The Incremental Validity of Transdiagnostic Dimensions of Personality and Psychopathology in Predicting Important Psychological Outcomes.

Dimensional models of psychopathology offer an alternative to traditional categorical systems, yet research examining the incremental validity of transdiagnostic dimensions over diagnostic categories remains limited. The current study uses data from 685 outpatients, who presented at an academic medical centre for psychological assessment, to determine whether transdiagnostic dimensions derived from commonly used clinical assessment measures (Fear/Distress, Narcissistic Antagonism, Attachment, Flexible Thinking, Somatization, External Coping and Anger/Aggression) increment the variance in suicidal ideation, cognitive functioning, psychosocial functioning, pain and quality of life explained by diagnostic categories. When considered in isolation, diagnostic categories significantly predicted pain (R2 = 0.08) but did not predict the other four outcome measures. When transdiagnostic dimensions were added to the model, all five outcome models were significant, and dimensions explained substantial additional variance: suicidal ideation (ΔR2 = 0.41), cognitive concerns (ΔR2 = 0.28), psychosocial functioning (ΔR2 = 0.55), pain (ΔR2 = 0.21) and quality of life (ΔR2 = 0.38). Across models, somatization emerged as the most robust predictor and was significantly associated with cognitive concerns, psychosocial functioning, pain and quality of life. When the order of entry was reversed, a trauma diagnosis significantly incremented transdiagnostic dimensions when predicting suicidal ideation. Overall, these results suggest that transdiagnostic dimensions demonstrate substantial incremental validity over categorical diagnoses in predicting clinically meaningful outcomes. These findings support dimensional approaches to psychopathology and suggest that existing clinical data can be leveraged to implement dimensional conceptualizations in practice.