Household Interview Questionnaires
The following questionnaires were administered by trained interviewers in the participant's home:
- Screener Questionnaire (also referred to as Screener Module 1): administered on the doorstep of the selected household to determine if anyone in the household is eligible to participate in the survey.
- Relationship Questionnaire (also referred to as Screener Module 2): administered in the home to establish the relationship of the household members to determine family "units" (e.g., a married couple) within each household.
- Family Questionnaire: administered in the home to obtain family-level information about health insurance coverage, housing characteristics, food security status, and family income, etc.
- Sample Person Questionnaire: used to collect individual level information on each participant regarding demographic characteristics, dietary behavior, and health-related history.
Mobile Examination Center (MEC) Questionnaires
During the visit to the MEC, additional questions were administered in a private setting to cover more sensitive topics (e.g., alcohol use) using the following questionnaires:
- Computer-Assisted Personal Interview (CAPI) Questionnaire: conducted by a trained MEC interviewer.
- Audio-Computer-Assisted Self-Interview (ACASI) Questionnaire: questions were read to respondents through headphones and respondents could simultaneously read questions on a computer screen in their chosen language. Participants responded using the touch screen.
Respondent and Proxy Rules
The screener and relationship questionnaires were administered to an adult household member aged at least 18 years or an emancipated minor determined by state-specific criteria. The family questionnaire was typically completed by the head of household (an adult family member aged 18 years or older or an emancipated minor) for every family unit sampled within the household.
The sample person questionnaire was administered to all participants or their proxies; however, eligibility for each specific questionnaire section was determined by the participant's age and gender. Participants 16 years of age and older and emancipated minors were interviewed directly. An adult proxy provided information for survey participants who were under 16 years of age and for participants who could not answer the questions themselves.
The MEC interview was administered to participants 8 years of age or older. Eligibility for each specific questionnaire section was determined by the participant's age (at the time of screening) and gender. The CAPI portion was administered using a proxy interview or an interpreter if needed. Due to the sensitive nature of the ACASI questionnaire, no proxies or interpreters were used. Therefore, mentally impaired individuals, or participants who were unable to understand English, Spanish, Korean, Vietnamese, or Chinese (traditional/Mandarin, simplified/Mandarin, or traditional/Cantonese) were not eligible. Please refer to dataset documentation for section-specific information on participant eligibility.
Questionnaire and Interview Languages
Extensive pretesting was completed prior to implementing the questionnaires in the field.
All NHANES questionnaires were translated into Spanish and can be administered in either English or Spanish based on respondent preference. To facilitate the oversampling of the Asian-Americans which began in 2011, selected survey materials were translated into Mandarin Chinese, both traditional and simplified, Korean, and Vietnamese. Materials translated to these Asian languages included hand cards, glossaries of terms, consents, examination scripts, and informational brochures. All translations were done using the forward translation process approved by the NCHS Research Ethics Review Board. A large percentage of the household interviewers and all MEC interviewers are bilingual in English and Spanish. Interpreters were used for non-English/non-Spanish speaking participants.
In addition to the English and Spanish versions, the 2011-2018 MEC ACASI questionnaire was translated into Chinese (traditional/Mandarin, simplified/Mandarin, and traditional/Cantonese), Korean, and Vietnamese for use with participants 20 years and older when necessary. The respondent chose their preferred language.
Automated Data Collection
NHANES household interview and MEC interview data were recorded electronically using computerized questionnaire forms. After data collection was completed, the interview data files were transmitted electronically to a central survey database system.
The NHANES automated interview systems had built-in edits and range checks for many question response options. When unusual, inconsistent, or unrealistic responses were recorded, the interviewer was alerted immediately and instructed to verify or edit the initial response. The systems also had online help screens built-in to assist interviewers in defining key terms used in the questionnaires.
Interviewer Training and Quality Control Monitoring
All NHANES interviewers completed a comprehensive training program which included interviewing techniques, role-playing exercises and practice interviews with live respondents. Interviewers also participated in a series of cultural competency trainings to help them recognize and respect cultural differences.
Several types of quality control monitoring procedures were implemented. Interviewers were frequently accompanied on interviews by field supervisors and NCHS staff to verify that the interviewing protocol was administered correctly. At least 10% of every household interviewer's work (including screening and interview) were randomly selected and validated by field supervisors via phone or field visit shortly after the completion of household data collection. Accuracy and completeness of selected key items (such as age, birth date, and gender) for all cases were reviewed by field office staff and MEC coordinators. In addition, each household and MEC CAPI interview was digitally recorded unless the survey participant specified that he/she did not want the interview recorded (the request for permission and the participant's response to record were recorded). The recorded interviews were reviewed by NCHS staff and interviewer supervisors. Interviewers were retrained on survey procedures when necessary.
NCHS used field staff and interviewer feedback to improve the questionnaires and survey materials. Survey staff debriefing and training sessions were conducted bi-annually. Interviewers were trained on new survey content and protocol changes prior to implementation in the field.
Data Preparation and Analytic Guidance
During data preparation, variable frequency counts, questionnaire "skip" patterns, plausibility of responses, and interviewer comments were reviewed and verified. Edits were made to some variables to ensure the completeness and consistency of the data. Edits were also made to address data disclosure concerns. Section-specific documentation describe the measures taken in greater detail.
We strongly encourage data users to read all relevant documentation on the survey overall and for the specific data files to be used in their analysis. Specific data file documentation can be found via the link next to the respective data file on the NHANES website. Data users should also review the NHANES Analytic Guidelines prior to beginning any analyses.