The Dodo Bird Conjecture: Are All Therapies The Same?

Do psychological therapies work? Yes, psychological therapies work. However, there are certain keys for this to really be the case. Claiming that therapy works is not the same as saying that all psychological therapies work or that they all have similar results. These controversial claims are set out in the Dodo bird verredict or the Dodo bird conjecture.

Saul Rosenzweig, an American psychologist, raised the Dodo Bird Conjecture in 1936, choosing that name after the homonymous character in Lewis Carroll’s Alice in Wonderland .

In this conjecture, Rosenzweig stated that all empirically validated psychotherapies, regardless of their specific, different and concrete elements, presented similar results.

What is an empirically validated therapy?

In the methodological study of psychological therapies, the validity of one or the other can be established. Rosenzweig, in the Dodo Bird Conjecture, did not say that any therapy was valid, but spoke exclusively of empirically validated therapies or well-established treatments.

Thus, depending on the criteria you meet, a therapy is considered:

• Well-established treatment – this is the group of therapies that the American psychologist talks about. For a therapy to be considered a well-established treatment, at least two group-design studies must have been conducted by different investigators. In those studies, the efficacy of the treatment had to be demonstrated.

If group design studies cannot be carried out, a treatment can also be considered well established if it has a large series of single case studies collecting data on its effects.

• Probably effective treatment : a therapy is established as probably effective when it proves more effective than the waiting list in the control group, that is, it is more effective than if people did not receive any type of treatment. Treatment would also be included in this group if, even with two studies with group design, both were developed by the same investigator. It also happens when the sample of studies is small.
• Treatment in experimental phase: this category includes promising therapies, but that do not meet the criteria of the previous phases.

What do the meta-analyzes say about the Dodo Bird Conjecture?

Wampold, Mondin et al. (1997) carried out a meta-analysis of the different results obtained in different psychotherapies, comparing them. They wanted to see if what Rosenzweig said in 1937 was true.

Is it true that all empirically validated therapies, be it cognitive-behavioral, or dialectic-behavioral, for example, have similar results?

Under this premise, what sense would the struggle between different psychological currents have, if in the end the effects are the same?

The results that Wampold et al. they obtained did not falsify the conjecture of the Dodo bird. In fact, they found evidence to support Rosenzweig’s conjecture. Comparing the results of the studied therapies, they observed that the efficacy of the empirically validated treatments was very similar, and their effect sizes were close to 0.

The superiority of cognitive behavioral therapy

The dominance of cognitive-behavioral therapy (CBT) has been defended tooth and nail by the psychological community. Its good results and efficacy are evident and therefore it constitutes a well-established treatment.

However, is it true that CBT achieves superior results than other therapies?

Wampold, Flückiger, Del Re et al. (2017) carried out three meta-analyzes of the different results obtained by cognitive-behavioral therapy.

The conclusion they reached is that the meta-analytical evidence shows that CBT is not superior to other therapies in terms of results. Therefore, it seems that CBT is also included in the Dodo Bird Conjecture.

What is common weighs more than what is different

In 1992, Lambert tried to identify the factors that influence the outcome of a therapy. Although his conclusions come from research and not from a meta-analysis -with a solid statistical basis-, he anticipated that the weight of the specific techniques of each therapy was 15 percent. On the other hand, it also reflects that the client’s expectations would also have a significant weight in the final result of the intervention.

The interesting thing is to observe how Lambert considered that the extra-therapeutic and specific factors of the patient constituted 40 percent of the therapeutic change, while 30 percent of the therapeutic change was attributed to the common factors of all the therapies.

Norcross and Lambert reviewed the study of the second in 2011. Among other conclusions, they stated that the chosen method or treatment (always speaking of course of empirically validated therapies) had a weight of only 8% in the therapeutic change.

What are the common factors of therapy?

Knowing the results of the different meta-analyzes made in this regard, it seems that there is no evidence to falsify the hypothesis of the Dodó bird conjecture: the exclusive elements of each therapy are only responsible for the therapeutic change in 15%.

The common elements of all therapies double their influence on therapeutic change. What are those elements that appear in all therapies?

Bergin and Garfield, assisted by Lambert, present in their Handbook of Psychotherapy and Behavior Change up to 33 common elements in all empirically validated therapies. Some of them are:

• Confidence.
• Cognitive learning.
• Changing expectations of personal efficacy.
• Warmth, empathy, respect, authenticity.
• Assimilation of problematic experiences.
• Cognitive mastery.
• Emotional regulation.
• Affective experience.

These studies seem to show that common elements in therapies, such as those discussed above, have more weight in therapeutic change than those different elements.

For this reason, it seems more important to work on the therapeutic alliance, cohesion, empathy or consensus on objectives, rather than seeking the superiority of one model or another.

Conclusions: the Dodó bird seems to be right

In this way, according to the various meta-analyzes, it seems that the Dodo bird conjecture is true. So far, empirically validated therapies seem to produce similar results – speaking of groups, not individual outcomes.

This is explained because in the process of change there are other variables with a lot of weight in the final result. Does that mean that the currents should disappear, and there should only be one type of therapy? This need not be so.

It is unknown whether a single therapeutic model would be beneficial to users. However, what we do know is that the diversity of therapies responds to a very heterogeneous human nature. Keeping these common elements, suggesting different therapies can be useful for the user.

Perhaps there are people who prefer the methodology of cognitive-behavioral therapy, others who are better adapted to a behavioral activation therapy and others who work more comfortably in an interpersonal therapy.

The approaches are usually different, being able to adapt better or worse to the particularities of each client. Thus, the most precise conclusion of this article would be that the conjecture of the Dodo bird has not been falsified.