Number 72 n January 6, 2014

Concordance Between Survey Report of Medicaid

Enrollment and Linked Medicaid Administrative

Records in Two National Studies

by Lisa B. Mirel, M.S., Agency for Healthcare Research and Quality; Alan E. Simon, M.D., Cordell Golden, B.A.,

Catherine R. Duran, B.S., and Kenneth C. Schoendorf, M.D., M.P.H., National Center for Health Statistics

Abstract

The National Health and Nutrition Examination Survey (NHANES) and the

National Health Interview Survey (NHIS) are population-based surveys that have

each been linked to administrative data from the Centers for Medicare &

Medicaid Services (CMS): the Medicaid Analytic eXtract (MAX) files. These

linked data were used to examine, among children under age 18 years,

respondent-level concordance between Medicaid or the Children’s Health

Insurance Program (CHIP) enrollment as reported in each survey (NHANES and

NHIS) and as indicated by administrative data from the MAX files. Concordance

was defined as having Medicaid/CHIP reported as a health insurance source in

the survey questionnaire and having a CMS Medicaid/CHIP administrative record

in the same month and year as the interview. Records were also considered

concordant if there was no report of Medicaid/CHIP coverage based on the

interview response and no match to the CMS administrative records for Medicaid

enrollment. Between NHANES and MAX, 88% of observations were concordant

with respect to Medicaid or CHIP enrollment, yielding a Kappa of 0.71. Between

NHIS and MAX, 89% of observations were concordant with respect to Medicaid

or CHIP enrollment, yielding a Kappa of 0.73. These concordance rates provide

support for the use of both administrative and NHANES and NHIS as a valuable

tool for public health researchers and survey methodologists.

Keywords: National Health and Nutrition Examination Survey • National Health

Interview Survey • linkage

Introduction Medicaid Analytic eXtract (MAX) files

were linked to several surveys The Centers for Disease Control conducted by NCHS, including the

and Prevention’s National Center for National Health and Nutrition

Health Statistics (NCHS) has developed Examination Survey (NHANES) and the

a record linkage program designed to National Health Interview Survey

maximize the scientific value of the (NHIS).

Center’s population-based surveys. NHANES is a nationally

Recently, the 1999–2008 Centers for representative, cross-sectional survey

Medicare & Medicaid Services (CMS) that collects information on the health

and nutritional status of adults and

children in the United States. NHIS is a

nationally representative, cross-sectional,

population health survey of children and

adults in the United States. Both surveys

also collect information on current

health insurance coverage of

respondents. The linked data offer the

opportunity to explore the accuracy of

program participation reporting in a

self-reported survey.

Previous studies have assessed

validity of health insurance and

utilization survey data compared with

administrative records. Recent

research (1) compared household

reported Medicare use in the Medical

Expenditure Panel Survey with

Medicare enrollment and claims data.

The authors found strong agreement for

reporting of inpatient stays and number

of nights in a hospital stay; however, the

authors observed an undercount of

approximately one-third for visits to

emergency departments and a 19%

undercount for office-based visits.

Similarly, a multiphase research project

referred to as the Medicaid Undercount

project was undertaken to explain why

discrepancies exist between survey

estimates of enrollment in Medicaid and

the number of enrollees reported in state

and national administrative data (2). The

project is called the SNACC project

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics
(SNACC is an acronym for the agencies

conducting the project: the University of

Minnesota’s State Health Access Data

Assistance Center, NCHS, the Agency

for Healthcare Research and Quality, the

U.S. Department of Health and Human

Services Assistant Secretary for

Planning and Evaluation, CMS, and the

U.S. Census Bureau). The main

conclusion from the project is that the

undercount is due to multiple factors,

including survey measurement error and

the reference periods being examined

through each method.

