RESEARCH WEEKLY: The Risk of Criminal Convictions in Co-Occurring Substance Use and Severe Mental Illness
Substance use disorders have a large impact on criminal justice involvement of individuals with severe mental illness, according to a recent Australian study on criminal offending, substance use and mental illness.
The contribution of substance use on criminal offending was the strongest in people with psychotic illnesses, including schizophrenia, severe bipolar disorder, and other non-organic psychosis, according to the results. Because there is such a high prevalence of co-occurring substance use disorders with serious mental illness, the results are important for considering what factors to address to decrease criminal justice involvement in this population.
People with severe mental illness are more likely to have a substance use disorder than people in the general population. In Australia, the rates of co-occurring disorders are 50.5% for alcohol use disorders and 54.5% for substance use disorders in people with severe mental illness. This is much higher than the prevalence of 24.7% for alcohol use and 8.9% for substance use disorder among the general population.
Methods and results
This study followed more than 400,000 children born between 1980 and 2001 in Western Australia into adulthood. The children were identified using birth records. Using complex data system integrations and linking a variety of different health and related records, researchers were able to understand diagnoses of individuals as well as their criminal convictions over time.
Participants were classified as having psychotic illness, other mental illness, or no mental illness. Conviction records identified any persons on parole, in custody, or in other community programs who had been found guilty or plead guilty to any crime after the age of 10 years old. Based on the available information, over 180,000 children were included in the final study that assessed conviction rates and the effect of having a mental illness.
Using this information, researchers developed incidence rate ratios for conviction of any type of crime. The incidence rate ratios represent the increased chance, or risk, of an individual facing a conviction based on a mental health diagnosis, substance use disorder, or other factors. The researchers also looked at parent history, race and socioeconomic background. Researchers compared the risk for people with a psychotic illness, other mental illness, and no mental illness across these factors.
Those with a psychotic illness were nearly four times more likely to face a conviction compared to those with no mental illness. However, this risk was dramatically reduced to 1.4 times more likely when rates were adjusted to account for co-occurring substance use disorders. This means that, in this study, 60% of the risk of criminal offending and conviction for people with schizophrenia or bipolar disorder is linked to substance use rather than severe mental illness alone.
Implications
It is clear that substance use has an effect on a person’s interactions with the criminal system. More research is needed to see the exact cause of this link. The impact of substance use disorders on criminal offending for people severe mental illness appears to be unique, and research should explore co-occurring substance use disorder and severe mental illness. Because of the previously mentioned high rates of the two disorders co-occurring in individuals, the Australian researchers suggest a greater focus on reducing substance use disorders in the population of people with severe mental illness. Additional research may help to bring substance use treatment into integration and crime reduction programs.
This research study was possible because of Western Australia’s shared healthcare data system. The United States currently does not have the ability to share data in a way to make this type of study possible. In order for researchers and policymakers to explore the connections between serious mental illness and other risk factors for criminal justice involvement, like substance use, information systems need to be better connected and integrated. Without such data, the extent of factors that contribute to law enforcement encounters and convictions, such as mental illness and substance use, will remain unknown.
