Louise Arseneault, Terrie E. Moffitt, Avshalom Caspi, Alan Taylor

Estimates of who is most at risk from violence by people with mental illness rest mainly on identified patient samples. This study, without such selection bias, examined the targets of violence committed by young adults with as-yet untreated alcohol dependence, marijuana dependence, or schizophrenia-spectrum disorders, to determine the extent to which their victims were co-residents or non-household members. In a total birth cohort of 21-year-olds (n=956), past-year prevalence of alcohol dependence, marijuana dependence and schizophrenia-spectrum disorders were diagnosed using standardized DSM-III-R interviews. None of the people with schizophrenia-spectrum disorder has been hospitalized in the past year. Past-year violence and victim targets were measured using self-reports. Compared with controls, cohort members with substance dependence or schizophrenia-spectrum disorders had higher prevalence and frequency rates of assault against co-residents, against non-household members, and also robbery and gang fights. Out of 39, five individuals with schizophrenia-spectrum disorder committed violent street crimes. Persons with substance dependence had similar proportions of violence against co-resident and non-household members, but persons with schizophrenia-spectrum disorders tended to victimize co-residents more than others. At the age when they are most likely to contribute to the community's violence burden, young untreated offenders with alcohol or marijuana dependence or with schizophrenia-spectrum disorders assault not only co-residents, but others as well, and commit violent street crimes. Families, schoolteachers and primary care physicians have an important potentially preventive role in early identification and treatment of the disorders.