Chapter 1. Demography (1999-2018)

Section 2. Eligible Sample

All survey participants who have a household interview record have a Demographics file record.

• The Demographics questionnaire items include family-level and individual-level information. The target age groups for the Demographics questions vary.
• Please review the NHANES 1999-2018 Family and Sample Person Demographics section questionnaires and codebooks carefully to review the content of the Demographic file and determine the target age groups for the questionnaire items.

Section 3. Interview Setting and Mode of Administration

Demographics information was collected in the home prior to the health examination.

• Computer-assisted personal interviewing (CAPI) methodology was used.
• Persons 16 years of age and older and emancipated minors were interviewed directly.
• A proxy provided information for survey participants who were less than 16 years of age and for individuals who could not answer the questions themselves.
• The survey participants selected the language of interview (English or Spanish) or requested that a translator be used.
• Hand cards showing response categories 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.

Section 4. Analytic Notes

• RIDRETH2 race/ethnicity recode should be used to compare NHANES 1999-2018 estimates of health measures with those of NHANES III.
• Income variables: None of the income values reported were imputed.
• DMDMARTL: Given the sample design changes for 2007-08 and possible disclosure risks, we are releasing marital status only for persons 20 years of age and over.
• Previously marital status was released for ages 14+.
• The number of married persons aged 14-19 is less than 1%'.
• Starting in 2007, a new sample design was implemented.
• All Hispanics were oversampled, not just Mexican Americans.
• In addition, for each of the race/ethnicity domains, the 12-15 and 16-19 year age domains were combined and the 40-59 year age minority domains were split into 10 year age domains 40-49 and 50-59.
• This has led to an increase in the number of participants aged 40+ and a decrease in 12-19 year olds when compared to domains in previous cycles.
• Lastly, pregnant women were no longer oversampled.
• Based on these changes, unweighted frequencies of certain variables may differ slightly in this survey cycle compared to survey cycles prior to 2007.
• For more details on the sample design, refer to the NHANES 2009 - 2010 Public Data General Release File Documentation, available on the NHANES website at: https://wwwn/cdc/gov/nchs/nhanes/continuousnhanes/default.aspx?BeginYear=2009.
• As noted in the “Component Description” section above, the sample design for NHANES 2011-14 includes an oversample of Asian Americans.

