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. 2008 Sep;193(3):185-91.
doi: 10.1192/bjp.bp.108.051904.

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

Jeremy Horwood  1 , Giovanni Salvi, Kate Thomas, Larisa Duffy, David Gunnell, Chris Hollis, Glyn Lewis, Paulo Menezes, Andrew Thompson, Dieter Wolke, Stanley Zammit, Glynn Harrison
Affiliations

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

Jeremy Horwood et al. Br J Psychiatry. 2008 Sep.

Abstract

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.

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Fig. 1
Fig. 1
Predicted probability of psychosis-like symptoms according to IQ scorea (fully adjusted model).
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