Supplementary Material for: The Italian Version of the Brief 21-Item Prodromal Questionnaire: Field Test, Psychometric Properties and Age-Sensitive Cut-Offs

Background: The Brief, 21-item version of the Prodromal Questionnaire (PQ-B) is a promising screener for psychosis-risk states that could be implemented in routine clinical practice. In this study, we assessed psychometric properties of the Italian version of the PQ-B (iPQ-B) in a sample of 243 help-seekers, aged 13–35 years. Sampling and Methods: After completing the iPQ-B, participants were assessed with the Comprehensive Assessment of At-Risk Mental States (CAARMS). Diagnostic accuracy (sensitivity, specificity, positive and negative predictive values [PPV and NPV], positive and negative likelihood ratios) and concurrent validity between PQ-B and CAARMS were determined using Cronbach’s alpha and Cohen’s kappa. We also tested the validity of the adopted PQ-B cut-offs through Receiver Operating Characteristic (ROC) curves plotted against CAARMS diagnoses and the predictive validity of the iPQ-B at 1-year follow-up. Results: The iPQ-B showed high internal consistency (Cronbach’s alpha = 0.868), acceptable diagnostic accuracy and concurrent validity (70% sensitivity, 67% specificity, 81% PPV, Cohen’s kappa = 0.335). ROC analyses pointed to threshold of ≥20 on the PQ-B total distress score as best cut-off. After 12 months of follow-up, 11% of participants who scored ≥4 on the PQ-B distressing item total score and did not meet CAARMS psychosis criteria at baseline, developed a psychotic disorder. Interestingly, age had significant negative correlations with iPQ-B scores and adolescents (aged < 18 years) showed higher iPQ-B scores than young adults. Conclusions: Overall, the psychometric properties of the iPQ-B were satisfactory. As iPQ-B scores appeared inversely associated to age, age-tailored cut-off scores are recommended for screening purposes in child-adolescent cohorts.