This analysis focuses on the

reporting of Medicaid in both NHIS and

NHANES compared with the MAX

files. While the SNACC project used

NHIS 2001 and 2002, this project is

unique because it is the first time a

comparison to the MAX files has been

done with NHIS data since the Medicaid

question was redesigned in 2004 and the

first time this has ever been done using

NHANES data. This report will assess

concordance between a participant’s

report in the survey of Medicaid or

Children’s Health Insurance Program

(CHIP) enrollment at the time of their

household interview in NHANES or

NHIS compared with the presence of a

Medicaid or CHIP enrollment record in

the MAX files for children under age 18

years. Children under age 18 were

chosen for this study because Medicaid

and CHIP provide a major source of

insurance for children (3). In addition,

Medicaid and CHIP eligibility criteria

change greatly at age 19. The

prevalence and characteristics of the

concordant and discordant pairs will be

compared. These results will be

discussed in the context of challenges

encountered in linkage and accurately

collecting self-report of Medicaid/CHIP

enrollment in the surveys.

Methods

Background on NHANES

NHANES is a continuous survey

(1999–present) that includes an

interview in the household followed by

an examination in a mobile examination

center (MEC). NHANES is a nationally

representative, cross-sectional sample of

the U.S. civilian noninstitutionalized

population that is selected using a

complex, multistage probability design.

Detailed descriptions of the NHANES

sample design have been described

elsewhere (4). Participants can be any

age.

The NHANES household interview

contains a section that includes sampled

participant (SP) level interview data on

health insurance coverage. One

reference person in each family

responds for each individual SP in the

family. The reference person or

responsible adult may or may not be an

SP. This section of the family interview

is asked for each individual SP.

The 1999–2004 NHANES data

were the most recent NHANES data

available that had been linked to the

MAX files and are, therefore, used in

this analysis. The sample size for the

1999–2004 NHANES was 31,126. The

interview response rate was 82% (5).

The 1999–2004 NHANES oversampled

black, Mexican-American, low-income

white persons, adolescents aged 12–19,

and persons aged 60 and over.

Background on NHIS

NHIS is a nationally representative,

cross-sectional household interview

survey that serves as an important

source of information on the health of

the civilian population of the

United States. It is a multistage sample

survey with primary sampling units of

counties or adjacent counties, secondary

sampling units of clusters of houses,

tertiary sampling units of households,

and finally, persons within households.

It has been conducted continuously

since 1957. Detailed descriptions of the

NHIS design have been described

elsewhere (6,7).

The 2005 NHIS data were the most

recent data available linked to the MAX

files, and are, therefore, used in this

analysis. The 2005 NHIS design has

Core questions and Supplemental

questions. The Core NHIS consists of

three major components: Family, Sample

Adult, and Sample Child. The Family

component collects limited demographic

information on all of the individuals

living in the household. The Family

component verifies and collects

additional information on all members

of each family in the house and collects

data on topics such as health status and

limitations, injuries, health care access

and utilization, health insurance, and

income and assets.

NHIS data are collected through a

personal household interview conducted

by interviewers employed by the U.S.

Census Bureau. In 2005, the sample

consisted of 38,509 households, which

yielded interviews with 98,649 persons

in 39,284 families. The 2005 NHIS

oversampled black and Hispanic

persons. The total household response

rate for 2005 was approximately 86.5%

(6).

Background on Medicaid/

CHIP

Detailed information on Medicaid

and CHIP can be found on the CMS

website (8). Medicaid is a needs-based

entitlement program administered by

CMS in collaboration with each state to

provide health care coverage to some

vulnerable populations in the

United States, including low-income

children, and the aged or disabled poor.

The MAX files are research-oriented

Medicaid claims files. Eligibility for

Medicaid varies by state. Federal law

during 1999–2005, when the surveys

assessed here were conducted, required

mandatory eligibility for pregnant

women with a family income below

133% of the U.S. Department of Health

and Human Services (HHS) poverty

guidelines, children under age 6 years

with family income below 133% of the

HHS poverty guidelines, and children

aged 6–18 years with family income

below 100% of the HHS poverty

guidelines. Additionally, as described

below, states may set eligibility

requirements that are less stringent,

allowing eligibility for those in families

of higher incomes.

CHIP is a state-based program

offered to children and pregnant women

whose incomes are too high to qualify

for Medicaid eligibility. CHIP funds are

capped with each state receiving a set

allotment. The federal government

matches state funding for CHIP. States

Page 2 National Health Statistics Reports n Number 72 n January 6, 2014
receive higher federal funding matching

rates for CHIP than Medicaid. Of

particular note for this project, the MAX

files are incomplete on CHIP because

states have the option of not reporting

standalone CHIP program data to the

Medicaid Statistical Information System

from which the MAX files are created.

