1

Linda McCaig and David Woodwell

2006 Data Users Conference

July 11, 2006

Analyzing Data from theNAMCS and NHAMCS

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICESCenters for Disease Control and PreventionNational Center for Health Statistics

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICESCenters for Disease Control and PreventionNational Center for Health 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

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

• 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)

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How are NAMCS and NHAMCS data used?

9

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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121/ Significant increase since 1997 (p<.01)

18.6

38

18.7

47.4

0

10

20

30

40

50

60

Min

utes

.0

1994 2004 1997 2004Office visit duration Waiting time in emergency

departments 1/

Average length of time for duration of office visits and emergency departments waiting

times

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Source: National Hospital Ambulatory Medical Care Survey, 1992-2001Citation: Edlow JA, Kim S, Pelletier AJ, Camargo CA Jr. National study on emergency department visits for Transient Ischemic Attack, 1992-2001. Acad Emer Med 2006;April 11

Percent of ED visits for transient ischemic attack in which a CT or MRI was

ordered or performed

15

Percent of pediatric ED visits with analgesic prescription by pain score

0

1 0

2 0

3 0

4 0

5 0

6 0

P a i n s c o r e

Per

cen

t o

f vi

sits

O p i o i d O t h e r a n a l g e s i c s

Drendel AL et al. Arch Intern Med 2006;117(5):1511-16.

16

Percent of ED visits for attempted suicide according to arrival time

0

2

4

6

8

1 0

1 2

1 4

2 : 0 0 4 : 0 0 6 : 0 0 8 : 0 0 1 0 : 0 0 1 2 : 0 0 2 : 0 0 4 : 0 0 6 : 0 0 8 : 0 0 1 0 : 0 0 1 2 : 0 0

T i m e o f a r r i v a l

Pe

rce

nt

of

vis

its Overall

Attempted suicide

Doshi A et al. Ann Emerg Med 2006;46(4):369-75.

a.m. p.m.

17

18

Trends in office-based visit rates by children and adolescents that included

antipsychotic treatment

02 0 04 0 06 0 08 0 0

1 0 0 01 2 0 01 4 0 01 6 0 0

1 9 9 3 -1 9 9 5

1 9 9 6 -1 9 9 7

1 9 9 8 1 9 9 9 2 0 0 0 2 0 0 1 2 0 0 2

Vis

its

per

100

,00

po

pu

lati

on

Olfson M et al. Arch Gen Psyc 2006;63:679-685

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Percent of prescriptions for UTI by drug class in physician offices, OPDs, and

EDs

0

1 0

2 0

3 0

4 0

5 0

Per

cen

t o

f p

resc

rip

tio

ns

Kallen AJ et al. Arch Intern Med 2006;116(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, FDA’s 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

• Patient’s 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

• Patient’s 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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0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5

> 1 0 , 0 0 0

4 , 0 0 0 - 1 0 , 0 0 0

< 4 , 0 0 0

S e p a r a t e p e d s w a r d N o s e p a r a t e p e d s w a r d D o e s n o t a d m i t c h i l d r e n

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

ED

pedia

tric

vis

it v

olu

me

Percent of EDsMiddleton KR, Burt CW. ADR #367.

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0 1 0 2 0 3 0 4 0 5 0

> 1 0 , 0 0 0

4 , 0 0 0 - 1 0 , 0 0 0

< 4 , 0 0 0

S e p a r a t e p e d s w a r d N o s e p a r a t e p e d s w a r d

D o e s n o t a d m i t c h i l d r e n

Cross-classification of pediatric ED visits by ED pediatric visit volume and inpatient

pediatric structure

Percent of pediatric ED visits

ED

pedia

tric

vis

it v

olu

me

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

0 2 0 4 0 6 0 8 0 1 0 0

N u c l e a re x p o s u r e

C h e m i c a le x p o s u r e

A n y b i o l o g i c a la g e n t

P e r c e n t o f h o s p i t a l s

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

0 1 0 2 0 3 0 4 0 5 0 6 0

N o d iv e r s io n s

U p t o 5 %

5 - 1 0 %

1 0 - 2 0 %

M o r e t h a n 2 0 %

M S A N o n - M S A

Tim

e o

n d

ivers

ion

Percent of EDs

Burt CW, McCaig LF, Valverde RH. Ann Emerg Med. 2006;47:317-326

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Percent of office-based physicians and hospital OPDs and EDs using electronic

medical records, 2001-2003

0

5

1 0

1 5

2 0

2 5

3 0

3 5

S e t t i n g t y p e

Per

cent

of

prov

ider

s

O f f i c e O P D E D

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 @ each for a total of 312 providers

– MDs, DOs, mid-level providers

• New stratum of oncologists (n=200)

• Increased sample to primary care physicians (n=50 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

69

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

5 5

6 0

6 5

7 0

7 5

8 9 9 0 9 1 9 2 9 3 9 4 9 5 9 6 9 7 9 8 9 9 ' 0 0 ' 0 1 ' 0 2 ' 0 3 ' 0 4

Y e a r

Per

cen

t

76

NHAMCS Response rates

5 0

6 0

7 0

8 0

9 0

1 0 0

9 2 9 3 9 4 9 5 9 6 9 7 9 8 9 9 ' 0 0 ' 0 1 ' 0 2 ' 0 3 ' 0 4

Y e a r

Per

cen

t

ED

OPD

77

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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84

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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

87

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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2001*

3- & 4-Stage

design variables

2003

2002

1-Stage design

variables only

1-Stage design

variables

3- & 4-Stage design

variables

Design Variables—Survey Years

*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)

92

Average comparison ratios by alternative standard error method and

type of setting

Type of setting

Masked 4-stage WOR SUDAAN

Masked 1-stage WR SUDAAN

Masked SURVEY- MEANS

GVC

All settings 1.03 1.03 1.02 0.84

Physician’s offices

1.02 1.02 1.01 0.93

Hospital OPD 0.99 1.03 1.02 0.94

Hospital ED 1.03 1.06 1.06 0.91

Source: Inquiry 40: 401-415 (Winter 2003/2004)

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0

5000000

10000000

15000000

20000000

25000000

30000000

35000000

40000000

45000000

0 5000000 10000000 15000000 20000000 25000000 30000000 35000000 40000000

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.htmhttp://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@cdc.gov

• Website: www.cdc.gov/nchs/r&d/rdc.htm

• Call (301) 458-4277

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Thank You• Linda McCaig – NHAMCS data

lmccaig@cdc.gov

• David Woodwell – NAMCS data

dwoodwell@cdc.gov