Symptom severity scale of the DSM5 for schizophrenia, and other psychotic disorders: diagnostic validity and clinical feasibility.

Innovations in DSM5 include dimensional diagnosis of schizophrenia (SZ) and other psychotic (OP) disorders using the symptom severity scale (SS-DSM5). We evaluated the psychometric properties and diagnostic validity of the SS-DSM5 scale using a cross-sectional design and an unselected convenience unselected sample of 314 inpatients and outpatients with SZ/OP and mood disorders who received standard care in routine clinical practice. The SS-DSM5 scale, the Clinical Global Impression-Severity scale (CGI-S), the Positive and Negative Syndrome Scale (PANSS), and the Bech-Rafaelsen Mania Scale (BRMS) were administered. Factor structure, reliability, internal consistency, convergent and diagnostic ability of the DSM5-SS were evaluated. Factor analysis indicated two latent factors underlying the SS-DSM5 (Psychotic and Deficit sub-scales). Cronbach's alpha was >0.70. Convergent validity of the SS-DSM5 was highly significant. Patients with SZ/PO disorders were correctly diagnosed (77.9%) using the SS-DSM5 scale (72% using PANSS). The agreement of the diagnostic decisions between the SS-DSM5 and PANSS was substantial for SZ/PO disorders (Kappa=0.75). Classifying participants with SZ/PO versus mood disorders using SS-DSM5 provided a sensitivity of 95%, and specificity of 34%. Thus, this study suggests that the SS-DSM5 has acceptable psychometric properties and that its use in clinical practice and research is feasible in clinical settings. The dimensional option for the diagnosis of schizophrenia and related disorders using SS-DSM5 is discussed.