Data linkage background

NHANES and NHIS participants

were eligible for linkage if they did not

refuse to provide their social security

number (SSN) or their health insurance

claim number (HIC) at the time of the

interview and if they provided sufficient

personally identifiable information for

linkage. SSNs for these participants

were verified at the U.S. Social Security

Administration and then sent to CMS

where data were extracted based on

exact matches for SSN, sex, and month

and year of birth. Eligibility for linkage

for an SP to obtain a CMS

administrative record was independent

of the questionnaire responses to the

health insurance question and

independent of a participant’s Medicaid

eligibility. Details of the linkage

methodologies and the linked data files

have been published previously (9).

Variables of interest

Health insurance was assessed in

NHANES as follows. An initial set of

questions in the health insurance section

of the NHANES interview determined

which SPs had health insurance

coverage. For those who had health

insurance coverage, respondents were

then asked, ‘‘What kind of health

insurance [do you/does SP] have?’’ The

respondent was shown a hand card and

asked to choose one from a list that

included both Medicaid and CHIP. The

state plan name for Medicaid was

indicated on the hand card. For the

1999–2004 NHANES, Medicaid and

CHIP were reported together. This was

changed after 2004.

Health insurance coverage, and

whether that coverage was Medicaid or

not, was assessed in the 2005 NHIS,

using multiple questions. Respondents

were asked, ‘‘What kind of health

insurance or health care coverage [does

the child] have?’’ Extensive response

choices were provided that included

both Medicaid and CHIP as separate

response categories. Also, another

question was asked that probed further

about the possibility of Medicaid

coverage. This question stated: ‘‘There

is a program called Medicaid that pays

for health care for persons in need. In

this State it is also called [fill in State

name]. Are you covered by Medicaid?’’

Based on affirmative responses to either

of these questions, Medicaid and CHIP

coverage were determined in the survey.

The main research goal was to

assess the accuracy of the survey

response to the questions on Medicaid/

CHIP by comparing the response with

the matched CMS records. Concordance

was defined as having Medicaid/CHIP

reported as a health insurance source in

the survey questionnaire and having a

CMS Medicaid/CHIP administrative

record in the same month and year as

the interview. The presence of a CMS

administrative record in the same month

and year of the interview indicated

active Medicaid enrollment status.

Records were also considered

concordant if there was no report of

Medicaid/CHIP coverage based on the

interview response and no match to the

CMS administrative records for

Medicaid/CHIP enrollment. Discordance

was defined as a report of Medicaid/

CHIP in the interview without CMS

evidence of enrollment, or, conversely,

no report of Medicaid/CHIP in the

interview while actually being enrolled,

according to the MAX files.

Analytic plan

The first step of the analysis was to

examine the overall analytic sample

breakdown and assess the overall

matched results, using weighted

percentages. All analyses included

sample weights from the survey that

accounted for the unequal probabilities

of selection and nonresponse. The

statistical weights were further adjusted

for linkage ‘‘nonresponse;’’ that is,

adjustment for respondents who were

not eligible to be linked (10). Then, the

percentage of concordance and

discordance between the response to the

Medicaid/CHIP question in the survey

and Medicaid or CHIP enrollment in the

same month and year that the survey

was conducted, according to the MAX

files, was explored. The denominator for

these analyses included all linkage

eligible SPs. Kappa statistics, adjusting

for survey weights, were used to assess

the overall concordance and

discordance.

Sociodemographic characteristics

were also examined, including the ratio

of family income to the poverty level,

sex, age, and race or ethnicity, for the

concordant and discordant pairs. The

concordant groups were ‘‘Yes/Yes’’

(those who linked to the CMS MAX file

and reported Medicaid/CHIP in the

survey), and ‘‘No/No’’ (those who did

not link to the CMS MAX file and did

not report Medicaid/CHIP in the

survey). The discordant groups were

‘‘No/Yes’’ (those who did not link to the

CMS MAX file but had reported

Medicaid/CHIP in the survey), and

‘‘Yes/No’’ (those who linked to the

CMS MAX file but did not report

Medicaid/CHIP in the survey).

