Sampling Procedures for the Collection of Electronic Health Record

NATIONAL CENTER FOR HEALTH STATISTICS

Vital and Health Statistics

NCHS reports can be downloaded from:

https://www.cdc.gov/nchs/products/index.htm.

Series 2, Number 203 June 2023

Sampling Procedures for the

Collection of Electronic Health

Record Data From Federally Qualified

Health Centers, 2021–2022 National

Ambulatory Medical Care Survey

Data Evaluation and Methods Research

All material appearing in this report is in the public domain and may be reproduced or

copied without permission; citation as to source, however, is appreciated.

Suggested citation

Williams SN, Ukaigwe J, Ward BW, Okeyode T, Shimizu IM. Sampling procedures for

the collection of electronic health record data from federally qualified health centers,

2021–2022 National Ambulatory Medical Care Survey. National Center for Health Statistics.

Vital Health Stat Series 2(203). 2023. DOI: https://dx.doi.org/10.15620/cdc:127730.

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Sampling Procedures for the

Collection of Electronic Health

Record Data From Federally

Qualified Health Centers,

2021–2022 National Ambulatory

Medical Care Survey

Data Evaluation and Methods Research

NATIONAL CENTER FOR HEALTH STATISTICS

Vital and Health Statistics

Series 2, Number 203 June 2023

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics

Hyattsville, Maryland

June 2023

National Center for Health Statistics

Brian C. Moyer, Ph.D., Director

Amy M. Branum, Ph.D., Associate Director for Science

Division of Health Care Statistics

Carol J. DeFrances, Ph.D., Director

Alexander Strashny, Ph.D., Associate Director for Science

Series 2, Number 203 iii NATIONAL CENTER FOR HEALTH STATISTICS

Contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Sampling Methods and Procedures, 2021 and 2022 NAMCS HC Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Sampling Frame Creation and Eligibility Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Sampling Strata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Distribution of Resulting HC Sample to Strata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Appendix I. Sampling Procedures for the 2021 National Ambulatory Medical Care Survey Health Center Component . . . .6

Appendix II. Sampling Procedures for the 2022 National Ambulatory Medical Care Survey Health Center Component . . . .8

Text Figure

In-person, manual data collection process for the 2012–2020 National Ambulatory Medical Care Survey

Community Health Center Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Text Table

Percent distribution of eligible and ineligible health centers used for sample frame creation for

the 2021–2022 National Ambulatory Medical Care Survey Health Center Component . . . . . . . . . . . . . . . . . . . . . .3

Series 2, Number 203 1 NATIONAL CENTER FOR HEALTH STATISTICS

Sampling Procedures for the Collection

of Electronic Health Record Data From

Federally Qualied Health Centers,

2021–2022 National Ambulatory Medical

Care Survey

by Sonja N. Williams, M.P.H., Joy Ukaigwe, M.S., Brian W. Ward, Ph.D., Titilayo Okeyode, M.Sc., and

Iris M. Shimizu, Ph.D.

Abstract

Background

As part of modernization efforts, in 2021 the National

Ambulatory Medical Care Survey (NAMCS) began

collecting electronic health records (EHRs) for ambulatory

care visits in its Health Center (HC) Component. As a

result, the National Center for Health Statistics (NCHS)

needed to adjust the approaches used in the sampling

design for the HC Component. This report provides

details on these changes to the 2021–2022 NAMCS.

Sampling Methods and Procedures

For the 2021 and 2022 NAMCS HC Component sampling

frame, NCHS received a listing of all federally qualified

health centers (FQHCs) and FQHC look-alikes in the

United States in 2020 from the Health Resources and

Services Administration (HRSA). An FQHC is an HC that

receives funding from HRSA to provide services to

people who are medically underserved. An FQHC look-

alike is similar but does not receive funding. This listing

included 1,463 HCs, of which 1,400 were eligible for the

sampling frame. A stratified (organized information into

groups based on certain criteria) random sample of 50

FQHCs and FQHC look-alikes was drawn as the primary

sample, along with a reserve (or backup) sample of 100

HCs.

Results

For the 2021 sample, 95.7% of HCs in the source files

from which the sampling frame was compiled were

eligible for selection based on eligibility criteria. Among

the 4.3% of ineligible HCs, 88.9% were ineligible because

they lacked an EHR system or did not provide healthcare

services to the public. For the 2022 sample, 85.6% of HCs

in the source file were eligible for selection based on the

eligibility criteria and the removal of all HCs selected for

the 2021 sample. Among the 14.4% of HCs not eligible

for the 2022 sample, 70.0% were selected for the 2021

sample, and 26.8% were ineligible because they lacked

an EHR system or did not provide healthcare services.

