title: A longitudinal cohort study of intelligence and later hospitalisation with mental disorder.
abstract: OBJECTIVE
  Few studies on the associations between pre-morbid IQ and mental disorders are based on comprehensive assessment of intelligence in both women and men and include a wide range of confounding variables. Thus, the objective of the present study was to examine the association between pre-morbid IQ and hospitalisation with any mental disorder, including possible gender differences in the association.
  
  
  METHODS
  The study population was born in 1959-61 and premorbid IQ was assessed with the WAIS between 1982 and 1994. Information on mental disorders was obtained from Danish hospital registers with a mean follow-up interval of 21.1years. A total of 1106 participants were analysed.
  
  
  RESULTS
  Those with a mental disorder had a significantly lower mean pre-morbid IQ score than those without. For women, the adjusted IQ difference was 8.5 points, and for men it was 5.1 points. A decrease of one standard deviation in pre-morbid IQ was associated with 83% greater risk of developing a mental disorder among women (HR=1.83, 95% CI: 1.41-2.36), and 36% among men (HR=1.36, 95% CI: 1.07-1.73). The interaction between gender and IQ was not statistically significant. Associations did not differ noteworthy between verbal and non-verbal IQ.
  
  
  CONCLUSIONS
  Pre-morbid IQ was found to be significantly associated with the development of mental disorder.
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Øster Farimagsgade 5, 2, 1353 Copenhagen K, Denmark. Electronic address: smik@niph.dk.
authors.forename: Stine Schou
authors.initials: SS
authors.lastname: Mikkelsen
authors.affiliation: Unit of Medical Psychology, Institute of Public Health, University of Copenhagen, Øster Farimagsgade 5, 15, 1353 Copenhagen K, Denmark.
authors.forename: Trine
authors.initials: T
authors.lastname: Flensborg-Madsen
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Øster Farimagsgade 5, 2, 1353 Copenhagen K, Denmark.
authors.forename: Marie
authors.initials: M
authors.lastname: Eliasen
authors.affiliation: Unit of Medical Psychology, Institute of Public Health, University of Copenhagen, Øster Farimagsgade 5, 15, 1353 Copenhagen K, Denmark; Center for Healthy Aging, University of Copenhagen, Denmark; Institute of Preventive Medicine, Bispebjerg Hospital, Capital Region of Denmark.
authors.forename: Erik Lykke
authors.initials: EL
authors.lastname: Mortensen
mesh_terms: D000328:Adult; D015331:Cohort Studies; D003718:Denmark; D005260:Female; D006760:Hospitalization; D006801:Humans; D007360:Intelligence; D008137:Longitudinal Studies; D008297:Male; D001523:Mental Disorders / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology*; D011594:Psychometrics / Q000706:statistics & numerical data; D011618:Psychotic Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D018570:Risk Assessment / Q000706:statistics & numerical data; D012737:Sex Factors; D013223:Statistics as Topic; D014888:Wechsler Scales / Q000706:statistics & numerical data; D055815:Young Adult