Table 1 Assessments instruments and assessment times planned for the study. A detailed description of each instrument can be found in Supplementary Material 1: Appendix 2

Diagnostic Measures

BPD diagnosis

International Personality Disorder Exam (BPD subsection) [45]

Interview

IPDE

●

●

Comorbidities

Mini International Neuropsychiatric Interview DSM-5 [46]

Interview

MINI

●

Premorbid Functioning

Test of Premorbid Functioning [47, 48]

Interview

TOPF

●

ADHD

Adult ADHD Self-Report Scale [51]

Self-Report

ASRS

●

Personality Dimensions

Personality Inventory for DSM-5 [52, 53]

Self-Report

PID-5

●

Demographics

Demographic Data Survey

Self-Report

DDS

●

Trauma Biography

Childhood Invalidation

Invalidating Childhood Environment Scale [54]

Self-Report

ICES

●

Childhood Trauma

Childhood Trauma Questionnaire [55]

Self-Report

CTQ

●

Complex Trauma

International Trauma Questionnaire [56]

Self-Report

ITQ

●

Embitterment

Posttraumatic Embitterment Disorder Questionnaire/Berner Embitterness Scale [57]

Self-Report

PTED/BEI

●

Unpredictability Childhood

Questionnaire of Unpredictability in Childhood [58]

Self-Report

QUIC

●

Bullying

Bullying Scale for Adults [59]

Self-Report

BSA

●

BPD-related Psychopathology

BPD Symptoms

Borderline Symptom Liste - Interview

Interview

BSL-I

●

●

●

●

●

●

●

BPD Symptoms

Borderline Symptom List 23 [60]

Self-Report

BSL-23

●

●

●

●

●

●

●

●

Suicide Severity

Columbia Suicide Severity Scale [61]

Interview

C-SSRS

●

●

●

●

●

●

●

Self-Harm

Deliberate Self-Harm Inventory [62, 63]

Self-Report

DSHI

●

●

●

●

●

●

●

Emotion Regulation Difficulties

The Difficulties in Emotion Regulation Scale– 16 Item Version [64]

Self-Report

DERS-16

●

●

●

●

●

●

●

Dissociation

Dissociative Symptoms Scale [65]

Self-Report

DSS

●

●

●

●

●

●

●

Complex Trauma

International Trauma Questionnaire [56]

Self-Report

ITQ

●

●

●

●

●

●

●

General Psychopathology

General Psychiatric Symptom Distress

Symptoms Checklist 27 [66]

Self-Report

SCL-27

●

●

●

●

●

●

●

Affective Suicidality

Acute Suicidal Affective Disturbance Interview [67]

Interview

ASAD-I

●

●

●

●

●

●

●

Affective Suicidality

Acute Suicidal Affective Disturbance Questionnaire [67]

Self-Report

ASADI-L

●

●

●

●

●

●

●

Severity Personality Disorder

Level of Personality Functioning Scale - Brief Form 2.0 [52]

Self-Report

LPFS-BF 2.0

●

●

●

●

●

Social Relationships and Affiliation

Loneliness

UCLA Loneliness Scale [68]

Self-Report

UCLA

●

●

●

●

●

Social Connectedness

Social Connectedness Scale– Revised [69]

Self-Report

SCS-R

●

●

●

●

●

Rejection Sensitivity

Rejection Sensitivity Questionnaire [70]

Self-Report

RSQ

●

●

●

●

●

Need to Belong

Need to Belong Scale [71]

Self-Report

NBS

●

●

●

●

●

Social Network Index

Social Network Index (+ Interpersonal Distance & Trust) [72]

Self-Report

SNI

●

●

●

●

●

Self-image and Self-esteem

Fear of Compassion

Fears of Compassion Scale [73, 74]

Self-Report

FCS

●

●

●

●

●

Self-Esteem

Rosenberg Self-Esteem Scale [75]

Self-Report

RSES

●

●

●

●

●

Self-Compassion

Self-Compassion Scale [76]

Self-Report

SCS

●

●

●

●

●

Shame

Test of Self-Conscious Affect-3 [77]

Self-Report

TOSCA-3

●

●

●

●

●

Aspects of Identity

Aspects of Identity Questionnaire [78, 79]

Self-Report

AIQ

●

●

●

●

●

Quality of Life and Wellbeing Outcomes

Functioning

Global Assessment of Functioning (Observation-Based) [80]

Interview

GAF

●

●

●

●

●

●

●

Quality of Life

Recovering Quality of Life [81, 82]

Self-Report

ReQoL

●

●

●

●

●

●

●

Psychosocial Functioning

Inventory of Psychosocial Functioning [83]

Self-Report

IPF

●

●

●

●

●

Functioning– Social, Interpersonal, Global

WHO Disability Assessment Schedule 2.0–12-Item Version [84]

Self-Report

WHODAS 2.0–12

●

●

●

●

●

Life Satisfaction

Quality of Life Enjoyment and Satisfaction Questionnaire– Short Form [85]

Self-Report

Q-LES-Q-SF

●

●

●

●

●

Meaning of Life

Meaning of Life Questionnaire [86]

Self-Report

MLQ

●

●

●

●

●

Mindfulness

Kentucky Inventory of Mindfulness Skills [87]

Self-Report

KIMS

●

●

●

●

●

Therapeutic Relationship and Acceptance Measures

Therapeutic Alliance

Working Alliance Inventory - Short Form, Client and Therapist [88]

Self-Report

WAI-S

●

(S1-4)

●

●

●

Group Climate

Group Climate Questionnaire [89]

Self-Report

GCQ

●

(S1-4)

●

●

●

Therapist Demographics

Therapist Demographic Questionnaire

Self-Report

TherDem

●

Acceptability of Intervention

Acceptability of Intervention Measure [90, 91]

Self-Report

AIM

●

●

●

Client Satisfaction

Client Satisfaction Questionnaire– 8 [92]

Self-Report

CSQ-8

●

●

●

Telehealth Usability

Acceptance and Use of Technology [93]

Self-Report

UTAUT

●

●

●

Treatment Termination Measures

Reason for Treatment Termination

Research Early Termination for the Client*

Self-Report

RET-C