Keywords: advanced practice provider • community

health center • EHR • federally qualified health center

look-alikes • healthcare provider • sampling design •

NAMCS

Background

The National Ambulatory Medical Care Survey (NAMCS),

administered by the National Center for Health Statistics

(NCHS), is a national survey designed to meet the need for

objective, reliable information about the provision and use

of ambulatory medical care services in the United States.

First fielded in 1973, the survey started with the collection of

data from a sample of visits to nonfederally employed office-

based physicians who were primarily engaged in direct

patient care. To broaden its ability to capture the provision

and use of ambulatory care, NAMCS also began sampling

health centers (HCs) in 2006. HCs are community-based and

patient-directed organizations that “deliver comprehensive

and affordable primary healthcare services to the nation’s

most vulnerable populations, including people experiencing

homelessness, agricultural workers, residents of public

housing, and veterans” (1). Federally qualified health centers

(FQHCs) are HCs that receive funding from the Department

of Health and Human Services’ Health Resources and

Services Administration (HRSA) to provide these services.

These HCs must meet specific requirements set by HRSA to

receive this funding. FQHC look-alikes are HCs that meet all

the requirements from HRSA but do not receive funding. This

expansion to include HCs in NAMCS was important because

FQHCs often serve as “safety net” care settings, where health

NATIONAL CENTER FOR HEALTH STATISTICS 2 Series 2, Number 203

care is provided for populations that are underserved or live

in areas underserved by healthcare resources, and they are

significant contributors in the primary care space (2,3).

The sampling of HCs continued until 2012, when it was

decided that a separate national sample of HC delivery sites

should be drawn. This independent sample of HC delivery

sites would allow for nationally representative estimates

on HCs to be produced, providing more information on

ambulatory care delivery at these locations. Before this

change, HCs were only included within the traditional NAMCS

physician sample, which limited the number of estimates

that could be produced in that setting (4). This new sample

of HC delivery sites included service sites of FQHCs and

FQHC look-alikes and urban Indian Health Service outpatient

clinics. Once a site was sampled, a facility interview was

conducted with the HC site director or similar representative

at that HC delivery site (Figure). This interview collected

basic characteristics about the site, as well as a listing of

all physicians, physician assistants, nurse practitioners, and

certified nurse midwives who were currently providing direct

patient care at the site. From this listing, up to three of these

HC providers were randomly selected to receive a provider

interview. Additionally, for each of these randomly selected

providers, a random sample of approximately 30 patient

visits seen by that provider was selected for which the visit

records would be manually abstracted (physical review and

gathering of information from medical records). These visits

were selected from a week that was predetermined for the

sampled site during the NAMCS HC sampling process before

fielding the survey. More details on this process can be found

in the NAMCS data documentation (5).

NAMCS continued using this sampling approach and

data collection procedures through 2020. However, in

recent years NCHS leadership has desired to modernize

NAMCS data collection procedures to better use electronic

health records (EHRs) and other electronic data, increase

the amount of data collected each year from survey

respondents, decrease burden for survey respondents, and

increase the timeliness and availability of the data collected.

In 2019, NCHS, partnering with HRSA, committed to change

its HC data collection procedures beginning with the 2021

NAMCS. This shift included three major changes. First,

NAMCS would move from conducting manual in-person

abstraction to collect patient visit data to collecting these

data through HC submission of EHRs using the NCHS “HL7

CDA R2 Implementation Guide: National Health Care Surveys

Release 1, DSTU Release 1.2—US Realm” (6). Second, instead

of collecting data from individual delivery sites and selected

HC providers, data would be collected from the entire

FQHC or FQHC network. Finally, NAMCS would move from

collecting only a sample of HC visits from a predetermined

week to collecting data for the entire calendar year.

These combined changes created what is now called the

NAMCS HC Component, and they are ultimately expected to

increase the timeliness and analytic capabilities of NAMCS.

However, as part of this change, new sampling procedures

Number equals about 30 visits.

NOTES: NAMCS is National Ambulatory Medical Care Survey. CHC is community health center.

SOURCE: National Center for Health Statistics, National Hospital Ambulatory Medical Care Survey, 2012–2020.

