Self-critical perfectionism, dependency and entropy during cognitive behavioural therapy for depression.

Objectives: This study examined whether 'personality vulnerability' (i.e., self-critical perfectionism or dependency) predicts the trajectory of change, as well as variability and instability (i.e., entropy) of symptoms, during cognitive behaviour therapy (CBT) for depression.

Design: Study participants were outpatients (N = 312) experiencing a primary mood disorder. Participants received CBT for depression group sessions over 15 weeks. Self-report measures of self-critical perfectionism, dependency, and depression were collected longitudinally.

Methods: A latent growth mixture modelling (LGMM) statistical approach was used to evaluate the presence of latent classes of individuals based on their longitudinal pattern of symptom change during CBT and to evaluate whether baseline self-critical perfectionism or dependency predicts class membership. A Latent Acceleration Score (LAS) model evaluated whether perfectionism or dependency led to variability in depression symptom change (e.g., velocity) by considering changes in velocity (e.g., acceleration and/or deceleration).

Results: LGMM indicated the presence of two latent classes that represent symptom improvement (N = 239) or minimal symptom improvement over time (N = 73). Elevated baseline self-critical perfectionism, but not dependency, predicted a greater likelihood of membership in the class of participants who demonstrated minimal symptom improvement over time. The second analysis examined whether baseline self-critical perfectionism also predicts depression symptom variability and instability. The LAS perfectionism model demonstrated that perfectionism accelerates depression symptom change during the first seven sessions of treatment, then has a decelerating effect on depression symptom change.

Conclusions: Results indicated that higher baseline self-critical perfectionism predicted higher variability and instability in depression symptoms and variability in acceleration and deceleration, over the course of treatment.