Variables of poor quality (n=129) were recoded as missing to increase overall accuracy. Each parental psychopathology variable was coded into a dichotomous yes/no variable based on answering yes to the stem question and endorsing one or more follow-up questions for depression, anxiety, alcohol problems and drug problems, and two or more follow-up questions for father's antisocial characteristics. Test–retest reliability estimates for these parental psychopathology variables among randomly selected participants re-interviewed 2–8 weeks after their original interviews were obtained: father [depression, k=0.66 (95% CI 0.48–0.83); anxiety, k=0.28 (95% CI 0.00–0.56); alcohol problems, k=0.80 (95 % CI 0.67–0.91); drug problems, k=1.0 (no discordant pairs); antisocial characteristics, k=0.66 (95% CI 0.46–0.86]; mother [depression, k=0.46 (95% CI 0.30–0.61); anxiety, k=0.29 (95 % CI 0.12–0.46); alcohol problems, k=0.46 (95% CI 0.30–0.62); drug problems, k=0.75 (95% CI 0.40–1.0)] (n=192). Co-twin information was combined for parental psychopathological variables, such that parents were coded positive for psychopathology variables if either twin reported parental psychopathology. In instances in which one twin was missing parental psychopathology information and the other co-twin was not [n ranging from 235 (mother alcohol) to 267 (father anxiety)], the missing parental psychopathological variable was coded based on the co-twin's response.
