Do all psychotherapies work equally well? The "Dodo bird verdict" debate

In Lewis Carroll's Alice's Adventures in Wonderland, the Dodo has everyone run around a lake until dry. Nobody measures who ran how far, and when asked who won, the Dodo says: "Everybody has won and all must have prizes." In 1936 the psychologist Saul Rosenzweig borrowed the scene to make a point about psychotherapy. The Dodo bird verdict is the claim that all empirically validated psychotherapies, whatever their specific components, produce equivalent outcomes.

Rosenzweig argued that "common factors" matter more than the technical differences between schools. The debate took flight in 1975, when Lester Luborsky and colleagues reported one of the first comparative studies showing few significant differences in outcomes among different psychotherapies. Supporters say therapies are equivalent because of shared ingredients, such as a relationship with a therapist who is warm, respectful and expects the client to succeed. One such factor is the therapeutic alliance, a partnership between patient and therapist that allows them to achieve goals through agreed-upon tasks. A meta-analysis of 295 studies and over 30,000 patients confirmed a moderate relationship between alliance and outcome.

Critics answer that specific techniques matter. They point to anxiety disorders, where CBT has been found beneficial and is reported to have produced effect sizes of 0.51 for generalised anxiety disorder and 0.62 for social anxiety disorder. Each side attacks the other's studies: one challenge to the critics is that some studies compared therapy with waiting lists or medication, while Bruce Wampold, a supporter of the verdict, argued in 2009 that a 2007 result favouring CBT in panic disorder rested on a single experiment with an uncharacteristically large effect.

Even the framing is disputed. According to one review, the common-versus-unique debate is widely recognised as a false dichotomy: therapists must use specific forms of therapy for common factors to have a medium through which to operate.