Helen Niemeyer, Noemi Lorbeer, Jil Mohr, Ella Baer, Christine Knaevelsrud

• Background: The current meta-review of meta-analyses on psychotherapy research for complex post-traumatic stress disorder (CPTSD) and samples at risk of complex traumatization has three aims: first, to provide an overview of efficacy of individual psychotherapies; second, to compare the quality of the meta-analyses; and third, to assess statistical power. Methods: The literature search was conducted until August 2020. Meta-analyses providing individual treatment effect estimates focusing on CPTSD or samples at risk of complex traumatization (i.e., victims of childhood sexual abuse (CSA), war or torture, refugees, and veterans with PTSD) were eligible for inclusion. The effect sizes were classified according to Cohen as small, medium, or large. The "A MeaSurement Tool to Assess systematic Reviews" (AMSTAR) was applied to assess the quality of the meta-analyses, and power was assessed post-hoc. Results: Twenty-four meta-analyses were suitable for inclusion. The efficacy of the interventions varied (g = -0.04 (CI -0.39; 0.48),Background: The current meta-review of meta-analyses on psychotherapy research for complex post-traumatic stress disorder (CPTSD) and samples at risk of complex traumatization has three aims: first, to provide an overview of efficacy of individual psychotherapies; second, to compare the quality of the meta-analyses; and third, to assess statistical power. Methods: The literature search was conducted until August 2020. Meta-analyses providing individual treatment effect estimates focusing on CPTSD or samples at risk of complex traumatization (i.e., victims of childhood sexual abuse (CSA), war or torture, refugees, and veterans with PTSD) were eligible for inclusion. The effect sizes were classified according to Cohen as small, medium, or large. The "A MeaSurement Tool to Assess systematic Reviews" (AMSTAR) was applied to assess the quality of the meta-analyses, and power was assessed post-hoc. Results: Twenty-four meta-analyses were suitable for inclusion. The efficacy of the interventions varied (g = -0.04 (CI -0.39; 0.48), controlled, to d = 2.73 (1.69; 3.76), uncontrolled). Overall, 16 effect estimates were large. On average, the quality of the meta-analyses was good (average AMSTAR total score 7.71 points (range 3-11). Considering quality assessments and power together, nine meta-analyses were evaluated as high quality. Limitations: No meta-analysis for CPTSD was eligible and the number of individuals with complex traumatization was not directly assessed in the at-risk groups. Conclusions: For at-risk groups for complex traumatization, on average, good-quality empirical evidence exists. Given the limited research on CPTSD, future studies are needed to further investigate the efficacy of interventions.…