The Dodo Bird and the need for scalable interventions in global mental health—A commentary on the 25th anniversary of Wampold et al. (1997)

About one billion people worldwide suffer from a mental disorder (World Health Organization [WHO], 2022). Depression (280 million people) and anxiety (301 million) are the largest groups, but also other disorders such as developmental disorders, ADHD, schizophrenia, and bipolar disorders affect millions of people worldwide. Mental disorders are the leading cause of years lived with disability across all disorders. Apart from the personal suffering of patients and their relatives, depression, and anxiety alone cost nearly US$1 trillion per year because of lost productive workdays (Chisholm et al., 2016).

More than 80% of people with mental disorders live in low- and middle-income countries (LMICs). For example, there are more people with depression in China than the total population of Spain. However, LMICs hardly have resources to invest in mental health care and the majority of people in LMICs suffering from mental disorders hardly have access to treatment. In order to reduce this enormous disease burden in LMICs, we need treatments that are brief, efficient but also scalable. Even if LMICs would have the resources, there are only few trained clinicians to deliver treatments. In low-income countries, there are fewer than one mental health worker per 100,000 population (WHO, 2022).

Most psychotherapy researchers would not consider the study by Wampold and colleagues in 1997 (Wampold et al., 1997) on the comparable effects of different types of therapy directly relevant to these challenges in global mental health, but it certainly is as I will explain later in this article. Most researchers consider the study by Wampold and colleagues relevant to the question of whether all therapies have comparable effects, the “Dodo Bird Verdict” and the “common factors” model. We have argued elsewhere that comparative effects may support the common factors model and the Dodo Bird Verdict, but there are also other explanations for comparative effects that would not support the common factors model (Cuijpers, Reijnders, et al., 2019). However, whether or not one agrees with the conclusions of Wampold and colleagues about the equivalence of psychotherapies, their 1997 study did start up these highly relevant discussions on common factors. This study generated a whole line of research on these topics. It also stimulated researchers and clinicians to think more critically about the working mechanisms of therapies and how these can be examined.

The 1997 study of Wampold also has major consequences for global mental health. Whether or not there are small differences between therapies and whether these effects are realized by common or specific factors, it is clear that most of the therapies work with no or only minor differences between them. And if all bona fide therapies work, one can raise the question of what is at least necessary for a therapy to work. Can we minimize therapies and take off elements without reducing the effects? And that is highly relevant if we want to develop minimal interventions that can be disseminating broadly across low-resourced setting at low cost and with no or minimal input from highly trained mental health professionals.

From a global mental health perspective, it would also be fine if a treatment is somewhat less effective than full therapies delivered by highly trained specialists. If it can be disseminated on a large scale, even a small effect can have a huge public health impact. But the finding that all bona fide therapies have roughly comparable effects, has the promise of developing minimized therapies that are scalable across low-resources settings, without reduced effects. Whether therapies work through common or specific factors is an important question from a scientific perspective and from a clinical perspective. However, the fact that therapies have roughly comparable effects and they may be minimized without reduced effects, has huge public health consequences that go beyond theoretical and clinical relevance. This may be a major factor in providing hundreds of millions of people across the globe with minimized, effective therapies.

Until now two major lines of research within the global mental health field have focused on minimizing psychological treatments. One important line of research is focused on so-called task-shared psychotherapies. Task-sharing is the delegation of tasks to community or primary care-based non-specialist workers and it has been advocated as a solution to address the lack of skilled mental health practitioners (Raviola et al., 2019). There is considerable evidence that brief psychotherapies delivered by lay-health counselors, often nurses working in primary care, is effective in LMICs (Karyotaki et al., 2022). Of course, it remains necessary that such interventions are culturally adapted to meet the local definitions of mental ill-health and how to handle them (Benish et al., 2011).

Another line of research is focused on guided self-help. There is considerable evidence that guided self-help is as effective as face-to-face treatments (Cuijpers, Noma, et al., 2019), while such treatments cost far less time from professionals and can also be delivered by mental health professionals with considerably less training than psychotherapists. Most research on guided self-help is conducted in high-income countries, but a growing number of studies is examining if such interventions can be successfully applied in LMICs. For example, we found in a randomized trial that a smartphone-based guided self-help intervention was effective in treating depression in Syrian refugees in Lebanon (Cuijpers et al., 2022a), as well as in other people living in Lebanon (Cuijpers et al., 2022b).

There are other ways to minimize psychological interventions and make them more efficient, for example by reducing the number of sessions, by delivering them by telephone or in groups, or as unguided interventions. Each of these options is now examined in more depth by several research groups across the globe, and they may come up with new, effective, and scalable interventions that may contribute to the reduction of the disease burden of mental disorders around the globe.

The 1997 Wampold study can very well be considered as the start of dividing the prizes of effective psychotherapies somewhat more equally across the world. Our proposed approach is a modest attempt to reduce the enormous global burden of mental disorders.

Disclosure Statement

No potential conflict of interest was reported by the author(s).