A Multilevel Meta-Analysis of Single-Case Research on Interventions for Externalizing Behavior Problems in Children and Adolescents

Objective: The overall effectiveness of interventions for youth externalizing behavior problems was studied using a review and a meta-analysis of published single-case research in children and adolescents. Method: Scientific databases and gray literature were searched for quantitative single-case studies concerned with the treatment of externalizing behavior problems in children and adolescents. Study and case characteristics were extracted, and the studies were rated for quality. Raw graph data from individual cases were aggregated and analyzed by means of multilevel meta-analysis for single-case research. Results: We identified 78 studies including 270 cases (mean age = 8.70 years; 71.48% male individuals). Overall, positive within-person changes during the treatment as opposed to baseline were observed. Reductions in symptoms did not carry through the follow-up phase. However, variations in treatment effects were observed, with larger variations among studies than among cases. Furthermore, studies using observational assessment methods yielded stronger results than studies using questionnaires to assess outcomes. Although the scores for the external validity of the studies were above average, the scores for internal validity were below average. Conclusion: Although part of the internal validity result can be attributed to underreporting certain quality standards in the studies, it is of great importance for the field of single-case research to start implementing existing methodological guidelines and to comprehensively report case-relevant information. This will, in addition, facilitate our understanding of the variability in treatment outcomes for specific children, and will enable us to learn more about the effects of interventions in diverse youth populations. Plain language summary: Single-case studies of youth with externalizing behaviors allow consideration of treatment effects within individuals over time, but meta-analyses of this research have been limited. This study aggregated and summarized the results from 78 published studies of 270 single-case research in the area of youth externalizing problems. Overall, positive changes in externalizing problems were found, and the studies that used observational methods to depict externalizing behaviors reported more changes than studies that used questionnaire methods. Results suggest the quality of single-case studies can be improved. Study registration information: Preregistration Meta-analysis of Single-Case Research on Interventions for Externalizing Behavioral Problems in Children and Adolescents; https://doi.org/10.17605/osf.io/4bewa