Linda McCaig and David Woodwell

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Overview of the NAMCSand NHAMCS

• Linda McCaig and David Woodwell
• Ambulatory Care Statistics Branch
• Division of Health Care Statistics

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Overview

• Background
• Data uses
• Survey methodology
• Current and proposed survey items
• User considerations
• Methodological studies
• Data dissemination
• NCHS Research Data Center

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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

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Original NAMCS survey goals

• National statistics
• Professional education
• Health policy formulation
• Medical practice management
• Quality assurance

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NAMCS history

• Survey began in 1973
• Annual data collection through 1981 (NORC)
• Conducted in 1985 (NORC)
• Annual began again in 1989 (Census)

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NHAMCS history

• Survey began in 1992
• Annual data collection (Census)

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How are NAMCS and NHAMCS data used?
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Data uses

• Understand health care practice
• Examine the quality of care
• Track certain conditions
• Find health disparities
• Measure Healthy People 2010 objectives
• Serve as benchmark for states

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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

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Total Ambulatory Care Visits
SOURCE CDC/NCHS, NAMCS and NHAMCS, 2001.
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Annual rate of injury-related ED visits for
seniors by patient residence
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Percent of physician office visits by type of
cardiac rhythm modifying agent
Fang et al. Arch Intern Med 2004164(1)55-60.
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Percent of selected ED visit characteristics
among released patients who had a blood culture
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Potentially inappropriate drug prescribing at
elderly physician office visits
Goulding. Arch Intern Med 2004164(3)305-312.
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Number and rate of physician office visits for
diabetes
Number of visits in millions
Rate per 100 persons
Grant et al. Arch Intern Med 2004164(10)1134-113
9.
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Annual rate of injury-related ED visits for
children by diagnosis
Head wound
Other wound
Intracranial
Poisoning
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Variations in drug mention rates for selected
therapeutic classes by source of payment
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Variations in drug mention rates for selected
therapeutic classes by MSA status
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HP2010 Objectives on antibiotic prescribing
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NAMCS and NHAMCS Methodology
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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 certain specialties

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In-Scope NAMCS locations

• Freestanding clinic/urgicenter
• Federally qualified health center
• Neighborhood and mental health centers
• Non-federal government clinic
• Family planning clinic
• HMO
• Faculty practice plan
• Private solo or group practice

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Out-of-Scope NAMCS locations

• Hospital EDs and OPDs
• Ambulatory surgicenter
• Institutional setting (schools, prisons)
• Industrial outpatient facility
• Federal Government operated clinic
• Laser vision surgery

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NAMCS Sample design

• 112 geographic PSUs
• 3,000 physicians
• 25,000 visits
• 1 week reporting period

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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

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NHAMCS Sample design

• 112 geographic PSUs
• 500 hospitals
• 400 EDs and 250 OPDs
• 37,000 ED and 35,000 OPD visits
• 4-week reporting period

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Gaining cooperation

• Advance letters
• Endorsement letters
• Public relations materials
• Conversion of refusal

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Data collection procedures

• Induction visit by Census field representative
  (FR)
• FR training of office/hospital staff
• Take every number
• Prospective or retrospective method

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Items collected on Patient Record form (PRF)

• Patient characteristics
• age, race, sex
• Visit characteristics
• reason for visit, diagnosis, medication
• Provider characteristics
• physician specialty, hospital ownership

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Repeating fields

• Reason for visit (3)
• Cause of injury (3)
• Diagnosis (3)
• Ambulatory surgical procedures (2)
• Medications (8)

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Data processing

• Data are coded and keyed by Constella Group Inc.
  (CG)
• Quality control procedures
• Edit checks by NCHS

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Coding systems used

• A Reason for Visit Classification (NCHS)
• ICD-9-CM
• diagnoses
• external causes of injury
• procedures
• Drug coding system (NCHS)
• National Drug Code Directory

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NAMCS and NHAMCS 2001-2004 PRFs
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Patient Record form - common items

• Patients zip code
• Date of visit
• Date of birth
• Sex
• Ethnicity

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Patient Record form- common items

• Race
• Source of payment
• Reason for visit
• Diagnosis

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Patient Record form common items

• Diagnostic/screening services
• Medications and injections
• Providers seen
• Visit disposition

