Table 1.

Overview of instruments

S Screening, B Baseline assessment; 3/6/9/12/15/18/21/24 = 3/6/9/12/15/18/21/24 months after start of the treatment phase, 6 FU Follow-up at 6 months after end of treatment, 12 FU Follow-up at 12 months after end of treatment, BPDSI-5 Borderline Personality Severity Index, fifth edition, BPD Borderline personality disorder, BSI Brief Symptom Inventory, DBT-WCCL Dialectical Behavior Therapy-Ways of Coping Checklist, DERS-18 Difficulties in Emotion Regulation Scale 18, DERS-SF Difficulties in Emotion Regulation Scale Short Form, ECR-RS Experiences in Close Relationships-Relationship Structures questionnaire, EQ-5D-5L 5-level EuroQol 5D version, ISI Insomnia Severity Index, MHQoL-7D Mental Health Quality of Life seven-dimensional Questionnaire, NFQ Nightmare Frequency Questionnaire, ORS Outcome Rating Scale, SCID-5 Structured Clinical Interview for DSM-5, SMI Schema Mode Inventory, WAI-S Working Alliance Inventory-Short, WHODAS 2.0 World Health Organization Disability Assessment Schedule 2.0

^aThe potential predictors of (differential) treatment response that are assessed only once at baseline are not included in this table

^bA shortened version

^cIncluding three to five idiosyncratic dysfunctional beliefs and one functional belief

^dDERS-18 subscale ‘Awareness’

^eExcluding the subscale ‘Awareness’

^fThree versions of the ECR-RS will be assessed, measuring general attachment style and attachment styles with respect to two targets (i.e., most important therapist and group members)

^gTwo versions, measuring attachment styles with respect to two targets (i.e., most important therapist and group members), are assessed after the third group session

^hSMI subscales Vulnerable Child, Angry Child, Impulsive Child, Detached Protector, Punitive Parent, and Healthy Adult

ⁱKey characteristics of a promoting therapeutic environment (i.e., genuineness, safety, and equality) are assessed by 13 items formulated by ST experts

^jAssessed after the third group session