Comparisons between each concordant

group and both discordant groups were

made. A t test was used to compare

means and proportions for the

demographic characteristics between

concordant and discordant groups, using

a two-sided p value < 0.05. Variances

were estimated using Taylor series

linearization, accounting for the complex

design. All statistical analyses were

performed using SAS (version 9.3 SAS

Institute Inc., Cary, N.C.) and SAScallable SUDAAN (version 10.0, RTI

International, Research Triangle Park,

N.C.) software. All estimates were

assessed for statistical reliability based

on the relative standard error and

degrees of freedom. Results are

presented for both NHANES and NHIS.

Results

NHANES

From the 1999–2004 NHANES,

11,586 participants under age 18 years

had responses to the questions about

type of health insurance and about

National Health Statistics Reports n Number 72 n January 6, 2014 Page 3
Page 4 National Health Statistics Reports n Number 72 n January 6, 2014

Medicaid/CHIP (less than 2% were

missing a response, n = 237). About

84% of these participants were eligible

for linkage. Of the 9,750 participants

who were eligible for linkage, 4,062

participants matched to the Medicaid

file within the same month and year of

the NHANES interview (Figure 1).

There are several different ways to

assess the matched results. First, the

overall concordant and discordant

weighted percentages for all NHANES

linkage-eligible participants (n = 9,750)

were assessed. The overall concordance,

using weighted percentages, was 88%.

Twenty-three percent said ‘‘Yes’’ in

NHANES and linked in the same month

and year of the NHANES interview to

the CMS MAX file. Sixty-five percent

said ‘‘No’’ in NHANES and did not link

to the CMS MAX file in the same

month and year of the NHANES

interview (Table 1). The Kappa statistic

was 0.71.

Of the respondents who responded

‘‘Yes’’ to the question in NHANES

about Medicaid/CHIP health insurance

coverage, using weighted percentages,

15% were not found in the CMS MAX

file (85% agreement among those who

responded ‘‘Yes’’ in the NHANES

interview). Of the respondents who

responded ‘‘No’’ to the question in

NHANES, using weighted percentages,

11% linked in the same month and year

of the NHANES interview (making the

agreement level of those who said ‘‘No’’

in NHANES 89%).

In NHANES, both discordant

groups had higher mean income-topoverty ratio than the ‘‘Yes/Yes’’ group

(Table 2). There were no statistically

significant differences between the

‘‘Yes/Yes’’ group and either of the

discordant groups with regard to the

percentage of children in the group who

were male and the percentage of

children who were under age 6 years.

The distributions of race and ethnicity in

the ‘‘Yes/Yes’’ group were similar to

those in both discordant groups, with

the exception of the percentage of

Mexican-American children. The

percentage of Mexican-American

children was lower in the ‘‘Yes/Yes’’

group than in the group of children who

did not link to the MAX file but

reported Medicaid/CHIP insurance in

NHANES.

Both discordant groups had a lower

mean income-to-poverty ratio than the

‘‘No/No’’ group. The percentage of

children under age 6 years was higher in

1

Indicates that participants did not refuse to provide a social security number (SSN) or health insurance claim (HIC) number at the 

NHANES interview; participants provided sufficient personally identifiable information for linkage and their SSN was verified at the

Social Security Administration.

NOTES: All percentages in figure are unweighted. NHANES is National Health and Nutrition Examination Survey; CMS is Centers for 

Medicare & Medicaid Services; MAX is Medicaid Analytic eXtract; CHIP is Children’s Health Insurance Program.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey/Centers for Medicare & Medicaid Services MAX linked data 

files, 1999–2004. 

NHANES sampled participants under age

18 years with a response to the type of health 

insurance question in NHANES: n = 11,586

Did not link to a CMS MAX file at 

any time or did not link in the same 

month and year of the NHANES 

interview: n = 5,688

Linked in same month and year 

of NHANES interview: n = 4,062 

(42% of linkage-eligible)

Did not report Medicaid/CHIP 

health insurance coverage in 

NHANES: n = 5,111

Reported Medicaid/CHIP 

health insurance coverage 

in NHANES: n = 3,003

Ineligible for linkage: 

n = 1,836 (16%)

Linkage-eligible1

: 

n = 9,750 (84%) 

