Everyone wins: the Dodo bird verdict and what science tells us about why psychotherapy works

If psychotherapy were like medicine or engineering, one might expect that decades of research, thousands of clinical trials, and the development of hundreds of new therapeutic models would have produced substantial improvements in patient outcomes. The evidence, however, suggests otherwise.

An umbrella review published by Leichsenring et al. (2022) in World Psychiatry — one that carefully evaluated study bias and used placebo or treatment-as-usual as comparators — found modest effect sizes (d = 0.34) for psychotherapies. After more than half a century of research, thousands of randomised controlled trials and millions in funding, effect sizes remain limited, suggesting a ceiling effect for treatment research as currently conducted.

The Dodo bird verdict: everyone wins, everyone deserves a prize

To understand why this happens, we need to go back to 1936, when psychologist Saul Rosenzweig published a brief but seminal paper observing that different therapeutic approaches produced similar outcomes — and that this was probably due to common elements: empathy, hope, the therapeutic relationship. Drawing on Alice in Wonderland, he applied the Dodo bird's words to psychotherapy: "Everyone has won and all must have prizes."

This idea gained empirical weight in the decades that followed. In 1975, Luborsky et al. published one of the first systematic comparative studies across different psychotherapies and found few significant differences. The definitive confirmation came with the work of Wampold et al. (1997), whose meta-analysis concluded that real differences in efficacy between bona fide psychotherapies are essentially zero.

So what is it that heals?

If it is not the technique, what explains the effectiveness of psychotherapy? The answer lies in what are called common factors: elements present across all psychotherapies regardless of their theoretical orientation. The therapist's empathy, unconditional positive regard, authenticity, and the warmth of the relationship.

Wampold (2001) estimated that only around 13% of the total variance in therapeutic outcomes is attributable to the treatment itself — including the alliance, the model, the technique and the therapist — while the remaining 87% corresponds to client factors and extra-therapeutic variables.

What humanistic psychotherapy knew before science did: relationship, presence and the therapeutic bond

There is something deeply significant in these findings for those of us who work from a humanistic perspective. Carl Rogers did not wait for meta-analyses to know that the therapeutic relationship was at the heart of the change process. He articulated it with precision and humility in the 1950s and 60s, precisely when humanistic psychotherapy was emerging as a response to the mechanistic models of the time.

Science, with its statistical tools and thousands of controlled trials, has taken decades to reach a conclusion that the humanistic tradition carried in its DNA from the very beginning: what heals is presence, attentive listening, and relationship.