Bridging the Categorical-Dimensional Divide: Exploring the PRiSM Diagnostic Instrument

For more than 40 years—at least since the advent of the DSM-III in 1980—the field of psychiatry has been fixated on diagnosis. The DSM’s categorical diagnostic system set off an intense debate among psychiatrists, philosophers of science, and the general public regarding the reliability, validity, and clinical usefulness of the DSM categories. Typically, the debate has focused on the advantages and disadvantages of categorical vs dimensional diagnosis—or, more radically, on the legitimacy of psychiatric diagnosis itself. These background issues have been thoroughly reviewed in several key papers.^1-3

Partly in response to several problems we (and many mental health professionals) have encountered using the DSM categories, we developed the Psychopathology Refracted into Seven Modalities (PRiSM) diagnostic tool.⁴ For example, the structure of the DSM does not entail hierarchical classification, and thereby encourages spurious comorbidities and multiple diagnoses. In other words, as our Tufts colleague, Nassir Ghaemi, MD, MPH, has explained⁵:

"An important feature of the DSM ideology is the rejection of the concept of a hierarchy of diagnosis, on the debatable ground that we cannot have hierarchies in the absence of etiology. If we do not know [the] causes of diseases, we cannot say which ones should be diagnosed preferentially [over] others. This perspective ignores the importance of differentiating diseases with many symptoms from those with fewer. If a symptom occurs as one of 20 in 1 illness, and 1 of 2 in another, then the first should be ruled out before the second is diagnosed. It is not biologically sound to diagnose ‘comorbid’ panic disorder every time someone has a panic attack in the setting of a depressive or manic episode. The panic symptoms are often caused by mood states, rather than being a separate, independent disease. We already take this approach with delusions and hallucinations; if they occur in mood states, we do not diagnose schizophrenia. This is an exception in the DSM system, though, which refuses to use the same logic for other psychopathological states."

In effect, Ghaemi’s argument is an application of Occam’s razor; ie, clinicians should aim to identify the most comprehensive diagnosis that accounts for all observed symptoms. This approach seeks to find the core illness or main driver, rather than simply labeling and treating every individual symptom, which, in turn, provides a more parsimonious and clinically relevant understanding of the patient's condition.

A goal of the PRiSM instrument is to promote such parsimony. By scoring the patient’s symptoms in each of 7 domains, we can arrive at the general category (ie, a cluster) with the highest score; for example, the Disturbances of Reality Perception cluster. This approach allows us to consider a categorical diagnosis, such as schizophrenia, as the most parsimonious explanation for an otherwise broad and heterogeneous collection of signs and symptoms.

Readers can best appreciate this by returning to the case vignette of “Jason,” a 17-year-old boy with a 2-year history of moderate-to-severe psychiatric symptoms. His chief complaint on intake evaluation is “feeling scared and confused, like my world is muddled and breaking up into tiny particles or bones.”⁴

To recap briefly: When evaluated in the 7 domains, Jason showed a diffusely positive response pattern, with 20 of 31 items reflecting some degree of dysfunction in all 7 domains. The highest score (14) was in the Disturbances of Reality Perception cluster, and the second highest score (8) was in the Disturbances of Thought Process, Organization, and Flow cluster. The next highest scores (both 5) are in the domains of Disturbances of Self-Integration and Disturbances of Mood Quality, Regulation, or Stability. Jason’s global picture suggested some type of chronic psychotic process compromising reality perception, thought process, self-integration, and mood, among other functions. Guided by the highest score of 14 in the Disturbances of Reality Perception cluster, the most parsimonious interpretation of Jason’s pathology—the best diagnostic fit with the manifest psychopathology—was to posit schizophrenia or some related condition, such as a schizoaffective illness.

Bridging the Divide

The PRiSM instrument is meant to bridge the divide between dimensional and categorical diagnoses.⁶ The 7 PRiSM domains of psychopathology (eg, disturbances of reality perception, disturbances of self-integration, etc) are roughly analogous to the dimensions of psychopathology now partially incorporated into the DSM-5: negative affectivity, detachment, antagonism, disinhibition, and psychoticism. But by quantifying the distribution of signs and symptoms among the 7 PRiSM domains, we can arrive at the most likely culprit in a very broad diagnostic sense. In at least some cases, this general cluster (such as disturbances of reality perception) can then point us to a single, categorical (DSM) diagnosis, such as schizophrenia, bipolar disorder, etc.

