Sudden gains and critical sessions in cognitive-behavioral therapy for depression.

In this study of cognitive-behavioral therapy for depression, many patients experienced large symptom improvements in a single between-sessions interval. These sudden gains' average magnitude was 11 Beck Depression Inventory points, accounting for 50% of these patients' total improvement. Patients who experienced sudden gains were less depressed than the other patients at posttreatment, and they remained so 18 months later. Substantial cognitive changes were observed in the therapy sessions preceding sudden gains, but few cognitive changes were observed in control sessions, suggesting that cognitive change in the pregain sessions triggered the sudden gains. Improved therapeutic alliances were also observed in the therapy sessions immediately after the sudden gains, as were additional cognitive changes, suggesting a three-stage model for these patients' recovery: preparation-->critical session/sudden gain-->upward spiral.