Mental illness and violence: an epidemiological appraisal of the evidence

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.

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.

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.

An association exists between mental illness and violence, but the many covariations that naturally affect the equation between them introduce uncertainties in establishing causality.