The Effectiveness of Group Psychotherapy for Cluster C Personality Disorders: A pragmatic RCT comparing Psychodynamic and Two Forms of Schema Group Therapy

Cluster C personality disorders are highly prevalent and related to
unfavourable outcome and chronicity of all common mental health disorders.
Until now evidence for the optimal treat-ment for these patients is lacking.
For patients with a cluster C personality disorder group psychotherapy is
commonly offered in clinical practice, but the effectiveness of group
psy-chotherapy for these patients is not established. Important questions to be
answered concern the optimal duration of group therapy and influence of
theoretical framework. Also, very little is known on the mechanisms of change
in these psychotherapies. Finding evidence on the differential effectiveness of
group therapy and the mechanisms of change is important to improve the quality
of care for cluster C patients.

In this study we will compare the (cost)- effectiveness of psychodynamic group
therapy (PG) with schema-focused group therapy (SFGT) and group schema therapy
(GST). The group formats differ both in amount of sessions (resp. 80, 60 and 30
sessions) and theoretical background. The main hypothesis is that the three
formats differ in (cost-) effectiveness in changing personality functioning and
reducing psychiatric symptoms in the treatment of cluster C personality
disorders. Next, we will investigate predictive factors and non-specific and
therapy specific mediators.

A mono-centre pragmatic randomized clinical trial with three conditions: 1) PG,
2) SFGT and 3) GST. Randomization on patient level will be pre-stratified on
type of cluster C personality disorder.

The three interventions differ in duration. PG is offered in weekly sessions of
90 minutes for the duration of 2 years (80 sessions). SFGT combines elements of
schema therapy with unstructured group dynamic therapy and is offered in weekly
sessions of 120 minutes (60 sessions). The total dose in minutes is equal for
PG and SFGT. GST is considerably shorter, consisting of 30 weekly sessions of
90 minutes, combined with a total of 300 minutes of additional individual
sessions.

Patients will be invited to a clinical screening interview prior to the start
of treatment and at 12 and 24 months after the start of treatment. Other
measurements can be done either online or on paper-and-pencil. Although the
burden includes a time-investment of the patient (by filling in questionnaires)
no risks are associated with participation in the study. Participants in all
conditions will receive specialized treatment for personality disorders, their
treatment and measurements will be well monitored and checked on adherence and
additional treatment is provided if necessary.