title: Premorbid intra-individual variability in intellectual performance and risk for schizophrenia: a population-based study.
abstract: BACKGROUND
  Some, but not most, schizophrenia patients have below-average intelligence years before they manifest psychosis. However, it is not clear if those whose intelligence falls within-normal-range nevertheless have cognitive abnormalities. We examined the association between intra-individual variability in intellectual performance and risk for schizophrenia in individuals with normal IQ.
  
  
  METHODS
  555,326 adolescents, mandatory assessed by the Israeli Draft Board were followed up over 8 to 17 years for psychiatric hospitalization by means of the Israeli National Psychiatric Hospitalization Case Registry. Data were available on 4 intelligence sub-tests, and on behavioral and psychosocial variables. Variability was computed from the variance of the four intelligence tests' standardized scores.
  
  
  RESULTS
  There was a significant monotonic association between increased intra-individual variability in intellectual performance and risk of schizophrenia in individuals with within-normal-range IQ. Individuals with the highest variability were 3.8 times more likely to have schizophrenia [95%CI: 2.32-6.08; p < 0.0001] compared with individuals with the lowest variability. This association held after controlling for the effects of potential confounders.
  
  
  CONCLUSIONS
  Despite within-normal-range premorbid IQ, apparently healthy adolescents who will later on manifest schizophrenia, nevertheless have cognitive abnormalities such as increased variability across intellectual tasks, possibly related to frontal lobe abnormalities.
authors.affiliation: Department of Psychiatry, Mount Sinai School of Medicine, New York, NY 10029, USA. avi.reichenberg@mssm.edu
authors.forename: Abraham
authors.initials: A
authors.lastname: Reichenberg
authors.forename: Mark
authors.initials: M
authors.lastname: Weiser
authors.forename: Michael A
authors.initials: MA
authors.lastname: Rapp
authors.forename: Jonathan
authors.initials: J
authors.lastname: Rabinowitz
authors.forename: Asaf
authors.initials: A
authors.lastname: Caspi
authors.forename: James
authors.initials: J
authors.lastname: Schmeidler
authors.forename: Haim Y
authors.initials: HY
authors.lastname: Knobler
authors.forename: Gad
authors.initials: G
authors.lastname: Lubin
authors.forename: Daniela
authors.initials: D
authors.lastname: Nahon
authors.forename: Philip D
authors.initials: PD
authors.lastname: Harvey
authors.forename: Michael
authors.initials: M
authors.lastname: Davidson
mesh_terms: D000293:Adolescent; D002648:Child; D003072:Cognition Disorders / Q000175:diagnosis / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D005625:Frontal Lobe / Q000002:abnormalities / Q000503:physiopathology; D006760:Hospitalization; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D011159:Population Surveillance / Q000379:methods*; D012042:Registries; D012307:Risk Factors; D012559:Schizophrenia / Q000453:epidemiology* / Q000503:physiopathology / Q000534:rehabilitation; D012720:Severity of Illness Index; D013997:Time Factors