title: Excess of non-right-handedness in schizophrenia: meta-analysis of gender effects and potential biases in handedness assessment.
abstract: BACKGROUND
  The notion that schizophrenia is characterised by increased non-right-handedness is a cornerstone of the theory that schizophrenia arises from, and is genetically linked to, abnormal brain lateralisation. Reviews and meta-analyses have reported higher rates of non-right-handers in patients with schizophrenia. However, this was suggested to be the result of a gender artefact or a hidden bias in self-report handedness questionnaires.
  
  
  OBJECTIVE
  To investigate using a meta-analytical approach whether the excess of non-right-handedness is seen in both females and males, and also when handedness is assessed behaviourally.
  
  
  METHODS
  Electronic databases were searched for studies that reported (a) the rate of female and male non-right-handers in schizophrenia compared with controls and (b) the rate of non-right-handers in schizophrenia (regardless of gender) based on behavioural handedness assessment.
  
  
  RESULTS
  The odds ratios (ORs) for females (OR = 1.63; based on 621 patients, 3747 controls) and males (OR = 1.50; based on 1213 patients, 3800 controls) differed significantly from 1.0, indicating both female and male patients were more often non-right-handed than controls. Moreover, there was an excess of non-right-handedness in patients with schizophrenia when handedness was assessed behaviourally: OR = 1.84 (1255 patients, 6260 controls). Even when both gender and behavioural handedness assessment were controlled for simultaneously, the excess of non-right-handedness persisted.
  
  
  CONCLUSIONS
  The findings clearly demonstrate that the excess of non-right-handedness in schizophrenia does not result from a gender artefact or from biased handedness questionnaires. It is a true empirical effect and may indeed reflect a genetic link between schizophrenia and brain lateralisation.
authors.affiliation: Marco Hirnstein, PhD, Department of Biological and Medical Psychology, University of Bergen; Kenneth Hugdahl, PhD, Department of Biological and Medical Psychology, University of Bergen, and Division of Psychiatry and Department of Radiology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Marco
authors.initials: M
authors.lastname: Hirnstein
authors.affiliation: Marco Hirnstein, PhD, Department of Biological and Medical Psychology, University of Bergen; Kenneth Hugdahl, PhD, Department of Biological and Medical Psychology, University of Bergen, and Division of Psychiatry and Department of Radiology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Hugdahl
mesh_terms: D015982:Bias; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D015995:Prevalence; D012559:Schizophrenia / Q000453:epidemiology*; D012737:Sex Factors