NAMCS sampled CHC

CHC sampled

Provider 1

Sampled calendar week

(assigned before fielding)

Sample of weekly visits

(drawn on site)

Patient visit data

abstraction

CHC sampled

Provider 2

Sampled calendar week

(assigned before fielding)

Sample of weekly visits

(drawn on site)

Patient visit data

abstraction

CHC sampled

Provider 3

Sampled calendar week

(assigned before fielding)

Sample of weekly visits

(drawn on site)

Patient visit data

abstraction

CHC Provider 3

induction interview

CHC Provider 2

induction interview

CHC Provider 1

induction interview

CHC facility induction

interview

(includes listing of

providers)

Figure. In-person, manual data collection process for the 2012–2020 National Ambulatory Medical Care Survey

Community Health Center Component

Series 2, Number 203 3 NATIONAL CENTER FOR HEALTH STATISTICS

for the NAMCS HC Component were needed. As described

previously, the previous NAMCS HC sample was based on

manual identification of providers within the HC and then on

sampling a small number of visits of the identified providers.

One of the goals of the redesign was to minimize burden

for the sampled HCs, and removing the need for identifying

providers was key in achieving this goal. This report provides

details on the procedures used to draw a sample of FQHCs

and FQHC look-alikes for the 2021 and 2022 NAMCS.

Sampling Methods and

Procedures, 2021 and 2022

NAMCS HC Component

Sampling Frame Creation and Eligibility

Requirements

Beginning in 2021, the targeted universe (specific population

targeted) for the NAMCS HC Component is FQHCs and FQHC

look-alikes in the 50 U.S. states and the District of Columbia,

which provide ambulatory (or direct outpatient) care to the

public and use an EHR system in one or more of their delivery

sites. Unlike previous years, Indian Health Service outpatient

clinics were not included in the targeted universe in the 2021

and 2022 NAMCS HC Component because of complexities of

the survey redesign and the changes to sampling procedures.

Although these Indian Health Service outpatient clinics

were not included in the 2021 and 2022 NAMCS, there is

potential for drawing a complementary sample of these

clinics for inclusion in future surveys after this new method

of collecting HC data through EHR transmission has been

established.

To create the sampling frame and draw the sample, NCHS

worked with HRSA to use a nationally representative

database that contains a list of all HCs in the United States.

For the 2021 sample, this list included 1,463 HCs. To ensure

that only survey-eligible FQHCs and FQHC look-alikes were

included, any HC that met the following conditions was

omitted from the sampling frame (Table):

● HCs that did not have an EHR system

● HCs that did not provide healthcare services to the general

U.S. population, such as those that exclusively serve

institutional populations (for example, prisons, nursing

homes or long-term care facilities, homeless shelters, etc.)

● HCs where only dental services were provided

● HCs located on a military installation or outside of the 50

U.S. states and the District of Columbia

Duplicate entries—HCs with the same name, address, and

administrator contact information—were removed from

the database. The resulting sampling frame of 1,400 HCs

was used to draw the primary and backup samples for the

2021 NAMCS HC Component. Of the 63 FQHCs and FQHC

look-alikes in the original database that were ineligible for

the 2021 NAMCS HC Component sampling frame, 24 were

omitted because they did not have an EHR system, 32 were

omitted for not providing healthcare services to the public or

only providing dental services, and 7 were omitted because

they were located on a military installation or outside of the

50 U.S. states and the District of Columbia or appeared as

duplicate listings.

To create a sampling frame for the 2022 NAMCS HC

Component, the same database for 2021 was updated and

used, which contained 1,482 HCs. Using financial support

from the Office of the Secretary Patient-Centered Outcomes

Research Trust Fund (OS-PCORTF) for fiscal year 2021 (7),

the 2022 NAMCS HC Component sample was expanded

to initially add 60 respondent HCs to the 50 respondent

HCs from the 2021 sample, resulting in patient visit data

being collected for 110 FQHCs and FQHC look-alikes during

the 2022 NAMCS. For this expansion, 60 HCs (54 FQHCs

ultimately fielded) were selected for the primary sample and

120 additional HCs for the backup sample. All the eligibility

Table. Percent distribution of eligible and ineligible health centers used for sample frame creation for the

2021–2022 National Ambulatory Medical Care Survey Health Center Component

Eligibility status

2021 2022

Number Percent Number Percent

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1,463 100.0 1,482 100.0

Eligible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1,400 95.7 1,269 85.6

Ineligible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

No electronic health record system . . . . . . . . . . . . . . . . . . . . . . . 24 1.7 26 1.8

Did not provide healthcare service to the general population

or only provided dental services . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.2 31 2.1

Other

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 0.5 7 0.6

Included in previous year’s sample . . . . . . . . . . . . . . . . . . . . . . . . … … 149 10.1

… Category not applicable.

