National Longitudinal Study of Adolescent Health
National Longitudinal Study of Adolescent Health
The National Longitudinal Study of Adolescent Health (Add Health) is an ongoing study of a nationally representative sample of more than 20,000 individuals that began with in-school questionnaires administered to adolescents in grades seven to twelve in the United States in 1994 and 1995. The in-school survey was followed by three waves of in-home interviews in 1995, 1996, and 2001–2002, with a fourth wave planned for2007–2008when the sample will be aged twenty-four to thirty-two.
Add Health was developed in response to a mandate from the U.S. Congress to fund a study of adolescent health and was designed by a nationwide team of multi-disciplinary investigators from the social, behavioral, and health sciences. The original purpose of Add Health was to understand adolescent health and health-related behavior with special emphasis on the forces that reside in the multiple contexts of adolescent life. Toward that goal, innovative features of the research design provided independent measurements of the social environments of adolescents, including contextual data on the family, neighborhood, community, school, friendships, peer groups, and romantic relationships.
The Add Health cohort has been followed over time as research questions turned to how adolescent experiences and behaviors were related to social, behavioral, and health outcomes in early adulthood. Across all interview waves, comprehensive data on health and health-related behavior were collected, including diet, physical activity, health service use, morbidity, injury, violence, sexual behavior, contraception, sexually transmitted infections, pregnancy and childbearing, suicidal intentions and thoughts, substance use and abuse, and delinquency. Data were also collected on such attributes as height, weight, pubertal development, mental health status, and chronic and disabling conditions. Achievement and academic progress were updated in each wave, including school performance, school problems, relationships with students and teachers, self-esteem, self-confidence, and future expectations for education, health, and family formation.
STUDY DESIGN AND DATA
Add Health used a school-based design in which a stratified sample of eighty high schools was selected from a sampling frame of all high schools in the United States. Schools were stratified by region, urbanicity, school type, ethnic mix, and size. For each high school selected, a feeder school was identified and recruited with probability proportional to its student contribution to the high school, yielding one school pair in each of eighty different communities. Overall, 79 percent of the schools contacted agreed to participate in the study.
During the1994–1995school year, in-school questionnaires were administered to over 90,000 students in selected schools. The in-school questionnaire provided measurement on the school context, friendship networks, school activities, future expectations, and a variety of health conditions. An additional purpose of the in-school questionnaire was to identify and select special supplementary samples of individuals in rare but theoretically crucial categories. School administrators also completed a questionnaire in the first and second waves of the study.
In a second stage of sampling using the school rosters of selected schools, adolescents and their parents were selected for in-home interviews constituting the Wave I (WI) in-home sample. To form a core sample, students were stratified in each school by grade and sex, and approximately 200 adolescents were sampled from each pair of schools. From answers provided on the in-school survey, supplemental samples were drawn based on ethnicity (Cuban, Chinese, and Puerto Rican adolescents), genetic relatedness to siblings (twins, full sibs, half sibs, and unrelated adolescents living in the same household), adoption status, and disability. Add Health also oversampled African American adolescents with highly educated parents. Finally, a special “saturated” sample was included in WI by selecting all enrolled students from two large schools and fourteen small schools for in-home interviews. Complete social network data were collected in the saturated field settings by generating a large number of romantic and friendship pairs for which both members of the pair have in-home interviews. The core sample plus the special samples produced a sample size of 20,745 adolescents in WI. The WI in-home sample is the basis for all subsequent longitudinal follow-up interviews. A parent also completed an interviewer-assisted interview at WI. Over 85 percent of the parents completed the parental interview.
In 1996 all adolescents in grades seven through eleven in WI (plus twelfth graders who were part of the genetic sample and the adopted sample) were followed up one year later for the Wave II (WII) in-home interview (N = 14,738). Response rates for the in-home interviews are 79 percent for WI and 88 percent at WII.
