National Health and Nutrition Examination Survey

Los Angeles (L.A.) County, California is the largest county in the United States in population size and comprises one of the most diverse populations in the world. Data from four NHANES cycles (1999-2000, 2001-2002, 2003-2004, and 2005-2006) were aggregated and re-weighted to match known population totals for L.A. County.

The demographics file provides individual-, family-, and household-level information on the following topics for NHANES participants selected from Los Angeles County in 1999-2006:

• Interview and examination status;
• Interview and examination sample weights;
• Variance units;
• Pregnancy status;
• Household and family income;
• Household and family sizes; and
• Other selected demographic information, such as gender, age, race/Hispanic origin, education, marital status, country of birth, citizenship, and years of U.S. residence.

Disclosure risks and issues pertaining to confidentiality protection prevents the National Center for Health Statistics (NCHS) from releasing the L.A. County Demographics file publicly. Analysis of these data must be done through the NCHS Research Data Center (RDC). Instructions for requesting access to these data are available from https://www.cdc.gov/rdc/.

Preliminary data for L.A. County from NHANES 1999-2004 were previously released through the RDC, and still available upon request.

All NHANES participants selected from Los Angeles County in the 1999-2006 survey cycles are included in this dataset. 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. 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 survey participants needed to answer the questions were used for some questions. The hand cards were printed in English and Spanish. 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.

Persons 16 years and older and emancipated minors were interviewed directly. A proxy provided information for survey participants who were under 16 and for participants who could not answer the questions themselves.

The NHANES 1999-2000, 2001-2002, 2003-2004, and 2005-2006 demographics questionnaires are available on the NHANES website.

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 NHANES 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 survey participants from 0 through 79 years of age. All responses of participants aged 80 years and older are coded as “80.”

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.

RIDAGEMN: The age in months, at the time of the screening interview, is provided for participants who were less than 960 months of age. If the exact date of birth was not provided by the respondent, the age in months was calculated based on the imputed age in years at the time of the screening interview.

RIDAGEEX: The age in months, at the time of examination, is provided for participants who were less than 960 months of age at the time of examination.

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).

DMDBORN: Country of birth was recoded into three categories: 1) Born in 50 U.S. states or Washington, DC; 2) Born in Mexico; 3) Born elsewhere.

DMDCITZN: Citizenship status is reported using two codes: 1) Citizen by birth or naturalization; or 2) Not a citizen of the United States. Persons who were born in the U.S. or U.S. territories were coded as U.S. citizens.

DMDMARTL: The marital status question was asked of persons 14 years of age and older. Due to disclosure risks, marital status is only released for persons 20 years of age and older.

RIDEXPRG: Pregnancy status at the time of the health examination was ascertained for females 8–59 years of age. Due to disclosure risks pregnancy status is only released for women 20-44 years of age. The information used to code RIDEXPRG values included self-reported pregnancy status and urine pregnancy test results. Persons who reported they were pregnant at the time of exam were assumed to be pregnant (RIDEXPRG=1). Those who reported they were not pregnant or did not know their pregnancy status were further classified based on the results of the urine pregnancy test. If the respondent reported “no” or “don’t know” and the urine test result was positive, the respondent was coded as pregnant (RIDEXPRG=1). If the respondent reported “no” and the urine test was negative, the respondent was coded “not pregnant” (RIDEXPRG=2). If the respondent reported did not know her pregnancy status and the urine test was negative, the respondent was coded "could not be determined” (RIDEXPRG=3). Persons who were interviewed, but not examined also have an RIDEXPRG value = 3 (could not be determined).

DMDYRSUS: This variable is the number of years the participant has lived in the United States. Participants who were born outside the U.S. were asked the month and year when they came to the U.S. to live (DMQ.160). A small number of records were imputed because the participant did not report the month of their arrival. A month value of 7 (July) was used to impute DMDYRSUS for these respondents. The responses to the question were recoded into 9 categories ranging from less than one year to 50 years or more.

DMDEDUC3: This variable provides information on the highest grade or level of education completed by participants 6-19 years of age. The responses were re-coded as follows: single years of education (grades 1-12), high school graduate/GED, and post-high school. Codes “55” (less than 5th grade) and “66” (less than 9th grade) were used to categorize older youth who had very low education levels.

DMDEDUC2: This variable is the highest grade or level of education completed by adults 20 years and older. The response categories are: less than 9th grade education, 9-11th grade education (includes 12th grade and no diploma), High school graduate/GED, some college or associates (AA) degree, and college graduate or higher.

INDFMINC: 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 respondents 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 poverty guidelines specific to the survey year. 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.

INDHHINC: 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 INDFMINC 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 $75,000, then INDHHINC was categorized as “$75,000 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”.

Sample Weights: The following 8-year weights based on population estimates for Los Angeles County, California, during 1999-2006, are provided for use to obtain variance estimates based on the Taylor Series Linearization method:

• WTLAI8YR is the 8-year L.A. sample interview weight;
• WTLAM8YR is the 8-year L.A. sample exam weight; and
• WTLAF8YR is the 8-year L.A. fasting sample weight.

Variance Units: For this RDC-access-only dataset, actual survey sample strata (LATVSTRA) and primary sampling units (LATVPSU) are provided for the purpose of variance estimation.

Replicate Weights: 52 replicate interview weights (WTLI8R01 to WTLI8R52), 52 replicate examination weights (WTLM8R01 to WTLM8R52), and 52 replicate fasting weights (WTLF8R01 to WTLF8R52) are also included in the demographics file for use to obtain variance estimates based on a replication method. These replicate weights were created using Fay’s-adjusted balanced repeated replication (Fay’s BRR) method with an adjustment factor of 0.5.

Please also 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.