Mental illness by itself does not predict future violent behavior

People with mental illness alone are no more likely than anyone else to commit acts of violence, a new study by UNC researchers concludes.

But mental illness combined with substance abuse or dependence elevates the risk for future violence.

"Our study shows that a link between mental illness and violence does exist, but it's not as strong as most people think," said Eric B. Elbogen, Ph.D., lead author of the study and assistant professor in the forensic psychiatry program at the University of North Carolina at Chapel Hill School of Medicine.

"We found that several other factors - such as a history of past violence or substance abuse or a recent divorce or loss of one's job - are much more predictive of future violence than mental illness alone," Elbogen said. "Only when a person has both mental illness and substance abuse at the same time does that person's risk of future violence outweigh anyone else's."

UNC co-author Sally C. Johnson, M.D. added, "These findings challenge the perception some people have, and which you often see reflected in media coverage, that mental illness alone makes someone more dangerous. Our study shows that this perception is just not correct."

Elbogen and Johnson's study is published in the February 2009 issue of Archives of General Psychiatry . To arrive at their findings, they conducted statistical analyses of data collected previously as part of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) conducted by the National Institute of Alcohol Abuse and Alcoholism.

A total of 34,653 people completed interviews during the two separate waves of NESARC. Wave 1 took place from 2001-2002 while wave 2 was from 2004-2005. Wave 1 data on severe mental illness - including schizophrenia, bipolar disorder and major depression - were analyzed to predict wave 2 data on violent behavior.

The results show "that if a person has severe mental illness without substance abuse and history of violence, he or she has the same chances of being violent during the next 3 years as any other person in the general population," Elbogen and Johnson wrote.

When mental illness is combined with substance abuse, the risk for future violence reaches the level of statistical significance. However, even mental illness combined with substance abuse ranks only ninth on the study's list of the top 10 predictors of future violence. The higher ranking predictors, listed in order of their predictive value, are age (younger people are more likely to commit acts of violence), history of violence, sex (males are more prone to violence), history of juvenile detention, divorce or separation in the past year, history of physical abuse, parental criminal history and unemployment for the past year. Victimization in the past year was the tenth predictor.

"The data shows it is simplistic as well as inaccurate to say the cause of violence among mentally ill individuals is the mental illness itself … the current study finds that mental illness is clearly relevant to violence risk but that its causal roles are complex, indirect, and embedded in a web of other (and arguably more) important individual and situational cofactors to consider," the study concludes.