IQ and non-clinical psychotic symptoms in 12-year-olds: results from the ALSPAC birth cohort

J. Horwood, G. Salvi, K. Thomas, L. Duffy, D. Gunnell, Chris Hollis, Glyn H Lewis, P. Menezes, A. Thompson, D. Wolke, Stanley Zammit, G. Harrison

Research output: Contribution to journalArticle (Academic Journal)peer-review

216 Citations (Scopus)


BACKGROUND: Non-clinical psychotic symptoms appear common in children, but it is possible that a proportion of reported symptoms result from misinterpretation. There is a well-established association between pre-morbid low IQ score and schizophrenia. Psychosis-like symptoms in children may also be a risk factor for psychotic disorder but their relationship with IQ is unclear. AIMS: To investigate the prevalence, nature and frequency of psychosis-like symptoms in 12-year-old children and study their relationship with IQ. METHOD: Longitudinal study using the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort. A total of 6455 children completed screening questions for 12 psychotic symptoms followed by a semi-structured clinical assessment. IQ was assessed at 8 years of age using the Wechsler Intelligence Scale for Children (3rd UK edition). RESULTS: The 6-month period prevalence for one or more symptoms was 13.7% (95% CI 12.8-14.5). After adjustment for confounding variables, there was a non-linear association between IQ score and psychosis-like symptoms, such that only those with below average IQ score had an increased risk of reporting such symptoms. CONCLUSIONS: Non-clinical psychotic symptoms occur in a significant proportion of 12-year-olds. Symptoms are associated with low IQ and also less strongly with a high IQ score. The pattern of association with IQ differs from that observed in schizophrenia.
Original languageEnglish
Pages (from-to)185-191
Number of pages7
JournalBritish Journal of Psychiatry
Issue number3
Publication statusPublished - 1 Sept 2008

Bibliographical note

Publisher: Royal College of Psychiatrists


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