Mental Illness Not Strongly Associated With Criminal Behavior

mental illness

Research conducted on 143 people with severe mental illness taken from a mental health court in Minneapolis has found that a relatively small number of the crimes they commit are directly related to the symptoms of their illness. The study, conducted by researchers at Normandale Community College in Bloomington, Minnesota, is the first to take a comprehensive look at the link between symptoms of mental illness and criminal behavior. The researchers looked at 429 crimes committed by this population, but failed to find a strong association between their illness and the crimes they committed. The participants (average age 40 years), completed a two-hour interview about their criminal behavior and mental health symptoms, covering an average of 15 years of their history. Symptoms assessed included delusions and hallucinations in schizophrenics; impulsivity and risky behavior in subjects with bipolar disorder; and hopelessness and thoughts of suicide in those with major depressive disorder. Additionally, the researchers looked at the subjects’ criminal histories and at their social workers’ files to examine if a crime was directly related, mostly related, or mostly unrelated to symptoms of the perpetrators’ mental illness. For example, if a schizophrenic was hearing voices on the same day that he got into a fight, but the voices were not present at the time of the fight, the crime would be considered “mostly related.”

The study did not find a strong association between symptoms of mental illness and criminal behavior. Of the 429 crimes, only 7.5 percent were found to be directly attributable to symptoms of a mental illness. When the ‘directly related’ and ‘mostly related’ categories were combined, it was found that three percent were attributable to symptoms of major depression, four percent were related to schizophrenia, and 10 percent were attributed to bipolar disorder, for a total of approximately 18 percent, but still less than one in five. The findings are important because of the popular, but erroneous perception of the mentally ill as violent and dangerous. This perception is made worse by sensationalist headlines when a mentally ill person does commit a crime.

Of the offenders who could directly attribute their criminal conduct to symptoms of their mental illness, two-thirds had also committed crimes for unrelated reasons – poverty, homelessness, unemployment, and substance abuse. According to the lead researcher, Dr. Jillian Peterson, they failed to find a small population of the mentally ill committing crimes repeatedly due to the symptoms of their illness. Of the crimes that were attributed to symptoms of mental illness, 62 percent were related to bipolar disorder, 23 percent to schizophrenia, and 15 percent to depression. The disproportionate fraction of the crimes committed by bipolar subjects may be inflated by abuse of drugs or alcohol, or by anger that could be mistaken for “mania.”  It should be noted that these figures do not include serious violent offenses committed by mentally ill persons, because the mental health court the subjects were drawn from did not adjudicate such offenses.  Also, the study did not consider the interaction between substance abuse with mental illness and their combined effect on criminality.

In conclusion, the study, published online in the American Psychological Association journal ‘Law and Human Behavior,’ failed to find a strong direct association between the symptoms of mental illness and criminal behavior. The fact remains, however, that 1.2 million inmates (more than half of the incarcerated population) are diagnosed with some form of psychiatric illness. This study is important to reducing the recidivism rate for offenders, and will inform efforts to expand programs beyond treatment for mental illness to cognitive-behavioral therapy, and anger management. Other programs that will be important for reducing recidivism will include drug treatment, and supported housing and employment programs.

By Laura Prendergast

Science Daily

American Psychological Association

Jillian K Peterson


2 Responses to "Mental Illness Not Strongly Associated With Criminal Behavior"