Background: The relationship between mental illness and violent crime is complex because of the involvement of many other confounding risk factors. In the present study, we analysed psychiatric and neurological disorders in relation to the risk of convictions for violent crime, taking into account early behavioural and socio-economic risk factors.
Methods: The study population consisted of 49,398 Swedish men, who were thoroughly assessed at conscription for compulsory military service during the years 1969-1970 and followed in national crime registers up to 2006. Five diagnostic groups were analysed: anxiety-depression/neuroses, personality disorders, substance-related disorders, mental retardation and neurological conditions. In addition, eight confounders measured at conscription and based on the literature on violence risk assessment, were added to the analyses. The relative risks of convictions for violent crime during 35 years after conscription were examined in relation to psychiatric diagnoses and other risk factors at conscription, as measured by odds ratios (ORs) and confidence intervals (CIs) from bivariate and multivariate logistic regression analyses.
Results: In the bivariate analyses there was a significant association between receiving a psychiatric diagnosis at conscription and a future conviction for violent crime (OR = 3.83, 95 % CI = 3.47-4.22), whereas no significant association between neurological conditions and future violent crime (OR = 1.03, 95 % CI = 0.48-2.21) was found. In the fully adjusted multivariate logistic regression model, mental retardation had the strongest association with future violent crime (OR = 3.60, 95 % CI = 2.73-4.75), followed by substance-related disorders (OR = 2.81, 95 % CI = 2.18-3.62), personality disorders (OR = 2.66, 95 % CI = 2.21-3.19) and anxiety-depression (OR = 1.29, 95 % CI = 1.07-1.55). Among the other risk factors, early behavioural problem had the strongest association with convictions for violent crime.
Conclusions: Mental retardation, substance-related disorders, personality disorders and early behavioural problems are important predictors of convictions for violent crime in men.