fourth edition (DSM-IV).25 We considered attention-deficit/hyperactivity disorder to be present if the child met DSM-IV criteria for this disorder at either 10 or 12 years of age; similarly, we deemed children to have conduct disorder if they met the relevant DSM-IV criteria at either of these ages. We classified children as having extreme borderline personality characteristics if they scored at or above the 95th centile on a shortened version of the Shedler-Westen assessment procedure-200 for adolescents (SWAP-200A),26 which mothers completed when the twins were aged 12.27 We calculated the score with the self harm item excluded. At age 12, children completed the 10 item version of the multidimensional anxiety scale for children (MASC).28 Children scoring at or above the 95th centile (raw score of 13 or more) constituted the “extreme” anxiety group. We used scores of 20 or more on the children’s depression inventory (CDI) to indicate clinically significant depressive symptoms.29 30 We assessed the definite presence of any psychotic symptoms during a private interview conducted with each child, as previously reported.31 Finally, we individually tested children’s IQ at age 12 by using a short form of the Wechsler intelligence scale for children, fourth edition.32 33
