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Session 25 July 13, 2004 10:30-noon

Using past visit information to enhance analysis of National Ambulatory Medical Care Survey (NAMCS) data. Session 25 July 13, 2004 10:30-noon. Session overview. Introduction and methodology for using past visit information – Catharine Burt

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Session 25 July 13, 2004 10:30-noon

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  1. Using past visit information to enhance analysis of National Ambulatory Medical Care Survey (NAMCS) data Session 25 July 13, 2004 10:30-noon

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

  3. U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Center for Health Statistics 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

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

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

  6. Pattern of ambulatory care visits according to patient age: NHIS, 2001 None 1-3 visits 4-9 visits 10 or more visits <06 6-17 18-24 25-44 45-64 65-74 75+ 0% 20% 40% 60% 80% 100%

  7. Patient age in years All ages 3.4 <06 4.2 6-17 1.9 18-24 1.9 25-44 2.7 45-64 4.1 65-74 6.7 75+ 7.8 0 2 4 6 8 10 Rate Rate of visits per population by patient age: NAMCS, NHAMCS-OPD, 2001

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

  9. NAMCS and NHAMCS background • NAMCS • Fielded 1973-1981, 1985, 1989-present • 3-stage sample • PSUs – physicians – visits during 1 week • NHAMCS • Fielded annually since 1992 • 4-stage sample • PSUs – hospitals – ED/OPD clinics – visits during 4 weeks records sample drugs SEs providers percents visits rates

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

  11. 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 • House calls, phone calls, emails, visits in hospital setting unless physician has private office there

  12. 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

  13. 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

  14. 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.

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

  16. Percent of visits 30 25 20 15 10 5 0 New patient 0 1-2 3-5 6+ Unknown Number of past visits Percent distribution for number of past visits within l2 months: NAMCS, 2001

  17. Percent of visits 35 PCP Other 30 25 20 15 10 5 0 New patient 0 1-2 3-5 6+ Unknown Number of past visits Percent distribution of past visit item by PCP status: NAMCS 2001

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

  19. Percent of visits 100 80 60 40 20 0 New patients 0 1-2 3-5 6+ Number of past visits Percent of visits to patient's primary care provider (PCP) by number of past visits within last l2 months: NAMCS, 2001

  20. Number of drugs per 100 visits 200 150 100 50 0 New patient 0 1-2 3-5 6+ Number of past visits Drug mention rate by past visits: NAMCS, 2001

  21. Number of drugs per 100 visits 35 Cardiovascular 30 CNS 25 20 15 10 5 0 New Patient 0 1-2 3-5 6+ Number of past visits Drug mention rates by number of past visits for selected therapeutic classes: NAMCS, 2001

  22. Number of drugs per 100 visits 35 Antimicrobials 30 Cardiovascular CNS 25 Pain relief 20 15 10 5 0 New Patient 0 1-2 3-5 6+ Number of past visits Drug mention rates by number of past visits for selected therapeutic classes: NAMCS, 2001

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

  24. 3 patients making a total of 7 visits V v v V V V V

  25. Probability of selecting a visit V v v V V V V 1/7 2/7 4/7

  26. Multiplicity factor V V V V V v v 1/7 2/7 4/7 1 .5 .25

  27. Creation of a re-weighting factor

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

  29. Re-weighting example Sum = 110 visits 31 patients

  30. Analysis using re-weighting • Comparison of visits and patients • Analysis of patients

  31. Percent 60 50 40 30 20 10 0 1 2-3 4-6 7+ 1 2-3 4-6 7+ Comparison of distributions for visits and patients: NAMCS 2001 Visits Patients

  32. Percent distribution for people making any health care visits by number of visits made in one year: NHIS, 1999-2000 Percent of persons 60 50 40 30 20 10 0 1-3 4-9 10+ Number of visits Rate of persons making no health care visit was 17.5.

  33. Patient age in years All ages 3.4 <06 4.2 6-17 1.9 18-24 1.9 25-44 2.7 45-64 4.1 65-74 6.7 75+ 7.8 0 2 4 6 8 10 Rate Rate of visits per population by patient age: NAMCS, NHAMCS-OPD, 2001

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

  35. Patient age in years All ages <06 6-17 Visits per patient 18-24 Patients per pop 25-44 45-64 65-74 75+ 0 0.5 1 1.5 2 2.5 3 3.5 Rate Rate of visits per patient and patients per population by patient age: NAMCS, NHAMCS-OPD, 2001

  36. Comparison of population-based and encounter-based estimates of ambulatory care utilization by patient age: NAMCS, NHAMCS-OPD, NHIS 2001 Probability Rate per pop 1 10 Any visits 0.8 8 Visits 0.6 6 4+ visits 0.4 4 0.2 2 Patients 0 0 <06 6-17 18-24 25-44 45-64 65-74 75+ Patient age Source: NHIS , NAMCS & NHAMCS-OPD

  37. Percent of visits and patients where the patient made 7 or more visits in the year by patient age: NAMCS 2001 Visits Patients

  38. Percent of visits and patients where the patient made only 1 visit in the year by patient age: NAMCS 2001 Visits Patients

  39. Primary care Surgical spec Medical spec OPD Patient age in years <15 15-24 25-44 45-64 65-74 75+ 0 50 100 150 200 250 Number of patients per 100 pop Rate per 100 pop of patients to same provider by type of setting and patient age: NAMCS, NHAMCS-OPD, 2001

  40. Rate per 100 pop of patients by number of visits within a year to same provider and PCP status: NAMCS, 2001 Number of visits 1 2-3 4-6 7+ PCP Non-PCP 0 10 20 30 40 50 60 Number of patients per 100 pop

  41. Private ins Medicaid Uninsured Rate per 100 pop of patients by number of visits within a year to PCP: NAMCS and NHAMCS-OPD, 2001 1 2-3 4-6 7+ 0 10 20 30 40 50 Number of patients per 100 pop

  42. Percent 30 27.3 23.7 25 20 15 10 5 0 Visits Patients Incidence of tobacco use cessation counseling at PCP visits: NAMCS & NHAMCS-OPD, 2001

  43. Percent of visits 40 30 20 10 0 New patient 0 1-2 3-5 6+ Number of past visits 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

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

  45. Comparison of drug mention rates for visits and patients DMR is number of drugs per 100 visits/patients.

  46. Ratio of drug mention rates based on visits and patients: NAMCS, 2001 1.8 1.6 1.4 , , 1.2 , , 1 0.8 0.6 Antimicrobial CNS Cardio Pain relief .

  47. 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 • Still is not equivalent to person-level estimates

  48. Information available on the Internet • NCHS website is www.cdc.gov/nchs • National Health Care Survey website • Ambulatory Health Care Data (AHCD) • Join our LISTSERV

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