A total of 117 depressed clients, stratified for severity, completed 8 or 16 sessions of manualized treatment, either cognitive-behavioral psychotherapy (CB) or psychodynamic-interpersonal psychotherapy (PI). Each of 5 clinician-investigators treated clients in all 4 treatment conditions. On most measures, CB and PI were equally effective, irrespective of the severity of depression or the duration of treatment. However, there was evidence of some advantage to CB on the Beck Depression Inventory (Beck, Ward, Mendelson, Mock, & Erbaugh, 1961). There was no evidence that CB's effects were more rapid than those of PI, nor did the effects of each treatment method vary according to the severity of depression. There was no overall advantage to 16-session treatment over 8-session treatment. However, those presenting with relatively severe depression improved substantially more after 16 than after 8 sessions.
Shapiro et al. (Sat,) studied this question.