Bockting, et al (2005) recruited 187 individuals with a history of recurrent major depression who were currently in remission then randomly assigned them to either treatment as usual (which ranged from on-going meds or counseling to no treatment) or treatment as usual plus 8 weekly sessions of group Cognitive Therapy. The presence of relapse was assessed at 3, 12, and 24 months.

The protective effect of CT was strongest in the high-risk group (5 or more previous episodes). For the high risk group, CT reduced the rate of relapse over a two-year period from 72% for the treatment as usual group to 46% for treatment as usual plus CT. CT also had a protective effect for participants with fewer than 5 previous episodes but it was smaller in magnitude.

Bockting, C. L. H., Svhene, A. H., Spinhoven, P., Koeter, M. W. J., Wouters, L. F., Huyser, J., & Kampuis, J. H. (2005). Preventing relapse/recurrence in recurrent depression with cognitive therapy: A randomized controlled trial. Journal of Consulting and Clinical Psychology, 73,647-657.