"Are all psychotherapies equivalent?".

Despite clear demonstrations by process researchers of systematic differences in therapists' techniques, most reviews of psychotherapy outcome research show little or no differential effectiveness of different psychotherapies. This contradiction presents a dilemma to researchers and practitioners. Numerous possible solutions have been suggested. Some of these challenge the apparent equivalence of outcome, arguing that differential results could be revealed by more sensitive reviewing procedures or by more differentiated outcome measures. Others challenge the seeming differences among treatments, arguing that, despite superficial technical diversity, all or most therapies share a common core of therapeutic processes. Still others suggest that the question of equivalence is unanswerable as it is usually posed but that differential effectiveness of specific techniques might be found at the leve ! of brief events within therapy sessions. In spite of their diversity, many of the proposed solutions converge in calling for greater precision and specificity of theory and method in psychotherapy research. Despite the ple thora of purpor tedly distinct psychotherapeutic t rea tments (Parloff, 1976, 1984), influential reviews of comparat ive outcome research (Luborsky, Singer, & Luborsky, 1975; Smith, Glass, & Miller, i 980) together with frequently cited studies (e.g., Sloane, Staples, Cristol, Yorkston, & Whipple, 1975) appear to suppor t the conclusion that ou tcomes o f diverse therapies are generally similar. Efforts to base public policy r ecommenda t ions concerning menta l health care service provisions on scientific evidence have yielded only "a consensus, o f sorts, . on the question o f the efficacy of psychotherapy as a generic t r ea tment p r o c e s s . , that psychotherapy is more effective than no t r ea tmen t " (VandenBos & Pino, 1980, p. 36). N o such consensus exists concerning the relative effectiveness of diverse therapies (e.g., DeLeon, VandenBos, & Cummings , 1983; Kiesler, 1985; Office of Technology Assessment, 1980). The verdict o f the Dodo bird in Alice's Adventures in Wonderland (Carroll, 1865/ 1962), used as a subtitle by Luborsky et al. (1975), "Eve rybody has won and all must have prizes," captures this si tuation mos t vividly x and invites the question o f our present title: "Are all psychotherapies equivalent? " The s ta tement that two (or more) therapies are equivalent could have three quite different meanings. The first is equivalence o f o u t c o m e t h a t t rea tments yield ou tcomes that cannot be distinguished (the " D o d o bird verdict"). The second is equivalence of c o n t e n t t h a t the behavior o f part icipants in different therapies cannot be distinguished. The third is equivalence o f m e c h a n i s m that different psychotherapies employ c o m m o n principles o f psychological change. In this article, we first delineate the apparen t paradox: the lack o f differential effectiveness contrasted with evident technical diversity, that is, ou tcome equivalence contrasted with content nonequivalence. We then consider the resolutions o f the paradox that have been put forward, along with the a rguments and evidence that have been adduced in their support . We believe that considering alongside one another the traditionally separated research domains of therapy process and ou tcome brings into clearer focus the current strategic issues for psychotherapy