“As a clinician I try to follow new research that is published, and I often see that trials and meta-analyses comparing different therapies usually do not find any significant differences between them. Doesn’t that mean that all therapies work equally well, and that human support is the most important factor in therapy, regardless of type?”
Many comparative studies find no differences — but the picture is more complex
It is true that many trials and meta-analyses examining the relative effects of different types of psychotherapy find no significant differences between treatments. However, there are several important points to keep in mind when reading these studies.
First, not all meta-analyses find that the effects of therapies are comparable across all mental health conditions — several do find significant differences. Second, if all therapies truly had comparable effects, their relative effects should also point in the same direction, and the variability between those differential effects (heterogeneity) should be small. That is certainly not what all comparative meta-analyses find.
The statistical power problem
Another important problem with these studies is that they almost never have the statistical power to identify differences between therapies — meaning that far too few patients are included. A randomized trial comparing two therapies needs more than 500 participants to be able to detect a small but clinically relevant difference. Such trials are hardly ever conducted in the psychotherapy field. Even when the results of such trials are pooled in a meta-analysis, the combined statistical power is in most cases still insufficient to identify clinically relevant differences.
“No significant difference” is not the same as evidence that two treatments are equivalent. In most cases, the study simply was not large enough to detect a real difference if one exists.
What are “bona fide” treatments — and why does it matter?
One important problem is that some therapies in research are often designed to fail. They are created merely to show that the “real” therapy is more effective by comparison — these are sometimes called “intent-to-fail” or non-bona fide treatments.
Bona fide (Latin for “in good faith”) treatments are therapies that are genuinely developed with therapeutic intent: theoretically grounded, structured, and delivered by trained clinicians. Non-bona fide treatments, by contrast, are minimal comparison conditions that were never expected to work well. Because non-bona fide treatments are often less effective than serious therapies, including them in trials and meta-analyses can create the appearance of differences between therapies where none may actually exist.
Proponents of the bona fide distinction argue that all differences between therapies can be explained by the inclusion of non-bona fide treatments. This is indeed a good argument — but it does not explain all the differences found in the literature, nor the remaining heterogeneity, and it does not resolve the problem of statistical power.
“Equally effective” does not mean “anything goes”
Perhaps the most important point to keep in mind is that all bona fide therapies are well-developed, standardized, and delivered by trained clinicians. Even if all therapies have comparable effects, that does not mean that a therapist can simply do whatever they please. Only well-developed and standardized therapies have been shown to work. Whether an unstructured approach would be equally effective has not been examined, and it is not known whether that works just as well.
Different roads can lead to the same destination
Even if therapies have comparable effects, that does not mean they work in the same way. It is possible that “many roads lead to Rome” — that mechanisms differ even when outcomes are the same.
For example, depression is a problem that affects many different areas of life. When someone learns to solve problems more effectively, that may lead to more positive thinking, more pleasant activities, and less depression. But increasing pleasant activities may also result in more positive thinking, better problem-solving skills, and less depression. And more positive thinking can itself lead to more pleasant activities, better problem-solving skills, and less depression. In such cases the mechanisms are completely different, but the effects are the same.
What happens when standard therapies are not enough?
It should also be kept in mind that most research focuses on protocolized and manualized therapies — and the effects of these therapies are limited. Across most mental disorders, response rates fall between 30 and 42%: roughly that proportion of patients see their symptoms halved by the end of treatment. This means that many patients do not get better, even after two or three treatments.
In these cases, the clinical experience of the therapist becomes even more important, and simply knowing how to conduct protocolized treatments is not enough. Equally, being empathic, non-judgmental, and reflective is not sufficient either, because those elements were already part of the earlier treatment(s). The clinician will need to discuss the next options, examine the patient’s personal situation more deeply, and search for new potential solutions. Clinical experience and a thorough understanding of the individual’s specific mental health problem is essential in these cases.
- For more on how psychotherapy trials are designed and what they can and cannot tell us, see What makes randomized controlled trials the gold standard?
- For a related discussion on change mechanisms, see Is the therapeutic alliance the most important part of therapy?
- For a closer look at whether one specific approach leads the field, see Is cognitive behavior therapy the best treatment for everyone?
Pim Cuijpers is professor emeritus of clinical psychology and scientific director of Metapsy. He has been involved in more than 1,100 scientific studies, mostly on psychological treatments of mental health problems. This is one of a series of evidence summaries in which Prof. Cuijpers tries to answer questions from patients and clinicians, based on what is known in science about treatments. The knowledge is mostly drawn from collective work of the Metapsy collaboration of at least 15 years. Do you have other questions you would like Prof. Cuijpers to discuss? Feel free to contact us.
Literature
- Cuijpers P, Reijnders M, Huibers MJH. (2019). The role of common factors in psychotherapy outcomes. Annual Review of Clinical Psychology, 15, 207–231.
- Cuijpers P, Harrer M. (2026). How to solve the problem of low power in comparative outcome studies in psychotherapy? Psychotherapy Research, epub ahead of print. https://doi.org/10.1080/10503307.2026.2666621
- Cuijpers P. (2016). Are all psychotherapies equally effective in the treatment of adult depression? The lack of statistical power of comparative outcome studies. Evidence-Based Mental Health, 19, 39–42.