This study aims at replicating existing preliminary evidence about the effectiveness of Evolutionary Systems Therapy for Schizotypy (ESTS). The present randomized controlled trial (RCT) will compare ESTS with Cognitive Behavioral Therapy (CBT) in treating Schizotypal Personality Disorder (SPD). The main questions our RCT aims to answer are:

1. Is ESTS more effective than CBT in treating SPD?
2. Is ESTS more feasible than CBT in treating SPD?

38 patients diagnosed with SPD will be recruited and randomly allocated to either the experimental group (i.e. ESTS) or the control group (CBT). Primary outcome will be reduction in general symptomatology, whereas secondary outcomes will be changes in target mechanisms (self-criticism and metacognition) and remission from diagnosis.

A previous study suggested how ESTS (experimental group; EG) may be not inferior in respect to a combine treatment comprising of CBT and psychopharmacological treatment (control group; CG). Despite the encouraging results, it has been suggested that the presence in the CG of a mandatory pharmacological treatment would have represented a bias. Indeed, a few partecipants refused pharmacological treatment.

Thus, the investigators outlined an RCT aimed at comparing the two interventions (ESTS and CBT) without any mandatory pharmacological treatment. Moreover, the investigators consider the need for a pharmacological treatment during the study as an exclusion criterion.

The investigators expect to extend our knowledge about the feasbility and effectiveness of ESTS for those diagnosed with SPD:

Inclusion Criteria:

• Diagnosis of Schizotypal Personality Disorder at SCID-5-AMPD Module III
• Age 18 or older
• Being capable of reading and signing the inform consent form in Italian
• Being capable of attending a talk therapy in Italian

Exclusion Criteria:

• Being diagnosed with schizophrenia spectrum disorders or other psychosis disorder
• Being diagnosed with neurodevelopmental or neurological disorders
• Being diagnosed with bipolar disorder
• Being under any psychological or pharmacological treatment

The data will be anonymized and shared through Open Science Foundation at the end of the study.

Study protocol, SAP, and ICF will be shared before the end of February 2023.

An experienced first clinician will make the initial assessment without knowing the assignment to the two groups. Similarly, a second expert clinician will evaluate the participants at the end of th.e intervention without knowing the assignment to the two groups. The data will then be anonymized and a statistician will analyze them without knowing which group corresponds to which treatment