THERE have been few convincing research studies on the effectiveness of the various psychotherapies. The studies of large scope have typically had insufficient or inadequate controls. Other studies, often more adequate in methodology, have been so limited in scope that any generalization of their findings must be very tenuous. Until recently, few studies have built cumulatively on earlier ones to provide comparable rather than conglomerate data. As a consequence, we have little systematic experimental knowledge of psychotherapy, of its effectiveness, and of the factors facilitating its effects. Certainly the practice of psychotherapy has been influenced very little by the research literature.
The major problems that must be faced by any attempt to evaluate psychotherapy are that we are dealing with a treatment modality which has not been defined, the effects of which are presumed to require a long period of treatment, and the evaluation of which demands long-term
Fiske DW, Hunt HF, Luborsky L, Orne MT, Parloff MB, Reiser MF, Tuma AH. Planning of Research on Effectiveness of Psychotherapy. Arch Gen Psychiatry. 1970;22(1):22-32. doi:10.1001/archpsyc.1970.01740250024004