Objective: The aim of the present study was to investigate the psychometric properties of the Bipolar Prodrome Symptom Interview and Scale-Prospective (BPSS-P), the first specific interview for emerging bipolar disorder (BD) symptoms. Methods: A total of 205 youth aged 12-23 years and/or their caregivers underwent BPSS-P interviews: 129 patients with mood spectrum disorders [depression spectrum disorder (n = 77), mood disorder not otherwise specified (NOS) (n = 27), BD-NOS (n = 14), bipolar I disorder (BD-I)/bipolar II disorder (BD-II)/cyclothymia (n = 11), 34 with non-mood spectrum disorders, and 42 healthy controls (HCs)]. We used Cronbach's α to assess internal consistency; intra-class correlation (ICC) for inter-rater reliability; Spearman's rho for convergent validity with the Young Mania Rating Scale (YMRS), General Behavior Inventory-10-item Mania Form (GBI-M-10), and Cyclothymic-Hypersensitive Temperament (CHT) scale; and analysis of variance for discriminatory power between diagnostic groups. Results: Internal consistency was good to very good for the BPSS-P Mania (Cronbach's α = 0.87), Depression (Cronbach's α = 0.89), and General Symptom indices (Cronbach's α = 0.74). Inter-rater reliability was high for the BPSS-P Total score (ICC = 0.939), and BPSS-P Mania (ICC = 0.934), Depression (ICC = 0.985), and General (ICC = 0.981) indices. Convergent validity was large (ρ ≥ 0.50) between the BPSS-P Mania Index and YMRS, GBI-M-10, and CHT; BPSS-P Depression Index and Montgomery-Åsberg Depression Rating Scale (MADRS) and CHT; and BPSS-P General Index and GBI-M-10 and CHT. Expectedly, convergent validity was small (ρ = 0.10 to < 0.30) between the BPSS-P Mania Index and MADRS, and BPSS-P Depression Index and YMRS. Furthermore, the BPSS-P and its subscales discriminated each patient group from HCs and from non-mood spectrum patients (except for the BPSS-P General Index). Moreover, the BPSS-P Total score discriminated BD-I/BD-II/cyclothymia from depression spectrum patients, and the BPSS-Mania Index differentiated all three bipolar spectrum groups from depression spectrum patients. Conclusions: The BPSS-P has good to excellent psychometric properties. Its use across multiple settings and predictive validity requires further investigation.
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