# Presentation: 674893

##  Understanding and Using NAMCS and NHAMCS Data:

**A Hands-On Workshop**
**Susan M. Schappert**
**Donald K. Cherry**

## Overview

- I.  Survey Background and Data Uses
- II. Technical Considerations
- III. Getting the Data – Navigate Our    	Website
- IV. SETS Hands-On Training
-  * * Break * *
- V. Using Raw Data Files
- VI. Advanced Topics
- VII. Summary

##          NAMCS and NHAMCS

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

## Original NAMCS survey goals

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

## Slide 5

## Sample design - NAMCS

- 112 PSUs (counties)
- Nonfederally employed, office-based physicians stratified by specialty
- About 30 visits per doctor over a randomly selected 1-week period

## Sample design - NHAMCS

- 112 PSUs (counties)
- Panel of 600 non-Federal, general or short stay hospitals
- Clinics (OPDs) and emergency service areas (EDs)
- About 200 visits per OPD,
-    100 per ED over random 4-week period

## 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
- Class, composition, control status, etc.

## Repeating fields (from text entries)

- Up to 3 fields each...
- Reason for visit
- Physician’s diagnosis
- Cause of injury
- Diagnostic services (6 fields)
- Surgical procedures (2 fields)
- Medications (6 fields)
- Drug ingredients (5 fields)
- Therapeutic class (3 fields – 2002 on)

## 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

## Drug Data in NAMCS/ NHAMCS

**	**
**    **What is a “Drug Mention” ?
-    Any of up to 6 medications (including Rx and OTC medications, immunizations, allergy shots, anesthetics, and dietary supplements) that were ordered, supplied, administered, or continued during the visit.
- 	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
- Composition Status
- Controlled Substance Status
- Up to 3 NDC Therapeutic Classes (4-digit)
- Up to 5 Ingredients (for multiple ingredient drugs)

## 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
- May capture different types of care for solo vs. group practice physicians

## A few words about item validity

- Counseling items from NAMCS and OPD are often used as analytic variables in research papers
- Medical records are accurate in reflecting diagnostic services, but not health habit counseling (Stange et al. 1998, Gilchrist et al. 2004)
- Our surveys may be underestimating counseling services especially where data are abstracted

## 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

## How Good are the Estimates?

- Depends on what you are looking at.  In general, OPD estimates tend to be somewhat less reliable than NAMCS and ED.
- Since 1999, our Advance Data reports include standard errors in every table so it is easy to compute confidence intervals around the estimates.

## Reliability of Estimates in NAMCS

- Estimate of office visits by white persons was 766.1 million in 2002, with a relative standard error of 3.5 percent –
- range of 714.0-818.2 million visits
- Estimate of office visits by black persons was  89.5 million in 2002 with a relative standard error of 9.1 percent –
- range of 73.6-105.3 million visits

## Reliability of Estimates in NHAMCS

- OPD = 9% and 12% RSE for visits by white persons vs. visits by black persons
- ED = 4% and 7% RSE for visits by white persons vs. visits by black persons
- A higher RSE means that an estimate has a wider confidence interval and is less reliable.

## 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

- Old way (least accurate) = Generalized variance curves
- Better way (recommended) = Masked design variables
- Multiple sampling stages
- Single stage of sampling or ultimate cluster design
- Most accurate way (expensive) = Actual design variables

## Comparison of RSEs Produced Using GVC, SUDAAN-True, and SUDAAN WR

## Comparisons of RSEs for Patient Race

-    Variances for clustered items (like race, diagnosis, type of provider) are predicted less accurately using the GVC.  If you use the GVC, use p = .01, not .05

## 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.

## NAMCS vs. NHAMCS

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

## Slide 29

## 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 more than 2,000 subscribers.
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