What a dimension does not tell you
In a new volume on dimensional diagnosis, Merlijn Olthof and Anna Lichtwarck-Aschoff have written a chapter that raises a question receiving little attention elsewhere in the book.
On the chapter by Olthof, Lichtwarck-Aschoff and colleagues in: C. J. Hopwood & C. Sharp (Eds.) (2026). Dimensional Diagnosis: Practical and Conceptual Issues in the Integration of Personality and Psychopathology. New York: The Guilford Press.
On the question of whether psychopathology can be better described dimensionally than categorically, there now seems to be broad agreement. The question that lies ahead is what this shift means for practice. That is the subject of the new volume Dimensional Diagnosis, and one chapter answers the question in a way that is of particular relevance to our platform.
A book of diptychs
The volume, edited by Christopher Hopwood and Carla Sharp, has an original design. Each chapter concerns a single question: what does dimensional diagnosis mean for assessment, treatment, training, stigma or research? Each question is answered by two teams of authors who wrote independently of each other and read each other's contribution only afterwards. The result is a series of diptychs that sometimes fit together well and sometimes clearly disagree. The editors themselves warn against what they call cheerleading: enthusiasm on the part of advocates that pushes the practical problems of implementation out of view.
Between persons and within one person
The diptych on psychotherapy research includes a chapter on the application of complexity science, co-authored by the Dutch researchers Merlijn Olthof and Anna Lichtwarck-Aschoff. They point to a limitation in principle that receives less attention in the rest of the book. Dimensional models such as the Hierarchical Taxonomy of Psychopathology (HiTOP) describe how people differ from one another at population level. That structure does not automatically generalise to the level of the individual patient: what holds for the differences between persons need not hold for the processes within one person (Molenaar, 2004).
To understand how symptoms arise, persist and change in this patient, a dynamic perspective is therefore needed, according to the authors. Olthof and Lichtwarck-Aschoff describe psychopathology as a pattern in a complex adaptive system, in which thoughts, feelings, behaviour and context sustain one another through feedback loops (see also Olthof et al., 2023). From this perspective, treatment consists of destabilising rigid patterns and building up and anchoring more flexible alternatives.
From theory to research design
The chapter does not stop at theory. The authors translate the dynamic perspective into concrete choices for psychotherapy research: intensive measurement over time instead of only a pre- and post-test, selecting participants on the degree to which they are stuck and dysfunctional rather than on diagnosis, and attention to sudden transitions in the treatment process. This makes it one of the few places in the book where the within-person perspective is given a full place alongside the between-person perspective.
Why this appeals to us
For those who work with process monitoring, for example with the Synergetic Navigation System, this will sound familiar. It fits the movement we are trying to make on this platform: from the question of which category or dimension applies to someone, to the question of how this person's pattern is put together, what sustains it, and where it may begin to move.
At the same time, the chapter brings to light a tension that the book as a whole does not resolve: how does the static, hierarchical framework of HiTOP relate to a dynamic, individualised perspective? We saw the same tension in Paul van Geert's Mensen zijn complex (People are complex), which values HiTOP while being critical of latent variables and population models. Perhaps each perspective answers its own question: dimensions help to describe where someone stands relative to others, dynamics help to understand how someone got there and how change becomes possible. How to connect the two in the consulting room is still largely unknown territory. That seems to us an agenda for the coming years rather than a reproach to the authors.
In closing
For those who wish to follow the classification debate beyond the opposition between defending and rejecting the DSM, Dimensional Diagnosis offers a picture of a field that is openly reflecting on its own future. For the question of what that future might mean for the individual patient, the chapter by Olthof and Lichtwarck-Aschoff seems to us a good starting point.