title: IQ and non-clinical psychotic symptoms in 12-year-olds: results from the ALSPAC birth cohort.
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.
  
  
  OBJECTIVE
  To investigate the prevalence, nature and frequency of psychosis-like symptoms in 12-year-old children and study their relationship with IQ.
  
  
  METHODS
  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.
authors.affiliation: Department of Social Medicine, University of Bristol, UK.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Horwood
authors.forename: Giovanni
authors.initials: G
authors.lastname: Salvi
authors.forename: Kate
authors.initials: K
authors.lastname: Thomas
authors.forename: Larisa
authors.initials: L
authors.lastname: Duffy
authors.forename: David
authors.initials: D
authors.lastname: Gunnell
authors.forename: Chris
authors.initials: C
authors.lastname: Hollis
authors.forename: Glyn
authors.initials: G
authors.lastname: Lewis
authors.forename: Paulo
authors.initials: P
authors.lastname: Menezes
authors.forename: Andrew
authors.initials: A
authors.lastname: Thompson
authors.forename: Dieter
authors.initials: D
authors.lastname: Wolke
authors.forename: Stanley
authors.initials: S
authors.lastname: Zammit
authors.forename: Glynn
authors.initials: G
authors.lastname: Harrison