Using past visit information to enhance analysis of National Ambulatory Medical Care Survey (NAMCS) data Session 25 July 13, :30-noon

Session overview  Introduction and methodology for using past visit information – Catharine Burt  Example of analysis of quality of care for hypertension – Esther Hing

Using past visit information to enhance analysis of ambulatory care from encounter data Catharine W. Burt, Ed.D. Chief, Ambulatory Care Statistics Branch July 13, 2004 Data Users Conference U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Center for Health Statistics

Topics  Introduction  Brief survey background  Past visit item  Re-weighting methodology  Analysis using re-weighting  Summary

Encounter vs. population-based surveys that measure ambulatory care utilization  Population-based National Health Interview Survey (NHIS) National Health Interview Survey (NHIS) National Health and Nutrition Examination Survey (NHANES) National Health and Nutrition Examination Survey (NHANES) Medical Expenditure Panel Survey (MEPS) Medical Expenditure Panel Survey (MEPS)  Encounter-based National Ambulatory Medical Care Survey (NAMCS) National Ambulatory Medical Care Survey (NAMCS) National Hospital Ambulatory Medical Care Survey (NHAMCS) National Hospital Ambulatory Medical Care Survey (NHAMCS)

Pattern of ambulatory care visits according to patient age: NHIS, 2001 < %20%40%60%80%100% None1-3 visits4-9 visits10 or more visits

Rate of visits per population by patient age: NAMCS, NHAMCS-OPD, All ages < Patient age in years Rate

Desired goals from adding number of past visits to encounter data Describe patterns of care by frequency of visiting the doctor Describe patterns of care by frequency of visiting the doctor Provide more information about patients from encounter-level data Provide more information about patients from encounter-level data Better describe quality of care to patients vs. describing content of encounter Better describe quality of care to patients vs. describing content of encounter

NAMCS and NHAMCS background  NAMCS Fielded , 1985, 1989-present Fielded , 1985, 1989-present 3-stage sample 3-stage sample PSUs –PSUs – physicians – physicians – visits during 1 week visits during 1 week  NHAMCS Fielded annually since 1992 Fielded annually since stage sample 4-stage sample PSUs –PSUs – hospitals – ED/OPD clinics – visits during 4 weeks visits during 4 weeks SEs rates percents drugs providers visits sample records

Scope of the NAMCS  Physicians must be: Primarily engaged in office-based, patient care Primarily engaged in office-based, patient care Non-federally employed Non-federally employed Not in anesthesiology, radiology, or pathology Not in anesthesiology, radiology, or pathology

In-Scope Visits for NAMCS  Basic unit of sampling is the physician- patient visit  Visit must occur in a physician’s office  Visits must be for medical purposes  Out-of-scope contacts include: Visits for administrative purposes Visits for administrative purposes House calls, phone calls, s, visits in hospital setting unless physician has private office there House calls, phone calls, s, visits in hospital setting unless physician has private office there

In-Scope NAMCS Locations  Freestanding private solo or group practice  Freestanding clinic/urgicenter  Neighborhood medical and mental health centers  Privately operated clinics  Non-Federal government clinic  Health maintenance organization  Federally qualified health center  Faculty practice plan

Out-of-Scope NAMCS Locations  Hospital ED’s and OPD’s  Ambulatory surgicenter  Institutional setting (schools, prisons)  Industrial outpatient facility  Federally operated clinic  Laser vision surgery

Scope of the NHAMCS  Basic unit of sampling is patient visit  Emergency and outpatient departments of non-federal, general and short-stay hospitals  Not Federal, military, or Veterans Administration facilities  Located in 50 states and D.C.

Items Collected  Patient characteristics Age, sex, race, ethnicity Age, sex, race, ethnicity  Visit characteristics Source of payment, continuity of care, reason for visit, diagnosis, treatment, medications ordered or provided Source of payment, continuity of care, reason for visit, diagnosis, treatment, medications ordered or provided  Provider characteristics Physician specialty, hospital ownership Physician specialty, hospital ownership  Drug characteristics Therapeutic class, composition, control status, ingredients, Rx or OTC Therapeutic class, composition, control status, ingredients, Rx or OTC

Percent distribution for number of past visits within l2 months: NAMCS, 2001 New patient Unknown Number of past visits Percent of visits

Percent distribution of past visit item by PCP status: NAMCS 2001 New patient Unknown Number of past visits Percent of visits PCPOther

Percent of visits where the patient made 6 or more visits in past year by patient age: NAMCS 2001

