Survey website Ambulatory Health Care Data (AHCD)Ambulatory Health Care Data (AHCD)

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