Bridging Gaps in Care: Optimizing Interventions for Youth with Mild Intellectual Disabilities or Borderline Intellectual Functioning and Externalizing Problems

Abstract

Externalizing behavior problems, such as aggressive or rule-breaking behavior, are common and persistent in young people with mild intellectual disabilities or borderline intellectual functioning (MID-BIF). These behavior problems are linked to a range of long-term negative outcomes, including mental and physical health problems, criminality, and even mortality. Yet, scientific understanding of how to mitigate externalizing problems in this population remains limited. This dissertation aimed to fill this gap. Its first aim was to examine outcomes of psychosocial interventions (i.e., non-pharmacological interventions addressing psychological and social factors) for youth with MID-BIF and externalizing problems. Chapter 2, a multilevel meta-analysis pooling data from 7 empirical studies with 14 effects, showed that psychosocial interventions for youth with MID-BIF aged up to 18 years are generally effective at reducing externalizing problems. Chapter 3 was a pilot study evaluating a school-based targeted prevention program for children aged 9–14 years with MID-BIF and externalizing problems. Although the study was based on a small sample (n = 13) and showed heterogeneous results across participants and informants, children significantly decreased in self-reported (but not teacher-reported) externalizing problems at the group level during the intervention. Chapter 4 presented secondary data analyses of an existing intervention trial, comparing adolescents aged 11-16 years with and without MID-BIF. Findings suggest that cognitive behavioral therapy (CBT) tailored to MID-BIF needs, can be more effective for reducing externalizing problems in adolescents with MID-BIF compared to those without MID-BIF, based on observer-reports (but not self-reports). Together, Chapters 2, 3, and 4 provide evidence that psychosocial interventions tailored to MID-BIF needs can reduce externalizing symptoms in youth with MID-BIF. This dissertation’s second aim was to increase understanding of treatment processes underlying these outcomes, including processes of therapy input (i.e., the influence of MID-BIF on the therapeutic process and effectiveness), therapeutic alliance (i.e., the degree to which the therapist and client engage in collaborative, purposeful work), and change mechanisms (i.e., social information processing: the social cognitive processes presumed to drive externalizing problems). First, findings suggest that MID-BIF has limited influence on intervention effects. Chapter 2 showed that effect sizes for youth with MID-BIF were comparable to those found in meta-analyses of youth without MID-BIF. In Chapter 4, adolescents with and without MID-BIF showed similar improvements in perceived competence for assertiveness, while observer-reported (but not self-reported) externalizing symptom reductions were greater for adolescents with MID-BIF. Second, Chapter 5, a scoping review on therapeutic alliance in interventions for MID-BIF, showed that alliance was considered imperative for outcomes by professionals, parents, and youth with MID-BIF across disciplines and interventions. Lastly, Chapter 4 found no evidence that social information processing drove CBT effects, although adolescents with MID-BIF reported increased competence for assertive responses, a clinically relevant factor. Overall, this dissertation demonstrates the feasibility and effectiveness of psychosocial interventions for youth with MID-BIF and externalizing problems. These findings may encourage researchers and clinicians to more often include this population in future work and to adopt a comprehensive approach to studying and implementing psychosocial interventions.