# Presentation: 125590

##  Understanding and Using NAMCS and NHAMCS Data

**Part 1 – Survey Overview and SETS**
**Susan M. Schappert**
**Ambulatory Care Statistics Branch**
**Division of Health Care Statistics**

- National Center for
- Health Statistics

## Overview

- Background
- Data Uses
- Survey Methodology
- User Considerations
- How to Get the Data
- SETS Hands-On Training

##          NAMCS and NHAMCS

- National Ambulatory Medical Care Survey (NAMCS)
- Visits to office-based physicians
- National Hospital Ambulatory Medical Care Survey (NHAMCS)
- Visits to hospital emergency and outpatient departments

## History of NAMCS

- Planning began in 1967
- Inaugurated in 1973
- Fielded 1973-1981, 1985, 1989-present
- Database covering more than 30 years

## Original NAMCS survey goals

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

## History of NHAMCS

- Planning began in 1976
- Inaugurated December 1991
- Fielded annually
- 15th year of operation

## How are NAMCS and NHAMCS data used?

## Data users

- Universities and medical schools
- Medical associations
- Government agencies
- Health services researchers
- Broadcast and print media

## Slide 9

##           Antibiotic prescribing rates at      physician office visits for children 

- Rate per 1000 population

- Rate per 1000 visits

## Slide 11

## Ambulatory care visit rates for white and black females for selected diagnoses

## NAMCS and NHAMCS Methodology

## NAMCS Sample Design

- Three stage design
- 112 PSUs
- Physician practices within PSUs
- Patient visits within practices
- One-week reporting period
- For 2004-- 3,000 doctors sampled;
-   data collected for 25,286 office visits

## Scope of the NAMCS

- Basic unit of sampling is the physician-patient visit
- In scope visits:
- Must occur in physician’s office
- Must be for medical purposes
- Administrative visits not sampled
- House calls, emails, phone calls not sampled

## Scope of the NAMCS

- Physicians must be:
- Classified by AMA or AOA as primarily engaged in office-based patient care
- nonfederally employed;
- not in anesthesiology, radiology, or pathology
- 65 percent response rate in 2004

## 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

## 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

## NAMCS Scope – How Much is Missed?	

- What about non-office based physicians?
- NAMCS excludes physicians whose main activity is teaching, research, administration, hospital-based, or who are unclassified as to activity
- 1980 and 1995-97 Complement Surveys tried to estimate missed volume of visits otherwise in-scope for NAMCS
- Results indicated that NAMCS estimates underestimate all office-based care by about 11 percent.

## NHAMCS Sample Design

- Multistage probability design
- First stage sample of 112 PSUs
- Hospitals within PSUs
- Clinics within OPDs, ESA within EDs
- Patient visits within clinics, ESAs
- 4-week reporting period
- 464 hospitals sampled in 2004; 36,589  ED visits and 31,783 OPD visits

## Scope of the NHAMCS

- Basic unit of sampling is patient visit
- Emergency and outpatient departments of noninstitutional general and short-stay hospitals
- Not Federal, military, or Veterans Administration facilities
- Located in 50 states and D.C.

## NHAMCS Scope – How Much is Missed?

- 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

## Data Collection

- Bureau of the Census is our field agent
- Introductory letter sent 2-3 months in advance of reporting period
- Induction interview to train staff, obtain data on practice or facility characteristics
- Physician’s office/hospital staff is responsible for completion of Patient Record forms; Census abstracts as a last resort

## Data Collection

- Patient Record Forms (PRFs)
- Nearly identical for NAMCS and OPD
- Some differences for ED
- Redesigned once every 2 years
- Copies in your documentation and at our website

## Data Items

- Patient characteristics
- Age, sex, race, ethnicity
- Visit characteristics
- Source of payment, continuity of care, reason for visit, diagnosis, treatment
-  Provider characteristics
- Physician specialty, hospital ownership...
- Drug characteristics added in 1980

## Multiple Response Fields

- Up to 3 reasons for visit, causes of injury, physician diagnoses can be reported for each visit (no cause of injury on NAMCS and OPD starting in 2005)
- Up to 8 medications and each medication can have up to 3 therapeutic classes and up to 5 ingredients
- Multiple procedure codes for NAMCS and OPD

## Coding Systems Used

- Reason for Visit Classification (NCHS)
- ICD-9-CM for diagnoses, causes of injury and procedures
- Drug Classification System (NCHS)
- National Drug Code Directory
- switching to Multum starting with 2005 data

## Drug Data in NAMCS/ NHAMCS

**	**
**    **Respondents can list up to 8 medications (including Rx and OTC medications, immunizations, allergy shots, anesthetics, and dietary supplements) that were ordered, supplied, administered, or continued during the visit.  Each entry is called a drug mention.  Visits with one or more drug mentions are called drug visits.
- 	Respondents are asked to report trade names or generic names only (not dosage, administration, or regimen).  Can’t link drugs with diagnosis.
**	**
**	**

**Notes:**
Several difficulties of collecting drug data on surveys that should be understood.
First, there are multiple names for any given product. There are at least the following 3 
The chemical name
the trade or brand name
chosen by the manufacturers
& then the generic name
which is assigned by the 
and it is really the official name of the drug & is more commonly used by the gov’t & researchers because it is not associated with a particular company. 
As a consequence of the multiple names, survey drug data collection is complicated by the fact that particpants may report the generic or trade names

## Drug Coding in NAMCS and NHAMCS

- Drug entries on the Patient Record form are coded twice, using two separate classifications, and yielding two separate types of information
- All entries are coded “as written” using the Drug Entry Coding List
- All entries are also coded according to their generic substance(s) using a separate classification of generic substance codes

## Drug Coding in NAMCS and NHAMCS (cont.)

- Drug entry codes and generic substance codes are independent of each other
- For example, there is a code for an entry of “acetaminophen” on the Patient Record form in the Drug Entry Classification and a separate code for acetaminophen in the Generic Classification.

