Lifetime-ever clinical data for each individual in the BDRN study were collected by a trained BDRN interviewer (research psychologist or psychiatrist) using a semi-structured psychiatric interview, the Schedules for Clinical Assessment in Neuropsychiatry (SCAN).14 Further clinical data were gathered from participants' psychiatric case notes. Clinical interview and case-note data were combined to make best-estimate lifetime-ever diagnoses according to DSM-IV and ratings of lifetime-ever clinical characteristics. The Global Assessment Scale (GAS) was used to provide a measure of overall level of functioning during each participant's worst lifetime episodes of both depression and mood elevation;15 scores on this scale range from 1 (severe psychiatric disturbance) to 100 (good mental health). In cases of doubt, clinical ratings were made by at least two members of the research team unaware of each other's ratings, and consensus was reached through discussion where necessary. Interrater reliability was high. Mean kappa statistics were 0.85 for DSM-IV diagnoses and 0.81–0.99 for other key clinical categorical variables; mean intraclass correlation coefficients were 0.91–0.97 for key clinical continuous variables.
