The (Cost-)Effectiveness of Generalist Versus Specialist Treatment for Severe Personality Disorders'

Schema therapy (ST) is an evidence-based, fully manualized, specialist form of psychotherapy for personality disorders (Bamelis et al., 2014; Sempértegui et al., 2013; Arntz et al., 2022). Eligible programs must adhere to the minimum standards described in the evidence-based literature. ST is an integrative treatment method, originally rooted in cognitive theory, but with additional influences from Gestalt, psychodynamic, and experiential methods. Schema therapy programs may differ in intensity and duration, even at the same site, but must include a minimum of either 40 sessions and/or a duration of 12 to 24 months. In addition, in order to be eligible, a schema therapy program must be of higher intensity or longer duration than the generalist treatment (GIT-PD) offered at the same site.

Mentalization-based treatment (MBT) is an evidence-based, fully manualized, specialist form of psychotherapy for personality disorders (Bateman \& Fonagy, 2008; Bateman \& Fonagy, 2009; Laurenssen et al., 2018; Juul et al., 2023). MBT is rooted in psychodynamic and attachment theory and aims to alter personality pathology by improving mentalizing and enhancing epistemic trust. Eligible programs must adhere to the minimum standards described in the evidence-based literature. MBT programs may differ in intensity and duration, even at the same site, but must include a minimum of either 40 sessions or a duration of 12 to 24 months. In additon, in order to be eligible, an MBT program must be of higher intensity or longer duration than the generalist treatment (GIT-PD) offered at the same site.

GIT-PD is a non-theoretical and non-methodological approach, based upon principles derived from common factors across evidence-based treatments for PD. GIT-PD has a flexible approach, enabling tailoring treatment to clinical needs of different types of patients. The treatment duration (start-end) is 12- 18 months. The treatment consists of three distinct phases. First, an assessment phase. Second, a modular treatment phase that offers either group or individual interventions. Third, a follow-up phase with limited treatment and focus on relapse prevention. In order to be eligible, GIT-PD should be less intensive than specialist psychotherapies offered in the control arm at the same location (i.e. MBT or ST). GIT-PD will not include evidence-based psychotherapy for personality disorders as described in previous RCTs.