Degree Name

Doctor of Philosophy


School of Psychology


Background. Disturbances of self and identity are central to personality disorder yet methods for measuring such disturbances are scarce.

Aim. The current thesis aimed to: (i) examine self and identity in borderline personality disorder (BPD), as assessed by the Differentiation of Self Inventory (DSI; Skowron & Friedlander, 1998); (ii) investigate change in DSI over treatment; and (iii) explore the subjective, lived experience of clients diagnosed with BPD in relation to self and identity.

Method. Sixty-two participants referred to the Illawarra Affect Regulation Clinic for assessment and treatment of BPD were administered semi-structured and self-report measures, including the DSI. Eighteen participants completed the measures again following a program of intensive psychotherapy; and participated in a qualitative analysis of differentiation of self.

Results. Participants were found to have impoverished levels of differentiation compared to normal controls, and significant relationships were found between the DSI and measures of borderline psychopathology, with greater severity of BPD symptoms being associated with lower DSI scores. The outcomes of treatment included a more developed sense of self, reductions in psychological distress, and greater global functioning. Participants who improved over the course of treatment had more cohesive and flexible narratives in terms of their relationship to self and others.

Conclusion. The results of the current thesis provide an understanding of the significance of differentiation of self in BPD, and the role of treatment in addressing disturbances of self and identity.