The NCS-A fieldwork was carried out by the same professional national field interview staff from the Survey Research Center (SRC) at the University of Michigan that carried out the NCS-R. There were 197 interviewers supervised by a team of 18 experienced regional supervisors. A study manager located at the central SRC facility in Michigan oversaw the work of the supervisors and their staff. Upon making in-person contact, the interviewer answered questions before obtaining written informed consent from the parent and then written informed assent from the adolescent. Interviews were never conducted with a non-emancipated adolescent unless at least one parent or guardian was present in the home during the interview. However, no parent consent was requested in the small number of cases where we interviewed an emancipated minor. Adolescents were paid $50 for participating in the survey. The Human Subjects Committees of both Harvard Medical School and the University of Michigan approved these recruitment, consent, and field procedures.