Design

The design of the study will be a 30-session (on a weekly basis), two-group (GST, GCBT) randomized controlled clinical trial with repeated measurements at baseline (T0), mid-test (T1), post-test (T2) and at 3 months follow-up (T3), half-year follow-up (T4) and 1-year follow-up (T5). Assessment will include diagnostic interviews, symptom questionnaires and quality of life, self-esteem, schema-related and emotion regulation measures. See Fig. 1 (Flow chart of enrolment, intervention and assessments) and Additional file 1 (Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) flow diagram) for an overview of the study; the SPIRIT checklist is presented in Additional file 2. Diagnostic interviews are based on the DSM-IV classification system [2], since the DSM-5 [8] was not yet available during the developmental phase of this study and there was an absence of diagnostic instruments based on the DSM-5 at the start of the study.

Flow chart of enrolment, intervention and assessments

After conclusion of the experimental part of the study (3 months after the last session of the treatment), patients will enter a naturalistic follow-up period in which they are allowed to seek help the way they would normally do when they feel in need for further treatment.

The study will be performed at two sites of PsyQ, a large ambulatory mental health organization in the Netherlands. Two departments of anxiety disorders of PsyQ will participate, one located in The Hague and the other in Rotterdam. Other departments, for instance, the departments of depression or personality disorders, in the regions of The Hague and Rotterdam will be informed of the study and will be asked to refer eligible patients. If necessary to guarantee a sufficient inclusion of eligible patients, more treatment centres will be approached for study participation.