SFT is a treatment for personality disorders that takes at least one group-session per week, for the duration of one year.

The PCL-5 is a self-reported PTSD symptom scale. It consists of 20 items, scored 0 ("not at all") to 4 ("Extremely"). This is summed for total self-reported PTSD-severity, range 0 (no self-reported PTSD-symptoms in the past month) to 80 (extreme self-reported PTSD-symptoms in the past month). There are subscales for the different PTSD symptom clusters; cluster B (question 1-5), C (6-7); D (8-14) and E (15-20).

The OQ-45 is a self-report questionnaire that measures general functioning and physical complaints in the past week. It consists of 45 items; 25 items on psychiatric symptoms and 20 on interpersonal, occupational and social functioning. These are rated from 0 ("Never") to 4 ("Almost always"). Some items need to be reversed in scoring. There are four subscales: Symptomatic Distress (25 items); Interpersonal Relationships (11 items) and Social Role (9 items). A higher score indicates worse functioning.

The BDI is a 21-item self-report questionnaire assessing the severity of depression. Each item consists of four statements indicating different levels of severity of a particular symptom experienced over the past week, ranging from low (0) to high (3) severity. Scores for all 21 items are summed to yield a single depression, with a maximum depression score of 63.

The AUDIT is a self-report questionnaire, with 10 items about alcohol use. These range from 0 ("Never") to 4 ("Daily"). The items are summed to create a total score from 0 (no alcohol risk) to 40 (maximum alcohol risk). The first three questions are about alcohol consumption, question 4-6 about alcohol dependency and question 7-10 about alcohol related problems.

The SCID-5-S is a clinician administered semistructured clinical interview to assess DSM-5 disorders (but not personality disorders). It consists of in total 14 modules, comparable to the DSM-5. Patients are assessed on the disorder, resulting in a score of absent/present for each disorder. In this study, we use the modules current depressive episode, current manic episode, current persistent depressive disorder, delusions & hallucinations, alcohol abuse, substance abuse, panic disorder, agoraphobia, specific phobia, generalized anxiety disorder, obsessive-compulsive disorder, current anorexia, bulimia and binge eating disorder.

WHODAS 2.0 is a 36-item self-report questionnaire assessing the daily function of activity and participation within the 30 previous days, including the following six domains: Cognition, Mobility, Self-care, Getting along, Life activities and Participation. The responses on each item range from no difficulty (1) to extreme difficulty (5). Responses to the six dimensions are weighted and summed to create a total score between 0 (no disability) and 100 (complete disability).

The EQ-5D-5L measures health-related quality of life and consists of five dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each dimension has 5 levels: no problems, slight problems, moderate problems, severe problems and extreme problems. The answer to each item results in a 1-digit number that expresses the level selected for that dimension. The digits for the five dimensions can be combined into a 5-digit number that describes the patient's health state, with higher numbers indicating more severe problems.

TiC-P is a self-report questionnaire assessing direct medical costs and productivity costs due to absence from work or reduced efficiency during work in patients with a mental disorder. The first part of the TiC-P includes 14 structured yes or no questions on the use of medical resources, each followed by a question on the volume of medical consumption. The second part includes five items on work absence, reduced efficiency at work and related productivity losses.

The NSSI screener consists of 7 multiple-choice items assessing non-suicidal self-injury. In case of an affirmative responses to the item 'Have you ever done any of the following with the purpose of intentionally hurting yourself?' engagement in NSSI is determined.

The Personality Assessment Inventory-Borderline Features (PAI-BOR) Scale is a self-report measure assessing the presence and severity of BPD. The BAI-BOR consists of four subscales of six items each, reflecting four main characteristics of BPD: affective instability, negative relationships, identity problems and self-harm. Each items is rated on a four-point scale, ranging from false (0) to very true (3). A total PAI-BOR score of 38 or more indicates the presence of significant BPD features, whereas a score of 60 or more indicates typical borderline personality functioning.

The YSQ-75 is a 75-item self-report questionnaire assesses 15 schemas: temporally stable, personal and interpersonal patterns of beliefs, feelings, sensations and thoughts. Items are rated on a 6-point scale ranging from 1 = Completely untrue of me to 6 = Describes me perfectly. There is evidence for adequate validity and reliability values. Although sparse, evidence suggests that dysfunctional schema reduction accompanies personality disorder symptom reduction after ST.

The SMI-118 is a 118-item self-report questionnaire assessing 14 schema modes, defined as "those schemas or schema operations - adaptive or maladaptive - that are currently active for an individual". Each item is rated on a 6-point scale ranging from 1 (never) to 6 (always). Adequate psychometric properties have been reported. Although sparse, evidence suggests that dysfunctional schema mode reduction accompanies symptom reduction after ST. Similar to dysfunctional schema reduction, evidence suggests that dysfunctional schema mode reduction accompanies personality disorder symptom reduction after ST.