IQ as a moderator of outcome in severity of children’s mental health status after treatment in outpatient clinics

BACKGROUND: Psychotherapy is an effective treatment for mental health disorders, but even with the most efficacious treatment, many patients do not experience improvement. Moderator analysis can identify the conditions under which treatment is effective or whether there are factors that can attenuate the effects of treatment. METHODS: In this study, linear mixed model analysis was used to examine whether the Full Scale IQ (FSIQ), Performance IQ (PIQ) and Verbal IQ (VIQ) on the Wechsler Intelligence Scale for Children – Third Edition, moderated outcomes in general functioning and symptom load. A total of 132 patients treated at three outpatient child and adolescent mental health services (CAMHS) were assessed at three different time points. The Children’s Global Assessment Scale (CGAS) and the Health of the Nation Outcome Scales for Children and Adolescents (HoNOSCA) were used to measure the severity of impairments in general functioning and symptom load. IQ was assessed at the start of treatment. RESULTS: Moderator analysis revealed that the FSIQ × time interaction predicted changes in CGAS scores (p < .01), and that the PIQ × time interaction predicted changes in HoNOSCA scores (p < .05). The slopes and intercepts in HoNOSCA scores covaried negatively and significantly (p < .05). The same pattern was not detected for the CGAS scores (p = .08). CONCLUSIONS: FISQ and PIQ moderated change in general functioning and symptom load, respectively. This implies that patients with higher IQ scores had a steeper improvement slope than those with lower scores. The patients with the highest initial symptom loads showed the greatest improvement, this pattern was not found in the improvement of general functioning.