In keeping with the expected rate of child conduct problems in the general population (Moffitt, 1993, 2003), 9.6% of participants evidenced clinically significant levels of CP (as defined in the CBCL and SCICA manuals) according to both parental report and child interview. Boys evidenced significantly higher rates of raw CP than did girls [mean = 1.98 (s.d. = 2.11) for boys and mean = 1.20 (s.d. = 1.49) for girls; Cohen’s d = 0.43, p < 0.05). Mean levels of parent–child conflict were also higher in boys as compared with girls (Cohen’s d = 0.23, p < 0.05). Although parent–child conflict was not significantly associated with twin age (r = 0.01, n.s.), CP demonstrated a small and negatively signed associated with age (r = –0.11, p < 0.05). Sex and age were thus regressed out of CP prior to analyses (McGue & Bouchard, 1984). As expected, CP was positively associated with both conflictive parenting (r = 0.41, p < 0.001) and observer ratings of parental negativity (r = 0.17, p < 0.01).
