National Longitudinal Study of Adolescent Health
The National Longitudinal Study of Adolescent Health (Add Health) is the only nationally representative study of adolescent health, which has spawned over 1500 peer-reviewed publications on many issues related to adolescent health and health risk behaviours.
The Add Health survey aims to investigate adolescent physical and mental health, as well as disparate factors that may influence health, such as neighbourhood safety, involvement in violence, social integration, family structure, and romantic relationship history. The unique aspect of Add Health is its focus on social networks as a means of understanding adolescent health. Rather than relying on subjects' reports of peer behaviour, Add Health obtains information directly from some subjects' peers.
In the late 1980s and early 1990s, the HIV/AIDS epidemic required a deep understanding of sexual risk-taking that social scientists could not provide; however, adolescent sexuality research was controversial. In May 1991, the National Institute of Child Health and Human Development (NICHD) approved a five-year national study of adolescent sexual risk-taking, which unleashed a firestorm of controversy. For instance, Senator Jesse Helms contended that the survey constituted "support for homosexuality and sexual decadence" (Boonstra 2001).
This political pressure on the Bush administration was so strong that only months after the initial grant was announced, Secretary of Health and Human Services Louis Sullivan withdrew the grant on the grounds that the survey would "inadvertently convey a message that would be counterproductive to our efforts to discourage casual sex among teenagers."
The United States Congress's 1993 National Institutes of Health reauthorization banned future research aimed exclusively at adolescent sexual behaviour, but proposed in its stead a more comprehensive study of adolescent health which would examine many health risk-taking behaviours in addition to sexual risks, including violence and the use of tobacco, alcohol, and illegal drugs.
Add Health is directed by Kathleen Mullan Harris (UNC, Chapel Hill), with fieldwork done by National Opinion Research Center (Waves I and II) and Research Triangle Institute (Waves III and IV). It is funded by the NICHD and 23 other federal agencies and foundations. The study was designed by J. Richard Udry, Peter Bearman, and Kathleen Mullan Harris, with special assistance from Ronald R. Rindfuss and Barbara Entwisle.
Sampling procedure 
Add Health used three sampling frames, only one of which was available prior to the study.
The initial sampling frame is a stratified list of 26,666 American high schools, defined as schools with an 11th grade and more than 30 students from which high schools were selected with probability proportional to size.
Eighty schools were selected from this list. Subsequently, for those high school without a 7th grade, a second sampling frame was created of high schools' corresponding feeder (middle) schools; a single feeder school for each of the 60 high schools without 7th grade was selected with probability proportional to percentage of high school's entering class that school contributed. Out of the 60 high schools, four had no predominant feeder schools, so 56 feeder schools were selected out of which 52 opted to participate. The total sample was 132 schools, with an overall participation rate of 80%.
A third frame comprising all students at these schools was created by combining a school-provided student roster with a list of students who completed the in-school survey but did not appear on the school roster.
Add Health used stratified, 2-stage element sampling. The primary sampling units were high schools chosen from a stratified list with probability proportional to size; stratification was by region (northeast, midwest, south, west), urban/suburban/rural, school size (30—125, 126—350, 351—775, 776+), school type (public, private, parochial), percent white (0, 1—66, 67—93, 94—100), percent black (0, 1—6, 7—33, 34—100), grade span and school type (K—12, 7—12, 9—12, 10—12, vocational, alternative, special ed). Not all combinations of the above parameters were available.
52 feeder schools (middle schools) for these high schools were selected as detailed above. All students in selected schools (N=132 agreed to participate, of which 129 opted to use class time to give the survey to students) were given the in-school Add Health questionnaire (N=90,118) in Sept 1994 – April 1995.
For the in-home questionnaire, the secondary and ultimate sampling units were students in the 134 selected schools chosen with unequal probability. The in-home subsample was selected from a school-selected roster plus those students who completed the in-school survey but did not appear on the school's roster. The in-home sample of 27,000 included a nationally representative core of 12,105 adolescents in grades 7 to 12 chosen with equal probability; all students from selected ``saturated schools (i.e., chosen with probability related to school size); a genetic oversample comprising twins, full siblings, half siblings, siblings of twins, and non-related adolescents residing together; minority oversamples of disabled, blacks from well-educated families, Chinese, Cubans, and Puerto Ricans. These oversamples were identified by students' answers on the in-school survey.
