All samples consisted of data on individual twins registered in the VTSABD on a previous 3-month history of CD at any of the four waves as assessed with the Child and Adolescent Psychiatric Assessment (CAPA) – Child and Parent Version (Angold & Costello, 2000), which is based on DSM-III-R criteria (APA, 1987). Symptoms were reported by maternal, paternal or child self-reports across all waves. A symptom was rated as being present when either of the two parents or the child endorsed an item at any wave of data collection. This rating algorithm is referred to as the ‘symptom-or’ rule and is advantageous because it uses responses from multiple informants rather than relying on a single respondent (Simonoff et al. 1997). A CD diagnosis was assigned if subjects had three or more symptoms of CD.
