Development and initial test of an identity disturbance skills module for borderline personality disorder: A series of N-of-1 trials

Identity disturbance (ID) is a transdiagnostic symptom that has unique connections with borderline personality disorder (BPD). ID is associated with psychopathology severity and self-injury, less favorable treatment outcomes, and suicidal behaviors. Empirical research on interventions targeting ID is lacking, despite calls for researchers to develop such interventions. The current study sought to develop and provide an initial test of an Identity Disturbance Skills (IDS) Module using a multiple-baseline single-case experimental design (SCED). The study consisted of three phases: baseline (A), intervention (B), and follow-up. Four participants with BPD were randomized to the baseline phase (A), followed by the five-week IDS Module (B), and a 2- and 4-week follow-up period. Participants completed weekly measures of identity- and self-related constructs in addition to nontargeted, related symptoms (i.e., interpersonal functioning, emotion regulation, depression, and anxiety). Results showed that participants had improvements in their identity functioning across the intervention, as assessed through visual inspection. Results also showed significant and reliable changes in self-concept clarity across all four participants, with all participants demonstrating a reliable change from pre- to post-intervention, and from pre-intervention to follow-up. There was also a significant effect size across participants for both treatment and follow-up phases for self-concept clarity, and all four participants had significant changes in level of nonoverlapping data between baseline and treatment, and between treatment and follow-up. Results were marked by variability for the nontargeted symptoms. Visual inspection showed improvement in interpersonal functioning, emotion dysregulation, and depression for one participant, however this did not occur across participants. There was a significant effect size for interpersonal functioning for the treatment phase across participants, indicating that the IDS Module led to large improvements in interpersonal functioning. Participants reported high levels of satisfaction with the IDS Module. Participant and therapist data indicated that the intervention was both acceptable and feasible. Based upon this initial test, it appears that the IDS Module is acceptable to participants, feasible to implement, and that there is promising support for its effectiveness in treating identity disturbance. Future research can build upon this preliminary test by using group comparison to eliminate confounds and clearly establish causal support for the IDS Module.