Percent of visits to patient's primary care provider (PCP) by number of past visits within last l2 months: NAMCS, 2001 New patients Number of past visits Percent of visits

Drug mention rate by past visits: NAMCS, 2001 New patient Number of past visits Number of drugs per 100 visits

Drug mention rates by number of past visits for selected therapeutic classes: NAMCS, 2001 New Patient Number of past visits Number of drugs per 100 visits Cardiovascular CNS

Drug mention rates by number of past visits for selected therapeutic classes: NAMCS, 2001 New Patient Number of past visits Number of drugs per 100 visits Antimicrobials Cardiovascular CNS Pain relief

Re-weighting methodology  Assumptions and definitions Dividing the visit weight by number of visits within year provides a measure of patients Dividing the visit weight by number of visits within year provides a measure of patients Patient is relation between person and sampled doctor Patient is relation between person and sampled doctor One person can be different patients to different doctors One person can be different patients to different doctors Assumes previous visits by same patient have similar visit characteristics Assumes previous visits by same patient have similar visit characteristics

3 patients making a total of 7 visits

4/7 2/71/7 Probability of selecting a visit

4/72/7 1/ Multiplicity factor

Creation of a re-weighting factor Item categories Past visits Annual visits Interval midpoint Viz ratio New

 Patient weight = Visit weight * Viz ratio  Visit weight → 880,487,000 visits ± 33,373,000 ± 33,373,000  Patient weight → 322,739,000 patients ± 13,073,000 ± 13,073,000

Re-weighting example Annual visits Interval midpoint Visit weight Viz ratio Patient weight Sum = 110 visits 31 patients

Analysis using re-weighting  Comparison of visits and patients  Analysis of patients

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

Percent distribution for people making any health care visits by number of visits made in one year: NHIS, Number of visits Percent of persons Rate of persons making no health care visit was 17.5.

Rate of visits per population by patient age: NAMCS, NHAMCS-OPD, All ages < Patient age in years Rate

Components of utilization rates Rate of visits per population = Rate of visits per patient multiplied by multiplied by Rate of patients per population

Rate of visits per patient and patients per population by patient age: NAMCS, NHAMCS-OPD, 2001 All ages < Patient age in years Rate Visits per patient Patients per pop

Comparison of population-based and encounter-based estimates of ambulatory care utilization by patient age: NAMCS, NHAMCS-OPD, NHIS 2001 Source:NHIS,NAMCS & NHAMCS-OPD < Patient age Probability Rate per pop 4+ visits Any visits Patients Visits

Percent of visits and patients where the patient made 7 or more visits in the year by patient age: NAMCS 2001 VisitsPatients

Percent of visits and patients where the patient made only 1 visit in the year by patient age: NAMCS 2001 VisitsPatients

Rate per 100 pop of patients to same provider by type of setting and patient age: NAMCS, NHAMCS-OPD, 2001 < Patient age in years Number of patients per 100 pop Primary careSurgical specMedical specOPD

Rate per 100 pop of patients by number of visits within a year to same provider and PCP status: NAMCS, Number of visits Number of patients per 100 pop PCPNon-PCP

Rate per 100 pop of patients by number of visits within a year to PCP: NAMCS and NHAMCS-OPD, 2001 Private ins Medicaid Uninsured Number of patients per 100 pop

Incidence of tobacco use cessation counseling at PCP visits: NAMCS & NHAMCS-OPD, VisitsPatients Percent

Percent of visits by tobacco users to their PCP with tobacco cessation counseling by number of past visits within l2 months: NAMCS & NHAMCS-OPD, 2001 New patient Number of past visits Percent of visits

Public health example  Women at risk for bearing children with birth defects Levothyroxine (evidence of hypothyroid) Levothyroxine (evidence of hypothyroid) 2.6 million visits 2.6 million visits 2.3 million patients 2.3 million patients Accutane Accutane 397 thousand visits397 thousand visits 272 thousand patients272 thousand patients

Comparison of drug mention rates for visits and patients Drug class Visit DMR Patient DMR Ratio CNS Cardio Pain relief Antimicrobial DMR is number of drugs per 100 visits/patients.

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

Summary  Past visits items provides depth to analysis of ambulatory care utilization  Visit records may be re-weighted to provide patient-level estimates  Re-weighted distribution more closely resembles population-based estimates  No change in sampling variance estimation procedure other than using the new weight  Caveats Assumption of similar characteristics is not applicable to all analytical variables Assumption of similar characteristics is not applicable to all analytical variables Still is not equivalent to person-level estimates Still is not equivalent to person-level estimates

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