Mental illness and violence: an epidemiological appraisal of the evidence.

OBJECTIVE: To conduct a critical review of the literature on the matter of mental illness and violence, to examine whether there is enough evidence to establish a causal link, and to provide epidemiological background to measure the risk to the population.
METHOD: Based on a computerized search of the literature on mental illness and violence previously conducted for Health Canada, studies in the area were critically reviewed and divided into 3 main categories: 1) studies of criminal and violent behaviour among psychiatric patients, 2) studies of psychiatric illness among offenders (prevalence studies in institutions, analytical studies, and community follow-up of offenders), and 3) epidemiological community-based studies on the issue of mental illness and violence (police-citizen encounters, representative samples, and other epidemiological studies). Causality rules and measures of risk were then applied to the evidence elicited.
RESULTS: The review of the literature suggests that only a small minority of hospitalized patients, typically those suffering from acute psychotic symptoms, are involved in violent incidents. Formerly hospitalized patients are at a higher risk of committing violence if they are not properly treated and are experiencing threat/control-override psychotic symptoms. Substance abuse disorders significantly raise the risk for violence. Family members are the most at risk of being victimized.
CONCLUSION: An association exists between mental illness and violence, but the many covariations that naturally affect the equation between them introduce uncertainties in establishing causality.