The early Hollywood rendition of a psychiatric patient is built around stereotypes of violent and dangerous behaviour. However, research findings have been far more mixed in terms of the violent behaviour associated with populations with different mental disorders.
Professor Seena Fazel is a forensic psychiatrist, investigating the relationship between mental illness and violent crime. His work addresses the nature of this relationship and the potential real-world applications of these findings. He also highlights the difficulties in such research: why is it so difficult to determine the true nature of the risk of violence associated with mental illness?
The first difficulty comes from not knowing exactly what to measure. How do you measure violence: by the number of lives taken, injuries caused or economic cost to society? Research has addressed this by calculating an overall measure of disease burden, or disability-adjusted life year (DALY) score. This represents the amount of potentially healthy life lost due to premature death or injury, as resulting from violent crime. Individuals and groups suffering from particular mental illnesses can then be compared in terms of the DALY score of their victims.
However, there are numerous confounds in this measurement. It is possible that apparent relationships between violence and mental illness may actually be mediated by a third variable, such as socio-economic status, age or gender. Rather than mental illness leading to increased risk of violence, it may also be that violent behaviour facilitates the detection and diagnosis of mental health problems which may otherwise not be noticed.
Research into the epidemiology of mental illness and violence also faces the massive problem of stigma. A balance must be found between raising awareness of increased risk associated with mental illness, so that appropriate interventions can be put in place, and creating stigma and stereotypes surrounding diagnoses of mental health conditions. Such stigma may in turn prevent individuals seeking treatment for mental illnesses, bringing about even greater long term harm.
So what’s the real link between mental illness and violence?
Despite the heterogeneity in individual studies, meta-analyses have suggested that mental illness is associated with increased risk of violent behaviour, with schizophrenia and other forms of psychosis associated with violent behaviour, and particularly homicide. However, this link was found to be mediated by substance abuse: individuals with psychosis in the absence of substance abuse were no more likely to be committed of a violent offence than those without such a mental illness. This indicates intervention strategies may be most beneficial in targeting substance abusers in order to reduce violent offending.
Similar findings were obtained in relation to other mental illnesses such as bipolar disorder. Although there was an increased risk of violent offending associated with a diagnosis of bipolar disorder, this relationship was mediated by substance abuse. There was also considerable heterogeneity within the sample, indicating that the risk factors associated with violent offending differed between individuals.
Knowledge about the link between mental illness and violent offending may be particularly important within prison settings. It has been estimated that around half of all prisoners reoffend every year. It is also known that the prevalence of mental illness is greater within prisoner compared to the general population. This is particularly apparent for juvenile prisoners, those aged 55 and over, and women. This suggests greater measures to address mental health problems within prisons may be most effective in reducing violent offending when prisoners return to the general population.