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

The LPFS-BF 2.0 is a self-report questionnaire consisting of 12 items (Weekers et al., 2018). Each item reflects a basic underlying impairment related to the 12 features of personality functioning according to Criterium A of the AMPD such as identity, self-direction, intimacy and relational functioning. The LPFS-BF 2.0 offers a severity index for personality pathology making it suitable for measuring treatment effects. Each item is scored on a scale from 1 (=very false or often false) to 4 (=very true or often true). Therefore, participants achieve a total score between 12 and 48 representing the severity of impairment in personality functioning. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The STiP-5.1 is a semi-structured clinical interview that provides a multi-item assessment of the severity of personality impairments according to the Level of Personal Functioning Scale (LPFS) of the AMPD included in Section III of DSM-5 (APA, 2013). The interviewer should rate the severity of each facet on a scale ranging between 'little to no impairment' (0) to 'extreme impairment' (4). It takes 45 minutes on average to administer the interview. A total score between 0 and 48 is given to indicate the participants global level of personality functioning . We administer the STiP-5.1 at 3 distinct time points. At the start and end of treatment and after 1 year follow up. All interviews are done by blinded research assistants, and the scores are directly logged in Castor. Interviews will be done either face to face or via video call.

The SIPP-SF is a dimensional self-report questionnaire measuring the severity of personality pathology by assessing the core components of adaptive personality functioning. The SIPP-SF is designed in line with the concept of personality disorders as defined in the AMPD. Participants rate the 60 items on a 4-point scale ranging from fully disagree (1) to fully agree (4). Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The BSI is a self-report questionnaire investigating symptom severity, consisting of 53 items which can be answered using a scale ranging from 1 (not at all) to 5 (extremely). The total score represents the number of symptoms that participants experienced during the past week. A global severity index and sub scores on all 9 domains are calculated by summing the values on all items and dividing by the number of items/domains. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

Suicidality is assessed using the C-SSRS. This self-report questionnaire covers 6 items and has been recommended by ICHOM as a standard outcome measurement in personality disorder research, due to its adequate psychometric properties (Prevolnik Rupel et al., 2021). The 6 items are answered with either 'yes' or 'no'. The total number of positive answers indicates suicide risk. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The SCID-5-PQ (First et al., 2016) is a self-report measure assessing different criteria for DSM-5 personality disorders according to Section II. Participants are presented with 106 items describing whom they are as a person providing them with a dichotomous 'yes' or 'no' answer scheme. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

Social and professional functioning will be measured using the WHODAS 2.0 self-report questionnaire, which includes 12 items. This questionnaire has been recommended by ICHOM for its good reliability, adequate validity and high sensitivity to change (Prevolnik Rupel et al., 2021). Participants answer 12 questions across 6 domains on their daily functioning during the last 30 days. Answers across the 6 domains are weighted and summed to create a total score of disability ranging from 0 to 100. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The EQ-5D-5L is a self-report questionnaire that covers 5 items measuring quality of life across 5 domains. Answer options consist of 5 levels ranging from 'no problems' to 'extreme problems'. The level indicates the health state for that domain and can be combined into a 5-digit number indicating the overall quality of life of the participant on that day. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The Q-LES-Q-SF is a self-report questionnaire consisting of 16 items.. Participants rate their satisfaction with different aspects of quality of life on a 5-point scale from "not at all or never" (1) to 'frequently or all the time" (5). The possible scores range from 14 to 70 with higher scores indicating greater satisfaction with life (Stevanovic, 2011). Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The TIC-P for Adults will be used to assess healthcare consumption and productivity loss during the last 3 months. Through 57 items the costs of different types of care are determined, e.g. for medication use, sessions with therapists, doctor's appointments and more indirect costs like loss of productivity and informal care by the participants network. The first section comprises 8 general questions. The second section includes 22 items regarding healthcare consumption. The last part consists of12 items on informal care and productivity loss. Some items feature multiple follow up questions resulting in the total number of 57 items. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The CTQ-SF employs 25 items to assess childhood trauma and distinguish between emotional neglect, physical neglect, emotional abuse, physical abuse and sexual abuse (Bernstein et al., 2003). All statements start with "When I was growing up..." and are answered on a 5-point scale ranging from 1 (never true) to 5 (very often true). Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The PCL-5 aims to screen for post-traumatic stress disorder using 20 items that correspond to the DSM-5 criteria (Blevins et al., 2015). Likewise, the four subscales correspond to the DSM-5's clusters B through E for PTSD. The 20 items are answered on a 4-point scale ranging from 0 (not at all) to 4 (extremely) resulting in scores ranging between 0 and 80. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The 5-item version of the Autism Spectrum Quotient (AQ-5) is a very brief screener, which has been derived from the AQ-10. The AQ-5 measures social communication deficits, corresponding to Criterion A of the ASD-diagnosis. The scale has acceptable internal consistency and convergent validity. Items are rated on a 4 point scale ranging from 'definitely disagree' to 'definitely agree'. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

Patient commitment to treatment is measured with a selection of items from the subscale Motivation to Engage of the TMS-F. The four items can be rated on a 7-point Likert scale . Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

A modified version of the SRIS is used to assess self- reflection and insight. The SRIS contains 20 5-point Likert scale items ranging from 1 (strongly disagree) to 5 (strongly agree). Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

Internal locus of control, defined as the extent to which a person experiences an outcome as the result of their own behavior or personal characteristics rather than external circumstance, is assessed by the Locus of Control scale (IE) . The IE contains 10 5-point Likert scale items. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The MHC-SF was developed by Keyes (2008) to measure hedonic and eudaimonic well-being, which can be seen as a separate, but related, dimension to mental "ill-being" (Franken et al., 2018; Keyes, 2007). The questionnaire contains 14 items and three dimensions: emotional well-being (3 items), psychological well-being (6 items) and social well-being (5 items). Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

By using the social problems list, derived from the (IAPT) program social problems (e.g., financial problems, housing problem, and unemployment) are assessed (Clark, 2011). Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The MSPSS (O'Toole et al 2012) is assessed to investigate perceived support from three sources: significant others, family, and friends. The MSPSS contains 12 items which can be rated on a 7-point Likert scale ranging from 1 (very strongly disagree) to 7 (very strongly agree). Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

PD has been associated to stigma of immutability (Aviram 2006) and we will use the five items scale as developed by Wibbelink et al (2022), measuring the extent to which participants believe that PD is resistant to treatment. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

Verbal Intelligence will be measured by the Dutch Reading Test for Adults ('NLV'). Psychometric properties have been shown to be satisfactory among various populations (Hermans et al., 2022). Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

By administering the 24-item QET, insight is gained into a person's developmental capacity to accept information as authentic, trustworthy, generalizable and relevant to the self (i.e. epistemic trust; Knapen et al., 2023). The instrument sheds light on four factors, referring to hypervigilance, curiosity/openness, expectation of help and openness to help. Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.

The PID-5-SF is a shortened 100 item version of the original PID-5 (Maples et al., 2015). It measures 25 facets across 5 domains of pathological personality traits, which corresponds to criterium B of the AMPD (American Psychiatric Association, 2022). Data collection is done digitally via Castor or with pen and paper, based on participants preference. Pen and paper results are copied into Castor by hand by research assistants. Raw data is digitalized and stored on a local drive.