There is a lot of evidence for the effectiveness of cognitive behaviour therapy (CBT) in treating a number of different mental-health problems, including depression, but it is unclear whether the cognitive part of the therapy (changing people's thought patterns) or the behavioural part (in the case of people with depression getting them to do pleasurable things again) is more effective. Researchers from Pacific University in Oregon and Harvard University studied the effect of CBT on 105 people receiving treatment in a private, psychiatric, partial-hospital setting. They found that a decrease in negative thoughts and an increase in positive behaviour both predicted a decrease in depressive symptoms. However, only a decrease in negative thoughts was predictive of patients' overall levels of psychological distress. The study found that a CBT intervention, adapted for use in a partial-hospital setting, could be an effective treatment for severe mood disorders.
Christopher, Michael S. ... [et al] - Cognitive and behavioral changes related to symptom improvement among patients with a mood disorder receiving intensive cognitive-behavioral therapy Journal of Psychiatric Practice March 2009, 15(2), 95-102