Assessing Psychotic Experiences in Childhood

Psychotic experiences were assessed with the Prodromal Questionnaire Brief Version [24 (link)] (PQ-B) and the Kiddie Schedule for Affective Disorders and Schizophrenia [25 ] (KSADS-5). The PQ-B is a 21-item child-report questionnaire designed to measure the presence and severity of psychotic-like experiences (PLEs) in childhood. PQ-B symptom scores (PQ-B_sym) were calculated as the total number of endorsed PLEs; severity score (PQ-B_sev) was calculated as the child-reported level of distress (range 1–5) across all endorsed items. In line with previous research indicating that unusual thought content and suspiciousness are most predictive of psychosis risk [26 ], a binary score (PP_bin) was developed by defining prodromal psychosis “cases” as youth who endorsed experiencing at least 3 PLEs reflecting suspicious or unusual thought content (i.e., PQ-B items 1, 4, 5, 7, 8, 11, 12, 13–18), significant distress related to these experiences (i.e., PQ-B distress scores > 6 across items 1, 4, 5, 7, 8, 11, 12, 13–18), and whose parents indicated the child experienced hallucinations, delusions, and associated psychotic symptoms on the KSADS-5 assessment; youth not meeting these criteria served as the “control” group. Cognitive and psychiatric variables from the reported C4 phenome-wide association study (PheWAS) can be found in Additional file 1: Table S3.
Rates and severity of childhood PLEs were non-normally distributed, with the majority of youth reporting zero or few PLE symptoms (PQ-B_sym; M = 2.55, SD = 3.52) and endorsing low levels of PLE severity (PQ-B_sev; M = 6.09, SD = 10.39; Fig. 1B).