The data for this analysis are from an interview study, conducted from 1999 to 2004, assessing DSM-IV axis I and axis II disorders (26). Interviewers were largely senior clinical psychology students at the end of their 6-year training course (including at least 6 months of clinical practice) and psychiatric nurses with years of clinical experience. They were trained by professionals with extensive experience with the instrument. The interviews were mostly conducted face-to-face, although for practical reasons 231 interviews (8.3%) were conducted by telephone. Each twin in a pair was interviewed by a different interviewer.