Includes health centers located on a military installation or outside of the 50 U.S. states and the District of Columbia, or that appeared as duplicate listings.

NOTE: The sampling frame was the total number of all eligible health centers for that year.

SOURCE: U.S. Department of Health and Human Services, Health Resources and Services Administration Electronic Handbooks Database.

NATIONAL CENTER FOR HEALTH STATISTICS 4 Series 2, Number 203

criteria noted previously were applied and duplicate entries

were removed. However, an additional step for the 2022

sampling process was that the 149 HCs sampled for 2021 (50

in the main sample, 99 in the backup sample, and 1 that was

dropped from the 2021 database) were removed from the

sampling frame that was used for selecting the sample added

in 2022. For 2022, this process yielded a sampling frame of

1,269 eligible HCs. The 2022 NAMCS HC Component target

respondent sample was reduced from 60 to 54 because of

budget restraints. To accommodate the needed change, six

randomly selected HCs were removed from the sample in

four strata.

Sampling Strata

The sampling strata were defined by U.S. Census region

(Northeast, Midwest, South, and West) and metropolitan

statistical area (MSA) status (MSA and non-MSA). Within

each stratum, HCs were randomly numbered to ensure

randomness in the selected sample from each stratum. To

minimize the risk of disclosing the identity of HCs in each

stratum, this report provides summaries by range instead of

single percentages.

For the 2021 NAMCS HC Component sampling frame, the

distribution of HCs by geographical region ranged from

17.0% to 33.5%. By MSA status, 70.7% of HCs in the sampling

frame were in an MSA. When combined, the regional and

MSA distribution ranged from 3.2% to 21.8%.

The 2022 NAMCS HC Component sampling frame had a

similar range in distribution, with 16.1% to 34.2% of HCs

located in the different geographical regions. By MSA status,

72.8% of HCs in the sampling frame were in an MSA. When

combined, the regional and MSA distribution ranged from

2.4% to 22.6%.

Within each sampling stratum, HCs were sorted by the nine

U.S. Census divisions and ordered within each division by

random numbers previously assigned to the HCs. From the

randomly ordered HCs in each stratum, systematic random

sampling was used to select two nonoverlapping samples.

The size of the first, or primary sample, was the targeted

number of participating sample HCs desired from the survey,

while the size of the second, or backup sample, was twice

the size of the primary sample. If any of the HCs in the

primary sample from a stratum were ineligible or declined

to participate in the NAMCS HC Component, HCs in the

backup sample from the same stratum were contacted for

participation as needed until the targeted number of sample

stratum HCs agreed to submit their EHRs for patient visits.

For 2021, the primary and backup samples included 50 and

100 HCs, respectively. For 2022, 54 (reduced from 60 after

the sample was drawn) and 120 HCs were included in the

primary and backup samples, respectively.

This method of using a backup sample had not been

previously used with NAMCS; however, it was implemented

beginning in 2021 to increase the likelihood that NCHS would

be able to collect visit data from 50 HCs in 2021, and an

additional 54 HCs in 2022. The procedures used to draw the

2021 and 2022 NAMCS HC Component samples can be found

in the technical appendixes. Appendix I provides details on

the 2021 NAMCS HC Component sampling procedures.

Appendix II provides details on the 2022 procedures.

Distribution of Resulting HC

Sample to Strata

An ideal sample has an equitable distribution of HCs relative to

the sampling frame across geographical areas. Small sample

sizes for the 2021 and 2022 NAMCS resulted in differences

between the population and sample distributions of HCs by

U.S. region, MSA status, and the combination of region and

MSA status (the sampling strata themselves). However, the

goal of mirroring the distribution of the HC population by

region and MSA status was achieved for each of the samples.

Regarding U.S. region and MSA status, the range of the

difference in the distribution for the 2021 samples relative

to the sampling frame was 3.7 to 7.0 percentage points.

