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Understanding and Using

NAMCS and NHAMCS Data:

A Hands-On Workshop

Susan M. SchappertDonald K. CherryU.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers 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

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Overview I. Survey Background and Data UsesI. Survey Background and Data Uses II. Technical ConsiderationsII. Technical Considerations III. Getting the Data – Navigate Our III. Getting the Data – Navigate Our

WebsiteWebsite IV. SETS Hands-On TrainingIV. SETS Hands-On Training * * Break * ** * Break * * V. Using Raw Data FilesV. Using Raw Data Files VI. Advanced TopicsVI. Advanced Topics VII. SummaryVII. Summary

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NAMCS and NHAMCS

National Ambulatory Medical National Ambulatory Medical Care Survey (NAMCS)Care Survey (NAMCS) Visits to office-based physiciansVisits to office-based physicians

National Hospital Ambulatory National Hospital Ambulatory Medical Care Survey (NHAMCS)Medical Care Survey (NHAMCS) Visits to hospital outpatient and Visits to hospital outpatient and

emergency departmentsemergency departments

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Original NAMCS survey goals

• National statisticsNational statistics• Professional educationProfessional education• Health policy formulationHealth policy formulation• Medical practice managementMedical practice management• Quality assuranceQuality assurance

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Sample design - NAMCS

• 112 PSUs (counties)112 PSUs (counties)• Nonfederally employed, office-Nonfederally employed, office-

based physicians stratified by based physicians stratified by specialtyspecialty

• About 30 visits per doctor over a About 30 visits per doctor over a randomly selected 1-week periodrandomly selected 1-week period

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Sample design - NHAMCS

• 112 PSUs (counties)112 PSUs (counties)• Panel of 600 non-Federal, general or Panel of 600 non-Federal, general or

short stay hospitalsshort stay hospitals• Clinics (OPDs) and emergency service Clinics (OPDs) and emergency service

areas (EDs)areas (EDs)• About 200 visits per OPD, About 200 visits per OPD, 100 per ED over random 4-week period100 per ED over random 4-week period

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Data Items 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, treatmentvisit, diagnosis, treatment

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

Drug characteristics added in 1980Drug characteristics added in 1980 Class, composition, control status, etc.Class, composition, control status, etc.

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Repeating fields (from text entries)

Up to 3 fields each…Up to 3 fields each… Reason for visit Reason for visit Physician’s diagnosisPhysician’s diagnosis Cause of injuryCause of injury

Diagnostic services (6 fields)Diagnostic services (6 fields) Surgical procedures (2 fields)Surgical procedures (2 fields) Medications (6 fields)Medications (6 fields)

Drug ingredients (5 fields)Drug ingredients (5 fields) Therapeutic class (3 fields – 2002 on)Therapeutic class (3 fields – 2002 on)

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Coding Systems Used

Reason for Visit Classification (NCHS)Reason for Visit Classification (NCHS) ICD-9-CM for diagnoses, causes of ICD-9-CM for diagnoses, causes of

injury and proceduresinjury and procedures Drug Classification System (NCHS)Drug Classification System (NCHS) National Drug Code DirectoryNational Drug Code Directory

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Drug Data in NAMCS/ NHAMCS

What is a “Drug Mention” ?What is a “Drug Mention” ?

Any of up to 6 medications (including Rx and OTC Any of up to 6 medications (including Rx and OTC medications, immunizations, allergy shots, medications, immunizations, allergy shots, anesthetics, and dietary supplements) that were anesthetics, and dietary supplements) that were ordered, supplied, administered, or continued ordered, supplied, administered, or continued during the visit. during the visit.

Respondents are asked to report trade names or Respondents are asked to report trade names or generic names only (not dosage, administration, or generic names only (not dosage, administration, or regimen). Can’t link drugs with diagnosisregimen). Can’t link drugs with diagnosis. .

