Validity of a two-item screen for early psychosis.

Well-validated screening tools have been developed to identify people at high risk for psychosis, but these are rarely used outside of specialty clinics or research settings. The development of extremely brief and simple screening tools could increase dissemination, especially in settings with low buy-in such as those with low base rates of psychosis and/or time constraints. We sought to identify such a brief measure by modeling participant responses to three psychosis screening questionnaires (Prime Screen; Prodromal Questionnaire-Brief; Youth Psychosis At Risk Questionnaire) in a sample of 139 help-seeking individuals and 335 college students (age range: 12-25). Two screening questions with especially strong information characteristics were identified: "Do you see things that others can't or don't see?" and "Have you ever felt that someone was playing with your mind?" (Alternative two-item screens with similarly strong properties were also identified and validated using uncertainty quantified through Bayesian modeling.) The resulting measure was validated against clinician ratings of psychosis. The screen performed with a sensitivity of 53% and specificity 98% for clinically significant hallucinations or delusions, and sensitivity of 32% and specificity 99% for identifying people in an early phase of psychosis (clinical high risk or first episode psychosis).