A longitudinal cohort study of intelligence and later hospitalisation with mental disorder
Stine Schou Mikkelsen, Trine Flensborg-Madsen, Marie Eliasen, Erik Lykke Mortensen
Volume 55, Issue 4, May 2014
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.
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 21.1 years. A total of 1106 participants were analysed.
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.
Pre-morbid IQ was found to be significantly associated with the development of mental disorder.