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Drug Coding in NAMCS and NHAMCS Drug entries on the Patient Record form are Drug entries on the Patient Record form are

coded twice, using two separate classifications, coded twice, using two separate classifications, and yielding two separate types of informationand yielding two separate types of information

All entries are coded “as written” using the Drug All entries are coded “as written” using the Drug Entry Coding ListEntry Coding List

All entries are also coded according to their All entries are also coded according to their generic substance(s) using a separate generic substance(s) using a separate classification of generic substance codesclassification of generic substance codes

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Drug Coding in NAMCS and NHAMCS (cont.) Drug entry codes and generic substance Drug entry codes and generic substance

codes are independent of each othercodes are independent of each other For example, there is a code for an entry For example, there is a code for an entry

of “acetaminophen” on the Patient Record of “acetaminophen” on the Patient Record form in the Drug Entry Classification and a form in the Drug Entry Classification and a separate code for acetaminophen in the separate code for acetaminophen in the Generic Classification.Generic Classification.

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Drug Characteristics Generic Name (for single ingredient drugs)Generic Name (for single ingredient drugs) Prescription StatusPrescription Status Composition StatusComposition Status Controlled Substance StatusControlled Substance Status Up to 3 NDC Therapeutic Classes (4-digit)Up to 3 NDC Therapeutic Classes (4-digit) Up to 5 Ingredients (for multiple ingredient Up to 5 Ingredients (for multiple ingredient

drugs)drugs)

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NAMCS or NHAMCS drug data can be NAMCS or NHAMCS drug data can be analyzed analyzed at the visit level (for example, the at the visit level (for example, the

number of visits at which a particular number of visits at which a particular drug was prescribed)drug was prescribed)

or at the medication level (for or at the medication level (for example, the number of “mentions” of example, the number of “mentions” of a particular drug at ambulatory care a particular drug at ambulatory care visitsvisits

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Some User Considerations

NAMCS/NHAMCS sample visits, not NAMCS/NHAMCS sample visits, not patientspatients

No estimates of incidence or No estimates of incidence or prevalenceprevalence

No state-level estimatesNo state-level estimates We do not sample by setting or by We do not sample by setting or by

non-physician providersnon-physician providers May capture different types of care for May capture different types of care for

solo vs. group practice physicianssolo vs. group practice physicians

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A few words about item validity Counseling items from NAMCS and OPD are Counseling items from NAMCS and OPD are

often used as analytic variables in research often used as analytic variables in research paperspapers

Medical records are accurate in reflecting Medical records are accurate in reflecting diagnostic services, but not health habit diagnostic services, but not health habit counseling (Stange et al. 1998, Gilchrist et al. counseling (Stange et al. 1998, Gilchrist et al. 2004)2004)

Our surveys may be underestimating Our surveys may be underestimating counseling services especially where data counseling services especially where data are abstractedare abstracted

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Sample Weight

Each NAMCS record contains a Each NAMCS record contains a single weight, which we call Patient single weight, which we call Patient Visit WeightVisit Weight

Same is true for OPD records and ED Same is true for OPD records and ED recordsrecords

This weight is used for both visits and This weight is used for both visits and drug mentionsdrug mentions

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Reliability of Estimates

Estimates should be based on at least 30 Estimates should be based on at least 30 sample records ANDsample records AND

Estimates with a relative standard error Estimates with a relative standard error (standard error divided by the estimate) (standard error divided by the estimate) greater than 30 percent are considered greater than 30 percent are considered unreliable by NCHS standardsunreliable by NCHS standards

Both conditions should be met to obtain Both conditions should be met to obtain reliable estimatesreliable estimates

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How Good are the Estimates?

Depends on what you are looking at. In Depends on what you are looking at. In general, OPD estimates tend to be general, OPD estimates tend to be somewhat less reliable than NAMCS somewhat less reliable than NAMCS and ED. and ED.

Since 1999, our Advance Data reports Since 1999, our Advance Data reports include standard errors in every table so include standard errors in every table so it is easy to compute confidence it is easy to compute confidence intervals around the estimates.intervals around the estimates.

