Lemmens, L.H.J.M., Arntz, A., Peeters, F., Hollon, S.D., Roefs, A., & Huibers, M.J.H. (2015). Clinical effectiveness of cognitive therapy v. interpersonal psychotherapy for depression: Results of a randomized controlled trial. Psychological Medicine, doi:10.1017/S0033291715000033
Generally, I prefer to report on meta analyses rather than individual studies mainly because findings from meta analyses are based on a larger number of studies and so are more reliable (see my November, 2013 blog). However, this study by Lemmens and colleagues represents a large clinical trial of 182 depressed patients who were randomized to cognitive therapy (CT), interpersonal psychotherapy (IPT), or a no-treatment control condition. The size of the trial provided the study with enough statistical power to test a hypothesis of non-inferiority of treatments. (A statistical note: A study finding of “non-inferiority” between treatments is sometimes unreliable because it is easier to detect such a finding with a small or poorly designed study. Studies with larger sample sizes provide greater statistical power, which in part makes a non-inferiority finding more reliable). A previous meta analysis showed both CT and IPT to be equally effective interventions for major depression. However, none of the studies in that meta analysis had sufficiently large sample sizes to reliably detect non-inferiority of interventions, none reported outcomes after post-treatment, and none of the studies used a no-treatment comparison condition. In their study, Lemmens and colleagues provided 16 to 20 sessions of individual therapy (45 minutes in length) to participants who met criteria for major depressive disorder. CT was based on Beck’s model and focused on identifying and altering cognitions, schemas, and attitudes associated with negative affect. IPT seeks to understand the social and interpersonal context of a patient’s depressive symptoms, and helps the patient to solve the interpersonal problem or change their relation to the problem, which may result in a resolution of the depressive symptoms. The study by Lemmens and colleagues was well designed in which: patients were randomized to conditions (CT, IPT, wait-list), 10 licensed therapists were expertly trained (5 CT therapists, 5 IPT therapists), and the therapies were competently delivered. Depressive symptoms significantly decreased for patients in both CT and IPT conditions with large effects, and these findings remained stable to 5 months post treatment. There were no differences between CT and IPT at post treatments and follow up, and both treatments were more effective than the waitlist control condition. Half of the sample had clinical improvements in symptoms, and 37% of patients were without depressive symptoms at 1 year follow up.
CT and IPT did not differ in the treatment of depression in the short (post-treatment) and long term (follow up). The study does not address why two very different treatments led to similar positive outcomes. The authors suggest two possible reasons: (1) different specific treatment pathways led to similar results, or (2) change was driven by factors common to both treatments like motivation and therapeutic alliance.