The Need for a Validity-Based Diagnostic Hierarchy in DSM-6

The DSM's loss of a diagnostic hierarchy has contributed to widespread diagnostic proliferation and a misunderstanding of comorbidity. The original concept of comorbidity referred to the co-occurrence of two distinct disease entities, each with its own etiology and pathology. In psychiatry, by contrast, comorbidity has come to mean the accumulation of multiple DSM diagnoses, many of which have overlapping criteria and limited construct validity. This shift accelerated after DSM-III, which emphasized reliability over parsimony and encouraged clinicians to treat symptom clusters as separate disorders. The authors argue that DSM-6 should restore a diagnostic hierarchy grounded in construct validity. Such a hierarchy would privilege disorders with strong empirical validators, distinguish true from false comorbidity, reduce diagnostic inflation, clarify etiological relationships, and improve treatment selection. Drawing on the original intentions of the concept of comorbidity, the historical contrast between DSM-II and DSM-III, and contemporary work, the authors outline a path toward a more coherent and scientific psychiatric classification.