The 2021 samples had a higher percentage of HCs in

MSAs (5.3 percentage point difference) compared with

the sampling frame. The range of the distribution of HCs

in the 2022 sample relative to the sampling frame ranged

from 0.8 to 8.2 percentage points. The 2022 samples had

similar percentages of HCs in MSAs (0.5 percentage point

difference) to the sampling frame.

For the 2021 NAMCS HC Component sampling strata (defined

by U.S. region and MSA status), all differences ranged from

-5.9 to 4.3 percentage points. For the 2022 NAMCS, all

differences ranged from -9.2 to 4.3 percentage points.

Summary

Although NAMCS has been the leading data collection tool for

ambulatory health care across the United States for almost

50 years and has been collecting patient visit data from HCs

since 2006, changes in the way healthcare information for

patients is recorded have required a change in how NAMCS

data are collected and how HCs are selected for participation.

Beginning in 2021, NAMCS began gathering ambulatory

healthcare data directly from a nationally representative

sample of FQHCs and FQHC look-alikes. This modernization

necessitated a new sampling approach for the 2021 and

2022 NAMCS HC Component. This method is expected to be

used in future years, whenever the HC sample is updated or

replaced.

Stratified (organized information into groups based on

certain criteria) random samples of HCs were selected for the

2021 and 2022 NAMCS HC Component with strata defined

by U.S. Census region and MSA status to ensure nationally

representative estimates. Additionally, primary and backup

Series 2, Number 203 5 NATIONAL CENTER FOR HEALTH STATISTICS

samples were used to enhance the ability to obtain targeted

numbers of participants for both years. The 2021 sample was

expanded in 2022 with support from the OS-PCORTF FY2021.

This report of the NAMCS HC Component sampling methods

is expected to give researchers a better understanding of

the sampling design and (once collected) how to use and

interpret these NAMCS HC Component data. Consequently,

researchers will have a better understanding of ambulatory

health care provided at FQHCs and FQHC look-alikes and can

help inform patient care at these “safety net” providers (3)

across the United States.

References

1. U.S. Department of Health and Human Services,

Health Resources and Services Administration. What

is a health center? 2021. Available from: https://bphc.

hrsa.gov/about-health-centers/what-health-center.

2. Politzer RM, Yoon J, Shi L, Hughes RG, Regan J, Gaston

MH. Inequality in America: The contribution of health

centers in reducing and eliminating disparities in

access to care. Med Care Res Rev 58(2):234–48. 2001.

3. Wakefield M. Federally qualified health centers

and related primary care workforce issues. JAMA

325(12):1145–6. 2021.

4. National Center for Health Statistics. 2012 NAMCS

CHC micro-data file documentation. 2015. Available

from: https://ftp.cdc.gov/pub/Health_Statistics/NCHS/

Dataset_Documentation/NAMCS/doc2012_chc.pdf.

5. National Center for Health Statistics. 2014 NAMCS

CHC micro-data file documentation. 2019. Available

from: https://ftp.cdc.gov/pub/Health_Statistics/NCHS/

Dataset_Documentation/NAMCS/doc2014_chc-508.pdf.

6. Health Level Seven International (HL7). HL7 CDA R2

implementation guide: National Health Care Surveys

(NHCS), release 1, DSTU release 1.2—US realm. 2021.

Available from: https://www.hl7.org/implement/

standards/product_brief.cfm?product_id=385.

7. U.S. Department of Health and Human Services, Office

of the Assistant Secretary for Planning and Evaluation.

Enhancing surveillance of maternal health clinical

practices and outcomes with federally qualified health

centers’ (FQHCs) electronic health records visit data.

2021. Available from: https://aspe.hhs.gov/enhancing-

surveillance-maternal-health-clinical-practices-

outcomes-federally-qualified-health.

NATIONAL CENTER FOR HEALTH STATISTICS 6 Series 2, Number 203

Appendix I. Sampling Procedures

for the 2021 National Ambulatory

Medical Care Survey Health Center

Component

This appendix provides instructions for selecting a stratified

(organized information into groups based on certain

criteria) list sample of health centers (HCs) for the 2021

National Ambulatory Medical Care Survey Health Center

(NAMCS HC) Component with sampling strata defined by

four U.S. Census regions (Northeast, Midwest, South, and

West) and metropolitan statistical area (MSA) status (MSA

and non-MSA). For 2021, a primary sample of 50 HCs was

drawn, in addition to a backup sample of 100 HCs.

