Table of Contents

Component Description

Cognitive health has emerged as an important public health concern, most notably for the nation’s aging population (1, 2). Decline in cognitive functioning has been associated with quality of life, personal relationships, and independence resulting in increased health care needs, as well as major caregiving and financial challenges (3). Cognitive functioning has been measured periodically in NHANES surveys, either during the household interview or as a component in the Mobile Examination Center. In 2011-12, a series of assessments in NHANES (variable name prefix CFQ) were re-introduced, including: 1) word learning and recall modules from the Consortium to Establish a Registry for Alzheimer’s disease (CERAD); 2) the Animal Fluency test; and 3) the Digit Symbol Substitution test (DSST). Although cognitive assessments cannot replace a diagnosis based on a clinical examination, they are useful to examine the association of cognitive functioning with the many medical conditions and risk factors measured during the NHANES examination.

Each assessment is described, in brief:

The CERAD Word Learning subtest (CERAD W-L) assesses immediate and delayed learning ability for new verbal information (memory sub-domain) (4). It has been used in major epidemiologic studies with diverse racial and cultural communities (5-8). The test consists of three consecutive learning trials, and a delayed recall. For the learning trials, participants are instructed to read aloud 10 unrelated words, one at a time, as they are presented. Immediately following the presentation of the words, participants recall as many words as possible. In each of the three learning trials, the order of the 10 words is changed. The maximum score possible on each trial is 10. In NHANES, the words for the learning trials were presented in large bolded letters on a computer monitor. Participants who were unable to read, due to literacy or visual impairment, were asked to repeat each word after it was read by the interviewer. The delayed word recall occurred after the other two cognitive exercises (Animal Fluency and DSST) were completed (approximately 8-10 minutes from the start of the word learning trials). In addition to scores for each word learning trial and the delayed word recall, a score for the number of intrusions (incorrect words that were not on the list) is included in the data file.

The Animal Fluency test examines categorical verbal fluency, a component of executive function (9). Scores have been shown to discriminate between persons with normal cognitive functioning compared with those with mild cognitive impairment and more severe forms of cognitive impairment, such as Alzheimer’s disease (10-12). The test demands awareness (e.g., naming animals), regardless of cultural context, that is not absolutely reliant on formal educational experiences of a particular culture (8). The Animal Fluency test has been used in large-scale screenings and epidemiologic studies (11-13). Participants are asked to name as many animals as possible in one minute. A point is given for each named animal. In NHANES, participants first were asked to name three items of clothing, another verbal fluency category, as a practice test. Participants who could not name three articles of clothing did not continue with the Animal Fluency exercise.

The Digit Symbol Substitution test (DSST), a performance module from the Wechsler Adult Intelligence Scale (WAIS III), relies on processing speed, sustained attention, and working memory (14). The DSST has been used in large screenings, epidemiological and clinical studies (15-17), and was administered during the household interview to participants 60 years and over during NHANES 1999-2002. The exercise is conducted using a paper form that has a key at the top containing 9 numbers paired with symbols. Participants have 2 minutes to copy the corresponding symbols in the 133 boxes that adjoin the numbers. The score is the total number of correct matches. A sample practice test is administered before the participants begin the main test. In NHANES, participants who could not correctly match the symbols with the numbers on their own during the pretest practice did not continue. Details on scoring can be found in the 1999-2000 NHANES CFQ questionnaire data file documentation https://wwwn.cdc.gov/Nchs/Nhanes/1999-2000/CFQ.htm.

Eligible Sample

Participants aged 60 years and older were eligible. Participants who did not understand or read English, Spanish, Korean, Vietnamese, traditional or simplified Mandarin, or Cantonese, or participants who needed a proxy informant were not administered the assessments. An overall completion status variable (CFASTAT) provides the completion codes for the full component, indicating persons who were either not eligible or did not take part in this component as a Mobile Examination Center (MEC) participant. Note that all participants did not complete every assessment. For more details on the overall component status, see Analytic Notes: CFASTAT.

Among eligible participants, if consent to audio-record was denied (requested for both quality control and scoring purposes), participants only were administered the DSST. 

Interview Setting and Mode of Administration

The assessments were administered by trained interviewers at the end of the face-to-face private interview in the Mobile Examination Center (MEC Interview). Before the assessments began, interviewers asked participants for consent to audio-record for the purpose of scoring and quality control.

Participants self-selected their preferred language (English, Spanish, Korean, Vietnamese, Chinese). All CERAD-WL words presented on the computer monitor were in the language chosen by the participant. Because the interviewers were bilingual only in English and Spanish, interpreters provided instructions for assessments administered in Korean, Vietnamese, and Chinese.

