Because caretaker and youth reports of symptoms are modestly correlated, many researchers obtain complementary information from multiple informants.22 Indeed, several studies indicate that the use of multiple informants improves the validity of assessments of psychopathology in children and adolescents, but the optimal informants are different at different ages and for different disorders. Children ≥ 9 years of age are reliable and valid informants on anxiety, depression, and conduct disorder (CD), but not on ODD and ADHD.23-25 Based on these considerations, parent and youth reports of symptoms of symptoms of anxiety disorders, depression, and CD were combined using the standard method of taking the higher rating of each symptom from the adult caretaker or youth.26 Only caretaker ratings defined ODD and ADHD. The present analyses were limited to 1,571 pairs of 9-17 year old twins in which both informants were interviewed. To ensure that combining parent and youth reports did not bias findings, the primary models were refitted using only parent ratings of all symptom dimensions for 6-17 year old twins with qualitatively identical results (available upon request).
