Research Synthesis of Psychological Interventions for Mental Health

This thesis explores state-of-the-art and novel methods of research synthesis to investigate psychotherapy and self-help interventions for common mental health disorders. By demonstrating a range of synthesis techniques, the thesis provides a comprehensive examination of the evidence currently available in the field. The thesis progresses from conventional meta-analyses to multiverse meta-analyses and meta-meta analyses to offer a broader understanding of the state of the research field. Through this systematic approach, the thesis aims to contribute to a deeper understanding of the factors influencing efficacy estimates of psychotherapy and self-help interventions, ultimately supporting evidence-based decision-making in clinical practice and informing future research directions. Chapter 1 provides a general overview of the concepts of this thesis, namely mental health disorders such as depression, anxiety, and irritable bowel syndrome; research synthesis techniques like meta-analyses, multiverse meta-analyses, and umbrella reviews; and psychological interventions including psychotherapy, internet-based and smartphone-based interventions. Chapter 2 uses conventional meta-analytic methods to investigate whether self-help interventions are effective in reducing symptoms of irritable bowel syndrome. The results suggest that self-help interventions, particularly online-based ones, are effective in reducing symptom severity and improving the quality of life for patients. Chapters 3 and 4 explore the effectiveness of psychotherapy for depression, and Chapter 5 investigates whether digital psychological therapies are effective, using a multiverse meta-analysis approach. This novel approach conducts extensive sensitivity analyses to investigate the robustness of meta-analytical findings by analyzing whether most meta-analytic strategies yield similar results. The results suggest that these therapies are all clinically meaningful. However, different data-analytical decisions—such as comparisons with wait-list control groups, inclusion of studies with high risk of bias, different statistical models, and the lack of correction for publication bias—may have inflated the effect sizes of these treatment outcomes. Chapter 6 combines multiverse meta-analyses with umbrella review methodology to investigate whether smartphone-based and web-based psychological interventions are effective for treating anxiety disorders. Results showed that guided and internet-based interventions were more effective than unguided and smartphone-based interventions. Notably, digital interventions were more effective for social and generalized anxiety disorders compared to other anxiety types. However, the low quality of evidence in most of the included studies warrants caution in interpreting the findings. Finally, the thesis concludes with a general discussion of the findings in Chapter 7. Limitations, suggestions for future research, and implications for clinical and research practice are presented.