Figure 1. Analytic sample for 1999–2004 NHANES sampled participants under age 18 years linked to CMS MAX file
National Health Statistics Reports n Number 72 n January 6, 2014 Page 5

both discordant groups than in the

‘‘No/No’’ group. The percentage of male

children was lower in the ‘‘No/No’’

group than in the discordant group of

those who linked to the MAX file but

reported that they did not have

Medicaid/CHIP in NHANES. However,

the percentage of male children in the

‘‘No/No’’ group was similar to the

percentage of male children in the

discordant group of those who did not

link to the MAX file but did report

Medicaid/CHIP in NHANES. The

percentage of non-Hispanic white

children in the ‘‘No/No’’ group was

higher than the non-Hispanic white

children in both discordant groups, and

the percentage of non-Hispanic black

children in the ‘‘No/No’’ group was

lower than the percentage of nonHispanic black children in both

discordant groups. The percentage of

Mexican-American children in the

‘‘No/No’’ group was lower than the

percentage in the discordant group who

did not link to the MAX files but

reported Medicaid/CHIP in NHANES.

The percentage of Mexican-American

children in the ‘‘No/No’’ group was

similar to the percentage in the

discordant group of those who did link

to the MAX files but reported that they

did not have Medicaid/CHIP in

NHANES.

NHIS

From the 2005 NHIS, 26,646

participants under age 18 years had a

response to the type of health insurance

question in NHIS (less than 1% were

missing a response, n = 168). About

49% of these participants were eligible

for linkage. Of the 13,034 eligible for

linkage, 4,197 participants matched to

the Medicaid file within the same month

and year of the NHIS interview

(Figure 2).

The overall concordant weighted

percentage for all NHIS linkage-eligible

participants (n = 13,034) was 89%.

Twenty-three percent said ‘‘Yes’’ in

NHIS and linked within the same month

and year of the NHIS interview to the

CMS MAX file, and 66% said ‘‘No’’ in

NHIS and did not link to the CMS

MAX file in the same month and year

of the NHIS interview or at any time

(Table 3). The Kappa statistic was 0.73.

As in NHANES, both discordant

groups in NHIS had higher mean

1

Indicates that participants did not refuse to provide a social security number (SSN) or health insurance claim (HIC) number at the NHIS 

interview; participants provided sufficient personally identifiable information for linkage and their SSN was verified at the Social Security 

Administration.

NOTES: All percentages in figure are unweighted. NHIS is National Health Interview Survey; CMS is Centers for Medicare & Medicaid 

Services; MAX is Medicaid Analytic eXtract; CHIP is Children’s Health Insurance Program.

SOURCE: CDC/NCHS, National Health Interview Survey/Centers for Medicare & Medicaid Services MAX linked data files, 2005.

NHIS sampled participants under age 

18 years with a response to the type of health 

insurance question in NHIS: n = 26,646

Did not link to a CMS MAX file at 

any time or did not link in the same 

month and year of the NHIS 

interview: n = 8,837

Linked within same month and 

year of NHIS interview: n = 4,197 

(32% of linkage-eligible)

Did not report Medicaid/CHIP 

health insurance coverage in 

NHIS: n = 8,102

Reported Medicaid/CHIP 

health insurance coverage 

in NHIS: n = 3,360

Ineligible for linkage: 

n = 13,612 (51%)

Linkage-eligible1

: 

n = 13,034 (49%) 

Figure 2. Analytic sample for 2005 NHIS sampled participants under age 18 years linked to CMS MAX file
income-to-poverty ratios than the

‘‘Yes/Yes’’ group (Table 4). No

statistically significant differences were

found in NHIS between the ‘‘Yes/Yes’’

group and either of the discordant

groups with regard to the percentage of

male children in the group. The

percentage of children under age 6 years

was higher in the ‘‘Yes/Yes’’ group than

in both discordant groups. The

percentage of non-Hispanic white

children and the percentage of nonHispanic other children in the ‘‘Yes/

Yes’’ group were similar to both

discordant groups. However, the

percentage of Hispanic children in the

‘‘Yes/Yes’’ group was lower than that in

the discordant group of those who did

not link to the MAX file but reported

Medicaid/CHIP in NHIS. The

percentage of Hispanic children in the

‘‘Yes/Yes’’ group was higher than in the

discordant group of those who linked to

the MAX file but did not report

Medicaid/CHIP in NHIS. Also, the

percentage of non-Hispanic black

children who were in the ‘‘Yes/Yes’’

group was higher than the percentage in

the discordant group who did not link to

the MAX file but reported Medicaid/

CHIP in NHIS. The percentage of

non-Hispanic black children in the

‘‘Yes/Yes’’ group was similar to the

percentage in the discordant group who

did link to the MAX file but did not

report Medicaid/CHIP in NHIS.

