Aim of the study:
While there has been some evidence supporting the relevance of patients’ perceptions of treatment credibility to the process and outcome of individual cognitive behavioural therapy (CBT), its importance to group CBT remains unknown. Moreover, no studies to date have explored potential mechanisms through which perceived treatment credibility may contribute to therapeutic change. To address this void, this pilot study investigated associations between patients’ perceptions of treatment credibility and outcome among psychiatric outpatients receiving group CBT for depression. A secondary aim was to determine whether the therapeutic alliance mediated the effect of credibility on treatment outcome.

Subject or material and methods:
Consecutively admitted outpatients (N=80) completed measures of credibility, alliance, and outcome.

Results:
Findings indicated that higher ratings of credibility were associated with greater improvement in interpersonal problems, but were unrelated to changes in depression, anxiety, and quality of life. We did not find evidence for the alliance serving as a mediator. Yet, we found a direct relationship between credibility and alliance.

Discussion:
Depressed patients who perceive treatment to be more credible may be more likely to engage in meaningful exchanges with fellow group members, thus leading to improvement in interpersonal problems.

Conclusions:
In a group context, there are many agents of influence, with the other group members, the therapist, and the group-as-a-whole each having some effect. This study has helped illuminate one aspect of the therapist's influence on the group, as perceived by patients.