Background: We report on mental disorders and violence for a birth cohort of young adults, regardless of their contact with the health or justice systems.
Methods: We studied 961 young adults who constituted 94% of a total-city birth cohort in New Zealand, April 1, 1972, through March 31, 1973. Past-year prevalence of mental disorders was measured using standardized DSM-III-R interviews. Past-year violence was measured using self-reports of criminal offending and a search of official conviction records. We also tested whether substance use before the violent offense, adolescent excessive perceptions of threat, and a juvenile history of conduct disorder accounted for the link between mental disorders and violence.
Results: Individuals meeting diagnostic criteria for alcohol dependence, marijuana dependence, and schizophrenia-spectrum disorder were 1.9 (95% confidence interval [CI], 1.0-3.5), 3.8 (95% CI, 2.2-6.8), and 2.5 (95% CI, 1.1-5.7) times, respectively, more likely than control subjects to be violent. Persons with at least 1 of these 3 disorders constituted one fifth of the sample, but they accounted for half of the sample's violent crimes (10% of violence risk was uniquely attributable to schizophrenia-spectrum disorder). Among alcohol-dependent individuals, violence was best explained by substance use before the offense; among marijuana-dependent individuals, by a juvenile history of conduct disorder; and among individuals with schizophrenia-spectrum disorder, by excessive perceptions of threat and a history of conduct disorder.
Conclusions: In the age group committing most violent incidents, individuals with mental disorders account for a considerable amount of violence in the community. Different mental disorders are linked to violence via different core explanations, suggesting multiple-targeted prevention strategies.