G-FORCE: the effectiveness of group psychotherapy for Cluster-C personality disorders: protocol of a pragmatic RCT comparing psychodynamic and two forms of schema group therapy.

Background: Cluster-C personality disorders (PDs), characterized by a high level of fear and anxiety, are related to high levels of distress, societal dysfunctioning and chronicity of various mental health disorders. Evidence for the optimal treatment is extremely scarce. Nevertheless, the need to treat these patients is eminent. In clinical practice, group therapy is one of the frequently offered approaches, with two important frameworks: schema therapy and psychodynamic therapy. These two frameworks suggest different mechanisms of change, but until now, this has not yet been explored. The purpose of the present G-FORCE trial is to find evidence on the differential (cost)effectiveness of two forms of schema group therapy and psychodynamic group therapy in the routine clinical setting of an outpatient clinic and to investigate the underlying working mechanisms and predictors of outcome of these therapies.

Methods: In this mono-centre pragmatic randomized clinical trial, 290 patients with Cluster-C PDs or other specified PD with predominantly Cluster-C traits, will be randomized to one of three treatment conditions: group schema therapy for Cluster-C (GST-C, 1 year), schema-focused group therapy (SFGT, 1.5 year) or psychodynamic group therapy (PG, 2 years). Randomization will be pre-stratified on the type of PD. Change in severity of PD (APD-IV) over 24 months will be the primary outcome measure. Secondary outcome measures are personality functioning, psychiatric symptoms and quality of life. Potential predictors and mediators are selected and measured repeatedly. Also, a cost-effectiveness study will be performed, primarily based on a societal perspective, using both clinical effects and quality-adjusted life years. The time-points of assessment are at baseline, start of treatment and after 1, 3, 6, 9, 12, 18, 24 and 36 months.

Discussion: This study is designed to evaluate the effectiveness and cost-effectiveness of three formats of group psychotherapy for Cluster-C PDs. Additionally, predictors, procedure and process variables are analysed to investigate the working mechanisms of the therapies. This is the first large RCT on group therapy for Cluster-C PDs and will contribute improving the care of this neglected patient group. The absence of a control group can be considered as a limitation.

Trial Registration: CCMO, NL72826.029.20 . Registered on 31 August 2020, first participant included on 18 October 2020.