Overview
The Dodo bird verdict/conjecture is a claim that all psychotherapies, when practiced with equivalent treatment fidelity, produce equivalent outcomes in a patient’s symptoms. Rather than being a concrete finding that devastated the field of clinical psychology, the claim leads us to difficult questions about the biases and subjective elements of evaluating evidence of effectiveness. Some therapies are harder to standardize and measure in a way that allows for randomized controlled trials (RCTs), such as humanistic therapies that are, by their core tenets, designed to be highly tailored for unpredictable individual needs while resisting the diagnostic categories researchers look for to set up experiments. Even meta-studies that examine hundreds of experiments are accused of cherry-picking research that aligns with the biases of the authors; publication biases mean that even if a study were conducted perfectly, its authors may not submit it for publication. An entire field called metascience exists that tackles these concerns.
As a result, people may understandably hold opinions ranging from a belief that most published studies indicate little about reality to the belief that the Dodo bird verdict is driven by charlatans and snake oil salesman who seek to undermine the credibility of mainstream scientific institutions while pushing their own brand of iconoclastic research. There are, of course, middle-grounds. Many argue that the Dodo bird verdict takes an overly broad understanding of “effectiveness” that overlooks how some therapeutic interventions may work much better for specific psychiatric disorders than others. If modality A reduces symptoms by 25% for condition X and 10% for condition Y, while modality B reduces symptoms by 25% for condition Y and 10% for condition X, they may appear to have an overall equivalent impact. In reality, we still have reasons to strongly prefer certain modalities for certain conditions or disorders. Many clinicians and researchers are also concerned that the Dodo bird verdict overlooks the active harm that can be caused by bad combinations of interventions and patient profiles. Technically, licensed therapists and psychologists don’t take the Hippocratic Oath to first do no harm, but it’s still understandably an ethical concern.
One of the most popular theories offered to explain the mechanisms of the Dodo bird verdict is the common factors theory, which argues that successful therapeutic interventions are driven primarily by the factors they have in common with other modalities. For instance, the therapeutic alliance, or the affirming connection between a client and a therapist that builds the confidence to be vulnerable and discuss solutions over a period of time, has been found in some meta-studies to account for up to 70% of the variation in therapeutic impacts. The specific type of therapy has sometimes been found to only account for 5% of the variation in outcomes.