Credibility and outcome of cognitive-behavioural and psychodynamic-interpersonal psychotherapy.

Depressed psychotherapy clients (N = 117) rated the treatment principle credibility of cognitive-behavioural (CB) and psychodynamic-interpersonal (PI) before they were randomly assigned to receive either eight or 16 sessions of one of these treatments, and they rated their expectations of the treatment to which they were assigned immediately before (initial credibility) and immediately after their first session (emergent credibility). Results indicated that before they were assigned to a treatment, clients rated CB treatment principle credibility higher than PI treatment principle credibility. After assignment, however, clients rated initial credibility similar regardless of whether they were assigned to CB or PI therapy, and their ratings of emergent credibility increased to a similar degree from immediately before to immediately after the first session in both treatments. Clients' endorsement of CB and PI treatment principle credibility predicted improvement in PI therapy but not improvement in CB therapy. Initial and emergent credibility of clients' assigned treatment predicted improvement for clients who received eight sessions of therapy, but not for clients who received 16 sessions of therapy. The implications of these findings are discussed.