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Injury/poisoning/adverse effect items

• External cause narrative text since 1997
• ED
• intentionality
• work related

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NAMCS and OPD PRF- unique items

• Does patient use tobacco
• Counseling/education/therapy
• Surgical procedures
• Time spent with physician (NAMCS only)

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2001-2004 NAMCS and OPD PRFcontinuity of care
items

• Patients primary care physician/provider
• Was patient referred for visit
• Patient seen before
• Seen how many times in past 12 months
• Major reason for visit
• Episode of care
• Other physicians share care

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ED Patient Record form- unique items

• Arrival time
• Discharge time
• Time seen by physician
• Mode of arrival
• Immediacy

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ED Patient Record form- unique items

• Presenting level of pain
• Alcohol related visit
• Work related visit
• Procedure checklist

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ED Patient Record form- continuity of care items

• Seen ED within last 72 hours
• Episode of care
• Initial or followup visit

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Recycled items on 2003-04 ED PRF

• On
• Time seen by physician
• Mode of arrival
• Presenting level of pain

• Off
• Visit related to an adverse drug event

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NAMCS and OPD PRF revisions 2005-06 emphasis on
chronic conditions
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NAMCS and OPD PRF- new items for 2005-06

• Arthritis
• Asthma
• Cancer
• Cerebrovascular disease
• CHF
• Chronic renal failure
• COPD

• Depression
• Diabetes
• Hyperlipidemia
• Hypertension
• Ischemic heart disease
• Obesity
• Osteoporosis

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NAMCS and OPD PRF - new items for 2005-06

• Vital signs
• Height
• Weight
• Temperature
• Blood pressure
• Disease management program
• Medication new or continued

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ED PRF- new items for 2005-06

• Homeless
• Discharged from any hospital within last 7 days
• Medication given in ED or prescribed at discharge
• Reason patient was transferred

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ED PRF- new items for 2005-06

• Admit to hospital
• Critical care/Intervention/Other bed
• Hospital admission time
• Hospital discharge date
• Principal hospital discharge diagnosis
• Alive/Dead

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Examples of Collaboration with Other Government
Agencies
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Emergency Pediatric Services and Equipment
Supplement (EPSES)

• Funded by the Health Resources and Services
  Administration
• Added as a supplement to the 2002-03 NHAMCS
• Services related to treating children
• Availability of pediatric supplies

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Attending Physician Specialty (available 24/7
in-house or on-call)
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Bioterrorism and mass casualty preparedness

• Funded by the DHHS Assistant Secretary for
  Planning and Evaluation
• 2003-4 NAMCS Physician induction interview
• Diagnosis of terror-related conditions
• Assistance in making a diagnosis
• Reporting a suspect case
• 2003-04 NHAMCS supplement
• Hospital response plan, training, and resources

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2003-04 NHAMCS Supplements

• Hospital inpatient occupancy rate
• ED capacity and staffing
• Number of treatment spaces
• Percent of vacant nursing positions
• Physicians employed by hospital or contractor
• Ambulance diversion
• Percent of days on diversion
• Mean number of hours on diversion

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Percent distribution of hospital emergency
departments by safety-net criteria
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Percent distribution of emergency department
visits by selected characteristics according to
size of annual visit volume
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Percent of physicians accepting new patients by
pay source
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Overview

• User considerations
• Encounter vs. person data
• Sampling error
• Nonsampling error
• Methodological studies
• HIPAA
• Data dissemination
• NCHS Research Data Center

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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
• Cannot calculate incidence or prevalence rates
  from our estimates

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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

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Sampling error

• NAMCS and NHAMCS are not simple random samples
• Clustering effects
• Providers within PSUs
• Visits within physician practice or hospital
• Must use generalized variance curve or special
  software (e.g., SUDAAN) to calculate SEs for all
  estimates, percents, and rates.

