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mental disorders and criminality

In order to empirically investigate the population impact of severe mental illness on violent crime, we examined data from high-quality national hospital and crime registers in Sweden covering the period 1988–2000. We calculated the population-attributable risk: the number of violent crimes committed per 1,000 persons in the whole population that would not have occurred if the risk factor—severe mental illness—had been absent, and the population-attributable risk fraction, which is the proportion of violent crimes in the whole population that may be attributed to individuals with severe mental illness. Because the population impact was the focus of the study, we included all categories of violent crime—not just homicide—which is a relatively rare event compared to other types of violent crime. We discuss these findings in light of the assumption of these methods that there is a causal relationship between risk factor and outcome.