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Reliability of Estimates in NAMCS Estimate of office visits by white persons was Estimate of office visits by white persons was

766.1 million in 2002, with a relative standard 766.1 million in 2002, with a relative standard error of 3.5 percent – error of 3.5 percent – range of 714.0-818.2 million visitsrange of 714.0-818.2 million visits

Estimate of office visits by black persons was Estimate of office visits by black persons was 89.5 million in 2002 with a relative standard 89.5 million in 2002 with a relative standard error of 9.1 percent – error of 9.1 percent – range of 73.6-105.3 million visitsrange of 73.6-105.3 million visits

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Reliability of Estimates in NHAMCS

OPD = 9% and 12% RSE for visits by white OPD = 9% and 12% RSE for visits by white persons vs. visits by black personspersons vs. visits by black persons

ED = 4% and 7% RSE for visits by white ED = 4% and 7% RSE for visits by white persons vs. visits by black personspersons vs. visits by black persons

A higher RSE means that an estimate has a A higher RSE means that an estimate has a wider confidence interval and is less reliable. wider confidence interval and is less reliable.

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Sampling Error NAMCS and NHAMCS are not simple NAMCS and NHAMCS are not simple

random samplesrandom samples Clustering effects of visits within the Clustering effects of visits within the

physician’s practice, physician practices physician’s practice, physician practices within PSUs, clinics within hospitalswithin PSUs, clinics within hospitals

Must use some method to calculate Must use some method to calculate standard errors for frequencies, standard errors for frequencies, percents, and ratespercents, and rates

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Calculating Variance with NAMCS/NHAMCS Estimates Old way (least accurate) = Generalized Old way (least accurate) = Generalized

variance curvesvariance curves Better way (recommended) = Masked design Better way (recommended) = Masked design

variablesvariables Multiple sampling stages Multiple sampling stages Single stage of sampling or ultimate cluster Single stage of sampling or ultimate cluster

designdesign Most accurate way (expensive) = Actual Most accurate way (expensive) = Actual

design variablesdesign variables

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Comparison of RSEs Produced Using GVC, SUDAAN-True, and SUDAAN WR

0

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Allages

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

GVCSUD-TUCD

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Comparisons of RSEs for Patient Race

Variances for clustered items (like race, diagnosis, type of provider) are Variances for clustered items (like race, diagnosis, type of provider) are predicted less accurately using the GVC. If you use the GVC, use p = .01, predicted less accurately using the GVC. If you use the GVC, use p = .01, not .05not .05

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White Black Asian NHOPI AIAN

GVCSUD-TrueUCD

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Ways to Improve Reliability of Estimates Combine NAMCS, ED and OPD data to Combine NAMCS, ED and OPD data to

produce ambulatory care visit estimatesproduce ambulatory care visit estimates Combine multiple years of dataCombine multiple years of data Aggregate categories of interest into Aggregate categories of interest into

broader groups.broader groups.

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NAMCS vs. NHAMCS Consider what types of settings are best Consider what types of settings are best

for a particular analysisfor a particular analysis Persons of color are more likely to Persons of color are more likely to

visit OPD’s and ED’s than physician visit OPD’s and ED’s than physician officesoffices

Persons in some age groups make Persons in some age groups make disproportionately larger shares of disproportionately larger shares of visits to ED’s than offices and OPD’svisits to ED’s than offices and OPD’s

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Additional Information

Call us at (301) 458-4600Call us at (301) 458-4600

Email me at SSchappert@cdc.govEmail me at SSchappert@cdc.gov

Visit our websiteVisit our website

Join the ACLIST. It’s a moderated newsgroup for Join the ACLIST. It’s a moderated newsgroup for persons interested in NAMCS/NHAMCS. It persons interested in NAMCS/NHAMCS. It currently consists of more than 2,000 subscribers. currently consists of more than 2,000 subscribers.