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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

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Ways to improve reliability of estimates

• Combine NAMCS, ED and OPD data to produce
  ambulatory care visit estimates
• Combine multiple years of data

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Nonsampling error

• Frame coverage
• Reporting and processing errors
• Biases due to survey and item nonresponse
• Incomplete responses

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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

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NAMCS Response rate
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NHAMCS Response rates
ED
OPD
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Attempts to improve response rate

• Publicity
• Eliminating questions that have a high item
  non-response
• Methodological studies

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Methodological studies

• Complement study 1997-1999
• 500 physicians in each year
• 17 of classified as nonoffice-based saw patients
• Represented 11 of total
• Difference not accounted for in weighting

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Methodological studies

• NAMCS Motivational insert
• Conducted last half of 2000
• Insert (n513) no insert (n499)
• RR - 68 vs. 64
• No difference in RR

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Methodological studies

• NAMCS and OPD PRF length
• Conducted 2001
• NAMCS short (n941) long (n969)
• OPD short (n132) long (n129)
• NAMCS RR - 68 (short) vs. 62 (long)
• NAMCS short PRF had a higher RR
• No effect on RR in OPD

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Methodological studies

• Incentives test
• Conducted last 3 quarters of 2002
• 3 groups control (n418), gift (n401), and
  monetary (n456)
• RR 73, 68, and 73, respectively
• No difference in RR between incentive groups

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HIPAA

• No directly identifiable information collected
• PHS Act 308(d) / Title 15
• Data Use Agreement w/ Limited Dataset
• IRB approval w/ waiver of patient authorization
• Accounting Document

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HIPAA

• 1-800 telephone number
• Respondent website
• www.cdc.gov/namcs
• www.cdc.gov/nhamcs
• Training
• Written instructions
• CD-ROM
• Self-study
• Follow-up

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Impact of HIPAA on 2003 NAMCS and NHAMCS

• Induction process in hospitals is longer due to
  additional levels of approval process
• Less likely to allow FR abstraction
• Response rate not affected
• 2004 may be more difficult

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Outside research

• Journal articles
• List on Ambulatory Care web site
• Text books
• Department level publications
• Health US

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Microdata files

• Downloadable files
• NAMCS, 1973-2002
• NHAMCS, 1992-2002
• CD-ROMs
• NAMCS, 1990-2002
• NHAMCS, 1992-2001 (2002 in Aug.)
• Tapes/cartridges (NTIS)
• NAMCS, 1973-1997
• NHAMCS, 1992-1997

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Enhanced public-use files

• New survey items and facility level data
• SAS input statements, variable labels, value
  labels, and format assignments
• 1993 2002 for NAMCS
• 1995 2002 for NHAMCS
• SPSS STATA input statements, variable labels,
  value labels, and format assignments in 2002

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Enhanced public-use files

• Sample design variables
• Masked variables for multi-stage sampling are
  available
• 1993-2002 NAMCS
• 1995-2002 NHAMCS
• In 2002, NAMCS NHAMCS will have masked
  variables for use in software using 1-stage
  sampling. Prior years with formula
• In 2003, we will only release masked variables
  for use in software using 1-stage

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Design VariablesSurvey Years
2002
2001
1-Stage design variables 3- 4-Stage design
variables
3- 4-Stage design variables
2003
1-Stage design variables only
Plan to re-release years with 1-stage design
variables.
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Ratio of masked to unmasked SUDAAN standard
errors using four-stage WOR
Source Inquiry 40 401-415 (Winter 2003/2004)
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Average comparison ratios by alternative standard
error method and type of setting
Source Inquiry 40 401-415 (Winter 2003/2004)
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Scatter plot of masked and unmasked 4-stage WOR
SUDAAN SE for all settings
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Future releases

• 2003 NAMCS NHAMCS in Spring 2005
• All settings Series report in Fall 2004 with
  NAMCS data for primary care and surgical and
  medical specialties

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Where to get more information

• Ambulatory Care information booth
• Ambulatory Care website
• Ambulatory Care listserve
• Call Ambulatory Care Statistics Branch at (301)
  458-4600

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http//www.cdc.gov/nchs/about/major/ahcd/ahcd1.htm
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NCHS Research Data Center
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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 gender and age, board
  certification, teaching hospital, medical school
  affiliation, ED size, provider weight
• Geographic state and county FIPS codes

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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

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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

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I need more information !

• Visit the Research Data Center booth
• E-mail rdca_at_cdc.gov
• Website www.cdc.gov/nchs/rd/rdc.htm
• Call [phone]

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Thank You

• Linda McCaig NHAMCS data
• lmccaig_at_cdc.gov
• David Woodwell NAMCS data
• dwoodwell_at_cdc.gov

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