Both discordant groups in NHIS

had a lower mean income-to-poverty

ratio than the ‘‘No/No’’ group. There

were no statistically significant

differences in NHIS between the

‘‘No/No’’ group and either of the

discordant groups with regard to the

percentage of male children in the

group. The percentage of children under

age 6 years in the ‘‘No/No’’ group was

lower than the percentage in the

discordant group who linked to the

MAX files but did not report Medicaid/

CHIP in NHIS. However, the percentage

of children under age 6 years in the

‘‘No/No’’ group was similar to the

percentage in the discordant group who

did not link to the MAX files but did

report Medicaid/CHIP in NHIS. The

percentage of non-Hispanic white

children in the ‘‘No/No’’ group was

greater than the percentage in either

discordant group, while the percentages

of both non-Hispanic black and

Hispanic children in the ‘‘No/No’’ group

were lower than the percentages in both

discordant groups. The percentage of

non-Hispanic other children did not

differ between the ‘‘No/No’’ group and

either discordant group.

Conclusions

Agreement between reporting of

children’s Medicaid/CHIP enrollment in

these two national health surveys

compared with actual CMS enrollment

data is ‘‘substantial’’ based on the

commonly used Kappa statistic

criteria (11). Correspondingly, there does

not appear to be substantial

misclassification among either the

program participants or the

nonparticipants; however, some

discordance exists.

It is possible that some of the

discordant pairs who responded ‘‘Yes’’

to being enrolled in Medicaid/CHIP in

NHANES and NHIS but did not link to

the CMS MAX file may be participants

with CHIP coverage; the MAX files are

incomplete on CHIP data (9). This may

result in a reduction in concordance.

The mean income-to-poverty ratio of 1.2

for respondents with this discordance in

NHANES and of 1.6 for respondents

with this discordance in NHIS suggests

that on average these respondents may

be eligible in most states for CHIP, as

income eligibility is slightly higher for

CHIP than Medicaid. Indeed, only four

states limit eligibility for children in

families at less than 200% of the federal

poverty level (Alaska, Idaho, North

Dakota, and Oklahoma). Further, in both

NHANES and NHIS, the discordant

group that responded ‘‘Yes’’ to being

enrolled in Medicaid/CHIP in the

surveys but did not link to the MAX

files (the ‘‘No/Yes’’ group) were more

similar based on the income-to-poverty

ratio and race and ethnicity distributions

to the ‘‘Yes/Yes’’ group than the

‘‘No/No’’ group.

The other form of discordance was

among respondents who did not report

enrollment in Medicaid/CHIP in the

survey, but were found to be enrolled,

according to the MAX files (the

‘‘Yes/No’’ group). Of those who

reported ‘‘No’’ in NHANES and linked

to the MAX files, 49% (weighted)

reported being covered by some other

private insurance in the NHANES

questionnaire and 52% (weighted)

reported they were covered by some

other government insurance in the

NHANES questionnaire. Similarly in

NHIS, of those who reported ‘‘No’’ in

NHIS and linked to the MAX files, 44%

(weighted) reported being covered by

some other private insurance in the

NHIS questionnaire and 33% (weighted)

reported they were covered by some

other government insurance in the NHIS

questionnaire. While the specific cause

of this discordance is unknown, the

demographic characteristics of this

discordant group (‘‘Yes/No’’) in

NHANES and NHIS is more similar to

those who reported receiving Medicaid/

CHIP health insurance coverage and

were linked (the ‘‘Yes/Yes’’ group) than

those who did not report receiving

Medicaid/CHIP and did not link (the

‘‘No/No’’ group) (Tables 2 and 4).

