Low intelligence test scores in 18 year old men and risk of suicide: cohort study

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Abstract
Objective To examine the association between intelligence test scores in men, measured at age 18, and subsequent suicide. Design Record linkage study of the Swedish military service conscription register (1968-94) with the multi-generation register, cause of death register and census data. Four tests were performed at conscription covering logic, language, spatial, and technical skills. Setting Sweden. Participants 987 308 Swedish men followed up for 5-26 years. Main outcome measure Suicide. Results 2811 suicides occurred during follow up. The risk of suicide was two to three times higher in those with lowest compared with the highest test scores. The strongest associations were seen with the logic test: for each unit increase in test score the risk of suicide decreased by 12% (95% confidence interval 10% to 14%). Associations were only slightly attenuated when we controlled for parents' socioeconomic position. Greatest risks were seen among poorly performing offspring of well educated parents. Conclusions Performance in intelligence tests is strongly related to subsequent risk of suicide in men. This may be due to the importance of cognitive ability in either the aetiology of serious mental disorder or an individual's capacity to solve problems while going through an acute life crisis or suffering from mental illness.