Screening items for CD were included in the first interview but our analyses herein focus on the more complete assessment in the second-wave SRQ. In this questionnaire, twins reported how often they had engaged in 11 specific antisocial behaviors in childhood and adolescence. As detailed previously,16 the DSM-III-R17 CD criterion regarding forced sex was omitted in the SRQ because of its very low expected prevalence and its potential offensiveness. Two other criteria with similar content (has broken into someone else's house, building, or car and has stolen without confrontation) were combined into a single item. For 9 of the 11 SRQ items, 4 responses were possible (0, 1-2, 3-5, and ≥6 times) and assessed for 2 different developmental periods: before age 15 years and ages 15 to 17 years. The current analyses used the higher-frequency category reported for these 2 periods. The remaining 2 items (physical fights and telling lies), which occurred with higher frequency, were assessed only for the period prior to age 15 years, using 4 response options (never, rarely, sometimes, and often). The response rate for 1
