At every assessment, each parent and twin is interviewed separately by a different interviewer. Interviewers have a B. A. or M. A. in psychology and have completed extensive training and observation. Our approach to diagnosis is based on DSM-IV, but to maintain comparability to previous MTFS samples, our interviews assess both DSM-IV and DSM-III-R criteria. Diagnoses at intake were lifetime, whereas diagnoses at the three-year follow-up assessments focus on symptoms occurring since the last assessment. Past 12-month diagnoses are available for some disorders as well (e.g., substance use disorders). The clinical assessment of parents was very similar to that described below for twins at their second (age 17-18) follow-up. Phone interviews are conducted only with those who are unable to visit; otherwise, all follow-up assessments are done during in-person visits to our laboratory.
