IQ in early adulthood and later risk of death by homicide: cohort study of 1 million men

Abstract

BackgroundRisk factors for homicide are emerging; however, the predictive value of IQ, for which there is a strong prima facie case, has yet to be examined.AimsTo examine the association between IQ and risk of death by homicide.MethodA cohort of 968 846 men, aged 18–19 years, were administered an IQ test battery at military conscription and then followed for mortality experience over two decades.ResultsThere were 191 deaths due to homicide during follow-up. In age-adjusted analyses, a high total IQ test score was associated with a reduced rate of homicide (hazard ratio (HR) per standard deviation increase in IQ score=0.49, 95% CI 0.42–0.57). A step-wise gradient was apparent across the three IQ groups (P-value for trend 50.001). After adjustment for indicators of socio-economic position and illness at conscription, this gradient was marginally attenuated (HR=0.57, 95% CI 0.49–0.67).ConclusionsHigh IQ test scores in early adulthood were associated with a reduced risk of death by homicide.