With respect to income, sex, and

being non-Hispanic white, both

NHANES and NHIS show similar

results based on concordant and

discordant pairs. The low linkage

eligibility rate for NHIS could bias the

results; however, the similarities in

results between the two surveys suggests

otherwise. Lastly, findings from both

surveys are similar to those results

reported for the Medicaid Undercount,

SNACC project (2). One possible

limitation in this analysis is the

restriction of the linkage to be within

the same month as the survey interview.

SPs with a change in coverage may be

reporting their past coverage, especially

if the interview occurred at the

beginning of the month.

Page 6 National Health Statistics Reports n Number 72 n January 6, 2014
In conclusion, 85% of those who

reported having Medicaid/CHIP health

insurance coverage in NHANES and

83% of those who reported having

Medicaid/CHIP health insurance

coverage in NHIS linked to the MAX

files within the same month and year of

the survey interview. There was some

misreporting in both surveys; however,

some differences between the survey

response and the administrative record

may be due to the lack of reporting of

CHIP data in the CMS MAX files. Still,

these concordance rates provide support

for the use of both administrative and

NHANES and NHIS data in research to

evaluate data quality and Medicaid

utilization. The linkages of NHANES

and NHIS to the Medicaid data offer

valuable tools for public health

researchers and survey methodologists.

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discrepancies between the National

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Population Survey (CPS) Annual

Social and Economic Supplement

(ASEC). 2008. Available from:

http://www.census.gov/did/www/

snacc/docs/SNACC_Phase_II_Full_

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2013].

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December 28, 2012].

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ftp.cdc.gov/pub/Health_Statistics/

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National Health Statistics Reportsn Number 72n January 6, 2014 Page 7
Table 1. Weighted percentages and standard errors for linkage-eligible NHANES sampled participants aged 0–17 years, comparing

response to NHANES question about Medicaid/CHIP to linkage status to the CMS MAX file

Characteristic

Linked to the CMS MAX

in same month of

NHANES interview

Did not link to the CMS MAX

file in same month of

NHANES interview

‘‘Yes’’ to question in NHANES about Medicaid/CHIP

health insurance coverage

Row . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Column ..............................

Cell ................................

‘‘No’’ to question in NHANES about Medicaid/CHIP

health insurance coverage

Row . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Column ..............................

Cell ................................

85.2 (1.3)

74.8 (2.1)

23.2 (1.2)

10.7 (1.1)

25.2 (2.1)

7.8 (0.8)

Percent (SE)

14.8 (1.3)

5.8 (0.5)

4.0 (0.4)

89.3 (1.1)

94.2 (0.5)

65.0 (1.5)

NOTES: For participants aged 0–15 years, the responses were answered by a knowledgeable adult proxy. NHANES is National Health and Nutrition Examination Survey; CHIP is Children’s Health

Insurance Program; CMS is Centers for Medicare & Medicaid Services; MAX is Medicaid Analytic eXtract; SE is standard error.

Table 2. Estimates and standard errors of demographic characteristics from the 1999–2004 NHANES participants aged 0–17 years who

were linkage-eligible to the CMS MAX database, based on concordance and discordance

Characteristic

Concordant

‘‘Yes’’ MAX file and

‘‘Yes’’ NHANES

n = 3,003

Discordant

‘‘No’’ MAX file and

‘‘Yes’’ NHANES

n = 577

Discordant

‘‘Yes’’ MAX file and

‘‘No’’ NHANES

n = 1,059

Concordant

‘‘No’’ MAX file and

‘‘No’’ NHANES

n = 5,111

Mean income-to-poverty ratio .................

Male .................................

Under age 6 years ........................

Race and ethnicity

Non-Hispanic white.......................

Non-Hispanic black.......................

Mexican American .......................

1.0 (0.03)

51.6 (1.0)

42.3 (1.6)

58.5 (3.3)

26.4 (2.5)

15.1 (2.3)

1,21.2 (0.06)

52.1 (3.4)

2

39.2 (3.2)

2

56.6 (4.7)

2

22.2 (3.7) 1,221.2 (3.8)

Estimate (SE)

Percent (SE)

1,21.2 (0.05)

2

55.8 (2.0)

2

36.5 (2.5)

2

56.2 (4.5)

2

32.5 (4.5)

11.3 (2.3)

3.2 (0.05)

50.4 (0.8)

28.9 (1.1)

83.3 (1.2)

8.0 (0.9)

8.7 (1.0)

1p value < 0.05 compared with concordant ‘‘Yes/Yes’’ group. 2p value < 0.05 compared with concordant ‘‘No/No’’ group.

