A new study renders indisputable the fact that the mentally ill are not inherently more prone to violence than those in the general population. Only when drug and alcohol addiction or traumatic pasts enter the equation does any propensity toward dangerous behavior emerge. When controlling for all other variables, incarceration, youth and substance abuse are the most accurate predictors of future violence.

The simple but exhaustive study, performed as part of a national epidemiological survey by researchers at the University of North Carolina, involved interviews with nearly 35,000 targeted individuals spanning various demographics who'd been treated at the School of Medicine's facilities in Chapel Hill. The interviews occurred in 2 parts over a 2-year period and their aim was to measure the amount of violence perpetrated by the participants and determine whether their mental health problems bore any significant link to future crimes. 

While individuals suffering from severe mental illness did more often report involvement in violent events, this correlation stemmed from the fact that they also more often exhibited other, more relevant behavioral variables: youth, juvenile detention, abusive parents, drug addiction and lack of gainful employment. These factors are far more directly tied to criminal activity than any psychiatric illness. Of those subjects surveyed, 10.8% had only a major mental illness, 21.4% suffered only from substance abuse or dependence and 9.4% had a severe mental illness and a substance problem. To the surprise of no one, the latter group was most likely to have perpetrated or witnessed violence in the year between the two interviews. "Dual-disordered subjects with a history of violence" were 10 times as likely as those with mental illness alone to engage in criminal aggression. 

The top ten things that predict violent behavior in order of relevance, based on this survey: 1) youth 2) history of violence 3) male gender 4) history of juvenile detention 5) recent divorce or separation 6) victim of past physical abuse 7) parents have a criminal history 8) recent unemployment 9) severe mental illness combined with substance abuse or addiction 10) being a victim of violent crime. Most significantly, the 3,000 people who reported severe mental illness without a history of violence or drug abuse collectively committed only 50 acts of violence between the two interviews.

This study's conclusions fall under the "common sense" heading, but they're significant in a culture where many read diagnoses like bipolar disorder or schizophrenia as signs of an undesirable or violent personality. These perceptions affect public policy. Victims then suffer even greater states of social isolation due to false perceptions fueled by the usual suspects in the American news media and entertainment fields - a National Health Association study found that, in television and film, schizophrenic individuals are depicted as the most dangerous of all character types. And this unfortunate impression subjects their real-life counterparts to a greater degree of discrimination and misplaced anger. The fact is that "people with psychiatric disabilities are far more likely to be victims than perpetrators of violent crime." And the vast majority of violent criminals suffer from no diagnosable mental illness. Funding for surveys like this one is justified if it can gradually wear down the false opinions that permeate our culture.