Quality Assurance & Quality Control

For interviews in English and Spanish, two interviewers transcribed verbatim responses from the audio recordings and scored the CERAD-WL and Animal fluency assessments. Transcription and scoring usually were done on the same day assessments were conducted. Tests conducted in Korean, Vietnamese and Chinese were transcribed verbatim and scored by consultants in those languages at a later date. The majority of DSST were also independently scored by two interviewers. Inconsistent scores were adjudicated by a third party, as necessary.

In addition, review of the audio-recordings of assessments were evaluated for consistency of interviewer instructions and to determine test score accuracy. Approximately 10% of recorded interviews were independently reviewed over the course of the data collection cycles.

Data Processing and Editing

Edits were made to ensure the completeness, consistency, and analytic usefulness of the data. When available, extensive review of the recorded interviews were conducted to clarify inconsistent responses, to evaluate the quality of the data, and to finalize the data set. 

Analytic Notes

Non-response to this component varied by age, education, race-ethnicity, and other factors. Because non-response to cognitive assessments may be related to cognitive functioning itself, analysts are encouraged to conduct a thorough non-response bias analysis of these data as part of their preliminary research plan.

Sample sizes availability differ for each assessment. Analysts are encouraged to combine NHANES data cycles, if possible, to increase sample sizes.

MEC exam sample weights should be used for the analyses and are available on the NHANES website at: https://wwwn.cdc.gov/nchs/nhanes/continuousnhanes/default.aspx?BeginYear=2011.

Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for further details on the use of sample weights and other analytic issues.

CFASTAT: This summary variable describes response rates and the completion status for the entire component. As the codes demonstrate, MEC participants did not always attempt or complete all of the tests. For the code CFASTAT=1, participants have scores for one or more of the CERAD-WL recalls, a summary result for the Animal fluency and DSST practice pretests. Scores for the Animal fluency and the DSST are available only for those who passed the practice pretests (CFDAPP=1 and CFDDPP=1). For codes CFASTAT= 1, 2 or 3, analysts are encouraged also to consult the CERAD administrative completion status variable (CFDCCS) and the animal fluency and DSST practice pretest summary result (CFDAPP, CFDDPP) codes to determine the sample size available for each assessment. CFASTAT coded as 4, 5, 6 indicate persons who did not do any of the assessments due to ineligibility or other reasons. These persons are coded as missing throughout the remainder of the data set. As is the case with other NHANES MEC components, some sample persons did not have the opportunity to participate (e.g., limited by time constraints) or did not have an interest in taking part in the cognitive component (e.g., refused).

CFALANG: The cognitive functioning component was conducted only in English, Spanish, Korean, Vietnamese, and Chinese. Language was determined by the participant at the time of the testing. In order to protect confidentiality, the language of participants speaking Chinese, Korean or Vietnamese is coded as “Asian language” (CFALANG=3).

CFDCCS and CFDCRNC: Complete data (3 learning trials and delayed recall) are not available for a small portion of participants. A reason code is provided for these participants (CFDCRNC) as well as for persons who did not perform any of the CERAD-WL assessments.

CFDCIT1, CFDCIT2, CFDCIT3, CFDCIR: These variables provide a count of incorrect words named during the three learning trial recalls or during the delayed recall.

CFDAPP: This variable provides a summary result for the practice pretest that took place before the animal fluency was administered. Persons who were unable to pass the pretest (CFDAPP=2) will have a missing score for Animal Fluency test (CFDAST=”.”).

CFDDPP: This variable provides a summary result for the practice pretest that took place before the DSST was administered. Persons who were unable to pass the pretest (CFDDPP=2) will have a missing score for DSST (CFDDS=”.”).

Questions on self-perceived cognitive functioning are included in MCQ_G of the Household Interview Questionnaire.

References

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SEQN
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number
Target:
Both males and females 60 YEARS - 150 YEARS

CFASTAT - Cognitive functioning status

Variable Name:
CFASTAT
SAS Label:
Cognitive functioning status
English Text:
Cognitive functioning status
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 3 tests 1416 1416
2 2 tests 56 1472
3 1 test 38 1510
4 Ineligible, proxy 30 1540 End of Section
5 Ineligible, other language 9 1549 End of Section
6 No test done 138 1687 End of Section
. Missing 0 1687

CFALANG - Language - Cognitive Functioning

Variable Name:
CFALANG
SAS Label:
Language - Cognitive Functioning
English Text:
Language - Cognitive Functioning
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 English 1300 1300
2 Spanish 166 1466
3 Asian language 44 1510
. Missing 177 1687

CFDCCS - CERAD: Completion Status

Variable Name:
CFDCCS
SAS Label:
CERAD: Completion Status
English Text:
CERAD: Number of recalls completed
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Four completed recalls 1451 1451 CFDCST1
2 One to three completed recalls 17 1468
3 Not done 42 1510
. Missing 177 1687

