title: Risk of adult schizophrenia and its relationship to childhood IQ in the 1958 British birth cohort.
abstract: BACKGROUND
  An inverse relationship between risk of schizophrenia and premorbid IQ is a robust empirical finding. Cognitive impairment may be a core feature of schizophrenia in addition to the clinical symptoms that have historically defined the disorder.
  
  
  OBJECTIVE
  To evaluate whether risk of schizophrenia increases linearly or nonlinearly with the lowering of premorbid IQ after adjustment for a range of confounding factors.
  
  
  METHODS
  IQ data from the 1958 National Child Development Study, a prospective national birth cohort (n = 17 419), were linked with psychiatric admissions in England and Wales over a 20-year period. Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition diagnoses were derived from case notes.
  
  
  RESULTS
  A clear nonlinear inverse relationship between general intelligence at ages 7 and 11 and risk of adult psychosis was found even after adjustment for potential social, behavioral, or demographic confounding factors. No such relationship was found for affective disorders.
  
  
  CONCLUSIONS
  The nonlinear relationship suggests an excess risk of schizophrenia in children with premorbid IQ in the learning disabilities range. Previous reports of a linear relationship are likely to be a result of less sensitive statistical methods for detecting nonlinearity.
authors.affiliation: To whom correspondence should be addressed; Centre for Life Span and Chronic Illness Research, School of Psychology, University of Hertfordshire, Hatfield, Hertfordshire AL10 9AB, UK; tel: +44 (0)1707286292, fax: +44 1707285104, e-mail: d.j.done@herts.ac.uk.
authors.forename: Joerg
authors.initials: J
authors.lastname: Schulz
authors.forename: Josefin
authors.initials: J
authors.lastname: Sundin
authors.forename: Stuart
authors.initials: S
authors.lastname: Leask
authors.forename: D John
authors.initials: DJ
authors.lastname: Done
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007360:Intelligence / Q000502:physiology*; D007859:Learning Disabilities / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D019964:Mood Disorders / Q000453:epidemiology; D011446:Prospective Studies; D012306:Risk; D012559:Schizophrenia / Q000453:epidemiology*; D006113:United Kingdom / Q000453:epidemiology; D055815:Young Adult
keywords: birth cohort; epidemiology; premorbid IQ; risk of schizophrenia