Linda McCaig and David Woodwell

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Analyzing Data from theNAMCS and NHAMCS

• Linda McCaig and David Woodwell
• 2006 Data Users Conference
• July 11, 2006

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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
• 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 practices
• Track certain conditions and prescribing patterns
• Find health disparities
• Examine the quality of care
• 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
• Institute of Medicine
• Health services researchers
• University and medical schools
• Broadcast and print media

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Average length of time for duration of office
visits and emergency departments waiting times
60
47.4
50
38
.0
40
Minutes
30
18.6
18.7
20
10
0
1994 2004 1997
2004
Waiting time in emergency
Office visit duration
departments 1/
1/ Significant increase since 1997 (plt.01)
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Percent of ED visits for transient ischemic
attack in which a CT or MRI was ordered or
performed
Source National Hospital Ambulatory Medical Care
Survey, 1992-2001 Citation Edlow JA, Kim S,
Pelletier AJ, Camargo CA Jr. National study on
emergency department visits for Transient
Ischemic Attack, 1992-2001. Acad Emer Med
2006April 11
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Percent of pediatric ED visits with analgesic
prescription by pain score
Drendel AL et al. Arch Intern Med
2006117(5)1511-16.
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Percent of ED visits for attempted suicide
according to arrival time
Overall
Attempted suicide
a.m.
p.m.
Doshi A et al. Ann Emerg Med 200646(4)369-75.
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Trends in office-based visit rates by children
and adolescents that included antipsychotic
treatment
Olfson M et al. Arch Gen Psyc 200663679-685
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Percent of prescriptions for UTI by drug class in
physician offices, OPDs, and EDs
Kallen AJ et al. Arch Intern Med
2006116(6)635-639.
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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.
• 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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Therapeutic classification system through 2004

• Since 1985, FDAs NDC therapeutic classification
  has been used
• Limitations
• Discontinued by FDA
• Only one level of sub-classification

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Therapeutic classification system - Multum Lexicon

• Starting in 2005
• Advantages
• Two levels of sub-classification
• Regular updates

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Example Classification of paroxetine

• NDC
• 0600 central nervous system
• 0630 antidepressants
• Multum Lexicon
• 242 psychotherapeutic agents
• 249 antidepressants
• 208 SSRI antidepressants

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2004 NAMCS PRF
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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
• Temperature and blood pressure
• 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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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
• Time seen by physician
• Discharge time
• Mode of arrival
• Immediacy
• Pulse and orientation

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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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Modifications to 2005-06 ED PRF

• On
• Patient residence
• Discharged from any hospital within last 7 days
• Drug given in ED or prescribed at discharge
• Reason patient was transferred

• Off
• Alcohol related visit
• Episode of care

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Modifications to 2005-06 ED PRF

• Information on patients admitted to from the ED
• Type of unit
• Admission time
• Hospital discharge date
• Principal hospital discharge diagnosis
• Discharged dead or alive

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Modifications to 2005-06 NAMCS/OPD PRFs

• On
• Pregnant
• (LMP) or gestation week
• Chronic disease checklist
• Disease management program
• Height and weight
• Medications new or continued
• Non-medication treatment

• Off
• Episode of care
• Do physicians share care
• Cause of injury

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ED PRF- new items for 2007-08

• Respiratory rate
• How many times seen in this ED in last 12 months?
• Type of MRI and CT scan
• Head or other
• Procedure checkboxes more specific

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NHAMCS induction form- new items for 2005-06

• Electronic medical records
• Mass casualty preparedness
• Drills, exercises
• ED staffing, capacity, and ambulance diversion
• Percent of ED board certified physicians
• Number of hours ED was on ambulance diversion
• Plans to expand ED physical space

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NHAMCS induction form- new items for 2007-08

• Critical Access Hospital (CAH)
• Transplant services
• Outsourcing of radiographs
• ED observation unit

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Examples of facility-level data
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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 and 2006
  NHAMCS
• Services related to treating children
• Availability of pediatric supplies

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Cross-classification of EDs by ED pediatric visit
volume and inpatient pediatric structure
ED pediatric visit volume

Percent of EDs
Middleton KR, Burt CW. ADR 367.
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Cross-classification of pediatric ED visits by ED
pediatric visit volume and inpatient pediatric
structure

ED pediatric visit volume
Percent of pediatric ED visits
Middleton KR, Burt CW. ADR 367.
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Bioterrorism and mass casualty preparedness

• Funded by the DHHS ASPE
• 2003-05 NAMCS 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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Percentage of hospitals that trained their staff
in emergency response by subject area
Niska RW, Burt CW. ADR 364.
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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

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Percent distribution of EDs by time on ambulance
diversion and metropolitan statistical area status
Time on diversion
Percent of EDs
Burt CW, McCaig LF, Valverde RH. Ann Emerg Med.
200647317-326
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Percent of office-based physicians and hospital
OPDs and EDs using electronic medical records,
2001-2003
Burt CW, Hing E. ADR 353.
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Overview

• Updates to NAMCS and new items on the Physician
  Induction Interview (PII)
• User considerations
• Methodological studies
• HIPAA
• Data dissemination
• NCHS Research Data Center

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Improvements to NAMCS in 2006

• New stratum of 104 Community Health Centers (FQHC
  Urban Indian Health Centers)
• 3 _at_ each for a total of 312 providers
• MDs, DOs, mid-level providers
• New stratum of oncologists (n200)
• Increased sample to primary care physicians (n50
  each GFP, IM, OB/GYN)

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NAMCS induction form- new item for 2005

• Electronic medical records
• If yes, does it include
• Patient demographics
• Computerized orders for prescriptions

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NAMCS induction form- new items for 2006

• On-site tests or procedures
• Electronic medical records
• If yes, does it include
• Patient demographics
• Computerized orders for prescriptions
• If yes, Are there warning for drug interactions
• Pay for performance (P4P)

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NAMCS induction form- new items for 2007-08

• Length of time for appointment
• Telemedicine

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Encounter vs. person data

• NAMCS and NHAMCS are record-based surveys
• Estimates are in terms of visits and not persons
• Not population-based surveys (NHIS)
• 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

• Estimate based on at least 30 raw cases are
  reliable
• Estimate has 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 improveresponse rate

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

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Methodological studies

• Complement study (1997-1999)
• Missing 11 of visits to physicians classified as
  not office-based
• Nonresponse follow-up survey (1998)
• Another in 2006

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Methodological studies

• NAMCS Motivational insert (2000)
• NAMCS and OPD PRF length (2001)
• Incentives test (2002)

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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
• Training
• Written instructions
• CD-ROM
• Self-study
• Follow-up

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Impact of HIPAA on 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 directly affected
• Easy reason to refuse

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Future releases

• 2005 NAMCS NHAMCS in Spring 2007
• 2003-04 medications report ADR combining all 3
  setting together

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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, 1973-2004
• NHAMCS, 1992-2004
• CD-ROMs
• NAMCS, 1990-2003
• NHAMCS, 1992-2003
• 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 for 1993-2004
• SPSS syntax files, Stata .do and .dct files for
  2002-2004

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Enhanced public-use files

• Sample design variables
• Masked variables for multi-stage sampling are
  available
• 1993-2004 NAMCS and NHAMCS
• Starting in 2002, NAMCS NHAMCS masked variables
  have been available for use in software using
  1-stage sampling. Prior years with formula
• Stating in 2003, we only released masked
  variables for use in software using 1-stage

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Design VariablesSurvey Years
2001
2002
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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Where to get more information

• Ambulatory Care information booth
• Call Ambulatory Care Statistics Branch at (301)
  458-4600
• Public Use Documentation
• or

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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