In a second continuation of the Add Health program project, a fourth in-home interview was conducted in 2008 with the original Wave I respondents*. The Wave IV study was designed as a follow-up of the nationally representative sample of adolescents first interviewed in 1994 and 1995. At Wave IV, we administered a comprehensive personal interview that included physical measurements and biospecimen collection.
The scientific purpose of Wave IV is to study developmental and health trajectories across the life course of adolescence into young adulthood using an integrative approach that combines social, behavioral, and biomedical sciences in its research objectives, design, data collection, and analysis. At the time of the interview, the Wave IV participants were 24 to 32 years old** and settling into young adulthood. At the same time that the Add Health cohort was assuming adult roles and responsibilities, they were also developing crucial health habits and lifestyle choices that set pathways for their future adult health and well-being. By integrating biological information into models of health and human development, the Wave IV design stimulates interdisciplinary research teams that bridge the social and biomedical sciences.
Through Wave IV data collection, we obtained longitudinal survey data on the social, economic, psychological, and health circumstances of our respondents, as well as longitudinal geographic data. Several features of Wave IV data collection represented new directions in Add Health, including methods to obtain more objective measures of health status and health behavior to capture prevailing health concerns, and methods to obtain biological markers of future chronic health conditions and disease. Wave IV employed innovations in the collection of biological measures in a field setting on a large national sample that were both practical and groundbreaking. We collected DNA on the entire national sample and obtained indicators of metabolic syndrome and immune functioning using noninvasive procedures. The combination of longitudinal social, behavioral, and environmental data collected over 10 years with new biological data expands the breadth of research questions that can be addressed in Add Health regarding pre-disease pathways, gene-environment interactions, the relationship between personal ties and health, factors that contribute to resilience and wellness, and environmental sources of health disparities.
*A pretest with 193 respondents occurred in 2007.
**52 respondents were 33-34 years old at the time of interview.
Wave IV data collection was carried out by RTI International under sub-contract to the University of North Carolina at Chapel Hill. At Wave IV, the Add Health sample was dispersed across the nation with respondents living in all 50 states. We located 92.5% of the Wave IV sample and interviewed 80.3% of eligible sample members. We collected survey data using a 90-minute CAPI/CASI instrument. Less sensitive questionnaire sections were administered with the assistance of an interviewer (computer-assisted personal interview, or CAPI). More sensitive questionnaire sections were self-administered using CASI technology (computer-assisted self interview). Immediately following the 90-minute interview, interviewers took physical measurements and collected biological specimens, which took around 30 minutes. We collected saliva samples for buccal cell DNA and blood spots for a lipid panel and assays of C-reactive protein (hsCRP), glycosolated hemoglobin (HbA1c), glucose (Glc), and Epstein-Barr virus (EBV) antibodies. Saliva samples were mailed by the interviewers to the Institute for Behavioral Genetics in Boulder, CO, the DNA subcontractor, where the DNA was extracted, quantified, genotyped, and stored. Dried blood spots were mailed to the University of Washington Medical Center Immunology Lab, in Seattle WA, for the hsCRP, glucose, and EBV assays and the lipids profile, and to , in Palm City, Florida, for assay for HbA1c. Interviewers also obtained residential latitude and longitude readings using a Global Positioning System (GPS) device.
In determining questionnaire content, Add Health consulted widely with experts on specific health outcomes and with representatives of NIH institutes who had contributed co-funding support to the project. The Wave IV survey maintained longitudinal elements from earlier waves of data collection, and added new questions and sections that were more pertinent to the lives of young adults. Questions that reflected continuity with earlier content included updates of sociodemographic transitions central to the movement into adulthood and information about continuity and change in multiple indicators of physical and mental health status and health care; in social, emotional, spiritual, and physical contexts, including contact and relationships with parents; in sexual patterns and reproductive health; and in risk taking, social, and antisocial behavior.
New data were collected in a number of domains, reflecting funded research needs and salient aspects of the young adult years of the 20s. Survey questions were expanded on educational transitions, economic status and financial resources and strains, sleep patterns and sleep quality, eating habits and nutrition, illnesses and medications, physical activities, emotional content and quality of current or most recent romantic/cohabiting/marriage relationships, and maltreatment during childhood by caregivers. An inventory of the “Big 5" personality dimensions was added, as were indicators of interpersonal and occupational stressors, loneliness, and attitudes about parenting. Expanded questions on substance addiction and dependency and items on intersections and balance between work and family responsibilities were also added. Finally, two memory tasks were added, supplementing earlier measures of oral vocabulary (AHPVT).
Wave IV collected information on the dates and circumstances of key life events occurring in young adulthood, including a complete marriage and cohabitation history, full pregnancy and fertility histories from both men and women, an educational history of dates of degrees and school attendance, contact with the criminal justice system, military service, and various employment events, including the date of first and current jobs, with respective information on occupation, industry, wages, hours, and benefits. We also collected a residential history of state locations since Wave III and recent mobility, and updated US citizenship status when applicable.
At Wave IV, geographic data was collected in two forms: home addresses and latitude/longitude coordinates from GPS devices. Geocodes were obtained from all reported addresses using state of the art methods as well as from the latitude and longitude coordinates of the home residence. Add Health does not release geocodes, but a set of core community variables are available to Add Health users as in previous waves.
Given the size and geographic spread of the Wave IV sample, and the non-clinical setting of our interviews, we chose methods to collect biological data that were noninvasive, innovative, cost-efficient, and practical for population-level research. Trained and certified interviewers used a finger prick to obtain whole blood spots that were dried and shipped for laboratory analysis. Saliva DNA was collected for genotyping a set of genetic markers.
Anthropometric Measures - Interviewers measured the weight, height and waist circumference of Wave IV participants according to standardized protocols.
Cardiovascular Measures - Interviewers measured the systolic blood pressure, diastolic blood pressure, and pulse of Wave IV participants according to a standardized protocol.
Metabolic Measures - Dried blood spots obtained from a finger prick were assayed for lipids, glucose, and glycosylated hemoglobin (HbA1c).
Measures of Inflammation and Immune Function - High sensitivity C-reactive protein (hsCRP) and Epstein-Barr virus (EBV) were assayed in dried blood spots.
Genetic Measures - In collaboration with the Institute for Behavioral Genetics (IBG) in Boulder, CO, Add Health collected, extracted, quantified, and stored DNA samples from all respondents in Wave IV.
Genome Wide Association Study
A Genome Wide Association Study (GWAS) will be conducted on the approximately 12,200 Wave IV saliva samples from respondents who agreed to archive their specimens for future research. Funding has been obtained to assay a subset of these specimens and additional funding is being pursued for the remainder of the work. No results will be released until all samples have been assayed and their quality confirmed. When released, the genetic data and a subset of the phenotypic data will be available through dbGaP (database of Genotypes and Phenotypes).
Intra-Individual Variation (IIV) Study
To estimate the intra-individual variation (IIV) of biological measures in the Add Health population at Wave IV, 100 Wave IV respondents were selected for repeat collection of biomarkers at a follow-up visit. Each respondent who consented to participate in the follow-up study was interviewed twice. At the first interview, a field interviewer administered the full Wave IV questionnaire and collected anthropometric measurements and biological samples. One or two weeks later, on or about the same day of the week and the same time of day, the same interviewer administered an abbreviated questionnaire and collected the same anthropometric measures and biological samples that were collected during the first visit. Analysis of the repeat observations provides important information on the reliability of the biological data collected at Wave IV. Add Health is the first major national social science study to include this innovation in its design and assessment of biological data collection.