The in-school and Waves I and II in-home interviews constitute the adolescent period in Add Health and contain unique data about family context, school context, peer networks, spatial networks, community context, and genetic pairs. School context data come from the in-school surveys based on the census of students in each school, as well as from school administrator questionnaires. Peer network data are obtained from the in-school questionnaire where adolescents nominated their five best male and five best female friends from the school roster such that links to friends’ survey responses can be made. Spatial data indicating the exact location of all households were collected using Global Positioning System (GPS) devices, and used to merge with extant data describing the neighborhood and community contexts in which adolescents are embedded. Finally, the “genetic pairs data,” based on more than 3,000 pairs of adolescents who have varying degrees of genetic relatedness, represent a fully articulated behavioral genetic design and are unprecedented for a national study of this magnitude.
At Wave III (WIII), all original WI in-home adolescent respondents were reinterviewed from 2001 to 2002 with a response rate of 77 percent. This interview captured the Add Health cohort during their transition to adulthood when they were aged eighteen to twenty-six. In WIII, quota samples of 500 partners each in married, cohabiting, and dating couples were recruited by Add Health respondents, resulting in the partner sample of 1,507. Spatial data were again attached to the WIII individual-level data using the geocodes of the home residence. New data on family formation, college attendance and context, mentoring, and civic participation were collected at WIII. Also new at WIII was the collection of several biospecimens. Urine and saliva were collected to test for STDs and HIV, and buccal cell DNA was collected from the twins and full siblings in the genetic sample. The Web site supported by the Carolina Population Center of the University of North Carolina provides information about Add Health’s design and data availability.
Add Health has been funded over the period1994–2010by the National Institutes of Child Health and Human Development (P01 HD031921), with co-funding from seventeen other federal agencies. Add Health has an enlightened dissemination policy in that the scientific community is given access to the data at the same time as are project investigators. As a result, Add Health has become a national data resource for over 3,000 Add Health researchers who have obtained more than 200 independently funded research grants and have produced hundreds of research articles published in multidiscipli-nary journals and research outlets.
ADD HEALTH RESEARCH
Add Health research has exploited its unique design to explore the role of social contexts in the lives of adolescents, including the importance of family, peer, school, and neighborhood context as factors influencing adolescent development, behavior, health and well-being, and outcomes in the transition to adulthood. Ground-breaking research is identifying the social contexts that facilitate genetic expression in health behaviors, including substance use, sexual behavior, and delinquency and violence. Add Health has also made possible important new research on the health status and health behaviors of special populations such as disabled youth, adopted youth, youth living with surrogate parents or relatives, multiracial youth, youth with same-sex romantic attractions or relationships, and adolescents in immigrant families.
Add Health has also been an ideal data set for conducting health disparities research. Large and persistent racial, ethnic, and socioeconomic disparities in health exist across the life course in the United States. The reduction and ultimate elimination of health disparities has been identified as a major public health goal, exemplified by Healthy People 2010, the nation’s promotion and disease prevention strategy for the first decade of the twenty-first century. Add Health tracks longitudinal trends in race and ethnic disparities in the leading health indicators from Healthy People 2010 across multiple domains from adolescence to young adulthood. The interdisciplinary design of Add Health has resulted in a multidisciplinary user base of researchers in sociology, economics, human development, public health, biomedical sciences, and related fields who are exploring social, behavioral, and biological factors in developmental and health trajectories from adolescence into young adulthood.
LIMITATIONS OF ADD HEALTH
The school-based design of Add Health misses high school dropouts in the initial in-school survey, although dropouts after this point are followed in all subsequent interviews. Research from 2003 by J. R. Udry and Kim Chantala, examining the impact of this potential bias of missing high school dropouts, reports minimal impact. In addition, because Add Health is an omnibus study, many standard sociometric scales for various measures are included in shortened forms. Thus, although the breadth of topics covered in the Add Health instruments is comprehensive, the depth may not be present for all topics.
SEE ALSO National Family Health Surveys; National Longitudinal Survey of Youth; Panel Study of Income Dynamics; Sample Attrition; Sampling; Survey; Surveys, Sample
BIBLIOGRAPHY
Add Health. The National Longitudinal Study of Adolescent Health. University of North Carolina, Carolina Population Center. http://www.cpc.unc.edu/addhealth.
Udry, J. R., and Kim Chantala. 2003. Missing School Dropouts in Surveys Does Not Bias Risk Estimates. Social Science Research 32 (2): 294–311.
Kathleen Mullan Harris
Hedwig Lee