CFDCRNC - CERAD: Reason Not Complete

Variable Name:
CFDCRNC
SAS Label:
CERAD: Reason Not Complete
English Text:
CERAD: Reason Not Complete
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Did not consent to audio record 13 13
2 Communication problem 2 15
3 Physical limitation 3 18
4 Quit or gave up 7 25
5 Refused 10 35
6 Equipment failure 24 59
7 Other 0 59
. Missing 1628 1687

CFDCST1 - CERAD: Score Trial 1 Recall

Variable Name:
CFDCST1
SAS Label:
CERAD: Score Trial 1 Recall
English Text:
CERAD: Score Trial 1 Recall
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 9 Range of Values 1467 1467
. Missing 220 1687

CFDCST2 - CERAD: Score Trial 2 Recall

Variable Name:
CFDCST2
SAS Label:
CERAD: Score Trial 2 Recall
English Text:
CERAD: Score Trial 2 Recall
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 10 Range of Values 1463 1463
. Missing 224 1687

CFDCST3 - CERAD: Score Trial 3 Recall

Variable Name:
CFDCST3
SAS Label:
CERAD: Score Trial 3 Recall
English Text:
CERAD: Score Trial 3 Recall
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 10 Range of Values 1458 1458
. Missing 229 1687

CFDCSR - CERAD: Score Delayed Recall

Variable Name:
CFDCSR
SAS Label:
CERAD: Score Delayed Recall
English Text:
CERAD: Score Delayed Recall
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 10 Range of Values 1454 1454
. Missing 233 1687

CFDCIT1 - CERAD: Intrusion word count Trial 1

Variable Name:
CFDCIT1
SAS Label:
CERAD: Intrusion word count Trial 1
English Text:
CERAD: Intrusion word count Trial 1
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 4 Range of Values 1467 1467
. Missing 220 1687

CFDCIT2 - CERAD: Intrusion word count Trial 2

Variable Name:
CFDCIT2
SAS Label:
CERAD: Intrusion word count Trial 2
English Text:
CERAD: Intrusion word count Trial 2
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 3 Range of Values 1463 1463
. Missing 224 1687

CFDCIT3 - CERAD: Intrusion word count Trial 3

Variable Name:
CFDCIT3
SAS Label:
CERAD: Intrusion word count Trial 3
English Text:
CERAD: Intrusion word count Trial 3
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 5 Range of Values 1458 1458
. Missing 229 1687

CFDCIR - CERAD: Intrusion word count Recall

Variable Name:
CFDCIR
SAS Label:
CERAD: Intrusion word count Recall
English Text:
CERAD: Intrusion word count Recall
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 10 Range of Values 1454 1454
. Missing 233 1687

CFDAPP - Animal Fluency: Sample Practice Pretest

Variable Name:
CFDAPP
SAS Label:
Animal Fluency: Sample Practice Pretest
English Text:
Animal Fluency: Sample Practice Pretest
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Passed 1449 1449 CFDAST
2 Failed 7 1456 CFDDPP
3 Not done 54 1510
. Missing 177 1687

CFDARNC - Animal Fluency: Reason Not Done

Variable Name:
CFDARNC
SAS Label:
Animal Fluency: Reason Not Done
English Text:
Animal Fluency: Reason Not Done
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Did not consent to audio record 13 13 CFDDPP
2 Communication problem 2 15 CFDDPP
3 Physical limitation 3 18 CFDDPP
5 Refused 8 26 CFDDPP
6 Equipment failure 28 54 CFDDPP
7 Other 0 54 CFDDPP
. Missing 1633 1687

CFDAST - Animal Fluency: Score Total

Variable Name:
CFDAST
SAS Label:
Animal Fluency: Score Total
English Text:
Animal Fluency: Score Total
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 to 40 Range of Values 1449 1449
. Missing 238 1687

CFDDPP - Digit Symbol: Sample Practice Pretest

Variable Name:
CFDDPP
SAS Label:
Digit Symbol: Sample Practice Pretest
English Text:
Digit Symbol Coding: Sample Practice Pretest
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Passed 1422 1422 CFDDS
2 Failed 52 1474 End of Section
3 Not done 36 1510
. Missing 177 1687

CFDDRNC - Digit Symbol: Reason Not Done

Variable Name:
CFDDRNC
SAS Label:
Digit Symbol: Reason Not Done
English Text:
Digit Symbol Coding: Reason Not Done
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
2 Communication problem 8 8 End of Section
3 Physical limitation 15 23 End of Section
5 Refused 11 34 End of Section
6 Equipment failure 0 34 End of Section
7 Other 2 36 End of Section
. Missing 1651 1687

CFDDS - Digit Symbol: Score

Variable Name:
CFDDS
SAS Label:
Digit Symbol: Score
English Text:
Digit Symbol Coding: Score
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 100 Range of Values 1422 1422
. Missing 265 1687