The prodromal questionnaire (PQ): Preliminary validation of a self-report screening measure for prodromal and psychotic syndromes

This study aims to establish preliminary validity of the Prodromal Questionnaire (PQ), a 92-item self-report screening measure for prodromal and psychotic symptoms. Adolescents and young adults (N = 113) referred to a prodromal psychosis research clinic completed the PQ and the Structured Interview for Prodromal Syndromes (SIPS [Miller, T.J., McGlashan, T.H., Woods, S.W., Stein, K., Driesen, N., Corcoran, C.M., Hoffman, R., Davidson, L., 1999. Symptom assessment in schizophrenic prodromal states. Psychiatric Quarterly 70(4), 273-287]), an interview with established validity for predicting future psychosis. When maximizing selection of true positive cases, scores on a subset of PQ items that assess positive symptoms predicted a concurrent prodromal or psychotic SIPS diagnosis with 90% sensitivity and 49% specificity. The PQ shows good preliminary validity in detecting individuals with an interview-diagnosed prodromal or psychotic syndrome, but it is less sensitive to the threshold between prodromal and full-blown psychosis.