Section 5. Data Processing and Editing

• SDDSRVYR represents the data release number. A code of ‘1’ denotes the NHANES 1999-2018 data release cycle.
• RIDSTATR is a recoded variable representing interview and examination status. The status codes for a small number of sample persons who were interviewed in their homes, but not examined, were recoded and these individuals are included in the “interviewed only” category.
• RIDEXMON is a variable indicating 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.
• RIDAGEYR: This is the age of the sample person at the time of the screening interview. Age in years is reported by single year of age for persons from 1 through 84 years of age. For older adults, age in years was top coded at 85 years to reduce the risk of disclosure. All adults 85 years and older have a RIDAGEYR value of ’85’. In NHANES 1999-2018, the weighted mean age for participants 85 years and older is 88 years.
  Otherwise, an imputed date of birth is created using the following procedures: When date of birth information is missing or refused, but age in years is provided by the sample person: If month of birth is missing or not given it is imputed as 7. If day of birth is missing or not given, it is imputed as 1. Corrections are made to this imputed information for sample persons who are less than 1 year of age at the time of screening.
• RIDAGEMN is age in months at household screening, provided only for those who were less than 85 years of age. If exact date of birth is not provided by the sample person, then the age in months is calculated based on the imputed age at screener to allow the sample person to proceed with the questionnaire and examination.
• RIDAGEEX was not calculated for individuals with an imputed age.
• RIDRETH1: This race/ethnicity variable is derived by combining responses to 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 race including non-Hispanic multiracial (RIDRETH1=5)
• RIDRETH2 is the race/ethnicity recode that can be linked to the NHANES III race/ethnicity variable. In other cases, the coding was similar to RIDRETH1.
• DMDBORN: Country of birth was recoded into three categories: 1) born in 50 US states or Washington, D.C.; 2) born in Mexico; and 3) born in any other location or foreign country
• INDFMINC: This variable is the total family income variable. NCHS used the US Bureau of the Census Current Population Survey (CPS) definition of “family” to group household members into one or more families (US Census, 2003). The CPS defines a family as: “a group of two people or more (one of whom is the householder) related by birth, marriage, or adoption and residing together;” all such people (including related subfamily members) are considered to be members of one family.
• Over eighty percent of the NHANES households were single-family households; the remaining households comprised 2 or more CPS families. After the information about sources of income was obtained in the Family Interview Income section questionnaire (INQ), the respondent was asked to report the total combined family income for themselves and the other members of their family in dollars (question INQ200).
• If the respondent refused to answer INQ200 or did not know the total combined family income, an income screener question was asked (question INQ220) to query if the total family income was < $20,000 or≥ $20,000.
• If the respondent answered INQ220, a follow-up question asked the respondent to select an income range (question INQ230) from a list of income ranges listed on a printed hand card
• If a household comprised a single CPS family, the family income value was used as previously described.
• When more than one CPS family resided in the household, two methods were used to compute estimated total household income.
• The income information provided by respondents for each CPS family (method 1) was used whenever possible because this information was considered to be more reliable than information provided by a household reference person who may or may not have had firsthand knowledge of the total household income.
• Total household income could not be calculated for multifamily households when income range data were reported by any of the families in the household and thus the household income data are coded as missing.
• The Department of Health and Human Services’ (HHS) poverty guidelines were used as the poverty measure to calculate this index. 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) (formerly Food Stamp Program), Special Supplemental Nutrition Program for Women, Infants, and Children (WIC), and the National School Lunch Program.
• The values were not computed if the income screener information (INQ 220: < $20,000 or ≥ $20,000) was the only family income information reported Values at or above 5, 00 or more because of disclosure concerns.
• DMDMARTL is the derived marital status variable. Marital status data were collected for sample persons 14 years of age and older. For a number of these persons marital status was imputed from other questionnaire items that made reference to their marital status. Marital status remains missing for 566 sample persons 14 years of age and older due to lack of sufficient data for imputation.
• PREGNANCY STATUS: Pregnancy status at the time of examination (RIDEXPRG) is reported for females 8-59 years of age. Females 8-59 years of age received a urine pregnancy test prior to the dual energy x-ray absorptiometry (DXA) exam.
• Persons who reported they were pregnant at the time of exam were assumed to be pregnant; if the urine test was negative, but the subject reported they were pregnant, the status was still coded as pregnant at exam (RIDEXPRG=1). If the urine pregnancy results were negative and the respondent said they were not pregnant, the respondent was coded not pregnant at examination (RIDEXPRG=2). Persons who were only interviewed have an RIDEXPRG value = 3 (could not be determined).
• Note: The pregnancy recode variable previously released with NHANES 1999-2000 was called RIDPREG. RIDPREG was created to allow analysts to exclude pregnant women from analyses; this determination was based on the most comprehensive information available at the time of data release.
• RIDPREG was a more conservative indicator of pregnancy status, and was derived using several sources of information. For subjects who were only interviewed, pregnancy status at the time of survey screening, and menstrual status were used to determine possible pregnancy status. Approximately 20-25 individuals in the NHANES 1999-2018 sample could have different pregnancy status values using the RIDEXPRG and RIDPREG algorithms.
• The following new variables are included in this updated NHANES 1999-2018 Demographic file: DMDCITZN: Citizenship status is reported using two codes: 1) citizen by birth or naturalization or 2) Not a citizen of the US Persons who were born in the US or US territories who acquire citizenship at birth were coded as US citizens.
• DMDYRSUS: This variable is the number of years the respondent has lived in the United States. Respondents who were born outside the US were asked the month and year when they came to the US to stay (DMQ 160). The responses to the question were recoded into 9 categories ranging from less than one year to 50 years or more.
• DMDHHSIZ: This variable is the number of people in the respondent’s household. The values for this variable range from 1 to 7 with 7 being the code used for households comprised of 7 or more members.
• DMDEDUC3: This variable provides information on the highest grade or level of education completed by respondents 6-19 years of age. The responses were recoded by NCHS as follows: single years of education (grades 1-12), high school graduate/GED, and post-high school. 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.
• DMDEDUC2 provides more detailed information on education levels of adults compared to the categories that were previously released in the NHANES 1999-2018 Demographic file.
• DMDSCHOL: This variable is school attendance status. It is asked for respondents 6-19 years of age. A code of ‘1’ denotes persons who were only interviewed and a code of ‘2’ denotes persons who were interviewed and examined.
• DMQMILIT: This variable provides information on veteran’s/military status. Veterans include persons who served in the armed forces of the United States, specifically, the US Army, Navy, Air Force, Marine Corps, and Coast Guard.
• Household Reference Person: The household reference person is defined as the first household member 18 years of age or older listed on the Screener household member roster who owns or rents the residence where members of the household reside. The household reference person is comparable to “family reference person” in previous NHANES. 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 (DMDHRBRN), education level (DMDHREDU), and marital status (DMDHRMAR).
• Additionally, information on the education level of the household reference person’s spouse is included (DMDHSEDU).
• SIAINTRP denotes if an interpreter was used during the Sample Person Questionnaire interview. The language spoken by the respondent is not reported.
• FIALANG is the language used during the Family Questionnaire interview.
• MIALANG is the language used during the Mobile Examination Center (MEC) interview.
• AIALANG is the language used for the audio-computer-assisted self interview (A-CASI) portion of the MEC interview.
• RIDAGEEX is provided for subjects under 80 years of age at the time of household screening (RIDAGEYR<80). All responses of age 80 years and older are coded as ‘80’. The reporting of age in single years for adults 80 years and older was determined to be a disclosure risk.
• Due to disclosure risks marital status will only be released for persons 20 years of age and older. In these instances, INDHHIN2 was coded as missing.
• Frequency counts were checked, “skip” patterns were verified, and the reasonableness of question responses were reviewed. Edits were made to some variables to ensure the completeness, consistency, and analytic usefulness of the data.
• When information was missing for any of the CPS families in the household, the estimated household income value, provided by a household reference person, was used to compute estimated total household income.
• RIDRETH1: This is the race-ethnicity variable that can be linked to the previous NHANES race-ethnicity variable in 1999-2010. Non-Hispanic Asian participants are grouped with other non-Hispanic races in code “5” (other non-Hispanic race including non-Hispanic multiracial) in RIDRETH1.
• RIDRETH3: This is the new race-ethnicity variable included in the demographics file since the xxxx-xxxx survey cycle to accommodate the oversample of non-Hispanic Asian. Code “5” was not used in RIDRETH3.
• DMDBORN4: Due to the concerns of disclosure risk, starting in 2011, country of birth was recoded into two categories: 1) Born in 50 US states or Washington, DC; and 2) Born in other countries, including US territories.
• DMQMILIZ: This is a new variable included in the 1999-2018 dataset to provide information on whether the participant has ever served on active duty in the US Armed Forces, military Reserves, or National Guard. Active duty does not include training for the Reserves or National Guard, but does include activation, for service in the US or in a foreign country, in support of military or humanitarian operations.
• DMQADFC: This is another new variable in the 1999-2018 dataset to provide veteran related information. It describes whether the participant has ever served in a foreign country during a time of armed conflict or on a humanitarian or peace-keeping mission. This would include National Guard or reserve or active duty monitoring or conducting peace keeping operations in Bosnia and Kosovo, in the Sinai between Egypt and Israel, or in response to the 2004 tsunami or Haiti in 2010.
• SIALANG: This variable indicates the language (English or Spanish) used during the sample person questionnaire interview conducted at the participant’s home. The language spoken by the respondent is only available through the NCHS Research Data Center (RDC). The ACASI portion was translated into Chinese (traditional/Mandarin, simplified/Mandarin, and traditional/Cantonese), Korean, and Vietnamese to accommodate the Asian oversampling. The three categories reported are: 1) English, 2) Spanish, and 3) Asian languages.
• The reported dollar amount was re-coded into range values. 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). If family income was reported as a more detailed category, the midpoint of the range was used to compute the ratio. The values were not computed if the income data was missing.
• INDHHIN2: This variable indicates the total annual household income in dollar ranges. 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.
• 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 4. 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’.
• DMDHHSZE: This variable is the number of adults aged 60 years or older living in the participant’s household. Due to disclosure concerns, households that are comprised of 3 or more adults aged 60 years or older are included in the category that is labeled ‘3 or more.
• Due to disclosure concerns, the household reference person’s age in years variable was recoded to a categorical variable (<20, 20-39, 40-59, or 60+ years); the household reference person’s education level and their spouse’s education level variables were recoded from the original 5 categories to 3 categories (1 = Less than high school; 2 = High school grad/GED or some college/AA degree; 3 = College graduate or above); and the household reference person’s marital status variable was recoded from the original 6 categories to 3 categories (1 = Married/Living with partner; 2 = Widowed/Divorced/Separated; 3 = Never married).