On the other hand, there are times when a patient’s clinical picture simply cannot be explained by or reduced to a single DSM diagnostic category. That is, sometimes Occam’s razor is simply the wrong tool to use. For example, a patient may indeed have 2 or more independent pathological entities as the drivers of their clinical presentation. In such instances, the PRiSM can help guide therapeutic interventions on an empirical, symptomatic basis. For example, a patient who has high scores in multiple PRiSM domains can be treated empirically with somatic or psychosocial interventions, or both, even absent a specific diagnosis. Thus, we see the PRiSM as a promising instrument when a patient presents with complex, multiform psychopathology that cannot be explained by one underlying condition.

Putting PRiSM into Practice

PRiSM has not yet been field-tested in clinical settings, and we do not have precise, quantitative data that can be applied to scoring. As such, results obtained with the use of PRiSM should be considered within the context of a comprehensive diagnostic evaluation, including all the standard tools of medical and psychiatric evaluation (eg, mental status exam, appropriate laboratory studies, standard psychometric testing, etc).

We believe Psychiatric Times' readers are in the ideal situation to help “field test” PRiSM. Together with Psychiatric Times—"the voice of psychiatry”—we invite you to leverage the PRiSM instrument in your clinical practice or research, and to share your experiences, reflections, and results. Entries will be reviewed and scored, and the winning entry will be published in Psychiatric Times and receive a modest honorarium. The deadline for entries is January 31, 2026. Full guidelines are available here.

Concluding Thoughts

The PRiSM instrument is not proposed as a replacement for existing diagnostic frameworks but as a complementary tool that may help reconcile the tension between categorical and dimensional models of mental illness. By focusing on underlying domains of psychopathology while still pointing toward parsimonious categorical diagnoses when possible, PRiSM offers clinicians a more flexible and pragmatic approach to complex presentations. Future research will determine its utility, but even in its current conceptual form, PRiSM invites clinicians to think more broadly, more rigorously, and perhaps more realistically about the nature of psychiatric illness.

We look forward to reviewing submissions, and we thank prospective investigators for their time, effort, and interest in the PRiSM.

Dr Pies is a professor emeritus of psychiatry and lecturer on bioethics and humanities at SUNY Upstate Medical University in Syracuse; a clinical professor of psychiatry at Tufts University School of Medicine in Boston, Massachusetts; and the editor in chief emeritus of Psychiatric Times (2007-2010). He is the author of a number of books, including several textbooks on psychopharmacology. A collection of his works can be found on Amazon. Dr Ruffalo is an assistant professor of psychiatry at the University of Central Florida College of Medicine in Orlando and adjunct assistant professor of psychiatry at Tufts University School of Medicine in Boston, Massachusetts.

References

1. Phillips J, Frances A, Cerullo MA, et al. The six most essential questions in psychiatric diagnosis: a pluralogue part 2: issues of conservatism and pragmatism in psychiatric diagnosis. Philos Ethics Humanit Med. 2012;7:8.

2. Herpertz SC, Huprich SK, Bohus M, et al. The challenge of transforming the diagnostic system of personality disorders. J Pers Disord. 2017;31(5):577-589.

3. Aftab A, Banicki K, Ruffalo ML, Frances A. Psychiatric diagnosis: a clinical guide to navigating diagnostic pluralism. J Nerv Ment Dis. 2024;212(8):445-454.

4. Pies RW, Ruffalo ML. Use of the PRiSM diagnostic instrument in clinical practice. Psychiatric Times. April 10, 2025. https://www.psychiatrictimes.com/view/use-of-the-prism-diagnostic-instrument-in-clinical-practice

5. Ghaemi SN. After the failure of DSM: clinical research on psychiatric diagnosis. World Psychiatry. 2018;17(3):301-302.

6. Ruffalo ML. Why we still need categories in personality diagnosis. Psychology Today. September 9, 2025. Accessed September 16, 2025. https://www.psychologytoday.com/us/blog/from-freud-to-fluoxetine/202509/why-we-still-need-categories-in-personality-diagnosis