AS A PROSPECTIVE client searches for a psychotherapist, numerous questions may spring to mind. How experienced is the therapist? Has he helped people with problems like mine? Is she someone I can relate to? Yet it may not occur to clients to ask another one: What type of therapy does the clinician deliver? People often assume that the brand of therapy offered is irrelevant to the effectiveness of treatment. Is this assumption correct?

Psychologists do not agree on whether the “school” of therapy predicts its effectiveness. In a survey in 2006 by psychologists Charles Boisvert of Rhode Island College and David Faust of the University of Rhode Island, psychotherapy researchers responded to the statement that “in general, therapies achieve similar outcomes” with an average score of 6 on a 7-point scale, indicating strong agreement. In contrast, psychologists in practice averaged a rating of 4.5, signifying that they agreed only moderately with that position.

As we will discover, both camps can justify their point of view. Although a number of commonly used psychotherapies are broadly comparable in their effects, some options are less well suited to certain conditions, and a few may even be harmful. In addition, the differences among therapies in their effectiveness may depend partly on the kinds of psychological problems that clients are experiencing.

Tale of the Dodo Bird

At least 500 different types of psychotherapy exist, according to one estimate by University of Scranton psychologist John Norcross. Given that researchers cannot investigate all of them, they have generally concentrated on the most frequently used approaches. These include behavior therapy (altering unhealthy behaviors), cognitive-behavior therapy (altering maladaptive ways of thinking), psychodynamic therapy (resolving unconscious conflicts and adverse childhood experiences), interpersonal therapy (remedying unhealthy ways of interacting with others), and person-centered therapy (helping clients to find their own solutions to life problems).

As early as 1936, Washington University psychologist Saul Rosenzweig concluded after perusing the literature that one therapy works about as well as any other. At the time, many of the principal treatments fell roughly into the psychodynamic and behavioral categories, which are still widely used today. Rosenzweig introduced the metaphor of the Dodo Bird, after the feathered creature in Lewis Carroll's Alice in Wonderland, who declared following a race that “everyone has won, and all must have prizes.” The “Dodo Bird verdict” has since come to refer to the claim that all therapies are equivalent in their effects.

This verdict gained traction in 1975, when University of Pennsylvania psychologist Lester Luborsky and his colleagues published a review of relevant research suggesting that all therapies work equally well. It gathered more momentum in 1997, when University of Wisconsin–Madison psychologist Bruce E. Wampold and his co-authors published a meta-analysis (quantitative review) of more than 200 scientific studies in which “bona fide” therapies were compared with no treatment. By bona fide, they meant treatments delivered by trained therapists, based on sound psychological principles and described in publications. Wampold's team found the differences in the treatments' effectiveness to be minimal (and they were all better than no treatment).

One explanation for the Dodo Bird effect is that virtually all types of psychotherapy share certain core features. In a classic 1961 book the late psychiatrist Jerome Frank of the Johns Hopkins University argued that all effective therapies consist of clearly prescribed roles for healer and client. They present clients with a plausible theoretical rationale and provide them with specific therapeutic rituals, he wrote. They also take place in a setting, usually a comfortable office, associated with the alleviation of distress. Later writers elaborated on Frank's thinking, contending that effective therapies require empathy on the part of the clinician, close rapport between practitioner and client, and shared therapeutic goals.

Today many authors argue that these and other common elements are even more powerful than the features that distinguish one therapy from another. To take just one example, Wampold concluded in a 2001 analysis that the therapeutic alliance—the strength of the bond between a therapist and his or her client—accounts for about 7 percent of therapeutic effectiveness but that the school of the therapy accounts for only about 1 percent. Most of the remaining 92 percent is presumably caused by other factors, such as the personalities of the therapist and client.

Is the Dodo Bird Extinct?

Although most researchers agree that common factors play key roles in psychotherapy, some doubt that all methods are equally effective. Even Wampold has been careful to note that his conclusion holds for only bona fide treatments; it does not extend to all 500 or so therapies. For example, few experts would contend that rebirthing therapy, premised on the dubious idea that we must “relive” the trauma of our birth to cure neurosis, works as well as cognitive-behavior therapy for most psychological conditions.

Moreover, research suggests that even among accepted therapies, the type of treatment does matter under certain circumstances. A 2001 review by University of Pennsylvania psychologist Dianne Chambless and Virginia Polytechnic Institute psychologist Thomas Ollendick revealed that behavior therapy and cognitive-behavior therapy are more effective than many, and probably most, other treatments for anxiety disorders and for childhood and adolescent depression and behavioral problems. In addition, in a 2010 meta-analysis psychologist David Tolin of the Institute of Living in Hartford, Conn., found that these same two therapy types produce better results than psychodynamic therapy for anxiety and mood disorders.

The Dodo Bird verdict must also be qualified by evidence indicating that several widely used therapies do not work and may actually harm. For example, in a 2003 review psychologist Richard McNally of Harvard University and his colleagues evaluated crisis debriefing. In this treatment for warding off post-traumatic stress symptoms, therapists urge those exposed to emotionally fraught events such as shootings or earthquakes to try to reexperience the feelings they had during the event soon after it. McNally's team concluded that this treatment is inert at best and possibly damaging, perhaps because it interferes with natural coping mechanisms.

In light of such findings, a search for a therapist should at least sometimes involve a consideration of the type of treatment he or she practices. It is true that ingredients, such as empathy, that cut across effective therapies are potent and that various established techniques are roughly equivalent for a broad range of difficulties. Yet under certain circumstances, the therapeutic method can matter. For example, if a clinician espouses an approach outside the scientific mainstream—one that does not fall under the broad categories we have listed here—you should not assume that this treatment will be as helpful as others. If you suffer from an anxiety disorder or one of the other conditions for which behavior and cognitive-behavior interventions work well, then someone who practices one of those two types is probably a good bet.

Of course, scientists have systematically assessed only a minority of the psychotherapies invented so far for their efficacy in treating the numerous psychological difficulties that afflict humankind. In the coming decade, we hope that further research clarifies whether the brand of therapy makes a difference in an individual's recovery from psychological distress.

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