# Presentation: 536583

## Linda McCaig and David Woodwell

Ambulatory Care Statistics Branch
Division of Health Care Statistics

- Ambulatory Care Statistics Branch
- Division of Health Care Statistics

**Overview of the NAMCS****and NHAMCS**

## Overview

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

## Slide 3

## 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

## Original NAMCS survey goals

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

## NAMCS history

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

## NHAMCS history

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

## How are NAMCS and NHAMCS data used?

## 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

## 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

## Slide 11

## Slide 12

## Total Ambulatory Care Visits

- SOURCE: CDC/NCHS, NAMCS and NHAMCS, 2001.

## Annual rate of injury-related ED visits for seniors by patient residence

| 
Age in years | Institution  | Community |
| --- | --- | --- |
|  | Number of visits per 100 persons  |  |
| 65-79 |   41 | 8 |
| 80+ |  37 | 14 |

## Percent of physician office visits by type of cardiac rhythm modifying agent

- Fang et al. Arch Intern Med 2004;164(1):55-60.

## Percent of selected ED visit characteristics among released patients who had a blood culture

| Visit
characteristic | Antibiotics prescribed | Antibiotics not prescribed | Total |
| --- | --- | --- | --- |
| Fever | 19% | 17% | 36% |
| No fever | 28% | 36% | 64% |
| Total | 47% | 53% | 100% |

## Potentially inappropriate drug prescribing at elderly physician office visits

- Goulding.  Arch Intern Med 2004;164(3):305-312.

## Number and rate of physician office visits for diabetes

- Number of visits in millions

- Rate per 100 persons

- Grant et al. Arch Intern Med 2004;164(10):1134-1139.

## Annual rate of injury-related ED visits for children by diagnosis

- Head wound

- Other wound

- Intracranial

- Poisoning

## Variations in drug mention rates for selected therapeutic classes by source of payment

## Variations in drug mention rates for selected therapeutic classes by MSA status

## HP2010 Objectives on antibiotic prescribing

|  | Ear infections
(Antibiotics per 1000 persons) | Common cold
(Antibiotics per 1000 persons) |
| --- | --- | --- |
| Baseline | 693 | 25 |
| 1998/99
 | 545 | 18  |
| 2000/01 | 595 | 18 |
| Target | 561 | 13 |

## NAMCS and NHAMCS Methodology

## 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

## 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

## 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

## NAMCS Sample design

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

## 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

## 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

##   Gaining cooperation

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

## Data collection procedures

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

## 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

## Repeating fields

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

## Data processing

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

## 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

## NAMCS and NHAMCS 2001-2004 PRFs

## Patient Record form - common items

- Patient’s zip code
- Date of visit
- Date of birth
- Sex
- Ethnicity

## Patient Record form- common items

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

## Patient Record form –common items

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

## Injury/poisoning/adverse effect items

- External cause – narrative text since 1997
- ED
- intentionality
- work related

## NAMCS and OPD PRF- unique items

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

## 2001-2004 NAMCS and OPD PRFcontinuity 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

## ED Patient Record form- unique items

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

## ED Patient Record form- unique items

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

## ED Patient Record form- continuity of care items

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

## 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

## NAMCS and OPD PRF revisions 2005-06 – emphasis on chronic conditions

## 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

## NAMCS and OPD PRF - new items for 2005-06 

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

## 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

## 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

## Examples of Collaboration with Other Government Agencies

## 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

## Attending Physician Specialty (available 24/7 in-house or on-call) 

| Medical Specialty | Number of EDs | Percent of EDs |
| --- | --- | --- |
| Board Certified Emergency Medicine Attending Physician | 
3,550
 | 
73
 |
| Board Certified Pediatric Emergency Medicine Attending Physician | 
1,270 | 
26 |
| Board Certified Pediatric Attending Physician | 
3,249 | 
67 |

**Attending Physician Specialty (available 24/7 in-house or on-call) **

**Notes:**
EPSES question: Does your emergency department have 24hr/7day access to the following attending physicians (either in-house or on call)?

Hospitals are least likely to have a BC Peds Emergency Attending, but similar percentages for BCEM and BC Pediatric attending

## 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

## Slide 56

## 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

## Slide 58

## Percent distribution of hospital emergency departments by safety-net criteria

## Percent distribution of emergency department visits by selected characteristics according to size of annual visit volume

## Percent of physicians accepting new patients by pay source

## Overview

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

## 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

## 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

## 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.

## 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

## Ways to improve reliability of estimates

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

## Nonsampling error

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

## 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

## NAMCS Response rate 

## NHAMCS Response rates

**ED**

**OPD**

## Attempts to improve response rate 

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

## 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

## Methodological studies

- NAMCS Motivational insert
- Conducted last half of 2000
- Insert (n=513); no insert (n=499)
- RR - 68% vs. 64%
- No difference in RR

## Methodological studies

- NAMCS and OPD PRF length
- Conducted 2001
- NAMCS: short (n=941); long (n=969)
- OPD: short (n=132); long (n=129)
- NAMCS RR - 68% (short) vs. 62% (long)
- NAMCS short PRF had a higher RR
- No effect on RR in OPD

## Methodological studies

- Incentives test
- Conducted last 3 quarters of 2002
- 3 groups: control (n=418), gift (n=401), and monetary (n=456)
- RR – 73%, 68%, and 73%, respectively
- No difference in RR between incentive groups

## 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

## HIPAA

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

## 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...

## Slide 80

## Outside research

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

## 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

## 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

## 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

## Design Variables—Survey Years

**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.

## Ratio of masked to unmasked SUDAAN standard errors using four-stage WOR

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

## 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)

## Scatter plot of masked and unmasked 4-stage WOR SUDAAN SE for all settings 

**Scatter plot of masked and unmasked 4-stage WOR SUDAAN SE for all settings **

## 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

## Where to get more information

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

## http://www.cdc.gov/nchs/about/major/ahcd/ahcd1.htm

## NCHS Research Data Center

## 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

## 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

## 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

## 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

## Thank You	

- Linda McCaig – NHAMCS data
**	****	****	**lmccaig@cdc.gov
- David Woodwell – NAMCS data
**	****	****	**dwoodwell@cdc.gov

## Slide 98