General Information About NHANES Interview Data
In general, persons 16 years of age and older, and emancipated minors were interviewed directly. A small number of NHANES questionnaire sections have different respondent rules. Please review the questionnaire documentation, questionnaires, and interviewer training manuals carefully prior to analyzing the data.
A responsible adult provided information for participants under 16 years of age, and for individuals who could not self-report. The interviewer training manuals and component-specific notes, provided with these files, give additional information about the use of proxy respondents.
Automated Data Collection Methodology
Household Interview and Mobile Examination Center (MEC) Interview data were recorded electronically using computerized questionnaire forms that were programmed using Blaise© software. The Household Interview questionnaires were programmed in Blaise© and installed on pentop computers for use in the field. The MEC interviews were also administered in an automated format, but the interview module formats included non-Blaise© software. After data collection was completed, the interview data files were transmitted electronically to a central survey database system.
NHANES Spanish Language Questionnaires
All NHANES questionnaires were translated into Spanish and were administered in computer-assisted personal interview (CAPI) format along with the English language versions.
Household Interview Component Questionnaires
- Screener Questionnaire
- Family Interview Questionnaire
- Sample Person Questionnaire
Mobile Examination Center (MEC) Questionnaires
- MEC Computer-Assisted Personal Interview (MEC CAPI)
- MEC Audio-Computer-Assisted Self Interview (MEC A-CASI)
The MEC Interview component is a two-part interview that addresses several health-related topics. The personal interview portion is conducted in a private room, by a trained interviewer. The Audio Computerized Self Administered (A-CASI) portion of the interview was conducted in a private room in the MEC without the interviewer being present. (The interviewers are present for a brief “training” session dealing with the use of the personal computer and interview system software) The A-CASI format permits the respondents to hear questions through earphones and to read questions on a computer screen. Respondents progress through the A-CASI questions at their own speed, as they touch the computer screen to indicate their response. The A-CASI portion of the interview consists of five separate sections, each of which deals with a sensitive health risk behavior topic.
All interviewers completed a comprehensive two-week training program. Many of the interviewers had prior interviewing experience. A large percentage of the household interviewers were bilingual in English and Spanish.
The MEC interviewers also received extensive interviewer training on personal and audio-computer-assisted interview administration. This training focused on the specific interview modules that were administered in the MEC dealing with mental health and smoking, drug use, alcohol, and sexual behavior.
NHANES interviewer training included role-playing exercises and practice interviews, all of which were monitored by NCHS and contractor staff. Detailed information about the interviewer training requirements is found in the NHANES Household Interviewer Training Manual.
Interviewer Quality Control Monitoring
Extensive pretesting was completed prior to implementing the questionnaires in the field. Pilot testing was conducted with the field and examination staff, to test all of the systems and procedures.
Several types of quality control monitoring methods were implemented to ensure that high quality data were collected during the survey. Interviewer monitoring was a major responsibility for NCHS and contractor staff. Interviewers were frequently accompanied on interviews and observed to verify that the interview protocol was administered correctly. Interviewers were retrained on survey procedures if necessary.
NCHS encouraged the interviewers to provide constructive comments and feedback based on their field experiences. NCHS used field staff and interviewer feedback to improve the questionnaires and survey materials. Survey staff debriefing and training sessions were conducted annually. NCHS and contractor staff participated in the debriefing meetings. Interviewers were trained on new survey content and protocol changes prior to implementation in the field. NCHS and contractor staff also reviewed tape recorded interviews, as part of the quality control process.
Data collection system consistency checks
The NHANES CAPI systems had built-in edit and range checks for many question response options. When unusual or unrealistic responses were recorded, the interviewer was alerted immediately and instructed to verify or edit the initial response.
Data Preparation: Reviews, editing, and derived variables
During data preparation, variable frequency counts were checked, questionnaire "skip" patterns were verified, and the reasonableness of responses to the questions were reviewed. When a variable was modified globally, as part of the editing process, the third letter in the variable name was changed from a Q (i.e. WHQ) to a D (i.e. WHD).
Check Items and Final Data Release Variables
The codebooks for each survey component include “check item” variables. Check item variables were used internally at NCHS as part of the quality control process to verify that the data collection process was correct. The check item variables are not part of the data release files, however. Analysts would need to re-create these variables to produce check item frequencies.