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  • 1. Linda McCaig and David Woodwell Ambulatory Care Statistics Branch Division of Health Care Statistics National Center for Health Statistics/CDC Using NAMCS and NHAMCS Data
  • 2. Overview
    • Background
    • Data uses
    • Survey methodology
    • Current and proposed survey items
    • User considerations
    • Methodological studies
    • Data dissemination
    • NCHS Research Data Center
  • 3.  
  • 4. National probability sample surveys
    • National Ambulatory Medical Care Survey (NAMCS)
      • Patient visits to non-federal office-based physicians
    • National Hospital Ambulatory Medical Care Survey (NHAMCS)
      • Patient visits to EDs and OPDs of non-federal short-stay hospitals
  • 5. Original NAMCS survey goals
    • National statistics
    • Professional education
    • Health policy formulation
    • Medical practice management
    • Quality assurance
  • 6. NAMCS history
    • Survey began in 1973
    • Annual data collection through 1981 (NORC)
    • Conducted in 1985 (NORC)
    • Annual began again in 1989 (Census)
  • 7. NHAMCS history
    • Survey began in 1992
    • Annual data collection (Census)
  • 8. How are NAMCS and NHAMCS data used?
  • 9. Data uses
    • To understand health care practice and find inequities
    • To track certain conditions
    • To establish national priorities
    • To serve as comparison points for states
    • To measure Healthy People objectives
  • 10. Data users
    • Over 100 journal publications in last 2 years
    • Medical associations
    • Government agencies
    • Health services researchers
    • University and medical schools
    • Broadcast and print media
  • 11. Setting government policy
    • ED as a “safety net” for the uninsured
    • Development of the Resource-Based Relative Value Scale (RBRVS)
  • 12.  
  • 13. Antibiotic prescribing rates at physician office visits for children Rate per 1000 population Rate per 1000 visits
  • 14.  
  • 15. Prescribing rates at physician office visits by specialty Psychiatry Ophthalmology Otolaryngology Orthopedic surgery
  • 16. Female ambulatory care visit rates for selected diagnoses by race
  • 17. Annual rate of illness and injury ED visits for seniors by race Illness, black 1 Illness, white 1 Injury, black 1 NOTE: 1 p < .01. Injury, white
  • 18. Diabetes visit rates per 10,000 persons by setting 49 147 1289 1998-99 38 157 1118 1996-97 36 117 865 1994-95 33 84 962 1992-93 ED OPD Office Year
  • 19. NAMCS and NHAMCS Methodology
  • 20. NAMCS 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 the certain specialties
  • 21. In-Scope NAMCS locations
    • Freestanding clinic/urgicenter
    • Federally qualified health center
    • Neighborhood and mental health centers
    • Non-federal government clinic
    • Family planning clinic
    • Health maintenance organization
    • Faculty practice plan
    • Private solo or group practice
  • 22. Out-of-Scope NAMCS locations
    • Hospital ED’s and OPD’s
    • Ambulatory surgicenter
    • Institutional setting (schools, prisons)
    • Industrial outpatient facility
    • Federal Government operated clinic
    • Laser vision surgery
  • 23. NAMCS Sample design
    • 112 NHIS PSUs
    • 3,000 physicians
    • 25,000 visits
    • 1 week reporting period
  • 24. 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
  • 25. NHAMCS Sample design
    • 112 NHIS PSUs
    • 500 hospitals
    • 400 EDs and 250 OPDs
    • 24,000 ED visits and 30,000 OPD visits
    • 4-week reporting period
  • 26. Gaining cooperation
    • Advance letters
    • Endorsement letters
    • Public relations materials
    • Conversion of refusal
  • 27. Data collection procedures
    • Induction visit by Census field representative (FR)
    • FR training of office/hospital staff
    • Random start number
    • Take every number
    • Prospective or retrospective method
  • 28. Items collected
    • Patient characteristics
      • age, race, sex
    • Visit characteristics
      • Reason for visit, diagnosis, medication
    • Provider characteristics
      • physician specialty, hospital ownership
  • 29. Repeating fields
    • Reason for visit (3)
    • Cause of injury (3)
    • Diagnosis (3)
    • Ambulatory surgical procedures (2)
    • Medications (6)
  • 30. Data processing
    • Data are coded and keyed by Analytical Sciences Inc. (ASI)
    • Quality control procedures
    • Edit checks by NCHS
  • 31. Coding systems used
    • A Reason for Visit Classification (NCHS)
    • ICD-9-CM
    • Drug coding classification system (NCHS)
    • National Drug Code Directory
  • 32. NAMCS and NHAMCS 1999-2000 PRFs
  • 33. Patient record form - common items
    • Patient’s zip code
    • Date of visit
    • Date of birth
    • Sex
    • Ethnicity
  • 34. Patient record form - common items
    • Race
    • Source of payment
    • HMO status
    • Reason for visit
  • 35. Patient record form – common items
    • Diagnosis
    • Diagnostic/screening services
    • Medications
    • Providers seen
    • Visit disposition
  • 36. Injury items
    • External cause – narrative text since 1997
    • Place of injury
    • Work related injury
    • Intent
  • 37. Office and OPD PRF - unique items
    • Was patient referred for visit
    • Patient’s primary care physician
    • Patient seen before
    • Major reason for visit
  • 38. Office and OPD PRF - unique items
    • Ambulatory surgical procedures
    • Therapeutic and preventive services
    • Time spent with physician (NAMCS only)
  • 39. ED Patient record form - unique items
    • Arrival time
    • Discharge time
    • Immediacy
    • Presenting level of pain
    • Procedures
  • 40. NAMCS and NHAMCS PRF revisions 2001-02 – emphasis on the continuity of care