NOTES: For participants aged 0–15 years, the responses were answ

Medicare & Medicaid Services; MAX is Medicaid Analytic eXtract; SE

ered by a knowledgeable adult

is standard error.

proxy. NHANES is National Health and Nutrition Examination Survey; CMS is Centers for

Page 8 National Health Statistics Reports n Number 72 n January 6, 2014
Table 3. Weighted percentages and standard errors for linkage-eligible NHIS sampled participants aged 0–17 years, comparing response

to NHIS question about Medicaid/CHIP to linkage status to the CMS MAX file

Characteristic

Linked to the CMS MAX

in same month of

NHIS interview

Did not link to the CMS MAX

file in same month of

NHIS interview

‘‘Yes’’ to question in NHIS about Medicaid/CHIP health

insurance coverage

Row . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Column ..............................

Cell ................................

‘‘No’’ to question in NHIS about Medicaid/CHIP health

insurance coverage

Row . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Column ..............................

Cell ................................

82.7 (0.8)

79.2 (1.1)

23.2 (0.6)

8.5 (0.5)

20.8 (1.1)

6.1 (0.3)

Percent (SE)

17.3 (0.8)

6.9 (0.4)

4.8 (0.3)

91.5 (0.5)

93.1 (0.4)

65.8 (0.7)

NOTES: For NHIS participants aged 0–17 years, the responses were answered by a knowledgeable adult proxy. NHIS is National Health Interview Survey; CHIP is Children’s Health Insurance

Program; CMS is Centers for Medicare & Medicaid Services; MAX is Medicaid Analytic eXtract; SE is standard error.

Table 4. Estimates and standard errors of demographic characteristics from the 2005 NHIS sampled participants aged 0–17 years who

were linkage-eligible to the CMS MAX database, based on concordance and discordance

Characteristic

Concordant

‘‘Yes’’ MAX file and

‘‘Yes’’ NHIS

n = 3,360

Discordant

‘‘No’’ MAX file and

‘‘Yes’’ NHIS

n = 735

Discordant

‘‘Yes’’ MAX file and

‘‘No’’ NHIS

n = 837

Concordant

‘‘No’’ MAX file and

‘‘No’’ NHIS

n = 8,102

Mean income-to-poverty ratio .................

Male .................................

Under age 6 years ........................

Race and ethnicity

Non-Hispanic white.......................

Non-Hispanic black.......................

Hispanic .............................

Non-Hispanic other.......................

1.2 (0.03)

50.4 (0.9)

42.8 (1.1)

36.7 (1.5)

26.3 (1.3)

31.2 (1.3)

5.8 (0.8)

1,21.6 (0.05)

47.6 (2.1)

1

31.9 (2.0)

2

34.2 (2.6) 1,218.6 (2.0) 1,242.1 (2.8)

5.1 (1.2)

Estimate (SE)

Percent (SE)

1,21.7 (0.08)

49.8 (2.0) 1,237.1 (2.1)

2

42.0 (2.9)

2

28.9 (2.8) 1,222.4 (1.7)

6.7 (1.4)

4.2 (0.07)

49.9 (0.6)

30.1 (0.6)

69.4 (0.8)

8.2 (0.4)

14.9 (0.6)

7.5 (0.5)

1p value < 0.05 compared with concordant ‘‘Yes/Yes’’ group. 2p value < 0.05 compared with concordant ‘‘No/No’’ group.

NOTES: For NHIS participants aged 0–17 years, the responses were

Medicaid Services; MAX is Medicaid Analytic eXtract; SE is standard

answered by a knowledgeabl

error.

e adult proxy. NHIS is National Health Interview Survey; CMS is Centers for Medicare &

National Health Statistics Reports n Number 72 n January 6, 2014 Page 9
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Suggested citation

Mirel LB, Simon AE, Golden C, et al.

Concordance between survey report of

Medicaid enrollment and linked Medicaid

administrative records in two national studies.

National health statistics reports; no 72.

Hyattsville, MD: National Center for Health

Statistics. 2014.

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