Common Notation Used for Sampling

Specications

Let

h stand for MSA status (MSA or non-MSA)

j stand for an HC

M,m stand for the total number of HCs in the sampling

frame and sample, respectively

I(B) stand for identity function

Int stand for the sampling interval used in selecting a

sample

r stand for U.S. Census region (Northeast, Midwest,

South, and West)

Sampling Procedures

Step 1. Prepare the 2021 NAMCS sampling frame

Using a national database, only eligible federally qualified

health centers (FQHCs) and FQHC look-alikes were included

in the sample. Any HCs that met the following conditions

were deemed ineligible and omitted from the sampling

frame:

● HCs that did not have an electronic health record (EHR)

system







if condition Bismet and

if condition Bisnot met



● HCs that did not provide healthcare services to the general

U.S. population, such as those that exclusively serve

institutional populations (for example, prisons, nursing

homes or long-term care facilities, homeless shelters, etc.)

● HCs where only dental services were provided

● HCs located on a military installation or outside of the 50

U.S. states and the District of Columbia

Additionally, duplicate entries in the U.S. Department of

Health and Human Services’ Health Resources and Services

Administration electronic handbooks—HCs with the same

name, address, and administrator contact information—

were also removed. Then, each HC sampling stratum was

defined by U.S. Census region r and MSA status h.

Step 2. Array (arrange) HCs within sampling

strata

To array HCs within the sampling strata:

a. Assign each HC a random number. This randomization

may be done in the whole sampling frame or within each

sampling stratum.

b. Within each sampling stratum r,h (defined by U.S.

Census region r and MSA status h), sort the HCs by U.S.

Census division.

c. Within U.S. Census division, order HCs by the random

numbers assigned in step 2a.

d. Serially number the randomly ordered HCs in each

sampling stratum r,h.

Step 3. Select the 2021 NAMCS sample of HCs

from each sampling stratum

The following instructions apply for the sample in each

sampling stratum r,h:

a. Calculate the sampling interval for selecting the primary

sample for the r,h stratum (carrying two decimal places):

ifcondtB

sm sm sm

() /

,, ,

= [3.1]

Series 2, Number 203 7 NATIONAL CENTER FOR HEALTH STATISTICS

where

r,h

= Total number of HCs listed in the sampling frame for

sampling stratum r,h [3.2]

r,h

= Total number of HCs to be selected to the primary

sample from sampling stratum r,h

b. Select a random start R

r,h

between 0 and Int(HC)

r,h

inclusive where Int(HC)

r,h

is defined in equation [3.1].

c. Select to the primary sample from stratum r,h the first

HC for which the serial number assigned in step 2d is the

nearest integer greater than or equal to

The total number of HCs selected from the sampling stratum

r,h should be within 1 of the sample number targeted for

that stratum according to equation [3.3]. That is, if

con

′

the number of HCs initially selected to the sample for

stratum r, then

con

′

should be in the range

co1

0±

d. Select a backup sample of HCs to use if any primary

sample HC should be ineligible or a nonrespondent. The size

of the backup sample from each stratum should be twice the

size mA of the primary sample from that stratum to minimize

the possibility that the backup sample will be depleted, or

completely used, before a total of mA

r,h

inscope

(HCs with

all required criteria) and respondent HCs are inducted from

stratum r,h.

First, remove the primary sample HCs from the frame in

each sampling stratum to form the “remaining” sampling

frame for the backup sample.

Let

iifc

on on

00 0



stand for the number of HCs remaining

in the frame for the r,h stratum after selection of the primary

sample.

stands for the sampling interval for selecting the backup

sample from the remaining frame for each r,h stratum,

where mA

r,h

is defined in equation [3.3] above.

Repeat steps b and c with the reduced sampling frame and

revised sampling interval

ifcon

e. For each contacted sample HC that is confirmed

ineligible or nonrespondent (from either the primary or the

backup sample), add to the sample an HC from the backup

sample, adding those HCs to the sample in order of the serial

numbers assigned to the HCs in step 2d.

f. After m

r,h

respondent HCs have been confirmed as a

participant and inducted from sampling stratum r,h, insert



2 ( )

1 = 1, 2, or 4

if cifond tBs

if c moe a [3.3]

1 = 3 11 if c moe a











( ) , 0, 1, 2, 3, ...

rh rh

R Int HC k k+=



,, ,

2( ) 2 / 2 [3.4]

rh rh rh

Int HC M mA







● HCs that did not provide healthcare services to the general

U.S. population, such as those that exclusively serve

institutional populations (for example, prisons, nursing

homes or long-term care facilities, homeless shelters, etc.)

