National Health and Nutrition Examination Survey (NHANES), 1999-2000

The most recent NHANES began in 1999. Every year, approximately 7,000 individuals, of all ages, are interviewed in their homes and of these, approximately 5,000 complete the health examination component of the survey. A majority of the health examinations are conducted in mobile examination centers (MECs). The MECs provide an ideal setting for the collection of high quality data in a standardized environment. In addition to the MEC examinations, a small number of survey participants receive an abbreviated health examination in their homes if they are unable to come to the MEC. The NHANES target population is the civilian, noninstitutionalized United States population. NHANES 1999-2000 includes over-sampling of low-income persons, adolescents 12-19 years of age, persons 60+ years of age, African Americans and Mexican Americans. Initially, households are identified for inclusion in the NHANES sample and an advance letter is mailed to each address informing the occupant(s) that an NHANES interviewer will visit their home. The household interview component is comprised of Screener, Sample Person, and Family interviews, each of which has a separate questionnaire (please refer to the data file documentation). Trained household interviewers administer all of the questionnaires. In most cases, the interview setting was the survey participant's home. The interview data are recorded using the Blaise computer-assisted personal interview (CAPI) system. When the interviewer arrives at the home, he or she shows an official identification badge and briefly explains the purpose of the survey. If the occupant has not seen the advance letter, a copy is given to them to read. The interviewer requests that the occupant answer a brief questionnaire to determine if any household occupants are eligible to participate in NHANES. If eligible individuals are identified, the interviewer proceeds with efforts to recruit these individuals. Initially, the interviewer explains the household questionnaires to all eligible participants 16 years of age and older, informs the potential respondents of their rights, and provides assurances about the confidentiality of the survey data (reiterating what is stated in the advance letter). A majority of the household interviews are conducted during the first contact. If this is inconvenient for the survey participant, an appointment is made to administer the household interview questionnaires later. Household interviews for survey participants under 16 years of age are conducted with a proxy (usually their parent or guardian). If there is no one living in the household who is over 16, participants under 16 years of age are permitted to self-report. Respondents are asked to sign an Interview Consent Form agreeing to participate in the household interview portion of the survey. For participants 16-17 years of age a parent or guardian consents and the child gives his/her assent. After the household interview is completed, the interviewer reviews a second informed consent brochure with the participant. This brochure contains detailed information about the NHANES health examination component. All interviewed persons are asked to complete the health examination component. Those who agree to participate are asked to sign additional consent forms for the health examination component. The interviewer telephones the NHANES field office from the participant's home to schedule an appointment for the examination. The interviewer informs the participants that they will receive remuneration as well as reimbursement for transportation and childcare expenses, if necessary.Target PopulationsThere are different target population groups for the topics within and between NHANES questionnaire sections. For example, in the Nutrition and Diet Behavior section, questions pertaining to infant nutrition and breast-feeding were asked of proxy respondents for children 6 years of age and younger, alcohol consumption frequency questions were asked of persons 20+ years of age, and senior meal program participation questions were asked of respondents 60+ years of age. Data users should review the survey questionnaire codebooks thoroughly to determine the target populations for each NHANES questionnaire section and sub-section.The NHANES Health Examination ComponentWhen a participant arrives at the MEC, the MEC Coordinator greets the participant and verifies all pertinent identifier information. The participant is given a disposable paper gown, a pair of slippers, and a urine specimen cup. MEC staff direct survey participants to the rooms where the examination components are conducted. Each MEC survey team consists of one physician, one dentist, two dietary interviewers, three certified medical technologists, five health technicians, one phlebotomist, two interviewers, and one computer data manager. Additionally, there is a person designated as the Coordinator who is responsible for managing the movement of participants between examinations, providing remuneration, and distributing a preliminary report of findings. Upon completion of the examination, each examinee is remunerated. Some of the medical findings of the examination are given to the examinees before they leave the MEC. The other reportable survey findings are mailed to participants after the laboratory assays and special tests are completed.MEC OperationsThree MECs are equipped for use in NHANES. Each MEC consists of four large, inter-connected trailer units. An advance team sets up the MECs prior to the start of the survey examinations. Water, sewer, electrical, and communication lines are connected during set-up. The MEC equipment and data collection systems must be checked and calibrated prior to the start of survey data collection. The MECs are open a total of five days per week, and the nonoperational days change on a rotating basis so that appointments can be scheduled on any day of the week. Two examination sessions are conducted daily. For the convenience of the survey participants, appointments can be scheduled during morning, afternoon, or evening hours. The examinations require up to three hours to complete. At any given time during the survey, examinations are conducted at two survey locations simultaneously. Staff vacations are scheduled for periods of about one month at New Years and about two weeks during the summer, leaving ten and one-half months to conduct examinations.Second Day Examinations and Dietary InterviewsSecond day (i.e., repeat) MEC examinations were pilot tested in 1999 and implemented in 2000. Approximately 5 percent of examined persons over 20 years of age from each survey location were asked to complete second day exams. Second day dietary interviews were completed on ten percent of all examined persons in 2000. The second day dietary interview is a primary data collection technique to improve the estimation of distributions of nutrient intakes. Second day examination and dietary data are not included in this data file.Home ExaminationsParticipants under 1 year of age or 60+ years of age, who are unable or unwilling to come to the MEC for an examination, are eligible to receive a home examination. Home examination data are not included in this data file.