Item-level endorsement on the Prodromal Questionnaire in a large non-clinical sample

Brief questionnaires, such as the Prodromal Questionnaire (PQ) positive scale, have been used to pre-screen individuals who may be at clinical high-risk (CHR) for psychosis. Despite the apparent utility of the PQ, few studies have examined response styles in non-clinical settings, which this study aimed to assess.

Response frequencies were examined for PQ positive subscale items in 3584 students (ages 18-35) from a nationally representative, semi-public undergraduate institution. Highly endorsed items were evaluated further in conjunction with established cutoffs and associated symptom ratings from the Structured Interview for Psychosis-risk Syndromes (SIPS) in a smaller subset of participants (n = 162). Positive subscale and distressing item responses were also evaluated by gender, race, and ethnicity using measurement invariance analyses and by comparing the relative proportion of individuals above established cutoffs.

Fifteen symptoms were endorsed by over 20 % of the sample with as high as 71 % of respondents endorsing them. Responses to 12 of these items were not associated with ratings on the SIPS. The PQ functioned similarly across demographic characteristics with strong evidence found for gender and race invariance across items and strong ethnicity invariance and partial invariance for positive subscale items and distressing items, respectively.

These findings suggest that a commonly used psychosis-risk questionnaire may not be appropriate for non-clinical samples, with the possibility of high false positive rates of those at CHR for psychosis. Future large-scale epidemiological studies should evaluate if psychosis-risk screeners can be improved to identify CHR individuals in community settings.