● HCs where only dental services were provided

● HCs located on a military installation or outside of the 50

U.S. states and the District of Columbia

Additionally, duplicate entries in the U.S. Department of

Health and Human Services’ Health Resources and Services

Administration electronic handbooks—HCs with the same

name, address, and administrator contact information—

were also removed. Then, each HC sampling stratum was

defined by U.S. Census region r and MSA status h.

Step 2. Array (arrange) HCs within sampling

strata

To array HCs within the sampling strata:

a. Assign each HC a random number. This randomization

may be done in the whole sampling frame or within each

sampling stratum.

b. Within each sampling stratum r,h (defined by U.S.

Census region r and MSA status h), sort the HCs by U.S.

Census division.

c. Within U.S. Census division, order HCs by the random

numbers assigned in step 2a.

d. Serially number the randomly ordered HCs in each

sampling stratum r,h.

Step 3. Select the 2021 NAMCS sample of HCs

from each sampling stratum

The following instructions apply for the sample in each

sampling stratum r,h:

a. Calculate the sampling interval for selecting the primary

sample for the r,h stratum (carrying two decimal places):

ifcondtB

sm sm sm

() /

,, ,

= [3.1]

into the record for each contacted sample HCj (including all

participants, nonrespondents, and ineligible HCs) that HC’s

sampling weight ω

j,2021

where

r,h

= Total number (before any sampling) of HCs listed in

the 2021 sampling frame for stratum r,h

r,h

= Total number of sample HCs that were contacted for

participation in the 2021 HC survey, regardless of scope or

response status determined for those HCs. This number

includes all respondents, nonrespondents, and ineligible

HCs among those contacted.

Note that according to the instructions above, the sample

selected from each sampling stratum r,h is an equal

probability sample. The sampling weight ω

j,2021

is the inverse

of the product of the probabilities of HC j being selected at

some time k, given that HCj was not selected to the sample

at times k–1 or earlier.

,2021

2021 ,

[3.5]

j is in sample in

region r and MSA status h









NATIONAL CENTER FOR HEALTH STATISTICS 8 Series 2, Number 203

Appendix II. Sampling Procedures

for the 2022 National Ambulatory

Medical Care Survey Health Center

Component

This appendix provides technical details for selecting a

stratified (organized information into groups based on

certain criteria) list sample of health centers (HCs) for the

2022 National Ambulatory Medical Care Survey Health

Center (NAMCS HC) Component with sampling strata

defined by four U.S. Census regions (Northeast, Midwest,

South, and West) and metropolitan statistical area (MSA)

status (MSA or non-MSA). For 2022, before it was reduced

to 54, a primary sample of 60 HCs was drawn, in addition

to a backup sample of 120 HCs. The HCs in the 2021 final

total sample are also included in the 2022 final total sample,

along with the 50 participants and all other HCs that were

contacted for participation but were either ineligible or

refusals (see Appendix I).

Common Notation Used for Sampling

Specications

Let

h stand for MSA status (MSA or non-MSA)

j stand for an HC

M,m stand for the total number of HCs in the sampling

frame and sample, respectively

I(B) stand for identity function

Int stand for the sampling interval used in selecting a

sample

r stand for U.S. Census region (Northeast, Midwest,

South, and West)







if condition Bismet and

if condition Bisnot met



Sampling Procedures

Step 1. Prepare the 2022 NAMCS sampling frame

Following the instructions given in Appendix I, step 1,

compile the 2022 sampling frame from lists of HCs obtained

from the Department of Health and Human Services’ Health

Resources Services Administration in 2021.

Step 2. Array (arrange) HC within sampling strata

Define the HC sampling strata by region r, and MSA status h.

Also assign numbers to the HCs and array them within strata

as instructed in Appendix I, step 2.

