The substantial and often recurrent distress and impairment associated with major depressive disorder (MDD) in youth has prompted increased interest in the identification and dissemination of effective treatment models. Evidence supports the use of several antidepressant medications, specific psychotherapies, and, in the largest treatment study of depressed teenagers, the combination of fluoxetine and cognitive-behavioral therapy (CBT) as effective treatments.1-3 CBT is the most extensively tested psychosocial treatment for MDD in youth, with evidence from reviews and meta-analyses that supports its effectiveness in that population.3-5
CBT is a time-limited, problem- focused intervention that seeks to reduce emotional distress through the modification of maladaptive beliefs, assumptions, attitudes, and behaviors.6 As outlined by Lewinsohn and Clarke,7 different CBT interventions emphasize different techniques to effect change, with some interventions primarily targeting cognitive factors and others primarily targeting behavioral factors. Reflecting this distinction, there have been 2 major theoretical approaches to CBT with adolescents.
The first approach, identified with the cognitive therapy of Beck and his colleagues,8 is based on a model in which cognitive processes are seen as the major maintaining variables associated with MDD. In Beck's model, the task of the therapist is to enhance the patient's ability to monitor mood; identify connections between mood and cognition; and identify, challenge, and modify automatic thoughts, assumptions, and core beliefs that sustain MDD. This model has been adapted by Brent and colleagues9 for treating adolescents.
The second approach is more behavioral and multifactorial. Associated with Lewinsohn and colleagues,10 this approach has been used with adults and adolescents and is based on the assumptions that behavior and thoughts sustain depressed mood, and that either behavioral or cognitive change can serve as the engine of therapeutic progress.
Despite different areas of emphasis, both of the major CBT approaches posit that cognitive factors such as cognitive distortions, negative automatic thoughts, dysfunctional attitudes, negative attributional style, and hopelessness play a major role in the onset and maintenance of depressive symptoms.6 However, the specific cognitive processes through which CBT works to counter MDD in young people are not well understood. Understanding treatment mechanisms is of both theoretical and practical importance. A clear understanding of therapeutic mechanisms would allow psychosocial treatment developers to focus on the intervention components that are most effective, thereby promoting amplification of the more active components and reduction or removal of the less active elements. In addition, a review by Kazdin and Nock11 proposes that studying mechanisms of therapeutic change can assist the adoption of effective treatments by practicing clinicians.
In this article we focus on cognitive factors that have been shown to influence the effectiveness of CBT for adolescent MDD. We identify factors that affect CBT treatment outcomes by examining 3 types of variables: predictors, moderators, and mediators. Predictors are variables present before treatment that influence treatment outcomes across all treatment conditions. For example, if, in a comparison of CBT and a different psychotherapy for MDD, adolescents with high levels of hopelessness had worse outcomes across both conditions, then hopelessness would be considered a predictor.
Moderators are pretreatment factors that interact with the treatment conditions to predict treatment outcome, and thereby represent factors that predict a differential response to CBT. For example, if adolescents with high levels of hopelessness had better outcomes with CBT than with an alternative psychotherapy, hopelessness would be a moderator. Mediators are factors that account for or explain the process of therapeutic change during CBT. For example, if it were shown that CBT treatment outcomes were attributable to a reduction in hopelessness during treatment, then hopelessness would be a mediator.
Mediational analyses are those that are most valuable in highlighting processes of change associated with effective treatment. The evaluation of mediators can help address the following 3 questions, which have been explored in the literature on adults with MDD and are only beginning to be studied in adolescents with MDD. First, does CBT lead to changes in cognition associated with MDD? Second, if CBT leads to cognitive change, does the cognitive change lead to a reduction in symptoms of MDD? Third, is change in depressive cognitions unique to CBT, or is it associated with other effective treatments for MDD? In this article, we explore the first 2 questions with reference to studies of CBT that emphasize cognition, studies of multifactorial CBT, and the largest treatment study of CBT for adolescent MDD to date.
Of note, most clinical trials are sufficiently powered to test their main hypotheses, which pertain to outcome, and to identify predictors. By contrast, most trials are not sufficiently powered to test adequately for moderators or mediators. Therefore, most analyses for moderators or mediators must be considered exploratory.
CBT emphasizing cognition
The first major stream of CBT research in adolescent MDD has been the work of Brent and colleagues,9 who used Beck's theoretical approach to cognitive therapy. They adapted the Beck model for adolescents by including psychoeducation, problem solving, affect regulation, and social skills training. Nevertheless, the primary focus of treatment is on identification and modification of dysfunctional, depressogenic thinking.
One randomized trial has evaluated the effectiveness of the Brent model of individual CBT relative to 2 alternative psychotherapy conditions: Systemic Behavioral Family Therapy and Nondirective Supportive Therapy.9 In the sample of adolescents with MDD, CBT was found to be more effective in alleviating depression after 12 to 16 weeks of treatment than either of the 2 comparison psychotherapy conditions. Cognitive variables measured in this study, which were directly targeted by the CBT intervention, included cognitive distortions and hopelessness. Cognitive distortions were measured using the overall score on the Children's Negative Cognitive Errors Questionnaire,12 while hopelessness was measured using the Beck Hopelessness Scale.13
An investigation of predictors of treatment effect revealed that higher levels of both of these cognitive variables at intake predicted continued depression and failure to attain remission at termination.14 An additional predictor of negative treatment outcome was entering the study as a clinical referral, rather than in response to an advertisement. The effect of clinical referral status on treatment outcome was mediated by hopelessness, which reflects that adolescents who were referred to the study had higher levels of hopelessness than did adolescents who answered an advertisement. When controlling for adverse predictors including cognitive variables the efficacy of nondirective supportive therapy declined significantly, but not that of the other treatments. These findings support the overall robustness of CBT with patients who have dysfunctional cognitive processes.
More recent analyses of this trial provided additional information about the process of cognitive change during CBT and the other 2 psychosocial treatments.15 During treatment, CBT had a significantly greater impact in reducing cognitive distortions than did either of the other psychotherapies. Furthermore, when analyses included data from a 2-year follow-up assessment, CBT demonstrated significantly greater and more consistent improvement for cognitive distortions in children than did nondirective supportive therapy. By contrast, there was no difference among treatments in their impact on hopelessness.
Despite evidence of treatment- specific effects, cognitive distortion failed to meet the criteria for mediation because of the absence of group differences over time in the severity of depressive symptoms. As noted by the investigators, mediation in a treatment arm may have been difficult to show within the relatively brief time frame of acute treatment, particularly when considering the episodic nature of MDD among adolescents. The lack of significant mediators was congruent with the results of the literature on adults, which has generally been unsuccessful in identifying mediators of treatment effects for CBT interventions among patients with a confirmed diagnosis of MDD .16 It is of interest to note that Ackerson and colleagues17 found evidence that dysfunctional attitudes mediated response to a form of cognitive bibliotherapy based on the Beck cognitive model in a sample of 22 adolescents with depressive symptoms (not diagnoses). However, support for mediation was found only when symptoms and cognitions were both measured by self-report.
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