NHANES National Youth Fitness Survey

The demographics file provides individual, family, and household level information on the following topics:

• Survey participant’s household interview and examination status
• Interview and examination sample weights
• Masked variance units
• Language of questionnaires used for the interviews conducted in the household
• Household and family income
• Household and family sizes
• Household composition
• Demographic information about the household reference person
• Other selected demographic information, such as gender, age, race/Hispanic origin, education, and country of birth

Disclosure risks and issues pertaining to confidentiality protection prevent NCHS from releasing all of the NNYFS demographic variables publicly. Additional information may be accessed through the NCHS Research Data Center (RDC). Instructions for requesting use of these data are available from https://www.cdc.gov/rdc/.

The target age groups for demographic variables in this file vary by the topic. Please review the codebook carefully.

The family and sample person demographics questionnaires were asked, in the home, by trained interviewers using Computer-Assisted Personal Interviewing (CAPI) system. An adult family member, aged 18 years or older, was interviewed as a proxy for the survey participant. The respondent selected the language of interview (English or Spanish) or requested that an interpreter be used. Hand cards, showing response choices or information that respondents needed to answer the questions, were used for some questions. The hand cards were printed in English, Spanish, Mandarin Chinese (both traditional and simplified), Korean, and Vietnamese. The interviewer directed the respondent to the appropriate hand card during the interview. When necessary, the interviewer further assisted the respondent by reading the response choices listed on the hand cards.

The NNYFS demographics questionnaires are available on the NNYFS website (https://www.cdc.gov/nchs/nnyfs/index.htm).

The CAPI system is programmed with built-in consistency checks to reduce data entry errors. CAPI also uses online help screens to assist interviewers in defining key terms used in the questionnaire.

After collection, interview data were reviewed by the NNYFS field office staff for accuracy and completeness of selected items. The interviewers were required to record interviews periodically and the recorded interviews were reviewed by NCHS staff and interviewer supervisors.

Frequency counts were checked, “skip” patterns were verified, and the reasonableness of question responses was reviewed. Edits were made to some variables to ensure the completeness, consistency, and analytic usefulness of the data. Edits were also made, when necessary, to address data disclosure concerns.

RIDSTATR: This status code is used to identify whether a participant was both interviewed at home and examined in the mobile examination center (MEC) or was only interviewed in the home but never went through the examination.

RIDAGEYR: Age in years, at the time of the screening interview, is reported for all survey participants. RIDAGEYR was calculated based on the participant’s date of birth. In rare cases, the actual date of birth was missing but the participant’s age in years was provided, then the reported age was used.

RIDEXAGY: The age in years, at the time of examination, is provided for all participants who were examined in the MEC.

RIDEXMON: This variable indicates the six-month time period when the examination was performed. A value of “1” indicates November 1st through April 30th; a value of “2” indicates May 1st through October 31st.

RIDRETH1: This race-ethnicity variable was derived from responses to the survey questions on race and Hispanic origin. Respondents who self-identified as “Mexican American” were coded as such (i.e., RIDRETH1=1) regardless of their other race-ethnicity identities. Otherwise, self-identified “Hispanic” ethnicity would result in code “2, Other Hispanic” in the RIDRETH1 variable. All other non-Hispanic participants would then be categorized based on their self-reported races: non-Hispanic white (RIDRETH1=3), non-Hispanic black (RIDRETH1=4), and other non-Hispanic races including non-Hispanic multiracial (RIDRETH1=5).

DMDBORN4: Country of birth was recoded into two categories: 1) Born in 50 U.S. states or Washington, DC; and 2) Born in other countries, including U.S. territories.

DMDEDUC3: This variable provides information on the highest grade or level of education completed by participants 6-15 years of age. The responses of grades 1-8 were released as single years of education. Reported education level at or above 9th grade are coded as “9.” Codes “55” (less than 5th grade) and “66” (less than 9th grade) were used to categorize older youth who had very low education levels.

SIALANG: This variable indicates the language (English or Spanish) used during the sample person questionnaire interview conducted at the participant’s home.

INDFMIN2: This variable indicates the total annual family income or annual individual income (for households with one person or households comprised of unrelated individuals). A family is defined as a group of two people or more (one of whom is the householder) related by birth, marriage, or adoption and residing together.

During the household interview, the respondent was asked to report total income for the entire family (or individual) in the last calendar year in dollars. The reported dollar amount was re-coded into range values.

If the respondent was not willing or able to provide an exact dollar figure, the interviewer asked an additional question to determine whether the income was < $20,000 or ≥ $20,000. Based on the respondent’s answer to this question, he/she was asked to select a category of income from a list on a hand card. For repondents who selected a category of income, their family incomes were set as the midpoints of the selected ranges. If the respondent was unable to report greater detail than < $20,000 or ≥ $20,000, then these two categories were used to report the family (or individual) income.