Step 3. Assign frame weights to HCs in the 2022

frame

Let

r,h,2022(HC)

= Total number of HCs listed in the 2022 sampling

frame for sampling stratum defined by region r, and MSA

status h, after completing step 1. These are HCs eligible for

the total 2022 HC sampling frame (including those selected

in the 2021 primary sample and in the 2021 backup sample).

r,h(2021HCsamp)

= Number of all HCs in the 2022 sampling

frame for region r and MSA status h that are also in the

2021 primary sample or the 2021 backup sample, regardless

of whether they were ever contacted to participate in the

survey. This number includes HCs in the 2021 primary and

backup samples that:

•

Participate in the survey

•

Were contacted but refused to participate in 2021

•

Were contacted but confirmed ineligible for the survey

•

Were never contacted and asked to participate

a. Obtain counts, M

r,h,2022(HC)

and m

r,h(2021HCsamp)

for each

sampling stratum defined by region r and MSA status h.

b. After obtaining the two counts in the previous step, delete

all m

r,h(2021HCsamp)

HCs from the 2022 sampling frame. The frame

remainder is referred to in the following as the sampling list

from which HCs will be selected for adding to the 2022 sample.

Series 2, Number 203 9 NATIONAL CENTER FOR HEALTH STATISTICS

c. In the record for each HC remaining in the frame, insert

the frame weight for the HC. That weight for HCs in region r

and MSA h is:

Step 4. Select the HCs to be added to the 2022

HC sample

The following instructions apply for the sample in each

sampling stratum r,h.

a. Calculate the sampling interval for selecting the initial

or primary sample for the stratum r,h (carrying two

decimal places):

where

r,h,2022(HC)

= Total number of HCs listed in the 2022

sampling lists for sampling stratum defined by region r

and MSA status h

r,h,2022

= Total number of HCs to be selected from

sampling stratum r,h from the 2022 sampling list

b. Select a random start R

r,h,2022

between 0 and Int(HC)

r,h,2022

inclusive where Int(HC)

r,h,2022

is defined in equation [4.2].

c. In the order arrayed in step 2, accumulate the frame

weights of HCs remaining in the 2022 HC list and assign

to each HC the cumulative sum that results after adding

the weight for that HC to the sum.

Then select to the sample the first HC whose cumulative

sum of frame weights is greater than or equal to

where R

r,h,2022

is defined in step b above. That is, if

′

110 00

is the number of HCs initially added to the

2022 sample for stratum r,h then

′

110 00

should be

in the range

co,,

2022

1±

d. For the 2022 added sample, select a backup sample of

HCs to use if any added primary sample HC should be

ineligible or a nonrespondent.

First remove the primary sample HCs selected from the

2022 sampling list in each sampling stratum to form the

“remaining” sampling list for the 2022 backup sample.

Let

if c

nd nd tB

nd tB

nd tBsmoe

,, ,, ()

,, ()

,( )

2022 2022

2022

2021



















[4.1]

ifcond tB

sm esmonsm

() /

,, ,, () ,,2022 2022 2022

= [4.2]





4 2 ( )

1 1, 2, or 4

if cifond tBs

if c moe a

if c

17 











1 3

[4.3]

moe a

, ,2022 , ,2022

( ) , 0, 1, 2, 3, ...

rh rh

R Int HC k k+=

( )

, ,2022 , ,2022

, ,2022

2 / 2

rh rh

Int HC B mA







Denote the sampling interval for selecting the backup

sample from the remaining sampling list for each r,h

stratum

where

r,h,2022

= Total of frame weights summed across all HCs

remaining in the stratum defined by region r and MSA

status h, after removing the primary sample selected

from the 2022 sampling list.

r,h,2022

is defined in equation [4.3] above.

Repeat steps b and c with the reduced sampling list and

revised sampling interval Int2(HC)

r,h,2022

e. For each contacted sample HC from stratum r,h that is

confirmed ineligible or nonrespondent, add one HC from

the backup sample from the same r,h stratum to the

sample. Add those HCs in the order of serial numbers

assigned to the HCs in the 2022 sampling list in step 2.

f. After m

r,h,2022

HCs have been confirmed participants

from sampling stratum r,h, insert into the record for

each contacted sample HCj (including all participants,

nonrespondents, and ineligible HCs) that HC’s sampling

weight ω

j,2022

where

= Int(HC)

r,h

• I(j is in sample added for 2022 in region

r and MSA status h)

[4.5]

For the backup sample HCs that are contacted, their

sampling weights would be the same as in equation

[4.5], with Int(HC)

r,h

the same as for selecting the primary

sample, given that the contacted backup sample HC

shares the same weight as the primary sample HC.

,2022 ,

()

2022, , [4.4]

j rh

j is in sample added

Int HC

FW I for in region r

and MSA status h













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