TUESDAY, April 22, 2014 (HealthDay News) -- Less than 10 percent of crimes committed by mentally ill people are directly linked to the symptoms of their disorders, a new study shows.
"When we hear about crimes committed by people with mental illness, they tend to be big headline-making crimes, so they get stuck in people's heads," said study author Jillian Peterson, a psychology professor at Normandale Community College in Bloomington, Minn. "The vast majority of people with mental illness are not violent, not criminal and not dangerous."
In the study, the researchers analyzed 429 crimes committed by 143 people in Minnesota who suffered from depression, schizophrenia or bipolar disorder. The study participants were interviewed about their criminal history and mental health symptoms, covering an average of 15 years.
Overall, the investigators found that only 7.5 percent of crimes were directly linked to mental illness symptoms: 3 percent to symptoms of depression; 4 percent to symptoms of schizophrenia; and 10 percent to symptoms of bipolar disorder.
Two-thirds of those who committed crimes linked to mental illness symptoms also committed unrelated crimes for other reasons, including substance abuse and being jobless, poor and homeless, according to the study published online April 15 in the journal Law and Human Behavior.
"Is there a small group of people with mental illness committing crimes again and again because of their symptoms? We didn't find that in this study," Peterson said in a journal news release.
Nearly two-thirds of the people in the study were men. The average age was 40, and 85 percent had substance abuse disorders. The researchers did not examine the interaction between substance abuse and mental illness in criminal activity. Forty-two percent of the participants were white, 42 percent were black and 16 percent were of other races.
More than 1.2 million people with mental illness are in U.S. jails or prisons, according to the federal Bureau of Justice Statistics.
The U.S. National Library of Medicine has more about mental disorders.