Section 6. Quality Assurance & Quality Control

The NHANES computer-assisted personal interview (CAPI) software program that was used to collect the interview data had built-in data edit and consistency checks.

• The data edit checks alerted the interviewer when unusual or potentially erroneous data values were recorded.
• Questionnaire “skip” patterns were pre-programmed in the questionnaires to reduce respondent burden.
• Online information screens provided the interviewers with standardized descriptions of the terminology and concepts that were used in the questionnaires.

After data collection, interview records were reviewed by the NHANES field office staff for accuracy and completeness.

• A subset of the household interviews was verified by re-contacting the survey participants.
• The interviewers were required to record several interviews and the audio-taped interviews were reviewed by NCHS and contractor staff.
• The NHANES quality assurance and quality control procedures are described in the field procedures manuals that are posted on the NHANES website.
• The CAPI system is programmed with built-in consistency checks to reduce data entry errors.

Section 7. References

1. U.S. Census Bureau. Current Population Survey (CPS) Definitions and Explanations. 2003. http://www.census.gov/population/www/cps/cpsdef.html.
2. U.S. Census Bureau. Current Population Survey (CPS) Definitions and Explanations. Revised 1/20/04. http://www.census.gov/population/www/cps/cpsdef.html.
3. U.S. Census Bureau. Current Population Survey (CPS) Definitions and Explanations. Revised 11/18/08. http://www.census.gov/population/www/cps/cpsdef.htm.
4. U.S. Department of Health & Human Services. Poverty Guidelines, Research, and Measurement. Washington, DC: U.S. Department of Health & Human Services, January 2011. http://aspe.hhs.gov/POVERTY/
5. U.S. Department of Health & Human Services. Poverty Guidelines, Research, and Measurement. Washington, DC: U.S. Department of Health & Human Services, January 2013. http://aspe.hhs.gov/POVERTY/index.shtml.
6. U.S. Department of Health & Human Services. Poverty Guidelines, Research, and Measurement. Washington, DC: U.S. Department of Health & Human Services. https://aspe.hhs.gov/prior-hhs-poverty-guidelines-and-federal-register-references