Does attachment change serve as a theory-specific mediator of depression reduction in interpersonal psychotherapy versus cognitive behavioral therapy?

OBJECTIVE: Although interpersonal psychotherapy (IPT) and cognitive behavioral therapy (CBT) for depression are comparably efficacious, less is known about the respective patient-level processes that help transmit their beneficial effect. Given its explicit and primary focus on attachment theory and relationship processes, it is plausible that IPT helps ameliorate depression specifically through decreasing patients' attachment insecurity. Testing this hypothesis, we examined whether IPT relative to CBT promoted greater increases in secure attachment during therapy, which in turn associated with lower posttreatment depression.

METHOD: Eighty patients were randomly assigned to 16 sessions of IPT or CBT and completed measures of attachment style and depression throughout treatment.

RESULTS: Multilevel structural equation models revealed a small but significant increase in attachment security across the full sample (d = .23). However, such adaptive change was comparable in IPT and CBT and therefore did not differentially mediate the effect of treatment on depression. Yet, across both treatments, an early increase in attachment security was associated with lower posttreatment depression.

CONCLUSION: Results support that increased attachment security early in treatment may be an important change process that is more theory-common than IPT-specific.