The saturated schools are intended to demonstrate peer effects on students in keeping with the focus of Add Health on environmental influences on student health decisions. For instance, the use of these saturated schools enabled researchers to discover that ``virginity pledges have a substantial effect on students in high schools where students socialize mainly with each other only when most others in their school do not make such a pledge, so such strategies cannot work universally.
The genetic oversample allowed researchers to attempt to decouple genetic and environmental effects by comparing the behavior of twins with that of full, half, and step siblings; such comparisons are useful because the tendency to engage in certain health risks is thought to be heritable, but there has been little study of the manifestation of these traits in adolescents, and no study that looked at the adolescents in their social contexts. Because there were not enough genetically related students in the original sample of 134 schools, additional schools were selected to augment the size of the genetic sample; these additional subjects lack sample weights, but are intended to be used only in analysis which do not require weights, such as comparisons between siblings and twins.
The minority oversamples allows researchers to study minority groups which would otherwise be too small, and provide information to shape minority adolescents' health programs.
The Wave I In-home interviews were conducted with 20745 adolescents and 17700 parents, April 1995 – Dec 1995.
Wave II occurred a year later, with 14,738 adolescent in-home interviews in April 1996 – August 1996 with those wave I subjects who could be found.
Wave III occurred six years after Wave I in order to examine the transition from adolescence to adulthood (Aug 2001 – Apr 2002, subjects aged 18—26) and correlations between adolescent behavior and health, education attainments, labor market participation, family status, community involvement.
The successive phases of the study allow researchers to attempt to make causal inferences by examining the effects of earlier factors on later health decisions.
Wave I was conducted in several modalities. Students completed an in-school written questionnaire and administrators completed a written questionnaire about the characteristics of their schools. The in-school questionnaire served as a screen and means of supplementing school rosters for sampling for the in-home interview, and it also allowed researchers to obtain information from entire peer groups.
More detailed information was obtained in in-person interviews of both students and parents; for topics such as sex and drug use, students listened to tape-recorded questions through earphones and entered their answers into a laptop (Boonstra 2001). The tape-recorded questions were used in order to avoid interview or parental response bias, and the laptop to assure students of the confidentiality of their answers.
In wave II, school information was updated via telephone interview. This interview could be done by telephone, at lower cost than an in-person visit, because school administrators are only used to provide contextual information.
In-home interviews were conducted as above for both waves II and III. Despite the massive size of the survey and the high cost of in-person interviews, the quality of the data was seen as worth the high cost.
Content of survey 
The in-home survey covers many topics, including:
- demographic variables,
- social or familial connections with other study participants,
- household composition,
- frequent activities including exercise and sports,
- feeling of belonging in school and neighborhood,
- close relationships with adults,
- measures of physical and mental health,
- previous day's food intake,
- access/use of medical care, weight and eating disorders,
- use of vehicle safety devices such as helmets and seatbelts,
- health education,
- school disciplinary record,
- sexual history and attitudes towards sexual relationships,
- sexually transmitted disease history,
- knowledge about birth control,
- detailed information about past and ideal romantic relationships,
- friend risk-taking behavior,
- illegal and legal drug use,
- ease of access to weapons and drugs,
- experiences with violence,
- connections between drugs and violence,
- reproductive history,
- religious attitudes and behavior,
- educational plans and future predictions, and
- interviewer description of respondent.
Much survey content remains the same, but some new topics such as more detailed nutritional self-report, use of sunblock, abusive relationships, more specific information about risky sexual behavior, were included in subsequent waves. In addition, the educational progress of participants raised new questions about their transition into work or college.
- Add Health homepage
-  Description and citation information provided by the Data Sharing for Demographic Research (DSDR), a project of the Inter-university Consortium for Political and Social Research (ICPSR)
- Bearman, Peter S., Jones, Jo, and Udry, J. Richard. (1997) The National Longitudinal Study of Adolescent Health: Research Design
- Boonstra H (2001) "The `Add Health' Survey: Origins, Purposes and Design", Guttmacher Report on Public Policy, 4:3, June 2001
- Chantala K, Tabor J (1999) "Strategies to Perform a Design-Based Analysis Using the Add Health Data", June 1999