We examine the association between rates of homicide resulting in a mental health disposition (termed mentally abnormal homicide [MAH]) and homicides without such a disposition, as well as to province-wide psychiatric hospitalisation and incarceration rates.
In this population-based study, we investigate all adult homicide perpetrators (n = 4402) and victims (n = 3783) in Ontario from 1987 to 2012. We present annual rates of mentally abnormal and non–mentally abnormal homicide and position them against hospitalisation and incarceration rates.
Among the total sample of homicide accused, 3.7% were mentally abnormal. Most (82.5%) had a psychotic disorder at the time of the offense. Contrasted with declining hospitalisation, incarceration, and population homicide rates, the rate of MAH remained constant at an average of .07 perpetrators per 100,000 population. The rate of MAH was not associated with discharges from or average length of stay in psychiatric hospitals (ρ = 0.10; 0.34, P > 0.10), incarceration rates (ρ = 0.16, P = 0.42), or the total homicide rate (ρ = 0.25, P = 0.22). The proportion of MAH perpetrators with a substance use disorder increased modestly over time (β = 0.35, R2 = 0.12, P = 0.08).
The rate of MAH has not changed appreciably over the past 25 years. Declining psychiatric service utilisation was not associated with the rate of homicide committed by people with mental illness and, secondarily, was not linked to increases in the population homicide or incarceration rates. Substance use has become a more prevalent problem for this population.