Hayes and Hofmann’s paper1 is much welcome. As they argue, there is a need to re-evaluate assessment and treatment prac­tices that are solely or primarily based on psychiatric diagnoses. Diagnoses do not sufficiently account for individual differences, and additional information is usually needed to implement a psychological intervention. In one of our clinical trials aimed at decreasing the symptoms of depression2, participants with an ICD-10 diagnosis of a depressive condition reported 5 to 15 additional psychological problems.

Several significant behavioral problems can be overlooked and left untreated if the treatment providers only focus on one or two syndrome categories. Diagnostic categories could be used, for example, when making decisions regarding financial support in the case of sick leave. However, alternative behavioral assessment models should be used when making decisions about the type of intervention methods that are needed.

If we complete an individual behavioral assessment, for example by applying a case formulation model, it appears that several factors have contributed and continue to contribute to symptoms of depression. Log­ically, this leads to the conclusion that there are several potential ways to treat depression, and that the treatment could focus on several maintaining factors. However, in the field of behavioral science, progress is not facilitated by increasing the number of behavioral treatment models; rather, it is linked to identifying the essential processes that explain the beneficial changes that occur due to psychological interventions.

As Hayes and Hofmann1 point out, we have seen a considerable increase in the number of studies on psychological processes of change in cognitive behavioral therapies (CBTs). Thus, the focus on intervention studies has turned more toward the question of why psychological interventions are effective instead of just asking if they are effective. However, psychological processes of change appear to be a very complex issue. Several processes may explain why psychological interventions are effective for reducing certain symptoms, and there can be different combinations of processes that are essential when treating symptom X in comparison to symptom Y.

In a study exploring – by the Five Facet Mindfulness Questionnaire (FFMQ)3 – which of the mindfulness facets (observing, describing, acting with awareness, non-judging, and non-reacting) mediated the effects of a mindfulness-, acceptance-, and value-based intervention on three burnout dimensions (exhaustion, cynicism, and reduced professional efficacy), we found that a large spread of mindfulness facets mediated changes in all the burnout dimensions during the intervention4. However, only im­provement in non-judging skills mediated the reduction in all burnout dimensions during the follow-up. So, the identification of the psychological processes that mediate changes in symptoms not only during but also after any intervention can help us increase the impact of that intervention and allow a more cost-effective use of resources.

The newer forms of CBT should include an individual behavioral assessment of psy­chological processes. This procedure is far more complex and sophisticated than labeling (or naming) individuals according to diagnostic categories. As Hayes and Hofmann state, the field needs to move towards a process-based functional analysis.

The authors also mention that recent findings would require a major shift in the competences needed for practicing CBT. At present, there is limited evidence of the relationship between therapeutic competence and outcome of psychotherapies, and this relationship is usually found to be weak5, 6. The focus on packages for syndromes, the difficulties in measuring competence, and the limited knowledge about and understanding of the processes of change may have contributed to this. Giv­en the emerging consensus on empirical­ly-established psychological processes of change, we need methods to assess whether the relevant competences have been acquired during training; for example, whether therapists are capable of identifying and targeting central processes of change. There is also a need to develop assessment procedures to evaluate whether professionals are capable of delivering process-based treatments.

Hayes and Hofmann review a significant number of studies identifying processes of change. They propose that it is useful to organize the large number of psychological processes into dimensions, and they classify them into six dimensions. However, it is challenging to limit the classification to so few dimensions. The following are examples of the possible challenges. The dimension “cognition” is suggested to include the process of non-reactivity. This is somewhat problematic, since in the FFMQ3 the subclass of non-reactivity also includes items regarding emotions (e.g., “I perceive my feelings and emotions without having to react to them”). The dimension “affect” is proposed to include distress tolerance. However, this has also been considered to be a behavioral measure of avoidance7. Thus, it remains to be seen whether empirically established psychological processes of change can be organized into the proposed six dimensions.

Overall, Hayes and Hofmann argue that the field is ready to move toward person-focused, evidence-based care models. Thus, more attention needs to be devoted to answering the question: why do we do the things we do? This evolution involves several opportunities (including the possibility to consider psychological skills training in prevention efforts at the level of the school environment), but also a variety of challenges.