  • 41. Office and OPD PRF - new items for 2001-02
    • How many visits in last 12 months
    • Initial or follow-up visit
    • Do other physicians share care
    • Total number of medications
  • 42. ED PRF - new items for 2001-02
    • Discharge time
    • Visit related to alcohol use
    • Patient seen in last 72 hours
    • Initial or follow-up visit
    • Visit related to adverse drug event
    • Initial vital signs
    • Total number of medications
  • 43. NAMCS and NHAMCS PRF revisions 2003-04
  • 44. ED PRF- revisions for 2003-04
    • New
      • oriented X 3
      • is visit work related
      • list up to 8 medications
    • Recycled
      • mode of arrival
      • presenting level of pain
      • time seen by physician
  • 45. 2001-02 Induction Interview revisions
    • NAMCS – e.g., electronic medical records, number of managed care contracts
    • NHAMCS – e.g., Pediatric Emergency Services and Equipment Supplement (HRSA)
  • 46. 2003-04 Induction Interview revisions
    • NAMCS – e.g., Physician was a member of a practice-based research network (PBRN)
    • NHAMCS – e.g., Daily census of occupied and available beds
  • 47. ED Overcrowding
    • Physician coverage hours
    • Log of ambulance diversion
  • 48. Analysis of Facility Level Data
  • 49. Percent of physicians who do not accept new patients by payment type
  • 50. Distribution of hospital EDs on average waiting time
  • 51. Overview
    • User considerations
      • Encounter vs. person data
      • Sampling error
      • Nonsampling error
    • Methodological studies
    • Data dissemination
    • NCHS Research Data Center
  • 52. Encounter vs. person data
    • NAMCS and NHAMCS are record-based surveys
    • Not population-based surveys (NHIS)
    • Estimates are in terms of visits and not persons
    • Can not calculate incidence or prevalence rates from our estimates
  • 53. Sample 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
  • 54. Sampling error
    • NAMCS and NHAMCS are not simple random samples
    • Clustering effects of visits within the physician’s practice and also physician practices within PSUs
    • Must use generalized variance curve or SUDAAN to calculate SEs for all estimates, percents, and rates.
  • 55. Reliability 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
  • 56. Ways to improve reliability of estimates
    • Combine NAMCS, ED and OPD data to produce ambulatory care visit estimates
    • Combine multiple years of data
  • 57. Nonsampling error
    • Frame coverage
    • Reporting and processing errors
    • Biases due to survey and item nonresponse
    • Incomplete responses
  • 58. Minimizing nonsampling error
    • Improve sample frame for better coverage
    • Encourage uniform reporting and eliminate ambiguities
    • Pretest survey items and procedures
    • Perform quality control procedures – consistency and edit checks
    • Train Census field representatives
  • 59. NAMCS Response rates
  • 60. NHAMCS Response rates ED OPD
  • 61. Attempts to improve response rate
    • Publicity
    • Eliminating questions that have a high item non-response
    • Incentives test
  • 62. Methodological studies
    • Nonresponse study
    • Complement study
    • Motivational insert
    • Form length
    • Incentive test
  • 63. Initial results of incentives test
    • Still very early
    • Participation in some “on the fence” cases
    • No effect on “extreme” cases
  • 64. Data dissemination
  • 65.  
  • 66. Outside research
    • Journal articles
      • List on Ambulatory Care web site
    • Text books
    • Department level publications
      • Health US
  • 67. Microdata files
    • Downloadable files
        • NAMCS, 1973-2000
        • NHAMCS, 1992-2000
    • CD-ROMs
        • NAMCS, 1990-2000
        • NHAMCS, 1992-2000
    • Tapes/cartridges (NTIS)
        • NAMCS, 1973-1997
        • NHAMCS, 1992-1997
  • 68. Enhanced public-use files
    • SAS variable labels, value labels, and format assignments (1997-2000)
    • Sample design variables
      • Allow use of SUDAAN and STATA
      • 1997-2000 NAMCS and NHAMCS
      • Files prior to 2000 have been updated on web site
  • 69. Comparison of RSEs Physician assistant Seen by Cardiac monitor IV fluids Admitted to hosp 0 5 10 15 20 RSE In-house Masked GVC
  • 70. Comparison of RSEs for ED visits by age Patient age in years In-house Public-use 1-stage gvc <15 15-24 25-44 45-64 65-74 75+ 0 5 10 15 RSE
  • 71. Future release
    • NAMCS Trend file
      • 1980-81, 1985, 1990-91, 1995-96, and 1999-2000
    • 2001 NAMCS and NHAMCS data
  • 72. Where to get more information
    • Ambulatory Care information booth
    • Ambulatory Care website
    • Call Ambulatory Care Statistics Branch at (301) 458-4600
    • Academy for Health Services Research and Health Policy seminar Fall, 2002
  • 73. http://www.cdc.gov/nchs/about/major/ahcd/ahcd1.htm
  • 74. NCHS Research Data Center
  • 75. 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 sex and age, board certification, teaching hospital
      • Geographic: state and county codes
  • 76. Data Center- 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
  • 77. Data Center rules
    • Submit a proposal
    • Cannot use data to identify patients or providers or geographic location of providers
    • Cannot remove data files
    • Fee – onsite / remote / file construction
  • 78. I need more information !
    • Visit the Research Data Center booth
    • E-mail: [email_address]
    • Website: www.cdc.gov/nchs/r&d/rdc.htm
    • Call (301) 458-4277
  • 79. Thank You
    • Linda McCaig – NHAMCS data
    • [email_address]
    • David Woodwell – NAMCS data
    • [email_address]
  • 80.  

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