Comorbidity of conduct disorder symptoms and internalising problems in children: investigating a community and a clinical sample.

Previous studies have demonstrated that many children with conduct problems (CP) also show internalising psychopathology (IP). However, it remains unclear whether the presence of IP serves as a protective or risk factor for the severity and development of CP. The aim of the present study was to assess the prevalence and associations of comorbid IP in children with CP in a community and a clinical sample. Data from boys as well as girls with CP in the clinical range were obtained from a community sample (n = 1,160) and a clinical sample diagnosed with disruptive behaviour disorder (n = 193) from two European countries. In the community sample, information was obtained using the strengths and difficulties questionnaire, whereas in the clinical sample, the child behaviour checklist was used. Internalising disorders, according to ICD-10, were also assessed in the clinical sample. For both samples, age, gender, and impact of comorbid IP in the clinical range (above 90th percentile) for CP were explored. Results revealed that in both samples, participants with CP showed a high rate of comorbid IP (community sample: 35%; clinical sample: 78%). Participants with comorbid IP were more likely to experience social problems with peers. In the clinical sample, comorbid IP rated by the parents was more prevalent than internalising disorders according to ICD-10. Boys with CP and comorbid IP demonstrated a higher severity of externalising behaviour than boys without comorbid IP in the clinical sample. We concluded that in both samples, we found a high co-occurrence of CP and IP. Based on the idea that the co-occurrence of IP and CP in children and adolescents may potentially lead to increased antisocial behaviour, internalising psychopathology should be carefully investigated. Effective strategies and specific risk factors must be evaluated to treat comorbidity as early as possible in children with CP and IP.