INDFMPIR: This variable is the ratio of family income to poverty. The Department of Health and Human Services (HHS) poverty guidelines were used as the poverty measure to calculate this ratio. These guidelines are issued each year, in the Federal Register, for determining financial eligibility for certain federal programs, such as Head Start, Supplemental Nutrition Assistance Program (SNAP), Special Supplemental Nutrition Program for Women, Infants, and Children (WIC), and the National School Lunch Program. The poverty guidelines vary by family size and geographic location (with different guidelines for the 48 contiguous states and the District of Columbia; Alaska; and Hawaii).

INDFMPIR was calculated by dividing family (or individual) income by the 2012 poverty guidelines. The value was not computed if the respondent only reported income as < $20,000 or ≥ $20,000. If family income was reported as a more detailed category, the midpoint of the range was used to compute the ratio. Values at or above 5.00 were coded as 5.00 or more because of disclosure concerns. The values were not computed if the income data was missing.

INDHHIN2: This variable indicates the total annual household income in dollar ranges. If a household was comprised of a single family or individual, the reported family income was used as household income as well. When more than one family, or one or more unrelated individuals, or a combination of a family and unrelated individuals resided in the household, the total household income was calculated by the sum of all reported family and/or individual income values. Please see above notes on variable INDFMIN2 for details on how the amounts of family income were determined.

When more than one family, or one or more unrelated individuals, or a combination of a family and unrelated individuals resided in the same household, they were asked to provide a total income estimate for the entire household, using similar questions as were used for family income. This estimated household income value was only used when: 1) the family income value was missing for one or more families in the household; and 2) the estimated value was equal or more than the sum of all known family incomes from the household. If different respondents in the household provided different estimates, the largest value was used. If none of the respondents provided a valid household income estimate, but the sum of known family and/or individual incomes was at least $100,000, then INDHHIN2 was categorized as “$100,000 and over.”

Similar to the family income category coding, the “$20,000 and over” and “under $20,000” categories were only used when no other valid value estimates were provided.

DMDFMSIZ: This variable is the number of people in the participant’s family. A family is defined as a group of people related by birth, marriage, or adoption and residing together. Due to disclosure concerns, families that are comprised of 7 or more people are included in the category that is labeled “7 or more”.

DMDHHSIZ: This variable is the number of people in the participant’s household. The values for this variable range from 1 to 7. Due to disclosure concerns, households that are comprised of 7 or more people are included in the category that is labeled “7 or more”.

DMDHHSZA: This variable is the number of children aged 5 years or younger living in the participant’s household. The values for this variable range from 0 to 3. Due to disclosure concerns, households that are comprised of 3 or more children aged 5 years or younger are included in the category that is labeled “3 or more”.

DMDHHSZB: This variable is the number of children aged 6-17 years old living in the participant’s household. The values for this variable range from 0 to 4. Due to disclosure concerns, households that are comprised of 4 or more children aged 6-17 years are included in the category that is labeled “4 or more”.

DMDHHSZF: This variable indicates whether there is at least one adult aged 60 years or older living in the participant’s household. Due to disclosure concerns, information on the number of adults aged 60 years or older in the household is only available through the NCHS Research Data Center (RDC).

Household Reference Person: The household reference person is defined as the first household member 18 years of age or older listed on the household member roster, who owns or rents the residence where members of the household reside. Analysts frequently use information about the reference persons to characterize the socioeconomic status of the households where survey participants reside. The Demographics file includes information on the household reference person’s gender (DMDHRGND), age (DMDHRAGE), country of birth (DMDHRBR4), education level (DMDHREDU), and marital status (DMDHRMAR).

Please refer to the NNYFS Analytic Guidelines (https://wwwn.cdc.gov/nchs/data/series/sr02_163.pdf) for details on the sample design and analytic guidance for the NNYFS data.

Age at screening: Age at screening was used to determine eligibility for an examination component and should be used for most analyses. As mentioned earlier, RIDAGEYR, age in years, at the time of the screening interview, is reported for all survey participants. To facilitate the analysis of anthropometric data, a variable, BMDBMIC, was created as part of the Body Measures Exam file to provide analysts pre-computed BMI categories for all NNYFS participants who were examined in the MEC. For further details refer to the Body Measures Data File and Documentation.

Masked Variance Units (MVUs): Fifteen masked primary sampling units (PSUs) are included in the NNYFS demographics file. All 15 PSUs belongs to the same stratum. These MVUs are a collection of sampling units that are aggregated into groups for the purpose of variance estimation. The variance estimates that are produced, using the MVUs, closely approximate the variances that would have been estimated using the “true” sample design variance units that are based on the actual survey sample strata and primary sampling units. MVUs are used to protect the confidentiality of information provided by survey participants and to reduce disclosure risks. The use of MVUs is described in the NNYFS Analytic Guidelines. Analysts should review the Guidelines carefully prior to analyzing the survey data.

Sample Weights: The full sample weights (WTINT, WTMEC) should be used for all NNYFS analyses.