## Drug Characteristics

- Generic Name (for single ingredient drugs)
- Prescription Status – Rx or OTC – caveats apply
- Composition Status – single or multiple ingredient
- Controlled Substance Status – DEA schedule
- NDC Therapeutic Class (4-digit)
- Up to 5 Ingredients (for multiple ingredient drugs)

## Drugs as Ingredients

- Generic substance codes are used for both single-ingredient and combination drugs.  For example, acetaminophen can occur both as a single-ingredient generic drug and as an ingredient in a combination product.  The same code is used for both.

## Example of Drug Codes

- If doctor writes “Tylenol #3” on PRF, it is coded as:
- 	32920 in the Drug Entry field
- 	51380 in the Generic Name field (combination product)
- 	50005 (acetaminophen) and 70231 (codeine) in the Ingredients field

## NAMCS or NHAMCS drug data can be analyzed 
at the visit level (for example, the number of visits at which a particular drug was prescribed)
or at the medication level (for example, the number of “mentions” of a particular drug at ambulatory care visits

- at the visit level (for example, the number of visits at which a particular drug was prescribed)
- or at the medication level (for example, the number of “mentions” of a particular drug at ambulatory care visits

## Some User Considerations	

- NAMCS/NHAMCS sample visits, not patients
- No estimates of incidence or prevalence
- No state-level estimates
- We do not sample by setting or by non-physician providers
- Note that, in 2006, we include a stratum of CHCs, and non-physician providers are sampled within  CHCs
- May capture different types of care for solo vs. group practice physicians

## NAMCS vs. NHAMCS

- Consider what types of settings are best for a particular analysis
- Persons of color are more likely to visit OPDs and EDs than physician offices
- Persons in some age groups make disproportionately larger shares of visits to EDs than offices and OPDs

## Slide 37

## Sample Weight

- Each NAMCS record contains a single weight, which we call Patient Visit Weight
- Same is true for OPD records and ED records
- This weight is used for both visits and drug mentions

## Reliability of Estimates

- Estimates should be based on at least 30 sample records AND
- Estimates with a relative standard error (standard error divided by the estimate) greater than 30 percent are considered unreliable by NCHS standards
- Both conditions should be met to obtain reliable estimates

## Sampling Error

- NAMCS and NHAMCS are not simple random samples
- Clustering effects of visits within the physician’s practice, physician practices within PSUs, clinics within hospitals
- Must use some method to calculate standard errors for frequencies, percents, and rates

## Calculating Variance with NAMCS/NHAMCS Estimates

- Generalized Variance Curve (GVC).   This is the least accurate method.
- NCHS Research Data Center for access to actual design variables.
- Masked design variables on our public use files from 1993-2004.  Allows users to run SUDAAN and similar software to do more sophisticated analysis.

## Calculating Variance with NAMCS/NHAMCS Estimates, cont.

- 1993-2002
- public use files contain multi-stage design variables for use with SUDAAN WOR design option
- 2002-forward
-  public use files contain ultimate cluster design variables (single stage) for use with SUDAAN WR design option, SAS, Stata, SPSS, etc.
- To analyze data across these periods, need to create CSTRATM and CPSUM variables for years prior to 2003 using code available at our website

## 2001

**2001**

- multi-stage design variables

**2003**

**2002**

- ultimate
- cluster variables only

- multi-stage design variables
- and ultimate cluster design variables

**History of Design Variables****on NAMCS/NHAMCS Public Use Files**

## Ways to Improve Reliability of Estimates

- Combine NAMCS, ED and OPD data to produce ambulatory care visit estimates
- Combine multiple years of data
- Aggregate categories of interest into broader groups.

## Caveat on Counseling Services

- Diagnostic services are reflected accurately on medical records, but counseling services may not be (Stange, 1998, 2004)
- NAMCS and OPD data may underestimate the amount of health habit counseling that occurs if it is not included in the medical record

## 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

## How to Get the Data

## http://www.cdc.gov/nchs/namcs.htm

## Slide 50

## Public Use Micro-data 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

## Enhanced Public Use Files

- SAS input statements, label statements, and format statements (1993-2004)
- SPSS and Stata code for 2002-2004
- Masked sample design variables
- Allow use of SUDAAN, Stata, etc.
- Available for 1993-2004

## NCHS Research Data Center

## Advantages of the Research Data Center

- Gain access to information not available on public use files
- Patient: ZIP code linked income, education, etc.
- Provider: physician sex and age, board certification, teaching hospital
- Geographic: FIPS state and county codes
- Special files and data supplements

## Research 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

## Research Data Center

- E-mail:  rdca@cdc.gov
- Website:   www.cdc.gov/nchs/r&d/rdc.htm
- Call (301) 458-4277

## Additional Information

- Call us at (301) 458-4600
- Email me at SSchappert@cdc.gov
- Visit our website
- Join the ACLIST. It’s a moderated newsgroup for persons interested in NAMCS/NHAMCS.  It currently consists of about 2,400 subscribers.
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