Assessing the preventive effects of cognitive therapy following relief of depression: A methodological innovation

Background: Strategies to compute benefits from continuing cognitive therapy for patients with recurrent major depression do not take into account whether discontinuing treatments may induce temporary increases in the risk that symptoms return (discontinuation-effect). Methods: We apply varying-effects analyses and compare findings with traditional methods to assess the effects of continuation-phase cognitive therapy. Two years of data came from 79 patients with recurrent major depression who responded to acute cognitive therapy. Patients were randomized to either an experimental cohort (n = 39) who received 10-session, protocol continuation-phase therapy for 8 months, or a control cohort (n = 40) who stopped protocol treatment after the acute-phase. Symptoms were assessed using the Longitudinal Interval Follow-up Evaluation (LIFE). Symptom risk rates were computed weekly by cohort as the proportion of patients at risk who were suffering from a major depressive episode. Results: Significant discontinuation-effects occurred when protocol treatments stopped for both experimental and control cohorts. Following acute-phase care, traditional computation methods (week 1-35) revealed treated patients had 18% of the risk for symptoms as controls. Expanding the observation period (week 1-74) to include these discontinuation-effects revealed more modest initial effect sizes (43%), but significant long-term effects (54% for week 75-101). Limitations: Limitations include limited sample size, one-site study, confounds from patient-level interactions, and off-protocol use of depression-related care. Conclusions: Varying-effects analyses can describe how outcomes from cognitive therapy may unfold over time for patients with major depression. These analyses reveal complex longitudinal patterns that otherwise are not detectable with traditional time-to-event methods. Specifically, we observed discontinuation-effects, or temporary spikes in symptom risks that occur after treatment ends. Further research is needed to identify the mechanisms driving these effects. Future studies are needed to determine if higher risks result from the patients' anxiety as they attempt to maintain gains independent of ongoing therapy, or reflect residual symptoms previously suppressed by treatment. We also observed longer-term preventive effects from therapy. Again, further research is recommended to determine the extent to which lower risks result from coping and compensatory skills learned during cognitive therapy. These findings suggest that varying-effects analyses may provide an appealing paradigm for understanding treatment-related effects in episodic illness.