Common versus specific factors in psychotherapy: opening the black box.

Do psychotherapies work primarily through the specific factors described in treatment manuals, or do they work through common factors? In attempting to unpack this ongoing debate between specific and common factors, we highlight limitations in the existing evidence base and the power battles and competing paradigms that influence the literature. The dichotomy is much less than it might first appear. Most specific factor theorists now concede that common factors have importance, whereas the common factor theorists produce increasingly tight definitions of bona fide therapy. Although specific factors might have been overplayed in psychotherapy research, some are effective for particular conditions. We argue that continuing to espouse common factors with little evidence or endless head-to-head comparative studies of different psychotherapies will not move the field forward. Rather than continuing the debate, research needs to encompass new psychotherapies such as e-therapies, transdiagnostic treatments, psychotherapy component studies, and findings from neurobiology to elucidate the effective process components of psychotherapy.